Harnessing residual material and energy value from waste plastics

Plastics’ good durability and low mass to volume ratio afford its use in myriad applications. But, poor biodegradability, its non-renewable origins, and emission of hazardous substances during incineration meant that plastics use incurs a significant environmental footprint. This essay aims to provide readers with a snapshot of the environmental challenges surrounding plastic use and the various methods available for retrieving residual energy and material value from waste plastic. The conceptual basis, advantages and disadvantages of different methods (mechanical, chemical/feedstock and thermal) for extracting residual value from plastics waste would be highlighted. While recovered polymers are usually employed in lower value applications compared to original use (known as “down cycling”), recent efforts have focused on “up-cycling” plastics waste for use as adsorbents in wastewater treatment. Efforts at extracting residual energy and material value from plastic such as feedstock and thermal energy production, while feasible conceptually and practically, also has an intrinsic high pollutive effect in particulates, metals and recalcitrant organic compounds emissions, primarily to the atmosphere. Hence, harnessing maximal value from a product as a concept in material design and economics necessitates an alternative view on the environmental sustainability in different phases of material use and applications, where after the usage phase lies a period of diminishing returns in relation to practical benefit versus environmental pollution ratio. Mechanical recycling such as polymer recovery is thus the best in class approach for handling plastic waste, but, it fell at the need for having a sizeable volume of pre-sorted plastic waste to ensure economic viability. Collectively, besides highlighting environmental sustainability challenges surrounding plastic use, this manuscript should also be useful as a general introduction to various plastic recycling methods as well as environmental concerns of each approch. Up-cycling approaches for repurposing plastic waste illuminates an important contemporary trend in environmental research: i.e., treading away from redeploying recycled materials for original or low value use to developing innovative approaches for converting waste into high performance materials. Such an approach, if successful, would provide a sizeable market for recycled plastics; thus, helping anchor recycling into the fabric of life by providing an economic incentive for an activity that hitherto relies on voluntary participation.