Meaning
A discarded volume of thermoplastic polymers consists primarily of polyethylene and polypropylene resins from post-consumer or industrial sources. In the recycling sector, polyolefin waste represents the largest fraction of plastic municipal solid waste due to the widespread use of these materials in single-use packaging. These materials are highly valued for mechanical and chemical recycling.
Sorting them by specific polymer type is critical for maintaining high recycle quality.
Recycling Difficulty
Post-consumer mixtures often contain both high-density polyethylene and polypropylene, which are immiscible and cannot be processed together without losing mechanical strength. Compatibilizers must be added to blend them into a useful recycled compound. Contamination from food residues or paper labels also reduces the value of the processed resin.
Melt filtration is used during extrusion to remove these solid contaminants.
Material Recovery
Mechanical recycling produces pellets that can replace virgin resins in non-critical applications. However, repeated extrusion cycles degrade the polymer chains and reduce the melt strength. This limits the recycled material to thicker-walled parts.
Economic Viability
The cost of collecting, sorting, and cleaning recycled plastics must remain below the market price of virgin resins to be profitable. When crude oil prices are low, virgin plastics become cheaper, which squeezes the recycling margins. Legislative mandates often drive the demand.
