EFFECT OF MATRIX DUCTILITY ON THE FRACTURE-BEHAVIOR OF RUBBER-TOUGHENED EPOXY-RESINS

This paper investigates the effect of matrix ductility on toughness in a carboxyl-terminated butadiene-acryionitrile copolymer (CTBN) toughe ned diglycidyl ether of bisphenol-A (DGEBA)-piperidine system. Two kin ds of epoxides were blended separately into this system to change the matrix ductility. One was a rigid and polyfunctional 4,4'-diaminodiphe nol methane (MY720), and the other was a flexible diglycidyl ether of propylene glycol (DER732). The matrix T-g was significantly changed, b ut without alteration of the microstructure of the dispersed rubbery p hase. The result of fracture energy tests reveals that the toughness o f the neat epoxy resins increases slightly with the increase in the re sin ductility. The toughness of the rubber-modified epoxy resins incre ases strongly with matrix ductility. Studies on the morphology of the toughened systems and their fracture surfaces indicate that the size o f the plastic deformation zone under constant rubbery-phase morphology is determined by the multiple but localized plastic shear yielding. I ncreasing matrix ductility increases the size of the plastic deformati on zone by inducing more extensive shear yielding. In addition, fractu re surfaces reveal that as the matrix rigidity is increased, an increa sing proportion of the fracture energy is dissipated by rubber cavitat ion during crack initiation.