What is polypropylene?

Do you know that in 1954, German and Italian chemists Karl Rehn and Giulio Natta first polymerized polypropylene to create a crystalline isotactic polymer? However, manufacturing of polypropylene on a large scale began in 1957 after its discovery.

Propylene serves as the polymer’s monomer in polypropylene (PP) (an organic hydrocarbon with the chemical formula C3H6). (C3H6)n is the chemical formula for polypropylene. Normally, a chain-growth polymerization procedure having propylene is used to create polypropylene. This material can also be remoulded since it is a thermoplastic polymer, which softens when heated. Additionally, it should be noted that polypropylene has a partly crystalline structure and is non-polar.

Types of polypropylene

You will find two main types of Polypropylene thermoplastics: 

  • Polypropylene copolymers 
  • Polypropylene homopolymers.

Only semi-crystalline propylene monomers are found in homopolymers. The most common applications of homopolymers are in textiles, packaging, pipelines, medical equipment, and electrical devices.

When propene and ethene are polymerized, two types of copolymers are created: random and block copolymers. The polypropylene in copolymers has more desired characteristics because of the greater ethylene content. They have greater impact strength but are softer than homopolymers.

Key characteristics of polypropylene

The main traits shared by practically all varieties of polypropylene are: 

  • It has a great melting point, which makes it a popular material for microwave containers. 
  • It won’t degrade readily since it doesn’t react with water, detergents, acids, or bases.
  • Even when bent, it resists tension and fracture.
  • Because of its great durability, it can resist normal use.
  • Polypropylene is a substance that burns easily.
  • It is vulnerable to microbial assaults from things like bacteria and mould.

What is polypropylene used for?

Do you know polypropylene is used in various industries; some of them are as follows:

Packaging Industry:

Polypropylene is used to make Pallets, bottles, jars, yoghurt containers, hot beverage cups, food packaging, and other items.

Industrial Applications:

It is useful for returnable transport packaging (RTP), chemical tanks, sheets, pipes, etc.

Medical Applications:

You can use polypropylene for making disposable syringes, meal trays, pans, intravenous bottles, specimen bottles, Petri dishes, diagnostic tools, and other items.

Consumer Products:

It is used for making products like transparent components, household goods, furniture, electronics, bags, toys, and more.

Automotive Applications:

It can also be found in door trims, instrument panels, interior trim, bumpers, fender liners, battery cases, and trays.

Fibres and Fabrics:

Raffia/slit-film, tape, strapping, bulk continuous filament, staple fibres, spun bond, and continuous filament are examples of polypropylene used in the fabric industry.

Frequently Asked Questions on Polypropylene

Here are some frequently asked questions about polypropylene.


1. How can you increase the surface energy of polypropylene?

Because it has a high percentage of C-H bonds, polypropylene has a low energy surface. None of the atoms near the surface has lone pairs that may interact with external dipoles, and these have no visible dipole moment.

In order to form polar C-O-H groups, the surface energy is often increased by oxidizing it. Because the surface is often static, it is challenging to achieve this chemically. Instead, the surface is often etched using oxygen plasma. Although the essential tools seem complex, they are surprisingly simple and generally accessible.


2. What does a low surface energy mean?

The surplus interaction energy at a substrate’s surface is referred to as surface energy. Depending on their chemical composition, surfaces have a range of energies from high to low, which impacts the molecular force of attraction. A strong molecular attraction indicates high surface energy (HSE), which makes bonding easier. A weak molecular attraction indicates low surface energy (LSE), making bonding more difficult.


3. How do they increase surface activity?

There are generally two ways to increase the surface energy:

4. Is polypropylene low surface energy?

Yes! Polypropylene and polyethylene often have low surface energies.

5. Best practice for bonding low surface energy plastic

Low surface energy polymers needed these types of treatments:

  • Abrasion
  • Flame treatment
  • Coronary Discharge Therapy (CDT)
  • Surface Plasma Treatment
  • Chemical Remediation 
  • Before bonding, use primers or adhesion promoters.

Flame treatment of polypropylene

Do you know that flame treatment is the process of applying a gas flame to a material’s surface in order to increase adhesion? Since polyethylene and polypropylene have weak bonds, coatings like glue and ink cannot be applied to them without a particular process. Polar functional groups are introduced, and molecular chains are disrupted by rapidly applying high temperatures to a surface.

How do you flame treat polypropylene?

Numerous gas jets (propane torches) are arranged in a continuous row on a single burner to treat a surface quickly. Simply oxidizing the plastic’s top layer invisible will make it more “hydrophilic” and improve its connection ability.

The treated material is quickly passed in front of or beneath the inner cones. Less than a second passes when the surface is in contact with the flame. The surface is treated immediately before the material has a chance to melt.

The reactive chemical species break long-chain molecules in the plastic material in the gas flame and connect to the break sites to form polar point charges on the surface. The surface also grows rougher, and the adhesion level rises to a microscopic level.

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