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What are the advantages of polypropylene?

Mar. 07, 2024
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What is polypropylene?

This article focuses on polypropylene, a polymer belonging to the thermoplastic family. We will discuss its main advantages and applications as well as the industries in which it is used. Polypropylene, sometimes called polypropene or PP, is a versatile thermoplastic used in a wide range of industries. Its mechanical properties are quite similar to plastics of the polyethylene family, such as HDPE. Although polypropylene is much stiffer and tougher than HDPE, both materials are often used in similar applications.

Homopolymer Polypropylene

Homopolymer polypropylene is made from a single type of monomer (polypropylene monomer). This material is the most widely used for general purposes. Some of its mechanical properties are different from those of copolymers: it is more durable, stronger and much stiffer. It is therefore important to evaluate which type is most suitable for the application.

Polypropylene copolymer

Unlike a homopolymer, a copolymer combines at least two different monomers. In the case of polypropylene, the copolymer version is less rigid and more flexible. This greater flexibility allows the copolymer polypropylene to be more resistant to impacts and more durable, so it is less likely to crack. Copolymer polypropylene is better suited for tanks since it can undergo some deformation under mechanical stress.

The main advantages of polypropylene

1. Resistant to chemicals

Since polypropylene is chemically inert, it does not react when in direct contact with chemical agents. Its excellent chemical compatibility makes it an ideal choice when designing corrosive storage units such as tanks.

2. Food safe

Polypropylene meets FDA and 3-A Dairy food standards. It can therefore be used in applications where it comes into direct contact with foodstuffs, including water tanks or other types of liquids intended for human consumption.

3. Durable and lightweight

Although very light and low density (about 900 kg/m3), it is exceptionally rigid, more so than most plastics in the polyethylene family. Polypropylene is able to resist impacts and shocks and has excellent bending strength. It is therefore used extensively in the advertising industry, mainly in its corrugated form (PPA), which is rigid yet ultra-light.

4. Weldable

Its weldability allows the design of larger parts. The plastic welds provide a tight and strong seal. The flexibility of this type of welding also reduces the risk of cracking. Homopolymer polypropylene is usually preferred when designing tanks because it is less expensive than the copolymer version.

5. Does not absorb moisture


Polypropylene does not absorb moisture, making it an excellent choice to manufacture tanks and containers used to store liquids and chemicals.

Polypropylene applications

Food

Polypropylene is FDA and 3-A Dairy compliant, so it can be used in direct contact with foodstuffs. In addition to tank design, it is also used in the manufacture of structures and parts for the food industry.

Medical and Pharmaceutical

Thanks to its food grade and excellent chemical resistance, polypropylene is an ideal choice for laboratory equipment and accessories. It is also available in more specialized grades, such as flame-retardant polypropylene, a material also used in the medical field and in laboratories.

Chemical

Like HDPE, polypropylene has good chemical compatibility. It can be used to store a wide variety of chemicals while maintaining its inherent properties. To learn more, see our article, The Advantages and Applications of HDPE.

Les limitations du polypropylène

Low temperatures

Polypropylene is not well suited for low temperature environments, which adversely affect some of its properties, such as its impact resistance. In this case, high-density polyethylene, which has a high molar mass, is more suitable and will continue to perform well even in the coldest environments. For example, TIVAR® 88 can tolerate temperatures as low as -200 °C (-328 °F).

UV resistance

Exposure to UV rays is a constraint that must be taken into consideration, especially when the plastic is used outdoors. Polypropylene will lose its mechanical properties when exposed to UV rays for prolonged periods of time.In this case, certain types of high-density polyethylene are preferable since they are highly resistant to UV rays. This is why HDPE is often used when designing playground equipment.

Polypropylene P

lastic

Polypropylene (PP) is one of the most commonly used thermoplastics in the world. Polypropylene uses range from plastic packaging, plastic parts for machinery and equipment and even fibres and textiles. It is a rigid, semi-crystalline thermoplastic that was first polymerised in 1951 and is used widely today in a range of domestic and industrial applications. Today, global demand for polypropylene is estimated at around 45 metric tons and this figure continues to rise exponentially.

Uses for polypropylene

Polypropylene has a slippery, tactile surface, making it ideal for

  • plastic furniture
  • low friction applications, such as gears in machinery and vehicles.

It is highly resistant to chemical corrosion, making it an excellent choice for packaging for

  • cleaning products
  • bleaches and
  • first-aid products

It offers excellent fatigue resistance and elasticity, securing it a well-deserved reputation for toughness and durability.Polypropylene has high insulation properties too, making it safe to use for plastic casing in electrical goods and cables. In its fibre form, polypropylene uses are not limited to not only useful for tote bags but also encompass a much wider range of other products, including ropes, twine, tape, carpets, upholstery, clothing and camping equipment. Its waterproof properties make it especially effective for the marine sector. In the automotive industry, polypropylene is also used widely, for example in for battery casings, trays and drink holders, bumpers, interior details, instrumental panels and door trims.

Finally, the medical world appreciates the waterproof properties of polypropylene too, as well as its flexible strength, resistance to mould, bacteria and chemical corrosion. It cleans well a sit can stand up to steam sterilisation methods. Some medical applications include,

  1. syringes
  2. medical vials
  3. Petri dishes
  4. pill containers
  5. specimen bottles

Material properties and types of polypropylene

This versatile thermoplastic and polymer are popular due to its highly flexible properties, lighter density and ability to adapt to a range of fabrication techniques. The different variations in polypropylene have led the material to be known as the ‘steel’ of the plastic industry, as it can be used and manipulated a number of ways.

There are two main types of polypropylene thermoplastics:

  1. homopolymers
  2. copolymers

Homopolymers contain only propylene monomers in semi-crystalline form Main uses include textiles, packaging, pipes, medical components and electrical applications.

Copolymers are divided into random copolymers and block copolymers, produced by polymerising propene and ethene together. Copolymers contain higher amounts of ethylene, which result in an increase in desirable properties within the polypropylene. They are softer than homopolymers but have better impact strength.

Polypropylene can function as both a plastic and fibre type of thermoplastic. This allows for a vastly increased range of uses. It can be used as a fibre, such as in the manufacture of promotional tote bags and ‘bag for life’ shopping carriers. It is soft, malleable and has a relatively low melting point, making it very easy to be used in the injection moulding process, where it is supplied in pellets. It flows well too, due to its low melt viscosity.

Advantages to Polypropylene

Due to the fact that polypropylene adapts well to the injection moulding process, it can be used to make incredibly thin layers of plastic. It is very suited to applications such as

  • hinges on medication pots,
  • lids on shampoo bottles
  • and other containers that will be bent and manipulated a lot and mustn’t break.

Polypropylene can even withstand twisting motions of up to 360 degrees without snapping and is very hard to snap as a result. It is relatively low cost and straightforward to produce and readily available in multiple countries and communities.

High chemical and fatigue resistance add to its durability and versatility as a packaging material and option for hinges and bottle tops attached to the main bottle by a thin layer of plastic. It can offer great versatility in colour, as it can be produced as an opaque or transparent thermoplastic and used when some transfer of light is desired. Its lighter density allows it to be used in applications where weight saving has to be a key consideration.

Polypropylene is waterproof and extremely resistant to moisture absorption, which adds to its packaging benefits and flexibility as a packaging material. Its semi-crystalline nature offers high flexural strength too, making it resilient to general wear and tear and ideal for items that must undergo higher levels of physical stress. It is also resilient against mildew, mould, rot and bacteria.

Polypropylene disadvantages

One key disadvantage when it comes to the wider environment and preservation of global resources is the fact that polypropylene is not conducive to being easily recycled. When it burns, it produces a chemical change that cannot be reversed. If you tried to re-heat polypropylene that has already been melted and formed, it would simply burn, rather than liquify for a second time. Other recycling or re-conditioning methods must be considered, at a significantly higher cost.

This low melting point also means that polypropylene is highly flammable and limited in its ability to withstand higher temperatures and it is also susceptible to UV degradation and oxidation. Finally, while polypropylene’s glossy finish makes it aesthetically pleasing and easy to handle, this exact same property also makes it harder to bond to other surfaces and materials, such as paints and glues. Alternative bonding methods, such as welding must be introduced when using polypropylene to make a joint or hinge.

Is polypropylene safe?

While some potentially toxic chemicals are used in the manufacture of polypropylene, it is generally regarded as a safe finished product and is commonly used in plastic packaging that includes food and drink products and medical supplies. While it is not considered very eco-friendly, due to difficulties in the recycling process, items made from polypropylene can be re-used safely and are strong enough to resist normal wear and tear for several uses. Another point that points towards the safety of polypropylene is that the thermoplastic is frequently used to make

  • disposable cups
  • plates
  • bottles
  • cutlery
  • safely contain, package and protect hot beverages and warm foods.

What are the advantages of polypropylene?

Polypropylene Plastic Uses & Applications

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