Featured image of What is Polypropylene (PP) – Everything You Need to Know in 2019
Plastic for Pros

What is Polypropylene (PP) – Everything You Need to Know in 2019

Picture of Rocío Jaimes Gutierrez
by Rocío Jaimes Gutierrez
May 21, 2019

Polypropylene (PP) is the second-most commonly used plastic in the industry. Learn more about its properties, benefits, drawbacks, and applications.

Have you ever wondered how come your shampoo lid is so resistant to use? Chances are that it’s made from PP. PP is widely available and comparatively affordable. Its properties make it an ideal material for resistant, robust products and durable goods. These include housewares, utensils, sportswear, toys, and medical and laboratory equipment for industrial applications.

Polypropylene (PP) is the second most widely used plastic in the world. It is a thermoplastic polymer resin with a semi-crystalline structure. Given its durability and outstanding characteristics, PP has spread throughout different industries.

Given its durability and the possibility to melt and reform into plastic pellets, PP is both reusable and recyclable for producing new goods. This triggers the material’s desirability, especially for the increasing environmental concerns in the plastic industry.

1

What is Polypropylene (PP) – Everything You Need to Know What Are the Benefits?

Image of What is Polypropylene (PP) – Everything You Need to Know: What Are the Benefits?

PP is known for being a versatile and durable thermoplastic that is lightweight and extremely rugged. Depending on the polymerization process used to create it, different properties and textures can be achieved. Here are some of its benefits:

  • Tensile strength: Despite being lightweight, the material is capable of withstanding heavy loads.
  • Elasticity and toughness: PP is regarded as a tough material because it can deform without breaking. It’s also very flexible, which makes it easy to mold in different shapes and ensures that it can take significant damage prior to breaking.
  • Fatigue resistance: This property is exactly why your shampoo lid is made from PP! Polypropylene retains its shape after being bent or subjected to torsion. This makes it suitable for living hinges.
  • Water resistance: PP is highly impermeable. This property is essential for total immersion applications in medical and industrial applications.
  • Transmissivity: When having a biaxial orientation, high transmissivity can be obtained. Aesthetics or transfer of light require this property.
  • Low cost: This makes it available to a wide range of users.
  • High melting point: When compared to other plastics available in the market, PP’s high melting point makes it an excellent option for food appliances (containers, kitchen utensils) where high temperatures are required, as a well as laboratory appliances.
  • Allows for the addition of colors: This process does not degrade the properties of the plastic (dying process).
  • Biological resistance: It does not mold or deteriorate by biological factors, such as bacteria or fungi (in the short term).
  • Insulation: Given its high resistance to electricity it is commonly used in electronic components.
2

What is Polypropylene (PP) – Everything You Need to Know What Are the Drawbacks?

Image of What is Polypropylene (PP) – Everything You Need to Know: What Are the Drawbacks?

As good as it sounds, PP has a number of drawbacks:

  • Highly flammable: This material can burn easily, but there are grades that are more resistant to this.
  • UV degradation: It is prone to damage from UV light.
  • Limited high-temperature uses: Though it can handle some heat, after a certain point it gets too hot for PP. This is because it has a high-temperature expansion coefficient.
  • Poor resistance to chlorinated solvents and aromatics.
  • Poor bonding properties: This makes it difficult to paint it and also affects its adherence to certain glues that are used as a contact point.  For instance, to install furniture. However, the adhesive strength can be enhanced, which would allow the use of paints and ink.
  • Susceptible to oxidation.
3

What is Polypropylene (PP) – Everything You Need to Know Which Grades Are Available?

Image of What is Polypropylene (PP) – Everything You Need to Know: Which Grades Are Available?

There are three types of polypropylene polymers currently available on the market. Their applications and costs usually overlap:

  • Homopolymers: PPH is the most commonly used general-purpose grade. It is composed of a propylene monomer in a semi-crystalline form. Characterized by being stronger and stiffer than other grades, PPH stands out for its good chemical resistance and weldability. In addition it has a high strength-to-weight ratio, which makes homopolymers suitable for a wide range of applications, including automobile parts, electrical applications, pipes, textiles, and packaging. Melting point: 160-165 °C.
  • Block copolymers: The group incorporates 5-15% ethylene and has an improved impact resistance which extends to temperatures below -20°C. It has co-monomer units which are arranged in a regular pattern. This makes block co-polymers tougher and less brittle than random copolymers (see below). By adding impact modifiers, their toughness can be further enhanced. They are great for industrial applications with high strength. Melting point: 135-159 °C.
  • Random copolymers: The polypropylene chain molecule incorporates co-monomer units which are arranged randomly. These polymers typically contain 1-7% ethylene and are selected when a lower melting point, more flexibility, and an optically clear finish are desired.
4

What is Polypropylene (PP) – Everything You Need to Know Where is PP Used?

Image of What is Polypropylene (PP) – Everything You Need to Know: Where is PP Used?

Its unique properties make PP an excellent choice for several different industries. They include:

  • Automobile industry: PP has become an increasingly popular material for the automobile industry. Used in bumpers, cladding, interior elements, and car batteries, PP has won this industry’s trust given its resistance-to-cost balance.
  • Flexible and rigid packaging: Thanks to its superior properties and lower price, PP tends to replace cellophane, metals, and paper in its flexible form. The main sector where it can be found is in food packaging, confectioneries, and the clothing industry. As for its rigid form, PP can be found in bottles and jars for packaging condiments, detergents, other house products, thin-wall containers like those used for yogurt and disposable hot drinking cups, pallets, and other storage solutions.
  • Fashion and sports industry: Given its resistance to environmental factors, such as physical stresses (tearing and wearing), sun, mold, bacteria, and water, PP is widely used in outdoor appliances, sports-clothes equipment, undergarments, and even tote and cinch bags.
  • Toys and plastic parts: Durability is an essential factor for toys.
  • Medical applications: Due to the sterilization and transparent processes, PP has also seen a growth in the medical industry. The ability to withstand cleaning agents, disinfectants, solvents, and relatively high temperatures, together with the moderate cost, promises application in this sector for the years to come. Its applications can be subdivided into three categories: medical devices, packaging and packaging systems for solid and liquid pharmaceuticals, and other medical liquids.
  • Housewares: Are you in need of a carpet that can stand heavy traffic and keep fresh colors for years? Then, go for PP. PP can be found in carpets, mats, and rugs and can sustain a good look for longer than many of the other options.
  • Household items: Microwave containers, plates, and components of other in-house electronics are commonly produced out of PP.
5

What is Polypropylene (PP) – Everything You Need to Know Which Methods of Production Are Available?

Image of What is Polypropylene (PP) – Everything You Need to Know: Which Methods of Production Are Available?
PP machining. Source: Sentinel Plastics Limited

PP’s capacity to adapt to different production methods makes it stand out for a wide range of applications. This meant a new challenge for conventional materials. Nowadays, injection molding, packaging, and molding industries have been reshaped with the use of PP. More recently, efforts have been made to incorporate it into the 3D printing industry.

PP resins. Source: ProtoPlastics.com

Injection molding: PP is a very common injection molding material due to the easiness to mold. Its versatility allows for many different uses, despite its semi-crystalline shape. PP is commonly available in the form of pellets for this purpose. Additionally, it shows a low-rate viscosity when melted, which account for larger possibilities for shaping. Shrinking is possible, but it can be overcome by changing its production factors.

CNC PP
CNC PP. Source: fictiv.com

CNC Machinable Plastic: An interesting method for producing PP, given the possibility to prototype living hinge products. PP is widely used as sheet stock for machine manufacturing. However, given its low annealing temperature, PP is subject to deform under heat. Yet, with some skill, the material can give outstanding pieces with great detail. CNC is usually applied when a small number of PP parts are required.

3d printing PP
3D printing PP. Source: Ultimaker.com

3D printing: PP is the newest material in the Ultimaker range! Even though 3D printing it might be quite challenging, PP filament is now available in the market. Take a look at Verbatim PP 3D Filament in Amazon.

6

What is Polypropylene (PP) – Everything You Need to Know Who Invented Polypropylene?

Isostatic polypropylene was discovered by the Italian chemist Guilio Natta in 1954 while working for the Italian company Montecatini. The production of PP at room temperature and atmospheric pressure was achieved by implementing the titanium-based catalyst for polymerization, invented by the German chemist Karl Ziegler. Both chemists were awarded the Nobel Prize of Chemistry in recognition of their Ziegler-Natta catalyst. Since the 1980s the production and applications of PP have increased, thanks to more efficient catalyst types and property enhancements.

7

What is Polypropylene (PP) – Everything You Need to Know Is PP Sustainable?

Image of What is Polypropylene (PP) – Everything You Need to Know: Is PP Sustainable?

PP is 100% recyclable! (Recycling code 5.) The recycling process consists of melting the plastic at 250 °C, followed by the removal of residual molecules under vacuum to get rid of contaminants. The solidification process that follows is at 140 °C. The recycled material can then be merged with virgin PP.

In terms of sustainability and in addition to being recyclable, PP has a long-life. So instead of using daily one-use plastic, opt for a long-term solution for storing and carrying purposes. PP is environmentally friendly if used properly. However, only about 1% of the PP bottles are recycled. So, even though PP can be sustainable, the ultimate success will depend on the users’ approach towards waste disposal.

8

What is Polypropylene (PP) – Everything You Need to Know Is PP Toxic?

Image of What is Polypropylene (PP) – Everything You Need to Know: Is PP Toxic?
Source: polymers.total.com

Good news! Polypropylene is considered to be the safest plastic on the market. Given its high heat resistance, Polypropylene can be exposed to relatively high temperatures without decomposing. PP is unlikely to leach even when exposed to hot water, so it is approved for storing food and hot liquids, over and over again.

9

What is Polypropylene (PP) – Everything You Need to Know What’s the Composition and Chemical Properties of PP?

Image of What is Polypropylene (PP) – Everything You Need to Know: What’s the Composition and Chemical Properties of PP?
Structures of polypropylene. Source: MachineDesign

Polypropylene is a linear, saturated hydrocarbon polymer, whose standard chemical formula is CnH2n (see BPF). The presence of methyl groups to the alternate backbone chain of carbon atoms make it differ from polyethylene in multiple ways, for instance increasing the crystalline melting point.

Polypropylene is produced by cracking naphtha, a crude oil light distillate. As well as higher alkanes, it is separated by low-temperature fractional distillation. Its production takes place in a solution or gas phase process, where the monomer is exposed to heat and pressure under the effect of a catalyst system (accelerating or triggering the process). This process is conducted under low temperature and pressure conditions, and varying the production conditions can also alter the plastic’s properties.

The table below indicates the level of resistance PP has to various chemicals.

Polypropylene chemical resistance
10

What is Polypropylene (PP) – Everything You Need to Know What Mechanical and Physical Properties Does PP Have?

Image of What is Polypropylene (PP) – Everything You Need to Know: What Mechanical and Physical Properties Does PP Have?

Polypropylene is known for being a versatile, durable, light-weight and extremely rugged thermoplastic. Depending on the polymerization process used to create it, different properties and textures can be achieved.

When having a biaxial orientation, its mechanical strength, impact, and optical properties can be enhanced. Additionally, a biaxial orientation helps in overcoming weakness in the transverse plane (Ajji, 1999).
PP can be used either as a molded plastic or as a fiber, tolerating anything between 160 to 320°C without melting. Some of its main characteristics include:

polypropylene physica properties
11

What is Polypropylene (PP) – Everything You Need to Know Where Can I Get PP?

Image of What is Polypropylene (PP) – Everything You Need to Know: Where Can I Get PP?
Source: First Impressions

PP is available from a large range of manufacturers, suppliers, and distributors around the globe. However, you can also purchase it on Amazon and other online retailers like GearBest, BangGood and AliExpress.

12

What is Polypropylene (PP) – Everything You Need to Know How to 3D Print With It

Image of What is Polypropylene (PP) – Everything You Need to Know: How to 3D Print With It
PP filament. Source: Amazon.com

Polypropylene is readily available in filament to 3D print!

Polypropylene Filament

Product image of Polypropylene Filament

When 3D printing PP, keep in mind there will be difficulties that are intrinsic to its properties. Its semi-crystalline structure causes the 3D print parts to heavily warp, which makes it a challenging material to 3D print . Varying the extrusion temperatures can result in different properties in the 3D printed part. For instance, increasing the temperature can help layer adhesion, resulting in stronger parts.

For successful prints, the cheapest and easiest solution that tackles warping would be to use polypropylene tape on the build plate. This would ensure better adhesion. Different brands might give slightly different results.

Also, ensure to have the proper nozzle (230-260 °C) and plate (85-100 °C) temperatures. Note that some 3D printers might not be designed to have temperatures rounding 260 °C, which may result in parts of your 3D printer melting (definitely not desired). Consider using our professional 3D printing service. Craftcloud - 3D Printing & Price Comparison Service by All3DP

Bear in mind that even though PP is food safe and non-toxic, the 3D printing process in not. Additionally, the infill might potentially host microbial growth. As for available colors, options are more restricted than other materials, given that polypropylene has had 3D printing filaments in the market for a very short time. This also means that it’s more expensive than other 3D printable plastics, such as PLA or ABS.

License: The text of "What is Polypropylene (PP) – Everything You Need to Know in 2019" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.

Subscribe to updates from All3DP

You are subscribed to updates from All3DP

You can’t subscribe to updates from All3DP. Learn more… Subscribe

You can’t subscribe to updates from All3DP. Learn more…

Recommended for you