Water Transport Performance And Mechanism Of Electrospinning Submicron Fiber/Cotton Composite Yarns

Cotton,as one the most important natural fibers in the textile industry,has been used as a raw material by mankind as early as 5000 years ago.At present,cotton fiber accounts for more than 90%of the natural fiber market and about 27% of the total fiber market.Because of its natural,soft and skin-friendly properties,cotton textiles are very suitable for close-fitting fabrics and light summer fabrics,and have always been the favorite of consumers.However,since the absorbed moisture in cotton fiber will be held firmly,the wet cotton fabric is generally heavy and intends to cling to the skin,bringing strong discomfort.Therefore,to improve moisture transport performance of cotton fabrics has become a difficult problem during the development of textile industry.Compared with traditional ultrafine fibers,electrospun submicron fiber materials have a smaller fineness scale,a higher specific surface area,and can provide richer capillary channels.The composite of sub-micron fibers and cotton fibers can promote water transport inside the fiber assemblies.By adjusting the physical and chemical properties of sub-micron fibers and the structure of composite yarns,the moisture wicking functionality could be realized.It provides an innovative and feasible technical strategy for improving liquid moisture transport performance of cotton textiles.At first,this thesis summarized the origin and development of the research on thermal and wet comfort in textile science,which was focused on the physical connotation of wet comfort and water transport.According to the related physical theories,the mechanism of water transport inside the fiber assemblies was analyzed.Computational fluid dynamics and computer numerical simulation were used to solve the problem.Based on in-depth analysis of the effect of electrospinning submicron fibers on water transport,structures of electrospinning submicron fiber/cotton composite yarns were designed.By using numerical simulation,the water transport behavior of liquid water in different yarn structures was investigated,and the factors affecting the moisture wicking performance of composite yarns were discussed.Subsequently,the water transport mechanism of "tree-like" composite yarns and "embedded" composite yarns were explored,respectively.A submicron fiber/cotton composite yarn with enhanced moisture wicking functionality that could be produced on a large scale has been developed successfully.The main contents of the thesis are as follows:(1)Based on the electrospinning submicron fiber yarn setup and industrial electrospinning device developed independently by our research group,two electrospinning submicron fiber/cotton composite yarns were designed and prepared,namely the "tree-like" composite yarn and the "embedded" composite yarn.Based on the hydrodynamic mathematical functions,a physical model of the liquid moisture transport in the cross-section of composite yarns was constructed.And the mechanism of these two composite yarn structures on water transfer was discussed.By using numerical simulation technology,combined with computational fluid dynamics,the process of water transfer in composite yarns was simulated to verify the correctness of mechanism proposed.The results showed that the water transport mechanism of the cross-scale composite yarns depended on the capillary effect produced by the submicron fiber channels and the cotton fiber channels,especially the differential capillary effect generated at the interface between them.The strength of this effect was positively related to the equivalent radius of capillaries and the cosine of fiber contact angles.The addition of electrospinning submicron fibers and the structural design of composite yarns can change the motion state of water flow,accelerating the transfer speed of liquid water,and improving the water transport performance of composite yarns.(2)In order to further explore the water transport mechanism of "tree-like" composite yarns,polyacrylonitrile(PAN)and polycaprolactone(PCL)electrospinning submicron fiber/cotton composite yarns were prepared.,the diameter of sub-micron fibers in the “tree-like” yarn was controlled by configuring different concentrations of the spinning solution;the core-sheath ratio of the “tree-like” yarn structure was adjusted by different covering times;the wettability of “tree-like”yarns was adjusted through surfactant modification.The research results showed that “tree-like”yarns with the relatively thin electrospinning submicron fiber layer(about 76 μm)and moderate surface wettability(contact angle of about 55°)achieved the best water transport performance(oneway moisture transport index of 1034.5%)in this work.The change of fiber size at the submicron level has little effect on the moisture wicking function of the "tree-like" composite yarns.The water transport mechanism of the "tree-like" composite yarn comes from the combined effect of its internal hydrostatic pressure and capillary pressure.The differential capillary pressure existing at the interface between the cotton fiber layer and the submicron fiber layer drives water to quickly moving through the sub-micron fiber layer.(3)In order to achieve a lower ratio composition of electrospinning submicron fiber and cotton fiber,and exert advantages of sub-micron fiber more efficiently,we explored the electrospinning submicron fiber and cotton fiber blended yarn technology.By using mechanical and statistical methods,Here,the migration behavior of two different electrospinning submicron fibers polyacrylonitrile(PAN)and polystyrene(PS)within cotton slivers in roller drafting was demonstrated through a combination of mechanical and statistical methods.The accelerated point distribution of electrospinning submicron fibers during roller drafting was determined and the effect of these fibers on their yarn properties was evaluated.The results showed that electrospinning fibers had a similar distribution to 15 mm tracer fiber under the small draft ratio,but when the ratio became larger,the accelerated points of electrospinning fibers distributed more widely than all the tracer fibers.Furthermore,the addition of PAN electrospinning submicron fibers had a positive impact on their yarn quality whereas PS electrospinning submicron fibers had an adverse impact on the physical properties except breaking strength.At last,by analyzing the relationship between electrospinning submicron fiber content and drafting force,the electrospinning fiber content should be controlled under 10 wt.% to guarantee high quality of composite yarns.(4)The water transport mechanism of the embedded composite yarn was explored.Here,PAN and PS electrospinning submicron fiber/cotton composite yarns were produced,respectively.Under fluorescence microscopic observation,electrospinning fibers within the composite yarns showed a uniform distribution.As a result,these composite yarn-based knitted fabrics obtained a good water transport ability and a fast water evaporation rate.According to the moisture management test,PS electrospinning submicron fiber composite yarn-based fabrics exhibited a relatively high one-way transport index R(400%),claiming an enhanced moisture management performance.Finally,specific surface area tests and finite element analyses were used to analyze the water transport mechanism inside the yarns.The results proved that a small number of electrospinning fibers played a predominant role in enhancing the moisture management ability of the composite yarns.This thesis constructed two different sub-micron fiber/cotton fiber composite yarn structures which were based on two different electrospinning technologies.Through the adjustment of the structure and the optimization of materials,the composition from high ratio to low ratio,and from low efficiency to high efficiency was realized.It provided experimental and theoretical basis for improving the moisture wicking functionality of cotton textiles.Meanwhile,it developed a feasible technical strategy for improving the water transport performance of cotton textiles,and also made an innovative attempt for the industrial application of electrospinning fibers,which had a driving effect and practical value for the development of the textile industry.