What is PP Material??

Polypropylene (PP) is a tough, rigid, and crystalline thermoplastic. It is made from propene (or propylene) monomer. This linear hydrocarbon resin is the lightest polymer among all commodity plastics. PP comes either as a homopolymer or as a copolymer and can be greatly boosted with additives.

PP has become a material of choice when you are looking for:

Superior strength in engineering applications (vs. Polyamide)
Cost advantage in blow molding bottles (vs. PET)

What is polypropylene?

Polypropylene (PP) is a type of polyolefin that is slightly harder than polyethylene. It is a commodity plastic with low density and high heat resistance. Its chemical formula is (C3H6)n.

Molecular Structure of PP

It finds application in packaging, automotive, consumer good, medical, cast films, etc. 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.

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

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

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:

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

Density - 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

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

Flammability: PP is a highly flammable material.

PP retains mechanical & electrical properties at elevated temperatures. This occurs in humid conditions and when submerged 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.

Learn more about all polypropylene properties and their values - ranging from mechanical and electrical to chemical properties; and make the right selection for your application.

What are the types of 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.

Polypropylene, Impact Copolymer

Propylene Homopolymer contains a co-mixed PP Random Copolymer phase. It has an ethylene content of 45-65%. It is useful in parts that require good impact resistance. Impact copolymers are mainly used in packaging, houseware, film, and pipe applications. They are also used in the automotive and electrical segments.

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.

Bio-based Polypropylene

It is a bio-based version of PP. Its monomer propylene is derived from renewable feedstocks. The bio-based content can vary anywhere between 30-100%. There are several suppliers offering pure PP bio-based grades such as:

PolyFibra® & Trifilon BioLite®
PP/PE blend - Terralene® PP 2509 and
In biocomposite form like Terratek®, Sappi Symbio PP, etc.