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There are hundreds of plastic materials for injection molding. Different plastic resins impart different end-use properties, such as tensile strength and impact resistance. Injection molded plastics also have specific processing requirements, such as melt temperature and molding pressure. There are also different grades of the same plastic material, including resin types with fillers such as glass or fiberglass.
Fictiv can help you select the right plastic material for your application and works with manufacturing partners who use the right injection molding machine for the job. Whether your project involves medical plastic injection molding, molded plastic components for the automotive industry, or something else, we can also help you go from design to production faster.
The Top 10 Plastic Materials
Here are ten of the most common plastic materials for injection molding:
- acrylic (PMMA)
- acrylonitrile butadiene styrene (ABS)
- nylon (polyamide, PA)
- polycarbonate (PC)
- polyethylene (PE)
- polyoxymethylene (POM)
- polypropylene (PP)
- polystyrene (PS)
- thermoplastic elastomer (TPE)
- thermoplastic polyurethane (TPU)
The following sections cover material properties, comparisons to other resins, examples of applications, and grades and trade names for each of these materials. They aren’t the only plastic resins that Fictiv can mold for you because other choices include specialty plastics and polymer blends.
Acrylic is a strong, clear thermoplastic that provides a lightweight, shatter-resistant alternative to glass. This material also offers excellent optical clarity so that a high percentage of light passes through. In addition, acrylic resists ultraviolet (UV) light and weather. Acrylic is also known as PMMA, or by its full chemical name: poly(methyl methacrylate)
Unlike some plastics, acrylic can withstand exposure to water. This injection molded plastic can also hold tight tolerances. PMMA won’t absorb odors, nor can it resist solvents. It’s also easily stained by greases and oils. Although acrylic has high tensile strength, it’s prone to stress cracking under heavy loads.
Applications for acrylic include windows, greenhouses, solar panels, bathroom enclosures, and other transparent components for architectural, lighting, and outdoor applications. Depending on you need, general-purpose and specialty grades of PMMA plastics are available.
- General-purpose acrylic is used in commodity products.
- Sign-grade acrylic is stronger and provides excellent light transmission for outdoor signage.
- Marine-grade acrylic resists continuous exposure to water.
Common brand names for acrylic plastics include Trinseo PLEXIGAS®, which is available with high heat resistance, and DuPont LUCITE®, which has excellent optical clarity and transparency.
Acrylonitrile Butadiene Styrene (ABS)
ABS is an engineering-grade plastic with a relatively low melting point that makes it easy to mold. This opaque polymer supports the use of colorants as well as various textures and surface finishes. It’s butadiene content delivers exceptional toughness, even at low temperatures, and its styrene content imparts a shiny, attractive finish to injection molded parts.
ABS is known for its strength and impact resistance, but it lacks strong resistance to sunlight (UV), water, and weather. Compared to acrylic, injection molded ABS is not a good choice for outdoor applications. ABS also generates significant smoke when burned and, unlike nylon, provides poor resistance to high friction.
Injection molded ABS is used in keyboard keys, protective headgear, electrical outlet wall plates, and automotive components such as dashboards, wheel covers, and auto body parts. It’s also used in consumer goods, sport equipment, and industrial fittings. Well-known brands of ABS include Samsung Starex®, Toray Toylac®, BASF Terluran®, and Ineos Lustran®.
Nylon Polyamide (PA)
Nylon is a synthetic polyamide (PA) that combines toughness and high heat resistance with high abrasion resistance, good fatigue resistance, and noise dampening properties. Nylon isn’t inherently flame resistant, but flame retardant versions are available. Similarly, although nylon can be degraded by sunlight, a UV stabilizer can be added to improve outdoor performance.
Compared to other plastics, nylon provides poor resistance to strong acids and bases. Nylon is not as strong as polypropylene and can’t match polycarbonate for impact resistance. And injection molding the material is challenging because nylon is prone to shrinkage and subject to inadequate mold filling.
Nylon is often used in strong mechanical parts such as bearings, bushings, gears, and slides. It’s also a good choice for casings and snap-fit closures, threaded inserts, kinetic parts, jigs and fixtures. Additional applications range from toothbrushes and wheels to medical implants and electrical connectors. With its low coefficient of friction, injected molded nylon is often used in high friction and wear applications.
Nylon comes in four main grades, and each has slightly different mechanical properties:
- Nylon 11 is used in outdoor applications and has greater resistance to dimensional changes.
- Nylon 12 has the lowest melting point of all four grades and resists water absorption.
- Nylon 46 has the highest operating temperature.
- Nylon 66 has a high melting point and resists acids used in chemical processing.
Nylon can also be filled with glass fibers for greater mechanical strength.
Polycarbonate is strong, lightweight, and naturally transparent. This plastic injection molding material has excellent optical properties to support light transmission but maintains its color and retains its strength when pigmented. Although it isn’t scratch resistant, polycarbonate is significantly stronger than glass and is extremely durable.
Injection molded polycarbonate is sometimes used instead of acrylic because PC maintains its physical properties over a wider temperature range. PC requires high processing temperatures, however, and this can make it more expensive to mold. With its predictable and uniform shrinkage, however, polycarbonate offers precise dimensional control for tighter tolerances.
Polycarbonate plastic is used in machinery guards, clear and tinted windows, diffusers and light pipes for light emitting diodes (LEDs), and in clear tubing. It can also be used to produce clear molds for urethane and silicone casting. Because it contains the chemical bisphenol A (BPA), polycarbonate is not recommended for food preparation or storage.
Polycarbonate plastic can be filled with glass and is available in grades that contain a relatively small percentage of stainless steel fiber. Popular brands include SABIC Lexan®, which is available in flame-resistant versions, and Covestro Makrolon®, which has glass-like transparency.
Polyethylene is the most commonly used plastic in the world and is the commercial polymer that can be selected according to its density. High density polyethylene (HDPE) and low density polyethylene (LDPE) both provide chemical resistance, but they differ in terms of their hardness, flexibility, melting point, and optical transparency.
PE plastics include polyethylene terephthalate (PET, PETE), a material that is not defined by its density. Like LDPE, PET can be as clear as glass; however, designers can also select grades of PET or PETE with different levels of optical clarity. HDPE, LDPE, and PET all resist moisture and chemicals, but LDPE is softer and more flexible than HDPE, which is an opaque material.
PE plastics may be limited to indoor applications because of their poor UV resistance. Because they are unable to withstand high service temperatures, these plastic materials may not be suitable for some processing applications. Often, injection molded polyethylene is used in products such as housewares, toys, food containers, and automotive parts.
PE plastics come in numbered grades where higher numbers generally indicate higher densities. For example, HDPE 500 has a higher density than HDPE 300. Both grades have a higher density than LDPE, which also uses a numbering system for grades. BASF and DuPont are two of the leading suppliers of PE for engineering (as opposed to general-purpose) applications.
Polyoxymethylene (POM) is an engineering plastic that is also known as acetal. It combines excellent rigidity with thermal stability and has a low coefficient of friction. This plastic material also has low water absorption and good chemical resistance. In terms of appearance, POM plastics are naturally opaque and white in color.
There are two main types of acetal plastics: homopolymers that provide higher hardness and tensile strength, and POM copolymers. Neither type of material can be fire-rated to a standard such as UL 94, and both experience relatively high shrinkage during injection molding.
With its low coefficient of friction, injection-molded POM is used in bearings, gears, conveyor belts, and pulley wheels. Additional applications include fasteners, eyeglass frames, parts for knives and firearms, lock systems, and high-performance engineering components. Because injected molded POM lacks resistance to sunlight, its outdoor applications are limited.
In its pure form, acetals have low impact strength and a very high rate of thermal expansion. Yet, POM also comes in grades that are reinforced with fiberglass or minerals for improved strength and stiffness. Compounds that are reinforced with both provide an excellent balance of mechanical properties. Popular brand names include DuPont Delrin® and Ensinger TECAFORM®.
Polypropylene is the second most commonly used plastic in the world. It provides good chemical resistance, retains its shape after torsion or bending, has a high melting point, and won’t degrade when exposed to moisture or water. Injected molded polypro, as PP is sometimes called, is also recyclable.
Despite its comparative advantages, polypropylene degrades with UV light and is extremely flammable. At temperatures above 100° C (212° F), this injection molded plastic dissolves into aromatic hydrocarbons, such as benzene and toluene, which are harmful to humans. Polypropylene plastic is also difficult to bond and paint.
Applications for polypropylene include toys, storage containers, sporting goods, packaging, appliances, and power tool bodies. Pure polypropylene is a commodity plastic with the lowest density, but high crystalline polypropylene (HcPP) is filled with glass fibers for rigidity. Semitron® from Mitsubishi Chemical Advanced Materials is a leading brand.
Polystyrene plastics are lightweight, relatively inexpensive, and resistant to moisture and bacterial growth. These commodity plastics also provide good chemical resistance to diluted acids and bases, and have excellent resistance to gamma radiation, which is used to sterilize medical devices.
There are two main types of polystyrene: general purpose polystyrene (GPPS) and high-impact polystyrene (HIPS). GPPS is brittle and has less dimensional stability than HIPS, which is compounded with butadiene rubber to enhance its material properties. GPPS also has a glass-like clarity whereas HIPS is opaque.
Polystyrene is used in medical, optical, and electrical and electronic applications. With its higher impact strength, HIPS is often used with appliances and equipment. Injection molded GPPS is used in plastic toys, cases, containers, and trays. Both materials are flammable and susceptible to UV degradation, however.
Polystyrene can be filled with glass for added strength or co-polymerized with acrylic for greater clarity and improved chemical and UV stability. Brand names include American Styrenics PolyRenew® and BASF Polystyrol®.
Thermoplastic Elastomer (TPE)
TPE is a blend of plastic and rubber materials. It is processed like a plastic but has the properties and performance of rubber. Known also as thermoplastic rubber (TPR), TPE can be stretched to moderate elongations and, upon the removal of this stress, returns to the material’s original shape. TPE can also be recycled repeatedly.
Compared to liquid silicone rubber (LSR), TPE is easier and less expensive to mold. Under sustained pressures, however, TPE is susceptible to creep, the tendency of a solid material to deform permanently. TPE also tends to lose its rubbery properties at higher temperatures and is significantly more expensive than other plastic injection molding materials.
Injection molded TPEs are used in footwear, medical devices, auto parts, and pet products. Automotive applications include weather seals and shock dust boots. Medical applications include breathing tubes, valves, catheters, and ventilation masks.
ISO 18064 defines generic classes of commercial TPEs. There are many different manufacturers and brand names, including Teknor Apex Telcar®, Kraiburg HIPEX®, and Dynaflex™ from Avient (formerly PolyOne). Healthcare grade TPEs are available.
Thermoplastic Polyurethane (TPU)
TPU is a type of TPE that is often called out separately because of its popularity. It has a rubber-like elasticity but can be used as a replacement for hard rubber because of its higher durometer. Injection molded TPU also has good load-bearing capabilities and can withstand exposure to ozone.
Compared to TPE, TPU has superior resistance to extreme temperatures and chemicals. TPUs may be too hard for some injection molded parts, however. Thermoplastic polyurethanes also tend to cost more and drying is required before processing.
Injection molded TPUs are used in footwear, gaskets, caster wheels, and sporting goods. Applications also include cases or enclosures for electronics and medical devices. In medical applications, TPUs are sometimes used instead of polyvinyl chloride (PVC), a plastic that may cause skin irritation.
Thermoplastic polyurethanes come in commercial, medical, and industrial grades. There are three main classes of TPU materials: polyester, polyether and polycaprolactone. Trademarked products are available from manufacturers such as Lanxess, Lubrizol, Texin, and Ultralast.
More Plastic Materials for Injection Molding
Because there are so many options, it helps to have an expert’s advice before choosing a plastic resin for your project. We can help you to select a plastic material and provide robust design for manufacturing (DFM) feedback and advice.
Fictiv is your operating system for custom manufacturing, and no matter where you are in the design process, we have the resources, know-how, and manufacturing network to make your next injection molding project a success. Learn more about our injection molding services and create an account to get a quote today.