What is Polypropylene (PP) and How is it Used?

Polypropylene (PP) is a thermoplastic “addition polymer” composed of propylene monomers. It is utilized in a wide range of applications, including consumer product packaging, plastic components for different sectors, including the automotive industry, unique devices such as live hinges, and textiles.

Polypropylene was originally polymerized in 1951 by Paul Hogan and Robert Banks of Phillips Petroleum, and subsequently by Natta and Rehn of Italy and Germany. It rose to prominence quickly, as commercial production began only three years after it was first polymerized by Italian scientist Professor Giulio Natta.

In 1954, Natta developed and synthesized the first polypropylene resin in Spain, and the capacity of polypropylene to crystallize sparked great interest. By 1957, its popularity had skyrocketed, and massive commercial manufacturing had begun across Europe. It is now one of the most widely manufactured polymers on the planet.

Child-Safe Lid with CNC Cut Polypropylene Living Hinge Prototype

Creative Mechanisms: CNC Cut Polypropylene Living Hinge Prototype Child Safe Lid

According to some estimations, the present worldwide demand for the material creates an annual market of roughly 45 million metric tons, with demand expected to increase to approximately 62 million metric tons by 2020.

The packaging sector utilizes over 30% of global polypropylene use, followed by electrical and equipment production, which consume approximately 13% each. Household appliances and the automobile industry each account for 10% of the market, with building materials accounting for 5%.

Other uses account for the remainder of worldwide polypropylene usage.

Polypropylene has a moderately slippery surface, making it a potential replacement for plastics such as Acetal (POM) in low-friction applications such as gears or as a contact point for furniture.

One disadvantage of this property is that it might be difficult to attach polypropylene to other surfaces (i.e., it does not adhere well to certain glues that work fine with other plastics and sometimes has to be welded in the event that forming a joint is required).

Although polypropylene is a molecularly slippery material, it has a relatively high coefficient of friction, which is why acetal, nylon, or PTFE would be employed instead. Polypropylene has a low density compared to other popular polymers, which means weight savings for producers and distributors of injection molded polypropylene products.

It possesses excellent resistance to organic solvents such as lipids at ambient temperature but is susceptible to oxidation at higher temperatures (a potential issue during injection molding).

One of the most significant advantages of polypropylene is that it may be made into a live hinge (through CNC or injection molding, thermoforming, or crimping). Living hinges are incredibly tiny plastic bits that can bend without breaking (even over extreme ranges of motion approaching 360 degrees).

They are not especially effective for structural purposes, such as holding up a hefty door, but they are extremely beneficial for non-load-bearing applications, such as ketchup or shampoo bottle lids. Polypropylene is ideal for living hinges since it does not break when bent repeatedly.

Another benefit is that polypropylene can be CNC machined to contain a live hinge, allowing for quicker prototype creation and lower costs than alternative prototyping techniques. Our ability to fabricate live hinges from a single piece of polypropylene distinguishes Creative Mechanisms.

Polypropylene also has the benefit of being readily copolymerized (basically mixed into a composite plastic) with other polymers such as polyethylene. Material characteristics considerably alter the material properties, enabling more robust engineering applications than would be achievable with pure polypropylene (more of a commodity plastic on its own).

Polypropylene is utilized in a multitude of applications because of the properties listed above and below, including dishwashing-safe plates, trays, cups, etc., opaque to-go containers, and various toys.

What are the polypropylene characteristics?

The following are some of the most important features of polypropylene:

Chemical Resistance: Because diluted bases and acids do not react quickly with polypropylene, it is an excellent option for containers containing such liquids as cleaning solutions, first-aid supplies, and more.

Polypropylene exhibits elasticity throughout a particular range of deflection (as do all materials), but it also exhibits plastic deformation early in the deformation process, making it a “tough” material. Toughness is an engineering term that refers to a material’s capacity to flex (plastically rather than elastically) without breaking.

Fatigue Resistance: Polypropylene maintains its form even after extensive twisting, bending, and/or flexing. This characteristic is extremely useful for creating living hinges.

Insulation: Polypropylene has high electrical resistance and is ideal for electronic components.

Although polypropylene may be made transparent, it is often manufactured to be naturally opaque in color. Polypropylene may be utilized in situations where light transmission is critical or where aesthetic value is desired. Plastics with high transmissivity, such as acrylic or polycarbonate, are preferable candidates.

Polypropylene is a “thermoplastic” (as opposed to a “thermoset”) substance, which refers to how the plastic reacts to heat. At their melting point, thermoplastic materials become liquid (roughly 130 degrees Celsius in the case of polypropylene).

The ability of thermoplastics to be heated to their melting point, chilled, and reheated without substantial deterioration is a key advantage. Instead of burning, thermoplastics such as polypropylene liquefy, allowing them to be readily injection molded and then recycled. pp granules manufacturers india

Thermoset polymers, on the other hand, can only be heated once (typically during the injection molding process). The initial heating causes thermoset materials to set (similar to a 2-part epoxy), resulting in an irreversible chemical change. A thermoset material would simply burn if heated to a high temperature a second time. Because of this property, thermoset materials are poor choices for recycling. hdpe granules traders india

Locate the Best Plastic for Your Prototype Part

Why is polypropylene so widely used?

Polypropylene is utilized in both residential and industrial settings. Its distinct characteristics and flexibility to adapt to diverse production procedures distinguish it as a desirable material for a broad variety of applications.

Another significant property is polypropylene’s capacity to behave as both a plastic and a fiber (like those promotional tote bags that are given away at events, races, etc.).

Polypropylene’s unique capacity to be made in a variety of ways and for a variety of uses meant that it quickly began to challenge many of the traditional alternative materials, particularly in the packaging, fiber, and injection molding sectors. Its expansion has continued throughout the years, and it is now a prominent participant in the global plastics business.

Polypropylene has been employed in a variety of applications at Creative Mechanisms throughout a wide range of industries. The ability to CNC manufacture polypropylene to incorporate a live hinge for prototype living hinge development is maybe the most intriguing example.

Polypropylene is a soft, flexible substance with a low melting point. Most individuals have been unable to adequately manufacture the material due to these problems. It clogs. It’s not a clear-cut case. It begins to melt as a result of the CNC cutter’s heat. To acquire anything like a completed surface, it is usually necessary to scrape it smooth.

However, we were able to tackle this issue, allowing us to construct new prototype live hinges out of polypropylene. Check out the video below:

What Are the Different Polypropylene Types?

Polypropylene is classified into two types: homopolymers and copolymers. Copolymers are further classified as “block copolymers” or “random copolymers.”

Each group is more suited to certain applications than the others. Polypropylene is sometimes referred to as the “steel” of the plastics industry due to the many ways in which it can be changed or altered to better suit a certain purpose.

This is generally accomplished by adding specific ingredients to it or producing it in a unique method. This versatility is essential.

Polypropylene homopolymer is a general-purpose grade. Consider this to be the polypropylene material’s default condition. Polypropylene block copolymer includes co-monomer units organized in blocks (that is, in a regular pattern) and contains anywhere from 5% to 15% ethylene.

Ethylene increases some qualities, like impact resistance, whereas other additions improve others.

In contrast to block copolymer polypropylene, the co-monomer units in random copolymer polypropylene are placed in irregular or random patterns along the polypropylene molecule.

They are often combined with anywhere from 1% to 7% ethylene and are used for applications requiring a more flexible, clearer result.

How is polypropylene manufactured?

Polypropylene, like other plastics, is primarily made by distilling hydrocarbon fuels into lighter groups known as “fractions.” Some of these are then mixed with other catalysts to create polymers (typically via polymerization or polycondensation).

Rapid Prototyping with Polypropylene on CNC Machines, 3D Printers, and Injection Molding Machines:

3D Model PrintingPolypropylene:

Polypropylene filament for 3D printing is not widely accessible.

Machining using CNC Polypropylene: Polypropylene is commonly utilized as sheet stock in the manufacture of CNC machines. We normally CNC make a limited number of polypropylene pieces while prototyping them.

Polypropylene has a reputation for being a difficult material to machine. This is due to its low annealing temperature, which causes it to deform when heated. Because it is a very delicate substance in general, accurate cutting needs an extraordinarily high degree of ability. Creative Mechanisms was successful in its endeavor.

Our staff may utilize a CNC machine to cut the polypropylene neatly and precisely. Furthermore, we can make living hinges out of polypropylene with a thickness of as small as.010 inch. Making live hinges is a challenging task in and of itself, which makes the use of a problematic material like polypropylene all the more astounding.

Polypropylene injection molding: Polypropylene is a highly useful material for injection molding and is normally supplied in the form of pellets. Despite its semi-crystalline form, polypropylene is simple to shape and flows nicely because of its low melt viscosity.

This feature considerably increases the pace at which the material can be filled into a mold. Polypropylene shrinkage is typically 1-2 percent, but it may vary depending on a variety of parameters such as holding pressure, holding duration, melt temperature, mold wall thickness, mold temperature, and the proportion and kind of additives.


Polypropylene, in addition to its normal plastic uses, lends itself well to fiber applications. This broadens its range of applications beyond injection molding. Ropes, carpets, furniture, apparel, and other similar items fall under this category.

Applications for Polypropylene Fiber: Rope

Image courtesy of Animated Knots.com

What are the pros and cons of polypropylene?

Polypropylene is widely accessible and reasonably priced.

Because of its semi-crystalline structure, polypropylene has a high flexural strength.

The surface of polypropylene is quite slick.

Polypropylene is very resistant to moisture absorption.

Polypropylene is chemically resistant to a broad variety of bases and acids.

Polypropylene has high fatigue resistance.

The impact strength of polypropylene is high.

Polypropylene has a high electrical insulating capacity.

What are the drawbacks to polypropylene?

Polypropylene has a high thermal expansion coefficient, limiting its use in high-temperature applications.

UV deterioration is a risk with polypropylene.

Polypropylene is sensitive to chlorinated and aromatic solvents.

Polypropylene is notorious for being difficult to paint due to its weak bonding qualities.

Polypropylene is a very flammable material.

Polypropylene is prone to oxidation.

Despite its flaws, polypropylene is an excellent material in general. It possesses a distinct set of properties that are not found in any other material, making it an excellent option for a variety of tasks.

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