Hydrophobic modification of cotton fabric

Carbohydrate Polymers 137(2016)549–555Contents lists available at ScienceDirectCarbohydratePolymersj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /c a r b p olHydrophobic modification of cotton fabric with octadecylamine via laccase/TEMPO mediated graftingYuanyuan Yu,Qiang Wang ∗,Jiugang Yuan,Xuerong Fan,Ping Wang,Li CuiKey Laboratory of Science and Technology of Eco-Textile,Ministry of Education,Jiangnan University,1800Lihu Ave.,Wuxi 214122,Jiangsu,PR Chinaa r t i c l ei n f oArticle history:Received 3September 2015Received in revised form 22October 2015Accepted 6November 2015Available online 10November 2015Keywords:Cotton Laccase GraftingOctadecylamine Hydrophobicitya b s t r a c tHydrophobic cotton fabrics were prepared by grafting octadecylamine (ODA)onto cotton fiber surfaces via the laccase/2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)treatment.The cotton fibers were oxidized by laccase/TEMPO to introduce aldehyde groups,which reacted with the amino groups of ODA to form Schiff base.First,ODA was coupled to glucan,used as a model compound of cellulose.The results of FT-IR and MALDI-TOF mass spectroscopy prove the formation of a Schiff base between ODA and glucan.More-over,the existence of ODA in the grafted cotton fibers was verified by ATR-FTIR,elemental analysis,X-ray photoelectron spectroscopy.Finally,the hydrophobicity of the ODA-grafted cotton fabrics was estimated.The surface hydrophobicity of the cotton fabrics increased after the enzymatic grafting reaction.©2015Elsevier Ltd.All rights reserved.1.IntroductionHydrophobic textiles are in active demand for diverse functional applications such as rainwear,stain resistant products,water repel-lent outdoors gear,and the fiber reinforced materials in composites.Textiles with hydrophobic surface on textiles can be obtained by increasing the surface roughness and/or lowering the free energy of the textile surface.Textile surface with increased roughness is achieved by the incorporation of various nanoparticles such as sil-ica and zinc oxide.Lowering the surface energy of textiles can be achieved via fiber modification using compounds with low surface free energy (hydrophobic monomer)(Sawatari,Sekiguchi,&Yagi,1998).To create hydrophobic surfaces on cotton fabrics,numerous approaches such as physical and chemical processing technologies can be applied to modify the fiber surface of fabrics using hydropho-bic compounds such as long-chain alkyl compounds (Jiang,Meng,&Qing,2005;Yuen,Li,Ku,Mak,&Kan,2005),fluorocarbons,or silicones (Nooy,Besemer,&van Bekkum,1995).These approaches have been applied to produce water repellent cotton fabrics;how-ever,their sustainability and environmental concerns limit their application.Finding new environment-friendly modified methods to replace current ways is urgently needed.One well-known procedure for the cellulose modification is the oxidation of hydroxyl groups into the corresponding aldehyde and/or carboxyl groups by 2,2,6,6-tetramethylpiperidine-1-oxyl∗Corresponding author.Tel.:+8651085912007.E-mail address:qiang wang@ (Q.Wang).(TEMPO)/NaBr/NaOCl system (Dang,Zhang,&Ragauskas,2007).Aldehyde and carboxyl groups on the oxidized cellulose can be used for further modification with amino compounds such as proteins and amino polysaccharides (Varavinit,Chaokasem,&Shobsngob,2001;Janjic et al.,2009;Nikolic et al.,2010).Araki,Wada,and Kuga (2001)prepared a sterically stabilized aqueous suspension of cellulose microcrystals by NaBr/NaOCl/TEMPO medi-ated carboxylation of cellulose and grafting of poly(ethylene glycol)with a terminal amino group using a water soluble carbodiimide.Aliphatic amines were introduced to the NaBr/NaOCl/TEMPO-oxidized nanowhisker surface via carboxyl/amine salt formation,and the modified nanowhiskers were found to be nanodispersible in isopropyl alcohol owing to the hydrophobicity of the aliphatic amines (Fujisawa,Saito,&Isogai,2012).Liu,Nishi,Tokura,and Sakairi (2001)prepared modified cotton with chitosan by the Schiff base reaction between the aldehyde groups of the oxidized cellu-lose and the amino groups of chitosan.Laccase (EC.1.10.3.2)is a family of blue multi-copper oxidases,which can catalyze the one electron oxidation of phenols and aro-matic or aliphatic amines to reactive radicals with the concomitant reduction of O 2to water (Kunamneni et al.,2008;Riva,2006).Moreover,diverse substrates such as alcohols,sugars,cellulose,and aromatic methyl groups can be oxidized by laccases in the combina-tion with chemical ccases have been used in diverse industrial applications such as the food,pulp,paper,textile,and cosmetics industries (Widsten &Kandelbauer,2008).In a recent study,in the TEMPO-mediated oxidation of cellu-lose fibers,NaBr/NaOCl has been replaced by laccases.Jauˇs ovec,Vogrinˇc iˇc ,and Kokol (2015)described a way of preparing and/10.1016/j.carbpol.2015.11.0260144-8617/©2015Elsevier Ltd.All rights reserved.550Y.Yu et al./Carbohydrate Polymers 137(2016)549–555Fig.1.Schematic illustration of the grafting reaction of ODA on cellulose bylaccase/TEMPO.Fig.2.ATR-FTIR spectra of unoxidized cotton and oxidized cotton treated with laccase/TEMPO.stabilizing highly reactive C6-aldehyde groups on cellulose using laccase/TEMPO under mild aqueous conditions.Xu,Song,Qian,and Shen (2013)reported the introduction of carboxyl and aldehyde groups to softwood-derived cellulosic fibers by the laccase/TEMPO treatment.Aracri,Vidal,and Ragauskas (2011),Aracri,Valls,and Vidal (2012)reported that the wet strength of paper improved by the laccase/TEMPO oxidation,because of the formation of a sub-stantial amount of aldehyde groups providing interfiber bonding through the hemiacetal linkages.The purpose of this study was to prepare the hydrophobic cot-ton with an octadecyl carbon chain by octadecylamine (ODA,a hydrophobic monomer),using the Schiff base reaction between the aldehyde groups on oxidized cellulose by the laccase/TEMPO treatment and the amino groups on ODA (Fig.1).The grafting of amino compounds onto cellulose by the laccase/TEMPO oxidization provides a new approach for cellulose modification.2.Experimental2.1.MaterialsLaccase (EC.1.10.3.2)from Trametes versicolor and TEMPO were purchased from Sigma-Aldrich (Shanghai,China).ODA was pur-chased from Aladdin (Shanghai,China).All other chemicals were of analytical grade.Cotton fiber and fabric were supplied by Wuxi No.1Cotton Textile Company (Wuxi,China).The specifications of the used woven cotton fabrics were as follows:thread density18.276tex,warp 13thread/cm and weft 7thread/cm,weight per area 150g/m 2.The geometrical roughness of cotton fabric mea-sured using a KES-FB-AUTO-A system was 5.8␮m.2.2.Preparation of oxidized cotton fibers by the laccase/TEMPO treatmentCellulose fibers (0.2g)were added to a buffer solution (40mL,pH 4.5).To that solution,1.4mg/mL TEMPO and 1.0mg/mL lac-case were sequentially added.The resulting slurry was stirred at 40◦C under air (the source of oxygen)by bubbling for 12h.Upon the completion of the reaction,the laccase/TEMPO-oxidized fibers were collected by filtration,followed by a two-step washing with ethanol and water.2.3.Grafting of ODA onto oxidized glucan by laccase/TEMPOGlucan (0.5g)was incubated for 12h in 50mL acetate buffer with 1.0mg/mL laccase,1.4mg/mL TEMPO,and ODA (0.1g)in a shaking bath.The pH of the acetate buffer was 4.5,and the tem-perature of the reaction was maintained at 40◦C for the optimum laccase activity.After the reaction,the reaction mixture was dia-lyzed to remove acetate,and then the product was collected by freeze-drying.2.4.Grafting of ODA onto oxidized cotton with laccase/TEMPOCotton (fibers or fabrics,4%w/v)was incubated in acetate buffer (pH 4.5)and 40◦C with laccase (1.0mg/mL),TEMPO (1.4mg/mL),and ODA (2%w/v)in a shaking bath for 12h.After the reaction,the cotton grafted with ODA was collected by filtration,followed by a two-step washing process using ethanol and water.2.5.Characterization of glucan grafted with ODAThe structure of the product (2.3)was investigated by FT-IR spectroscopy with the KBr pellet technique.Matrix-assisted laser-desorption/ionization time-of-flight mass spectra (MALDI-TOF MS)of glucan and the product (2.3)were obtained using a Bruker Proflex instrument equipped with a nitro-gen laser (Smartbeam II,modified Nd:YAG laser).Data collection and processing were performed by flexControl and flexAnalysis version 3.3software.Y.Yu et al./Carbohydrate Polymers137(2016)549–555551Fig.3.(a)FT-IR spectra of untreated glucan,ODA and the grafted glucan with ODA,(b)MALDI-TOF mass spectra of glucan,(c)MALDI-TOF mass spectra of glucan grafted with ODA,(d)the proposed pathway of grafting reaction.552Y.Yu et al./Carbohydrate Polymers137(2016)549–555Table1The m/z of MALDI-TOF mass spectrum of glucan and glucan grafted with ODA.Sample Compound Predicted m/z(Da)Detected m/z(Da) Glucan Fig.3(a)H(C6H10O5)4OH666658.6;675.5H(C6H10O5)5OH828820.6;837.9H(C6H10O5)6OH990983.3;1000.5H(C6H10O5)7OH11521146.0;1163.3H(C6H10O5)8OH13141308.8;1326.1H(C6H10O5)9OH14761471.4;1488.8H(C6H10O5)10OH16381634.1;1651.6 Glucan grafted with ODA Fig.3(b)H(C6H10O5)5OH828784.1;798.1;812.4H(C6H10O5)5OH+1ODA−4H−1O10781037.3;1052.0;1066.7H(C6H10O5)5OH+2ODA−8H−2O13281290.6;1304.2;1319.6H(C6H10O5)5OH+3ODA−12H−3O15781555.92.6.Characterization of cotton grafted with ODAAttenuated total reflection(ATR)-FTIR spectra of the untreated, oxidized,and modified cotton fabrics were recorded using a Nicolet IS10infrared spectrophotometer(Thermo Nicolet,USA)with an ATR attachment.Absorbance measurements were performed in the wavelength range650–4000cm−1at a resolution of4cm−1and16 scans per sample.Elemental analyses of the untreated and modified cotton fab-rics were performed using a Vario ZLIII Elementar(Elementar, Germany).X-ray photoelectron spectroscopy(XPS)analyses of the untreated and modified cotton fabrics were carried out using a RBD upgraded PHI-5000C ESCA system(Perkin Elmer)with Mg K␣radi-ation(h =1253.6eV).The entire spectra in the range0–1100eV and the narrow spectra of all the elements with a high resolution were recorded using a RBD147interface(RBD Enterprises,USA)by using AugerScan3.21software.The surface morphology of the cotton samples was investigated using a SU-1510scanning electron microscope(Hitachi,Japan).A thin layer of platinum,functioning as a conductive layer,was sprayed onto thefiber sample surface prior to the SEM analysis. 2.7.Hydrophobicity of cotton samplesWater contact angle of the cotton samples was measured using a SL200B static contact angle/interfacial tension meter(Shanghai zhongchen digital technic apparatus Co.,China)after conditioning the fabric samples to the equilibrium moisture content.In washing fastness experiment,the cotton samples were washed with water containing1g/L detergent in a SW-12A Launderometer(Wenzhou Darong Company,China)at room tem-perature for40min,and then dried at80◦C.2.8.Mechanical properties of cotton samplesThe tensile strength of the cotton fabrics was determined by the strip method according to ASTM D1682-64using a YG(B)026D-250Tensile Strength Tester(Wenzhou Darong Company,China). Samples were testedfive times and the values were averaged.3.Results and discussion3.1.Characterization of cotton fabrics after thelaccase/TEMPO-mediated treatmentThe structural characteristics of the untreated cotton fabrics and oxidized cotton fabrics by the laccase/TEMPO treatment were analyzed by ATR-FTIR spectroscopy to verify the presence of alde-hyde groups on cotton fabrics after the laccase/TEMPO-mediated treatment.As shown in Fig.2,the spectra of the unoxidized and oxi-dized cotton fabrics both show several stronger peaks at2900and 1646cm−1,corresponding to the O H stretching vibration and sat-urated C H stretching vibration,pared to the spectrum of the unoxidized cotton fabrics,the spectrum of the oxi-dized cotton fabrics shows two new peaks at1750and2820cm−1.A previous study has shown that the TEMPO-derived oxoammonium ion in the absence of laccase could introduce surface aldehyde and carboxylic groups to cellulosefibers,and therefore,the new peaks at1750and2820cm−1were mainly attributed to the presence of the C O and C H stretchings in aldehyde,respectively.The results of the ATR-FTIR analysis indicate that the hydroxyl groups of the primary alcohol of C6-carbon in cellulose were oxidized to aldehyde groups.3.2.Characterization of glucan grafted with ODA using thelaccase/TEMPO treatmentGlucan has the same repeat glucose units in the chain as pared to cellulose,glucan is water soluble and has a lower molecular weight;therefore,it will have better reactivity with ODA in water.To study the mechanism of the surface modification of cot-tonfiber with ODA,ODA wasfirst coupled to glucan,used as the cellulose model compound,via the laccase/TEMPO treatment.The structural characteristics of the untreated glucan,ODA,and glucan treated with laccase/TEMPO/ODA were investigated by FTIR and MALDI-TOF MS.The chemical structural characteristics of the untreated glucan, ODA,and glucan treated with laccase/TEMPO/ODA were verified by FTIR,as shown in Fig.3(a).The characteristic absorption peaks of ODA at1410,1560,2850,and2915cm−1were observed in the FTIR spectrum of the glucan treated with laccase/TEMPO/ODA,indi-cating that ODA was bound onto glucan after the laccase/TEMPO treatment.However,the C O stretching(1740cm−1)peak was not observed in the FTIR spectrum of the glucan treated with laccase/TEMPO/ODA,probably because the aldehyde groups in glucan generated by the laccase/TEMPO treatment reacted with the amino groups in ODA.Moreover,a new absorption peak at 1640cm−1was observed in the FTIR spectrum of the glucan treated with laccase/TEMPO/ODA.The absorption peak at1640cm−1cor-responded to the C N stretching,confirming the Schiff base reaction between the aldehyde groups in glucan and the amino groups in ODA.MALDI-TOF MS has been successfully utilized for the characteri-zation of biomolecules and synthetic polymers and is considered to provide highly reliable information on the molecular weight of the polymer(Ikeda,Sugihara,Uyama,&Kobayashi,1996;Chaudhary, Critchley,Diaf,Beckman,&Russell,1996).In this study,the molecular conformations of glucan and the glucan treated with lac-case/TEMPO/ODA were investigated by MALDI-TOF MS.Fig.3(b) shows the MALDI-TOF mass spectrum of the untreated glucan withY.Yu et al./Carbohydrate Polymers137(2016)549–555553Fig.4.(a)FT-IR spectrum of ODA at wavenumbers2600–3100cm−1,(b)ATR-FTIR spectra of untreated cotton and cotton grafted with ODA at wavenumbers 2600–3100cm−1,(c)ATR-FTIR spectra of untreated cotton and cotton grafted with ODA at wavenumbers1500–1900cm−1.Table2(a)Elemental composition of cottonfibers before and after the different treatments and(b)surface elemental composition of cottonfibers before and after the different treatments.Sample N(%)C(%)H(%)Untreated cotton0.05242.527.044 Cotton treated with laccase/TEMPO0.06043.41 6.782 Cotton treated with laccase/TEMPO/ODA0.27043.527.008 Sample N(%)C(%)O(%)Untreated cotton0.767.831.5Cotton treated with laccase/TEMPO0.7866.2832.94 Cotton treated with laccase/TEMPO/ODA 4.171.324.6a series of peak groups representing oligomers of different lengths (m/z from600to1700).The main peaks of the successive groups were separated by162Da,corresponding to the mass of one glu-cose unit(C6H10O5,162Da).The predicted and detected M w s of glucan are listed in Table1.Although MALDI-TOF MS spectrum is comparatively tolerant to the presence of buffer salts and deter-gents,these compounds can affect the intensity and quality of the signal(Mock,Sutton,&Cottrell,1992).Thus,slight differences were observed between the detected and predicted M w s of glucan. The proposed pathway of grafting reaction is shown in Fig.3(d). Theoretically,when one ODA molecule is grafted onto glucan,the molecular weight of the polymer will increase by250Da.As shown in Fig.3(c),the MALDI spectrum of the glucan treated with lac-case/TEMPO/ODA was characterized by a series of peak groups separated by252Da,indicating that ODA was successfully grafted onto glucan.The results of FTIR and MALDI-TOF MS of the glucan treated with laccase/TEMPO/ODA by the laccase/TEMPO treatment provide the theoretical evidence for the ODA-grafted cotton.3.3.Characterization of cotton grafted with ODA by thelaccase/TEMPO treatment3.3.1.ATR-FTIR analysisIn this study,the surface structural characteristics of the cot-tonfibers after grafting reaction were investigated by ATR-FTIR. Fig.4(a)shows the FTIR spectrum of ODA at wavenumbers in the range2600–3100cm−1.Fig.4(b)and(c)show the ATR-FTIR spec-tra of the untreated and ODA-grafted cotton.Fig.4(b)shows a prominent peak at2850cm−1in the ATR-FTIR spectrum of cot-tonfibers after the laccase/TEMPO/ODA treatment,relating to the absorbance of the methyl group in ODA(Fig.4(a)),indicating that the laccase/TEMPO/ODA treatment was successful in grafting ODA onto cottonfipared to Fig.2,the peak at1750cm−1also appeared in the ATR-FTIR spectrum of the cotton grafted with ODA(Fig.4(c)),indicating that the carboxylic groups or unreacted aldehyde groups oxidized by the laccase/TEMPO treatment were present in the ODA-grafted cottonfibers.However,the absorption peak of Schiff base(C N)at1640cm−1was not observed in the ATR-FTIR spectrum of the ODA-grafted cotton grafted,because the peak at1640cm−1also appeared in the ATR-FTIR spectrum of the untreated cottonfibers.3.3.2.Elemental analysisElemental compositions of the untreated and treated cotton fibers are listed in Table2(a).As expected,the relative amounts of C and N in the untreated cottonfibers were42.52and0.052%, respectively.The nitrogen content of the cottonfibers treated with laccase/TEMPO was close to that of the untreated cottonfibers. However,the nitrogen content of the grafted cottonfibers increased to0.27%after the laccase/TEMPO/ODA treatment,because the554Y.Yu et al./Carbohydrate Polymers 137(2016)549–555Fig.5.The photos of water contact angle of the (a)untreated,(b)laccase/TEMPO treated and (c)ODA alone treated cotton fabrics (digital photographs captured at 3s after water drop on the surfaces of cotton fabrics).nitrogen content of ODA (5.20%)is higher than that of cotton (0.05%).These results indicate that ODA was present in the grafted cotton fibers.3.3.3.XPS analysisTo study the structure of the ODA-grafted cotton fibers treated with laccase/TEMPO/ODA,it is important to investigate the sur-face structure of the cotton fibers,because the grafting reaction mainly occurs on the surfaces of cotton fibers.Surface elemental compositions of the untreated and treated cotton fibers determined from the XPS analysis are listed in Table 2(b).One advantage of XPS over elemental analysis is that XPS also investigates the sam-ple surface in finite depth (∼10nm deep).The XPS results show an increase in the nitrogen content of the cotton fibers after ODA grafting reaction,indicating the coupling of ODA onto cotton fiber surfaces.The increase in the nitrogen content from 0.7%(untreated cotton fibers)to 4.1%(the ODA-grafted cotton fibers)could be attributed to the incorporation of ODA onto the cotton fiber sur-face,as ODA has a high nitrogen content of 5.20%.The nitrogen contents of the untreated and laccase/TEMPO-treated cotton fibers were slightly pared to the results of the elemen-tal analysis,the nitrogen content in the surfaces of grafted cotton fibers was significantly higher than those of the grafted cotton fibers,confirming that the ODA grafting site was mainly at the fiber surfaces.3.3.4.SEM analysisAs shown in Fig.S1,the changes in the surface morphol-ogy of the untreated cotton fibers (bleached cotton fibers),the laccase/TEMPO-treated,and ODA-grafted cotton fibers were stud-ied by SEM.The untreated and the laccase/TEMPO-treated cotton fibers both show relatively smooth surfaces (Fig.S1a),indicating that the laccase/TEMPO treatment did not change the surface mor-phology of the fibers.After the laccase/TEMPO/ODA treatment,the cotton fiber surface became rough and irregular,and the new mate-rials existed on the fiber surfaces.The materials observed on the grafted cotton fibers could possibly be regarded as the grafted ODA.The SEM images clearly show the attachment of ODA on the sur-faces of cotton fibers after the laccase/TEMPO/ODA treatment.3.4.Hydrophobicity of cotton fabrics grafted with ODAThe wettability of the cotton fabrics was examined by water con-tact angle (WCA)measurements.The images of the time-dependent WCA of a water drop on the untreated,laccase/TEMPO-treated,and ODA-treated cotton fabrics are shown in Fig.5.The untreated,laccase/TEMPO-treated,and ODA alone treated cotton fabrics were at an angel of 0◦at 3s after water drop on the surfaces of the cot-ton fabrics.The pristine cotton fabrics can be completely wetted by water owing to the abundant hydroxyl groups in its structure (Xu &Cai,2008).No significant change in the wettability of thecottonFig.6.(a)The water contact angle of the ODA-grafted cotton fabrics,(b)washing fastness of the ODA-grafted cotton fabrics.fabrics was observed after the laccase/TEMPO treatment or ODA alone treatment.As shown in Fig.6(a),the WCAs of the ODA-grafted cotton fabrics were 117.3,105.8,and 92.7◦at 30,300,and 600s after a water drop on the fabric surfaces,respectively.The enhanced hydrophobicity of the ODA-grafted cotton fabrics supported the presence of ODA containing long hydrocarbon chains on the surface of the cotton fibers.As shown in Fig.6(b),the washing fastness was determined by measuring the WCAs of the ODA-grafted cotton fabrics (0,2,4,6,8,10repeated washing cycles)at 300s after a water drop on the fabric surfaces.The results shows that the WCAs on the ODA-grafted cotton fabrics do not change much until 8washing cycles have been completed.After 10washing cycles,the WCAs decreased from ∼110to ∼96◦,showing high washing durability.Y.Yu et al./Carbohydrate Polymers137(2016)549–5555553.5.Mechanical properties of cotton fabrics grafted with ODAThe effect of the grafting process on the tensile strength of the cotton fabrics was shown in Fig.S2.The untreated cotton fabric samples showed the tensile strength of526N.The cotton fab-ric samples treated with laccase/TEMPO or laccase/TEMPO/ODA showed the tensile strength of521N and534N,respectively.The results show that the tensile strength of all cotton fabrics was not changed significantly after laccase/TEMPO or laccase/TEMPO/ODA treatments.4.ConclusionsIn summary,ODA was grafted onto cottonfibers via the Schiff base reaction between the amino groups on ODA and the alde-hyde groups on oxidized cellulose with laccase/TEMPO.The cotton fabrics treated with laccase/TEMPO/ODA showed hydrophobic surface,and the WCA reached117.3◦.The structures of the ODA-grafted glucan confirmed by the FTIR and MALDI-TOF MS provided a theoretical evidence for the cotton-grafted with ODA by the laccase/TEMPO treatment.Subsequently,the results of ATR-FTIR, elemental analysis and XPS of the ODA-grafted cottonfibers con-firmed the occurrence of grafting reaction.This study demonstrated an eco-friendly way to enhance the hydrophobicity of the surface of cottonfibers.Moreover,other functional cottonfibers could be obtained via the grafting reaction between functional monomer and oxidized cottonfiber after the laccase/TEMPO treatment.AcknowledgementsThis work wasfinancially supported by the Program for New Century Excellent Talents in University(NCET-12-0883),the Fun-damental Research Funds for the Central Universities[JUSRP11504, JUSRP51312B],the program for Changjiang Scholars and Innovative Research Team in University(IRT15R26).ReferencesAraki,J.,Wada,M.,&Kuga,S.(2001).Steric stabilization of a cellulose microcrystal suspension by 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