Ester Bond Hydrolysis Kinetics in Molten Polyethylene Terephthalate
Polyethylene terephthalate ester bonds hydrolyze rapidly in melt above 270 °C, requiring drying below 30 ppm moisture to prevent intrinsic viscosity collapse.
Rheological Stability
Meaning
Property measurement defines the consistency of a melt’s resistance to flow over a sustained period at processing temperature. This value determines whether the polymer will behave predictably during the high-pressure filling of a mold or the tension of an extrusion line. High rheological stability indicates that the material resists thermal breakdown and maintains its molecular structure despite high heat exposure.
Viscosity Control
Variations in the molecular network can lead to thinning or thickening that renders automated settings useless. If the material starts to shift its flow behavior during the run, the weight of each part will fluctuate outside the accepted statistical bands. Operators prioritize grades with known levels of consistency to avoid the need for constant pressure adjustments.
Molecular Weight
Stable resins possess chains that are resilient to scission and cross-linking at typical operating values. When rheological stability is low, the plastic can become too fluid and create flashing or too stiff and result in short shots. This behavior is often tested by holding the melt in a rheometer and monitoring its change over fifteen to thirty minutes.
Machine Sync
Syncronizing the screw speed with the material properties depends on having a predictable resistance to move through the machine. Any drift in the flow properties creates thermal surges that further degrade the batch. Reliable materials allow for faster cycles and narrower process windows.