A zone drawing method to determine optimum initial concentration of poly(vinyl alcohol) to make films with different degrees of saponification

To prepare poly(vinyl alcohol) (PVA) films for various industrial and biomaterial applications, the effects of polymer concentration and degree of saponification (DS) on the draw ratio and physical properties of PVA films were investigated. Atactic PVA (a-PVA) films were prepared by casting in water with different polymer concentrations of 2.5, 5.0, 7.5, 8.5, and 9.5 g/dl, respectively. The a-PVA films were zone-drawn under various conditions. Using the optimum polymer concentration of the a-PVA/water solutions caused a significant change in the draw ratio of the films. Draw ratios of a-PVA films were maximized at the initial polymer concentrations of 7.5 and 8.5 g/dl, but gradually decreased at higher or lower concentrations. Furthermore, the birefringence, degree of crystal orientation, and tensile properties of a-PVA films having the same draw ratios were the highest at these optimum polymer concentrations. These optimum concentrations were reconfirmed by viscometry. Optimum conditions of the film casting of atactic PVAs with various DSs have been established by the zone drawing method. The agreement between the optimum concentration values obtained by zone drawing and viscometry suggests that the zone drawing method is an appropriate and convenient way to establish the optimum concentration for maximum draw ratio, birefringence, degree of crystal orientation, and tensile properties.