Polypropylene (PP)

Description

Polypropylene (PP) is a linear hydrocarbon which belongs to polyolefin family of polymers. It is shown as CnH2n. It can be used as plastic or fiber in different industries like automotive, consumer goods and furniture. Propylene in made by polymerization of propene monomer which can be achieved at low temperature and pressure. In compare with polyethylene, PP has lower density, higher rigidity and higher softening points. There are three different types of PP with different prices and specifications: Homopolymers, Random Polypropylene copolymers and Block copolymers.

Polypropylene Homopolymers is the most used type and contains only propylene monomer in a semi-crystalline solid form. It is used in packaging, textiles, healthcare, pipes, automotive and electrical applications.

Random copolymers – Polypropylene Random Copolymer is produced by polymerizing together ethene and propene. It features Ethene units, usually up to 6% by mass, incorporated randomly in the polypropylene chains. Such polymers typically are selected where a lower melting point, more flexibility and enhanced clarity are advantageous.

Block copolymers – in Polypropylene Block Copolymer, ethene content is larger (between 5 and 15%). It has co-monomer units arranged in regular pattern (or blocks). The regular pattern hence makes thermoplastic tougher and less brittle than the random co-polymer. These polymers are suitable for applications requiring high strength, such as industrial usages.

Polypropylene specifications should be considered while choosing a thermoplastic for an application.

Melting point : Homopolymer: 160-165°C / Copolymer: 135-159°C

Density: In comparison with all commodity plastics, PP is one of the lightest polymers. Density of three polypropylene are:

Homopolymer: 0.904 – 0.908 g/cm3

Random Copolymer: 0.904 – 0.908 g/cm3

Impact Copolymer: 0.898 – 0.900 g/cm3

Flammability: Polypropylene is a highly flammable material

retains mechanical & electrical properties at elevated temperatures, in humid conditions and when submersed in water. It is a water-repellent plastic

PP has good resistance to environmental stress cracking, It is sensitive to microbial attacks, such as bacteria and mold, It exhibits good resistance to steam sterilization

Polypropylene Chemical Resistance: Excellent resistance to diluted and concentrated acids, alcohols and bases,Good resistance to aldehydes, esters, aliphatic hydrocarbons, ketones,Limited resistance to aromatic and halogenated hydrocarbons and oxidizing agents

Disadvantages of Polypropylene:

Poor resistance to UV, impact and scratches, Embrittles below -20°C

Low upper service temperature, 90-120°C

Attacked by highly oxidizing acids, swell rapidly in chlorinated solvents and aromatics Heat-aging stability is adversely affected by contact with metals

Post molding dimensional changes due to crystallinity effects – this can be solved with nucleating agents

Poor paint adhesion