Polypropylene or PP is a low cost thermoplastic of high clarity, high gloss and good tensile strength. It has a higher melting point than PE, which makes it suitable for applications that require sterilization at high temperatures. It also has less haze and higher gloss.
Generally, the heat-sealing properties of PP are not as good as those of LDPE. LDPE also has better tear strength and low temperature impact resistance.
PP can be metallized which results in improved gas barrier properties for demanding applications where long product shelf life is important. PP films are well suited for a broad range of industrial, consumer, and automotive applications.
PP is fully recyclable and can be easily reprocessed into many other products for many different applications. However, unlike paper and other cellulose products, PP is not biodegradable. On the upside, PP waste does not produce toxic or harmful by-products.
The two most important types are cast unoriented polypropylene (CPP) and biaxially oriented polypropylene (BOPP). Both types have high gloss, exceptional optics, good or excellent heat-sealing performance, better heat resistance than PE, and good moisture barrier properties.
Cast Polypropylene Films (CPP)
Cast unoriented Polypropylene (CPP) generally finds fewer applications than biaxially oriented polypropylene (BOPP). However, CPP has been steadily gaining ground as an excellent choice in many traditional flexible packaging as well as non-packaging applications. The film properties can be customized to meet specific packaging, performance, and processing requirements. In general, CPP has higher tear and impact resistance, better cold temperature performance and heat-sealing properties than BOPP.
Biaxially Oriented Polypropylene Films (BOPP)
Biaxially oriented polypropylene or BOPP1 is the most important polypropylene film. It is an excellent alternative to cellophane, waxed paper, and aluminum foil. The orientation increases tensile strength and stiffness, lowers elongation (harder to stretch), and improves the optical properties, and somewhat improves vapor barrier properties. In general, BOPP has higher tensile strength, higher modulus (stiffness), lower elongation, better gas barrier, and lower haze than CPP.
PP film is used for many common packaging applications such as cigarette, candy, snack and food wraps. It also can be used for shrink wrap, tape liners, diapers and sterile wrap used in medical applications. Because PP has only average gas barrier properties, it often is coated with other polymers such as PVDC or acrylic which greatly improve the gas barrier properties.
Due to the low odor, high chemical resistance and inertness, many PP grades are suitable for packaging applications under FDA regulations.
1”Biaxially oriented" means that the PP film is stretched in two different directions to increase strength and modulus (lower elongation and higher stiffness).