Thermal degradation of polyvinyl alcohol with various plasticizers

Polyvinyl alcohol-glycerol (PVA-G) and polyvinyl alcohol-D-sorbitol (PVA-D) polyblends were obtained by blending polyvinyl alcohol with different molecular weights (PVA17 and PVA24) and plasticizers (glycerol and D-sorbitol) in various blended ratios through melting process. Furthermore, the various plasticizers and contents effects on the characteristics of polyvinyl alcohol were investigated. Thermalgravimetric analysis (TGA) indicated that polyblends with various plasticizers presented different thermal degradation behaviors. PVA-G polyblends revealed three stages of degradation; the first stage at about 200∼230°C resulted from glycerol degradation and polyvinyl alcohol decomposition led to the second stage at about 225∼410°C and third stage at about 400~535°C. PVA-D polyblends manifested two stages of degradation; the overlapping degradations of D-sorbitol and polyvinyl alcohol brought about the first stage (220∼400°C) and the second stage (400∼560?) associated with polyvinyl alcohol degradation. The thermal degradation analysis of polyvinyl alcohol with different molecular weights demonstrated that PVA17 had closed characteristic degradation temperatures to PVA24, exhibiting the similar degradation behaviors. Two degradation kinetics methods, Ozawa and Horowitz-Metzger, were employed to analyze the activation energies of polyblends. The activation energies calculated from both methods were varied but showed the same tendency. PVA-D polyblends revealed thermal stability at relative low temperature and PVA-G polyblends presented thermal stability at relative high temperature.