Surface Hydrophobic Modification Of Cotton Fabrics Using In Situ Esterase-catalyzed Polymerization

Cotton fibers are abundant in nature and present excellent properties such as low cost,light mass density,high strength,and renewability.However,the strong polarity and hydrophilicity of the cotton fibers makes them easy to stain,they present poor wrinkle resistance and reduced antimicrobial properties.Also,the interfacial bonding between nonpolar resins and cotton fibers would not be strong because of the hydrophilic character of cotton fibers.Therefore,it is necessary to modify the surface of cotton fibers in order to reduce their hydrophilicity and overcome some of the limitations associated with the application of cotton fiber materials.In this study,the abundance of hydroxyl groups on cotton fabrics and the esterase-catalyzed transesterification in absence of water,were used to initiate the grafting of hydrophobic groups oleic acid from triolein onto the surface of cotton fabrics,resulting in lower hydrophilicity of cotton fabrics.On the other hand,enzymatic in situ coating of hydrophobic polyesters,polyol polyesters and fluorinated polyol polyesters on the surface of cotton fabrics was implemented using the esterase-catalyzed synthesis of functional polyesters by transesterification reactions.A novel and efficient enzymatic functional modification system in heterogeneous system on the surface of cotton fabrics was established.In order to improve the reaction rate and degree of polymerization of polyesters,lipase-catalyzed transesterifications between a dicarboxylate ester and a diol ester,a dicarboxylate ester and a polyol?such as ethylene glycol/glycerol?,and a fluorinated dicarboxylate ester and a ethylene glycol were systematically investigated.Using these in situ modification reactions the hydrophobicity of cotton fabrics was improved.Detailed research contents and main conclusions are as follows:?1?The oleic acid ester of triolein was grafted onto the cellulose of cotton fabrics in heterogeneous system using the unique catalytic character of cutinase in absence of water and the abundance of hydroxyl groups on cotton fabrics.The wettability changes of the modified cotton fabrics were characterized by recording the water-drop absorption time and using the bromophenol blue droplet test.It took 1.91 s to absorb one drop of water for the modified cotton fabrics,and the absorption time was three times higher than that of control samples.The wetting time of bromophenol blue droplet was 3 s after modification.A series of characterizations such as SEM,ATR-FTIR,LC-MS,MALDI-TOF MS were used to analyze the surface morphology and the chemical structure changes of the modified cotton fabrics.It was proved that oleic acid ester was successfully chemically grafting onto the cellulose molecule.And the surface modification mechanism of the cutinase-catalyzed grafting reaction was expounded.?2?Poly?ethyleneglutarate?wasenzymaticallysynthesizedusingthe ultrasound-assisted polyesterification of ethylene glycol diacetate and diethyl glutarate in absence of water and solvent.The immobilized Candida antarctica Lipase B?CALB?was used as catalysts.The product was characterized using the ¹H NMR and MALDI-TOF MS.The influence of ultrasound treatment on the initial reaction kinetics,the degree of polymerization and the monomer conversion rate was investigated respectively.Under the same enzyme loading condition,the reaction time was shortened from 24 h to 7 h with the application of ultrasound without affecting the size of produced polyesters.Ultrasound can strengthen the initial reaction kinetics,and improve the monomer conversion rate and the degree of polymerization of the synthesized polyesters.The surface of cotton fabrics was modified using the in situ lipase-catalyzed synthesis of poly?ethylene glutarate?based on previous work,resulting in a hydrophobic surface.The hydrophobicity and anti-wrinkle properties were studied by recording the static contact angle and wrinkle recovery angle.The static contact angle of modified cotton fabrics was 127.01°,and the wetting time of bromophenol blue droplet was much longer than 32 s,which was obviously higher than that of modified cotton fabrics with cutinase and triolein?3 s?.The wrinkle recovery angle was increased 30.13%compared with the untreated cotton.The modified cotton fabrics was analyzed by MALDI-TOF MS and ¹H NMR.And the results indicated that oligomers of poly?ethylene glutarate?was lipase-catalyzed in situ synthesized on the surface of cotton,forming a polyester coating on the surface of cotton fabrics.As a result,the surface of cotton fabrics showed an excellent hydrophobicity.?3?Four kinds of novel polyol polyesters were produced using immobilized CALB catalyzed polyesterification of a dicarboxylate ester?dimethyl adipate/dimethyl succinate?and a polyol?ethylene glycol/glycerol?under vacuum.They are poly?adipate glycol?,poly?succinate glycol?,poly?adipate glycerol?and poly?succinate glycerol?.These polyol polyesters were characterized by ¹H NMR and MALDI-TOF MS,and the effect of the chemical structure of reaction substrates on the average of polymerization and the monomer conversion rate was studied.It indicated that dimethyl adipate was more reactive than dimethyl succinate,and ethylene glycol are more reactive than glycerol.Among the four enzymatic polymerization schemes,the enzymatic synthesis of poly?adipate glycol?achieved the highest monomer conversion rate of 88.5%,and those of other three reaction schemes were all below 50%.The average degree of polymerization of the produced polyol polyesters were between 2 and 3,and they were all oligomers.?4?The surface of cotton fabrics was modified by the lipase-catalyzed in situ synthesis of polyol polyesters based on previous work.The lipase is from Thermomyces lanuginosus.The hydrophobic modification process was optimized using orthogonal experimental design method.The static contact angle was chosen as the index,and reaction temperature,enzyme loading and reaction time was chosen as the factors.The optimization conditions of the lipase-catalyzed in situ synthesis of poly?adipate glycol??A₀?,poly?succinate glycol??B₀?,poly?adipate glycerol??C₀?and poly?succinate glycerol??D₀?on the surface of cotton were,respectively,A₀–vacuum 45?,50%v/w lipase,8 h;B₀–vacuum 55?,35%v/w lipase,8 h;C₀-vacuum 45?,50%v/w lipase,8 h;D₀-vacuum 35?,50%v/w lipase,6 h.The static contact angels of modified cotton fabrics under the optimal conditions were respectively,111.99°±3.61°?A₀?,136.89°±2.76°?B₀?,130.05°±4.98°?C₀?,132.40°±1.80°?D₀?.Compared with the static contact angle of cotton fabrics modified by in situ synthesis of poly?ethylene glutarate?,except the one with in situ synthesis of poly?adipate glycol?,the static contact angles of other three modified cotton fabrics under optimal conditions were increased by 7.78%?B₀?,2.39%?C₀?and 4.24%?D₀?,respectively.The surface morphology and chemical changes of cotton fabrics was studied using SEM and ATR-FTIR.The results showed that the surface hydrophobicity of cotton fabrics was improved by a layer of enzymatically in situ synthesized polyol polyesters oligomers with flake,particle or mesh structures.?5?Three fluorinated polyol polyesters were synthesized from fluorinated dicarboxylate esters and ethylene glycol using immobilized CALB as catalysts based on the lipase-catalyzed polymerization of a dicarboxylate ester and ethylene glycol.They are poly?ethylene tetrafluorosuccinate?,poly?ethylene hexafluoroglutarate?and poly?ethylene octafluoroadipate?.These fluorinated polyol polyesters were characterized using ¹H NMR,¹⁹F NMR,MALDI-TOF MS,ATR-FTIR and TGA methods.The effects of the reaction substrates'type and size,reaction temperature,reactors'type,reaction time and presence or absence of catalysts on the monomer conversion rate were discussed.And the enzymatic synthesis process of fluorinated polyol polyesters was optimized.The results indicated that lipase CALB showed higher catalytic activity on short chain fluorinated diesters.Among three enzymatic polyesterification reactions,the monomer conversion rate of enzymatic polymerization from dimethyl tetrafluorosuccinate and ethylene glycol was higher.Lipase CALB did not obviously promote the synthesis of fluorinated polyol polyesters.When not using lipase CALB,monomer conversion rate at 40?can reach the high conversion rate level at 70?.The effect of ultrasound treatment on the monomer conversion rate was positively correlated with the molecular weight of the fluorinated diester substrates.The optimal conditions were that the reaction firstly proceed with ultrasound treatment for 1 h at 40?,then transfer to vacuum bath of 2 mbar for 6 h at 40?.The monomer conversion rate and average degree of polymerization of fluorinated polyol polyesters were proportional to the molecular size of fluorinated diester substrates.The thermal stability of the synthesized fluorinated polyol polyesters was inversely proportional to the content of fluorinated methylene inside.On the basis of lipase-catalyzed synthesis of fluorinated polyol polyesters,the fluorinated polyol polyesters were in situ synthesized on the surface of cotton fabrics.The wetting time of bromophenol blue droplet on the surface of modified cotton fabrics using in situ synthesis of poly?ethylene tetrafluorosuccinate?was longer than 60 min.and the hydrophobic modification of the surface of cotton fabrics using enzymatic in situ polymerization was realized.