The increasing use of recycled polypropylene in food packaging raises concerns about chemical migration. FDA’s surrogate testing protocol... Show moreThe increasing use of recycled polypropylene in food packaging raises concerns about chemical migration. FDA’s surrogate testing protocol using hexane or heptane as a diluent has evaluated the efficiency of industrial recycling processes in removing contaminants from reclaimed polyethylene terephthalate (PET). Different conditions to optimize surrogate testing of polypropylene (PP) may be needed due to the different sorption behavior of PP relative to PET. This study examines how the interaction between the surrogate contaminant, diluting solvent, and polymer impacts the sorption of surrogate contaminants into PP. Methyl salicylate (MS) and phenylcyclohexane (PCH) were selected as surrogate contaminants based on the current FDA testing protocol and solubility parameters. Swelling and sorption experiments were performed at 40°C for up to 14 days on different types of PP (monophasic homopolymer polypropylene (h-PP), monophasic random copolymer (r-PP), and/or heterophasic block copolymer (heco-PP)) in n-hexane, 2-propanol, and ethanol as diluting solvents. Sorption of 1% (v/v) MS and PCH from each diluting solvent into h-PP was quantified by GC-MS. Results showed that the PP polymers in n-hexane swelled 10%-155% more than the alcohols. Both MS and PCH sorption in n-hexane required a much shorter time, approximately 12 h, to reach equilibrium in comparison to the alcohols, which required 2–10 days. The equilibrium sorption concentration of 1% MS into h-PP from n-hexane was 55% and 136% higher, respectively, compared to sorption of MS from 2-propanol and ethanol. On the other hand, the equilibrium sorption concentration of 1% PCH into h-PP from 2-propanol and ethanol was 11-12% higher compared to the sorption of MS from n-hexane. Our data indicates that solvent swelling cannot be overlooked when determining realistic initial contamination levels in PP. This research will assist the FDA in updating the Recycled Plastics Guidance for Industry and enhance the FDA’s ability to fulfill its mission of protecting and promoting public health. Show less
