Parameters Affecting the Crystalinity of Poly (vinyl alcohol) Prepared at Different Reaction Conditions

Various samples of poly (vinyl alcohol) have been prepared under different conditions. Temperature and time in the presence of catalyst were assumed as important parameters affecting the properties of poly (vinyl alcohol). The degree of hydrolysis and molecular weight، as dependent parameters، were determined. First the temperature was kept at 45°C and hydrolysis reactions were conducted at different times. To investigate the effect of temperature on hydrolysis process the time was kept constant at 40 min and the reaction was carried out at various temperatures. By considering the various uses of poly (vinyl alcohol) and the properties of its various grades such as solubility، surface tension، resistance in tension، viscosity، the crystallinity properties of various prepared samples were investigated using differential scanning calorimetry. Increasing the time and temperature of the reaction led to higher degree of hydrolysis and lower molecular weight. Molecular weight، thermal treatment، degree of hydrolysis and the type of configuration of the molecules were the most important parameters affecting the crystallinity. Increasing the degree of hydrolysis increased the crystallinity and reduction in molecular weight and in this respect the effect of degree of hydrolysis on crystallinity was more evident than the molecular weight. In order to have similar molecular configuration for raw material the same polyvinyl acetate was used in all the tests. FTIR results showed that syndiotactic structure was dominant and favored the crystallinity. By considering the variation in three parameters during reaction the individual and associated effects of degree of hydrolysis، molecular weight and configuration was investigated on the crystallinity and melting point.