What is polypropylene (PP) and what is it used for?
Polypropylene (PP) is a thermoplastic polymer made from a combination of propylene monomers. It is used for the packaging of consumer products, plastic parts for various industries including the automotive industry, special devices such as live hinges and textiles. Polypropylene was first polymerized in 1951 by a pair of Phillips petroleum scientists, Paul Hogan and Robert Banks, and later by Italian and German scientists Nata and Rahn. The product rose to prominence very quickly, as commercial production began almost three years after Italian chemist Professor Giulio Natta first polymerized it. Nata perfected and synthesized the first polypropylene resin in Spain in 1954, and the ability of polypropylene to crystallize created a lot of excitement. By 1957, its popularity soared and widespread commercial production began throughout Europe. Today, it is one of the most common plastics produced in the world.
According to some reports, the current global demand for this material produces about 45 million metric tons annually, and the demand is estimated to increase to 62 million tons by 2020. The major final consumers of polypropylene are the packaging industry. , which consumes about 30% of the total, followed by electricity production and equipment, each of which uses about 13%. Household appliances and automotive industries both consume ten percent, and construction materials are in second place with five percent of the market. Other applications together account for the rest of the global polypropylene consumption.
Polypropylene has a relatively slippery surface that can replace plastics such as polyethylene (POM) in low-friction applications such as gears or for use as furniture contact points. Perhaps the downside of this quality is that polypropylene is difficult to bond to other surfaces (i.e. it doesn't stick well to certain adhesives that work well with other plastics and sometimes needs to be welded if bonding is required.) Polypropylene is slippery at the molecular level, but has a relatively high coefficient of friction - that's why acetyl, nylon or PTFE are used instead. Polypropylene also has a lower density than other common plastics, which means weight savings for manufacturers and distributors of injection molded polypropylene parts. It has exceptional resistance at room temperature to organic solvents such as fats, but is subject to oxidation at higher temperatures (a potential problem during injection molding).
One of the major advantages of polypropylene is that it can be manufactured (either through CNC or injection molding, thermoforming, or crimping) into a permanent hinge. Permanent hinges are very thin pieces of plastic that bend without breaking (even through an extreme range of motion of nearly 360 degrees). They are not very useful for structural applications such as holding heavy lids, but they are very useful for non-load bearing applications such as ketchup or shampoo bottle caps. Unique polypropylene is suitable for permanent hinges because it does not break if repeatedly bent. Another advantage is that polypropylene can be CNC machined, which includes a permanent hinge, which allows prototype development to be faster and less expensive than other prototyping methods. Creative Mechanisms is unique in our ability to machine permanent hinges from a single piece of polypropylene.
Another advantage of polypropylene is that it can be easily copolymerized (essentially combined into a composite plastic) with other polymers such as polyethylene. Copolymerization significantly changes the properties of the material, resulting in stronger engineering than pure polypropylene (more of a commodity plastic on its own).
The properties listed above and below mean that polypropylene is used in a variety of applications: dishwasher-safe plates, trays, cups, etc., frosted to-go containers, and many toys.
What are the characteristics of polypropylene?
Some of the most important properties of polypropylene are:
Chemical resistance: Diluted bases and acids do not easily react with polypropylene, which makes it a good choice for containers of such liquids as detergents, first aid products, and more.
Stretch and hardness: Polypropylene behaves elastically within a certain range of deflection (like all materials), but it also experiences plastic deformation in the early stages of deformation, so it is generally considered a 'hard' material. Hardness is an engineering term defined as the ability to deform (plastically, not elastically) without breaking.
Abrasion resistance: Polypropylene retains its shape after being twisted, bent, or bent a lot. This feature is especially valuable for making permanent hinges.
Insulation: Polypropylene has a very high resistance to electricity and is very useful for electronic components.
Transferability: Although polypropylene can be made transparent, it is usually produced in a naturally opaque color. Polypropylene can be used in cases where light transmission is important or where aesthetics are of great importance. If high portability is desired, plastics such as acrylic or polycarbonate are better options.
Polypropylene is classified as a 'thermoplastic' (as opposed to 'thermoset') material, which refers to how the plastic reacts to heat. Thermoplastic materials liquefy at their melting point (approximately 130°C in the case of polypropylene). An important useful property of thermoplastics is that they can be heated to their melting point, cooled, and reheated again without significant degradation. Instead of burning, thermoplastics are liquefied like polypropylene, which allows them to be easily injection molded and then recycled. In contrast, thermoset plastics can only be heated once (usually during the injection molding process). The first heating causes the thermoset material (such as a 2-part epoxy) to set, resulting in a chemical change that is irreversible. If you try to heat a thermal plastic to a high temperature a second time, it will simply burn. This feature makes thermoset materials unsuitable for recycling.
Why is polypropylene used so much?
Polypropylene is used for domestic and industrial purposes. Its unique properties and ability to adapt to different manufacturing techniques make it stand out as a valuable material for a wide range of uses. Another valuable feature is the ability of polypropylene to act as both a plastic material and a fiber (such as promotional bags given out at events, competitions, etc.). The unique ability of polypropylene to be produced through different methods and different applications caused it to soon challenge many old alternative materials, especially in the packaging, fiber and injection molding industries. It has continued to grow over the years and remains a major player in the plastics industry worldwide.
At Creative Mechanisms, we have used polypropylene in a number of applications across a wide range of industries. Perhaps the most interesting example involves our ability to CNC machine a polypropylene that includes a permanent hinge for the initial development of a permanent hinge. Polypropylene is a very flexible and soft material with a relatively low melting point. These factors have made most people unable to machine the material properly. It begins to melt from the heat of CNC cutting. Normally it has to be smoothed to get anything close to the finished surface. But we have managed to solve this problem, which allows us to create a new prototype of permanent hinges from polypropylene.
What are the different types of polypropylene?
There are two main types of polypropylene: homopolymers and copolymers. Copolymers are further divided into block copolymers and random copolymers. Each category fits applications better than others. Polypropylene is often referred to as the 'steel' of the plastics industry because of the many ways it can be modified or customized to best serve the purpose. This is usually achieved by introducing special additives to it or by making it in a special way. This consistency is a critical feature.
Polypropylene homopolymer is a generic grade. You can think of this state as the default state of the polypropylene material. Block copolymer polypropylene has monomeric units that are arranged in a block-like manner (i.e. with a regular pattern) and contains between 5 and 15% ethylene. Ethylene improves certain properties such as impact resistance while other additives enhance other properties. Random copolymer polypropylene - in contrast to block copolymer polypropylene - has homo-monomer units in irregular or random patterns along the polypropylene molecule. They usually contain between 1 and 7% ethylene and are chosen for applications where a more flexible and transparent product is desired.
How is polypropylene made?
Polypropylene, like other plastics, usually starts by distilling hydrocarbon fuels into lighter groups called 'fractions', some of which are combined with other catalysts to produce plastics (usually via polymerization or polycondensation). Polypropylene for prototype development on CNC machines, 3D printers and injection molding machines, 3D Printing Polypropylene Polypropylene is not readily available as filament for 3D printing.
CNC Machining Polypropylene:
Polypropylene is widely used as a sheet for CNC machine manufacturing. When we prototype a small number of polypropylene parts, we usually CNC machine them. Polypropylene is known as a material that cannot be machined. This is because it has a low baking temperature, which means it starts to deform under heat. Since it is generally a very soft material, it requires very high skill to cut accurately. Creative Mechanisms has succeeded in doing this.
Injection molded polypropylene:
Polypropylene is a very useful plastic for injection molding and is usually available in pellet form for this purpose. Despite its semi-crystalline nature, polypropylene is easily molded and flows very well due to its low melt viscosity. This feature significantly increases the speed of filling the mold with material. Shrinkage in polypropylene is about 1-2, but it can vary based on several factors such as holding pressure, holding time, melting temperature, mold wall thickness, mold temperature, and the percentage and type of additives.
Other:
In addition to conventional plastic applications, polypropylene also lends itself well to fiber applications. It offers a wider range of applications that go beyond injection molding. These include ropes, carpets, upholstery, clothing and the like.
What are the advantages of polypropylene?
- It is readily available and relatively inexpensive.
- Due to its semi-crystalline nature, it has high bending strength.
- It has a relatively slippery surface.
- It is very resistant to moisture absorption.
- It has good chemical resistance in a wide range of bases and acids.
- It has good resistance to fatigue.
- It has good impact power.
- It is a good electrical insulator.
What are the disadvantages of polypropylene?
- It has a high coefficient of thermal expansion, which limits its high temperature applications.
- Susceptible to UV damage.
- It has poor resistance to chlorinated and aromatic solvents.
- Polypropylene is difficult to paint because it has poor adhesion properties.
- It is highly flammable.
- It is susceptible to oxidation.
- Despite its shortcomings, polypropylene is overall an excellent material. It has a unique combination of properties not found in any other material, making it an ideal choice for many projects.
What are the characteristics of polypropylene?
Technical name: Polypropylene (PP)
Chemical formula: molecular composition of polypropylene (C3H6) n
Resin identification code (used for recycling)
Polypropylene (PP) resin identification code 5 (for plastic recycling purposes)
Melting point: 130 degrees Celsius (266 degrees Fahrenheit)
Typical injection mold temperature: 32-66°C (90-150°F)
Heat Deflection Temperature (HDT): 100°C (212°F) at 0.46 MPa (66 PSI)**
Tensile strength: 32 MPa (4700 PSI)
Flexural strength: 41 MPa (6000 PSI)
Specific gravity: 0.91
Drop Rate: 1.5 - 2.0% (.015 - .02 in/in)
In standard mode (at 25 °C (77 °F), 100 kPa
Polypropylene (PP) is a thermoplastic polymer made from a combination of propylene monomers. It is used for the packaging of consumer products, plastic parts for various industries including the automotive industry, special devices such as live hinges and textiles. Polypropylene was first polymerized in 1951 by a pair of Phillips petroleum scientists, Paul Hogan and Robert Banks, and later by Italian and German scientists Nata and Rahn.
