Study Of PVA Hydrogels System Prepared By Freezing-thawing Method

In this paper, poly (vinyl alcohol)(PVA) composites were studied. First,preparation and properties of atactic poly (vinyl alcohol)(a-PVA)/syndiotactic poly(vinyl alcohol)(s-PVA) blend hydrogels were investigated on the basis of PVA tacticity.Secend, the influence of preparation conditions on the properties of hydrogel infreezing-thawing process were explored. Third, PVA solutions were treated withfreezing-thawing method, the nanofibers electrospun from untreated and treatedsolutions were compared.Contents and conclusions:1. The hydrogels of a-PVA and s-PVA with different blend ratios were preparedby freezing-thawing processes. The results show that with the increase of s-PVA, blendsolution is easier to gel. The increase of cross-linking caused by s-PVA in the blendhydrogels results in denser structure, which in turn leads to increased gel fraction (G)and Hardness. The results also demonstrate s-PVA favors improvement of hydrogelscrystallinity and thermal stability. However, the equilibrium degree of swelling (EDS)and equilibrium water content (EWC) of hydrogel decrease with the increase of s-PVA.50/50(a-PVA/s-PVA) blend hydrogel has a denser structure with EWC of73.6%,Hardness of22.8HA and Tmof236.15oC, which is better than others.2. The a-PVA/s-PVA blend hydrogels were prepared under different preparationconditions. The effects of preparation conditions on hydrogels were investigated. Theincrement in Tgmof hydrogel and the enhancement in crystallinity and thermal stabilitywere observed with increasing freezing-thawing cycles or decreasing freezingtemperature. Thus, the better properties could be obtained by altering preparationconditions on the basis of blending a-PVA with s-PVA.3. The nanofibers were electrospun from treated and untreated solutions withfreezing-thawing method. According to SEM images of nanofibers, spinnability ofsolution and continuity of nanofibers were improved after treated, and the diameter ofnanofibers becomes larger with increasing freezing-thawing cycles. The crystallinity and thermal stability were enhanced which were found after treated, and the effect wasobvious with increasing freezing-thawing cycles.