CORRELATION BETWEEN STRESS-WHITENING AND FRACTURE-TOUGHNESS IN RUBBER-MODIFIED EPOXIES

Fracture toughness of rubber modified epoxy systems was evaluated in r elation to stress-whitening. The epoxy systems consisted of diglycidyl ethers of bisphenol A (DGEBA)based epoxy resin, 4,4' diaminodiphenyl sulphone (DDS) as curing agent, and carboxyl-terminated butadiene-acry lonitrile (CTBN) rubber. It was found that a peak value of fracture to ughness occurs at a small amount of rubber content (similar to 4 phr) and closely corresponds to that of stress-whitening size. Other proper ties such as flexural strength and flexural modulus were also found to display maxima at a similar amount of rubber content. (C) 1996 John W iley & Sons, Inc.