Mechanical Recycling of Packaging Plastics: A Review

Abstract

The current global plastics economy is highly linear, with the exceptional performance and low carbon footprint of polymeric materials at odds with dramatic increases in plastic waste. Transitioning to a circular economy that retains plastic in its highest value condition is essential to reduce environmental impacts, promoting reduction, reuse, and recycling. Mechanical recycling is an essential tool in an environmentally and economically sustainable economy of plastics, but current mechanical recycling processes are limited by cost, degradation of mechanical properties, and inconsistent quality products. This review covers the current methods and challenges for the mechanical recycling of the five main packaging plastics: poly(ethylene terephthalate), polyethylene, polypropylene, polystyrene, and poly(vinyl chloride) through the lens of a circular economy. Their reprocessing induced degradation mechanisms are introduced and strategies to improve their recycling are discussed. Additionally, this review briefly examines approaches to improve polymer blending in mixed plastic waste streams and applications of lower quality recyclate.

Single-Use Plastics in the Food Services Industry: Can It Be Sustainable?

“…This group includes polypropylene (PP), polyethylene (PE), low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), polyvinyl chloride (PVC), polyurethane (PU), polyethylene terephthalate (PET), and polystyrene (PS). PET, PP, PVC, PS, and PE are the five most used polymers for packaging applications (Schyns and Shaver 2020). Aside from its use as a base material, plastics can also be used as complementary material in a multi-layered or multi-material foodware (Geueke et al 2018).…”

“…For example, for PET, its high elongation at break value weakens significantly by a factor of 4 after being mechanically recycled 4 to 5 times. As for PP, multiple recycling reduces its molecular weight, critical to its material performance (Schyns and Shaver 2020). Thus, to make recycled plastics usable, virgin plastics are usually added to the final product to balance its product performance.…”

“…Further, by restricting treatment to a specific plastic-type, it complicates the entire plastic recycling operation and dampens the facilities' ability to amass the economy of scale needed to treat its plastic waste at a relatively lower cost. Even as plastics from the packaging sector are deemed more economically feasible to recycle than plastics from other sectors, its poor underlying unit economics, and technological constraints remain an impediment for the broader community to accept plastics recycling as a viable treatment method (Schyns and Shaver 2020).…”

Development of Tensile Properties and Crystalline Conformation of Recycled Polypropylene by Re-Extrusion Using a Twin-Screw Extruder with an Additional Molten Resin Reservoir Unit

“…Extrusion is a mechanical process that is mainly used in plastic mechanical recycling. The degradation of recycled plastics in the extrusion process is caused by chain scission or the forming of cross-links [7,8]. From our previous work, it can be found that the degradation of plastics was not caused by chemical degradation but that the physical degradation was the main reason [9,10].…”

Integrated User-Oriented Service for 3D Printing Environments with Recycled Material from Maritime Plastic Waste

“…A review of these policies can be found in [32,33], which highlights the reduction in consumption, greater collection of plastic, regulation of the entire plastic value chain, and recycling. Recycling is one of the most essential actions to avoid increases in environmental pollution [34]. Recycling involves different agents throughout the whole management chain for the recycling of marine plastic waste, including collection, sorting, cleaning, volume reduction and separation [35].…”