Cured epoxy resins show less resistance to crack initiation and propagation. What might be the reason for the same?
Dear Manjunath Shettar, it is due mainly to the high crosslink density and chain stiffness induced by the presence of benzene rings in the main backbone. The following RG link and the attached files give additional information. My Regards
https://www.researchgate.net/post/Is_it_possible_to_change_the_brittleness_of_epoxy_resin/amp
yes i agree with @ Abdelkader,, due to its crosslink density , the cured epoxy will have brittle nature (or poor fracture toughness)
While the macroscopic reason for the easy crack initiation and propagation is the brittleness of the material, the molecular reason for this is due to the abundant chain ends that act as local defects. This is common phenomena for all thermosetting resins. Thus, if you use oligomeric epoxy precursors where main chain is extended without branching, rather than a monomeric precursor, the crack initiation and propagation will be less. This was molecularly shown by designing main-chain type benzoxazine oligomeric precursors. See:
“Synthesis and properties of a new crosslinkable polymer containing benzoxazine moiety in the main chain,” Chernykh, A.; Liu, J.P.; Ishida H., Polymer 2006, 47, 7664-7669.
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