Predicting the Effect of Hardener Composition on the Mechanical and Fracture Properties of Epoxy Resins Using Molecular Modeling

S Pal and K Dansuk and A Giuntoli and TW Sirk and S Keten, MACROMOLECULES, 56, 4447-4456 (2023).

DOI: 10.1021/acs.macromol.2c02577

Improvingthe toughness of brittle epoxy while keeping its highstrength- to-weight ratio is challenging, as these two properties workagainst each other. Fracture processes are difficult to ascertainwith experiments, as they occur at nanoscopic lengths and time scalesand require higher efficiency than what can be attained with atomisticsimulations. To overcome this challenge, we utilize a recently developedchemistry specific coarse-grained model to examine two different hardeners,diamine 4,4 '-methylene-bis(cyclohexyl-amine) (PACM)and propylene oxide diamine (Jeffamine), to cure bisphenol A diglycidylether (DGEBA) at varying stoichiometries and understand how hardenercomposition influences the elasticity, yield strength, and fracturetoughness of epoxy resins. The results indicate that PACM mainly contributesto the modulus and that long Jeffamine chains increase fracture toughnessby making the epoxy ductile, whereas short Jeffamine chains significantlyimprove the yield strength. Longer Jeffamines also lead to largervoids and the formation of fibrils that carry a significant amountof stress and contribute to toughness. Interestingly, the Ashby plotsreveal that epoxies with intermediate-length Jeffamine chains (D800and D2000) outperform other systems, as the toughness enhancementfrom flexible Jeffamine chains and the stiffness due to PACM helpto overcome the strength-toughness trade- off. Our modelingframework and findings establish a path toward resin design from predictivemultiscale models with no empirical input and reveal new insightsinto the molecular failure mechanisms of epoxy resins.

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