Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is a white, mechanically rugged material which has a high chemical resistance. As well as this, it is tough and lightweight with low water absorption, and it is often chosen for its resistance to corrosion. It is also the second most widely produced commodity plastic (after polyethylene). It does not present stress cracking problems and offers excellent electrical and chemical resistance to higher temperatures. While the properties of Polypropylene are like those of polyethylene, there are specific differences such as a lower density, higher softening point (PP does not melt below 160°c), and higher rigidity and hardness.
Polypropylene is used in both household and industrial applications. Its unique properties and ability to adapt to various fabrication techniques make it stand out as an invaluable material for a wide range of uses. In general it is chemically less resistant than polyethylene, however it does offer good resistance to non-oxidizing acids, bases, fats, and most organic solvents. It is not compatible with strong oxidants and becomes brittle below 0°C.
Polypropylene (PP) is FDA approved, but it is not as rigid as polyethylene, so it is not a good choice for food chopping boards. However, it is an ideal plastic material for food processing applications such as wall cladding and light use components.
Polypropylene (PP) is recyclable, and around 30% is recycled from major industries each year. However, it is not as economically viable to recycle PP as it is to recycle other polymers, in particular HDPE, LDPE and PET. With advancements in recycling, it is hoped that this will change soon.
Polypropylene is available in two main grades: Polypropylene Homopolymer (PPH) and Polypropylene Copolymer (PPC).
Both have remarkably similar properties, but appearance and performance differences are distinctive between the two types. PPH is stronger and stiffer than copolymer and more widely used. The combination of excellent chemical resistance and ability to be joined and welded by heat fusion makes this an ideal plastic for chemical tanks and structures in corrosive environments.
PPC is tougher and more malleable and durable than PPH. Although Polypropylene Copolymer is softer, it offers better impact strength and tends to have better stress resistance and toughness even at low temperatures compared to PPH. Overall, Polypropylene is an excellent material choice that has many benefits and comes at a low cost.
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