Effect of recycled polypropylene on migration of six processing aids in polypropylene film to milk

Mechanically recycled plastics used in food packaging are consistent with the current circular economy concept. In this study, the effects of recycled polypropylene (rPP) content on film properties and the migration of processing aids in the film to food simulant and milk were studied by self-made rPP films. The results showed that the rPP and processing aids increased the transparency of the films. However, the presence of tiny particles in the rPP film reduced its elongation at break. Furthermore, rPP and processing aids decreased the thermal stability of the film. At 70 °C for 2 h, the total migration order of the processing aids to food simulant and milk was 50 % ethanol (55.78–64.17 mg/kg) > whole milk (10.32–10.66 mg/kg) > low-fat milk (6.39–7.04 mg/kg) > skim milk (4.88–5.47 mg/kg). The migration of processing aids into milk in films containing 50 % and 100 % rPP was similar to that of virgin polypropylene (vPP) films, which indicates that rPP does not promote processing aid migration. Moreover the overall migration order of processing aids to 2 % (w/v) food ingredient aqueous solution was lecithin (3.05 mg/kg) > glyceryl trilaurate (2.68 mg/kg) > cholesterol (1.33 mg/kg) > NaCl (0.33 mg/kg) > casein (0.32 mg/kg) > lactose (0.29 mg/kg) > water (0.16 mg/kg). This confirmed that milk fat was the primary cause of processing aids migration from the film, and the kind of milk fat also had an effect on processing aids migration. Therefore, as long as the basic performance and food safety of packaging are met, a certain proportion of rPP can be added to vPP to achieve sustainable development of packaging.