Why must different thermoplastics be sorted before recycling?

Different thermoplastics must be sorted by type before recycling because mixing them significantly degrades the quality and utility of the resulting material.12

Sorting is essential for several technical reasons:

• Incompatibility of Properties: Even within a single polymer type, variations in molecular weight are engineered for specific manufacturing processes, such as injection molding versus sheet forming. Mixing these variations results in a material that is often unsuitable for the original applications.1
• Contamination: Recyclable plastics can be contaminated by nonplastics or by different polymer types. Furthermore, the presence of different pigments or dyes complicates the recycling process, as does the degradation of polymers—such as oxidation or changes in molecular weight—that occurs during their initial use.1
• Performance Limitations: Because of these inherent differences and the difficulty in achieving perfect separation, recycled plastics often possess inferior properties compared to virgin materials. Consequently, they are typically repurposed into less-demanding applications, such as plastic "lumber," which is inherently weaker than the original polymers due to its heterogeneous composition.1

Proper sorting ensures that the material maintains the consistency required for effective remelting and reforming.12