What is Polymers(pp)?

Polymers(pp) is a type of polyolefin that is slightly harder than polyethylene. It is a commodity plastic with low density and high heat resistance. It finds application in packaging, automotive, consumer goods, medical, cast films, etc. Its chemical formula is (C₃H₆)_n.

Polymers(pp)

Polypropylene – Manufacturing & Properties

How is PP produced?

It is made from the polymerization of propene monomer. There are two main syntheses to produce polypropylene:

• Ziegler-Natta polymerization or
• Metallocene catalysis polymerization

Polymers(pp)

Upon polymerization, PP can form three basic chain structures. They depend 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

Polymers(pp)

Basic Chain Structures of PP

Depending on how it is produced and formulated, PP can be:

• hard or soft,
• opaque or transparent,
• light or heavy,
• insulating or conductive,
• neat or reinforced with cheap mineral fillers, short or long glass fibers, natural fibers, or even self-reinforced.

What are the properties of PP?

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. 1. Melting Point – The melting point of PP occurs at a range.
      • Homopolymer: 160 – 165°C
      • Copolymer: 135 – 159°C

1. 1. Density – PP is one of the lightest polymers among all commodity plastics. This feature makes it a suitable option for lightweight 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

1. 1. Chemical Resistance
      • Excellent resistance to dilute and concentrated acids, alcohols, and bases
      • Good resistance to aldehydes, esters, aliphatic hydrocarbons, ketones
      • Limited resistance to aromatic and halogenated hydrocarbons and oxidizing agents

1. 1. Flammability: PP is a highly flammable material.

1. 1. PP retains mechanical & electrical properties at elevated temperatures. This occurs in humid conditions and when submerged in water. It is a water-repellent plastic.

1. 1. PP has good resistance to environmental stress cracking.

1. 1. It is sensitive to microbial attacks, such as bacteria and mold.

What are the types of Polymers(pp)?

The major types of polypropylene available in the market are as follows:

Polypropylene Homopolymer

PP 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

This family is produced by polymerizing propene and ethane. It is further divided into random copolymers and block copolymers.

PP Random Copolymer is produced by polymerizing ethene and propene together. It usually features ethene units up to 6% by mass. These units are randomly incorporated into the polypropylene chains. These polymers are flexible and optically clear. This makes them suitable for applications requiring transparency. Also, suitable for products requiring an excellent appearance.

While in PP Block Copolymer, ethene content is larger. It ranges between 5 and 15%. It has co-monomer units arranged in regular patterns or blocks. The regular pattern makes thermoplastic tougher and less brittle than the random copolymer. These polymers are suitable for applications requiring high strength, such as industrial usage.

The potential applications of PP homopolymer and PP copolymer are nearly identical. Because of their extensively shared properties, the choice between these two materials is often made based on non-technical criteria. Some of the non-technical criteria are described in the table below.
It exhibits good resistance to steam sterilization.

Expanded Polypropylene

EPP is a closed-cell bead foam with ultra-low density. It produces three-dimensional polymer foam products. EPP bead foam has:

• higher strength-to-weight ratio,
• excellent impact resistance,
• thermal insulation,
• chemical and water resistance.

EPP is used in automobiles, packaging, construction products, consumer goods, and more.

Polypropylene Terpolymer

PP Terpolymer is composed of propylene segments joined by monomers ethylene and butane (co-monomer). These monomers appear randomly throughout the polymer chain. PP terpolymer has better transparency than PP homopolymer. Also, the incorporation of co-monomers reduces crystalline uniformity in the polymer. This makes it suitable for sealing film applications.

Polypropylene, High Melt Strength

It is a long chain-branched material. It combines both high melt strength and extensibility in the melt phase. The key features of PP HMS grades include:

• wide mechanical property range,
• high heat stability, and
• good chemical resistance.

HMS PP is widely used to produce soft, low-density foams for food packaging applications. Also used in the automotive and construction industries.