Polymer Thermal Degradation

Degradation Mechanism

High temperatures cause the covalent bonds to rupture, creating free radicals. These radicals initiate a chain reaction that leads to chain scission. This results in the loss of mechanical strength and the formation of volatile compounds.

Process Control

Processors prevent degradation by optimizing the temperature profile of the extruder and reducing the residence time. Using a screw design that minimizes shear heat also helps maintain the temperature below the degradation limit. Thermal stabilizer additives can be compounded into the resin to protect it during processing.

These measures are essential for high-heat runs.

Defect Mitigation

Molded parts produced from degraded resin will exhibit brittle behavior and cosmetic flaws like splay or discoloration. Molders can identify this issue by measuring the melt flow index of the processed material and comparing it to the virgin datasheet. If the index has increased significantly, the process parameters must be adjusted to lower the thermal stress.

It protects the quality of the finished parts.