Optimizing Desiccant Drying Parameters to Prevent Hydrolytic Degradation in Recycled Polyester
Optimize rPET desiccant drying at 160-170°C with -45°C dew point dry air to maintain moisture under 30 ppm and prevent intrinsic viscosity drop.
PVC Contamination
Meaning
Foreign polymer inclusion introduces severe thermal instability into scrap resin streams during re-processing operations. Flake sorters detect PVC contamination in recycled polyethylene terephthalate streams, where minute concentrations cause acid generation during melt processing. Polyvinyl chloride degrades at lower temperatures than host engineering resins, releasing hydrochloric acid gas that corrodes injection moulds and barrel liners.
Contamination boundaries are measured in parts per million, above which entire recycled resin batches face rejection.
Degradation Reaction
Chemical breakdown of chlorinated resin molecules releases acidic byproducts that attack host polymer chains. Hydrochloric acid promotes catalytic scission of ester linkages, rapidly dropping the molecular weight of the surrounding resin batch. Extrusion of material containing PVC contamination generates black specks, gas bubbles, and severe surface haze in finished articles.
Processing equipment suffers pitting corrosion when exposed to these acidic fumes.
Tool Damage
Corrosive gases erode polished cavity surfaces and vent channels in production tools. Surface pitting requires expensive re-polishing and replating to restore mould functionality.
Recycling Yield
Optical and electrostatic sorting systems eliminate chlorinated plastic flakes prior to melt compounding. Contamination levels exceeding fifty parts per million render recycled flake unusable for food-grade packaging applications. Strict purity verification protects processing machinery from acid attack while preserving mechanical performance in recycled polyesters, where PVC contamination must be held below strict limits.