Why are recycling rates for plastic generally lower than recycling rates for glass, paper, iron, and aluminum?

Plastic recycling rates are generally lower than those for materials like glass, paper, iron, and aluminum due to significant technical and economic challenges in the recovery process.12

Unlike traditional materials, plastics present several unique processing difficulties:

• Processing Limitations: Plastics have a low melting point, which prevents contaminants from being effectively driven off during heating and reprocessing. Furthermore, even within a single polymer type, variations in molecular weight—often tailored for specific original uses—make mixing different plastic products unsuitable for high-quality reuse.13
• Contamination and Degradation: Recyclable plastics are frequently contaminated by nonplastics, different polymer types, or additives like dyes and pigments. Additionally, plastics often undergo chemical changes during their initial use, such as oxidation or the breaking of polymer chains, which degrades their quality.3
• Economic Hurdles: Because of these inherent quality disadvantages, recycled plastics are often relegated to less-demanding applications, such as plastic lumber, rather than being repurposed into their original forms. Consequently, many plastic recycling operations are not economically attractive without government mandates or deposit schemes.31

While materials like glass and metal are more efficiently recovered as scrap, the heterogeneity and degradation of synthetic plastics make them inherently more difficult to recycle on a large scale.31