Meaning
Polycondensation reactions involving glycols produce specific residual levels of diethylene glycol content within polyethylene terephthalate polymer chains. Residual amounts of this byproduct dictate hydrolytic stability during high temperature injection moulding cycles. Elevated impurity fractions lower the melting temperature and degrade the intrinsic viscosity of the raw polyester pellets.
Regrind incorporation compounds the thermal degradation because repeated melting stages accelerate chain scission. Material datasheets report baseline purity grades, but the actual concentration shifts during downstream processing due to moisture exposure and thermal history.
Thermal Degradation
Excessive residual monomer concentrations drive polymer chain scission inside the heated barrel of an injection moulding machine. Extruded parts suffer from localized yellowing and diminished mechanical strength when moisture reacts with unstable end groups during the melt phase. Processors adjust barrel temperature profiles and drying times to mitigate hydrolytic cleavage during compounding.
Viscosity Drift
Molecular weight reduction directly correlates with elevated ether glycol fractions present in the incoming resin feed. Inconsistent melt flow rates prevent uniform cavity filling during thin wall moulding operations. Part specifications demand strict control over melt index values to prevent dimensional warpage in finished enclosures.
Resin Specification
Virgin polymer supply agreements establish strict chemical purity thresholds to protect processing equipment from corrosive volatile emissions. Component manufacturers reject batches exceeding specified byproduct limits because inconsistent polymer architecture ruins post consumer recycling streams. Finished moulded articles retain structural integrity only when raw material suppliers maintain rigorous transesterification controls.
