Study of cross-linking conversion effect on mechanical and thermomechanical properties of h-BNNS reinforced epoxy...

Diglycidyl ether of bisphenol A (DGEBA) is widely used as an epoxy resin due to its excellent mechanical strength, thermal stability, and chemical resistance, making it suitable for structural composites, adhesives, and coatings. However, its intrinsic properties can be enhanced through nanofiller reinforcement such as h-BNNS, graphene, or CNTs. Understanding the combined influence of crosslink density and nanoscale reinforcement is important for evaluating the mechanical and thermomechanical performance of high-performance epoxy systems.

This study extends the authors' prior work through an integrated computational-experimental framework to quantitatively evaluate the individual and synergistic effects of cross-linking conversion obtained after curing and h-BNNS reinforcement on the thermomechanical performance of epoxy nanocomposites. Molecular dynamics (MD) simulations were employed to predict elastic and thermal properties, and results were validated through controlled fabrication and systematic mechanical and dynamic mechanical characterization. Neat epoxy systems were first synthesized at precisely regulated cross-linking conversion levels of 80% (EP80), 85% (EP85), and 90% (EP90). Corresponding nanocomposites containing 1, 2, and 3 wt.% h-BNNS were then prepared under identical curing conditions to assess reinforcement influence. MD predictions yielded higher elastic modulus values than experimental measurements; however, both approaches consistently demonstrated stiffness enhancement with increasing curing density. Simulations indicated a monotonic modulus increase with 1, 2, and 3 wt.% of h-BNNS reinforcement, whereas experiments showed improvement up to 2 wt.% followed by a slight reduction at 3 wt.% for stoichiometric ratios of epoxy and hardener, suggesting dispersion or interfacial limitations. Tensile strength increased progressively from EXP80 to EXP90 across all compositions, confirming that higher curing stichometries improve load-bearing capability and deformation resistance. The predicted glass transition temperature at 90% curing stoichiometry was 385-395 K, while DMA measurements across all stoichiometry ratios produced Tg values of 353-390 K, demonstrating close agreement between atomistic predictions and bulk behavior.