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Polypropylene

This versatile thermoplastic polymer got heads turning when it came onto the scene in the 1950’s. Petroleum scientists Hogan and Banks, as well as European scientists Rehn and Natta were responsible for its rapid development and it quickly became available commercially. Since then, polypropylene has enjoyed huge popularity and is now the second most widely used synthetic plastic in the world, second only to polyethylene. You can find polypropylene in packaging, electrical work, equipment, appliances and construction work, among other applications. Investors speculate that the global demand for polypropylene will exceed 60 million metric tons by 2020.

Physical and Chemical Properties

Polypropylene is a linear hydrocarbon polymer, saturated, semi-rigid and available as either a fiber or a plastic. It is white and translucent in appearance. Applying the polyethylene catalysts and technology to propylene gas allows polypropylene to crystallize, and it can also be co-polymerized (normally with ethylene) to enhance material properties such as toughness and flexibility. Polypropylene has a low density, a slippery surface and a low co-efficient of friction. It resists heat, electricity, fatigue, chemicals and organic solvents well. Polypropylene can be produced flexibly to suit certain applications: the main forms on the market are homopolymers, block copolymers and random copolymers.

Polypropylene Production and Processing

The two most common ways to make polypropylene are bulk slurry or gas phase production. In both cases, propylene, the monomer, is exposed to pressure, high temperatures and a catalyst. Bulk slurry processing facilitates polymerization by adding liquid propylene to the reactor. This method produces homopolymers and block copolymers successfully. For gas phase processing, gaseous propylene is placed with a solid catalyst inside a loop reactor, producing a fluidized bed. Random copolymers require the use of a gas phase reactor.

Applications

Polypropylene’s unique qualities and ability to adapt make it suitable for an extremely wide range of applications. Its chemical resistance makes it useful as a material for solvent containers. Living hinges are created from polypropylene thanks to its shape retention and fatigue resistance properties. Electronic components use polypropylene to insulate, and it is suitable for injection molding. Other very common uses for polypropylene include packaging, piping, food containers, clear plastic bags, ropes, carpets and concrete reinforcement. Polypropylene fibers are used in clothing and diapers.