Effect of poly(amic acid) and polyimide on the adhesive strength and fracture toughness of epoxy resin

We investigate the effect of polyimide and poly(amic acid) contents on the properties of epoxy resin. Charpy impact strength increases by 80% and 70% with the addition of 10 wt.% poly(amic acid) and 15 wt.% polyimide, respectively. However, the flexural strength is improved by 95% and 73% (as compared with the neat epoxy resin) by the addition of 5 wt.% polyimide and 5 wt.% poly(amic acid), respectively. Moreover, the addition of 10 wt.% polyimide resulted in a twofold increase in the impact adhesive strength, while the tensile adhesive strength of the epoxy increases by 70% with only 5 wt.% polyimide. The infrared spectra show that the obtained compositions containing polyimide or poly(amic acid) exhibit semiinterpenetrating polymer network structures characterized by a relatively high flexibility and very good mechanical properties.