Polypropylene (PP) can be recycled and used as food packaging in a wide variety of uses, according to a study conducted in Europe.
As a rugged polymer, PP is resistant to many chemical solvents and therefore is popular for packaging and labeling, textiles, plastic parts, stationery, car parts, laboratory equipment, and reusable containers. But can it be recycled and used in food packaging?
That is what the study, commissioned by the Waste & Resources Action Program (WRAP) in England, wanted to find out, reports Plastics News. Using 18,000 pounds of post-consumer PP packaging material, the study examined how best to recycle the material, whether it could meet European Union standards, its ability to be made into new packaging, and whether the process is economically feasible.
The source material was decontaminated and pelletized with a vacuum chamber at a high temperature. The material was then made into several food-packaging containers: injection molded pots, thermoformed pots, and thermoformed trays.
The material could be molded as well as typical virgin copolymer material. It met physical and impact requirements as well, showing that high-speed manufacturing of recycled PP is possible, the researchers found.
In good news for chocolate lovers, chocolate placed on trays made with recycled PP rated better than chocolate placed on trays made with virgin material, relative to contamination, the researchers said. Also, a panel to perform blind odor tests on the virgin and recycled containers found no significant differences.
The researchers also screened the recycled containers to see what chemicals made its way onto them. They focused on compounds such as oligomers, fatty acids, antioxidants, and clarifier residues. Plastics News describes what the screenings uncovered:
Three of the substances found in the container had restriction limits — di(2-ethylhexyl) phthalate or DEHP, Tinuvin 326: an ultraviolet absorber/antioxidant, and clarifier residue 3,4-dimethylbenzaldehyde. Researchers performed migration tests simulating severe conditions — microwaving and up to six months ambient chilled or frozen storage. They did not detect migration of DEHP or Tinuvin 326 in containers made of clear or colored recycled PP and housing aqueous or fatty foods.
The 3,4-dimethylbenzaldehyde did migrate into aqueous and fatty foods, the researchers found, but at levels below that for concern. Containers with this material could be suitable for use, but more research is needed to be sure.
One bit of disappointing news: Recycled PP did not pass migration tests for fatty foods at aggressive conditions, the study found. However, the material seemed to pass muster for a range of aqueous and acidic foods, such as butter, ice cream, meat, bread, chocolate, dried foods, cheese, and soup, under extreme heating and storage conditions.
Next, the researchers will investigate whether any problems could be caused by in-mold labels or direct printing inks. Also, they are examining whether PP packaging could be automatically sorted into food and non-food categories.