Polypropylene is a relatively new plastic that has overcome the shortcomings this material had in its early days, such as its sensitivity to light and cold. Known by the abbreviation PP, it is a very hard and durable plastic; it is opaque and highly heat-resistant, as it softens at a temperature higher than 150 °C.
It is highly impact-resistant, although it has low density and can be bent very easily; it can withstand repeated bending, which is why it is used as a material for hinges.
It is also highly resistant to corrosive substances. It is primarily derived from propylene extracted from natural gas, and polypropylene is produced through the polymerization of propylene.
In 1954, the Italian scientist G. Natta, building on the work of K. Ziegler in Germany, succeeded in producing a type of polypropylene with a very regular structure known as isotactic polypropylene. Its commercialization in Europe and North America began rapidly in 1957, in applications for household goods.
The work of Natta and Ziegler, which made it possible to produce ethylene polymers from olefins, paved the way for the production of other polymers. This plastic, which also had a semicrystalline structure, surpassed polyethylene in mechanical properties; it had the lowest density of all plastics, and its price was also very low. However, it was highly sensitive to cold and ultraviolet light, causing it to age rapidly. For this reason, its use was limited to just a few applications.
However, the discovery of new light stabilizers, the improved cold resistance achieved through propylene-ethylene polymerization, the ease with which PP can incorporate reinforcing fillers such as glass fiber, talc, and asbestos, and its low price led to a significant boom in the use of this material.