Roles of Small Polyetherimide Moieties on Thermal Stability and Fracture Toughness of Epoxy Blends.

Bisphenol A diglycidyl ether (DGEBA) was blended with polyetherimide (PEI) as a thermoplastic toughener for thermal stability and mechanical properties as a function of PEI contents. The thermal stability and mechanical properties were investigated using a thermogravimetric analyzer (TGA) and a universal test machine, respectively. The TGA results indicate that PEI addition enhanced the thermal stability of the epoxy resins in terms of the integral procedural decomposition temperature (IPDT) and pyrolysis activation energy (Et). The IPDT and Et values of the DGEBA/PEI blends containing 2 wt% of PEI increased by 2% and 22%, respectively, compared to those of neat DGEBA. Moreover, the critical stress intensity factor and critical strain energy release rate for the DGEBA/PEI blends containing 2 wt% of PEI increased by 83% and 194%, respectively, compared to those of neat DGEBA. These results demonstrate that PEI plays a key role in enhancing the flexural strength and fracture toughness of epoxy blends. This can be attributed to the newly formed semi-interpenetrating polymer networks (semi-IPNs) composed of the epoxy network and linear PEI.