Meaning
Chemical fragments result from the thermal, oxidative, or mechanical cleavage of polymer chains during processing or service life. These degradation products alter the molecular weight distribution and physical properties of the plastic. Residues often introduce discoloration or brittleness in the finished component.
Thermal Stability
High temperatures during extrusion or injection moulding accelerate the breakdown of resin molecules. Increased shear forces in the screw barrel trigger localized heating that initiates chain scission. Small molecular species accumulate within the melt as these mechanisms proceed.
Excessive dwelling time or high temperatures force the material toward this unstable state.
Material Specification
Resin datasheets state the temperature limits that keep these undesirable constituents at low levels. Laboratory testing uses thermogravimetric analysis to define the onset of mass loss. Moulders verify the impact of these changes by measuring the melt flow rate across a production run.
Virgin material remains stable until the operating window is exceeded, while the inclusion of regrind increases the population of these species due to prior heat histories.
Production Cost
Scrap rates rise when contamination levels deviate from the required threshold. Increased venting or downstream filtration helps manage the gaseous portions of these materials during high speed production. Parts fail to meet mechanical requirements when excessive scission reduces structural integrity.
Proper thermal control remains the primary method for maintaining resin quality.
