Effects of liquid rubber modification on the behaviour of epoxy resin

The aim of this study was to investigate the behaviour of brittle epoxy resin when modified by liquid rubber for toughening purposes. The changes in mechanical and thermal properties of diglycidyl ether of bisphenol-A based epoxy resin with hydroxyl terminated polybutadiene (HTPB) (1% and 1.5%) have been studied. A silane coupling agent (SCA) was also utilized to improve the compatibility of HTPB and epoxy matrix. Four groups of specimens were prepared by using different orders of mixing of HTPB with SCA and hardener. Tension and impact tests were performed in order to observe the effect of rubber modification, SCA and mixing processes on the mechanical properties. Tensile strength and impact toughness values were increased in the specimens containing 1% HTPB and 2% SCA. Furthermore, it was found that rubber modification markedly increased the plastic strain at failure due to the possible decrease in crosslinking density with the change in path of the reactions. The changes in storage modulus and glass transition temperatures of all specimens were also evaluated by dynamic mechanical analysis. Fracture surfaces of all specimens were examined by scanning electron microscope. Use of SCA and different mixing orders improved the interaction between HTPB and epoxy matrix. The deformed rubber domains and higher amounts of deformation lines in some specimens indicated the improvement in toughness.