Study On Mechanical Properties Of Starch-PVA Blend Film For Warp Sizing

The main aim of the paper is that natural starch sizes were modified by chemical method in order to enhance its sizing properties. Two kinds of esterification starch sizes were prepared by using sodium tripolyphosphate and vinyl acetate as esterifying agent respectively. And the starch esters with different degree of substitution were obtained by varying the feed ratio of esterifying agent to cornstarch. The dependences of molecular structure of PVA, modification extent of phosphorylated starch, the blending ratio of phosphorylated starch to PVA on mechanical properties of starch-PVA blend film were investigated. The experimental results demonstrate that the molecular structure, modification extent, and the blend ratio show evident influences on mechanical properties of the film. For the phosphorylated starch, as the degree of substitution increases, the breaking elongation increases, while the breaking strength of the film increases initially and then decreases. A maximal strength appears when the degree of substitution is 0.016. As the content of starch in the film rises, the breaking elongation decreases, whereas the breaking strength initially decreases and then increases. Maximal breaking strength is obtained when the content is 50 percent. Increasing the molecular weight and degree of hydrolysis of PVA favors enhancing the mechanical strength and bent-fatigue resistance of the film. For the acetylated starch, as the degree of substitution increases, the breaking strength, the breaking elongation and flexibility increases, while wear loss of the film decrease. As the content of starch in the film rises, the breaking elongation and flexibility decreases, whereas wear loss of the film increases. Maximal breaking strength is obtained when the content is 50 percent. Increasing the molecular weight and degree of hydrolysis of PVA favors enhancing the mechanical strength and bent-fatigue resistance of the film.