Abstract


Cellulose crosslinkingis a very important textile chemical process, and is the basis for a vast arrayof durable press- and crease-resistant finished textile products. N-methylolcrosslinkers containing formaldehyde give fabrics desirable properties of mechanical stability (e.g. crease resistance, anti-curl, shrinkage resistance, durable press), but also impart strength loss and the potential to releaseformaldehyde, a known human carcinogen. Other systems, e.g. polycarboxylicacids, have been tested with varying degrees of success. We have developedmethods of forming ionic crosslinks that provide outstanding crease-anglerecovery performance, as well as complete strength retention in treated goods,without the potential for releasing any low-molecular weight reactivematerials, such as formaldehyde. Our work is based on reactions of cellulosewith materials that impart an ionic character to the cellulose, e.g.chloroacetic acid for negative charges or 3-chloro-2-hydroxypropyl trimethyl ammonium chloride for positive charges. These reactions produce ioniccelluloses that can then sorb a polyionic material of opposite charge to formcrosslinks. Cellulose treated with cationized chitosan after carboxymethylationshowed significant increases in crease recovery angles without strength loss.


Keywords


Cellulose crosslinking,ionic crosslinking, durable press, wrinkle resistance

 

Introduction


The crosslinking of cellulose is acrucial textile chemical process, and provides the textile manufacturer a multitudeof commercially important textile products. The most commonly used crosslinkingsystems are based on N-methylol chemistry. These crosslinkers give fabrics manydesirable mechanical stability properties (e.g. crease resistance,anti-curl, shrinkage resistance, durable-press), but also impart strength lossand the potential to release formaldehyde, a known human carcinogen. [4] Otherchemical systems that do not contain formaldehyde, e.g. polycarboxylic acids,have been explored with varying degrees of success.[9,10] In this work wereport on methods of forming ionic crosslinks, rather than the typical covalentcrosslinks, to provide crease-angle recovery performance without formaldehyderelease.


Ionic cellulose can be produced with a variety of reagents. Figure 1 provides examples of obtaining anionic celluloseby reacting chloroacetate with cellulose and cationic cellulose by a similarreaction with 3-chloro-2-hydroxypropyl trimethyl ammonium. These reactions produce ionic celluloses that can then sorb a polyelectrolyte of opposite charge to formcrosslinks.


There are numerous strategies for producing ionic crosslinks. In this work, we will discuss the use of cationized chitosan tocrosslink cotton which has been made anionic with chloroacetate.


The reaction of chitosan with3-chloro-2-hydroxypropyl trimethyl ammonium leads to a cationized polymer thatmaintains its cationic character regardless of pH (Figure 3).

 


Peter J. Hauser & C. Brent Smith - North Carolina State University, Raleigh, North Carolina, USA

Mohamed M. Hashem - National Research Center, Cairo, Egypt

 

Chitosan is obtained by alkaline hydrolysis of the naturally occurring polysaccharide chitin (Figure 2).

 

Experimental


Anionic cellulose was produced with various carboxymethyl content (up to 125 mmol per 100 g fabric) by a method similar to those previously reported [1, 2, 5, 6, 7, 8]. Bleached cellulosic fabric was impregnated with 20% aqueous NaOH for 10 minutes at room temperature, followed by padding to a wet pickup of 100%. Samples were dried at 60oC. These alkali-treated samples were then steeped for 5 minutes at room temperature in aqueous solutions of chloroacetic acid that had been neutralized with sodium carbonate at various concentrations (0 to 3.0 M). These samples were then squeezed to 100% wet pickup, sealed in plastic bags and heated at 70oC for 1 hour. The samples were then washed and dried at room temperature. Blanks were included. This produced 7 different levels of carboxymethylation, i.e. 6.15, 30.2, 60.7, 87.1, 97.3, 114.5, and 123.7 mmols of carboxymethyl groups per 100 grams of fabric, as determined by titration.

 

Cationic chitosan was produced by the reaction of 85% N-deacetylated chitin with 3-chloro-2-hydroxypropyl trimethyl ammonium chloride using a method that differed somewhat from the method previously reported by Kim et al. [3]. 161 grams of 85% N-deacetylated chitin was slurried in 1156 grams of 69% w/w solution of 3-chloro-2-hydroxypropyl trimethyl ammonium chloride. NaOH (50% w/w) was added dropwise to maintain pH of 10 to 11. The slurry was stirred overnight; then the temperature was raised to 95oC for 4 hours, cooled to room temperature and adjusted to pH 7 with acetic acid. The resulting reaction product was soluble in the reaction mixture. When recovered by drying, the resulting product was easily re-dissolved in room-temperature water at pH 7.


To accomplish the ionic crosslinking, cationized chitosan was applied to the anionic cellulosic fabrics by padding through solutions of cationized chitosan in water at 100% wet pickup, then drying at 105oC. Various concentrations of cationic chitosan were used in the padding bath, i.e. 0, 0.5, 2, 4, and 6% solution concentration.


Materials


The materials used are presented in Table I.

 

All chemicals were used as received.

 

Methods of Analysis


Nitrogen analysis was provided by Dow Chemical Company using a Leuco HCN Analyzer.


Carboxymethyl content of cellulosic fabrics was determined as follows. Samples were steeped overnight in 0.1% HCl solution at room temperature. These were then washed with distilled water until the wash water showed no presence of chloride by an AgNO3 drop test. Samples were dried at 105oC, then brought to standard conditions. Exactly 0.3 grams of each sample was carefully weighed and combined with 100 mL distilled water and 20 mL of 0.05N NaOH in a beaker. This mixture was titrated with standardized HCl solution to a phenolphthalein end point. The carboxymethyl content was calculated as follows.


mmols carboxymethyl content per 100 grams = 100 * (Vo V) * (NHCl) / (0.3)


where V is the titer for the sample, Vo is the titer for the blank, and NHCl is the normality of the HCl titrant.


Crease angle measurements were made by AATCC Standard Test Method 66, Wrinkle Recovery of Fabrics: Recovery Angle Method. The presented results are the sum of the recovery angle of the tested fabric in the warp and weft directions. Breaking strength was determined with an Instron tensile tester using ASTM test method D1682.


Results and Discussion


The nitrogen content of the treated fabrics are shown in Table II. As expected, the nitrogen content increases as the application level of cationized chitosan increases. Laundering the treated fabrics did not decrease the nitrogen content, indicating that a durable finish was obtained.

 

 

The dry and wet wrinkle recovery angles measured for the treated fabrics are given in Table III and Figures 4 and 5. As can be seen, both recovery angles increase as the carboxymethyl content and the cationized chitosan application level increase. The wet recovery angles in particular show remarkable increases.

 

 

 

 

 

The breaking strengths of the treated fabrics are given in Table IV and Figure 6. Unlike other crosslinking systems, this ionic system not only does not adversely effect the fabric breaking strength, but also the strength actually increases as the treatment level is increased.

 

 

 

 

Conclusions


Wrinkle resistance in cellulosic fabrics can be achieved with ionic crosslinks. Carboxymethylated woven cotton fabric treated with cationized chitosan showed significant increases in wrinkle angle recovery without strength loss. This process allows for enhanced wrinkle resistance without the chance of formaldehyde release.


References


  1. Daul, G., et al, Studies on the Partial Carboxymethylation of Cotton, Textile Res. J., 22(12), 1952, p 787.
  2. Hashem, M. et al, Synthesis of Reactive Polymers and Their Applications to Cotton Fabrics as Permanent Size, Molecular Crystals and Liquid Crystals Science and Technology Section A: Molecular and Liquid Crystals, 353, 2000, p 109.
  3. Kim, Y. et al, Synthesis of a Quaternary Ammonium Derivative of Chitosan and Its Application to a Cotton Antimicrobial Finish, Textile Res. J., 68(6), 1998, p 428.
  4. Peterson, Harro, Cross-Linking with Formaldehyde-Containing Reactants, Chapter 2 in Functional Finishes, Volume II, Part B; Lewis, M.; Sello, S. B. Eds.; Dekker, New York, 1983; p 200.
  5. Racz, I. et al, Crystallinity and Accessibility of Fiberous Carboxymethyl Cellulose by Pad-Roll Technology, J. Applied Poly. Sci., 62, 1996, p 2015.
  6. Racz, I. and Borsa, J., Carboxymethylated Cotton Fabric for Pesticide-Protective Work Clothing, Textile Res. J., 68(1), 1998, p 69.
  7. Racz, I. et al, Fiberous Carboxymethyl Cellulose by PAd Roll Technology, Textile Res. J., 65(6), 1995, p 348.
  8. XiQuan, L. et al, Kinetics of the Carboxymethylation of Cellulose in the Isopropyl Alcohol System, Acta Polymerica, 41(4), 1990, p 220.
  9. Yang, C. et al, Nonformaldehyde Durable Press Finishing of Cotton Fabrics by Combining Citric Acid with Polymers of Maleic Acid, Textile Res. J., 68(5), 1998, p 457.
  10. Yang, C. and Wei, W., Evaluating Glutaraldehyde as a Nonformaldehyde Durable Press Finishing Agent for Cotton Fabrics, Textile Res. J., 70(3), 2000, p 230.


Acknowledgment


The authors thank Dow Chemical Company for financial support and nitrogen analyses.



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