Interfacial Interaction and Sintering Mechanism of Cellulose/Polylactic Acid Composites in Selective Laser Sintering: A Molecular Dynamics Simulation

Polylactic acid (PLA) is a biodegradable polymer suitable for selective laser sintering, yet the atomic-level sintering mechanisms of plant-fiber-reinforced PLA remain largely unclear. Here, all-atom molecular dynamics simulations are used to investigate the sintering behavior and interfacial interactions of cotton stalk cellulose/PLA nanocomposites with cellulose contents of 0–20 wt%. The nanoparticle coalescence proceeds through three sequential stages: initial van der Waals-driven contact, thermally activated neck formation, and isothermal interfacial densification. Cellulose content exerts a non-monotonic effect on interfacial bonding. At 15 wt% cellulose, an optimal, continuous hydrogen-bond network forms between cellulose hydroxyls and PLA carbonyls, maximizing interfacial adhesion while simultaneously suppressing unfavorable dipole stacking among PLA chains. At this critical loading, cellulose acts as a rigid scaffold that directs PLA chain extension and directional migration across the sintering neck, as evidenced by atomic displacement and radius-of-gyration analyses. In contrast, excess cellulose (20 wt%) induces self-aggregation, which disrupts interfacial continuity and hinders long-range chain diffusion. These results identify 15 wt% as the optimal cellulose content for achieving enhanced interfacial bonding and chain mobility, providing atomistic criteria for the formulation design of cellulose/PLA composite powders for selective laser sintering processing.