Food container design and construction play a significant role in determining the shelf life of a food product. The right selection of container and packaging materials and technologies maintains product quality and freshness during distribution and storage. Materials that have traditionally been used in food container include glass, metals (aluminum, foils and laminates, tinplate, and tin-free steel), papers, and plastics. Moreover, a wider variety of plastics have been introduced in both rigid and flexible forms. Today's food containers often combine several materials to exploit each material's functional or aesthetic properties. As research to improve food containers continues, advances in the field may affect the environmental impact of food containers.
Plastics are made by condensation polymerization (polycondensation) or addition polymerization (polyaddition) of monomer units. In polycondensation, the polymer chain grows by condensation reactions between molecules and is accompanied by formation of low molecular weight byproducts such as water and methanol. Polycondensation involves monomers with at least two functional groups such as alcohol, amine, or carboxylic groups.
While, in polyaddition, polymer chains grow by addition reactions, in which two or more molecules combine to form a larger molecule without liberation of by-products. Polyaddition involves unsaturated monomers, and double or triple bonds are broken to link monomer chains.
Generally speaking, there are several advantages to using plastics for food Plastic Container and packaging. Fluid and moldable, plastics can be made into sheets, shapes, and structures, offering considerable design flexibility. Because they are chemically resistant, plastics are inexpensive and lightweight with a wide range of physical and optical properties. In fact, many plastics are heat sealable, easy to print, and can be integrated into production processes where the container is formed, filled, and sealed in the same production line. However, the major disadvantage of plastics is their variable permeability to light, gases, vapors, and low molecular weight molecules.
Harder, denser, and more transparent than polyethylene, polypropylene has good resistance to chemicals and is effective at barring water vapor. Its high melting point (160 °C) makes it suitable for applications where thermal resistance is required, such as hot-filled and microwavable food container. Popular uses include yogurt containers and margarine tubs. When used in combination with an oxygen barrier such as ethylene vinyl alcohol or polyvinylidene chloride, polypropylene provides the strength and moisture barrier for catsup and salad dressing bottles.