MATRICES THAT EXPAND ON CURING FOR HIGH-STRENGTH COMPOSITES AND ADHESIVES

All available thermosetting matrices, including epoxy resins and unsaturated polyesters, undergo a shrinkage in volume upon curing. In a composite in which the reinforcing fiber has a high modulus, this shrinkage will set up large internal stresses which can be relieved either by an adhesive failure in which the matrix pulls away from the fiber or by a cohesive failure with the formation of voids or microcracks. Either of these failures will result in a weak composite. In these laboratories it was discovered that, if monomers were used in which at least two rings were opened for every new bond that was formed in the backbone of the polymer, matrices that do not shrink on curing or that expand up to 19% could be developed. The addition of such monomers to an epoxy resin produced a composite with a high strength. In a similar manner strong adhesives and coatings were developed. © 1990.