Lipases were used to restore partially
the strength losses of cotton fabrics crosslinked with 1,2,3,4- utanetetracarboxylic acid. The enzymatic hydrolysis of the ester linkages at low temperature and neutral
pH resulted in 10% strength recovery, coupled with a slight deterioration of the crease-resistance effect. The conventional alkaline hydrolysis provided higher strength
recovery, however provoked considerable change in the durable press performance of the fabrics

Betcheva, Rossica

Paulo, Artur Cavaco

Stamenova, Maria

Tzanov, Tzanko

Macromolecular Materials and Engineering

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Universidade do Minho: RepositoriUM

462Lipases to Improve the Performance of Formaldehyde-Free Durable Press Finished Cotton FabricsTzanko Tzanov,1 Maria Stamenova,2 Rossitza Betcheva,2 Artur Cavaco-Paulo* 11 Departamento de Engenharia TÞxtil, Universidade do Minho, Campus de Azurm, 4800-058 Guimar¼es, PortugalFax: +351 253 510293; E-mail: artur@det.uminho.pt2 University of Chemical Technology and Metallurgy, 1756 Sofia, BulgariaKeywords: butanetetracarboxylic acid; crosslinking; lipases; strength recovery;IntroductionNowadays the fabrics produced from cotton fibers havethe largest share in the textile market. However, theircrease-resistance is not satisfactory to meet the contem-porary requirements for “easy-care” textile materials.When cotton fabric is deformed, the numerous H-bondswhich exist between cellulose molecules are destroyedand consecutively created fixing the new deformed stateof the fabric. The conventional durable press finishes toimprove the crease-resistance of cotton fabrics are mostlyachieved on the basis of a condensation reaction at hightemperature between N-methylol compounds, such asdimethyloldihydroxyethylene urea (DMDHEU) or itsderivatives and cellulose. However, the formaldehyde,which is released during the fixation procedure, has beenidentified as a potential human carcinogen. In the lastyears many efforts have been made to develop formalde-hyde-free crosslinking agents. For this purpose someproduct with lower formaldehyde content have been sug-gested, i.e., a-hydroxyalkylamides, polymers from ureaand glutaraldehyde, and diamidodihydroxyethane pro-ducts, all of them crosslinking the cellulose trough etherbond formation.[1, 2] The most promising formaldehydefree reagents, however, are the polycarboxylic acids –1,2,3,4-cyclopentanetetracarboxylic acid, 1,2,3,4-butane-tetracarboxylic acid (BTCA), or a combination of citricacid and polymers of maleic acid. The reaction with thecellulose substrate proceeds trough ester crosslinking,catalyzed by sodium hypophosphite.[3, 4] A major draw-back of any crease-resistance finish on cotton is thedecreased fabric strength, which increases as the degreeof crosslinking increases. The crosslinking of cellulosereduces the mobility of the macromolecules and greaterstress, which could not be uniformly distributed along thepolymer chains, is accumulated in the fabric structure,leading to its disruption. The crosslinking of cellulosemolecules with polycarboxylic acids causes partiallyreversible strength loss and some irreversible acid cata-lyzed degradation of cellulose at elevated tempera-ture.[5–7–16] In other words, the strength loss of cottonesterified with polycarboxylic acid is a consequence ofboth acid depolymerisation and crosslinking. While thefabric strength loss caused by degradation is an irreversi-ble process, the ester crosslinks might be removed byalkaline hydrolysis, gradually restoring the strength loss.The alkaline treatment could cause an undesirable reduc-tion in the durable press performance of the finish fabrics.A milder, ecologically clean, and controlled hydrolysis ofthe ester linkages could be achieved using enzymes.Lipases (triacyl glycerol acyl hydrolases EC 3.1.1.3) areCommunication: Lipases were used to restore partiallythe strength losses of cotton fabrics crosslinked with1,2,3,4-butanetetracarboxylic acid. The enzymatic hydro-lysis of the ester linkages at low temperature and neutralpH resulted in 10% strength recovery, coupled with aslight deterioration of the crease-resistance effect. Theconventional alkaline hydrolysis provided higher strengthrecovery, however provoked considerable change in thedurable press performance of the fabrics.Macromol. Mater. Eng. 2002, 287, No. 7 iWILEY-VCH Verlag GmbH, 69469 Weinheim 2002 1438-7492/2002/0707–0462$17.50+.50/0{k}3B2/JOBS/MME/E02_022.3D 11. 7. 2002 Name:Mechanism of the lipase catalysis.Macromol. Mater. Eng. 2002, 287, 462–465Lipases to Improve the Performance of Formaldehyde-Free Durable Press Finished Cotton Fabrics 463an unique class of hydrolases,[17, 18] which are catalyticallyactive in water, in mixtures of water and a water-immisci-ble organic solvent and in organic solvent, catalyzingboth hydrolysis and esterification reactions. The largeexcess of water favors the hydrolysis reaction. Most oflipases are serine hydrolases, containing a serine residuein their active site, and forming an intermediate acyl-enzyme substrate complex (Scheme 1).The objective of this research was to provide an effi-cient biocatalytic ester hydrolysis to restore partially thestrength loss of polycarboxylic durable press finished cot-ton fabrics, without deteriorating the crease-resistanceeffect.Experimental PartTextile Material and Durable Press FinishThe fabric used in this study was a desized, scoured andbleached cotton. The cotton fabric was impregnated on fou-lard (100% wet pick-up) with a solution containing 1,2,3,4-butanetetracarboxylic acid (BTCA) (from Aldrich), andanhydrous sodium hypophosphite (from Sigma) as the cata-lyst, with a BTCA/catalyst ratio of 3 :2 wt.-%.[8, 13] Theimpregnated fabric was dried at 808C for 5 min and thencured in a Werner Mathis curing machine at 1808C for2 min. Afterward the treated fabric was washed extensivelyto remove the remaining unreacted acid and catalyst.Enzyme TreatmentLipase (EC 3.1.1.3) type VII from Candida rugosa, 724units N mg–1 solid, was purchased from Sigma and applied tothe crosslinked cotton fabrics in different concentrations andfor different time at pH7.5 (0.1 m phosphate buffer) and378C, as indicated by the producer, in a shaker with100 rpm.Wrinkle Recovery Angle, Tensile Strength, FT-IR Analysisand Dyeability with Cationic DyesWrinkle recovery angle (WRA) and tensile strength of theBTCA treated fabrics were measured according to AATCCtest method 66-1990 and ASTM method D5035-90, respec-tively. Diffuse reflectance spectra of some of the sampleswere collected by Bomem MB-series FT-IR spectrometer,performing 100 scans for each spectrum. No smoothingfunction and baseline correction were applied. Potassiumbromide was used to obtain the background spectrum. Theeffectiveness of the lipase deesterification was assessed com-paring the ester carbonyl band intensity at 1724 cm–1.[8–15]The fabrics were treated for 2 min at room temperature with0.1 m NaOH to convert the free carboxyl to carboxylate.Otherwise the carboxyl carbonyl band overlaps the ester car-bonyl band.[11] The lipase treated samples (1 g each) weredyed with 20 N 10–6 m C.I. Basic Dye 9 purchased from Farm-italia Carlo Erba S.p.A., at 508C, for 1 h, in bath to fabricratio 50:1. The color of the dyed fabrics was evaluated usinga reflectance measuring Datacolor apparatus at standard illu-minant D65 (LAV/Spec. Incl., d/8, D65/108) in terms of K/Svalues. The Kubelka-Munk relationship (K/S), where K is anadsorption coefficient and S is a scattering coefficient, isapplied to textiles under the assumption that light scatteringis due to the fibers, while adsorption of light is due to thecolorant.Results and DiscussionEnzyme ConcentrationThe effect of the enzyme concentration on tensilestrength and wrinkle recovery angle (WRA) of BTCAtreated fabrics was investigated. Tensile strength nor-mally increases as the hydrolysis of the crosslinked fabricprogresses. In our experiment the tensile strength of theBTCA crosslinked fabrics increased when up to 0.4 g N l–1lipase was applied for hydrolysis of the ester bonds.Above this enzyme concentration a further improvementof the fabric tensile performance was not observed (Fig-ure 1). This limitation of the hydrolysis could beexplained with the restricted accessibility to the enzy-matic attack of the BTCA/cellulose ester crosslinks in thedense cellulose structure. The ester groups have a slightlyhigher concentration in the interior of the fabric than inits near surface.[9] The large enzyme molecule is not ableto get in contact with the substrate and to form the inter-mediate enzyme-substrate complex. The dimension of theprotein molecule is a self-limiting factor for undesirablefurther hydrolysis of the BTCA/cellulose crosslinkagesand lessening of the crease-resistance effect.It is known that the electrostatic enzyme/substrateinteractions play an important role in the enzyme cataly-sis. It was found that the active site of Candida rugosalipases becomes negatively charged at pH 6[19] (in ourexperiments the lipases were applied at pH 7.5). Thenegative charge in the active site is needed for the expul-sion of the negatively charged hydrolysis products and istherefore essential for the maximum activity of theenzyme. After cleavage of the ester bond, an ionized acidwill be ejected from the active site due to electrostaticrepulsion. If the active site was positively charged, aproduct inhibition would occur due to interaction of theactive site with the negatively charged polycarboxylicacid. In the case of crosslinking of cellulose with polycar-boxylic acids, four ester bonds per acid molecule are pos-sible. Even though the enzyme hydrolyzed some of theseester crosslinkages, the product still remains on the fabricScheme 1. Mechanism of the lipase catalysis.464 T. Tzanov, M. Stamenova, R. Betcheva, A. Cavaco-Paulodue to singly bonded acid side groups.[9] Thus hydrolysisof the ester groups is faster than the rate of BTCA mole-cule removal. With the progress of the hydrolysis reactionthe fabric will become more negatively charged and theenzyme will be rejected from the fabric’s surface, imped-ing further hydrolysis. As more hydrolysis occurs, theintermediate binding between enzyme and substratebecomes more difficult due to electrostatic repulsion.This might be another explanation, apart from the stericconstraints, why the hydrolysis did reach a maximum andafterwards remained steady independently on the enzymeconcentration.A comparatively mild chemical hydrolysis was per-formed using 0.1 m NaOH, at 378C for 1 h. The alkalinehydrolysis was accompanied with considerable loss of thedesired durable press effect – nearly 40% decrease ofWRA vs. 30% of strength improvement. At the same con-ditions, samples treated with enzyme showed about 4%decrease of wrinkle recovery angle (WRA), which corre-sponds to nearly 10% strength recovery (Figure 1). Eventhough BTCA molecules were gradually removed fromthe fabric as a result of hydrolysis, the effectiveness ofthe remaining BTCA molecules as a crosslinking agentdecreased only slightly. The change of WRA was twicelower than the tensile strength recovery of BTCA cross-linked cotton.The dyeing with basic dye (methylene basic blue 9) isan indirect indication for the state of the enzymatic pro-cess. The dyeability of BTCA treated fabrics decreasedafter 1 h hydrolysis with up to 0.4 g N l–1 lipase (Figure 1).Significant correlation could be found between the tensilestrength recovery and the decrease in dyeability of thehydrolyzed cotton. We expected that the presence offreecarboxyl and carboxylate groups on the BTCA treatedcotton after the cleavage of the ester bonds would make itdyeable with basic dyes. However, the removal of theproduct during the enzymatic hydrolysis reduces the affi-nity of the cationic dye toward the fabric. The alkalihydrolyzed BTCA cotton was dyed the worst (about 50%decrease of K/S), while the untreated cotton was not dye-able with cationic dyes.The IR spectroscopy data in Figure 2 show a decreaseof the intensity of the ester carbonyl peak at 1724 cm–1with increasing lipase concentration. Above 0.4 g N l–1lipase, where the highest tensile strength recovery wasobserved, the curve of the carbonyl band intensityreached a plateau, e.g. no further hydrolysis occurred.Hydrolysis TimeAt fixed concentration (0.4 g N l–1) the effect of the hydro-lysis time on fabric tensile performance and crease-resist-ance was also examined. The process time was variedfrom 30 min to 25 h. The tensile strength recoveryreached a maximum during the first hour of the processand remained constant for the next 24 h of treatment (Fig-ure 3). The decrease of WRA follows the same tendency.Inactivation of the enzyme by the hydrolysis productsand long operational time is equally possible, apart fromFigure 1. Tensile strength recovery, WRA decrease anddecrease in dyeabilitywith cationic dye of BTCA treated cotton(6% BTCA/4% NaH2PO2), hydrolyzed by different concentra-tion of lipase for 1 h.Figure 2. Ester carbonyl band absorbance at 1724 cm–1 of cot-ton treated with 6% BTCA/4% NaH2PO2 and hydrolyzed withdifferent concentrations of lipase.Figure 3. Tensile strength recovery, WRA decrease anddecrease in dyeability with cationic dye of BTCA treated fabrics(6% BTCA/4% NaH2PO2), hydrolyzed by 0.4 g N l–1 lipase fordifferent times.Lipases to Improve the Performance of Formaldehyde-Free Durable Press Finished Cotton Fabrics 465the above stated steric and electrostatic considerations.The decrease of the intensity of the ester carbonyl peak inthe IR spectrum of the fabric corresponds to the inhibitionof the enzyme hydrolysis (Figure 4).ConclusionIn this research a safe, ecologically acceptable enzymatichydrolysis process to restore the tensile strength of BTCAtreated cotton fabrics was established, as an alternative tothe conventional alkaline treatment. The application oflipases in low concentration for short treatment timerestored partially the strength loss of the fabrics due tothe polycarboxylic crosslinking. The lipase treatmentimproved the tensile strength with up to 10%, causingjust 4% alteration of the crease-resistance of the fabrics.A steady state of the tensile recovery was reached, possi-bly due to steric difficulties to form the enzyme/substrateintermediate complex, or due to electrostatic repulsionbetween the negatively charged binding/catalytic site ofthe lipase and the increasing negative charge of the cottonduring the hydrolysis. The alkaline hydrolysis of theBTCA durable press finish resulted in substantial reduc-tion of the crease-resistance effect, whose deteriorationovercomes the gain in tensile strength. Data from FT-IRspectroscopy confirmed the occurrence and then theinhibition of the hydrolysis of the polycarboxylic cross-linkages. With proceeding enzymatic hydrolysis the dye-ability of the BTCA treated cotton decreased due to theremoval of the product.Acknowledgement: We would like to thank the HPMF-CT-2000-00868 project for providing the grant to Dr. Tzanov.Received: February 14, 2002Revised: April 22, 2002Accepted: May 29, 2002[1] J. Frick, R. Harper, Text. Res. Inst. 1982, 2, 141.[2] D. Lmmermann, Melliand Textilber. 1992, 73, 274.[3] US Patent 4,820,307 (1989), United States of America,Department of Agriculture, invs.: C. Welch, B. Andrews.[4] C. Welch, Text. Res. J. 1988, 8, 480.[5] I.-S. Kang, C. Q. Yang, W. Wei, G. Lickfield, Text. Res. J.1998, 68, 865.[6] W. Wei, C. Q. Yang, Y. Jiang, Text. Chem. Color. 1999,31, 34.[7] W. Wei, C. Q. Yang, Text. Res. J. 1999, 69, 145.[8] C. Q. Yang, G. Bakshi, Text. Res. J. 1996, 66, 377.[9] C. Q. Yang, Text. Res. J. 1991, 61, 298.[10] C. Q. Yang, Text. Res. J. 2001, 71, 201.[11] C. Q. Yang, Text. Res. J. 1991, 61, 433.[12] C. Q. Yang, Z. Mao, G. Lickfield, Text. Chem. Color.2000, 32, 43.[13] C. Q. Yang, X. Wang, Text. Res. J. 1996, 66, 595.[14] C. Q. Yang, X. Wang, I.-S. Kang, Text. Res. J. 1997, 67,334.[15] C. Q. Yang, L. Xu, S. Li, Y. Jiang, Text. Res. J. 1998, 68,457.[16] C. Q. Yang, D. Wang, Text. Res. J. 2000, 70, 615.[17] “Lipases: Structure, Mechanism and Genetic Engineer-ing”, L. Alberghina, R. D. Schmid, R. Verger, Eds., VCH,Weinheim 1990.[18] B. Borgstrm, H. L. Brockman, “Lipases”, Elsevier,Amsterdam 1984.[19] M. Petersen, P. Fojan, S. Petersen, J. Biotechnol. 2001, 85,115.Figure 4. Ester carbonyl band absorbance at 1724 cm–1 of cot-ton, treated with 6% BTCA/4% NaH2PO2 and hydrolyzed with0.4 g N l–1 lipase for different times.Communication: Lipases are used to par-tially restore the strength of cotton fabricscrosslinked with 1,2,3,4-butanetetracar-boxylic acid. Enzymatic hydrolysis of theester linkages at low temperature and neutralpH results in a 10% strength recovery, asso-ciated with slight deterioration of the crease-resistance effect. Conventional alkalinehydrolysis provides higher strength recov-ery, but causes considerable changes in thedurable press performance of the fabrics.The mechanism of the lipase-catalyzed esterhydrolysis is outlined in the Scheme.Lipases to Improve the Performance ofFormaldehyde-Free Durable Press FinishedCotton FabricsT. Tzanov, M. Stamenova, R. Betcheva,A. Cavaco-Paulo*Macromol. Mater. Eng. 2002, 287, 462–465Graphical Abstract for the Contents Page:Please check

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Lipases to Improve the performance of formaldehyde-free durable press finished cotton fabrics

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