Meaning
The presence of foreign polymers, adhesives, or organic residues within recycled polyester flakes diminishes the purity and processability of the recycled material. In the plastics recycling supply chain, polyethylene terephthalate contamination determines the market value and the potential applications of the recycled resin. This impurities issue can cause processing interruptions during extrusion and degrade the physical properties of the final blow-molded bottles.
Quality Assessment
Testing protocols like automated optical sorting and melt filtration are employed to identify and quantify the level of impurities in incoming flake shipments. Purchase contracts establish strict limits on the parts-per-million of PVC, polyolefins, and metals allowed in the flakes. If the contamination levels exceed these limits, the buyer has the right to reject the entire shipment or renegotiate the purchase price.
Processing Hazard
During thermal processing, incompatible polymers can melt at different temperatures, leading to unmolten particles that block extruder screens. For example, PVC contaminants degrade at the processing temperatures of polyester, releasing corrosive hydrochloric acid that damages the extrusion equipment. This degradation also causes yellowing and black specks in the recycled polymer, making it unsuitable for food-contact packaging.
Commercial Penalty
Supply contracts for recycled resin include detailed specification sheets with escalating price deductions for each tier of contamination. When a recycler delivers a batch with high polyethylene terephthalate contamination, they must compensate the buyer for the downtime and filter replacement costs incurred during extrusion. These commercial terms protect the manufacturer from the high operational costs associated with processing low-grade recycled material.
In severe cases of persistent non-compliance, the contract may be terminated, forcing the recycler to find alternative, lower-value markets for their contaminated material.
