Molecular Dynamics Simulation Insight into the Aggregate Structure–Mechanical Property Relationship of Double-Crosslinked Epoxidized Natural Rubber/Polylactic Acid Composites

Abstract

With the increasing depletion of petroleum resources, using renewable feedstocks to fully or partially replace petrochemicals has become an important strategy for developing sustainable bio-based materials. Polylactic acid (PLA), a representative biodegradable polymer, exhibits great potential for replacing traditional plastics but suffers from inherent brittleness that severely limits its practical applications. Epoxidized natural rubber (ENR), as a bio-based engineered elastomer, possesses excellent flexibility and tunable structural characteristics. The active epoxy groups on its polymer backbone provide the potential for strong interfacial compatibility and chemical crosslinking with PLA, making PLA/ENR blending a promising toughening strategy. Although previous experimental studies have provided valuable macroscopic insights, it remains difficult to directly observe molecular-level structural evolution and the underlying load-bearing mechanisms of crosslinked networks. In this work, coarse-grained molecular dynamics simulations were employed to investigate PLA/ENR blends with different ENR chain lengths and dual crosslinking networks, including PLA–ENR interfacial crosslinks and ENR–ENR self-crosslinks. The results reveal a nonmonotonic dependence of mechanical reinforcement on ENR chain length. Short ENR chains mainly act as isolated local junctions, whereas excessively long chains undergo severe phase aggregation and form self-crosslinked domains. In contrast, intermediate ENR chains construct an effective interwoven bridging network, leading to enhanced chain orientation, stable interfacial coupling, and superior strain-hardening behavior. Bonded-stress analysis further demonstrates that intra-ENR self-crosslinking bonds sustain substantially higher stress than PLA–ENR interfacial bonds, identifying the internal elastomer network as the dominant load-bearing element. This work provides molecular-level insights into the role of elastomer network architecture in PLA/ENR composites and offers theoretical guidance for designing high-performance bio-based polymer blends.