Cross-Linked Polyolefins: Opportunities for Fostering Circularity Throughout the Materials Lifecycle.

Cross-linked polyolefins (XLPOs) constitute a significant portion of the plastics commercial market, with a market size of a similar order of magnitude to those of polystyrene and polyethylene terephthalate. However, few aspects of XLPO materials circularity have been examined relative to thermoplastic polyolefins. The cross-linking of polyolefins imparts superior performance properties, such as impact strength, chemical and electrical resistance, and thermal stability vs thermoplastic analogues, but it also makes the reprocessing of XLPOs to valuable products more challenging, as XLPOs cannot be molten. Thus, most XLPOs are incinerated or landfilled at the end of the first lifecycle, even though XLPO products are commonly collected as a relatively clean waste stream-providing a unique opportunity for valorization. In this review, we discuss approaches to improve XLPO circularity throughout the entire materials lifecycle by examining biobased feedstocks as alternative olefinic monomer sources and by assessing both traditional mechanical and advanced XLPO recycling methods based on industrial feasibility and potential product value. We also consider how advancing materials longevity can reduce environmental impacts and lifecycle costs and how recyclable-by-design strategies can enable better end-of-life opportunities for future generations of XLPO materials. Throughout this review, we highlight XLPO circularity routes that have the potential to balance the performance, circularity, and scalability necessary to impart economic and environmental viability at an industrial scale.