Cellulose crosslinking is a very important textile chemical process, and is the basis for a vast array of durable press- and crease-resistant finished textile products. N-methylol crosslinkers 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 release formaldehyde, a known human carcinogen. Other systems, e.g. polycarboxylic acids, have been tested with varying degrees of success. We have developed methods of forming ionic crosslinks that provide outstanding crease-angle recovery performance, as well as complete strength retention in treated goods, without the potential for releasing any low-molecular weight reactive materials, such as formaldehyde. Our work is based on reactions of cellulose with 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 ionic celluloses that can then sorb a polyionic material of opposite charge to form crosslinks. Cellulose treated with cationized chitosan after carboxymethylation showed significant increases in crease recovery angles without strength loss.
Cellulose crosslinking, ionic crosslinking, durable press, wrinkle resistance
The crosslinking of cellulose is a crucial textile chemical process, and provides the textile manufacturer a multitude of commercially important textile products. The most commonly used crosslinking systems are based on N-methylol chemistry. These crosslinkers give fabrics many desirable mechanical stability properties (e.g. crease resistance, anti-curl, shrinkage resistance, durable-press), but also impart strength loss and the potential to release formaldehyde, a known human carcinogen.  Other chemical systems that do not contain formaldehyde, e.g. polycarboxylic acids, have been explored with varying degrees of success.[9,10] In this work we report on methods of forming ionic crosslinks, rather than the typical covalent crosslinks, to provide crease-angle recovery performance without formaldehyde release.
Ionic cellulose can be produced with a variety of reagents. Figure 1 provides examples of obtaining anionic cellulose by reacting chloroacetate with cellulose and cationic cellulose by a similar reaction with 3-chloro-2-hydroxypropyl trimethyl ammonium. These reactions produce ionic celluloses that can then sorb a polyelectrolyte of opposite charge to form crosslinks.
There are numerous strategies for producing ionic crosslinks. In this work, we will discuss the use of cationized chitosan to crosslink cotton which has been made anionic with chloroacetate.
The reaction of chitosan with 3-chloro-2-hydroxypropyl trimethyl ammonium leads to a cationized polymer that maintains 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