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PP Thermoplastic
Vacuum formed from PP plastic
PP   - Polypropylene

Polypropylene (PP) is a thermoplastic polymer used for a broad spectrum of applications, such as packing, textiles, reusable containers, laboratory equipment, automotive parts and much more. As an additional polymer made from the monomer propylene, it is resistant to many chemical solvents, acids and bases.

In 1951, Paul Hogan and Robert L. Banks discovered polypropylene as they attempted to make dimers and trimers of ethylene and propylene for gasoline use and accidentally produced crystalline polypropylene and linear polypropylene. Phillips Petroleum patented this process at the beginning of 1953.

In 1954, the Italian scientist Giulio Natta, as well as the German chemist Karl Rehn, polymerized it for the first time to a crystalline isotactic polymer through the additional reaction of propylene gas with the stereospecific catalyst titanium trichloride. From 1957 onwards, this innovative discovery was followed by extensive commercial production of isotactic polypropylene. Syndiotactic polypropylene was first polymerized by Guilo Natta and his fellow workers. In 1963, both Karl Rehn and Giulio Natta were awarded the Nobel price in Chemistry; Karl Ziegler for his finding of first titanium based catalysts and Giulio Natta for using them for the preparation of stereoregular polymers.

The industry uses various brand names for polypropylene, such as Herkulon, Moplen, Profax, and others. There are three product groups offered, with the following market share:

Homopolymer (HP): approx. 65-75%
Impact copolymer (ICP): approx. 20-30%
Random coplymer (RCP): approx. 5-10%

In 2001, 30 million tons of polypropylene was produced. In the year 2007, the production volume was already over 45 million tons and represented a value of 47,4 billion Euros.

PP Properties

Polypropylene is quite a versatile material and offers a great combination of properties, such as stiffness and flexural retention. It is strong, lightweight and heat resistant. Besides these and the many more properties, it is easily fabricated and may be subjected to a broad range of fabrication methods and applications.

Production is done by a slurry solution or gas phase process where the propylene monomer is exposed to heat and pressure by the aid of a catalyst system. Polymerisation is procured at low temperature and pressure, so the resulting product is translucent, but completely colored. To alter the properties of the plastic, variances in catalyst and production conditions may be used.

PP does not show any stress-cracking problems and provides excellent electrical and chemical resistance at higher temperatures. Properties of polypropylene are similar to those of polyethylene, though there are some particular differences, such as a lower density, a higher softening point and higher rigidity and hardness. To protect the polymer during processing and to achieve a higher end-use performance, all commercially produced polypropylene resins have additives applied.

Various grades are available on the market and are dependent on the particular processing method and application.

PP Applications

Generally homopolymers may be used for items such as household goods, medical equipment, housings and film tapes. Copolymers are preferably used for applications exposed to cold and are broadly used for cooler containers, seat shells, boat hulls, outdoor furniture and automotive parts.

Since polypropylene can be manufactured to a high level of purity, it is well suited for usage in the semiconductor industry. Due to its resistance to bacterial growth it is suitable for the use in medical equipment. Non-woven fabrics, such as ropes, are made of polypropylene and are used in industries like fishing and agriculture. For flexible packing applications (for example yoghurt containers, syrup bottles etc.), in the automotive industry and in the construction sector (e.g. drainage pipes, pumps) polypropylene is the material of choice.

Other commonly used thermoplastics

ABS Acrylonitrile butadiene styrene
HDPE High Density Polyethylene
LDPE Low Density Polyethylene
PC Polycarbonate
PET Polyethylene terephthalate
PMMA Polymethyl methacrylate
PS Polysytrene
PVC Polyvinyl chloride
Vacuum formed from PP plastic

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