Preparation And Characterization Of The Materials Derived From α-PVA/s-PVA/NaCl Blending System

In this study, sodium chloride(NaCl) and syndiotacticity-rich poly(vinyl alcohol)(s-PVA) were blended with atactic PVA(a-PVA). On one hand, the whole tacticity of the system was improved, and it helped to form the crystal phase, so properties of the materials from this system were strengthed for this reason. On the other hand, inorganic ions were considered to disrupt the inter- and intra-molecular hydrogen bonding of the PVA chains, to change the crosslink structure and finally to increase the thermal and mechanical properties of the samples. a-PVA/s-PVA/NaCl blend films, electrospun nanofibers and hydrogels were prepared and characterized in the experiments. The work was composed of three parts as follows:Firstly, a-PVA/s-PVA of different ratios and NaCl of various contents were blended in water solvent, and dissolved into uniform solutions at a high temperature. Then the blend films were prepared by casting the solutions into glasses. And the blend films were tested in several measurements. The results showed in this part that the FT-IR spectra were weakened as the s-PVA ratio was increased, and the melting temperature(Tm), thermal stability and mechanical properties were improved as well. The Tm of the film was increased for 2℃by increasing 10% s-PVA , the tensile strength and elastic modulus were increased for 3 and 4 times respectively when the content of s-PVA were increased from 0% to 40%. There was a maximum of Tm and mechanical value at 3wt% NaCl.Secondly, a small content of s-PVA and NaCl were added into a-PVA water solutions. The blend solutions were frozen at a lower temperature and then electrospun into nanofibers. Properties of nanofibers electrospun from original and frozen solutions were analyzed. Adding NaCl into the blend solution could obviously improve the conductivity of the solution. For the lower concentration of the solution in this part, the average diameter of the nanofibers electrospun from solution containing NaCl was increased. The rheological property of the blend solution was changed by s-PVA. As the s-PVA content was increased, the average diameters of the nanofibers were decreased and the number of the spindle-like beads was increased, Tm and mechanical property were improved, too. And the most exciting result was that the tensile strength of the blend nanofibers electrospun from frozen solution was 7~8 time higher than that of the nanofibers from original ones.Finally, a-PVA/s-PVA/NaCl blend hydrogels were prepared by a freeze treatment. Expect the concentration of solution and freeze/thaw cycle, s-PVA and NaCl also had a great impact on the gelling of the blend solution. As the s-PVA and NaCl content were increased, gelling time of the solution was shortened, gelling temperature of the solution approached the room temperature, and Tm and elastic modulus of the blend hydrogel and dried gels were improved as well. But excessive NaCl, as a plasticizer, caused the blend dried gels incompact in morphology.