Reactive Processing of Polyethylene with Azidotriazine: From Modified Thermoplastics to Injection Moldable Covalent Adaptable Networks

The increasing consumption of polyethylene (PE) is an important concern for society because the rate of PE recycling remains low compared to the scale of PE production. There is thus great interest in strategies for revalorizing PE waste. In this context, our group recently reported an approach for transforming PE into nanostructured covalent adaptable networks (CANs) with azidotriazine grafting agents using reactive extrusion. These CANs feature polyazane cross-links that undergo thermomechanically activated exchange reactions, permitting the material to flow when subjected to high temperature and strain. Herein, we exploited this chemistry to develop modified PE materials with intriguing thermomechanical properties and exceptional processability. A family of compositions was prepared by reactively extruding PE with varying amounts of the azidotriazine grafting agent, and the resulting materials were studied using a combination of electron microscopy, small-angle X-ray scattering, calorimetry, rheometry, and mechanical testing. As the loading of the azidotriazine grafting agent was increased from 0.05 to 1.0 mol %, the materials transitioned from being thermoplastic-like to thermoset-like, revealing a balance of mechanical properties, melt strength, and high-temperature creep resistance. Surprisingly, all samples─even the CANs prepared with high loadings of the azidotriazine─could be easily shaped by injection molding. We believe that this approach is a promising, industrially relevant way to enhance the thermomechanical properties of polyolefins.