analysis of alternatives and socio-economic assessment

ANALYSIS OF ALTERNATIVES

and

SOCIO-ECONOMIC ASSESSMENT

Legal name of applicant(s): Maflon Spa

Submitted by: Maflon Spa

(jointly developed with Acton Technologies Ltd)

Substance: bis(2-methoxyethyl) ether (diglyme):

EC 203-924-4: CAS 111-96-6

Use title: Use of bis(2-methoxyethyl) ether (diglyme) as a carrier

solvent in the formulation and use of sodium naphthalide

etchant for fluoropolymer surface modification whilst

preserving article structural integrity (in-house processes).

Use number: 1


Use number: 1 Maflon Spa 2

CONTENTS

LIST OF ABBREVIATIONS ....................................................................................................................................... 5

DECLARATION .......................................................................................................................................................... 6

1. SUMMARY ............................................................................................................................................................ 7

2. ANALYSIS OF SUBSTANCE FUNCTION.......................................................................................................... 9

2.1. The requirement to modify the surface of fluoropolymers ............................................................................. 9 2.1.1 Fluoropolymers ................................................................................................................................... 9 2.1.2 Chemistry of surface modification ...................................................................................................... 11 2.1.3 Solvated Electrons in surface modification and the use of sodium metal ........................................... 12 2.1.4 Radical anions in surface modification and the use of sodium naphthalide ........................................ 12 2.1.5 The measurement of the extent of surface modification...................................................................... 13

2.1.5.1 Change in colour ..................................................................................................................... 14 2.1.5.2 Change in surface physical characteristics (surface roughness) .............................................. 14 2.1.5.3 Change in surface chemical composition ................................................................................ 14 2.1.5.4 Change in surface wettability behaviour ................................................................................. 15 2.1.5.5 Change in bonding strength after application of an adhesive .................................................. 18

2.1.5.5.1 Etching and successful surface adhesion .............................................................. 18 2.1.5.6 Industry Standards applied for fluoropolymer etching applications ........................................ 19

2.1.5.6.1 ASTM Standards .................................................................................................. 19 2.1.5.6.2 Specific Industry Standards .................................................................................. 19

2.2. Technical function of diglyme in the wet chemical treatment fluoropolymer surfaces .................................. 21 2.2.1 Chemical functionality ........................................................................................................................ 21

2.2.1.1 Solubility of sodium naphthalide complex .............................................................................. 21 2.2.1.2 Thermal Stability ..................................................................................................................... 22 2.2.1.3 Flash Point ............................................................................................................................... 22

2.2.2 Process functionality ........................................................................................................................... 22 2.2.2.1 Process Temperature ............................................................................................................... 22 2.2.2.2 Process Reaction Time ............................................................................................................ 23 2.2.2.3 Solvent Viscosity ..................................................................................................................... 23 2.2.2.4 Bond strength .......................................................................................................................... 23 2.2.2.5 Polymer range .......................................................................................................................... 24 2.2.2.6 Tribology of surface requiring etching .................................................................................... 24 2.2.2.7 Diglyme recovery and recycling .............................................................................................. 24 2.2.2.8 In-house versus contract etching services ................................................................................ 24

3. ANNUAL TONNAGE............................................................................................................................................ 25

4. IDENTIFICATION OF POSSIBLE ALTERNATIVES ......................................................................................... 26

4.1. List of possible alternatives ............................................................................................................................ 26

4.2. Description of efforts made to identify possible alternatives .......................................................................... 28 3.2.1 Research and development .................................................................................................................. 28 3.2.2 Data searches ....................................................................................................................................... 28 3.2.3 Consultations ....................................................................................................................................... 28

5. SUITABILITY AND AVAILABILITY OF POSSIBLE ALTERNATIVES ......................................................... 29

5.1. WET CHEMICAL TREATMENTS .............................................................................................................. 29 4.1.1 Sodium – Ammonia System ................................................................................................................ 29

5.1.1.1 Technical feasibility ................................................................................................................ 29 5.1.1.2 Economic feasibility ................................................................................................................ 31



5.1.1.3 Reduction of overall risk due to transition to the alternative ................................................... 31 5.1.1.4 Availability .............................................................................................................................. 31 5.1.1.5 Conclusion on suitability and availability for sodium–ammonia etching alternative .............. 32

5.1.2 Sodium – Naphthalene – Alternative Solvents .................................................................................... 32 5.1.2.1 Substance ID and properties .................................................................................................... 32 5.1.2.2 Technical feasibility ................................................................................................................ 35

5.1.2.2.1 Physico-chemical Properties................................................................................. 35 5.1.2.2.2 Toxicological Properties ....................................................................................... 36 5.1.2.2.3 Process performance ............................................................................................. 36

5.1.2.3 Economic feasibility ................................................................................................................ 41 5.1.2.4 Reduction of overall risk due to transition to an alternative solvent ....................................... 41 5.1.2.5 Availability .............................................................................................................................. 42 5.1.2.6 Conclusion on suitability and availability for Alternative Solvent .......................................... 43

5.1.3 Other reductive pre-treatments involving radical anions ..................................................................... 44 5.1.3.1 Substance ID and properties ................................................................................................................ 44

5.1.3.2 Technical feasibility ................................................................................................................ 44 5.1.3.3 Economic feasibility ................................................................................................................ 44 5.1.3.4 Reduction of overall risk due to transition to the alternative ................................................... 44 5.1.3.5 Availability .............................................................................................................................. 45 5.1.3.6 Conclusion on suitability and availability ............................................................................... 45

5.2. Electrochemical Treatments ........................................................................................................................... 45 5.2.1.1 Substance ID and properties .................................................................................................... 46 5.2.1.2 Technical feasibility ................................................................................................................ 46 5.2.1.3 Economic feasibility ................................................................................................................ 46 5.2.1.4 Reduction of overall risk due to transition to the alternative ................................................... 46 5.2.1.5 Availability .............................................................................................................................. 46 5.2.1.6 Conclusion on suitability and availability for electrochemical treatments .............................. 46

5.3. Plasma Treatment ........................................................................................................................................... 46 5.3.1.1 Plasma treatment description ................................................................................................... 47 5.3.1.2 Technical feasibility ................................................................................................................ 48 5.3.1.3 Economic feasibility ................................................................................................................ 49 5.3.1.4 Reduction of overall risk due to transition to the alternative ................................................... 49 5.3.1.5 Availability .............................................................................................................................. 49 5.3.1.6 Conclusion on suitability and availability for plasma treatment ............................................. 50

6. OVERALL CONCLUSIONS ON SUITABILITY AND AVAILABILITY OF POSSIBLE ALTERNATIVES FOR USE ............................................................................................................................................................................... 51

6.1. The use of surface modified fluoropolymers .................................................................................................. 51

6.2. Overall conclusions on alternatives ................................................................................................................ 51

7. SOCIO ECONOMIC ANALYSIS .......................................................................................................................... 53

7.1. Socio-Economic Analysis (SEA) in the context of Adequate Control ........................................................... 53

7.2. Economic benefits of polytetrafluoroethylene (PTFE) ................................................................................... 53 7.2.1 PTFE Etching – Market Sectors and Uses ........................................................................................... 55

7.3. The most likely non-use scenario ................................................................................................................... 56

7.4. Economic impact assessment ......................................................................................................................... 57 7.4.1 Redundancy costs ................................................................................................................................ 57 7.4.2 Loss of sales and profits ...................................................................................................................... 58 7.4.3 Reduced operational costs ................................................................................................................... 58 7.4.4 Relocation costs ................................................................................................................................... 58 7.4.5 Loss of investment in research and development ................................................................................ 58



7.4.6 Downstream impacts ........................................................................................................................... 59

7.5. Social impact assessment ................................................................................................................................ 60 7.5.1 Loss of earnings .................................................................................................................................. 60

7.6. Summary ......................................................................................................................................................... 61

7.7. Conclusion ...................................................................................................................................................... 61

8. REFERENCES........................................................................................................................................................ 62

TABLES

TABLE 2.1 FLUOROPOLYMER DEFINITION ................................................................................................................. 10 TABLE 2.2 EXAMPLES OF CHANGES IN PTFE SURFACE CHEMISTRY BY CHEMICAL ETCHING ..................................... 15 TABLE 2.3 RELATIONSHIP BETWEEN CONTACT ANGLE AND SURFACE ENERGY .......................................................... 16 TABLE 3.1 COMPOSITION OF TYPICAL ETCHANT SOLVENT ....................................................................................... 25 TABLE 4.1 PROCESS CRITERIA MATRIX..................................................................................................................... 27 TABLE 5.1 SODIUM AND AMMONIA SUBSTANCE PROPERTIES ..................................................................................... 29 TABLE 5.3 SOLVENT CRITERIA MATRIX – PHYSICO-CHEMICAL PROPERTIES ............................................................. 34 TABLE 5.4 EFFECT OF SOLVENT STRUCTURE OF SODIUM NAPHTHALIDE EQUILIBRIUM REACTION ............................. 37 TABLE 5.5 CORRELATION OF ETCHANT ACTIVITY WITH SOLVENT DIELECTRIC CONSTANT (MARSH, 2006B) ............. 38 TABLE 5.6 BOND STRENGTH AFTER ETCHING PTFE WITH A THF-SODIUM NAPHTHALIDE ETCHANT ......................... 39 TABLE 5.7 COMPARATIVE BOND STRENGTH OF ETCHED STANDARD PTFE STRIPS (MARSH, 2006A, B) ............................ 39 TABLE 5.8 BONDING STRENGTH, PEEL TEST (MAFLON SPA, 2015, UNPUBLISHED LABORATORY RESULTS) ............... 39 TABLE 5.9 COMPARISON OF PTFE SURFACE MODIFICATIONS USING ALTERNATIVE SOLVENTS (MARSH, 2006B) ...... 40 TABLE 5.10 LABORATORY COMPARISON OF PTFE SURFACE MODIFICATIONS USING ALTERNATIVE SOLVENTS

(MAFLON SPA, 2015, UNPUBLISHED LABORATORY RESULTS) .................................................................................. 40 TABLE 5.11 OTHER COMMERCIAL SOLVENT-BASED FLUOROPOLYMER ETCHANT SYSTEMS ......................................... 42 TABLE 5.12 SUBSTANCE ID AND PROPERTIES ............................................................................................................. 44 TABLE 1.1 CRITICAL PTFE APPLICATIONS ................................................................................................................ 55 TABLE 1.2 ORDER OF MAGNITUDE OF KEY IMPACTS .................................................................................................. 61

FIGURES

FIGURE 2.1 CHANGE IN COLOUR ON CHEMICAL ETCHING OF PTFE SHEET .................................................................. 14 FIGURE 2.2 CONTACT ANGLE AND WETTABILITY ...................................................................................................... 16 FIGURE 2.3 RELATIONSHIP BETWEEN SURFACE ENERGY AND CONTACT ANGLE FOR ETCHED PTFE SURFACES ........... 17 FIGURE 5.1 COLOUR COMPARISON OF PTFE SHEET ETCHED BY SODIUM NAPHTHALIDE IN THREE DIFFERENT SOLVENTS

UNDER PRODUCTION PLANT CONDITIONS ................................................................................................................. 41 FIGURE 7.1 FLUOROPOLYMERS, HOMOPOLYMERS AND COPOLYMERS ........................................................................ 54 FIGURE 7.2 OVERVIEW OF THE MAIN NON-USE SOCIO-ECONOMIC IMPACTS ................................................................ 57 FIGURE 7.3 END USE APPLICATIONS OF MAFLON'S ETCHED PTFE .............................................................................. 59



LIST OF ABBREVIATIONS

AFM Atomic Force Microscopy

APT Atmospheric pressure plasma treatment

ASTM American Society for Testing and Materials

CAS Chemical Abstract Service

DNEL Derived No Effect Level

DPG-ME Dipropylene glycol dimethyl ether

EGDME Ethylene glycol dimethyl ether

ETFE Ethylene-tetrafluoroethylene copolymer

FEP Fluorinated ethylene-propylene copolymer

FSS Fluoroetch Safety Solvent

HMPA Hexamethylphosphoramide

LPT Low pressure plasma treatment

LUMO Lowest Unoccupied Molecular Orbital

PFA Perfluoroalkoxy copolymer

PTFE Poly(tetrafluoroethylene)

PVDF Poly(vinylidene fluoride)

SCE Standard Calomel Electrode

SET Solvated Electron Transfer

SPM Scanning Probe Electroscopy

TAPPI Technical Association of the Pulp and Paper Industry

TBAT Tetrabutylammonium tetrafluroborate

TEGDME Triethylene glycol dimethyl ether

THF Tetrahydrofuran

XPS X-ray Photoelectron Spectroscopy



DECLARATION

We, Maflon Spa, request that the information blanked out in the “public version” of the Analysis of Alternatives is not disclosed. We hereby declare that, to the best of our knowledge as of today February 8th 2016 the information is not publicly available, and in accordance with the due measures of protection that we have implemented, a member of the public should not be able to obtain access to this information without our consent or that of the third party whose commercial interests are at stake.

Signature: Date: 8th February, 2016 Place: Castelli Calepio, Italy

Agostino Fenaroli

Managing Director

Maflon Spa



1. SUMMARY

Maflon Spa is applying for an authorisation for the use of bis(2-methoxyethyl) ether (diglyme) as a carrier solvent in the formulation and use of sodium naphthalide etchant for fluoropolymer surface modification whilst preserving article structural integrity (in-house processes). Maflon Spa operate two production lines for the in-line continuous single surface modification of perfluoropolymer (PTFE) sheets which are subsequently supplied to downstream users for a variety of applications in different industrial sectors where the virgin surface properties of PTFE can be exploited by bonding the polymer sheets to the relevant substrate materials. Bis(2-methoxyethyl)ether (diglyme) is used as a solvent for sodium naphthalide to produce an etchant for the surface modification of fluoropolymers, especially perfluoropolymers such as polytetrafluoroethylene (PTFE), by reductive defluorination in order to increase the surface adhesion properties of such polymers. Diglyme provides sufficient solvation of the radical anion salt to generate the active chemical species in order to promote this reductive defluorination. Other physico-chemical parameters, such as a relatively high flash point, a viscosity similar to that of water and thermal stability during storage and solvent recovery, provide an etchant that can be handled with reduced process risk in a number of process configurations (batch and continuous) to process a range of physical forms of polymer articles (e.g. sheets, seals, tubes etc). Etchants formulated using diglyme as the solvent are used in the surface modification of fluoropolymer components in a range of industrial and medical applications, where the bonding of the fluoropolymer, and PTFE in particular, provides the final bonded manufactured product with the critical non-reactive properties of the virgin fluoropolymer surface and where the specific structural integrity of the components must otherwise be maintained. Sodium-ammonia etchant systems are commercially available but this methodology is significantly more expensive than the diglyme solvent alternative, is more restricted in its application due to the aggressive and penetrating nature of the generated solvated electron reductant and has a different but significant risk profile in the use of liquid ammonia. As such it can only be implemented at specialist facilities and cannot be used for small scale industrial etching facilities or for components where maintenance of specific structural integrity is required. Other alternative polar solvents that provide similar sodium napthalide solvation characteristics have been identified and some are also known to be available commercially. However, these solvents either have a similar toxicity profile to diglyme (e.g. monoglyme, triglyme) or pose signficantly greater process risk through lower flashpoint, greater volatility, reduced thermal stability at room and elevated process temperatures or generation of explosive peroxides during solvent recovery and recycling processes (e.g. monoglyme, tetrahydrofuran). Other glyme alternatives also provide additional process restrictions through increased viscosity due either to the extent of solvation of sodium naphthalide (monoglyme) or increased inherent viscosity (triglyme and tetraglyme). Formulated etchants using either dipropylene glycol dimethyl ether or diethyl glyme have not been demonstrated to produce the same degree of fluoropolymer surface modification in either laboratory of pilot production tests which would allow commercial application of these solvent alternatives. Other wet chemical methods, including the electrochemical generation of solvated electrons and radical anions, do not provide the same extent of consistency of surface modification, particularly for PTFE, and none have been demonstrated or implemented commercially.



Alternative treatment methods for fluoropolymer surface modification, such as plasma treatments, are available for some fluoropolymers but have not been particularly successful for PTFE. Fully fluorinated polymers are reported to undergo surface modification but this is not necessarily concomitant with required adhesion properties in the final application. In addition, the shelf life of such ‘etched’ surfaces is considerably shorter than that achieved with the solvent etchants and that, combined with the requirement for expensive equipment in a number of configurations to cover the range of fluoropolymer articles requiring etching and the resistance of the downstream user market for products etched by this technique, have resulted in limited applications of such techniques. In summary, diglyme is the preferred solvent for formulation and use of a sodium naphthalide etchant for perfluoropolymer surfaces as it provides the optimum balance of adequate solvation to maximise the availability of the radical anion reductant, either at or to a limited depth of the perfluoropolymer surface, with process characteristics of relatively low flashpoint, low viscosity and thermal stability, that permits the economic operation of the etching process at elevated

temperatures of up to 65⁰C whilst minimising overall process risk. Alternative solvents or alternative etching technologies do not provide the flexibility of an etchant of sodium naphthalide formulated in diglyme to produce a consistent surface modification of sufficient enhanced wettability, increased surface energy and increased final adhesive bonding strength across the range of critical perfluoropolymer bonding applications that require mandatory attainment of and qualification to end user specification. Maflon Spa formulate a diglyme-based fluoropolymer etchant for use in their own production facility only for surface treatment of fluoropolymer articles. It should be noted that the terms for the sodium – naphthalene system are referred to as both ‘sodium – naphthalene’ and ‘sodium naphthalide’ and are used interchangeably. The term ‘sodium

naphthalide’ is used primarily in this analysis of alternatives. Justification for Review Period

In conjunction with another authorisation applicant for the same use (Acton Technologies Ltd) Maflon Spa has undertaken an extensive review of both alternative methodologies for perfluoropolymer surface modification and of alternative solvents for the formulation of etching solutions that can deliver the equivalent quality and consistency of bonding characteristics and overall operability. The Chemical Safety Report, submitted as part of this Application for Authorisation, demonstrates that the use of diglyme is adequately controlled, with risk characterisation ratios significantly less than 1 for all worker contributing and man via the environment scenarios. Maflon Spa is therefore requesting a review period of 12 years for the use of bis(2-methoxyethyl) ether (diglyme) as a carrier solvent in the formulation and use of sodium naphthalide etchant for fluoropolymer surface modification whilst preserving article structural integrity (in-house processes).



2. ANALYSIS OF SUBSTANCE FUNCTION

2.1. The requirement to modify the surface of fluoropolymers

Fluoropolymers were discovered in the late 1930’s with the development of polytetrafluroethylene (PTFE) by Dupont. They are a group of polymers that possess excellent chemical ultra-violet radiation resistance, high temperature resistance, good insulating properties, stability to weathering, low surface energy, low coefficients of friction and low dielectric constants – all properties which arise from the stability of the carbon-fluorine covalent bonding and the unique intra and intermolecular interactions within the polymer matrix (Teng, 2012).

Because of the unique physico-chemical properties of this polymer group, they are widely used throughout industry in chemical, electrical and electronic, space, defence, construction, automotive and medical applications.

However, the very low surface tension of fluoropolymers results in almost negligible adhesion of other polar materials to the polymer surface. The further use of fluoropolymers in many engineering and technological applications therefore requires some form of surface treatment or modification to enhance surface adhesion. The function of diglyme is as a solvent with an optimum combination of physico-chemical properties in the formulation and use of a chemical reagent that is sufficiently active to achieve such surface modifications in this group of inert polymers.

2.1.1 Fluoropolymers

There are two types of fluoropolymers:

1. Perfluoropolymers, in which all the hydrogen atoms in the analogous hydrocarbon polymer structure are replaced by fluorine atoms. Typical examples are:

• Poly(tetrafluoroethylene) (PTFE)

• Fluorinated ethylene-propylene copolymer (FEP)

2. Partially fluorinated polymers, in which only a proportion of the hydrogen atoms are substituted with fluorine atoms. Typical examples are:

• Poly(vinylidene fluoride) (PVDF)

• Perfluoroalkoxy copolymer (PFA)

Table 2.1 summarises some of the relevant key properties of these fluoropolymers.



Table 2.1 Fluoropolymer Definition

Polymer CAS Type Fluorine Content Structure Elemental Composition (% w/w, XPS)

Surface Energy mJ/m2

Carbon Fluorine Oxygen

Polytetrafluoroethylene PTFE

9002-84-0 Fully fluorinated 4H replaced by F

33.3 66.8 0 19.1

Polyvinylidene fluoride PVDF

24937-79-9 Partially

fluorinated 2H replaced by F

51 49 0 23.9

Polyvinyl fluoride PVF

24981-14-4 Partially

fluorinated 1H replaced by F

70.4 28.8 0.8 30.3



It is extremely difficult to achieve any adhesion to fully fluorinated polymers, and even partially fluorinated polymers can prove problematical in certain circumstances. There is, therefore, a requirement to modify the surface of fluoropolymers if there is a technical application requirement to achieve adhesion to the polymer surface. The surface pre-treatment process by which such surface modification is achieved depends upon the particular fluoropolymer and sections 2.2, 4 and 5 of this analysis discusses the potential range of alternative surface modification methodologies that have been examined over the past 70 years.

However, the primary requirement is to achieve the surface modification of perfluoropolymers. This has required the development of very reactive wet chemical treatment systems in which diglyme has become the primary solvent of choice. This analysis of alternatives therefore focusses upon the surface modification of perfluoropolymers but it should be noted that partially fluorinated polymers are also treated using wet chemical etchants formulated in diglyme. This is further discussed in section 2.2.2.5.

2.1.2 Chemistry of surface modification

The primary method for the modification of the surface of perfluoropolymers is by treatment with powerful reducing agents. A possible reaction mechanism for this chemical transformation has been suggested by Brewis and Dahm (2006) as follows:

• Step 1 is postulated to involve electron transfer from the electron source to the fluoropolymer. Elimination of fluoride generates a neutral radical in the polymer.

• This neutral radical can then react further to produce new carbon-carbon bonds, resulting in either cross-linking (step 2) or



• Acceptance of a further electron by the radical to form a carbanion which either reacts with a protic solvent (HS) to yield carbon-hydrogen bonds or results in the further elimination of fluorine with the formation of carbon-carbon double bonds (step 3).

2.1.3 Solvated Electrons in surface modification and the use of sodium metal

Powerful reducing agents are therefore required to promote these reactions on the surface of perfluorinated polymers. One of the most powerful reducing agents that has been used in such surface treatment has been generated through the dissolution of sodium metal in liquid ammonia.

(4) Na + NH3 → Na+ + en(NH3)

There are a number of significant drawbacks with the use of this chemical combination (further discussed in section 5.1.1), including the extreme reactivity of sodium, the toxicity of liquid ammonia and the extremely low temperatures at which the working reductant has to be maintained. Therefore, safer methods for handling the very reactive sodium species have been developed.

2.1.4 Radical anions in surface modification and the use of sodium naphthalide

Dissolution of sodium metal and naphthalene in certain solvents leads to the generation of another powerful reducing species, the radical anion salt, in which the electron is taken up by the naphthalene ring and can be transferred from there to the electron deficient carbon backbone.

A number of different solvents have been used for the dissolution of the reactant species and generation of the radical anion salt and the properties, advantages and disadvantages of a variety of different solvents, in comparison to diglyme, are examined in detail in sections 2.2 and 5.

The formation of radical anions occurs in a single electron transfer process (SET). The electron transferring species are most often the alkali metals (Li, Na, K, Rb, Cs) or the reduction at the cathode of an electrochemical cell. Initially, the electron occupies a LUMO of its acceptor molecule, which subsequently may undergo several types of reactions, such as cleavage, solvation, condensation or protonation.

In aromatic systems, some of the resulting radical anions are stable under aprotic conditions. In particular, condensed aromatics systems, like naphthalene, anthracene and perylene are well known for the formation of stable radical anions, which can even be isolated in the form of their alkali metal salts.

Radical anions have very powerful reducing properties, the E0 being almost that of the alkali metal itself.

For this reason, sodium naphthalide has found considerable interest in organic chemistry as a powerful reducing agent, being able to even reduce the most robust chemical electron receptors under relatively mild conditions. These reducing systems are, almost without exception, a solution of sodium naphthalide in an aprotic solvent.



In general, two equilibria have to be considered in the reaction of alkali metals and aromatic hydrocarbons:

1. M + Ar = Ar.-/M+ reduction of the aromatic hydrocarbon

2. (Ar.-/M+)ion-pair = Ar.- + M+ ion-pair dissociation

Due to the ability of glycol ethers to chelate the cation, the yield of the reduction of aromatic hydrocarbons (reaction 1) is highest when ethylene glycol ethers are used as solvent.

Being an ionic species, the ionic state in solution of the ion-pair of the alkali cation and radical anion strongly depends on the interaction between the two ions (reaction 2). Typically, low polarity aprotic solvents like THF or dioxane favour the formation of tight contact ion pairs whilst in high polarity solvents, like HMPA, the ion pairs are loosely bound.

Furthermore, classical factors, such as ion size, polarizability and temperature, have a strong influence on the ionic state, typically the close-contact ion pairs being observed with smaller cations, and small condensed aromatic systems. The dissociation of the ion pair to the loose ions is exothermic. Hence, an increase in temperature, in general, will lead to stronger ion pairing in solution.

The reducing properties of aromatic radical ions are governed by the half-wave potential E0 of the respective aromatic system and the electron transfer rate from the radical anion – cation pair to the alkyl halide.

As a rule of thumb, the more negative the half-wave potential and the tighter the ion-pair, the higher the electron transfer rate and reducing power will be (although this is not always true in all systems).

Sodium naphthalide in this respect forms a unique system with a strong negative half wave potential of approximately -2.5 V vs SCE and the ion pairs being tight in low polarity solvents and exhibits a strong reducing power even to chemically inert C-F bond.

Section 2.2 defines the technical function of diglyme as the preferential solvent in the formulation and use as a surface modification agent (etchant) for fluoropolymers. Section 2.2.1.1 discusses further the influence of the solvent on the solvation of the sodium naphthalide radical anion salt.

2.1.5 The measurement of the extent of surface modification

A fluoropolymer surface that has been subject to a reducing agent and therefore undergone, to some degree, modification of the surface chemistry will demonstrate the following changes:

1. Change in colour

2. Change in surface physical characteristics (surface roughness)

3. Change in surface chemical composition

4. Change of surface wettability behaviour

5. Change in bonding strength after application of an adhesive

The extent to which the treatment penetrates the polymer surface varies and the depth and rate of the defluorination process depends upon the nature and conditions of the solvated radical or radical



anion salt chemistry employed. Etching can occur at depths of up to 6µm into the polymer surface (Marsh, 2006b).

2.1.5.1 Change in colour

Surface etching can lead to polymer discolouration ranging from off-white to yellow to brown to reduction to a black carbonaceous layer. Colour changes are often used as the most useful indication of the extent and regularity of the surface etching process.

Figure 2.1 Change in colour on chemical etching of PTFE sheet

The extent of colour change is often used in quality control procedures and it is a rapid and convenient method of the assessing the potential extent of surface modification. This method can be standardised, for example, by using ASTM D1535, Standard Practice for Specifying Colour by the Munsell System using Munsell Matte colour standards.

2.1.5.2 Change in surface physical characteristics (surface roughness)

Atomic force microscopy (AFM) or scanning force microscopy (SFM) is a very high-resolution type of scanning probe microscopy (SPM), with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction limit. Using this technique it is possible to measure the roughness of a surface and to quantify differences in surface roughness achieved by different etching techniques. Surface roughness at this molecular level is reported to correlate with the changes in surface chemistry, wettability and, to a certain extent, surface adhesion.

2.1.5.3 Change in surface chemical composition

The reduction of the fluoropolymer surface leads to the reduction in fluorine content and carbon: fluorine ratios with a corresponding increase in hydrogen and oxygen content, depending on the nature of the reduction and post-reduction steps employed. These changes in surface chemistry can be quantified by X-ray photoelectron spectroscopy (XPS), in which the solid surface is bombarded with X-rays of known energy and the characteristics of the ejected photoelectrons determined. XPS can be used to study such changes at depths up to 10 nm. Untreated PTFE has a carbon and

Unetched Etched



fluorine composition of approximately 40 and 60% respectively. Treated PTFE surfaces can change significantly to >80% carbon, <1% fluorine and 15% oxygen, for example.

Table 2.2 Examples of changes in PTFE surface chemistry by chemical etching

Polymer Treatment Colour Surface Composition (% by XPS)

Carbon Fluorine Oxygen

PTFE None White 38.4 61.6 0

PTFE THF – Na – Naphthalene

(10 seconds) Brown 87.6 0.8 11.6

PTFE Diglyme – Na –

Naphthalene (30 seconds)

Brown 80.7 1.7 16.3

The changes in surface chemical composition have been reported in published papers describing different etchant methodologies (see, for example, Brewis and Dahm, 2005), using XPS as a research tool. It is reported that some companies set standards for surface etching on the basis of changes of surface chemical composition (C:F ratio) but this is not routinely practiced in the industry.

2.1.5.4 Change in surface wettability behaviour

One of the key requisites for adequate adhesion is a good level of contact between the mobile adhesive phase and the polymer surface. As a general rule, acceptable bonding adhesion is achieved when the surface energy of a substrate (measured in dynes/cm) is approximately 10 dynes/cm greater than the surface tension of the liquid. In this situation, the liquid is said to “wet out” or adhere to the surface.

Surface tension, which is a measurement of surface energy, is the property (due to molecular forces) by which all liquids, through contraction of the liquid surface, tend to bring the contained volume into a shape with the least surface area. The higher the surface energy of the solid substrate relative to the surface tension of a liquid, the better will be its “wettability”, and the smaller the contact angle.



Figure 2.2 Contact Angle and Wettability

Many plastics are hydrophobic and are not naturally “wettable”. Pretreatment of the surface to increase adhesion can therefore also be monitored by measurement of the change in surface energy of the solid substrate upon treatment of by measurement of the liquid contact angle. For untreated PTFE surface, the surface energy ranges from 18-22 mJ/m2 (dynes/cm) and the water contact angle

with PTFE is approximately 110⁰.

The relationship between the surface contact angle and the surface energy of the etched PTFE is described by the following formula:

�� 72 �� 1

0.025

where Es in the surface energy (in dynes per cm) and θ is the contact angle (in degrees).

Table 2.3 Relationship between contact angle and surface energy

Material Contact Angle (⁰) Surface energy (dynes/cm) Degree of Etching

PTFE, native 109.2 19.4 Not etched

PTFE, etched 20 – 55 55 – 70 Excellent

PTFE, etched 55 - 60 52 - 55 Good

PTFE, etched 60 - 90 32 – 52 Fair

PTFE, etched >90 <32 Poor



Figure 2.3 Relationship between surface energy and contact angle for etched PTFE

surfaces

ASTM D7334-08 (2013) specifies the Standard Practice for Surface Wettability of Coatings, Substrates and Pigments by Advancing Contact Angle Measurement.

A semi-quantitative test for assessing the surface energy of plastic films is the ‘Dyne Pen Test’ in which a series of mixtures (of formamide and 2-ethoxyethanol) of incrementally increasing surface tension are applied to a treated surface until a mixture is identified that just wet the surface (no visible contraction of the applied drawn line). The critical surface tension of the surface is estimated from the surface tension of that particular limit mixture. This method is described in the following standards:

• ASTM D2578-09: Standard Test Method for Wetting Tension of Polyethylene and Polypropylene Films

• TAPPI T698: Determination of Wetting Tension of Polyethylene and Polypropylene Films and Coatings (Modified Visking Analytical Technique)

• ISO 8296 (2003): Plastics – Film and sheeting – Determination of wetting tension

However, it should be noted that contact angle is not the only, or necessarily accurate, indicator of whether the etching process has contributed to the success or failure of the final end user application. This is discussed in more detail below.



2.1.5.5 Change in bonding strength after application of an adhesive

The final test on the extent of surface modification is the degree to which the adhesion or bondability characteristics have been improved through the specific surface modification treatment.

Changes in the adhesion properties of modified polymer surfaces are normally characterised by a prescribed bonding methodology in which the following parameters are controlled:

• Surface area to be bonded: e.g. 20 mm wide x 10 mm long

• Type of adhesive used: two-part epoxide adhesive; cyanoacrylate adhesive

• Type of load test: failure load (Newtons); peel strength (kg/m); joint strength (mPa)

Untreated PTFE surfaces (bonded area 20 mm x 10 mm, two-part epoxide adhesive) have failure loads of approximately 420 N (joint strength 2.1 mPa). Bond strength increases by an order of magnitude (to 4260 N, 21.3 mPa) on surface treatment.

It has been demonstrated that the evaluation of bond strength for the purposes of comparison of different etching regimes is extremely dependent of the adhesive system used (Marsh, 2006a). Dta is presented in section 5.1.2.2.3 to illustrate this.

2.1.5.5.1 Etching and successful surface adhesion

This analysis has detailed various methods of monitoring the efficiency and extent of fluoropolymer surface modification as indicators of the subsequent ability of the modified surface to adhere and function adequately in the final end user application. However, there are a number of contributing factors to the success of the final application and the etchant manufacturer/service provider does not necessarily have visibility of the technical reasons for the perceived success or failure of a particular etchant technique for surface modification. There are a number of additional application specific factors that, in addition to the chemical and physical surface modification, contribute to the success of the final bonding application in the manufacture of the perfluoroplymer bonder application.

For example, the surface modification parameters (contact angle, wettability, surface roughness) may indicate a particular extent of surface modification but the success of the final bonding of the polymer will also depend on:

• Choice of adhesive system employed

• End user requirement in terms of the strength of bonding for the specific application

• Type of end application testing for adhesive strength (destructive, non-destructive or end point not related to adhesion characteristics).

In the automotive sector, for example, bonded perfluoropolymers gaskets on seals and flanges are tested in situ via dynamic integrity testing. The PTFE seal, bonded to a metal substrate, is placed in a rotating jig and the force required to peel off the seal is measured. The company providing either the etchant or etched perfluoropolymer is not necessarily party to any subsequent failure analysis and whether the failure is attributable to a failure in the etching process itself.

The surface modification indicators are therefore used primarily for quality control testing of the etching process by the applicability of the etched surface in the final bonding use is application specific.



2.1.5.6 Industry Standards applied for fluoropolymer etching applications

A number of industry standards are applied in the assessment of the quality and extent of fluoropolymer etching:

2.1.5.6.1 ASTM Standards

• ASTM D897-08 (2010): Standard test method for tensile properties of adhesive bond.

• ASTM D903-98 (2010): Standard test method for peel or stripping strength of adhesive bonds.

• ASTM D1002-10 (2010): Standard test method for apparent shear strength of single-lap-joint adhesively bonded metal specimens by tension loading (metal to metal).

• ASTM D2578-09: Standard Test Method for Wetting Tension of Polyethylene and

Polypropylene Films

• ASTM D5946-09 (2010): Standard test method for corona-treated polymer films using water contact angle measurements.

• ASTM D7334-08 (2013): Standard practice for surface wettability of coatings, substrates and pigments by advancing contact angle measurement.

2.1.5.6.2 Specific Industry Standards

• Aerospace

o SAE Aerospace Material Specification (AMS2491, 2015): Surface Treatment of

Polytetrafluroethylene (PTFE). Preparation for Bonding.

� Specifies the engineering requirements for preparing surfaces of PTFE for bonding and properties resulting from that treatment.

� Specifies the use of a solution of sodium or other alkali metal in anhydrous liquid ammonia, THF-naphthalene or naphthalene in other suitable solvents.

� Extent of etching judged on

� Extent and uniformity of surface colour change

� Tensile strength according to ASTM D897

� Shear Strength according to ASTM D1002

o SAE Aerospace Recommended Practice ARP6167 (2013): Etching of fluoropolymer

insulations.

o Hamilton Standard HS1801 (1999): Bonding, Fluoroplastics for Surface

Preparation of, Specification

o Boeing Process Specification P.S. 18165 (2002): Chemical Etching to provide a

bondable surface.

� Specifies the use of commercial etchant solutions (such as TetraEtch or FluoroEtch Safety Solvent: see Table 5.8).



� Extent of etching judged via a surrogate wettability test (ink beading test).

• Automotive

o End application testing as described in section 2.1.5.5.1.

• Other sectors of use, such as the medical, electronics and wire and cable sector: these sec tors have the own internal specifications, which will be similar to those described above.



2.2. Technical function of diglyme in the wet chemical treatment fluoropolymer surfaces

Diglyme is used as the solvent of preference for the dissolution of the reaction products of sodium metal and naphthalene (commonly referred to a sodium naphthalide: CAS 3481-12-7; EC 222-460-3) for the generation of the radical anion salt for the removal of fluorine from perfluoropolymers surfaces.

Diglyme is the preferred solvent of choice both for its inherent chemical characteristics and for the subsequent process advantages that it provides for the etching process. These characteristics will be compared with other potential alternative solvents in section 4. These properties are summarised in Tables 4.2 and 4.3.

2.2.1 Chemical functionality

2.2.1.1 Solubility of sodium naphthalide complex

Section 2.1.4 described the formation of the sodium naphthalide radical anion salt as follows:

The transfer of a single electron from the sodium metal atom to the naphthalene molecule generates a new aromatic species containing an odd number of electrons and thus possesses a radical nature, the minus sign indicating the presence of a negative charge. The added electron occupies the lowest unoccupied π orbital of the parent hydrocarbon and is delocalised throughout the naphthalene molecule, producing a univalent radical anion.

This reaction is a reversible equilibrium and the value of the equilibrium constant depends on the solvent and the temperature. This also determines the nature of cation-anion pairing in the solvent which can be either as

• free ions

• loose ion pairs

• contact (tight) ion pairs or

• larger aggregates.

Studies in the late 1960s (Shatenshtein et al, 1967 reviewed in Holy, 1974) showed that the highest yield of radical ions was obtained for ethylene glycol ethers because of the ability of these solvents to form comparatively stable five-membered chelate rings. In highly polar solvents free ions are preponderant, in solvents such as dimethyl ether ion pairs are most typical whereas in solvents of low polarity and coordinating ability, such as THF and dioxane, contact ion pairs are the most likely pairing.

The mechanism, extent and rate of solvation of the ion species is therefore dependent on the solvent used and will determine the availability of the radical anion for participation in the reductive defluorination of the fluoropolymer surface. The magnitude of the solvation of the metal ion and the naphthalene anion is the principle factor in determining the equilibrium constant for the



reaction. Rates constants for electron transfer between the naphthalene molecule and its anion range between 106 and 108 liter.mol-1.sec-1 (Stinnett, 1971: Vora, 1972), depending on the solvent.

Diglyme is a low molecular ethylene glycol ether and produces a high yield of the sodium metal / naphthalene reaction system. This allows high concentrations of sodium naphthalide, generating the strongly reducing solution suitable as an etching agent for fluorinated polymers like PTFE on a commercial scale.

It has been reported (Marsh, 2006b) that there is a relationship between the solvent dielectric constant and the reactivity of the sodium naphthalide complex. Solvents with a dielectric constant of greater that 5.5 are required to achieve the necessary extent of dissolution of the sodium naphthalide (see section 5.1.2.2.3 Process Performance: Availability of the radical anion).

2.2.1.2 Thermal Stability

Diglyme is relatively stable over the temperature range at which the etching operation is carried out

(20 – 65⁰C). It is stated that thermal decomposition to methyl vinyl ether (CAS 107-25-5; EC 203-475-4) is of the order of 10% of that associated with monoglyme (CAS 110-71-4; EC EC 203-794-9) under similar circumstances (Ebnesajjad, 2014). Methyl vinyl ether is an extremely flammable gas (H220, H280, H412).

A sodium naphthalide etchant formulated from diglyme has a recommended shelf life of 6 months, but can be stored for up to one year at room temperature without undergoing significant degradation (oral communication; Acton Technologies Ltd and Maflon Spa).

2.2.1.3 Flash Point

Diglyme is a highly flammable liquid (H225) but with a flashpoint (51⁰C) this risk is reduced in comparison with other alternative solvents. The minimisation of flammability hazard during the use of the solvent in etchant formulation and subsequent application is a significant factor in the selection of the solvent.

2.2.2 Process functionality

2.2.2.1 Process Temperature

One of the advances in the development of an etchant solvent system that provides an optimum balance of minimising chemical hazard from the components of the etchant system with operational requirements, which provide an economic treatment process, is the rate of the defluorination reaction. As stated above, the selection of diglyme reduces the overall flammability risk, but also

allows operation of the etchant process at elevated temperatures (up to 65⁰C), which significantly enhances the rate of the surface defluorination reactions. More radical anion is made available in the diglyme-based etchant at higher temperature (displacement of the equilibrium for radical anion formation, Holy 1973), resulting in reduced etchant times and increased final bond strengths of between 50 and 75% of that obtained at room temperature (Ebnesajjad, 2014). Operation at elevated temperature also reduces solvent viscosity (see section 2.2.2.3).



2.2.2.2 Process Reaction Time

Etching times are important in the commercial application of etching agents and etchants based on diglyme provide the standard of etching required, as demonstrated by bonding strength (see section 2.2.2.4) after treatment of the fluoropolymer surface for periods ranging from 30 seconds to 5 minutes, depending on the nature process (batch/continuous etc) and the complexity of the surface to be treated.

2.2.2.3 Solvent Viscosity

The viscosity of the etchant, which is determined by the viscosity of the solvent and the extent of dissolution of the sodium naphthalide in the solvent, is an important factor in the controlled etching of confined areas, such as areas of small diameter and high aspect ratio (e.g holes in printed circuit boards, woven PTFE fabrics etc). Uniform etching is promoted by low viscosity etchants, which are able to flow more easily over the surfaces to be etched. Diglyme has a viscosity similar to that

of water which is further reduced at operational temperatures of 50-65⁰C to ensure a much more consistent and uniform etched polymer surface, irrespective of the article tribology.

The viscosity of the etchant solution is also important in determining the extent of decontamination of the etched product in the subsequent washing steps. Higher viscosity etchants may result in the contamination of etched surfaces with residual deposits of naphthalene and fluoride residues, which will then require more aggressive cleaning regimes.

Control of etchant viscosity in the etchant bath at increased operational temperatures is therefore an important operational parameter in order to balance potential evaporative loss of the solvent against potential changes in solution viscosity. The use of diglyme as a solvent simplifies the management of the etching solution and subsequent downstream cleaning of etched fluoropolymer surfaces

2.2.2.4 Bond strength

As discussed above, the requirement of an etchant is to increase the bond strength from 420 N (joint strength 2.1 mPA) for the untreated perfluoroplymer surface to up to 4260 N (21.3 mPa) for a treated surface.

Although the specific solvent used in the formulation of the wet chemical etching methods based on sodium naphthalide may not be the sole influence on the extent, reproducibility and consistency of the increase in the bonding strength of the etched surface (see 2.1.5.5.1), the specific properties of the solvent allow these technical process specifications to be achieved using a methodology that:

• Minimises the hazards of a system composed of very hazardous components

• Allows the use of small scale etching systems, in either batch or continuous process mode, whilst implementing economic risk management measures that ensure adequate process control

• Provides an etchant system that is portable and can be implemented with relative ease without requiring a significant capital outlay for specialised technical equipment

• Provides access to the most powerful and reproducible etchant system available.



2.2.2.5 Polymer range

Whilst this analysis of alternatives has focussed on the use of the diglyme formulated etchant solution in the surface modification of perfluoropolymers, and specifically PTFE, it should be noted that the etchant is also used in a number of applications requiring the surface modification of other fluorinated polymers such as FEP, ETFE or PFA. Whilst other types of etchant processes or formulations may provide adequate surface modification for such polymers, the qualification of the use of specific etchants and etchant techniques are subject to the same validation and verification requirements that are discussed later in relation to potential alternatives in section 4.

2.2.2.6 Tribology of surface requiring etching

The nature and physical dimensions of the surface to be etched also dictates the strength and aggressiveness of the etching method for surface defluorination.

Diglyme based etchants are the etchant of choice in the surface preparation of PTFE skived tapes and sheets of thicknesses down to as low as 0.025 mm (0.25 µm) without prejudicing the integrity and performance of the PTFE performance in subsequent applications (such as lamination of PCB circuit boards). In contrast, for example, ammonia-based etchants are too aggressive and are limited to skived sheets thicknesses of not less than 0.25 mm

2.2.2.7 Diglyme recovery and recycling

Diglyme can be easily and economically recovered from spent etchant solution and recycled into the formulation of further etchant, thus reducing the overall annual consumption of the solvent by the applicants. Diglyme is recovered from spent etchant generated by in-house production by both applicants.

The recovery and recycling of diglyme from spent waste etchant reduces the annual consumption of diglyme by between 55 and 70%.

Diglyme is recovered by vacuum distillation at 90⁰C, is thermally stable under these conditions and does not undergo any significant extent of degradation.

2.2.2.8 In-house versus contract etching services

Wet chemical etchant technology can either be used in-house or contracted out to contract service organisation with the requisite experience in the etching of fluoropolymers. Organisations requiring the surface modification of fluoropolymers for incorporation into their own products may lack the time, space or expertise for in-house etching and outsource the etching process to third parties that provide a complete line of batch and continuous contract etching services.

The use of such third party services offering proprietary techniques optimises the sodium etching process for custom applications, for both small and large production, through the development of application-specific surface modification techniques (including secondary treatments) to provide tailored, specific adhesion for each bonding situation. Such customised etching services offer the end customer an economic way of generating a bondable surface with fast turnaround to ISO 9001/14001 certified reliability.

The use of diglyme as a solvent provides a greater degree of flexibility in the tailoring of application specific surface modification of fluoropolymers.



3. ANNUAL TONNAGE

Maflon Spa is also a downstream user of diglyme also at a rate of up to mt tonnes per annum, which is used for the in-house formulation of their own etchant solution, using sodium naphthalide purchased from Acton Technologies Ltd.

Table 3.1 Composition of Typical Etchant Solvent

Substance CAS Number EC Number % (w/w)

Diglyme 111-96-6 203-924-4 80 – 90

Sodium naphthalide 3481-12-7 222-460-0 10 – 20



4. IDENTIFICATION OF POSSIBLE ALTERNATIVES

The surface treatment of plastics and polymers has been the subject of intense research and study over many years. The low surface energy of polymer surfaces results in intrinsically low adhesion without some form of surface treatment. These surface treatments can be broadly classified as follows:

• Cleaning

• Mechanical treatments

• Wet Chemical Treatments

• Plasma Treatments, including flame and corona

• Photochemical Treatments and Laser treatment

Surface changes occur as a result of four distinct processes (cleaning, ablation, cross-linking and surface chemical modification), all of which serve to increase the surface energy of the polymer surface through surface oxidation of the polymer chains. In the case of fluoropolymers, this requires significant defluorination of the polymer surface.

For the purpose of this analysis of alternative methodologies for the surface modification of fluoropolymers surface cleaning, for the removal of contaminants, and mechanical abrasion, to roughen the surface and increase contact area for subsequent adhesion, will not be further addressed as they play little part in the chemical modification of fluoropolymeric surfaces.

4.1. List of possible alternatives

The following alternative methodologies, which have been identified from both industry knowledge and experience and from a review of publicly available literature sources, are examined in further detail in this document:

• Wet Chemical Treatment

o Generation of solvated ions and radical anions by chemical means

� Sodium – ammonia systems � Sodium – naphthalene systems in solvents other than diglyme � Other chemical systems

o Generation of solvated ions and radical anions by electrochemical means

� Indirect � Direct � Metal amalgams

• Plasma Treatments

o Plasma o Corona o Flame

Table 4.1 provide a comparative summary of these alternative techniques.



Table 4.1 Process Criteria Matrix

Process Suitability for Polymer

Type Treatment

time Treatment

Temperature Adhesion Wettability Scale

Suitable for complicated shapes

Commercially available

Hazards

Fully

fluorinated Partially

fluorinated

Wet Chemical Methods

Solvated electrons and radical anion salts

Yes Yes Seconds to

minutes <65⁰C Excellent Excellent Portable Yes Yes

Hazardous solvents

Strong aqueous bases No Yes NA 80⁰C Good Good Portable Yes No Strong bases

Other reductive pre-treatments No Yes Hours Unknown Unknown Unknown Portable Yes No Variable

Electrochemical Treatment Methods

Direct Possibly Yes Unknown Room Good Variable Fixed Possibly No

Indirect Possibly Possibly Unknown Unknown Unknown Unknown Fixed Possibly No

Metal amalgams Possibly Possibly Unknown Unknown Unknown Unknown Fixed Possibly No

Plasma Treatments Possibly Yes Variable Room Poor/variable Variable Fixed Poorly Yes

Flame Treatment Methods No Yes Unknown Unknown Unknown Unknown Fixed Yes No



4.2. Description of efforts made to identify possible alternatives

3.2.1 Research and development

Maflon Spa has developed its own etching process and, in doing so, has undertaken cooperative development with Acton Technologies Ltd. Maflon Spa has been operating the etching process for 25 years and, during that time, has investigated the use of alternative solvents for wet chemical techniques and alternatives technologies. Acton Technologies Ltd have been a leader in the development and application of fluoropolymer etching systems for over 50 years and have a consolidated reputation in the industry. Acton Technologies Ltd have undertaken a range of research and development activities for the assessment of alternative solvents for wet chemical etching (Marsh, 2006a; 2006b), for evaluation of alternative etching methodologies and for the development and validation of etching methodologies in a number of industry sectors. Maflon Spa and Acton Technologies Ltd, due to their close technical co-operation, have therefore jointly developed this Analysis of Alternative.

3.2.2 Data searches

Maflon Spa have undertaken, independently, an evaluation of the publicly available literature, including the patent literature, to keep informed of developments in techniques for fluoropolymer surface modification that may be of significance to their own applications. Acton Technologies Ltd have engaged an external consultant to undertake an extensive literature search on the availability of alternative solvents for wet etching and alternative etching techniques.

3.2.3 Consultations

Maflon Spa has not undertaken any additional external consultations to identify alternatives except as identified above as part of their own Research and Development programme. Both Maflon Spa and Acton Technologies Ltd have consulted with chemical suppliers (Dow, BASF, Brenntag) to evaluate other diglyme solvent alternatives that have been made available and which are described in the section 5.1.2. Acton Technologies Ltd have undertaken a detailed co-operative research and development programme over the period 1996 – 2006 in order to evaluate the use of alternative solvent (Marsh, 2006a; 2006b). These studies are referenced in the Analysis of Alternatives.



5. SUITABILITY AND AVAILABILITY OF POSSIBLE ALTERNATIVES

5.1. WET CHEMICAL TREATMENTS

Wet chemical systems are based on the generation of a solvated electron transfer (SET) chemical species which can functionalise a fluoropolymer surface. SET donors are available in different chemistries and the suitability of each of these alternatives is summarised in Table 4.1 and discussed in more detail in the sections below.

4.1.1 Sodium – Ammonia System

Solvated electrons can be generated by the chemical reaction of alkali metals in liquid anhydrous ammonia. The most commonly used alkali metal is sodium and this provides very harsh reduction conditions.

Exposure of fluoropolymers to this system often leaves the treated surface black due to the extent of the reduction reactions. Other alkali metals, such as magnesium, can be used to provide more mild reduction conditions but it is reported that electrochemical methods are also required to assist in the dissolution of the magnesium (Zhang et al., 2014).

Table 5.1 Sodium and ammonia substance properties

CAS EC CLP Classification

Sodium 7440-23-5 231-132-9 H314: Causes severe burns and eye damage H260: In contact with water releases flammable gases whish may ignite spontaneously

Liquid ammonia, anhydrous 7664-41-7 231-635-3

H221: Flammable gas H280: Contains gas under pressure, may explode if heated H314: Causes severe skin burns and eye damage H331: Toxic if inhaled H400: Very toxic to aquatic life Contact with liquid may cause cold burns/frostbite

5.1.1.1 Technical feasibility

The sodium–ammonia etching system for fluoropolymers was the original surface treatment method for this polymer group. The reagent is prepared by the dissolution of metallic sodium in liquid anhydrous ammonia to give a dark blue solution with a sodium concentration of 0.5–1.0 % (w/w). An exposure of between two and twenty seconds is required to achieve an etched surface, after which the treated article is removed from the etchant bath and ammonia allowed to evaporate from the surface of the etched article. The article is then further cleaned by an ethanol wash. In a continuous process the product is removed from the etchant and transferred to a water wash. Etching times are dependent upon the freshness of the etching solution and the etchant has a limited lifetime. Etchant solution life span is limited by the rate of evaporation of the anhydrous ammonia and the sodium metal oxidation rate (which itself is accelerated by humidity). As this process is performed under ambient conditions the brief effective pot life can be measured in minutes. To



enable continuous processing larger volumes of solution (100 litres) need to be available for continuous feed to the point of etching. Etched surfaces vary from black to brown in colour. There is no recovery of ammonia in a sodium ammonia etching system. However, the use of these materials requires investment in cryogenic equipment for the handling of liquid ammonia, control of the process environment to restrict the ingress of moisture due to the reactivity of sodium with water, emission control technology to ensure that emissions of ammonia from the process are minimised and control of subsequent effluent discharge carrying high levels of hydroxides and fluorides. As a consequence, this technology alternative can only be offered at fixed commercial installations as a contract service, unless the volume requirement for etching for a particular end-use is sufficient to justify the economics of installation of such technology. In addition, the reductant power of this system is often too aggressive for the article/surface to be etched. Too long an immersion time can reduce the adhesion achieved if the surface becomes significantly altered and weakened by too extensive a defluorination process. The small molecular size of the ammonia system creates an aggressive and deep penetrating behaviour that in many instances makes it ineffective for controlled use. Fluoropolymer skived tapes, sheet or tubes with a wall thickness of less than 0.25 mm cannot be treated in a controlled manner by this etchant. An example of this would be thin wall fluoropolymer tubing for use in medical catheters. The deep penetration of an ammonia treatment would penetrate fully through the thin wall of this polymer lining, creating pinholes and defeating the required integrity of the medical tubing. In comparison, a diglyme-based sodium etching solution limits the surface treatment only to the outer surface of this tubing, leaving the inside surface of the tubing “virgin” fluoropolymer and thus able to deliver the intended material characteristics of untreated fluoropolymers, i.e. non-stick. Another example of the over penetration of this treatment is in PTFE coated fiberglass cloth in thin dimensions, where a sodium-ammonia treatment would permeate throughout the fabric and, in the application in the construction of multi-laminate industrial belting, the desired non-stick characteristic would defeated wherever “bleed-through” of the etching solution had occurred. The adhesion achieved from etching PTFE with a sodium–ammonia solution is stated to be 15% weaker than that observed with a corresponding diglyme system etchant (http://www.polyfluor.nl/en/archive/fluoro-etch--etching-fluid/). In a comparative study carried out for Acton Technologies by Lehigh University Department of Chemistry, the impact of two commercial etching techniques on the final surface bonding of PTFE strips using identical adhesion regimes was examined (Acton Technologies Ltd, unpublished research). This study demonstrated that a statistically significant increase in final bond (peel) strength was achieved after use of a diglyme-based etchant (FSS) in comparison with a commercial sodium-ammonia etchant based process. However, it is difficult to corroborate this as a more general statement of extent of adhesion because, as stated in section 2.1.5.5.1, there are a number of other factors in addition to the nature of the etchant that define the extent and suitability of promoted adhesion in each specific end user application.



5.1.1.2 Economic feasibility

The use of a sodium-ammonia etching system is also a less economic alternative, both from the investment required in the equipment to handle the sodium and liquid ammonia reactants and also in the cost of the consumables, as ammonia is not recovered in this process. The use of the sodium–ammonia system is therefore at least a factor of times more expensive than the equivalent diglyme system (Acton Technologies Ltd, personal communication). Making further allowance for the recovery and recycling of diglyme will increase this comparative cost ratio.

5.1.1.3 Reduction of overall risk due to transition to the alternative

The fluoropolymer etching industry moved away from the sodium–ammonia etchant system on the basis of the hazards and economics of the use of metallic sodium and liquid anhydrous ammonia. Although the system can etch a wide range of fluoropolymers there are a number of significant disadvantages:

• The etchant is very aggressive and is not self-limiting, resulting in a surface that may not have the required bonding characteristics.

• There is a limitation in the minimum thickness of materials that can be etched (not less than 0.25 mm). In today’s applications of PTFE in the electronics, aerospace and medical sectors where smaller and lighter components are being developed continuously, this is a significant disadvantage.

• The required use of the etchant at very low cryogenic temperatures can result in the distortion of PTFE components

• The health and environmental risks are substantially different from the system which is subject to this authorisation. Transition back to this alternative will not reduce overall risk to health and the environment.

• A sodium–ammonia etchant is not pourable, is difficult to store and handle and has a significant odour.

• Ammonia cannot be recovered and recycled from this use

5.1.1.4 Availability

Fluoropolymer etching using a sodium-ammonia system is offered commercially in the European Union from the following service providers:

• Fluorten s.r.l. (Italy) (http://www.fluorten.com/eng)

• SA Pirep (France) (http://www.pirep.fr/finitionEN.html)

• Fluorocarbon UK Ltd, http://www.fluorocarbon.co.uk/products/solutions/ptfe-sheet-and-tape;

• Holscot, http://holscot.com/glossary/fluoroplastic-etching/;



The process is described as ‘the most effective etching medium available’ but also one in which ‘only a few companies in the world are able to run and manage with environmental compliance’, reflecting the aggressive nature of the reduction conditions provided. As indicated above, this is offered primarily as a fixed installation, contracted etching service and is not suitable for smaller scale fluoropolymer etching operations.

5.1.1.5 Conclusion on suitability and availability for sodium–ammonia etching

alternative

Sodium–ammonia etching is available on a commercial basis for the larger scale custom etching of fluoropolymer surfaces but is of limited application due to the aggressive nature of the etchant itself and the inability to employ the etching technique cost effectively at many downstream users sites where fluoropolymer etching is integrated into the manufacturing process. As a consequence the sodium-ammonia etching system has not been the primary etchant of choice for PTFE surface modification and is only provided on a contract basis at fixed, bespoke installations where the risks of handling liquid ammonia can be completely assured. A number of historic incidents of the release of ammonia from such systems are known.

5.1.2 Sodium – Naphthalene – Alternative Solvents

The dispersion of sodium in naphthalene in a number of solvents to provide a more economic and convenient method of etching fluoropolymers has been described in the literature over the last thirty years. The mechanism by which this is achieved and the generation of the solvated anion which is key to the reduction process is described in greater detail in sections 2.1.2, 2.1.3, 2.1.4 and 2.2.2.1.

A number of alternative carrier solvents for the sodium-naphthalene reductant system have been described and commercialized to a limited extent and this section compares the suitability of these solvents based on the criteria developed above for the use of diglyme (see summary Tables 5.2 and 5.3). These solvents are selected primarily on the solubility of sodium napthalide and the generation of the solvated anion. Typical formulations are 1:1 molar ratios of sodium and naphthalene in the appropriate solvent.

5.1.2.1 Substance ID and properties

Table 5.3 lists the solvents that are examined as possible alternatives to diglyme in a sodium – naphthalene – solvent system. Alternative solvents have been selected for further examination in this section based on either reports of their use for the formulation of solvents for etching of fluropolymers or their ability to generate solvated anion species in a sodium – naphthalene system.



Table 5.3 Solvent Criteria Matrix – Classification

Common name Chemical name CAS EC Hazard Classification REACH

Annex XIV

REACH Candidate

List

Diglyme Bis(2-methoxyethyl) ether 111-96-6 203-924-4 H226

H360 1B EUH019

Yes Yes

Tetrahydrofuran Tetrahydrofuran 109-99-9 203-728-8

H225 H302 H319

H351 Cat 2 H335

Highly flammable liquid or vapour Harmful if swallowed Causes serious eye irritation Suspected of causing cancer May cause respiratory irritation

No No

Monoglyme 1,2-dimethoxyethane

Ethylene glycol dimethyl ether (EGDME)

110-71-4 203-794-9 H225 H332

H360 1B

Highly flammable liquid or vapour Harmful if inhaled May damage fertility or the unborn child

No Yes

Triglyme 1,2-bis(2-methoxyethoxy)ethane

Triethylene glycol dimethyl ether (TEGDME)

112-49-2 203-977-3 H360Df EUH019

May damage fertility or the unborn child May form explosive peroxides

No Yes

Tetraglyme bis(2-(2-methoxyethoxy)ethyl) ether 143-24-8 205-594-7 H360 1B May damage fertility or the unborn child No No

1,4-dioxane 1,4-dioxane 123-91-1 204-661-8

H225 H319 H335 H351

Highly flammable liquid or vapour Causes serious eye irritation May cause respiratory irritation Suspected of causing cancer

No No

Dipropylene glycol dimethyl ether

Dipropylene glycol dimethyl ether (DPG-ME)

111109-77-4 404-640-5 Not classified No No

Diethyl glyme Bis(2-ethoxyethyl) ether 112-36-7 203-963-7 H315 Causes skin irritation No No



Table 5.2 Solvent Criteria Matrix – Physico-chemical properties

Common name Boiling Point

Flash Point Density Viscosity Evaporation rate Odour Thermal stability

⁰C

1,010.8 hPA ⁰C

Closed cup g/ml 20⁰C

mPa.sec 20⁰C

n-butylacetate = 1

Diglyme 160.16 51 0.95 1.06 0.36 Mild ethereal Non-residual

<10% degradation to methyl vinyl ether compared to monoglyme

Tetrahydrofuran 65 -21.2 0.883 0.456 6.3 Ethereal

Monoglyme 84.45 2 0.87 0.47 4.99 Ethereal

Non-residual

At temperatures >0⁰C, spontaneously decomposes to

methyl vinyl ether

Triglyme 216.25 111 0.99 3.39 <0.001 Mid-ethereal Non-residual

Tetraglyme 276.49 141 1.012 4.01 <0.001 Very mild ethereal

Non-residual

1,4-dioxane 101.3 11 1.03 1.19 2.2 Mild, ether-like

Dipropylene glycol dimethyl ether 175 65 0.903 1 0.13 Very mild

Diethyl glyme 188 82.2 0.91 1.4 0.04 Mild

Non-residual

1Some data derived from BASF: High Performance Solvents: Glymes, 1,3 dioxalane and 1,4 dioxane (http://www.standort-ludwigshafen.basf.de/group/corporate/site-ludwigshafen/en/literature-

document:/Brand+Ethyl+Glyme-Brochure--High+performance+solvents+Glymes+1+3+Dioxolane+and+1+4+Dioxane-English.pdf)




The alternative solvents listed above have all been used or purported to have been used in the formulation of sodium-naphthalene etching solutions, with the exception of dipropylene glycol dimethyl ether and diethyl glyme, which have been tested as potential alternatives by the current applicants. However, comparison of their physico-chemical and toxicological properties demonstrates that:

• None of the alternative solvents offer any significant advantage in the reduction of risk from use as a formulating solvent, apart from of dipropylene glycol dimethyl ether and diethyl glyme

• Most of the alternatives have the same combination of physico-chemical properties as diglyme in providing the most suitable solvent for this application. Dipropylene glycol dimethyl ether has similar boiling point, flash point and density to diglyme.

The comparison of solvent properties, described below, is summarised in Table 4.3. 5.1.2.2.1 Physico-chemical Properties

Flash Point

The flash points of tetrahydrofuran (-21.2⁰C), 1,4-dioxane (11⁰C) and monoglyme (2⁰C) are significantly lower than that of diglyme and increase the flammability risk in the use of these

solvents for the etching process. Dipropylene glycol dimethyl ether has a flash point of 65⁰C, which is higher than that of diglyme.

Boiling Point and Evaporation Rate

The boiling points of tetrahydrofuran, 1,4-dioxane and monoglyme are substantially lower than that of diglyme. As a consequence the evaporation rates for these solvents at process temperatures will be significantly higher than diglyme, leading to additional requirements for emission controls. These higher evaporation rates combined with decreased flash points, in comparison with diglyme, present significant handling risks in the application of such solvent-based etchants.

Dipropylene glycol dimethyl ether has a boiling point of 175⁰C, which is slightly higher than that of diglyme, and a lower evaporation rate.

Thermal Stability

Monoglyme undergoes spontaneous decomposition to methyl vinyl ether (CAS 107-25-5, EC 203-

475-4) at temperatures in excess of 0⁰C. Methyl vinyl ether is an extremely flammable gas (H220). The decomposition of diglyme is approximately 10% of the rate on monoglyme and therefore substitution of diglyme with monoglyme substantially increases the process risk through the

generation of a flammable gas by-product (Ebnesajjad, 2014). At temperatures above 0⁰C, monoglyme-based etchants will begin this spontaneous decomposition and will consume some of the active etching ingredient, sodium, in the process.



Viscosity

The viscosities of triglyme and tetraglyme are significantly greater than diglyme and restricts the applicability of the resultant etchant for the surface modification of controlled areas of small diameter or high aspect ratio. Monoglyme-based etchants also have a high viscosity, due to the higher degree of solvation of sodium and naphthalene in this solvent. In combination with increased rates of evaporation, this leads to additional difficulties in the control of etchant viscosity and the subsequent removal of process residues from etched surfaces. Open weave fluoropolymer fabrics or woven glass clothes, for example, should not be etched with monoglyme-based solvents as this higher viscosity leads to lower rates of removal from treated materials which can then give rise to a flammable vapour on evaporation under atmospheric conditions.

Dipropylene glycol dimethyl ether has a similar viscosity to diglyme.

5.1.2.2.2 Toxicological Properties

Reproductive toxicity

Both monoglyme and triglyme are substances of very high concern that have been prioritised on the ECHA Candidate List for the same reproductive hazard as diglyme. Substitution of diglyme with either of these solvents would not therefore reduce the potential reproductive hazard. Tetraglyme is also classified for the same reproductive toxicity end point but is not on the Candidate List at present. Dipropylene glycol dimethyl ether is not classified for this hazardous end-point.

Carcinogenicity

Both tetrahydrofuran and 1,4-dioxane are classified as suspected carcinogens.

5.1.2.2.3 Process performance

Etchant shelf life

There are two different solvent-based etching solutions that are commercially available.

The monoglyme-based etchant has a manufacturer defined storage life of 6 months when stored at

or below 0⁰C. In use at ambient temperatures (20-25⁰C) the etchant shelf life is a maximum of 7 days. THF based etchant is also reported to have a maximum shelf life of 6 months. A diglyme-based etchant, in comparison, has a shelf life of one year at room temperature and can be used both

and ambient temperatures and at temperatures up to 60⁰C.

Availability of the radical anion

In section 2.2.1.1 the chemical mechanism of solvation of the sodium naphthalide complex was discussed. The mechanism, extent and rate of solvation of the ion species is dependent on the solvent used and will determine the availability of the radical anion for participation in the reductive defluorination of the fluoropolymer surface. The magnitude of the solvation of the metal ion and the naphthalene anion is the principle factor in determining the equilibrium constant for the reaction. Rates constants for electron transfer between the naphthalene molecule and its anion range between 106 and 108 liter.mol-1.sec-1 (Stettin, 1971: Vora, 1972), depending on the solvent.

There is little data in the public literature detailing the solvation of sodium naphthalide in different solvents. Holy (1973) tabulates the effect of a number of solvents upon the equilibrium constant of sodium naphthalide which gives some indication of the impact of different solvent but does not provide a comparative basis for the solvents considered as alternatives for fluoropolymer etchants.



Table 5.3 Effect of solvent structure of sodium naphthalide equilibrium reaction

Solvent Structure CAS EC Equilibrium

constant

Diglyme CH3OC2H4OC2H4OCH3 111-96-6 203-924-4 No data

Dimethyl ether CH3OCH3 115-10-6 204-065-8 0.2

Diethyl ether C2H5OC2H5 60-29-7 200-467-2 0.02

Dimethoxyethane (monoglyme) CH3OC2H4OCH3 110-71-4 203-794-9 1.0

Methoxyethoxyethane* (ethylene glycol ethyl methyl ether)

CH3OC2H4OC2H5 5137-45-1 225-893-6 1.0

Methoxypropoxyethane* CH3OC2H4OC3H7 77078-18-3 0.85

Dibutoxyethane* C4H9OC2H4OC4H9 112-48-1 203-976-8 0.2

Dimethoxymethane* CH3OCH3OCH3 109-87-5 203-714-2 0

1,1 dimethoxyethane* CH3O(CH2)2OCH3 534-15-6 208-589-8 1.0

1,1 dimethoxypropane* CH3O(CH2)3OCH3 4744-10-9 225-258-3 0.5

1,1 dimethoxybutane* CH3O(CH2)4OCH3 4461-87-4 - 0.2

1,1 dimethoxypentane* CH3O(CH2)5OCH3 26450-58-8 247-716-1 0.05

*not currently registered under REACH at this time

The use of glymes in the solvation of sodium naphthalide is of particular significance as glymes contain multiple ether-type oxygen atoms and flexible alkyl chains that allow them to behave like crown ethers in solvating metal ions such a sodium through oxygen-ion complexing (Tang and Zhao, 2014). The equilibrium constant for sodium naphthalide in tetraglyme is reported at 200-300

M-1 at 27⁰C and forms loose ions pairs (Hoefelmann et al. 1969, reported in Tang and Zhao (2014)). The behavior of sodium in a range of glyme solvents has been studied using sodium iodide as a model system and the type of ion pairing shown to vary from free ions, to loose ion pairings to clusters of ion pairs, depending on the concentration of the salt and the structure of the solvent. The reactivity of free ions and solvent-separated ion pairs is very high compared to that of contact ion pairs (Bakskaran and Muller, 2007).

[R-M+]n nR-M+ R-//M+ R- + M+

Aggregated ion

pairs

Contact ion pairs Solvent separated

ion pairs

Free ions

The flexibility of glymes enables the formation of many stable structures within a narrow energy range with very different geometrical arrangements of ether oxygens. At least four geometries have been identified for metal-glyme complexes of sodium (Tang and Zhao, 2014).

Analytical attempts to detect or quantify the ionic species by UV spectroscopy for after the dissolution of sodium naphthalide in tetrahydrofuran, diglyme and dipropylene glycol dimethyl ether were not successful (Marsh, 2006b). However, a relationship between solvent dielectric



constant and therefore solvent polarity, sodium naphthalide solubility and extent of fluoropolymer surface modification was observed during the course of this study.

Table 5.4 Correlation of etchant activity with solvent dielectric constant (Marsh, 2006b)

Organometallic salt

Solvent Dielectric Constant

Colour of solution

Surface etched?

Colour of etched surface

Sodium naphthalide

Diglyme 7.2 Green Yes Dark

Tetrahydrofuran 7.5 Green Yes Medium

Dipropylene glycol dimethyl ether 5.5 Green Yes Light

Dioxane 2.2 Red-brown Insoluble complex

No NA

From this study it was concluded that the dielectric constant of the solvent needed to be greater than 5.5 in order to adequately solvate the sodium naphthalide. Attempts to improve solvation by the addition of a cosolvent with a high dielectric constant were not successful (Marsh, 2006b)

It can therefore be concluded that the solvation of sodium naphthalide will be highly dependent on the nature of the chosen solvent, the degree of solvation and form of complexation which will determine the overall activity of the radical carbanions necessary for fluoropolymer surface defluorination reactions.

The unique properties of diglyme, to complex alkali metal ions in solution, make it difficult to find suitable alternatives, which also allow

• economic and low risk recycling of the solvent by way of distillation

• fine tuning operational reducing power by adjustment of temperature and concentration and

• sufficient complexing properties to allow high yields of the alkali metal with naphthalene.

Alternatives such as propylene glycols also have complexing properties to alkali metal ions, albeit weaker than that of the ethylene glycols.

End group modification of the diethylene glycol ether will leave the complexation capacity greatly intact but the resulting significant reduction in the vapor pressure will make economic distillative workup for solvent recycling more difficult.

Process reaction time and bond strength

The concentration of the radical anion available in the solvent-sodium naphthalide system will determine both the rate and extent of the surface modification reaction and will therefore determine both the etching process time and the final bond strength that can be achieved. There are no definitive comparative studies comparing the performance of sodium naphthalide in different solvents for the surface modification of the same fluoropolymer surface and with the final modified surface tested with the same bonding system. As described in section 2.1.5.5.1, bonding adhesion tests do not necessarily characterize the extent of fluoropolymer surface modification.



Table 5.5 Bond strength after etching PTFE with a THF-sodium naphthalide etchant

Solvent Polymer Reaction time Adhesion Reference

THF PTFE 10 seconds 21.4 MpA Joint strength

Brewis et al., 1993 Brewis and Dahm, 2004

THF PTFE 10 seconds 4,280 N Failure load

Bonded area 20 x 10 mm, two part epoxide adhesive

Brewis and Dahm, 2004

THF PTFE (skived tape) 10 seconds 30 seconds

4 hours

2,420 N 2,730 N 2,760 N

Failure load Bonded area 12 x 12 mm, epoxy

adhesive

Brewis and Dahm, 2004

The bond strength achieved with different adhesive systems was reported during a comparison of sodium naphthalide etchants formulated in diglyme and dipropylene glycol dimethyl ether (Marsh 2006a).

Table 5.6 Comparative bond strength of etched standard PTFE strips (Marsh, 2006a, b)

Etchant Loctite

Cyanoacrylate adhesive

Araldite Epoxy resin

adhesive

Loctite Silicone adhesive

Spunfab copolyamide

adhesive Contact Angle

Peel Strength (pli) ⁰

Diglyme – sodium naphthalide 0.35 11.15 9.88 7.75 54-61

Dipropylene glycol dimethyl ether – sodium naphthalide

1.92 3.01 Not tested Not tested 66

Note: Bond strength here is peel strength for test PTFE strips and is quoted in units of lbs per linear inch (pli)

Table 5.7 Bonding strength, peel test (Maflon Spa, 2015, unpublished laboratory results)

Etchant Contact Angle Surface tension

Peel Strength (N/cm)

Diglyme – sodium naphthalide 44.4 60.58 2.88

Dipropylene glycol dimethyl ether – sodium naphthalide 80 38.95 2.03

Ethyl glyme - sodium naphthalide 62.3 50.59 1.92

In both independent evaluations dipropylene glycol dimethyl ether based etchant did not give a suitable bonding strength in comparison with the diglyme based etchant across a range of formulations and adhesive systems. The use of ethyl glyme as solvent also did not produce an etchant of comparable performance in terms of bonding strength.



Surface Modification

The performance of etching solutions prepared from dipropylene glycol dimethyl ether and diglyme has been compared in experimental work using analytical techniques which determine the extent of chemical and physical modification of the PTFE surface. The results are tabulated below which demonstrates that the extent of etching is both more extensive and more consistent with the diglyme-based solvent system (Table 5.9 and Table 5.10).

Table 5.8 Comparison of PTFE surface modifications using alternative solvents (Marsh,

2006b)

Technique Dipropylene glycol dimethyl ether

based etchant (CAS 111109-77-4)

Diglyme based etchant

Wettability – Contact Angle (Unmodified PTFE 109⁰)

70⁰ (30 second etch) 58⁰ (60 second etch)

35⁰ (30 second etch) 48⁰ (60 second etch)

Surface Chemistry by XPS Analysis Similar levels of reduction in levels of surface CF2 which do not correlate with

contact angle data.

Surface topography (roughness) by AFM

Surface roughness of 0.5 – 0.8% deviation from smooth

Surface roughness 2.9-3.0% deviation from smooth

It was concluded that these test results demonstrated that the extent of surface modification achieved by this alternative etchant formulation as judged by both degree of wettability and surface topography measurements, was not compatible with that required for commercial applications.

Table 5.9 Laboratory comparison of PTFE surface modifications using alternative

solvents (Maflon Spa, 2015, unpublished laboratory results)

Technique

Dipropylene glycol dimethyl ether based

etchant (CAS 111109-77-4)

Diethyl glyme based etchant

(CAS 112-36-7)

Diglyme based etchant (CAS 111-96-6)

Wettability – Contact Angle (Unmodified PTFE 109⁰)

Good Good Good

Wettability- Dyne Pen testing

Good Good Good

Colour of etched surface Brown Brown Brown

Table 5.10 reports the laboratory testing of two alternative solvents by Maflon Spa (2015) in which dip etching of PTFE skived tape was used to assess the extent of etching from sodium naphthalide etchants of the same concentration in three different solvents. In the laboratory a similar level of surface treatment was obtained, as judged by change of surface colour, contact angle measurement and wettability using the dyne pen test to derive a value for surface energy. However, when transferred to the production plant for plant trials, significantly worse results were obtained with



lower and less consistent colour, less wettability and higher contact angles in comparison with a diglyme-based etchant.

Figure 5.1 Colour comparison of PTFE sheet etched by sodium naphthalide in three

different solvents under production plant conditions

Both Acton Technologies Ltd and Maflon Spa have concluded that although dipropylene glycol dimethyl ether is, theoretically, a potential alternative solvent for the formulation of sodium-naphthalene etchants, the performance of such etchants has not been successful from both laboratory and production pilot trials, for either batch or continuous etching applications.

Neither company is, at this time, planning further investment on research and development of this solvent system on the basis of these negative results.


Maflon Spa have estimated the increase in overall cost of etching for their continuous PTFE sheet etching process (defined as € per metre) for the use of both dipropylene glycol dimethyl ether and diethyl glyme, should either of these alternative solvents have produced commercially acceptable quality etched products. Maflon Spa have concluded that the continuous production line speed would be reduced by up to 30% and result in an overall increase in cost of between 2 and 4%. However, as the formulated etchants did not produce the required commercial final quality, the replacement of diglyme with these alternative solvents was not pursued.

5.1.2.4 Reduction of overall risk due to transition to an alternative solvent

Two of the alternative solvents examined, monoglyme and triglyme, have been prioritised for the REACH Candidate List on the basis of their reproductive toxicity. The increased volatility of monoglyme would potentially increase the risk of exposure. Tetraglyme is also classified for the same endpoint but has not been prioritised to the REACH Candidate List. The lower volatility of triglyme and tetraglyme would reduce the risk of exposure but substitution of one solvent with another with the same hazard classification that resulted in the prioritisation of diglyme to REACH Annex XIV is not considered a sensible viable alternative strategy.

Diglyme Ethyl Diglyme dipropylene glycol dimethyl

ether



There are significant additional safety issues associated with the high vapour pressure and low flash point of monoglyme and tetrahydrofuran as alternative solvents, which has caused the industry to move away from their use over the last twenty years. The formation of peroxides and the increase in process risk during solvent recovery is also a significant issue to take into consideration. Monoglyme is not a solvent that can be recovered easily, due to its thermal instability and can more readily form explosive peroxides, and etchant formulations using this solvent are essentially single use with no recovery.


The alternative solvents examined in the sections above are all considered commercially available on the basis that they have all been registered in full at an appropriate tonnage band by at least one EU legal entity under REACH. Formulated sodium-naphthalene etching solutions, that are either currently commercially available or to which references can be found in an internet search for PTFE etchants, are listed in the following table:

Table 5.10 Other commercial solvent-based fluoropolymer etchant systems

Solvent Supplier Trade Name

Monoglyme W.L. Gore Tetra-Etch

W.L. Gore produced a tetrahydrofuran-based etchant historically and such an etchant is referred to in much of the literature on sodium-naphthalene based etchant systems. However, the THF-based etchant has not been available

commercially for over twenty years

Monoglyme Tetra-Etch Products Ltd Tetra-Etch

Triglyme Matheson Gas Poly-Etch W

Tetraglyme Matheson Gas Poly-Etch

Matheson Gas is a United States Supplier Only

Safety data sheets are available for these Matheson products but their availability is uncertain (It is understood that they have not been available for over twenty years)

Either diglyme or monoglyme

Artilabo International Fluoroplastic-Etch

Monoglyme Technetics Group PrimeEtch

PrimeEtch Plus PrimeEtch II

Technetics Group is a United States Supplier Only

Diglyme Reltek (US) Bond-It

Reltek is a United States Supplier Only

Diglyme APC (Scotland) Ltd Bond-Prep

Monoglyme Fluortech (US) Not Known

Fluortech is a United States Supplier Only

Monoglyme Fulcrum Chemical (US)

Natrex 25 Natrex 19

Natrex VisReduce Natrex High FP

Fulcrum Chemical is a United States Supplier Only

Not known Adtech Customised etching service

Ammonia and diglyme based

etchants Holscot Customised etching service



5.1.2.6 Conclusion on suitability and availability for Alternative Solvent

The selection of an alternative solvent for this use requires an optimum combination of the following physico-chemical and process characteristics:

1. Adequate solvation of sodium naphthalide to maximise the availability of the radical anion at the fluoropolymer surface. This dictates the use of a polar solvent that can solvate the sodium ions through oxygen complexing but in a form that makes sufficient concentrations of the active ions available for the defluorination reaction.

2. Physico-chemical properties of a relatively high flash point and good thermal stability at room temperature to minimise the risk during handling and storage of the formulated etchant.

3. A viscosity close to that of water to ensure that the etchant is able to access and etch all

exposed surface in an even manner and to be subsequently removed, together with the process residues, by the subsequent washing steps.

4. Produce an etch that provides the right degree of surface modification in a controlled and

even manner, as judged by wettability testing. As illustrated in section 2.2 an acceptable

etch would achieve a reduction in the contact angle to <60⁰.

5. Produce an etch that is suitable for subsequent bonding applications for the etched PTFE component, as judged by specific application based adhesion tests.

Selected solvents that have been used in the formulation of commercial etchants, tetrahydrofuran and monoglyme, do produce an acceptable etch across the range of fluoropolymers. However, there are significant additional safety issues associated with the high vapour pressure and low flash point of these two solvents which has caused the industry to move away from their use over the last twenty years. Monoglyme has been prioritised onto the Candidate for reproductive toxicity and THF is suspected carcinogen The other alternative glymes (triglyme, tetraglyme) that have been reported as alternatives do not produce such a good etch as diglyme, due to the reduced availability of the active components of the etch, and also have a viscosity which would provide additional process difficulties for the removal of the etchant and etchant residues across the range of etched PTFE products. Triglyme has been prioritised onto the Candidate for reproductive toxicity and tetraglyme is classified for the same hazardous end point. There are two potential alternative glymes, dipropylene glycol dimethyl ether and diethyl glyme, which have similar physicochemical properties to diglyme and which have been demonstrated in the laboratory to produce etchants of reasonable characteristics. However, such formulated etchants have failed to produce the required consistency of results in etching applications on the production scale. Diglyme is recovered in a controlled and cost effective manner from the spent etchant solution via vacuum distillation and subsequently recycled. Recovery and recycling of either THF or monoglyme presents unacceptable process risk because of the low flash points and potential for the



generation of explosive peroxides. Spent etchant formulated with diglyme can be either be recycled internally or returned by downstream users to the manufacturer for recovery and disposal.

5.1.3 Other reductive pre-treatments involving radical anions

A further chemical system that functions through the generation of an SET mechanism, comparable with the sodium-naphthalene system is the potassium salt of the benzoin dianion in dimethyl sulphoxide (Costello and McCarthy, 1987; Hung and Burch, 1995; Brewis and Dahm, 2005; Zhang et al., 2014).


Table 5.11 Substance ID and Properties

Substance CAS EC CLP Classification

Dimethyl sulphoxide 67-68-5 200-664-3 Not classified

Benzoin 119-53-9 204-331-3 Not classified

Potassium t-butoxide 865-47-4 212-740-3 H228, Flammable solid

H252, Self-heating in large quantities

H314, Causes severe skin burns and eye damage

EUH014, Reacts violently with water


This method for the reduction of PTFE surfaces was undertaken as an academic research project and has never been commercialised at any scale to the applicants’ knowledge. From the literature reports, the method requires extended reaction times of up to 24 hours and reaction temperatures of

up to 50⁰C (Castello, 1987; Hung and Burch, 1995; Brewis and Dahm, 2005).


No economic evaluation of this experimental methodology has been undertaken. However, the extended reaction times required for surface modification (from minutes to hours) would make its routine application impractical and significantly reduce etching process throughput.


Whilst none of the reactants have a hazard profile similar to diglyme, potential increased process risk from the reactivity of the butoxide would require careful control.




This methodology has not been tested commercially and its performance against standard sodium-naphthalene etching technologies is unclear.

5.1.3.6 Conclusion on suitability and availability

This alternative chemical treatment is not a suitable alternative because it has not been tested commercially to determine whether it is either technically or commercially feasible. Extended reaction times would make commercial implementation impractical.

5.2. Electrochemical Treatments

Electrochemical methods for the reduction of PTFE have also been reported in the literature (Brewis and Dahm, 2001; 2005) as the reducing species required can be generated electrochemically by an SET mechanism (Brewis and Dahm, 2001; 2005; Zhang et al, 2014). The appearance of electrochemically treated PTFE is reported to be similar to that obtained in other wet chemical treatments reported above but it is also stated (Brewis and Dahm, 2001) that the nature of the surface modification is fundamentally different in that involves almost the complete conversion of the polymer into carbon in a surface layer up to several microns in thickness

A number of electrochemical methodologies have been demonstrated for the surface treatment of PTFE

1. Indirect electrochemical pre-treatment

Electrochemical generation of tetrabutyl ammonium naphthalenide at a platinum cathode from a solution of tetrabutylammonium tetrafluoroborate (TBAT) and naphthalene in dimethyl formamide was reported to be as effective in the surface modification of PTFE as sodium naphthalenide in tetrahydrofuran (commercial Tetra-Etch).

Electrochemical methods have been used to generate solvated electrons with magnesium counter-ions from a solution of ammonium tetrafluroborate in liquid ammonia (Brace et al,

1997; Brewis and Dahm, 2001; 2005). However, this methodology has the same restrictions and disadvantages as the wet chemistry system based on sodium in anhydrous liquid ammonia.

2. Treatment with metal amalgams

Electrochemical reduction and carbonisation of PTFE can also be achieved using alkali metal mercury amalgams, in which direct chemical interaction occurs between the amalgam and polymer surface followed by defluorination reactions to carbonise the surface. To the applicant’s knowledge there are no commercial applications of metal amalgam systems being used for the surface modification of fluoropolymers.



3. Direct electrochemical pre-treatment

Brewis and Dahm (2005) have also demonstrated the direct electrochemical reduction of PTFE by direct contact on a metal cathode with a PTFE surface under a solution of tetrabutyl ammonium tetrafluoroborate in dimethyl formamide. Bonding strength expressed as failure load (for treated PTFE skived tape in a lap shear test of 12 x 12 mm overlap using an epoxy adhesive) of 3,240 N were obtained electrochemically in comparison with 2,400 – 2,700 N obtained by surface treatment with a sodium naphthalide/tetrahydrofuran etchant.

The applicants are not aware of any commercial applications of electrochemical methods for the surface modification of perfluoropolymers. Such methods have so far only been reported in the academic literature. The applicants have not, therefore, pursued investigation of such methodologies during their own extensive research and development of etching technologies over the last 50 years. Sections 5.2.1.1 through to 5.2.1.4 are not therefore further addressed in this analysis of alternatives.


Not further considered.








There are no known commercial applications for the electrochemically mediated surface modification of PTFE.

5.2.1.6 Conclusion on suitability and availability for electrochemical treatments

Electrochemical reduction for the surface modification of PTFE is not further examined as there are no known examples of the commercial application of such techniques.

5.3. Plasma Treatment

Plasma treatment is a common method for the surface modification of polymers to improve adhesion and wettability characteristics and there has been significant research effort into the development of these techniques for the pretreatment of fluoropolymers in response to the increasing regulatory pressure on the use of many substances used for the wet chemical treatment techniques described above.



Plasma treatments, which are all based on dielectric barrier discharge phenomenon, can be categorized as follows:

• Flame treatment: this is a commercial process in which the polymer article is passed over an oxidising flame of oxygen-rich hydrocarbon. It is applicable to a number of polymers, particularly polyolefins and polyethylene terephthalates but is not effective in the surface modification of PTFE.

• Corona discharge treatment: corona discharge treatment of polymer films has also been commercially available for many years. A corona discharge gas a high voltage arc in air. When air is ionised, electrons generated collide with the surface material to disrupt molecular bonds, create free radical and generates atomic oxygen which chemically reacts with surface carbon and hydrogen to form polar functional groups on the polymer surface. It makes use of atmospheric pressure air plasma. This treatment is only applicable to a limited number of polymer materials (for example, polyethylene, polypropylene) and objects of simple three dimensional shape. Corona treatment of PTFE is reported to be more difficult (http://www.bde-equipements.fr/images/tigres-publication-32_corona-treatment-of-cable-7b33 ).

• Plasma treatment at reduced pressures (LPT): plasma, in general, consists of a mixture of partially ionised gases that is produced by subjecting a gas at low pressure to a high intensity electric field. The ionised particles are accelerated to energies that are comparable or exceed the bond energies of the polymer surface and impact will promote the structural and chemical modification of the polymer surface. The adhesion of polymer surfaces is improved due to the removal of low molecular mass materials, stabilisation of polymer surfaces by cross-linking, surface roughening and surface functionalization. Commercial plasma treatments are available for perfluoropolymers as described below.

• Plasma treatment at atmospheric pressure (APT): this technique has the advantages of plasma technology as an alternative to LPT and overcomes the short comings of corona treatments. It has been reported to be demonstrated for perfluoropolymers. It is marketed under such proprietary technology brands as ‘Aldyne’ (www.softal.de).

5.3.1.1 Plasma treatment description

The major developments in the use of plasma technology for the surface modification of perfluoropolymers have in LPT treatments and these are now available for commercial scale application for the routine treatment of polymer surfaces. Plasma treatment has the following advantages:

• Able to treat complex tribologies

• Do not produce chemical wastes

• Can be modified to deliver specific surface modifications

• Can be used to treat heat sensitive materials

• Processes are controllable through regulation of the process parameters such as power, pressure, gas type and processing time.



A variety of gases can be used in the LPT and are characterised as follows:

• Inert gas plasma: helium, argon and neon

• Oxygen containing plasma: oxygen

• Nitrogen containing plasma: nitrogen, ammonia,

• Fluorine containing plasma: fluorine

• Other plasmas: hydrogen, carbon dioxide The principle of the technique is that the support gas is excited with electrical energy at low pressure (10-2 to 10-3 mbar) to generate charged particles – positive and negative ions and free radicals. The charge particles are electrically conductive and can be influenced by a magnetic field. They are also intensively reactive and are very versatile in stimulating surface modification through the following mechanisms:

• Removal of contaminating surface materials

• Surface reactions between the gas phase and surface atoms and chemical groups

• Reactions between surface species to produce functional groups and crosslinking on the polymer surface.

The surface modification is confined to the top several tens of nanometers of the polymer surface and does not affect the bulk properties of the polymer. Oxygen, nitrogen and ammonia are the most common gases used in LPT for perfluoroploymer treatment, causing the generation of free surface radicals, the rupture of covalent bonds and the polarisation of the surface.


Whilst is has been found that perfluoropolymers do not respond as well to plasma treatments as well as other fluoropolymers, the effectiveness of the technique in comparison to wet chemical etching techniques has not been widely reported in the literature. Some reports have stated that the LPT treatment of PTFE does not impart sufficient strong adhesion to the polymer surface, giving about half the bonding strength compared to sodium naphthalide etching. Other published studies have reported that PTFE surfaces undergo high rates of fluorine loss coupled with low extent of oxygen incorporation.

Ammonia and nitrogen plasma treatments of PTFE using the Planartron for 50 seconds have been reported to provide significant increases in bonding strength from 0.5 to 5.9 N.mm-2.

The applicants have reviewed these application of plasma technologies to the etching of PTFE surfaces. Most plasma systems provide a surface modification that provides considerably lower bond strengths, primarily because the technique primarily improves surface roughness.

In addition the shelf life of the treated surface is much shorter than that for the wet chemical sodium naphthalide technique. Atmospheric plasma treated PTFE surfaces have shelf lives of the order of minutes to days and vacuum plasma treatment may extend this shelf life to a number of weeks, The guaranteed shelf life for sodium naphthalide etched surfaces, protected from ultraviolet light and moisture, is one years and will last substantially long. The consequence of this is that treatment by this method would require immediate use of the etched PTFE surface for the bonding applications (data from Acton Technologies Ltd and Maflon Spa).



There may be specific applications where plasma mediated etching on perfluoropolymers is the preferred methodology, especially where a colour change on etching is undesirable or where chemical residues may be problematic.


LPT treatments are of higher unit cost due to

• Higher capital cost equipment – each discreet material type requires specific equipment for their configuration: for example PTFE film, machined parts or tubing each require at least a different equipment for their material profile and therefore multiple set-ups may be required for differing sizes of the same part types.

• The requirement for low pressure systems

• Lower productivity throughput

Acton Technologies Ltd have made a significant investment in the development of plasma treatment technology for perfluoropolymer surface treatment over the last 20 years but have not seen a return on that investment through the widespread adoption of either the technology or the etched products produced by the technology. Whilst there may be niche markets for this technology for perfluoropolymer surface modification, wet chemical methods will remain the predominant technology because of the ease of use for multiple configurations of surfaces and consistency of performance in a number of validated product areas.

Plasma treatments are, however, finding much wider acceptance for the surface modification of partially fluorinated polymers and other polymeric surfaces.


The use of plasma treatment would avoid the need for the use of hazardous chemicals.


Commercial plasma treatments for the surface modification of PTFE are reported to be available from:

• Diener Electronic: (http://www.plasma.de/en/plasmatechnique/etching.html)

• Henniker Plasma: (http://plasmatreatment.co.uk/henniker-plasma-technology/plasma-treatments/plasma-surface-activation-to-improve-adhesion/)

• Acton Technologies Ltd: Acton Technologies Ltd has developed the most effective and longest lived plasma surface treatment in the market place. This has been deployed in pilot scale processing for fluoropolymer films. However, despite more than ten years of application development, the technique and products produced have not gained market acceptance. Adhesion performance is reported by the downstream users of etched products to be lower and the treatment has been deemed by the market place to not be an adequate replacement for sodium naphthalene etching. As discussed in section 2.1.5.5.1, the downstream user of etched products does not always reveal to the etchant technology supplier the reasons for end application failure and whether this lies with the etchant technology, the adhesion technology or the application characteristics.



5.3.1.6 Conclusion on suitability and availability for plasma treatment

Brewis and Dahm (2006) concluded that ‘plasma treatments can result in the introduction of

substantial quantities of functional groups into fully fluorinated polymers but adhesion levels are

moderate at best, probably as a failure to eliminate weak boundary layers’. The conclusions from the development work carried out and shared by Acton Technologies confirms that this is still the market situation today and that there are only limited applications where plasma treatment might be used, for example if there was a requirement for the etched surface not to be coloured (i.e. the etched surface is required to be white) or in applications where there are severe constraints on the presence of possible chemical residues on the etched product. In both cases there would be a compromise in the acceptance of low adhesive properties of the etched surface.



6. OVERALL CONCLUSIONS ON SUITABILITY AND AVAILABILITY OF POSSIBLE

ALTERNATIVES FOR USE

6.1. The use of surface modified fluoropolymers

Surface treatments of fluoropolymers are utilised in many critical applications where the failure of the bonded fluoropolymer surface is both expensive and would subject the end user to high risk. Some key examples of these uses include:

• medical tubing for use in heart catheters and stroke-treatment catheters

• automotive crankshaft sealing applications,

• aerospace components

• fire-resistant data cable (used to prevent fire-spreading in commercial buildings). In virtually all of these applications there is extensive, mandatory qualification work performed to specify a particular manufacturing process for each component to be utilized in the overall product. In each of these instances switching from the current diglyme-based sodium etchant to another treatment, if technically and economically feasible, would require re-qualification of the manufacturing route and the component performance. For example, it has been reported to the applicant that the automotive Product Part Approval Process (PPAP) required for component qualification has an average cost of €90,000 ($100,000). In the case of an automotive supplier this would mean a requalification cost for each engine platform crankshaft seal and, using a conservative estimate of 30 seals being processed to support 15 different engine platforms, could result in €2,700,000 requalification testing alone for surface treatment substitution. The actual seal count is understood to be significantly higher. An analogous qualification process is required for the numerous applications where surface treated fluoropolymer tubing is being utilized in many different medical device assemblies. Such re-qualifications could be reasonably estimated at the same €90,000 cost and taken in whole could result in significant costs in testing and specification changes. Aerospace qualifications could result in many additional requalification requirements with further significant costs.

6.2. Overall conclusions on alternatives

Bis(2-methoxyethyl)ether (diglyme) is used as a solvent for sodium naphthalide to produce an etchant for the surface modification of fluoropolymers, especially perfluoropolymers such as polytetrafluoroethylene (PTFE), by reductive defluorination in order to increase the surface adhesion properties of such polymers. Diglyme provides sufficient solvation of the radical anion salt to generate the active chemical species in order to promote this reductive defluorination. Other physico-chemical parameters, such as a relatively high flash point, a viscosity similar to that of water and thermal stability during storage and solvent recovery, provide an etchant that can be handled with reduced process risk in a number of process configurations (batch and continuous) to process a range of physical forms of polymer articles (e.g. sheets, seals, tubes etc). Etchants formulated using diglyme as the solvent are used in the surface modification of fluoropolymer components in a range of industrial and medical applications, where the bonding of the



fluoropolymer, and PTFE in particular, provides the final bonded manufactured product with the critical non-reactive properties of the virgin fluoropolymer surface and where the specific structural integrity of the components must otherwise be maintained. Sodium-ammonia etchant systems are commercially available but this methodology is significantly more expensive than the diglyme solvent alternative, is more restricted in its application due to the aggressive and penetrating nature of the generated solvated electron reductant and has a different but significant risk profile in the use of liquid ammonia. As such it can only be implemented at specialist facilities and cannot be used for small scale industrial etching facilities or for components where maintenance of specific structural integrity is required. Other alternative polar solvents that provide similar sodium napthalide solvation characteristics have been identified and some are also known to be available commercially. However, these solvents either have a similar toxicity profile to diglyme (e.g. monoglyme, triglyme) or pose significantly greater process risk through lower flashpoint, greater volatility, reduced thermal stability at room and elevated process temperatures or generation of explosive peroxides during solvent recovery and recycling processes (e.g. monoglyme, tetrahydrofuran). Other glyme alternatives also provide additional process restrictions through increased viscosity due either to the extent of solvation of sodium naphthalide (monoglyme) or increased inherent viscosity (triglyme and tetraglyme). Formulated etchants using either dipropylene glycol dimethyl ether or diethyl glyme have not been demonstrated to produce the same degree of fluoropolymer surface modification in either laboratory or pilot production tests which would allow commercial application of these solvent alternatives. Other wet chemical methods, including the electrochemical generation of solvated electrons and radical anions, do not provide the same extent of consistency of surface modification particularly for PTFE, and none have been demonstrated or implemented commercially. Alternative treatment methods for fluoropolymer surface modification, such as plasma treatments, are available for some fluoropolymers but have not been particularly successful for PTFE. Fully fluorinated polymers do undergo surface modification but the resulting shelf life of such ‘etched’ surfaces is considerably shorter than that achieved with the solvent etchants and that, combined with the requirement for expensive equipment in a number of configurations to cover the range of fluoropolymer articles requiring etching and the resistance of the downstream user market for products etched by this technique, have resulted in limited applications of such techniques. In summary, diglyme is the preferred solvent for formulation and use of a sodium naphthalide etchant for perfluoropolymer surfaces as it provides the optimum balance of adequate solvation to maximise the availability of the radical anion reductant, either at or to a limited depth of the perfluoropolymer surface, with process characteristics of relatively low flashpoint, low viscosity and thermal stability, that permits the economic operation of the etching process at elevated

temperatures of up to 65⁰C whilst minimising overall process risk. Alternative solvents or alternative etching technologies do not provide the flexibility of an etchant of sodium naphthalide formulated in diglyme to produce a consistent surface modification of sufficient enhanced wettability, increased surface energy and increased final adhesive bonding strength across the range of critical perfluoropolymer bonding applications that require mandatory attainment of and qualification to end user specification.



7. SOCIO ECONOMIC ANALYSIS

7.1. Socio-Economic Analysis (SEA) in the context of Adequate Control

The submission of an SEA is not mandatory for applicants following the ‘adequate control’ route to Authorisation. Maflon has not provided a full SEA for the following reasons.

• The procedure for Applications for Authorisation (AfA) by the adequate control

route has been followed meticulously;

• Maflon is in no doubt that the adequate control of diglyme in this use has been

demonstrated;

• This is supported through quantitative monitoring for inhalation exposure and

qualitative modelling for dermal exposure;

• As the exposure levels for all workers and man via the environment are well below

the risk characterisation ratio of 1 in all cases, there is no human health impact from

Maflon’s use of diglyme; and

• Cessation of use of diglyme in this case would not provide any human health benefit.

If for some unforeseen reason, RAC disagrees with the case for adequate control, Maflon would be prepared to provide SEAC with additional data, based on the following key socio-economic argumentation.

7.2. Economic benefits of polytetrafluoroethylene (PTFE)

Polytetrafluoroethylene (PTFE) is the predominant fluoropolymer on the world market, accounting for almost two thirds of the global production of fluoropolymers. As shown in Figure 7.1, PTFE comes from the homopolymer family of fluoropolymers.

According to the ECHA PFOA Restriction Proposal (2014) (1), the global demand for fluoropolymers in 2011 was 267,000 mt, of which 20% (53,400 mt) came from the EU. The Restriction Proposal also states that PTFE accounts for up to two thirds of the demand for fluoropolymers and this equates to an EU demand for PTFE of 32,000 metric tonnes per year.

(1) ECHA PFOA Restriction Proposal October 2014: Table B2-1, Page 30



Figure 7.1 Fluoropolymers, homopolymers and copolymers

Virgin PTFE is predominant in many industrial polymer applications due to the following unique surface properties.

• Outstanding temperature stability and performance of mechanical properties over a

wide range of temperatures (-260 to 260⁰C);

• Excellent and stable electrical properties across a wide range of temperatures and

environmental conditions;

• Excellent chemical resistance over a wide range of temperatures;

• Excellent resistance to weathering and ultra-violet resistance; and

• Extremely low coefficient of friction.

Due to the high cost, use of PTFE in many applications is minimised by the application of a thin PTFE film or layer. In many instances this necessitates surface modification, or etching, of the PTFE in order to enable effective bonding to the base substrate. Etching of PTFE is achieved using skived tapes, moulded sheets, and PTFE woven materials.

In terms of PTFE that has been surface treated with etchant, Maflon estimates that approximately mt per annum of PTFE are produced in the EU, and that this is evenly split between the

sodium/ammonia and the sodium/naphthalene/solvent routes for surface etching. This split is based primarily on the nature of the PTFE surface to be etched as the sodium/ammonia system is too aggressive to etch thin PTFE sheets and skived tapes in a controlled manner.



7.2.1 PTFE Etching – Market Sectors and Uses

There are a wide range of applications for PTFE and PTFE-lined surfaces in almost every industrial sector in the EU. The applications which require the bonding of a PTFE lining to another base substrate can be broadly summarised as follows.

1. Fluid technologies where PTFE provides chemically inert and resistance to

aggressive chemical and abrasive environments, typically;

i. fluid conveying systems (gaskets, packings, bearings, brushes); and

ii. chemical processing equipment (pipes, tubing, storage tanks, jackets, seals.

2. Electronic technologies where PTFE provides chemical inertness and excellent

dielectric, thermal dissipation and antistatic properties.

3. Wear resistance technologies where PTFE provides excellent abrasion resistance, a

low coefficient of friction, self-lubrication, dimensional stability, flexibility, and

fatigue stress resistance.

The following table lists some of the market sectors where bonded PTFE finds critical applications.

Table 7.1 Critical PTFE applications

Industry Sector Products Examples of economic benefits

Chemical / Petrochemical Tank linings

Valve seats

Valve and Pump linings

Resource efficiency (leakage reduction, process efficiency)

Automotive Crankshaft sealing applications

Valve seats

Bearings and bushings

Gaskets

Safety, durability

Aerospace Fuel and lubricant resistant tubes and seals Safety, durability

Medical Catheters

Tubing, seals and gaskets

Improved patient care, human health benefits

Construction Thermal expansion sliding and bearing pads

Fire resistant cabling

Durability, fire safety

Food Sealing elements

Bearings and bushings

Increased manufacturing throughput, safeguarding of product purity, less product wastage, reduced cleaning downtime

General mechanical industry Sealing elements

Standard and special bearings

Sliding elements for machine tools (lathes, boring and milling machines, grinding machines)

Reduced equipment maintenance costs



Industry Sector Products Examples of economic benefits

Valve seats

Solenoid valves

Semiconductor / electronics Transformers

Coils

Terminal insulation

Wire/cable insulation

Circuit boards

Durability, life cycle benefits

7.3. The most likely non-use scenario

It has been clearly demonstrated in the AoA that there is currently no economically or technically feasible alternative solvent that Maflon could use as a replacement for diglyme in fluoropolymer etchant formulation.

The non-use scenario would therefore involve the permanent closure of EU-based fluoropolymer surface treatment. Detailed economic modelling to determine whether Maflon would a) completely abandon their EU etching business, or b) relocate to outside the EU, is deemed disproportionate where adequate control has been clearly demonstrated. Instead, an outline of key socio-economic considerations is presented.

In the event that Maflon is not granted Authorisation, the socio-economic impacts presented in Figure 7.2 would result.



Figure 7.2 Overview of the main non-use socio-economic impacts

7.4. Economic impact assessment

The scope of the economic impact assessment directly affecting Maflon is limited to redundancy costs, loss of profits, relocation costs, and loss of investment in R&D. The impact on the immediate downstream supply chain is also considered.

Due to the high degree of uncertainty, direct economic impacts such as contract penalties and legal fees were excluded, although these could be considerable if Authorisation is not granted.

Wider economic impacts and distributional impacts were also excluded on the basis that they would be unlikely to be significant compared to the direct economic impacts.

7.4.1 Redundancy costs

If Maflon’s contract PTFE etching operation was forced to close, three employees would lose their jobs. This includes two production workers (machine maintenance and cleaning) and one supervisor.

In Italy, individual redundancy pay is equal to severance pay on dismissal (2). The amount payable is equal to the sum of each annual salary divided by 13.5. In addition, a new unemployment benefit (Nuova Assicurazione sociale per l'impiego (NASPI)), is provided, under certain circumstances, to people who have been dismissed. The benefit, which is funded by the employer, is approximately

(2) http://uk.practicallaw.com/2-503-3122?q=&qp=&qo=&qe=#a540437

Authorisation is not granted

Relocation to outside of the EU

Main impacts

Redundancy costs, loss of profits, reduced operating costs

Other impacts

Relocation costs

Social impacts

Loss of wages to the European economy

Permanent closure

Main impacts

As above for relocation

Other impacts

Loss of investment in R&D

Social impacts

Loss of wages to the European economy



equal to a maximum of €1,300 per month, paid for a number of weeks equal to half of the contributions weeks of the previous four years.

Based on a typical monthly salary of a Maflon employee of € , and assuming all three redundant employees had been in post for a minimum of four years, the amount Maflon would be required to pay would be in the region of € to € per employee.

7.4.2 Loss of sales and profits

Key facts and figures are provided as follows.

• In 2015, Maflon etched tonne of PTFE in a European market of tonne, representing

a market share of %;

• The majority of Maflon’s PTFE production (around 95%) is focussed on sheet/film and

skived tape production;

• These products have a thickness of 0.025 mm to 3 mm thickness and are typically 1.3 m to

1.5 m wide;

• Maflon typically produces metres of sheet/film per month;

• Maflon has an annual turnover of € million;

• The annual turnover of the contract etching business is € million per annum; and

• PTFE contract etching generates gross profits in the region of € million per annum.

7.4.3 Reduced operational costs

The costs of closure and decommissioning would be offset to some extent by a reduction in operational overheads. Although the data is not currently available, it is expected that savings from reduced operational costs would only be a fraction of the overall loss of profits.

7.4.4 Relocation costs

Other than the plant in Italy, Maflon does not operate any other PTFE etching facility, either inside or outside of Europe. Assuming that Maflon would relocate to China, India or other Asian country, the estimated investment cost would be in the region of € million. This estimate is based on previous experience of the design and construction of the existing continuous etching plant.

Ninety-five percent of Maflon’s etched PTFE market is in Europe, therefore, in addition to the upfront investment cost for relocation, Maflon would also incur the cost of shipping products from Asia to Europe. Under these conditions, the economic sustainability of the company would come under threat.

7.4.5 Loss of investment in research and development

Maflon was founded in 1996 as a result of a collaborative research project with the Fluorine Chemistry Laboratory of Padua University. Maflon continues to work closely with academic researchers specialising in Fluorine Chemistry.



Maflon’s R&D department is constantly innovating new fluorinated materials to meet the specific requirements of the customers. The main role of the R&D department is to develop new formulations and to set up products from laboratory scale to full production. All R&D activities are developed in the laboratories located in the Headquarters in Northern Italy.

Maflon has been operating the diglyme-based etching process for 25 years and, during that time, has investigated heavily in the development of the process. In the last five years alone, Maflon has invested € million in the PTFE etching department.

7.4.6 Downstream impacts

Surface treatments of fluoropolymers are used in many critical applications where the failure of the bonded fluoropolymer surface would incur i) a significant financial burden to the manufacturer, and ii) an increase in risk to the end user.

In such instances there are extensive technical and performance criteria developed for both the bonded fluoropolymer surface and the bonded surface adhesion characteristics. The latter will be critically dependent upon the nature and extent of the surface modification employed. As such, the methods of surface modification are specified and qualified from a technical and performance perspective and any change in the manufacturing methodology for critical components would require significant financial resource and development time. Furthermore, alternative methods would need to be tested and qualified for use in either ongoing manufacture on new products or legacy spare parts.

The main end use applications of Maflon’s etched PTFE are presented in Figure 7.3

Figure 7.3 End use applications of Maflon's etched PTFE

As stated above, Maflon represents % of the etched PTFE market. It is unlikely therefore that those supplying the remaining % of the market could easily step in and make up the shortfall in production, primarily because sodium/ammonia etching systems are unable to provide a controlled



etching of PTFE sheets and skived tapes of low thickness whilst preserving the overall structural integrity of the PTFE articles.

The potential downstream impact of such a shortfall, although expected to be significant, has not been estimated here. Given that Maflon operates primarily through distributors, the company does not have visibility of the individual market sector size or financial value for products that incorporate the Maflon etched PTFE sheets and skived tapes.

Even if the shortfall could be compensated for within the global market, this would require the revalidation of a significant number of products across a number of sectors. As discussed above, product revalidation is both costly and time consuming. To properly quantify the potential cost impacts of revalidation, further supply chain engagement and data collection would be required.

7.5. Social impact assessment

The following social impact assessment is limited to the loss of wages from the European economy in the event that Maflon’s workers would be made redundant.

7.5.1 Loss of earnings

Given that only three employees would be affected in a closure non-use scenario, the impact on European society as a whole would not be significant. However, given the relatively high unemployment rate in this semi-urban area on the outskirts of Bergamo of 8.2% (2014) (3), and the national unemployment rate of 11.4% (4), it is fair to assume that Maflon’s employees may not immediately find new employment.

Typical earnings in Italy are €2,167.84 per month (5). Assuming all three workers are unemployed for at least one year, the economic impact in the first year of unemployment would be in the region of €70K - €80K.

(3) http://www.asr-lombardia.it/RSY/employment/labour-force-survey/lombardia-and-provinces/tables/13565/

(4) http://www.tradingeconomics.com/italy/unemployment-rate

(5) http://www.tradingeconomics.com/italy/wages



7.6. Summary

Table 7.2 Order of magnitude of key impacts

Non-use scenario Impact Order of magnitude

Relocation to outside the EU

Human health benefit Zero (Adequate Control therefore no benefit to human health)

Redundancy costs €30,000 - €40,000

Relocation costs € million

Wages lost to the European economy €

Permanent closure Human health benefit As above

Redundancy costs As above

Loss of investment in R&D € million

Wages lost to the European economy As above

7.7. Conclusion

Despite the limited data, it is clear that the cessation of diglyme activities in the EU would result in significant socio-economic costs to Maflon and the immediate downstream supply chain. The magnitude of the downstream validation costs alone would more than likely be sufficient to support Maflon’s continued use of diglyme, given that under adequate control there is no impact to human health.

Given that Maflon has demonstrated that there is no impact to human health in relation to the use of diglyme, the preparation of full SEA was not deemed necessary. In the unlikely event that RAC disagrees with the case for adequate control, Maflon would be prepared to provide supplementary socio-economic data and analysis, based on the key impacts and costs identified above.



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