polypropylenetypes

What Is Polypropylene?

 

Polypropylene is a term used to describe any textile product that is derived from the thermoplastic polymer polypropylene. This type of plastic is part of the polyolefin group, and it is non-polar and partially crystalline. Next to polyethylene, polypropylene is the second-most commonly produced plastic in the world, and it is more commonly used in packaging, straws, and other types of consumer and industrial goods than it is in textile production.

This type of plastic was originally developed by the American corporation Phillips Petroleum in 1951. Chemists Robert Banks and J. Paul Hogan were attempting to derive gasoline from propylene, and they accidentally created polypropylene. While this experiment was deemed a failure, it was quickly recognized that this new compound has the potential to be on par with polyethylene in many applications.

It wasn’t until 1957, however, that polypropylene was made into a substance suitable for mass production. In 1954, the Italian chemist Giulio Natta and his German colleague succeeded in forming this substance into an isotactic polymer, and the Italian corporation Montecatini quickly started producing this substance for commercial and consumer use.

Polypropylene was originally marketed under the name “Moplen,” and this name is still a registered trademark of the LyondellBasell corporation. However, it is much more common to find this substance referred to as polypropylene or “polypro” for short.

Deckchair with canopy and sling in Polypropylene in dove grey

As the use of polypropylene became more and more popular in a number of consumer and industrial applications, it was gradually discovered that this type of plastic also showed potential as a textile. Polypropylene is a nonwoven textile, which means that it is made directly from a material without any need for spinning of weaving. The main benefit of polypropylene as a fabric is its moisture transfer abilities; this textile cannot absorb any moisture, and instead, moisture passes through Polypropylene entirely.

This attribute allows moisture that is exuded while wearing a polypropylene garment to evaporate much more quickly than it would with a moisture-retaining garment. Therefore, this fabric is popular in textiles that are worn close to the skin. However, polypro has a tendency to absorb and retain body odors when it is used for undergarments, and it also melts at relatively low temperatures. Molten polypro fabric can cause serious burns, and this issue also makes it impossible to wash this fabric at high temperatures.

Polypropylene is one of the lightest synthetic fibers in existence, and it is incredibly resistant to most acids and alkalis. In addition, the thermal conductivity of this substance is lower than that of most synthetic fibers, which means that it is ideally suited for cold weather wear.

Beige and White Basket Woven Polypropylene Upholstery Fabric
Beige and White Basket Woven Polypropylene Upholstery Fabric

Furthermore, this fabric is highly resistant to abrasion, and it also resists insects and other pests. Due to its notable thermoplastic qualities, it’s easy to mold polypro plastic into various shapes and forms, and it can be reformed through melting. This plastic is also not very susceptible to stress cracking.

However, polypro is notoriously hard to dye after it is manufactured, and it is also difficult to shape this fabric into different textures. This fabric is susceptible to UV damage, and it does not adhere well to latex or epoxies. Like every other synthetic textile, Polypropylene also has a significantly negative impact on the environment.

Types of Polypropylene

Polypropylene can be produced flexibly to suit certain applications: the main forms on the market are homopolymersblock copolymers and random copolymers.

Here is an overview of materials for polypropylene describing certain aspects of each type of polymer or polymer combination.

Material Description and benefits
PP homopolymer It is the most common general-purpose grade of PP. It is semi-crystalline, solid, contains only PP monomers, and is suitable for a wide variety of applications, from plastic packaging to automotive and healthcare.
PP block copolymer Ethylene-containing co-monomers (5 – 15% ethylene) are positioned in regular patterns called blocks. It is a tough and strong material with high impact resistance, suitable for industrial high-strength applications.
PP random copolymer Ethylene-containing co-monomers (1 – 7% ethylene) are positioned in irregular patterns throughout the PP molecule. It has high flexibility and optical clarity, suitable for applications with optical transparency and good appearance requirements.
PP impact copolymer It is a PP homopolymer with a co-mixed PP random copolymer phase, containing between 45 – 65% ethylene. With its high impact resistance, it is suitable for packaging, pipe and automotive applications.
PP terpolymer It is a combination of propylene segments and randomly positioned monomers of ethylene and butane. It has high optical transparency and low crystalline uniformity and is a suitable material for sealing film applications.
PP high melt strength (HMS PP) A long chain branched PP that has both high melt strength and stretchability. This polymer has a wide range of mechanical properties and high thermal and chemical properties, making it suitable to be used as low-density foams for various applications.
Expanded polypropylene (EPP) It is a greatly versatile closed-cell bead foam with low density. It exhibits distinctive properties, such as high impact resistance, energy absorption, thermal insulation, and high strength-to-weight ratio. It is also used in many industries, such as automobiles, construction, and packaging.

Polypropylene Production and Processing

The two most common ways to make polypropylene are bulk slurry or gas phase production. In both cases, propylene, the monomer, is exposed to pressure, high temperatures and a catalyst.

Bulk slurry processing facilitates polymerisation by adding liquid propylene to the reactor. This method produces homopolymers and block copolymers successfully.

For gas-phase processing, gaseous propylene is placed with a solid catalyst inside a loop reactor, producing a fluidized bed. Random copolymers require the use of a gas phase reactor.

As a highly versatile polymer, polypropylene can adapt to various production methods. These include injection moulding, blow moulding, extrusion, and general-purpose extrusion. Some manufacturers are pushing to optimise or blend PP to be able to use it in additive manufacturing. The challenge lies in its semi-crystalline structure and severe warping.

 

Application in 3D Pringting

 

As a tough, fatigue-resistant, and durable polymer, PP is ideal for low-strength applications. It is currently difficult to use PP for 3D Printing processes due to its:

semi-crystalline structure and
heavy warping

Several manufacturers have optimized PP properties or even created blends with improved toughness. This makes it suitable for 3D Printing applications. Hence, it is recommended to thoroughly refer to the documentation provided by the supplier for printing temperature, printing bed, etc.

Polypropylene is suitable for:
Complex models
Prototypes
Small series of components, and
Functional models

Discover other processing methods for PP
Browse injection blow molding PP grades Browse injection stretch blow molding PP grades Browse extrusion blow molding PP grades
Browse compression molding PP grades
Browse thermoforming PP grades
Browse rotational molding PP grades
Some grades are designed for your specific conversion mode like blow molding, compression molding, thermoforming, etc. Check out PP grades with various conversion modes here »

TIP: To meet specific requirements, try using the “Conversion mode” facet to narrow down your search.

Sustainability Aspect of PP

PP is 100% recyclable

All plastics have a ‘Resin Identification Code/ Plastic Recycling Code’ based on the type of resin used. PP’s resin identification code is 5. PP is 100% recyclable. View recyclable PP grades in our database.

Polypropylene recycling process

The PP recycling process includes:

Melting waste plastic to 250°C to get rid of contaminants.
Removal of residual molecules under vacuum and solidification at approximately 140°C.

This recycled PP can be blended with virgin PP at a rate of 50%.

PP recycling – The main challenge

The main challenge in PP recycling is related to the amount consumed. Currently, 1% of PP bottles are recycled as compared to the 98% recycling rate of PET & HDPE bottles together.

Uses of recycled polypropylene (rPP)

A few applications of rPP include:

Automobile battery cases,
Signal lights,
Battery cables,
Brooms,
Brushes,
Ice scrapers, etc.

 

How does PP challenge polyethylene terephthalate?

In blow-molded bottle applications, PP has emerged as a strong competitor to PET. Compared to PET, the key features of PP include:

Less expensive,
Lighter in weight,
More resistant to the high temperatures of hot filling, and
Less permeable to moisture.

PP bottles can be hot-filled at temperatures up to 100°C. While PET cannot withstand filling temperatures above 76°C.

In its pure state, PP is less clear than PET. Also, the gas barrier properties of PP are not as high as PET, and PP also falls below PET in stiffness. PP has about five times the moisture barrier properties of PET. But PP is about 30 times more permeable than PET to gases such as oxygen and carbon dioxide.

The production cycles of PP bottles have generally been longer than PET bottles. PP also has a narrower range of processing temperatures than PET.

But producers of PP resins and the additives that go into them are making important strides in overcoming these deficits, such as:

Inserting clarifiers into PP enables it to match PET’s transparency. Clarified grades of PP have a clarity and gloss comparable to PET.

Nucleators can speed up crystal formation in PP during cooling. This thereby shortens cycle times, and sometimes also improves clarity as well. Explore several nucleated PP grades here »

Barrier layers (EVOH sandwich, coatings, etc.) enable PP to compete on a cost basis with both glass and PET containers in many food and beverage applications while offering good barrier properties.

The above steps make PP competitive with PET and can narrow that cost advantage considerably. But PP still comes out as the more economical packaging choice than PET for many applications.

Get a comprehensive review about PET before you make the final decision on the material of your choice »

How is nylon different from PP?

Nylon and polypropylene vary in their chemical structures. Both these polymers offer superior strength to the final parts. There are some significant distinctions you should consider when choosing any of them.

The key benefit of PP is its low melt viscosity, and it offers strength and elasticity. A low melt viscosity enables materials to be easily used in injection molding. It also opens more opportunities and capabilities.
While Nylon is more heat-resistant and malleable than PP. It can offer designers greater design flexibility i.e., easy bending than breaking.

From the end application perspective, both polymers have poor UV stability performance. They require suitable additives to mitigate UV damage risk.


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