Strengthening-toughening epoxy resin system with paraffin:an experimental and molecular dynamics simulation study
A special epoxy resin(D12)with flexible alkyl side chains was synthesized through thiol-ene click chemistry,and then using it as a compatibilizer,n-eicosane(C20,paraffin model compound)was uniformly mixed into the epoxy resin matrix(DGEBA).A series of D12 and C20 synergistic toughening epoxy resin systems(EPDA-X systems)were obtained by curing.The strengthening-toughening mechanism of DGEBA/D12/C20 ternary system was systematically studied by combining experimental and molecular dynamics simulation methods.The research results showed that,(1)When the mass ratio of D12 and C20 was 1∶2 and their mass fraction in the curing system was 2.5％,the system had the best comprehensive performance,with the tensile strength of 99.3 MPa,the tensile modulus of 2.8 GPa,and the elongation at break of 4.5％.All three were higher than the pure EP system,achieving a synergistic improvement in the strength,modulus,and toughness of epoxy resin.(2)There was a microphase separation structure in the EPDA_X system,and it had been preliminarily proven that the microphase separation structure in the system was caused by the self-assembly of C20 around the D12 side chain.The physical entanglement structure formed by the self-assembly effect could provide additional physical crosslinking points for the system,thereby achieving a synergistic improvement in the strength,modulus,and toughness of epoxy resin.(3)Molecular dynamics simulation was used to calculate the Young's modulus of all systems,and it was found that the modulus of EPDA-X system was higher than that of the pure EP system.The calculation results of the radial distribution function of EPDA-X system indicated that the main chain interaction between C20 and D12 was weak,but the side chain interaction with D12 was strong.This further confirmed the self-assembly effect of C20 around the side chains of D12,thereby proving the mechanism of synergistically strengthening-toughening of epoxy resin by C20 and D12 self-assembly at the molecular and atomic scales.
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