Individual and combined roles of CTBN and fly ash in epoxy system under compression: Correlation between microscopic features and mechanical behavior

Epoxy containing fillers of either fly ash or poly(acrylonitrile-co-butadiene), carboxy terminated (CTBN) as single reinforcing material in one program and both the filter materials as hybrid reinforcements into the system in the second were cast and the test coupons cut from the cured slabs were subjected to axial compression strength. The filler proportions in the composites were varied with a view to study the effects of differing characteristics bearing filler materials. The nondeforming, oxide bearing ceramic-type fly ash when incorporated into epoxy showed an increase in compressive strength values with fly ash content up to 10% by weight inclusion after which a drop was noticed. In the case of CTBN, the trend of recording a rise was noticed up to 5% by weight. When the two fillers were introduced simultaneously, the maximum in strength was recorded at a composition constituted by equal amounts of both the fillers comprising a total of 5% by weight. The work was extended to microscopic examination where features like morphology of fillers, the role of matrix-filler interface region as well as the part played by the two fillers when they are present as individual reinforcements were examined. Features such as shear deformation, stepped-appearance, crack blunting and elongation of the rubbery phase, crack pinning, and formation of debonds around the fly ash and CTBN were noticed. The work attempts at correlating the mechanical data to microscopic details. Thus, the drop in strength at higher levels of elastomers (10 and 20% by weight) could be traced to the coalescing of particles. The initial rise in strength noticed in these systems, could be related to the resistance to deformation offered by the well-bonded elastomeric fillers.