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Polypropylene (PP)

Last updated: March 28, 2019

What Does Polypropylene (PP) Mean?

Polypropylene is a type of thermoplastic polymer resin with the chemical formula C3H6. It is useful in many packaging applications as a structural plastic or as a fiber-type plastic. It is easy to customize, lightweight and very flexible, and has high melting point and a low level of electrical conductivity.

Polypropylene has shown excellent resistance to organic solvents and degreasing agents as well as electrolytic attack. Polypropylene produces fewer solid wastes by weight than polyethylene terephthalate (PET), polystyrene (PS) or polyvinyl chloride (PVC). It also produces significantly less CO2 equivalents by weight than PET, PS or PVC.

Polypropylene is mostly unaffected by many inorganic acids, alkalis, and aqueous solutions at room temperature, but at elevated temperatures some concentrated acids and oxidizing agents can attack them.


Corrosionpedia Explains Polypropylene (PP)

Polypropylene (PP) is an addition polymer made from the monomer propylene. It is extremely resistant to many chemical solvents, bases and acids. It has shown similar characteristics to polyethylene in many aspects, particularly in solution behavior and electrical properties. The presence of an additional methyl group in polypropylene helps to improve its mechanical properties and thermal resistance but decrease its chemical resistance.

Mechanical properties:

  • Low density
  • Tough and flexible
  • Good resistance to fatigue

Thermal properties:

  • Large thermal expansion but less than polyethylene
  • Below 0 °C (32 °F), it becomes brittle

Chemical properties

  • Isotactic and has an intermediate level of crystallinity
  • Resistant to fats and almost all organic solvents at room temperature
  • Solved in low polarity solvents at elevated temperature


  • Liable to chain degradation from exposure to heat and UV radiation
  • Oxidation occurs at the tertiary carbon atom present in repeating units
  • A network of fine cracks and crazes appear in external applications

Microbial organisms are also capable of degrading polypropylene. The degraded material forms a tree bark-like layer at the surface of mesh fibers. The polypropylene degradation can be prevented by using anti-oxidants.

Polypropylene is recyclable and is being recycled in many applications such as battery cases, paint cans, home storage, flowerpots, pallets, crates, composite lumber and more.


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