Response Surface Methodology for Investigating the Effects of Hydrolysis Reaction Parameters on Molecular Structure and Performance of Polyvinyl Alcohol as Primary Suspending Agent

Abstract

This study presents the synthesis of polyvinyl acetate (PVAc) by solution polymerization and its partial hydrolysis to polyvinyl alcohol (PVA) using alkaline alcoholysis. The influence of the molar ratio of hydrolysis catalyst (NaOH) to PVAc and the time and temperature of the saponification reaction on the degree of hydrolysis and molecular weight of the PVA were investigated using response surface methodology. Statistical analysis of the results revealed that the degree of hydrolysis and molecular weight of PVA were strongly dependent on the molar ratio of NaOH/PVAc. It was also found that the second-order interactions between the investigated parameters were not statistically significant. The optimal conditions for synthesizing PVA as a primary suspending agent were obtained as T = 45°C, t = 33 min and NaOH/PVAc (molar ratio) = 0.05. The chemical structures of the PVAc and the optimum PVA were studied by Fourier transform infrared spectroscopy. The distribution of acetate groups in the optimum PVA was determined using 13C nuclear magnetic resonance spectroscopy. It was found that addition of benzene as well as one-step addition of NaOH (when compared with drop-wise addition) result in more blockiness in the acetate group distribution of PVA. The performance of the optimum PVA was also investigated for a typical suspension polymerization of vinyl chloride and the particle morphology of the product was studied using scanning electron microscopy.