Rheological Measurements and the Plastic Extrusion Process

July 13, 2022

Polymer degradation has an immediate impact on the final plastic product and its properties. In the plastic extrusion process, increased temperatures, as a result of the melt processing, in combination with the time that polymers spend in the barrel, can influence the molecular weight of the extrudates.

The mechanical shear from the screw’s rotation, especially in cases of rapid extrusion, can lead to degradation and chain scission in polymer molecules.

Scission of long molecules, as a result of degradation, relates to an increase of MFI or a decrease in the overall IV level. On the other hand, degradation can also lead to cross-linking of decomposed polymers, which can lead to an increase in IV or a decrease in MFI.

Conducting rheological measurements of a compound before, during and after the melt processing is an effective way to identify if any thermomechanical degradation has taken place throughout the extrusion process

Why is it Important to Avoid Degradation and Keep Polymers in Specification?
Polymer degradation has an immediate impact on the characteristics of the final plastic product.

Changes in molecular weight impact short-term and long-term characteristics such as fatigue resistance, impact resistance and environmental stress cracking resistance.

As recycling standards state that corporations must incorporate a certain percentage of recycled content, it is vital to keep producers’ reprocessed scrap or the purchased recycled material as close as possible to their pure product’s specifications to preserve quality.

Also, the polymer is a “blind item.” Recyclers and manufacturers are not able to determine the polymers’ specifications just by visual inspection alone.

Verification of the rheological properties of polymers is critically important to minimize degradation during the recycling process and to ensure that the polymer does not degrade and negatively impact the quality of the product

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