Can nanoparticle toughen fiber-reinforced thermosetting polymers?
Many tougheners have been developed for thermosetting resins. Numerous studies indicate that the mode-I fracture toughness of a thermosetting resin (GIC_Resin) can be effectively enhanced by rubber tougheners such as liquid rubber and core–shell rubber, and inorganic rigid particles such as silica, clay, carbon nanotubes, or graphene. Can these additives also toughen fiber-reinforced polymers (FRPs)? In particular, can they improve the mode-I interlaminar fracture toughness of FRPs (GIC_Comp)? To answer how much toughness improvement is transferred from resin to FRPs, we reviewed data from more than 50 publications related to interlaminar toughening. The performance of various types of tougheners in the resin and/or FRPs is summarized, and toughening mechanisms are also discussed. We found a wide range of improvement in fracture toughness in FRPs with the addition of nanoparticles, from negative improvement in some silica and carbon particle studies to an improvement ratio equal to that achieved in the resin. Overall, rubber tougheners are the most effective tougheners, but on average, only about 30% of the relative improvement in resin toughness translated to GIC_Comp increase. The enhancement in GIC_Comp after incorporating rigid particles tougheners is even less, but rigid particles do not decrease the strength and modulus of the final FRPs. Other toughening strategies, such as using multiple types of tougheners, and coating or depositing nanoparticle onto the fiber reinforcements are also discussed, and we suggest some strategies to design FRPs with optimal delamination resistance.