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Polypropylene(PP)

Polypropylene
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.
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.

                                      

Homopolymers 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 Copolymer family is further divided into random copolymers and block copolymers produced by polymerizing of propene and ethane:

    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 of applications requiring transparency and for products requiring an excellent appearance.

  1. While 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, 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.
Properties of Polypropylene
Keeping information about the properties of a thermoplastic beforehand is always beneficial. This helps in selecting the right thermoplastic for an application. It also assists in evaluating if the end use requirement would be fulfilled or not. Here are some key properties and benefits of polypropylene:
  1. Melting Point of Polypropylene - The melting point of polypropylene occurs at a range.
    • Homopolymer: 160 - 165°C
    • Copolymer: 135 - 159°C
  1. Density of Polypropylene - PP is one of the lightest polymers among all commodity plastics. This feature makes it a suitable option for lightweight\weight saving applications.
    • Homopolymer: 0.904 – 0.908 g/cm3
    • Random Copolymer: 0.904 – 0.908 g/cm3
    • Impact Copolymer: 0.898 – 0.900 g/cm3
  2. 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.
  3. Flammability: Polypropylene is a highly flammable material.
  4. PP retains mechanical & electrical properties at elevated temperatures, in humid conditions and when submersed in water. It is a water-repellent plastic.
  5. PP has good resistance to environmental stress cracking.
  6. It is sensitive to microbial attacks, such as bacteria and mold.
  7. It exhibits good resistance to steam sterilization.
Applications
  • Packaging Applications: Good barrier properties, high strength, good surface finish and low cost make Polypropylene ideal for several packaging applications.
  • Consumer Goods: Polypropylene is used in several household products and consumer goods applications including translucent parts, housewares, furniture, appliances, luggage, toys etc.
  • Automotive Applications: Due to its low cost, outstanding mechanical properties and moldability, polypropylene is widely used in automotive parts. Main applications include battery cases and trays, bumpers, fender liners, interior trim, instrumental panels and door trims.
  • Fibers and Fabrics: A large volume of PP utilized in the market segment known as fibers and fabrics. PP fiber is utilized in a host of applications including raffia/slit-film, tape, strapping, bulk continuous filament, staple fibers, spun bond and continuous filament. PP rope and twine are very strong and moisture resistant very suitable for marine applications.
  • Medical Applications: Polypropylene is used in various medical applications due to high chemical and bacterial resistance. Also, the medical grade PP exhibits good resistance to steam sterilization. Disposable syringes is the most common medical application of polypropylene. Other applications include medical vials, diagnostic devices, petri dishes, intravenous bottles, specimen bottles, food trays, pans, pill containers, etc.
  • Industrial Applications: Polypropylene sheets are widely used in industrial sector to produce acid and chemical tanks, sheets, pipes, Returnable Transport Packaging (RTP), etc. because of its properties like high tensile strength, resistance to high temperatures and corrosion resistance.