Engineering Plastics from Lignin. X. Enthalpy Relaxation of Prepolymers

Abstract

A linear relationship between the enthalpy relaxation and the logarithm of time was observed for a variety of lignins and lignin derivatives annealed at temperatures below their glass transition temperature. While the behavior is noticeably affected by differences in lignin structure in terms of origin, chemical functionality and molecular weight, the sub-Tg annealing temperatures were found to be the primary factor determining the rate d ER/d log t (where ER represents enthalpy relaxation and t time), and this ranged from 0.2 to 0.4. This time dependent reduction in enthalpy is the result of a non-equilibrium chain conformation and has been shown to correlate with mechanical and several other physical properties for a number of material systems.