| Citric acid(CA)is one of the formaldehyde-free anti-wrinkle finishing agents,which is cost-effective,non-toxic and renewable,and is considered to be one of the most promising antiwrinkle finishing agents.However,the anti-wrinkle property of the CA finished cotton fabric is not good enough and it needs to be further enhanced.Also,the CA finished cotton fabric has severe fabric yellowing and fabric tensile strength reduction problems.These shortcomings of CA finishing severely restrict its wide application in fabric anti-wrinkle finishing.In view of the above problems,this research is mainly divided into two parts.The first part is mainly focusing on enhancing the anti-wrinkle property of the CA finished cotton fabric.Mercerizingliquid ammonia joint pretreatment and CA/waterborne polyurethane(WPU)anti-wrinkle joint finishing were proposed.Also,the mechanisms of these treatments were studied from the perspective of fiber’s internal pore structure changes.The second part is mainly focusing on elevating the whiteness and tensile strength property of the CA finished cotton fabric.An activated peroxide post-bleaching method was proposed and the corresponding mechanism was studied.The contents and the conclusions of the research are as follows:(1)Carrying out single-factor experimental analysis on traditional CA anti-wrinkle finishing and exploring the improvement of the anti-wrinkle performance of CA finished cotton fabric by pretreatments.The single factor experimental conditions cover the concentration of CA,the dosage of catalyst sodium hypophosphite,the p H of the finishing solution,the curing temperature and the curing time.By taking wrinkle recovery angle as the primary consideration,and taking into account fabric whiteness and tensile strength retention rate,the optimized CA finishing conditions were determined,which built the experimental foundation for the whole research.What’s more,by comparing the fabric properties of CA anti-wrinkle cotton fabrics pretreated by only mercerization and mercerizing-liquid ammonia joint pretreatment,it is found that the cotton fabric treated with mercerizing-liquid ammonia joint pretreatment has lower fiber crystal content and more compact and uniform fiber structure,which is beneficial to increase the transverse hydrogen bonding,then obtain better fabric anti-wrinkle property,fabric smoothness appearance after the laundering,fabric softness and fabric tensile strength retention rate.Thus,in order to achieve a better fabric anti-wrinkle performance,a mercerizing-liquid ammonia joint pretreatment was suggested.(2)Using eco-friendly WPU mixed with CA for joint anti-wrinkle finishing to further enhance the anti-wrinkle property of cotton fabric.Six commercial WPUs were added into the citric acid finishing solutions at different concentrations for joint finishing.The finished cotton fabric wrinkle recovery angle,softness,tensile strength,whiteness,smoothness appearance grade and wettability were measured and analyzed.The results show that there is a synergistic effect between WPU and CA during the joint finishing,as adding waterborne polyurethane into CA solution could greatly improve the wrinkle recovery property of the finished cotton fabric.However,the final anti-wrinkle performance of the joint finished cotton fabric may closely relate to the adding WPU’s hard and soft segments’ structure.What’s more,through the observation of SEM morphology,it is found that the main action mode of WPU on the finished cotton fabric is film formation.The smooth and elastic WPU film can repair the damage of acid degradation during finishing,and meanwhile,provide a systematic restoring force to enhance the fabric anti-wrinkle performance.(3)Using a differential scanning calorimetry(DSC)to test and analyze the cotton fiber pore structure changes before and after anti-wrinkle finishing and then try to explain the antiwrinkle finishing mechanism from these changes.Overall,the DSC method could be divided into two steps.Step one,an isothermal endothermic curve of the wet cotton sample was measured.Step two,the freezing bound water contents corresponding to different pore sizes were calculated using the step one isothermal endothermic curve.Then,the pore size distribution of the tested cotton sample was obtained indirectly by drawing a plot between the freezing bound water content and its corresponding pore size.In this part of the experiment,we first tested and analyzed the pore size distribution of desizing cotton,desizing-scouringbleaching cotton,desizing-scouring-bleaching-mercerizing cotton,desizing-scouringbleaching-mercerizing-liquid ammonia pretreating cotton and their corresponding CA antiwrinkle finished cotton fabrics.It is found that after the CA anti-wrinkle finishing,the cotton fiber’s total pore volume was increased,the average pore size was decreased,and the pore distribution was tended to be more evenly and concentrated,which results in more internal interaction of the cotton fabric.And then the increase of internal force is beneficial to improve the elasticity and wrinkle recovery property of the fiber.Meanwhile,the tensile strength retention was reduced due to the fluffy fiber structure.Then we also measured and analyzed the pore distribution of CA/WPU joint finished cotton fabric in this part of the experiment.The results suggest that the increase of the wrinkle recovery property of the CA/WPU joint finished cotton fabric is not only because of the elastic WPU film formation on the cotton fiber surface but also because of the pore-filling effect inside the cotton fiber pore structure by adding WPU.(4)Using a post-bleaching method to improve the fabric whiteness and tensile strength retention of yellowish anti-wrinkle cotton fabrics.N-[4-(triethylammoniomethyl)benzoyl]-caprolactam chloride(TBCC)-activated peroxide system could promote the whiteness of the anti-wrinkle fabrics by destroying the unsaturated double bond substances and destroying the conjugated chromophores.At the same time,its mild bleaching conditions would not significantly damage the cross-linking ester bonds of the anti-wrinkle cotton fabric but would help recover partial fabric tensile strength.After this post-bleaching,the CIE whiteness of the anti-wrinkle cotton fabric is greater than 80,the tensile strength retention rate is increased by12%.Moreover,this method could help to save the traditional cotton fabric bleaching pretreatment before the anti-wrinkle finishing.Only one-step impregnating post-bleaching could obtain the CA finished cotton fabric with excellent whiteness,which is energy-saving and environmental-friendly.After the one-step post-bleaching,the CIE whiteness of the antiwrinkle cotton fabric is greater than 75,and the tensile strength retention rate is also increased by 5%.Furthermore,in order to save more energy and time,a rapid pad-steam post-bleaching was constructed.The actual liquid amount(pick-up)on the fabric of the pad-steam postbleaching was small and the pad-steam post-bleaching time can be as short as 2 mins.After the pad-steam post-bleaching process,the CIE whiteness of the anti-wrinkle cotton fabric still can be greater than 70,the tensile strength retention rate can also be improved to a certain extent.This project aimed to provide eco-friendly solutions to solve the problems of the CA antiwrinkle cotton fabric finishing,such as low wrinkle-resistant property,serious fabric yellowing and great fabric tensile strength loss.The experimental parameters and mechanisms were well investigated and studied.This research helps to promote a wide application of CA on antiwrinkle finishing and provides more information for eco-friendly anti-wrinkle fabrics’ development and production. |
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