A study on fracture toughness of nano-structured carbon black-filled epoxy composites

Carbon black (CB)-filled epoxy nanocomposites were produced by mixing the desired amount of nano-structured CB (CBNFs) from biomass waste (i.e., bagasse, bamboo, and oil palm shell) with the epoxy resin. The fracture toughness characteristics of epoxy nanocomposites with 1%, 3%, 5%, and 10% (based on wt.% of epoxy) filler loading were observed using the Vickers hardness test, and the surface morphology was analyzed using transmission electron microscopy and scanning electron microscope. The results showed a decrease in fracture toughness, mainly due to cracked bridging of CB nanograins formed onto the epoxy matrix. The size of the cleavage plane decreased after the infusion of the CBNFs. It implied that the path of the crack tip was distorted because of the CBNFs, making crack propagation more difficult. The physical and mechanical properties increased when the epoxy composites containing 1% to 5% CBNFs although it was decreased at 10% CBNFs filler loading. One key finding was the morphological interaction between the CNBFs and epoxy matrix shows that various types of fracture toughness were identified, such as voids, crack propagation paths, bridging effect, and branching effects of cracks.