Polyolefin Degradation Mechanics in Post-Consumer Resin Recyclate Streams
Polyolefin recyclate degradation occurs via PP chain scission and PE crosslinking; verification requires dual-weight MFR sweeps and 30-minute OIT testing.
Zero Shear Viscosity Shift
Meaning
Difference in the plateau viscosity of a polymer melt at rest before and after a thermal processing cycle. Measuring the zero shear viscosity shift reveals whether a resin has undergone chain scission or cross-linking due to thermal-oxidative degradation during molding. It is a highly sensitive metric used to evaluate the processing stability of polymers.
Measurement Protocol
Rotational rheometers perform low-frequency oscillation tests on molten polymer samples. This zero shear viscosity shift indicates changes in the average molecular weight of the polymer. An upward shift suggests cross-linking, while a downward shift indicates chain scission.
Moulding Consequence
Inconsistent melt viscosity caused by resin degradation can lead to short shots or flashing during the injection cycle. This zero shear viscosity shift highlights when a mold is running too hot or when dwell times in the barrel are too long. Moulders use this information to adjust process temperatures.
Recycled Resin Quality
Degradation is common in recycled polymers and regrind due to their multiple heat exposures. This zero shear viscosity shift helps quality control managers evaluate the stability of recycled polymer batches, providing a reliable measure of whether the material can be molded into high-quality parts or if it must be blended with higher-grade virgin resin to avoid structural defects and mechanical failures in the finished components during their service life.