What is the difference between the types of polypropylene? (2023)

Polypropylene (PP) is a rigid crystalline thermoplastic used in everyday objects. There are different types of PP available: homopolymer, copolymer, high impact, etc. Its mechanical, physical, and chemical properties make it ideal for applications ranging from the automotive and medical industries to packaging.

What is polypropylene?

Polypropylene is made from propylene (or propylene) monomer. It is a linear hydrocarbon resin. The chemical formula of polypropylene is (C3H6)norte. PP is among the cheapest plastics available today and has the leastdensityamong standard plastics. After polymerization, PP can form three basic chain structures depending on the position of the methyl groups:

  • Attack (aPP).Irregular methyl group (CH3) agreement
  • isotático (iPP).methyl groups (CH3) located on one side of the carbon chain
  • Sindiotática (sPP).Alternating methyl group (CH3) agreement

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

Different types of polypropylene.

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

Propylene-Homopolymerit is the most common general purpose class. Contains only propylene monomer in semi-crystalline solid form. Major applications include packaging, textiles, healthcare, pipelines, automotive and electrical applications.

Polypropylene-CopolymerIt is divided into random copolymers and block copolymers, which are produced by the polymerization of propylene and ethane:

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  1. Propylene random copolymer is produced by copolymerizing ethylene and propylene. It has ethylene units, generally up to 6% by weight, randomly incorporated into the polypropylene chains. These polymers areflexible and optically clear, making them suitable for applications that require transparency and for products that require excellent appearance.
  2. The propylene block copolymer contains a higher ethylene content (between 5 and 15%). It has conomic units arranged in a regular pattern (or blocks). The regular pattern makes the thermoplastic stronger and less brittle than random copolymer. These polymers are useful in applications that require high strength, such as B. industrial applications.

Another type of polypropylene is the impact copolymer. A propylene homopolymer containing a mixed phase of propylene random copolymer having an ethylene content of 45-65% is called a PP impact copolymer. Impact copolymers are used primarily in packaging, housewares, film and tube applications, as well as in the automotive and electrical industries.

Polypropylene suppliers include A. Schulman, Borealis, ExxonMobil Chemical, LyondellBasell, SABIC, and RTP Company. For a full list of PP commercial grades and suppliers, visitClick here.

Polypropylene-Homopolymer vs. Polypropylene-Copolymer

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

Polypropylene-Copolymerit is a bit softer but has better impact resistance. It is stronger and more durable than propylene homopolymer. Tends to have better resistance to stress cracking andtoughness at low temperaturesthan homopolymer at the expense of some reduction in other properties.

Applications of PP homopolymers and copolymers

The applications are almost identical due toits generalized properties. Therefore, the choice between these two materials is usually made based on non-technical criteria.

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It is always an advantage to know in advance the properties of a thermoplastic. This helps select the right thermoplastic for an application. It also helps to assess whether or not the end use requirement would be met. Here are some of the key properties and benefits of polypropylene:

Melting point of polypropylene.The melting point of polypropylene is in a range.

  • Homopolymer: 160–165°C
  • Copolymer: 135–159 °C

polypropylene density.PP is one of the lightest polymers among all mass-produced plastics. This property makes it a suitable choice for light/light applications.

  • Homopolímero: 0,904-0,908 g/cm3
  • Random copolymer: 0.904-0.908 g/cm3
  • Impact copolymer: 0.898-0.900 g/cm3

Chemical resistance of polypropylene

  • Excellent resistance to diluted and concentrated acids, alcohols and bases
  • Good resistance to aldehydes, esters, aliphatic hydrocarbons and ketones
  • Limited resistance to aromatic and halogenated hydrocarbons and oxidizing agents

Other amounts

  • Flammability: Polypropylene is a highly flammable material.
  • PP retains its mechanical and electrical properties at elevated temperatures, in humid conditions and when immersed in water. It is a waterproof plastic.
  • PP has good resistance to environmental stress and cracking.
  • It is sensitive to microbial attack (bacteria, fungi, etc.)
  • It has good resistance to steam sterilization.

Polymeric additives such as clarifiers, flame retardants, glass fibers, minerals, conductive fillers, lubricants, pigments and many other additives can further improve the physical and/or mechanical properties of PP. For example, PP has poor UV resistance, so light stabilization with hindered amines increases durability compared to unmodified polypropylene.

Disadvantages of polypropylene

  • Low resistance to UV rays, shocks and scratches
  • Brittle below -20°C
  • Low top service temperature, 90-120°C
  • Attacked by strong oxidizing acids, it swells rapidly in chlorinated and aromatic solvents.
  • The thermal aging stability is negatively influenced by contact with metals.
  • Dimensional changes after molding due to crystallinity effects
  • Poor color adhesion

Polypropylene Applications

Polypropylene is used in many applications due to its good chemical resistance and weldability. Some common uses of polypropylene are:

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packaging applications

Good barrier properties, high strength, good surface finish, and low cost make polypropylene ideal for many packaging applications.

Flexible packaging.The excellent optical clarity of PP films and low water vapor permeability make them suitable for use in food packaging. Other markets include shrink wrap, films for the electronics industry, graphic applications, and disposable diaper covers and caps. PP film is available as cast film or biaxially oriented PP (BOPP).

Rigid packaging.PP is blow molded to make boxes, bottles and jars. Thin-walled PP containers are widely used for food packaging.

consumer goods.Polypropylene is used in a variety of household and consumer goods applications, including sheers, housewares, furniture, appliances, luggage, and toys.

automotive applications.Polypropylene is widely used in auto parts due to its low cost, excellent mechanical properties, and formability. Major applications include battery housings and trays, bumpers, fender panels, interior trim, instrument panels, and door panels. Other key features ofPP Automotive Applicationscontainlow coefficient of linear thermal expansionand specific gravity, high chemical resistance and good weather resistance, processability and impact/stiffness balance.

If you like that new car smell, thanks polymers. Most of the odor comes from plastics and adhesives that release chemicals. This is in small amounts, so it is not considered harmful.

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fibers and fabrics.PP is used in large quantities in the fiber and fabric market segment. PP fibers are used in a number of applications including staple film/raffia, tapes, strapping, continuous filament, staple fiber, continuous filament and spunbonded. PP rope and wire are very strong and moisture resistant, well suited for marine applications.

medical applications.Polypropylene is used in various medical applications due to its high chemical and bacterial resistance. Also, medical grade PP has good resistance to steam sterilization.

Disposable syringes are the most common medical application for polypropylene. Other uses include medical bottles, diagnostic devices, petri dishes, IV bottles, sample bottles, food dishes, pans, and pill containers.

industrial applications.Polypropylene sheet is widely used in the industry for making acid and chemical tanks, sheets, pipes, returnable transport packaging (RTP) and other products due to its properties such as high tensile strength, high temperature resistance and resistance to corrosion.

PP is 100% recyclable. Car battery boxes, flashlights, battery cables, brooms, brushes and ice scrapers are some examples of products that can be made from recycled polypropylene (rPP).

The PP recycling process mainly consists of melting plastic waste at 250°C to remove impurities, followed by removal of residual molecules under vacuum and solidification at nearly 140°C. This recycled PP can be mixed with virgin PP up to 50%. The biggest challenge in PP recycling is related to the amount used: around 1% of PP bottles are currently recycled, compared to a 98% recycling rate for PET and HDPE bottles combined.

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The use of PP is considered safe, since it does not have significant effects from the point of view of occupational safety in terms of chemical toxicity. To know more about PP, check ourguide, which includes information processing and much more.

Paul Martin is Head of Content atspecial chemical.


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