| As one of the most widely used synthetic fibers,polyester(polyester fiber)has many excellent properties such as high strength,tensile resistance,wrinkle resistance and ironing,good wear resistance,machine washability,etc.However,due to its low moisture regain(only0.4%under standard environment),polyester fabric has the shortcomings of poor hydrophilicity,air permeability,dyeing and antistatic.In order to improve the hydrophilic properties of polyester,researchers used hydrophilic finishing agent,surface oxidation,surface grafting and biological enzyme technology to improve the hydrophilicity of polyester.Biological enzyme technology showed great advantages over the other methods,due to its mild operating conditions,friendly to the environment,and almost no damage to the fiber.However,the poor modification effect and low reaction speed limites the enzymatic surface modification of polyester.Therefore,it is necessary to improve the catalytic efficiency of the enzyme and improve the modification effect.To solve these problems,this project selected cutinase recombinantly expressed by the State Key Laboratory of Food Science and Technology of Jiangnan University to modify the surface of polyester.Different pretreatment methods was introduced and their effect on the surface modification of polyester catalyzed by enzyme was explored.Based on this,ultrasonic wave combined with cutinase modification of polyester was systematically studied and the mechanism was explored.The main contents and conclusions are as follows:Firstly,based on the characteristics of high enzyme activity and good thermal stability of cutinase,the enzymatic surface modification system of polyester was constructed under specific conditions,and the reaction solution and modified polyester fabric were characterized.The amount of products in the reaction system was used to measured by ultraviolet spectrophotometer.High performance liquid chromatography(HPLC)was used to identify the products.The surface morphology and chemical structure of polyester were characterized by scanning electron microscopy(SEM)and Fourier Transform infrared spectroscopy(FTIR-ATR).The hydrophilicity and dyeing properties of polyester were tested by water contact angle and methylene blue staining.The results showed that the suitable process conditions for cutinase surface modification of polyester were as follows:cutinase concentration 100 U/m L,reaction time 72 h,p H 8.5 and reactiom temperature 60?.Under the optimal condition,two kinds of hydrolysate TPA and MHET was released,and the total hydrolysates reached 120.85 mg/L.The addition of Trition X-100 surfactant increased the release of the hydrolysate by 136%,and decreased the contact angle of polyester fabric from93.4°to 83.1°.The rougher of the fiber surface,the breaking of the C=O and C-O,and the number of–COO—groups increased,indicating the ester bonds on the surface of polyester was hydrolyzed by cutinase,and the hydrophilic properties of polyester were improved.Secondly,four different pretreatment methods,including ultrasonic synchronous method,step method,plasma treatment and Ultraviolet irradiation treatment,were used to modify the surface of polyester,and the influence of pretreatment on the modification effect was studied.The pretreated polyester fabric was placed in a cutinase-catalyzed modification system,and the surface properties,thermal properties and hydrolysis effects of the treated polyester were tested.The results showed that all the preatement method get different degrees of etching,and no obvious difference in infrared spectra,and there was almost no change in Tg and melting temperature,indicating that these pretreatment methods were relatively mild.Compared with single cutinase shaker treatment,the release of hydrolysate of four kinds of pretreated polyester increased by 39.19%,10.94%,28.7%and 8.2%,respectively;and the amount of the hydrolysate of ultrasonic/enzyme simultaneous treatment was the highest.Study on the relationship between ultrasonic wave and cutinase catalytic reaction revealed that the ultrasonic treatment can slightly increase the activity of cutinase,and the product release of the ultrasonic/enzymactic treatemt was significantly higher than the single process,which indicated a synergistic effect of ultrasonic and cutinase.The 2 h product release amount was161.53%higher than that of the single cutinase treatment,and with the increase of the reaction time of the two,the release amount of the hydrolysate gradually increased within 2 h.Finally,the synergistic effect between ultrasonic and enzyme,the influence of ultrasonic combined with cutinase treatment on the hydrophilic modification of polyester surface was investigated.The product generated by enzymatic hydrolysis of polyester has an absorption peak at 240 nm in the UV region.By measuring the OD240 value and fitting it into the standard curve of terephthalic acid,the release amount of hydrolyzed product can be obtained.The appropriate process conditions for ultrasonic treatment are as follows:treatment time 60 h,power 275 W.Under the optimal condition,the product release amount of ultrasonic combined with cutinase was 403.32 mg/m L,which was 287.29%higher than that of single cutinase shaker treatment.The results of high performance liquid chromatography showed that the release of TPA and MHET by ultrasound combined with cutinase increased 134.45%and 287.73%respectively compared with cutinase alone.After ultrasonic combined with cutinase treatment,the contact Angle of polyester fabric decreased from 93.4°to 81.5°,the K/S of the dyed fabric increased significantly between 550-600nm,and the number of–COO—groups generated on the surface of the polyester increased.After the reaction,the strength of polyester fabric does not decrease significantly,and the settling time is reduced from 720minutes without sedimentation to 82 minutes.Various analysis methods were used to explore the relevant mechanism of ultrasonic treatment to improve the effect of cutinase-catalyzed polyester hydrolysis.It was found that ultrasonic waves did not reduce the activity of cutinase,and maintained high enzymatic activity within 72 hours.Ultrasonic treatment increases the adsorption capacity of enzyme protein on polyester and provides more possibilities for catalytic reaction between the two.Ultraviolet absorption and fluorescence spectra of cutinase liquid before and after ultrasonic treatment showed that the cutinase configuration did not change,but the amount of tryptophan on the surface increased.The change of protein molecular secondary structure content indicated that the flexibility and flexibility of cutinase are improved,and the substrate was easy to contact with the enzyme activity center,which was conducive to improving the catalytic efficiency of the enzyme and maintaining the activity of cutinase better. |
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