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.
Recycled Polyester
Meaning
Reclaimed thermoplastic resin derived from post-consumer bottles or industrial waste streams replaces virgin polymer in moulding applications. Compounders process recycled polyester by washing, flake sorting, re-extruding, and pelletising scrap material. Thermal history from prior processing loops reduces polymer chain length, lowering intrinsic viscosity compared to prime resin grades.
Material specifications limit its application in thin-wall structural parts unless combined with virgin resin or chain extenders.
Viscosity Loss
Repeated heat history during original conversion and subsequent recycling breaks covalent bonds along the polymer backbone. Lower intrinsic viscosity reduces melt strength, increasing the likelihood of parison sag during blow moulding. Blending virgin material with recycled polyester restores melt processing stability to acceptable operating windows.
Chain extenders are introduced during compounding to rebuild molecular weight.
Processing Adjustment
Melt processing of reclaimed flake requires lower drying temperatures and extended desiccant drying cycles to prevent hydrolytic degradation. Residual moisture reacts with hot polymer, causing further loss of mechanical properties.
Economic Impact
Material cost advantages depend on raw scrap availability and flake purification costs. Quality variations between scrap lots require frequent moulding process adjustments to maintain part weight tolerances. High-purity recycled polyester reduces reliance on fossil-based virgin resins while maintaining structural compliance for container packaging.