100% Virgin PP Resin/Polypropylene CAS No.9003-07-0 CAS NO.9003-07-0

Polypropylene, a synthetic resin built up by the polymerization of propylene. One of the important family of polyolefin resins, polypropylene is molded or extruded into many plastic products in which toughness, flexibility, light weight, and heat resistance are required. It is also spun into fibres for employment in industrial and household textiles. Propylene can also be polymerized with ethylene to produce an elastic ethylene-propylene copolymer.

The chemical structure of the propylene molecule is CH₂=CHCH₃. Under the action of polymerization catalysts, however, the double bond can be broken and thousands of propylene molecules linked together to form a chainlike polymer (a large, multiple-unit molecule). In such a molecule each propylene repeating unit has the following structure:.

What Are The Different Types of Polypropylene

There are two main types of polypropylene available: homopolymers and copolymers. The copolymers are further divided into block copolymers and random copolymers.

Each category fits certain applications better than the others. Polypropylene is often called the “steel” of the plastic industry because of the various ways in which it can be modified or customized to best serve a particular purpose.

This is usually achieved by introducing special additives to it or by manufacturing it in a very particular way. This adaptability is a vital property.

Homopolymer polypropylene is a general-purpose grade. You can think of this like the default state of the polypropylene material. Block copolymer polypropylene has co-monomer units arranged in blocks (that is, in a regular pattern) and contain anywhere between 5% to 15% ethylene.

Ethylene improves certain properties, like impact resistance while other additives enhance other properties.

Random copolymer polypropylene – as opposed to block copolymer polypropylene – has the co-monomer units arranged in irregular or random patterns along the polypropylene molecule.

They are usually incorporated with anywhere between 1% to 7% ethylene and are selected for applications where a more malleable, clearer product is desired.

Why is Polypropylene used so often

Polypropylene is used in both household and industrial applications. Its unique properties and ability to adapt to various fabrication techniques make it stand out as an invaluable material for a wide range of uses.

Another invaluable characteristic is polypropylene’s ability to function as both a plastic material and as a fiber (like those promotional tote bags that are given away at events, races, etc).

Polypropylene’s unique ability to be manufactured through different methods and into different applications meant it soon started to challenge many of the old alternative materials, notably in the packaging, fiber, and injection molding industries. Its growth has been sustained over the years and it remains a major player in the plastic industry worldwide.

At Creative Mechanisms, we have used polypropylene in a number of applications across a range of industries. Perhaps the most interesting example includes our ability to CNC machine polypropylene to include a living hinge for prototype living hinge development.

Polypropylene is a very flexible, soft material with a relatively low melting point. These factors have prevented most people from being able to properly machine the material. It gums up. It doesn’t cut clean. It starts to melt from the heat of the CNC cutter. It typically needs to be scraped smooth to get anything close to a finished surface.

But we have been able to solve this problem which allows us to create novel prototype living hinges out of polypropylene. Take a look at the video below:

How is Polypropylene made

Polypropylene, like other plastics, typically starts with the distillation of hydrocarbon fuels into lighter groups called “fractions” some of which are combined with other catalysts to produce plastics (typically via polymerization or polycondensation).

Polypropylene for Prototype Development on CNC Machines, 3D Printers, & Injection Molding Machines:

3D Printing Polypropylene:

Polypropylene is not readily available in filament form for 3D printing.

CNC Machining Polypropylene:

Polypropylene is widely used as sheet stock for CNC machine manufacturing. When we prototype a small number of polypropylene parts we typically CNC machine them.

Polypropylene has gained a reputation as a material that cannot be machined. This is because it has a low annealing temperature, which means that it starts to deform under heat. Because it is a very soft material in general, it requires an extremely high skill level to be cut with precision. Creative Mechanisms has been successful in doing so.

Our teams can use a CNC machine and cut the polypropylene cleanly and with extremely great detail. In addition, we are able to create living hinges with polypropylene that have thickness as little as .010 inches. Making living hinges is a difficult endeavor on its own, which makes using a difficult material like polypropylene even more impressive.

Injection Molding Polypropylene:

Polypropylene is a very useful plastic for injection molding and is typically available for this purpose in the form of pellets. Polypropylene is easy to mold despite its semi-crystalline nature, and it flows very well because of its low melt viscosity.

This property significantly enhances the rate at which you can fill up a mold with the material. Shrinkage in polypropylene is about 1-2% but can vary based on a number of factors, including holding pressure, holding time, melt temperature, mold wall thickness, mold temperature, and the percentage and type of additives.

Other:

In addition to the conventional plastic applications, polypropylene also lends itself well to fiber applications. This gives it an even wider range of uses that go beyond just injection molding. Those include ropes, carpets, upholstery, clothing, and the like.

What are the Characteristics of Polypropylene

Some of the most significant properties of polypropylene are:

1. Chemical Resistance: Diluted bases and acids don’t react readily with polypropylene, which makes it a good choice for containers of such liquids, such as cleaning agents, first-aid products, and more.  
2. Elasticity and Toughness: Polypropylene will act with elasticity over a certain range of deflection (like all materials), but it will also experience plastic deformation early on in the deformation process, so it is generally considered a "tough" material. Toughness is an engineering term that is defined as a material's ability to deform (plastically, not elastically) without breaking.
3. Fatigue Resistance: Polypropylene retains its shape after a lot of torsions, bending, and/or flexing. This property is especially valuable for making living hinges.
4. Insulation: polypropylene has a very high resistance to electricity and is very useful for electronic components.
5. Transmissivity: Although Polypropylene can be made transparent, it is normally produced to be naturally opaque in color. Polypropylene can be used for applications where some transfer of light is important or where it is of aesthetic value. If high transmissivity is desired then plastics like Acrylic or Polycarbonate are better choices.

Polypropylene is classified as a “thermoplastic” (as opposed to “thermoset”) material which has to do with the way the plastic responds to heat. Thermoplastic materials become liquid at their melting point (roughly 130 degrees Celsius in the case of polypropylene).

A major useful attribute about thermoplastics is that they can be heated to their melting point, cooled, and reheated again without significant degradation. Instead of burning, thermoplastics like polypropylene liquefy, allow them to be easily injection molded and then subsequently recycled.

By contrast, thermoset plastics can only be heated once (typically during the injection molding process). The first heating causes thermoset materials to set (similar to a 2-part epoxy) resulting in a chemical change that cannot be reversed. If you tried to heat a thermoset plastic to a high temperature a second time it would simply burn. This characteristic makes thermoset materials poor candidates for recycling.