Silicone softeners for stain repellent and stain release fabric finishing

Dow Corning Corporation

Greensboro, N.C

ABSTRACT

During the last few years the use offluorochemicals to provide stain repellency and/or stain release properties to apparel goods has rapidly grown. The use of fluorochemicals as well as durable press resins, however, has a detrimental effect on the fabric softness. Providing premium softness is key to satisfy the highly demanding aesthetic requirements of many oftodays apparel products. Although softeners based on conventionalaminofunctional silicones are well known to provide excellent hand, theysignificantly impair both the stain repellency and the stain release properties of fluorochemical treated fabrics. This paper presents the results from a recentstudy where current and new selected organo-modified silicones provide very good softness with minimumtono impact on the fluorochemical properties.

INTRODUCTION

During the last few years the easy careconcept has rapidly expanded to include stain resistant features in manyapparel applications. The easy care concept now encompasses both minimizationof ironing and easiness to clean garments that might have become stained ineveryday use. The use of finishes that provide stain release and stainrepellency to apparel fabrics, particularly cotton, has shown an amazing growthduring these last years.^1,2

Fabric manufacturers and chemical manufacturershave made advances in finishing processes to ease stain removal and prevent stain penetration. Today, stain release finishing for apparel cotton fabrics is mostlyimparted by the incorporation of low surface energy fluorochemicals. Stainrelease fluorochemical finishes allow oil and water stains to penetrate thefabric; however, when the fabric is laundered, the stains are easily removed. ³Fluorochemicals also dominate the stain repellency textile apparelmarket. Out of all existing textile chemicals, only fluorochemicals have shownthe unique property to provide fabrics a low surface energy film with both highoil and water repellency properties to resist penetration of oil andwater-based stains (polar and non polar liquids). The repellent products prevent the textile substrate from wetting and soiling by repelling the soilingsubstances and the adhesion of dry soil. ⁴ Fluorochemicalhybrid finishes, also called dual effect, which contain hydrophilic groups,have also been developed and improved successfully over the most recent yearsto impart both stain repellency and stain release properties.

Most fabrics finished with durable press resins and fluorochemicals have, however, an important drawback; their handle is generallynot acceptable and actually can be considerably harsh. Although selectedconventional organic softeners can be used in these systems to overcome thisissue, the degree of softness they can provide has fallen short for manyapparel applications. This is particularly true with todays high performanceand durability requirements where normally higher levels of finishing chemicalsare used, which in turn, results in a higher detrimental effect on the fabrichandle. Even higher levels of conventional organic softeners may not give thesoftness level required or these levels may have a negative effect on the stainrepellency or release properties, not evident when lower levels where used. Inaddition to performance requirements, todays highly productive and complexfinishing operations require the use of easy to use and trouble freefinishing products that can offer stability over a broad range of process conditions and compatibility with most textile chemicals. ⁵ Thus, theselection of the right softener in order to achieve both premium hand andoptimum processability becomes extremely important.

SILICONE SOFTENERS FOR FLUORO-CHEMICAL TEXTILEFINISHING

Silicones, particularly amino-modifiedsilicones, are well recognized as premium fabric finishing agents as they notonly provide unsurpassed softness but also improve many fabric physical properties.^6,7 However, conventional aminofunctional silicones have shown to impairsignificantly both the stain repellency and the soil release properties of most fluorochemical treated fabric substrates.

During the last several years, specialtyorgano-modified silicones have been used in stain release and stain repellencytextile finishing, imparting various degrees of softness without degradingsignificantly the properties provided by fluorochemicals. These materials aregenerally silicone copolymers or terpolymers and have chemical structures wherehydrophilic groups, such as polyalkylene oxide polymers, are arranged indifferent ways onto the main siloxane backbone. These organo-modified siliconepolymers may also contain additional reactive organic groups, such as amines,amides and epoxides, which normally contribute to the softness and/ordurability.

Most recently, modified versions of the above as well as new silicone chemistries are being introduced which offer improved softness coupled with the benefit of not impacting the stain repellency and/or stain release properties. More interestingly, some of these silicones have even shown synergistic effects, which result in improvements of the properties provided by the fluorochemicals.

In addition, some of these selected organo-modified silicones are water dispersible or soluble which make them extremely stable in most extreme textile finishing conditions and also compatible with most textile chemicals.

EXPERIMENTAL

The effect of several selected organo-modified silicones on stain release and stain repellency properties were evaluated. The silicone softeners included in the study were: 1) Conventional aminosilicone (microemulsion), 2) Reactive silicone copolymer (currently used in the application), 3) Silicone terpolymer and 4) New silicone copolymer. Water based emulsions and/or dispersions were prepared containing 20% actives of each of the silicones listed above.

The finishing bath consisted of the silicone softener emulsion, a fluorochemical emulsion, a durable press reactant and its catalyst, and a non-rewetting wetting agent. The bath formulation is shown in Table 1. The systems were applied to khaki cotton twill (8 oz/sqyd) and to bleached 65/35 polyester/cotton broadcloth. In addition, a 100% interlock cotton knit was also included in the stain repellency study.

The fabrics were treated by padding (65% Wet pick-up) and dried/cured at 170^oC for 90 seconds. A fluorinated urethane polymer was used for the stain release finishing whereas a fluoroacrylate copolymer was used for the stain repellent finishing.

For the stain release testing, finishing formulations were designed so that 1% silicone solids and 1% fluorochemical solids were added on both fabrics. For the stain repellency testing also 0.5% silicone add on was used. The reasons behind using relatively high quantities of silicone on fabric were that, first, the real impact of these silicones on the fluorochemical properties wanted to be determined and lower levels might have hidden their potential impact, and second, the high amounts of finishing chemicals such as durable press resins and fluorochemicals being used in some applications may require higher levels of silicone softener in order to satisfy premium softness requirements.

Stain release performance was assessed using AATCC method 130-2000. Fabrics were stained with three types of oily soils, dirty motor oil, mineral oil and vegetable oil (Wesson corn oil) and rated after one home laundering tumble-dry cycle (HLTD). On the other hand, stain

repellency performance was assessed by measuring fabrics oil and water repellency using AATCC methods 118-2000 and 22-2000 respectively. Softness was evaluated through a hand panel where evaluators rated the fabrics by giving 5 points to the softest and 1 point to the least soft. The average rating was recorded.

a. Both the stain release fluorochemical and the stain repellent fluorochemical have 30% total solids.

b. Buffered glyoxal reactant, 40% solids.

c. A non-rewetting surfactant type was used for the stain repellent finish

RESULTS:

STAIN RELEASE FINISHING

Table 2 shows the stain release ratings of untreated and treated fabrics after 1 HLTD cycle. As expected, the conventional aminosilicone had a significant impact on the stain release properties of both the cotton twill and polycotton woven fabric.

On Cotton Twill, the stain release ratings dropped 1.2 1.4 points when this fabric was treated with the aminosilicone as compared to the fluorinated urethane treated fabric. In contrast, the cotton twill treated with the selected organo-modified silicones showed minimumtono impact on the stain release properties provided by the fluorinated urethane polymer. The differences in stain release ratings between the selected organo-modified silicones and the fluorochemical only-treated fabrics go from a decrease in 0.3 units (reactive copolymer/vegetable oil) to an improvement of 0.4 units (new copolymer/ motor oil). The new silicone copolymer actually shows the best average performance as compared to the fluorochemical only-treated cotton twill. As anticipated, all silicones improved the softness of the resin/fluorochemical treated-only fabric. The new silicone copolymer also provided very good softness, better than any of the other silicone polymers designed for the application and not far from that provided by the aminosilicone.

a. Ratings according to AATCC 130- 2000.

b. Average rating from hand panel evaluation where 5 = Softest, 1 = Least soft/harshest.

On the 65/35 polycotton fabric, the impact of the selected organo-modified silicones on the stain release properties was higher than that seen on the cotton twill but still shows a very important improvement as compared to that obtained when the fabric is treated with the aminosilicone. The selected organo-modified silicones impacted the stain release ratings 0.1-1 points. Both the terpolymer and the new silicone copolymer also showed the best performance with stain release ratings only about 0.4 points (on average) higher, respectively, than those obtained with the fluorochemical only-treated fabric. As expected, softness was again improved with the addition of all the silicones. Although the best softness was obtained with the aminosilicone, both the reactive silicone copolymer and the terpolymer were very close. The new silicone copolymer provided a good hand improvement as well, however, this was perceived relatively inferior to that provided by the other two silicones designed for the application.

STAIN REPELLENT FINISHING

Table 3 shows the stain repellency performance of the treated fabrics, measured as a function of oil and water repellency. As expected, the conventional aminosilicone had a significant impact on oil repellency of both the fabrics. Overall, oil repellency rating differences for the aminosilicone went from 3.5 (for polycotton) to as high as 6.5 points (for the cotton fabrics) when compared to the fluorochemical only-treated fabrics.

On cotton twill, the selected organo-modified silicones showed little-tono impact on the oil repellent properties provided by the fluoroacrylate copolymer. The terpolymer gave the best performance as far as impact on the oil repellency provided by the fluorochemical. The new silicone copolymer provided the second best performance impacting the oil ratings only 0.5-1 points.

As far as water repellency is concerned, the reactive silicone copolymer gave the best performance on cotton twill and actually slightly improved the water repellency provided by the fluoroacrylate copolymer alone. When compared to the fluorochemical treated-only fabric, both the silicone terpolymer and the new silicone copolymer show some impact on the water repellency. In both cases, the water repellency performance drops as the silicone added on increases. This is also true for the aminofunctional silicone.

All the silicones improved the softness of the resin/fluorochemical treated-only fabric. The reactive silicone copolymer provided the best softness among the organo-modified silicones and the second best overall after the aminosilicone. On this fabric, the new silicone copolymer provided the second best softness at 1% silicone add-on level and only 0.5 points away from the aminosilicone. Overall, the reactive silicone copolymer provided the best balance of properties on cotton twill.

On 65/35 polycotton, the results for all the three organo-modified silicones were very good. The impact on either oil repellency or water repellency was practically non-existent. The silicone terpolymer seemed to perform slightly better than the others in terms of the oil repellency impact on this fabric. It is interesting to notice that for the polycotton and cotton knit fabrics, the higher the amount of the new silicone copolymer, the better the oil repellency rating.

The softness provided by the three organo-modified silicones was similar for the 0.5% silicone add-on levels, yet inferior as compared to that provided by the aminosilicone. Overall, the reactive copolymer was the closest to the aminosilicone. For the 1% add on levels, the softness gap between the amino silicone and the other organo-modified silicones broadened showing rating differences of as much as 2.5 points. In this particular case, the new copolymer did not provide as good softness as that obtained on the cotton twill.

a. Oil repellency ratings according to AATCC 118-2000 Method.

b. Spray Ratings according to AATCC 22 2000 for twill and polycotton. Ratings for knit were using the water/IPA drop absorbency test.

c. Average rating from hand panel evaluation where 5 = Softest, 1 = Least soft/harshest.

On cotton knit, both the silicone terpolymer and the new copolymer had perfect performance showing no impact on either oil repellency or water repellency as compared to the fluorochemical treated-only fabric. Interestingly, it can be seen that higher silicone add on levels on fabric actually improve both the oil repellency and the water repellency ratings. The new silicone copolymer provides the best balance of properties as it also provides a good improvement on the fabric softness. The reactive silicone shows a slight impact on both water and oil repellency at 1% silicone add on levels but shows to provide the best softness overall. Although the aminosilicone provides a very good hand on this type of fabric as well, it shows the highest negative impact on both oil and water repellency.

CONCLUSION

Several organo-modified silicones are available for use as premium softeners in stain repellent and stain release fabric finishing. These softeners provide very good softness with littletono impact on the properties provided by fluorochemicals. No single silicone system seems to provide a complete or ideal solution for all fabric substrates or fluorochemical system. This last fact and as well as the awareness that fabric hand preferences vary with several factors such as fiber type, fabric construction and even geographical region, suggest that a comprehensive evaluation of the selected organo-modified silicones is needed in order to identify the optimum solution for any given fluorochemical system and/or fabric substrate.

REFERENCES

1. Cote, G., New Fluorochemical Technologies for Protective Textile Finishes, Book of papers, 2002, AATCC International Conference.

2. Bender, D. Innovations in Fabric Protection, 2004, Textile Technology International, p.66.

3. Franchina, G., The Chemistry and Properties Behind Designed Fluoroprotectants for Textiles, Book of Papers, 2001, AATCC International Conference.

4. Nabi, W. New Effects in Textile Finishing with Innovative Technologies and Application of Fluorochemicals.

5. Vazquez, F., Trouble Free Performance in Finishing Conditions, 2004, Textile Technology International, p.58.

6. Vazquez, F., Silicones: Beyond Softening in Garment Finishing, Book of Papers, 1999, AATCC Garment Finishing Symposium.

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