The internal pressure, mechanical properties, and water absorption of carbon fibre composites with spiro-epoxy copolymer matrices

Abstract

High-performance fibre composites embodying a new principle have been manufactured and tested. In these composites the polymer matrix exerts a controlled pressure on the fibres. Although some pressure between fibres and matrix is necessary to permit the transfer of loads, the pressure normally present (about 40–50 M Pa) is much in excess of what is needed for carbon fibre composites (roughly 10 M Pa). This leads to undesirably high internal stresses, and is a primary cause of the low Izod impact strength of these composites, as compared with glass fibre composites. A four-year investigation of carbon fibre reinforced epoxies has shown that spiro orthocarbonate monomers, copolymerized with the epoxy, can reduce shrinkage pressures by nearly 70%, and increase the impact strength by about the same amount. At the same time fatigue life is improved. No important change in other mechanical properties is observed, and the water resistance of the composite is increased slightly.