The Use of Thermoplastic Polyester Reinforcing Fibers to Enhance the Toughness of Thermoset Polyester Resin Laminates

The toughness or impact resistance of thermoset resin laminates can be enhanced by the addition of low cost thermoplastic polyester fibers. A continuous thermoplastic polyester fiber mat manufactured by Hoechst Celanese Corp., trade name Trevira, has been successfully utilized to enhance the toughness and reduce the density of marine laminates. This thermoplastic polyester fiber mat has been used in both E-glass and carbon fiber laminates, with and without cores. The laminates are primarily hand lay-up in open molds, some with vacuum bagging. The polyester mat has elastic modulus and strength values similar to the resin, however the strain to failure of the fibers is about 30 percent. These tough fibers inhibit crack formation and growth in the laminate, and allow higher inter-ply shear strains when interleaved between plies of high modulus reinforcing fibers. The same thermoplastic polyester fiber mat has been incorporated into both Sheet Molding Compound (SMC) and Resin Transfer Molded (RTM) laminates with varying amounts of E-glass. The SMC laminates are flat panels approximately 30 cm square by 3 mm thick. The RTM laminates are flat panels approximately 60 cm square by 3 mm thick. These panels were cut into test coupons for tension, compression, flexural and impact testing. The tensile and compressive modulus and strength varied with the amount of E-glass in the laminate. The flexural modulus and strength were less dependant on the amount of E-glass, since the laminate acts as a sandwich, with the polyester mat forcing the E-glass to the surface of the laminate. Strain energy density increases significantly with increasing polyester fiber content. The impact toughness also increased as the amount of polyester fiber in the laminate increased. Thus the thermoplastic polyester fiber mat can be used to enhance impact toughness and flexural properties, in addition to reducing the density of the laminate.