What is the best type of thermoplastic to use for your product design? We’ve put together a quick-hit list of some thermoplastics as a good starting point.
Not all polymers are the same, and each type of polymer or co-polymer has specific characteristics. Before you can go down the path of designing a product, material selection should be first of mind. So, you aren’t designing something that won’t be manufacturable. You have to be aware of not only your application but also the material and how it will flow through your injection mold.
If you approach designing with this type of mindset, you will have a far greater chance for minimal major changes once you bring this design to an injection molding company like Crescent Industries.
What are your application intentions?
While some people may believe that regardless of what type of thermoplastic you use, the design isn’t affected until you get into the final stages, you will be losing efficiencies in the design process. There are significant design best practices to keep in mind when you’re using a commodity grade polypropylene vs an engineered grade glass filled nylon regardless if the fundamentals remain the same.
The starting point is to think about the application and look at 4 main areas:
- What will this product do?
- What environment will this product be in?
- What are the most important characteristics/functionality of the product?
- What is the expected lifecycle of this product?
Once you have determined the above you can start to narrow down your main thermoplastic families to determine which direction you should go down.
What is a Thermoplastic?
A thermoplastic is a plastic material, a polymer, that becomes pliable or moldable above a specific temperature and solidifies upon cooling.
Most thermoplastics have a high molecular weight. The polymer chains associate through intermolecular forces, which weaken rapidly with increased temperature, yielding a viscous liquid. Thus, thermoplastics may be reshaped by heating and are used to produce parts by various polymer processing techniques such as injection molding, compression molding and extrusion.
Above its glass transition temperature and below its melting point, the physical properties of a thermoplastic change drastically without an associated phase change. Some thermoplastics do not fully crystallize below the glass transition temperature, retaining some or all of their amorphous characteristics. Amorphous and semi-amorphous plastics are used when high optical clarity is necessary, as light is scattered strongly by crystallites larger than its wavelength. Amorphous and semi-amorphous plastics are less resistant to chemical attack and environmental stress cracking because they lack a crystalline structure.
Brittleness can be decreased with the addition of plasticizers, which increases the mobility of amorphous chain segments to effectively lower the glass transition temperature. Modification of the polymer through copolymerization or through the addition of non-reactive side chains to monomers before polymerization can also lower it.
Commodity or Engineered Grade?
There are two main categories in the plastics industry when referring to thermoplastics, commodity and engineered grade. The commodity grade materials are the most common in light weight applications and typically things that will be thrown away over a short period of time or disposables. Although, some commodity grade materials can be robust under certain designs, applications, and environments.
The engineered grades are more robust and have a vast range of different polymer blends, additives and advancements to produce the most robust performing material for difficult environments.
Below is a list of some common Thermoplastics used today.
Acrylic, a polymer called poly(methyl methacrylate) (PMMA), is also known by trade names such as Lucite, Perspex and Plexiglas. It serves as a sturdy substitute for glass.
Acrylonitrile butadiene styrene (ABS) is a terpolymer synthesized from styrene and acrylonitrile in the presence of polybutadiene. ABS is a light-weight material that exhibits high impact resistance and mechanical toughness.
Nylon belongs to a class of polymers called polyamides. It has the ability to be very lustrous, semi-lustrous or dull. Nylon is a tough material with excellent abrasion resistance and chemical resistance. A good substitute for die cast metal with the advantage of weight reduction.
Polycarbonate (PC) thermoplastics are known under trademarks such as Lexan, Makrolon, Makroclear, and arcoPlus. They are easily worked and molded for many applications.
Polyether sulfone (PES) or polysulfone is a class of specially engineered thermoplastics with high thermal, oxidative, and hydrolytic stability, and good resistance to aqueous mineral acids, alkalis, salt solutions, oils and greases.
Polyoxymethylene (POM), also known as acetal, polyacetal and polyformaldehyde, is an engineering thermoplastic used in precision parts requiring high stiffness, low friction, and excellent dimensional stability. As with many other synthetic polymers, it is produced by different chemical firms with slightly different formulas and sold variously by such names as Delrin, Celcon, Ramtal, Duracon, Kepital and Hostaform.
Polyether ether ketone(PEEK) is a colorless organic thermoplastic polymer in the polyaryletherketone (PAEK) family, used in engineering applications. It has attractive properties like good abrasion resistance, low flammability and emission of smoke and toxic gases.
Polyetherimide (PEI), produced by a novel nitro displacement reaction involving bisphenol A, 4, 4’-methylenedianiline and 3-nitrophthalic anhydride, has high heat distortion temperature, tensile strength and modulus.
Polyethylene (polyethene, polythene, PE) is a family of similar materials categorized according to their density and molecular structure. It may be of low density or High density depending upon the process used in its manufacturing. It is resistant to moisture and most of the chemicals. It is flexible at room temperature (and low temperature) and can be heat sealed. Since it is an inexpensive plastic it is made in large amounts to cater demand.
Polyphenylene sulfide (PPS) obtained by the condensation polymerization of p-dichlorobenzene and sodium sulfide, has outstanding chemical resistance, good electrical properties, excellent flame retardance, low coefficient of friction and high transparency to microwave radiation. Particular grades of PPS can be used in injection molding at temperatures (300 to 370 °C) at which PPS particles soften and undergo apparent crosslinking.
Polypropylene (PP) is useful for a diverse range of products. Although relatively inert, it is vulnerable to ultraviolet radiation and can degrade considerably in direct sunlight. Polypropylene is not as impact resistant as the polyethylenes (HDPE, LDPE). It is also somewhat permeable to highly volatile gases and liquids.
Polyvinyl chloride (PVC) is a tough, lightweight material that is resistant to acids and bases. Adding plasticizers can make this flexible enough for multiple applications.
While the list may seem overwhelming, it’s a starting point to give you a foundation of which direction to go into. By working with your injection molding partner, they should be able to provide some good guidance into specific grades that would be best suited for your application. Crescent Industries has an extremely knowledgeable internal team to assist with all of your design questions as they work through a project with you.
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