Mechanical properties of glass fibre composites based on nitrile rubber toughened modified epoxy resin

To improve the impact behaviour of composite laminates and to reduce the problem of the complex damages after dynamic loads, a two-component commercial epoxy resin was modified with a commercial nitrile liquid rubber modified DGEBA epoxy prepolymer that, prior the cure, has been mechanically dispersed at two concentration levels (20%w/w; 30%w/w). Experimental characterization of both neat and modified resins was performed to investigate the effect of the rubber addition on the resin properties, i.e. glass transition temperature, modulus and dynamic mechanical characteristics. Further, the rubber domain distribution in the epoxy resin was analyzed by scanning electron microscopy (SEM). The hybrid rubber modified resins did not show high viscosity allowing to manufacture E-glass fiber reinforced composites by vacuum infusion process. The laminates were characterized by tensile mechanical tests that evidenced an overall enhancement of maximum stress and deformation for the hybrid composites. In particular, results demonstrated an improvement of 10% for the shear failure stress and of 110% for the shear failure strain. Further, impact tests were carried out at penetration, to evaluate the improvement of the impact resistance over the conventional epoxy resin system, and at increasing energy levels, 5 J, 10 J and 20 J, to investigate the damage start and propagation. A higher indentation has been observed for the modified composite samples related with a lower delamination extension.