EFFECT OF MATRIX CROSSLINK DENSITY, VARIED BY STOICHIOMETRY AND RESIN MOLECULAR WEIGHT, ON FRACTURE BEHAVIOR OF EPOXY RESINS

摘要

The role of method of changing the matrix cross-link density (XLD) on toughenability of neat and core-shell rubber modified diglycidyl ether of bisphenol A (DGEBA) based epoxy was investigated. Matrix XLD was varied by changing epoxy equivalent weight and using non stoichiometric amounts of hardener. The samples were cured using di amino di phenyl methane (DDM) and were modified with 10wt% of poly butyl acrylate- poly methyl metacrylate core-shell particles. Fracture toughness values of neat and CSR modified epoxy samples increased with increasing the pre-polymer molecular weight but the fracture energy decreased with lowering the XLD via deviating from stoichiometric point. Scanning electron microscopy was used for-analyzing the fracture surface of the samples. The SEM results showed that decreasing the XLD via deviating from stoichiometric ratio causes in variation of crack propagation mode from unstable brittle to stable brittle. For analyzing the deformation behavior of epoxy resins DMTA was utilized. DMTA results showed a suppression of β transition relaxation in non stoichiometric systems which caused antiplasticization of non stoichiometric systems however β relaxation motions in networks with different pre-polymer molecular weights did not change. Results suggest that cross-link density can not be used as a general term for describing the fracture behavior of epoxy resins and it would be more reasonable to use matrix ductility for describing the fracture behavior of epoxy resins.