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When to use polypropylene

Polypropylene is very young, but its history is characterized by explosive growth. J. Paul Hogan and Robert Banks first polymerized this plastic in 1951, and three years later Giulio Natta and Karl Rehn polymerized this material into a crystalline isotactic polymer. This pioneering discovery propelled polypropylene into large-scale commercial production by 1957, and it’s now the second most popular and most profitable plastic in the manufacturing industry.

According to recent research, the global market for polypropylene was worth about $126.03 billion in 2019, and the current demand for this plastic is close to 62 million tons annually. What’s more, polypropylene sales are expected to grow 5.8% per year through 2021. This incredibly popular and versatile material can be found in many consumer products, from carpeting to activewear to medical laboratory equipment.

What is polypropylene? How is it made? Get to know everything about one of the most popular plastics in the manufacturing industry today, from chemical properties to when to use it.

What is polypropylene?

Polypropylene is a thermoplastic polymer resin that’s made from chain-growth polymerization from the monomer propylene. This material is often dubbed an “addition” polymer because it is easily copolymerized, meaning it can be easily combined with other composite plastics or polymers like polyethylene. Copolymerization changes the plastic’s materials properties slightly to expand its engineering applications.

The two main types of polypropylene are homopolymers and copolymers, and copolymers can be further divided into block copolymers and random copolymers. Homopolymer polypropylene is the all-purpose polypropylene and the variety most commonly used. Block copolymer polypropylene’s co-monomer units are arranged in a regular pattern and comprised of between five to 15% ethylene, which makes the material more impact resistant.

In contrast, random copolymer polypropylene’s co-monomer units are arranged in an irregular pattern and are compromised of only one to seven% ethylene, which makes it more suitable for use-cases where a more malleable product is required.

Polypropylene’s adaptability, strength, and versatility have made it a favorite among manufacturers and a major player in this rapidly changing industry. Common applications include ropes, upholstery, car batteries, packaging, car dashboards, and reusable containers. Polypropylene is also one of the few manufacturing materials that can function as both a plastic material and a fiber.

In fact, polypropylene is frequently found in thermoplastic fiber-reinforced composites. Polypropylene is very well-suited for injection molding — polypropylene pellets are remarkably fast and easy to mold because of its low melt viscosity. Polypropylene can be used with CNC machining as well, as long as the engineer has high-quality equipment that ensures the material doesn’t gum up or melt from the heat of the CNC cutter.

Chemical and mechanical properties

Polypropylene is often called the “steel” of the plastic industry because it’s an exceptionally tough material. It’s resistant to sun, mold, rot, bacteria, oils, solvents, water, and high levels of physical stress, all while remaining lightweight and flexible. Polypropylene is very elastic and deforms without breaking under a lot of bending or flexing, making it particularly useful for creating living hinges. Polypropylene can be found in many electrical components because it’s waterproof and highly resistant to electricity.

From a design standpoint, many project managers prefer to work with polypropylene because it can easily be made transparent even though it’s normally opaque upon production. For applications where some light transfer is important or will add to the aesthetic value of the product, polypropylene is an excellent choice.

Advantages and disadvantages of polypropylene

Polypropylene’s excellent chemical and mechanical properties make it very popular among engineers. It’s readily available, inexpensive to manufacture with, and the newer versions of polypropylene have a rubber-like composition that can be used for even more innovative use-cases. Polypropylene is also easily recyclable and a good alternative to BPA packaging.

However, polypropylene does have its drawbacks. For example, this material’s high flammability and high thermal expansion coefficient limit its high-temperature applications. It is also at risk of oxidation, UV degradation, and chlorinated solvents. Further, designers should note that polypropylene can be difficult to paint because it has a slippery surface that is difficult to bond with other materials.

Get started with Fast Radius

These pain points notwithstanding, polypropylene is a material that every manufacturer should have in their repertoire. It’s durable, cost-effective, and its excellent chemical and mechanical properties make it applicable to a wide variety of use-cases. Connecting with an experienced manufacturing partner can help you make the most of this material.

If you’re interested in using polypropylene for your next project, the Fast Radius team is happy to lend a hand. Our project designers and engineers have years of industry experience working with this material and hundreds of others. We’ll be able to guide you through the entire manufacturing process, from design and prototyping to fulfillment, and offer key considerations for optimizing your part along the way. Contact us today for a quote.

To learn more about manufacturing materials, check out the related blog articles in the Fast Radius resource center.

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