Recycled Plastic Food Contact Compliance and Non Intentionally Added Substance Testing Methods
Recycled plastic food contact compliance requires rigorous surrogate challenge testing, non-target NIAS screening, and lot-traced migration verification.
Degradation Chemistry
Meaning
Chemical reactions that break down polymer chains during processing alter the molecular weight distribution and physical properties of the plastic. In injection moulding, degradation chemistry describes the thermal and oxidative pathways that reduce the average molecular weight of a resin. Polymer temperature and residence time in the heating cylinder govern these reaction rates.
Part strength and cosmetic appearance suffer when molecular weights drop too low.
Polymer Cleavage
High temperatures and high shear in the extruder trigger the rupture of covalent bonds within the polymer backbone. Molecular breakdown during degradation chemistry creates free radicals that propagate further chain scission. Polypropylene undergoes rapid chain scission, which lowers melt viscosity and raises the flow rate beyond the datasheet specifications.
Zone temperature settings on the extruder barrel are the primary variables used to control these reaction rates.
Processing Defect
Volatiles from chemical breakdown accumulate at the flow front during injection. Surface defects like silver streaks or splay marks often arise from degradation chemistry. Cosmetic specifications for finished parts cannot tolerate these flaws, which increases scrap rates.
Material Recovery
Regrind economics depend heavily on the extent of polymer breakdown during the first heat cycle. Mechanical recycling limits the fraction of runner scrap that can be blended with virgin resin due to degradation chemistry. Processors must monitor the melt flow index of the blended material to ensure it does not deviate from the baseline values.
Excess regrind content also depletes the primary antioxidants, leaving the finished part vulnerable to environmental stress cracking over its service life.