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NOVEL HYDROPHILIC SOFTENERS FOR TISSUE AND TOWEL APPLICATIONS

Authors

Dr. Craig Poffenberger Ms. Yvonne Deac Mr. William ZemanSenior Scientist Marketing/R&D Manager ManufacturingGoldschmidt Chemical Corp. Goldschmidt Goldschmidt Chemical Corp.Dublin, Ohio Steinau, Germany Janesville, Wisconsin

ABSTRACT

Cationic surfactants, primarily fatty-alkyl quaternary ammonium compounds, are extensively used as softener/debondersin the production of premium tissue, paper towels, and fluff pulp. A new generation of wet-end softeners has beendeveloped to overcome many of the performance shortcomings of the commercial products.

Test results will demonstrate that the new specialty surfactants exhibit premium water absorbency while enhancing bulkand maintaining softness. The way in which the products are constructed determines the balance of absorbency andsoftness, which traditionally have been mutually exclusive in fatty-based softeners. The new softener/debonders havealso been designed to provide beneficial environmental behavior through incorporation of ester functionalities thatundergo facile hydrolyses that leads to improved biodegradation.

As these new softener/debonders are solvent-free fluids, are very low odor, are very thermally stable, and are highlysubstantive to fibers, many of the environmental and safety concerns at the plant site are also circumvented whether theproducts are added in the wet-end or administered topically.

INTRODUCTION

In the premium tissue market, the following ranking represents the 3 primary characteristics employed by the consumer toevaluate product quality and performance (1):

1. Softness

2. Absorbency

3. Strength

This order of preferred attributes is rearranged for premium quality paper towels (1):

1. Absorbency

2. Strength

3. Softness

Several techniques are available to the tissue and towel manufacturer to respond to and adjust these performancecharacteristics. One such method, introduction of wet-end softener/debonders to the tissue furnish, usually modifies allthree of these properties.

CH3

+ R - N - R X-

CH3

Figure 1. Typical Difatty Quaternary Ammonium Softener/Debonder for Tissue

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Due to the presence of large fatty alkyl chains and the affinity of the cationic charge of the ammonium salt towards thenegatively charged fibers, hydrogen bonding between separate fibers is disrupted (2). This “debonding” results in areduction in strength as measured by tensile and a bulk enhancement as determined by sheet density. Although increasedvoids are created for accumulation of liquids in the tissue or towel, the fatty groups of the debonders are hydrophobicwhich causes a net reduction in absorbency. On the other hand, the fatty moieties are responsible for imparting thelubricating, soft feel to the fibers. These properties are qualitatively compared against softener/ debonder dosage inFigure 2.

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0 1 3 5 8 10INCREASING DEBONDER DOSAGE---->

INC

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DENSITY

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TENSILESOFTNESS

Figure 2: Impact of Softener/Debonders on Tissue Properties

Clearly, there is a predicament with most commercial wet-end debonders: increased softness is often accompanied by anundesired loss of absorbency. To mitigate against this decreased absorbency, many softener/debonders are formulated toinclude rewet aides. Solvents are also used to dilute the effective concentration of the hydrophobic softener, for ease ofhandling and for increased water dispersibility. The use of these additives leads to the presence of materials whichcontribute to VOC levels and which can accumulate in whitewater systems.

Another environmental concern is the biodegradability of the fatty-based quaternary ammonium softener/debonders.Many in use today exhibit biodegradation profiles under 40%. In fact, one softener used for fabric care (and also tissue)has been discontinued in northern Europe due to its accumulation in river sediments. Therefor, the evolving trend for newsofteners is the construction of quaternary ammonium compounds that incorporate ester funtionalities (3-6). As shown inthe sequence below, these esters are subject to hydrolytic cleavage which generates readily biodegradable fatty acids.

R2 R2

+ + R1C(O)-O-CH2CH2NCH2CH2-O-C(O)R1 ⇒ HOCH2CH2NCH2CH2OH + 2 R1C(O)OH

⇑ ⇑ H2O CH3 H2O CH3 FATTY ACID

R2 = CH3, CH2CH2OH

Figure 3. Fatty Ester Quats as Cleavable Surfactants for Improved Biodegradation

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The objective of the work herein is to describe how tissue and toweling softener/debonders can be designed so as tobalance hydrophobic and hydrophilic properties, to improve biodegradability with ester funtionalities, and to eliminate orsignificantly reduce the need for formulating solvents and rewet aides. This paper summarizes the test data that we havecollected on handsheet trials with a new class of fatty ester quaternary ammonium tissue softeners conducted at ourlaboratories in Ohio and Germany.

EXPERIMENTAL

Preparation of New Softener/Debonder AROSURF Z-QUAT ESTER QUATS

As shown below, the new ester quats are prepared in a straightforward 3-step process (7). The first step involvesethoxylation of a primary fatty amine. This intermediate is then esterified with fatty acid to form a mixture of mono- anddiesters. The final step is quaternization with an alkylating agent to form a quaternary ammonium salt of an amineethoxylate ester.

1. R1-NH2 + EO ⇒ R1-N[(CH 2CH2O)YH] 2

(CH2CH2O)YC(O)R2

(CH2CH2O)YC(O)R2 (CH2CH2O)YC(O)R2

3. R1-N + (CH3)2SO4 ⇒ R1-N+-CH3 + CH3SO4

-

(CH2CH2O)YC(O)R2 (CH2CH2O)YC(O)R2

Figure 4. Synthesis Scheme for New Softener/Debonder Ester Quats

The finished quaternary products are obtained in high yield at 100% actives in a physical form ranging from solid pastesto easy to handle liquids. The esters of the amine ethoxylates formed in the second step of the reaction are isolated aslow viscosity liquids.

Handsheet Preparation and Testing at Both Laboratories

All furnishes, virgin and recycled, were provided by tissue manufacturers. Handsheets treated with softener/debonderswere prepared according to TAPPI test Method T205 sp-95 and conditioned according to TAPPI test Method T402 om-93. Handsheet tensile and density were measured according to TAPPI test method T220 sp-96. Absorption rate andcapacity data were collected according to TAPPI Method T561 pm-96.

Where applicable, handsheets were also treated with commercial softener/debonders manufactured by GoldschmidtChemical Corporation for performance comparison with the new ester quats. These products are hereinafter referred toas COMM A and COMM B. Typical softener/debonder dosages were 0.05-0.4% by weight of fiber.

Hand panels were conducted to measure and rank the relative softness of treated fibers. Tensile reduction was also usedas an indicator of increased sheet softness in lieu of handpanels during much of the screening developmental stage.

Testing of New Softener/Debonder Ester Quats

The rate of exhaustion and the substantivity of the new ester quats was determined by extraction of treated handsheets,followed by titration for % quaternary.

Thermogravimetric Analyses were performed with neat samples on a Dupont Instruments 951 ThermogravimetricAnalyzer.

2. R1-N[(CH 2CH2O)YH] 2 + 2 R2C(O)OH ⇒ R1-N + 2H2O

(CH2CH2O)YC(O)R2

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PERFORMANCE OF THE QUAT ESTERS OF AMINE ETHOXYLATES

There are several structural components of the new ester quaternary ammonium compounds which can be varied inresponse to the performance requirement(s) of the tissue softener/debonder. These include the degree of ethoxylation, thedegree of esterification, the composition of the fatty amine, and the composition of the fatty acids used for esterification.For the sake of brevity, hand panels demonstrated the following trends as a function of composition:

1. Diesters that have a total of 3 fatty groups afford a higher level of softness as compared to monoesters with only 2total fatty groups

2. Diesters prepared from long-chained fatty acids impart the highest level of softness

3. Softness is improved when the fatty group of the amine ethoxylate is saturated and when the fatty acids used foresterification are saturated.

Recognizing that the fatty groups in terms of number and composition are the primary contributors to softness, the factorsinfluencing absorbency were studied in extensive detail in both laboratories. These will be reviewed in the followingsections.

Degree of Esterification

Since the diester derivatives of the amine ethoxylate quats impart premium softness, there was concern that the presenceof the 3 hydrophobic fatty moieties would result in a tissue/towel product with a substantially reduced absorbency. Totest this possibility, handsheets were prepared with one of these new softener/debonder compositions wherein only thedegree of esterification differed. The test data is presented in Figure 5. Since the absorbency capacity and rate datamirror each other, only the capacity data will be reported here to indicate the trends for both.

Figure 5. Tensile Reduction and Absorbency Changes on a SW/HW Fiber Blend Treated with the NewSoftener/Debonders

Indeed, the absorbency of the diester is lower than the monoester species, but it is important to note that the absorbencyof the SW/HW fiber blend treated with the diester species is virtually the same as the untreated blank. In other words, thetreated handsheet, which is softer and bulkier, has the same absorbency as the untreated sheet, so the diester represents anacceptable compromise of performance.

Degree of Ethoxylation

An improvement in the sheet absorbency was predicted and subsequently confirmed when amines with higher degrees ofethoxylation were converted to the esters. What was not anticipated was the improvement in the handling and liquidity ofquaternary ammonium derivatives of the higher ethoxylates.

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As shown in Figure 6, for a homologous series of these ester quats, one observes an increase in absorbency capacity asthe degree of ethoxylation increases from 2 to 10 and, finally, to 15 moles of EO for the fatty amine precursor.

Figure 6. Tensile and Absorbency as a Function of the Degree of Ethoxylation

There is very little variation between the ethoxylate species in terms of tensile reduction, but, at the higher levels ofethoxylation, the absorbency capacities have recovered to that of the untreated material. Therefor, the sheets haveexcellent absorbency, softness, and bulk as a result of the treatment with these hydrophilic amine ethoxylate ester quats.

For a homologous series of these ester quats where only the degree of ethoxylation is varied, one finds the followingchanges in the physical state of the materials:

Table I. Physical Characteristics as a Function of Ethoxylation

Moles of EO Appearance at 20° C

2 Hard Paste

6 Paste

8 Flowable Paste

10

12

Thick, Hazy Liquid

Flowable Liquid

15 Liquid

Increasing liquidity with increasing ethoxylation is a very fortuitous happenstance as the test data also demonstrates thatthese materials are the best balances of softening/debonding and absorbency performance. Also, as the degree ofethoxylation increases, the aqueous solubility/dispersibility increases, so the need for solvents as formulation aides isdiminished. The environmental benefits of solvent removal will be discussed below.

Fatty Acid Type

Although tallow is the predominant source for fatty acids and their derivatives in the United States, concerns about “madcow disease” or B.S.E. in Europe has created a shift towards consumption of natural fatty acids from vegetable sources.This, combined with religious and cultural aversions to animal tallow in various parts of the world, led to preparation ofidentical offsets, in terms of the degree of ethoxylation and esterfication, of these new ester quats from tallow andpartially-hardened palm stearine.

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Figure 7 demonstrates that the tallow and palm derivatives are comparable in debonding performance as measured bytensile reduction. However, the palm ester quat exhibits a reduced absorbency. This is attributable to the increasedsaturation of the fatty chain for the palm which renders the material slightly more hydrophobic (7).

Figure 7. Tensile and Absorbency for Tallow- and Palm -Based Offsets of A New Ester Quat

However, since the net loss of absorbency is relatively minor, the hydrophilic polyethoxylate chains are able tocompensate for this. As a consequence, the combination of tallow and palm derivatives allows for these products to besuitable for global consumption.

Performance Comparison versus Commercial Products

After optimization of the structural properties of these new softener/debonders, their performance was compared withcommercial softener/debonders. In Figure 8, tensile and absorbency data are provided for handsheets which were treatedwith two commercial softener/debonders and one of these new ester quats.

On a typical SW/HW (60/40) tissue fiber blend, the data shows that the new ester quat A is a very effective debonder andthat it is more absorbent than either of the two commercial materials. Interestingly, both commercial products areformulated for ease of handling and COMM B even contains absorbency aides. In other words, ester quat A at 100%actives is more absorbent than a formulated product containing a lower amount of hydrophobic quat and an absorbencyaide additive.

Figure 8. Tensile and Absorbency for a New Ester Quat Compared against Commercial Products

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TAL L OW PAL M

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02468

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BLA NK COMM A COMM B ESTERQUA T A

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Generally, furnishes containing recycled fibers do not debond particularly well due to presence of permanent bonds andincreased levels of fines and anionic trash which scavenge the debonder. As depicted below, a SW/RF blend respondsbetter to ester quat B than to a commercial debonder, since the tensile is more reduced and absorbency is increased.

Figure 9. Tensile and Absorbency for A New Ester Quat Using a Softwood/Recycle Fiber Blend

Hand panels on treated sheets produced on a semi-continuos sheetmaker confirmed that ester quat B outsoftened COMMB. This data in combination with the tensile and absorbency data demonstrate that these new materials comparefavorably with incumbent products.

ENVIRONMENTAL PROPERTIES OF THE QUAT ESTERS OF AMINE ETHOXYLATES

Biodegradation

The construction of these new hydrophilic softener/debonders with ester functionalities results in materials with verygood environmental and fish toxicity profiles. Many of the commercial softener/debonders are less than 40%biodegradable as measured by the 28 day Sturm test. As presented in the table below, the new ester quats exhibit animproved biodegradability which is actually very good for quaternary ammonium softeners. From the data, it is evidentthat esters such as those represented in Figure 3 that do not have the long polyethoxylate chain are more biodegradable.However, numbers in the 60-70% theoretical CO2 range are excellent for quats and confirm that these materials will beultimately biodegradable.

Table II. Comparative Biodegradation of Fatty Ammonium Salts

MATERIAL % BIODEGRADATION

Ditallowdimethylammonium Quat(Figure 1) <40%

Difatty Ester Quats from TEA or MDEA(Figure 3) >80%

DMS Quats of Esters of Amine Ethoxylates 52-60%

Acid Salts of Esters of Amine Ethoxylates 58-70%

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C O M M B ES TER Q U A TB

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Substantivity

Figure 10 confirms that this new class of softener/debonders exhausts rapidly and completely onto the tissue fiber blend.The test dosage of 0.4% closely approaches the saturation point wherein all the active sites on the fiber are depleted.

Figure 10. Substantivity of New Softener/Debonder on a SW/HW Fiber Blend as Function of Time

This rapid and complete exhaustion of the new ester quats implies that there will be no build-up of unreacted material inthe whitewater system. It is also very important to point out that the ester quat in this substantivity test was one that is aliquid at 100% actives. Since there are no solvents present as formulation or rewet aides, the combined beneficial effectsinclude:

1. No accumulation of solvents nor unreacted softener in the whitewater contributing to foam and environmental load.

2. Reduced materials hindering runnability such as solvent interference with the Yankee adhesive.

3. No solvents with low flash points.

4. No VOC emissions from solvents.

THERMAL STABILITY OF THE NEW ESTER QUATS

In Figure 11, Thermogravimetric (TGA) diagrams for one of the new ester quats and a home laundry dryer sheet softenerare presented. Basically, the diagrams represent weight loss versus temperature. This technique identifies where thermaldecomposition begins. As expected for a softener exposed to the heat of a clothes dryer, the quaternary ammonium salt isstable to about 280°C. For the commercial dryer softener, one observes a 10% weight loss up to 280°C, whichcorresponds to volatilization of a high flash solvent.

The TGA diagram for the new ester quat shows that it is also stable to 280°C and that, up to this temperature, there are novolatiles of any type generated. Clearly, these new materials will be robust to the temperature conditions encountered atthe skin of a Yankee dryer or those used in the newer TAD processes for drying the tissue web.

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THEORETICAL

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< - - N e w E s t e r Q u a t

D r y e r Q u a t - - >

Figure 11. TGA Diagram for a New Ester Quat and a Dryer Sheet Softener

CONCLUSIONS

A new class of hydrophilic softener/debonders has been developed in response to continued demands by tissue andtoweling manufacturers for new products which, in addition to imparting a premium softness, contribute to absorbencyand also exhibit good biodegradability.

These new materials can be “designed” for performance: the key for increased hydrophilicity is the incorporation ofethoxylate functionalities and the key for improved biodegradation and softening is the formation of fatty esters. Thepresence of several fatty groups in the quaternary ammonium debonder ensures that these materials soften and lubricatetissue surfaces.

Another outcome of the design of these new ester quats is that they can be used at 100% actives without the need forsolvents which have low flash points, which contribute to VOC emissions, which can accumulated in the water cycle, andwhich create foam.

The liquid nature of these materials and their intermediates affords many opportunities for their consumption in tissueand toweling applications. Several are undergoing active investigation.

LITERATURE CITED

1. Quarles, R. P., Tappi Journal 79(7): 88(1996).

2. Poffenberger, C. A. and Jenny, N., “Evaluation of Cationic Debonding Agents in Recycled Paper Feedstocks,”Proceedings from the 1996 Tappi Recycling Symposium, New Orleans, La.

3. Pi, R., Paper Technology, October 1998: 47(1998).

4. Phan, D. V., and Trokhan, P. D., U.S. Patent 5,262,007.

5. Phan, D. V., and Trokhan, P. D., U.S. Patent 5,264,082.

6. Levinson, M. I., Journal of Surfactants and Detergents 2(2): 223(1999).

7. Poffenberger, C. A., Zeman, W., and Deac, Y., U.S. Patent Application Serial Number 09/307,521.