Interpenetrating polymer networks: Engineering properties and morphology

Interpenetrating polymer networks (IPNs) were prepared by the sequential mode of synthesis using epoxy resin as the plastomer and poly (n-butyl acrylate) as the elastomer components, respectively. The full and semi IPNs of these two constituents were characterized with respect to their mechanical properties like tensile strength, elongation at break, modulus and toughness. Resistance to thermal degradation of the IPNs was compared to that of pure epoxy resin by conventional thermogravimetric analysis. The glass transition behaviours of some of the IPNs of varying compositions were compared by using differential scanning calorimetry. Scanning electron microscopy (SEM) and polarized light microscopy (PEM) were used to study the fracture mechanics during tensile deformation and the surface morphology, respectively. The mode of changes in the above mentioned properties with changes in IPN compositions was studied. A gradual decrease in modulus and tensile strength with consequent increases in percent elongation at break and toughness was observed as the proportions of elastomeric PEA were increased steadily. The full IPNs however had higher modulus and tensile strength in comparison to the semi IPNs of corresponding compositions. The thermogravimetric results indicated that instead of a stepwise unzipping process of depolymerization as observed with various methacrylates, a C-C bond scisson occurred without formation of free radicals in the case of PEA. DSC tracings exhibited inward shifting of the glass transition temperature and a broadening transition. The morphology suggested by SEM indicates a decrease in shear yielding with consequent increase in crazing mode of failure as the mechanism of fracture. Two particle size system is indicated by the polarized light microscopy. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.