Evaluating Thermal and Oxidative Polyolefin Flake Degradation
Thermal and oxidative degradation alters polyolefin flake viscosity and residual stability, demanding MFR, OIT, and Carbonyl Index verification before processing.
Degradation Kinetics
Meaning
Mathematical models describe the rate at which polymer chains break down under the influence of heat, oxygen, or mechanical shear over time. When processing post-consumer recyclate, degradation kinetics govern how quickly the material loses its molecular weight during compounding. Extrusion and molding processes must be optimized to stay below the critical times and temperatures that trigger rapid chain scission.
Understanding these rates prevents the loss of mechanical strength in the finished part.
Thermal Stability
High processing temperatures accelerate the cleavage of covalent bonds in the polymer backbone. Activation energy determined through thermogravimetric analysis represents the energy barrier required to initiate this breakdown. A high activation energy indicates that the resin resists thermal damage during short spikes in temperature.
Process Influence
Shear stress generated by the rotation of the extruder screw contributes to mechanical degradation in the melt phase. This mechanical strain lowers the temperature at which chemical degradation begins, thereby altering the degradation kinetics of the melt. Moulders must control both shear rate and barrel temperature to prevent cosmetic defects and brittle parts.
Lifetime Prediction
Long-term durability estimates for molded articles rely on Arrhenius equations to project how fast the material will weaken under service conditions.