Effect of matrix deformability on the fracture properties of epoxy resins modified with core–shell and cross‐linked rubber particles

Abstract

AbstractThe effect of matrix deformability on the mechanical and fracture properties of epoxies containing dispersed core–shell rubber (CSR) and cross‐linked rubber (CLR) particles was studied. The deformability of the matrix phase was varied using two types of curing agents, dicyandiamide (DICY) and piperidine, wherein the matrix phase cured with DICY has lower deformability than that cured with piperidine. Tensile and compression tests were conducted for the DICY‐ and piperidine‐cured epoxies. Under tensile load conditions, typical for CSR‐ and CLR‐modified epoxies, the DICY‐cured epoxies were brittle, whereas the piperidine‐cured epoxies failed under plastic deformation. Under compression loads, the 0.2% proof stresses of both rubber‐modified epoxies cured by DICY were higher than those cured by piperidine, wherein the proof stresses for both the DICY‐ and piperidine‐cured epoxies decreased with increasing rubber content. The results of fracture toughness tests for both types of cured epoxies indicated that the J‐integral (Jc) values of the DICY‐cured epoxy containing rubber particles were ~0.3–0.5 times that of the piperidine‐cured epoxy, which implied that the fracture toughness of the rubber‐modified epoxies decreased with decreasing deformability of the matrix phase. In addition, the ratio of Jc for CLR‐modified epoxies to those of Jc for CSR‐modified epoxies for piperidine cured epoxies were about 1.5 times greater than those of DICY cured ones. Microscopy observations were conducted to explore the effect of the deformability of the matrix phase on the fracture mechanism.