Polypropylene (PP) is a rigid crystalline thermoplastic used in everyday objects. There are various types of PP available: homopolymer, copolymer, impact, etc. Its mechanical, physical, and chemical properties work well in applications ranging from automotive and medical to packaging.

What is Polypropylene?

Polypropylene is produced from propene (or propylene) monomer. It is a linear hydrocarbon resin. The chemical formula of polypropylene is (C3H6)n. PP is among the cheapest plastics available today, and It has the lowest density among commodity plastics. Upon polymerization, PP can form three basic chain structures depending on the position of the methyl groups:

Atactic (aPP): Irregular methyl group (CH3) arrangement

Isotactic (iPP): Methyl groups (CH3) arranged on one side of the carbon chain

Syndiotactic (sPP): Alternating methyl group (CH3) arrangement

PP belongs to the polyolefin family of polymers and is one of the top-three most-used polymers today. Polypropylene has applications—both as a plastic and as a fiber—in the automotive industry, industrial applications, consumer goods, and the furniture market.

Different Types of Polypropylene

Homopolymers and copolymers are the two main types of polypropylene available in the market.

PP Homo (PPH-Propylene homopolymer)

Propylene homopolymer is the most widely utilized general-purpose grade. It contains only propylene monomer in a semi-crystalline solid form. Main applications include packaging, textiles, healthcare, pipes, automotive, and electrical applications.

PP Copo (PPC-Polypropylene copolymer)

Polypropylene copolymer is divided into random copolymers and block copolymers produced by polymerizing of propene and ethane:

PP Random (PPR-Propylene random copolymer)

Propylene 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. These polymers are flexible and optically clear, making them suitable for applications requiring transparency and for products requiring an excellent appearance.

PP Block (PPB-Propylene block copolyme)

Propylene block copolymer contains a higher ethene content (between 5 and 15%). It has co-monomer units arranged in a regular pattern (or blocks). The regular pattern makes the thermoplastic tougher and less brittle than the random co-polymer. These polymers are suitable for applications requiring high strength, such as industrial usages.

Another type of polypropylene is impact copolymer. A propylene homopolymer containing a co-mixed propylene random copolymer phase which has an ethylene content of 45-65% is referred to PP impact copolymer. Impact copolymers are mainly used in packaging, houseware, film, and pipe applications, as well as in the automotive and electrical segments.

Polypropylene Homopolymer vs. Polypropylene Copolymer

Propylene homopolymer has a high strength-to-weight ratio, and is stiffer and stronger than the copolymer. These properties combined with good chemical resistance and weldability make it a material of choice in many corrosion resistant structures.

Polypropylene copolymer is a bit softer but has better impact strength. It’s tougher and more durable than propylene homopolymer. It tends to have better stress crack resistance and lower temperature toughness than homopolymer at the expense of a small reduction in other properties.