Chemically Inert Nanoparticles Enhance Mechanical Degradation in Flowing Polymer Nanocomposites

Flow can be used to mechanically degrade polymer chains by transmitting macroscopic strain into the tension of chain backbones. Established models for flow-induced scission work well for highly dilute polymer solutions where chain scission events are uncorrelated, but scalable mechanical recycling processes must be designed for concentrated and messy plastics with significant intermolecular entanglement, particulate contamination, and catalytic material. This study applies molecular dynamics simulations to explore the flow-induced degradation of highly entangled polymer melts and polymer nanocomposites. Simulations show that incorporating nanoparticles into melts can significantly enhance flow-induced chain scission and substantially lower the specific work required to degrade the melt. This enhancement is due to a nonlinear coupling between chain alignment and nanoparticle ordering. Aligning chains induces nanoparticles to organize into aggregates, which in turn enhances the local stretching of chains squeezed between aggregates. This feedback loop rapidly builds chain tension at the entanglement length scale, causing chains to break prior to full extension and at lower strain rates than are needed to degrade neat melts.