Permanent chemical cross-linking of polyolefins by reactive extrusion or related processing methods is practiced industrially at major scales, e.g., cross-linked polyethylene, also called PEX, XPE, or XLPE, is used in household pipework systems as well as pipes for transport of natural gas and insulation for electrical cables. Such thermosets can exhibit upcycling of properties relative to the thermoplastics from which they are made, such as improved high-temperature creep resistance. Unfortunately, thermosets with permanent cross-links cannot be mechanically recycled because these cross-links prevent melt flow. In this study, thermoplastic low-density polyethylene and ethylene-based copolymers have been upcycled into covalent adaptable networks (CANs) with dynamic covalent cross-links by melt-state, free-radical grafting of dialkylamino disulfide linkages. A simple, one-step, lab-scale, melt processing technique was used to transform the polymers and copolymers into reprocessable networks with the aid of a dynamic cross-linker with dialkylamino disulfide linkages and a peroxide initiator. The ethylene-based CANs exhibit excellent reprocessability with full cross-link density recovery after multiple recycles. Importantly, relative to the thermoplastics from which they were made, the reprocessable ethylene-based networks demonstrate improved resistance to elevated-temperature creep. The effect of thermoplastic ethylene-based polymer composition and architecture on the transformation to CANs and creep performance will be discussed.

Dynamic crosslinking of ethylene-based copolymers into thermoreversible covalent adaptable networks with elevated-temperature creep resistance via one-step melt-state processing

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ACS Fall 2022

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