All You Need to Know About Polypropylene (PP) for 3D Printing

Today’s additive manufacturing sector is characterized by a wide variety of materials, from plastics and metals to ceramics and concrete. If we look at the family of polymers, the diversity is great, with many thermoplastics that are more or less easy to print. Among them is polypropylene (PP), a semi-crystalline material belonging to the family of polyolefins, also known as polyalkenes. Widely used in the plastic injection industry, it has a number of interesting characteristics for industrialists such as lightness, resistance to chemicals, to fatigue, and good electrical insulation. On the 3D printing market, however, it remains quite rare. Difficult to print, it requires rigorous control in its heat treatment and particular attention to adhesion, whether on a plate or between layers.

Polypropylene is a semi-crystalline thermoplastic, i.e. it has an ordered molecular structure with very precise melting points, unlike amorphous materials which soften gradually as the temperature rises. This structure influences its crystallinity and orientation. Didier Fonta, Director of Operations at Pollen AM, explains: “Polypropylene has very clear melting points and will be very demanding in terms of its transformation. This is why temperature fluctuations have to be limited in order to regain homogeneous properties.” Depending on the polymerization conditions (temperature, pressure and reagent concentrations) different grades of polypropylene can be obtained. There are currently 3 forms of polypropylene which depend on the arrangement of the methyl groups in relation to the plane of the main carbon chain.

A methyl group. The arrangement of the methyl groups influences the type of Polypropylene (PP) obtained.

The characteristics of Polypropylene

PP is one of the most widely used thermoplastics in the industrial sector, with global demand expected to reach 45 to 62 million tonnes by the end of the year. It is mainly found in the packaging industry (30% of the total market), in the manufacture of electrical products and equipment (13%), in the automotive industry (10%) and in household appliances (10%). Among its main benefits are its low price, low weight and low friction which makes its surface relatively slippery. In terms of characteristics, PP has good resistance to chemical products and is hydrophobic, making it an ideal material for the manufacture of containers for cleaning products, foods, etc. It also has very good fatigue resistance, which will allow it to retain its shape even after many torsions, which is why it is used to produce hinges. Finally, it has good impact resistance and excellent electrical insulation.