Mode I interlaminar fracture toughness of carbon nanotube web-modified polymer composites

Carbon nanotube 'webs' (CNTWs) are used as interlayers between marine grade (HMC/SE84LV) and aerospace grade (IM7/977-2) carbon fibre-reinforced polymer (CFRP) composite laminates to explore their influence on mode I interlaminar fracture toughness (ILFT). Inserting CNTW in SE84LV laminates improves the mode I ILFT by 4% whereas inserting CNTW in 977-2 laminates reduces the mode I ILFT by 85%. Fractography and interfacial analysis show that SE84LV resin penetrated and adequately wetted the CNTW whereas 977-2 resin failed to penetrate and wet the CNTW which resulted in large void formation and created a weak interlaminar region. To counter the poor penetration of 977-2 resin, CNTW was impregnated with neat 977-2 resin prior to its insertion in the prepreg layup. Inserting preimpregnated CNTW resulted in a 68% reduction in mode I ILFT. It is proposed that the reduction in mode I ILFT of IM7/977-2 system interleaved with CNTW was due to the restricted resin mobility in the CNTW region and the poor interaction between CNTW and 977-2 resin. The 977-2 remains at minimum viscosity for a shorter time than SE84LV. Remaining at low viscosity for a longer period allows the resin to flow in the CNTW region. The weak interaction between CNTW and the 977-2 resin is discussed in terms of the polarity of the constituent polymer molecules. 977-2 is more polar than SE84LV thus has a very low affinity to interact with CNTW.