Dynamic Rheological Investigation during Curing of a Thermoset Polythiourethane System

Weiping Du,Huifang Chen,Lianjiang Tan,Yang Zhang,Haipeng Yang

doi:10.1155/2019/8452793

Abstract

A polythiourethane thermoset system based on a diisocyanate and a trithiol was investigated by dynamic rheological measurements. Strain sweep was performed to determine the linear elastic region of the thermosetting system. The changes of characteristic parameters including elastic modulus, viscous modulus, and complex viscosity were recorded in a heating ramp to trace the cross-linking and structural evolution during the curing process. Time sweep at constant temperatures was also performed to explore possible curing strategy at reduced temperatures. In addition, frequency sweep was conducted to confirm the temperature- and time-dependent viscoelastic properties of the thermoset system during the curing process. Both continuous heating and isothermal aging gave rise to solidification of the polythiourethane with similar critical structure, as evidenced by the critical values of relaxation exponent. A combination of isothermal aging and heating is expected to be a facile strategy for fabricating thermoset polythiourethane polymers at lower temperature or/and reduced curing time. A kinetic study was done to confirm the gelation characteristics of the polythiourethane system, and the activation energy was also calculated.

Highlights

Transparent polymers have attracted great interest as alternative optical materials due to their excellent impact strength, lightness, good processability, and low cost
These results showed that the curing proceeded more rapidly at a relatively high temperature
We further investigated the viscoelastic behavior of the polythiourethane system during frequency sweep in order to gain more information of the temperature effects on the curing of the polythiourethane systems

Summary

Introduction

Transparent polymers have attracted great interest as alternative optical materials due to their excellent impact strength, lightness, good processability, and low cost. Optical polymers with enhanced refractive index and low chromatic dispersion are needed for producing lenses. A good way to increase the refractive index of optical polymers is to introduce sulfur atoms into polymer backbones. Polythiourethane is increasingly used as an optical material because of its high refractive index [3,4,5,6]. Rheological testing is a powerful tool for studying the research and development of thermoset polymers and is frequently used in combination with differential scan calorimetry (DSC) and chromatography [11]

Methods

Results

Conclusion