Computational and Experimental Investigation Into Yield Behavior and Cure Rate Dependence of Thermoset Polymers

This dissertation is broken down into two primary sections: firstly, the development and improvement of molecular dynamics simulations of thermoset matrix polymers including their use in understanding molecular response to applied strain deformation and secondly, the discernment of a cure heating ramp rate dependence of the final molecular and macro-molecular properties of thermoset matrix polymer. The molecular dynamics section will discuss the development of molecular dynamics simulations of thermoset epoxy/amine matrix polymers, and the implementation of this work to determine the underlying molecular level events that cause thermoset matrix polymer yield. It will report a novel method for the determination of the strain at yield for thermoset matrix polymers and is based on the monitoring of the van der Waals potential energy. A correlation exists between the uptake of the van der Waals energy in the matrix polymer and the yield strain of the matrix. This analysis is a method to simulate the polymer yield and a method of understanding the nature of material yield. The second section of this dissertation will discuss a cure heating ramp rate dependence for thermoset matrix polymers based on epoxy/amine chemistry. Initially, this dependence was studied for a 33DDS/DGEBF matrix polymer. Using DSC and NIR it was found that the network growth mechanism is altered significantly by the cure heating ramp rate, which results in differences in the final network architecture for these polymers. These differences are most apparent in changes in the free volume hole size and the dielectric responses for these networks. It was found that the hole size decreased from approximately 65 to 50 Å3 when changing the cure ramp rate from 1–10 °C/min. Furthermore, the distribution of relaxation times G(τ) was altered by a variation of the cure heating ramp rate. In addition to the di-functional epoxide DGEBF, matrix polymers comprised of TGDDM/33DDS and TGDDM/44DDS were also studied for cure ramp rate dependence. It was found that these polymers also exhibit cure ramp rate dependence; however, the dependence itself appears to be chemistry specific, as the responses for the TGDDM systems are different than those for the DGEBF matrix