Proteases to Improve the Mechanical Characteristics of Durable Press Finished Cotton Fabrics Maria Stamenova, 1 Tzanko Tzanov, 2 Rossitza Betcheva, 1 Artur Cavaco-Paulo* 2 1 University of Chemical Technology and Metallurgy, 1756 Sofia, Bulgaria 2 Departamento de Engenharia Teˆxtil, Universidade do Minho, Campus de Azure´m, 4800-058 Guimara˜es, Portugal Fax: þ351 253 510293; E-mail: artur@det.uminho.pt Keywords: crosslinking; enzymes; proteases; strength recovery Introduction Durable press finishing processes are widely used in the textile industry to impart wrinkle-resistance to cotton fabrics and garments. Methylolamide adducts of formal- dehyde and amides are common crosslinking agents for finishing of cellulosic fibers materials. Nowadays only a few formaldehyde-free finishing agents are commercia- lized and are still quite expensive to replace entirely the traditional resins. The adducts of amides have large share in the pallet of conventional durable-press products for textile application. [1] One product of low formaldehyde content that became of commercial importance is the N-hydroxy- methylacrylamide. It reacts by N-methylol group with cellulose in a single step, using an acid-acting catalyst: zinc nitrate. [2,3] The crease-resistance effect is provided by the formation of a network of ether bonds between each molecule of the reagent and cellulose (Scheme 1). It is a well-known drawback of any crease-resistance treatment on cotton fabrics that the improvement of the dimensional stability and wrinkle resistance is always cor- related with significant decrease of the tensile strength. [4,5] The loss of fabric mechanical strength has been attributed to two main factors: acid-catalyzed depolymerisation and crosslinking of cellulose molecules. [4,6] The fabric strength loss caused by crosslinking is described as a reversible process and could be restored by removing chemically the crosslinks. [7] However, the partial removal of the cross- links, so that the desired crease-resistance is preserved, requires the use of reagents that have minimal or controlled penetration beyond the fiber surface. Normally the classical alkaline or acid hydrolysis (depending on the bonds to be broken) is difficult to be controlled and might damage seriously the durable press effect and even the fabrics. In our previous work lipases were used to restore partially the strength loss of cotton fabric crosslinked with 1,2,3,4- butanetetracarboxylic acids. It was shown that the enzy- matic hydrolysis of the ester linkages resulted in 10% strength recovery, coupled with slight deterioration of the crease resistance effect. [8] Considering the hydrolysis options existing in the structure shown in Scheme 1 it could be concluded that currently there is no commercially available enzymatic system, which specifically could attack the ether links between N-hydroxymethyl acrylamide and cellulose. However, several proteases have the potential to destroy the amide bonds in N-hydroxymethylacryl- amide. The proteolytic enzymes (proteases) catalyze the hydrolysis of certain peptide bonds in protein molecules. Full Paper: N-Methylol reagents are conventional cross- linking agents that are still widely used in textile industry to produce crease-resistant cotton fabrics. In this work serine proteases were used to recover the strength of fabrics, cross- linked with N-hydroxymethylacrylamide. Nearly one half of the strength loss of crosslinked cotton fabrics could be restored after protease treatment, while the wrinkle recovery angle (WRA) decreased only slightly. The enzymatic hydro- lysis of the amide cross-links in the durable pressed cellulose was confirmed by FT-IR analysis and dyeability with an acid dye. Effect of protease concentration on the tensile strength re- covery, WRA and acid dye dyeability at 30 min reaction time. Macromol. Mater. Eng. 2003, 288, 71–75 71 Macromol. Mater. Eng. 2003, 288, No. 1 ß WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2003 1438-7492/2003/0101–71$17.50þ.50/0