Nano-reinforced Poly(vinyl Alcohol) Fiber By Wet-spinning

Poly(vinyl alcohol)(PVA)is a kind of water-soluble polymer notable for its ability to undergo complete biodegradation with positive effects on the environment,thus making them preferable candidates for current generation environmental friendly composite fibers.On the other hand,the preparation of graphene oxide(GO),chitin nanocrystals(CHN),chitin nanofibrils(CNF)and montmorillonite(MMT)via reasonable chemical or physical approaches presents them as effective reinforcement materials to prepare composite fibers.As one of the commonest spinning approaches,wet spinning,a double diffusion process have proved to be an easy and efficient technique to produce composite fibers enhanced properties.In this thesis,montmorillonite,chitin nanocrystals,chitin nanofibrils and graphene oxide were blended with PVA to fabricate environmental-friendly composite nanofibers through wet spinning process.The mode of preparation and properties of the wet-spun environmentally-friendly composite nanofibers were studied.Montmorillonite(MMT)with nanoscale dimensions was defibrillated through wet-grinding and homogenizing process and was mixed with PVA to prepare PVA/MMT composite fiber using wet-spinning.Particularly,the enhanced effect of the special two-dimensional geometry of montmorillonite made it had a greater advantage at less dosage.The morphology,structure and mechanical properties of the as spun fiberswere investigated.Furthermore,investigations from mechanical properties of the as spun fibers showed higher tensile strength with the addition of 2wt%MMT and reached to 0.701 cN/dTex.Moreover,the composite fiber showed lower water absorption capacity and the moisture uptake of the PVA/MMT composite fiber was only 53%compared with pure PVA.Secondly,chitin nanocrystals(CHN)with an average size of about 250 ± 50nm were obtained by hydrochloric acid hydrolysis.Altematively,chitin nanofibrils(CNF)defibrillated through wet-grinding and homogenizing process was obtained.Separately,CHN and CNF were mixed with PVA to prepare PVA/CHN and PVA/CNF compositefibers by wet-spinning in ethanol,respectively.The morphology,structure and mechanical propertiesof PVA/CHN and PVA/CNF composite fibers were investigatedand compared accordingly.The test results showed that PVA/CHN composite fiber inherited the liquid crystal of CHN.In comparison,the mechanical properties of PVA/CHN was better than PVA/CNF attributed to the liquid crystal property due to the CHN.The composite fibers showed higher tensile strength with the addition of 7wt%CHN and reached to 0.843 cN/dTex,two times that of pure PVA fiber.Furthermore,the moisture uptake of PVA/CHN composite fiber was only 51.32%compared with pure PVA.Graphene oxide(GO)sheets were obtained by modified Hummers’ method,and the GO sheets had an average size of about 1.2 μm.Then,GO sheets mixed with PVA to prepare PVA/GO compositefibers by wet-spinning in ethanol at two different temperature(-5 ℃,25 ℃).The composit fiber spun at low temperature showed higher strength and liquid crystral.The morphology,structure and mechanical propertieswere investigated through comparison of the as spun fibers at different temperature of coagulation bath and with different solid content of graphene oxide.The test results showed that the composite fibers have highest tensile strength with the addition of lwt%GO,and tensile strength of composite fiber spun at low temperature and high temperature increased by 60%and 40%,respectively.It is found that the composite fiber prepared by low temperature coagulation bath has a smoother and compact structure,and the composite fiber has a liquid crystal structure under the polarizing microscope,which makes the composite fiber have better mechanical properties.