cab-o-sil ts-720

MS Polymer sealant formulationA typical MS Polymer sealant formulation contains polymer, fillers, pigments, adhesion promoters, moisture scavengers, heat and UV stabilizers, catalyst and a thixotropic agent. Many formulations utilize micronized amide waxes as the thixotropic agent.

Amide wax increases viscosity at low shear rate providing sag resistance. As amide wax is a thixotropic agent, viscosity decreases at high shear rates enabling easy dispensing of the sealant.

Table 1: MS Polymer sealant formulationKaneka DKB-5 General Purpose Sealant FormulationComponent phr weight %MS™ Polymer S303H1 100 33%Plasticizer DIUP (diisoundecylphthalate) 50 17%Filler Calcium Carbonate Winnofil® SPM2 120 40%Pigment Tronox® RFK-2 TiO2

3 20 7%Thixotropic Agent Crayvalllac SLX4 or CAB-O-SIL fumed silica4 5 2%Dehydration Agent vinyltrimethoxysilane 2 1%Adhesion Promoter n-2-aminoethyl-3-aminopropyltrimethoxysilane 3 1%Hardening Catalyst dibutylbis (pentane-2, 4-dionato-O, O') tin 1.5 0%Total 301. 5 100%

n Use of amide wax

Amide waxes require high temperature processing to achieve stable, thixotropic behaviour necessary to prevent sagging and slumping and shear-thinning for ease of application. Full activation of the amide wax is generally obtained after 30-60 minutes at 60-80°C5.

The time to cool a large mixing vessel of sealant can take days. Sealant formulators need alternative thixotropic agents with faster, easier processing to simplify, streamline their sealant manufacturing.Cabot’s CAB-O-SIL fumed silica provides a solution to improved processability demanded by sealant manufacturers.

www.cabot-corp.com/Silicas-And-AluminasCAB-O-SIL® is a registered trademark of Cabot CorporationMS™ is a trademark of Kaneka Corporation

Notice and Disclaimer. The data and conclusions contained herein are based on work believed to be reliable; however, Cabot cannot and does not guarantee that similar results and/or conclusions will be obtained by others. This information is provided as a convenience and for informational purposes only. No guarantee or warranty as to this information, or any product to which it relates, is given or implied. CABOT DISCLAIMS ALL WARRANTIES EXPRESS OR IMPLIED, INCLUDING MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE AS TO (i) SUCH INFORMATION, (ii) ANY PRODUCT OR (iii) INTELLECTUAL PROPERTY INFRINGEMENT. In no event is Cabot responsible for, and Cabot does not accept and hereby disclaims liability for, any damages whatsoever in connection with the use of or reliance on this information or any product to which it relates.

Cabot in the worldWith business extending in 19 countries, Cabot has 6 fumed metal oxides manu-facturing facilities in the world, besidesresearch and development facilities focused in developing new products and technology and bringing new solutions to our customers.

Technical centers:

• Billerica, MA - USA

• Rheinfelden - Germany

• Shanghai - China

North AmericaCabot CorporationBusiness and Technical Center157 Concord RoadBillerica, MA 01821-7001USATel: +1 978 663 3455Tel: 800 462 2313 (Technical Service)Fax: +1 978 670 7035 Tel: 800 526 7591 (Customer Service)

EuropeCabotInterleuvenlaan, 15 iB - 3001 LeuvenBELGIUMTel: +32 16 39 24 00Fax: +32 16 39 24 44

South AmericaRua do Paraíso, 148 - 5th floorParaíso CEP 04103-000 São Paulo SP BRASILTel: +55 11 2144 6400Fax: +55 11 3253 0051Tel: 0800 195959 (Customer Service)

Middle East/AfricaCabot Specialty Chem. Inc.Jebel Ali Free ZoneLOB 15, Office 424 - PO Box 17894DubaiUNITED ARAB EMIRATESTel: +971 4 8871 800Fax: +971 4 8871 801

ChinaCabot (China) Limited558 Shuangbai LuWujing Shanghai, 201108 CHINATel: +86 21 5175 8800Fax: +86 21 6434 5532

JapanCabot Specialty Chemicals Inc.Sumitomo Shiba-Daimon Bldg. 11F2-5-5 Shiba Daimon, Minato-kuTokyo 105-0012, JAPANTel: +81 3 6820 0255Fax: +81 3 5425 4500

F U M E D M E T A L O X I D E S

CAB-O-SIL® TS-720 in MS™ Polymer Sealants

MS Polymer sealantsMS Polymers are silyl-terminated polyethers (STPEs) used in one-component, moisture-curable sealants and adhesives. These poly-mers combine the performance advantages of silicone and urethane polymers. Because MS Polymer sealants are solvent and isocyanate free, their usage is increasing as customer demand for worker and environmentally friendly products grows.

Figure 1: Chemical Structure of STPE

CH3 CH3 CH3

(H3CO)2 Si O (CH-CH2O)n Si(OCH3)2

Summary

n Cabot’s CAB-O-SIL TS-720 in MS Polymer sealants offers:

n Faster and simplified processing - No heating required to achieve stable thixotropic behaviour - No long, controlled cooling time required

n Storage stability- Minimal viscosity increase during storage

n Thixotropic behaviour - Sag resistance and shear thinning

n Adhesion:- Good adhesion to difficult substrates such as polycarbonate- Low adsorption of adhesion promoter

n Reinforcement - Higher tear strength, elongation and modulus

n Viscosity and sag resistance- Equal to amide wax at 5 phr- No need to reformulate

Table 2: Comparative summary

CAB-O-SIL Fumed Silica

Amide Wax TS-720 TS-610 M-5

Processing

Controlled heating and cooling. Required NOT REQUIRED

Formulating

Hygroscopic Slightly Minimal Moderate Extreme

Loading Required Equal to Amide Wax

Performance

Viscosity Stability + ++ - - -

Adhesion + ++ - - -

Reinforcement Greater than Amide Wax

Figure 2: Processing of amide wax

Processing time

Heating cycle up to 80°C

Cooling cycle to <50°C

30-60min

n Use of amide wax

Technical centers:

CH3 CH3 CH3

Summary

Processing

Formulating

Performance

Adhesion + ++ - - -

Processing time

30-60min

Chart 1: Viscosity of thixotropes in MS Polymer sealant

Shear Rate, sec-1

10,000

100,000

0.01 0.1 1 10

No ThixotropeAmide WaxM-5

TS-610TS-720

Shear Rate, sec-1

0.01 0.1 1 10

Amide WaxM-5

TS-610TS-720

All sealant formulations shown in Charts 1-5 use the formulation in Table 1 and contain 5 phr of fumed silica or amide wax. All fillers and fumed silica were dried prior to mixing. Sealants were mixed as recommended.

n Viscosity Without any thixotropic agent, the sealant formulation has low viscosity and poor sag resistance. The addition of amide wax increases the low shear viscosity, providing sag resistance, but exhibits shear-thinning at high shear rate necessary for ease of application. Replacing equivalent phr of amide wax with the fumed silica in the sealant formulation resulted in equivalent viscosity, sag resistance, and shear thinning behaviour. Consequently there is no need to reformulate when switching from wax to fumed silica in this formulation. n Viscosity stability A critical requirement for any sealant is stable viscosity and sag resistance during storage. With moisture curing sealants, cross-linking in the cartridge can occur resulting excessively high viscosity at usage or complete cure.

Chart 2 compares the stability of the sealant formulations after undergoing accelerated aging at 50°C for 28 days. The change in viscosity is determined as:

% Change in Viscosity = Final – Initial x 100 Initial

Sealants formulated with amide wax show an average viscosity increase of 25% across the measured range of shear rates. The sealants formulated with M-5, untreated silica, and TS-610, partially treated silica, showed excessive increase in viscosity with aging. The aged performance of the sealants formulated with these silicas is not acceptable for use. Only the fully treated silica, TS-720 showed stable viscosity on aging for all measured shear rates.

Performance comparison of fumed silica with amide wax in MS Polymer sealant

Aging at 50°C for 28 days

n Reinforcement Fumed silica is a well known and widely used thixotropic and reinforcing agent for silicone sealants. In MS Polymer sealants, fumed silica provides both functions too. In comparison to amide wax, all fumed silicas significantly increase mechanical properties such as elongation, modulus, and tear strength.

Chart 5 compares the tear strength of sealants formulated with amide wax and silicas. All silicas increased tear strength in comparison to amide wax. At the low loading level in this formulation, no differentiation among silicas was expected. At higher silica loading, some silicas may provide better reinforcement than others.

The greater reinforcement of fumed silica provides the formulator with the potential to optimize silica loading to match reinforcing properities of amide wax.

n Stringing

In applying a sealant, stringing or threading is undesirable. Figure 3 compares string length for sealants formulated with amide wax and TS-720. Average string length with TS-720 was 70% less than with amide wax.

n Transparency

There are applications which require transparency. Fumed silica has a refractive index of 1.46 which is close to that of many polymers. Amide wax provides no transparency. Figure 4 compares mixes of polymer, plasticizer and amide wax or TS-720. The mixture with amide wax is opaque while the mixture with TS-720 is transparent.

Figure 3: Stringing of sealants

Figure 4: Transparency

Amide Wax

Average String Length

TS-720

CAB-O-SIL TS-720

n Adhesion strength For this general purpose sealant formulation, adhesion to a range of substrates is desirable. Adhesion was assessed by the “Hand Peel” method on stainless steel, aluminum, glass, birch, and polycarbonate substrates. For all sealant formulations, adhesion to birch and glass was excellent; only cohesive failure was observed.

As shown in Chart 3, with stainless steel and aluminum substrates, sealant formulated with TS-720 showed slightly better adhesion than with amide wax, M-5 or TS-610. However, on a difficult to adhere substrate, such as polycarbonate, significant differences in adhesion were observed. Sealant formulated with M-5 had poor adhesion to polycarbonate, TS-610 and amide wax performed similarly, and TS-720 showed the best adhesion performance. As described previously, the surface of untreated silica, M-5, is composed of silanols which will react with silanes used as moisture scavengers and adhesion promoters. Although TS-610 and TS-720 are surface treated, some silanols remain, particularly on TS-610 which is only partially treated.

Chart 4 shows the relative adsorption of adhesion promoter by the silicas. Relative to M-5, TS-610 adsorbed 53% less adhesion promoter. TS-720 adsorbed the least amount of the adhesion promoter.

Adsorption of adhesion promoter by the fumed silicas explains the differences in adhesion performance observed, particularly on a challenging substrate like polycarbonate where TS-720 clearly outperformed amide wax, M-5 and TS-610.

Chart 3: Adhesion by “Hand Peel” method6

Polycarbonate

Stainless Steel Aluminium

Amide WaxM-5

TS-610TS-720

Performance improves from chart center

TS-720 TS-610 M-50

Untreated Fumed Silica Treated Fumed Silicas

CAB-O-SIL M-5 CAB-O-SIL TS-610 CAB-O-SIL TS-720

Treating agent:Dimethyldichorosilane

Treating agent:Polydimethylsiloxane

Hydrophilic Hydrophobic

Cabot’s fumed silica as a replacement for amide wax to achieve easier, faster processingCAB-O-SIL fumed silicas are commercially available in range of surface areas and both untreated and treated surfaces. The surface chemistry of untreated silica is composed of silanols or hydroxyl groups.

With treated fumed silicas some, to almost all, hydroxyl groups are reacted with a silane. In the case of CAB-O-SIL TS-610, the treating agent, dimethyldichlorosilane, reacts with only adjacent hydroxyls leaving many isolated hydroxyls. For this reason CAB-O-SIL TS-610 is considered only partially treated.

For CAB-O-SIL TS-720, the surface treating agent polydimethyl-siloxane reacts with almost all of the hydroxyls and covers any unreacted hydroxyls consequently TS-720 is the most hydrophobic commercial fumed silica.

H HH H

o o o o

Si Si Si Si Si Si Si SiSi

CH3 CH3CH3Si Si

SiSiSiSiSiSiSi

oo o o

CH3CH3

Si Si Si Si Si Si SiSi

n Formulating and processing with fumed silica

Unlike amide waxes, fumed silicas do not require heating and controlled cooling to achieve stable thixotropic behavior. To adequately disperse fumed silicas, the following order of addition is recommended:n Polymer, plasticizer and 2/3 of dehydration agentn Fillers and pigmentsn Silican 1/3 of dehydration agent and adhesion promoter

Chart 2: Viscosity stability of thixotropes in MS Polymer sealant

Chart 4: Adsorption of adhesion promoter by fumed silica7

Chart 5: Tear strength8

Amide Wax M-5 TS-720TS-6100

Footnotes 1 MS Polymer is a trademark of Kaneka Corporation2 Winnofil is a registered trademark of Solvay Chemicals3 Tronox is a registered trademark of Tronox Incorporated4 Crayvallac is a trademark of Cray Valley5 One-Component Moisture Curing Methoxysilane Sealants; Cray Valley6 ISO 10365:1966 Adhesive – Designation of main failure patterns7 Adsorption measured by gas chromatography and mass spectroscopy8 Tear strength measured using ASTM D624

Sealant cured at 25°C and 50% relative humidity for 7 days

Shear Rate, sec-1

10,000

100,000

0.01 0.1 1 10

TS-610TS-720

Shear Rate, sec-1

0.01 0.1 1 10

Amide WaxM-5

TS-610TS-720

n Stringing

n Transparency

Amide Wax

TS-720

CAB-O-SIL TS-720

Polycarbonate

Amide WaxM-5

TS-610TS-720

TS-720 TS-610 M-50

H HH H

o o o o

CH3 CH3CH3Si Si

SiSiSiSiSiSiSi

oo o o

CH3CH3

Shear Rate, sec-1

10,000

100,000

0.01 0.1 1 10

TS-610TS-720

Shear Rate, sec-1

0.01 0.1 1 10

Amide WaxM-5

TS-610TS-720

n Stringing

n Transparency

Amide Wax

TS-720

CAB-O-SIL TS-720

Polycarbonate

Amide WaxM-5

TS-610TS-720

TS-720 TS-610 M-50

H HH H

o o o o

CH3 CH3CH3Si Si

SiSiSiSiSiSiSi

oo o o

CH3CH3

Shear Rate, sec-1

10,000

100,000

0.01 0.1 1 10

TS-610TS-720

Shear Rate, sec-1

0.01 0.1 1 10

Amide WaxM-5

TS-610TS-720

n Stringing

n Transparency

Amide Wax

TS-720

CAB-O-SIL TS-720

Polycarbonate

Amide WaxM-5

TS-610TS-720

TS-720 TS-610 M-50

H HH H

o o o o

CH3 CH3CH3Si Si

SiSiSiSiSiSiSi

oo o o

CH3CH3

n Use of amide wax

Technical centers:

CH3 CH3 CH3

Summary

Processing

Formulating

Performance

Adhesion + ++ - - -

Processing time

30-60min

n Use of amide wax

Technical centers:

CH3 CH3 CH3

Summary

Processing

Formulating

Performance

Adhesion + ++ - - -

Processing time

30-60min

cab-o-sil ts-720

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