Although polypropylene is chemically relatively like PE, it is much harder, stronger, and thermally more resilient. It is the standard plastic with the lowest density (0.9 g/cm³). The maximum continuous operating temperature is about 100 °C. Below 0 °C, the material becomes brittle and its impact sensitivity increases more than with PE. Special types with different tacticity allow both higher and lower operating temperatures. Most types of polypropylene have a uniform structure. This leads to a high degree of crystallization and thus to comparably higher strength and stiffness as well as melting and service temperature ranges.
Due to its low density and good compatibility with almost all organic solvents, polypropylene is a popular plastic in the automotive and carpet industries. It is physiologically harmless and biologically inert, so it is widely used in the pharmaceutical and food industries.
