Upcycling LDPE to Dynamic Covalent LDPE Networks: Improved Mechanical Properties and High-Temperature Creep Resistance from Free-Radical Grafting of Dialkylamino Disulfide Bonds

Current methods for recycling spent polyolefins like low-density polyethylene (LDPE) most commonly result in their eventual downcycling to lower value products via thermal-mechanical degradation that occurs during extrusion. Recently, potential solutions have involved enriching waste plastics with dynamic covalent bonds, thereby enhancing mechanical properties through the introduction of crosslinks at use temperatures while maintaining the reprocessability that is characteristic of the original thermoplastic materials. For the first time, LDPE was upcycled to dynamically crosslinked LDPE networks by way of melt-state, free-radical graft copolymerization to incorporate dialkylamino disulfide bonds capable of dissociative reversible pathways at high temperature. These dynamic LDPE networks exhibit improved mechanical properties over a wide range of temperatures relative to LDPE as well as full recovery of crosslink density and associated properties with successive compression molding cycles at mild conditions. In addition, elevated-temperature viscous creep deformation is suppressed over long periods of time in the dynamic LDPE networks relative to LDPE.