Meaning
Amount of water absorbed by recycled polyethylene terephthalate prior to melt processing. Controlling rpet moisture content is critical because recycled resin is highly hygroscopic and prone to severe degradation when heated in the presence of water. Excess moisture causes a drop in molecular weight and degrades the mechanical properties of the finished product.
Hydrolysis Risk
Water molecules chemically react with the polymer chain at high melt temperatures, breaking the ester bonds. This reaction when processing rpet moisture content leads to a reduction in the intrinsic viscosity of the melt. Chain scission results in brittle parts that fail to meet mechanical requirements for load-bearing applications.
Desiccant drying systems must be monitored continuously to prevent this type of chemical degradation.
Viscosity Loss
Lower melt viscosity causes the polymer to drool from the nozzle and flash the mould. The physical change makes the moulding process unstable and increases scrap rates. Regular testing using a moisture analyser is required before the resin enters the extruder.
Processing Threshold
Recyclers must dry the material to a concentration of less than fifty parts per million. Maintaining this dry condition throughout the run protects the mechanical integrity of the parts. Desiccant dryers are the standard equipment used for this purpose.
