Abstract:

There is structural heterogeneity in polyvinyl alcohol (PVA) films prepared by solvent evaporation. In this study, PVA with molecular weights (M_w) of 27000, 47000, 75000 and 98000 were used for experiments. It was focused on the process of formation, structure and properties of PVA films, and the influence of polymerization degree (DP) on the rheological properties, structural homogeneity, hygroscopic and water-resistant properties of the PVA films, as well as its mechanical properties and optical properties were investigated. The results showed that with the increase of DP, the required concentration for liquid-solid transformation of PVA aqueous solution decreased and the structural heterogeneity of PVA films in the longitudinal section also decreased. Besides, the contact angle of PVA film increased with the increase of DP, which was attributed to the decrease of surface roughness. PVA-1 (M_w≈27000), the lowest DP, had the highest sensitivity to moisture and the worst water resistance. Both the DP and the moisture content indicated the significant impact on the mechanical properties of PVA film. When the moisture content reached to 5%, the yield point just disappeared, resulting in the obvious stress whitening phenomenon during the tensile process. It was attributed to the water in the PVA film which was treated as a stress concentration point during loading, resulting in micropores formation.

Key words: polyvinyl alcohol, rheological property, structural heterogeneity, mechanical property, water resistance

摘要：

通过溶剂蒸发法制备的聚乙烯醇（PVA）膜存在结构异质性。本文以分子量（M_w）分别为27000、47000、75000和98000的PVA为研究对象，重点研究了 PVA的成膜过程、膜结构和膜性能，探究聚合度对PVA成膜过程中流变性能、PVA膜结构均匀性以及其吸湿性、耐水性、力学性能和光学性能的影响。结果表明，随聚合度增加，PVA水溶液发生液体-固体转变所需浓度下降，所制备PVA膜在纵截面上的结构异质性也下降，并且PVA膜表面粗糙度逐渐降低，导致其表面的水接触角逐渐增大。聚合度最小的PVA-1（M_w≈27000）对水分的敏感性最高，耐水性最差。聚合度和含水率都能对PVA膜的力学性能产生显著影响，当含水率为5%时，屈服点消失。此后，PVA膜在拉伸过程中具有明显的应力发白现象，这归因于PVA膜中的水分在承受拉应力时作为应力集中点，并随着拉伸过程逐渐形成微孔。

关键词: 聚乙烯醇, 流变性能, 结构异质性, 力学性能, 耐水性能