Polypropylene (PP) is a rigid and crystalline thermoplastic used widely in everyday objects like packaging trays, household products, battery cases, medical devices, etc. Explore this comprehensive guide and learn everything you need to know about this widely used thermoplastic.
Polypropylene is a tough, rigid and crystalline thermoplastic 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.
Polypropylene homopolymers are thermoplastic resins produced through the polymerization of propylene with Ziegler-Natta catalysts. The homopolymers can be used in different processing technologies, such as injection molding, blow molding, film, fiber, sheet extrusion and thermoforming.
PP belongs to polyolefin family of polymers and is one of the top three widely used polymers today. Polypropylene has applications both as a plastic and a fiber in:
Consumer Goods, and
It has the lowest density among commodity plastics.
These days, polypropylene is made from polymerization of propene monomer (an unsaturated organic compound - chemical formula C3H6) by:
Structure of PP Monomer
Or Metallocene Catalysis
Structure of Polypropylene
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
Types of Polypropylene & their BenefitsHomopolymers and Copolymers are the two major types of polypropylene available in the market.
Polypropylene 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.
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. These polymers are flexible and optically clear making them suitable for applications requiring transparency and for products requiring an excellent appearance.
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Polypropylene, Impact Copolymer – Propylene Homopolymer containing a co-mixed Propylene Random Copolymer phase which has an ethylene content of 45-65% is referred to PP impact copolymer. It is useful in parts which require good impact resistance. Impact copolymers are mainly used in packaging, houseware, film, and pipe applications, as well as in the automotive and electrical segments.
Expanded Polypropylene - It is a closed-cell bead foam with ultra-low density. EPP is used to produce three-dimensional polymer foam products. EPP bead foam has higher strength to weight ratio, excellent impact resistance, thermal insulation, and chemical and water resistance. EPP is used in various applications ranging from automobiles to packaging, from construction products to consumer goods and more.
Polypropylene Terpolymer - It is composed by propylene segments joined by monomers ethylene and butane (co-monomer) which appear randomly throughout the polymer chain. PP terpolymer has better transparency than PP homo. Also, the incorporation of co-monomers reduces crystalline uniformity in the polymer making it suitable for sealing film applications.
Polypropylene, High Melt Strength (HMS PP)– It is a long chain branched material, which combines both high melt strength and extensibility in the melt phase. PP HMS grades have a wide mechanical property range, high heat stability, good chemical resistance. HMS PP is widely used to produce soft, low density foams for food packaging applications as well as used in automotive and construction industries.
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