Meaning
Chemical byproducts emerge during the thermal or oxidative breakdown of polymer chains under processing conditions. A degradation product shifts the molecular weight distribution of the melt by breaking long chains into smaller segments or inducing crosslinking between active radical sites. These species act as chain terminators or structural impurities that alter the final physical integrity of a molded component.
Thermal Sensitivity
Polymers lose mechanical properties when excessive shear heat or prolonged residence time triggers chain scission. Excess temperatures in the barrel break covalent bonds along the backbone, creating low molecular weight fragments that migrate to the surface of a part. These fragments create dull zones or streaks that fail aesthetic standards while simultaneously reducing the tensile strength of the structural matrix.
Economic Impact
Virgin resin pricing relies on the assumption of a narrow, predictable molecular weight distribution that facilitates predictable flow behavior during injection. Incorporating regrind increases the cumulative history of thermal exposure and forces the inclusion of more degradation product into the melt stream. This reality caps the allowable percentage of recycled material in high-performance applications because the resulting drop in impact resistance carries a high risk of field failure for structural parts.
Specification Boundary
Datasheet values represent the performance of pristine resin tested under controlled laboratory conditions rather than the reality of a production floor. A molder must hold processing variables within the manufacturer window to prevent excessive buildup of chemical markers that separate the mechanical performance of a batch from the expected property profile. Each molded part stores the thermal history of its parent material, and the concentration of these broken molecules acts as the physical record of how close the process came to destroying the material integrity.
