Study On Preparation Methods Of Micro/Nano Helical Fibers

Nature is like a magician,creating all kinds of fine and wonderful biological structures,which endow organisms with unique functions.Among them,the helical structure continues to inspire human creativity because of its three-dimensional geometric structure,good tensile and shape recovery performance.The multi-level structure micro/nano helical fiber formed by the combination of helical structure and micro/nano fiber not only maintains the high specific surface area and high porosity of micro/nano fiber,but also adds excellent elasticity and flexibility.The spatial structure of spiral can also provide more cavities.Based on these excellent properties,micro/nano helical fibers have great potential applications.In this study,using melt-blowing and electrospinning technologies,two methods of preparing micro/nano helical fibers were discussed.Firstly,based on two-component spinning,micro/nano helical fibers were generated by asymmetric shrinkage or elongation formed by the rigidity difference between components;At the same time,a new method of preparing micro/nano helical fibers by ultraviolet(UV)crosslinking was studied.In Chapter 2,the materials include thermoplastic polyurethane(TPU)and polymers with different rigidity,including polypropylene(PP),polyamide(PA)and cellulose acetate(CA).Two kinds of polymer materials with different rigidity were spun by two-component meltblown and two-component electrospinning,and micro/nano helical fibers with excellent morphology were obtained.The molecular chain structure and differential scanning calorimetry(DSC)were used to analyze the rigidity of the polymer.The results showed that the rigidity difference between the two components would affect the preparation efficiency of spiral fibers and the greater the rigidity difference,the more micro/nano helical fibers were obtained.In Chapter 3 and Chapter 4,a UV crosslinked micro/nano fiber was prepared based on electrospinning technology,and the micro/nano helical fiber was successfully obtained by UV irradiation.In Chapter 3,an isocyanate terminated polyurethane prepolymer(PPU)material was prepared by chemical synthesis.Firstly,in Chapter 3,an isocyanate terminated polyurethane prepolymer(PPU)was prepared by chemical synthesis.The preparation conditions of PPU were explored by Fourier infrared spectroscopy(FT-IR)and Second-order reaction kinetic model.It was found that the method used could prepare PPU in line with the expectation.The preparation of PPU is obviously affected by temperature.The second-order reaction rate curve fitted at lower temperature has obvious linearity,indicating that there are few side reactions.Then,in Chapter 4,the prepared PPU and hydroxyl terminated polybutadiene(HTPB)were miscible in toluene for reaction,and then UV cross-linked micro/nano fibers were prepared by electrospinning,which were irradiated by UV light under certain stress to prepare micro/nano spiral fibers.UV light will crosslink the surface of the elastomer fiber containing carbon-carbon unsaturated double bond and change the physical properties,which makes the difference of elongation or shrinkage properties in the axial direction of the fiber.This difference makes the fiber form a helical structure after being stressed.At the same time,the helical morphology was characterized by helical curvature k.It was found that micro/nano helical fibers with different k values could be prepared under different UV time and stress.The more compact helical pitch can be obtained by prolonging UV irradiation time and greater stress,and the fiber has a larger k value accordingly.