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.
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:
As good as it sounds, PP has a number of drawbacks:
There are three types of polypropylene polymers currently available on the market. Their applications and costs usually overlap:
Its unique properties make PP an excellent choice for several different industries. They include:
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.
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 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 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 at Amazon.
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.
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.
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.
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 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 is readily available in filament to 3D print!
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.
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