There are three types of polypropylene used in rigid food packaging: homopolymer polypropylene, collisional copolymer polypropylene, and random copolymer polypropylene. Each of them differs in its chemical composition, properties, and uses.
Rigid polypropylene containers are formed on an injection machine in a series of stages, starting with the melting of the polypropylene balls, then forming them inside a mold, all the way to the cooling process after molding.

These concerns generally focus on the levels of residual monomers and plastic additives such as plasticizers and solvents found in custom polymers in direct contact with food. All polymers contain small amounts of free monomers left unreacted by the polymerization reaction, and these components are potentially available to migrate into the food contained within. Package.
To determine the extent of the transfer of free molecules or monomers from the packaging to the food, migration is measured by simulating food materials. Food mimetics are used as food substitutes due to the simplification of chemical analysis. Chemical and quantitative detection requires specific analytical methods for each chemical that are developed specifically for each type of food. Food simulations vary in their chemical properties, representing several different types of foods. This is to differentiate between the different types of polypropylene used in rigid packaging containers in terms of the least migration, depending on the nature of the food being packaged, in a way that reduces harm to the health of the consumer.