Analysis on Thermal Degradation of Poly(gamma-glutamic acid) Sodium Salt by means of Light Scattering and Viscometry

Abstract

The thermal degradation experiment of sodium salt of poly(gamma-glutamic acid) (PGGNa) has been carried out in both its solid phase and solution phase at the range of 57 similar to 120 degrees C and their molecular weight decreasing effect was analyzed as a function of time by means of viscometry and light scattering. Based on the solid phase degradation results, it was supposed that the bond scission rate in a polymer chain kept constant and that the bond scission was occurred on a randomly located position in a polymer chain. For the degradation in solution phase, it was also found that all data at various temperatures were dropped on a single master curve when the reduced time t/t* was used in the plot of the reciprocal intrinsic viscosity (or molecular weight). This degradation curve in solution phase could be expressed as the SUM of a single exponential and a linear equation and especially, the single exponential character appeared only at the beginning stage. The activation energy was measured as 107 similar to 115 kJ/mol in this study and agreed with the literature values.