First developed in the 1950’s. Polypropylene (PP) is an economical material offering a combination of outstanding physical, mechanical, thermal, and electrical properties, not found in any other thermoplastic. Because it’s particularly suited to injection molding, PP can be found used in the packaging industry, electrical and equipment manufacturing, household appliances, automotive applications and construction materials. Noted for its excellent chemical resistance in corrosive environments, PP provides excellent resistance to organic solvents, degreasing agents and electrolytic attack. It is lightweight, resists staining, and has a low moisture absorption rate.
Polypropylene is available as either homopolymer or copolymer material. Polypropylene Homopolymer (PPH) is the most widely used. PPH offers a high strength to weight ratio, and is stiffer and stronger than copolymer (PPC). This feature, combined with good chemical resistance and weldability, allows PPH to be used in applications requiring corrosion resistance. Polypropylene Copolymer (PPC) is a bit softer but has better impact strength. It is also tougher and more durable than PPH. PPC tends to have better stress crack resistance and low temperature toughness than PPH at the expense of quite small reductions in other properties.
+ Key Strengths:
PP is relatively inexpensive, and more economical than most polyethylenes and other thermoplastics. Compared to LDPE or HDPE, PP has a lower impact strength, but offers superior working temperature and tensile strength. It has high flexural strength due to its semi-crystalline nature. PP has a low coefficient of friction and is very resistant to moisture. Additionally, it shows good chemical resistance over a wide range of bases and acids, has good fatigue resistance, impact strength, and a resistance to electricity which makes it a good electrical insulator.
- Key Drawbacks:
PP has high flammability, and lower impact strength than virtually all polyethylenes (LDPE, HDPE, UHMW-PE). It also has a high thermal expansion coefficient, which limits its use in high temperature applications. PP is susceptible to UV degradation and oxidation, has poor resistance to chlorinated solvents and aromatics, and has poor bonding properties thus making difficult to weld ultrasonically or to paint.