Polypropylene (PP) is a semi-crystalline thermoplastic material with a unique blend of properties. It is used in a wide variety of applications, ranging from commodity use to specialty engineering performance. While it offers reasonably good mechanical properties, it provides exceptional chemical resistance at a relatively low cost.
There are two main types of polypropylene: homo polymer, and co-polymer, with homo polymer PP being the most widely used type. In general, it is stiffer and stronger than the co-polymer type. Copolymer PP is generally softer than homopolymer, but is tougher and more durable, with better low temperature toughness. Copolymer is usually divided into sub-groups: i.e. block copolymer, random copolymer, impact modified copolymer, etc.
block copolymer – consists of two or more homopolymers bonded together in a linear pattern (the term blocks refers to the distinct units that are bonded together). The properties depend on the pattern and ratio of the blocks.
random copolymer – consists of two or more homopolymers bonded together in a random pattern. In PP, a random copolymer offers a balance of toughness and transparency.
impact modified copolymer – this is typically a block copolymer with a rubbery component as one of the components of the matrix. In PP, this rubbery component is typically EPDM (ethylene propylene diene monomer, a synthetic rubber)
All of these types of polypropylene are readily available from a wide variety of suppliers and distributors.