Types of Plastic Materials Used in Injection Molding

16 Apr.,2024

 

Types of Plastic Overview

What are the Materials Used in Plastic Injection Molding?

Injection molding is considered to be one of the fastest and most optimized methods of producing large numbers of identical plastic components at one time. Injection molding is used for nearly every consumer plastic product and is the most common plastic manufacturing method around. Because of the wide range of applications and industries where plastics are used, different chemical formulations are required for the plastic injection molding process.

The professionals at Retlaw Industries use a wide variety of plastics when manufacturing our molded products, depending on what type of plastic product our customers need.

Our expert plastic part designers will work on your new or existing design concept to find the best material for your particular application. Whether you need electronic enclosures molded from ABS or pull-out drawer handles made from acetal (POM), our experts will address your needs and help you build the best part possible out of the best materials available.

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Here are some of the plastic materials our experts use in plastic injection molding:

Also known as Plexiglas, acrylic is a hard transparent plastic material often used in electronics and automotive parts. Other forms of acrylic are also used in everyday products due to its natural transparency and coloring properties, everything from eyewear lenses, acrylic paint, and even acrylic nails. Acrylic can also be colorized to be either translucent or opaque.

In commercial applications, acrylic falls under #7 (OTHER). This can include other types of plastics including polycarbonate, polylactic fibers, nylon, and fiberglass. 

Advantages of Acrylic:

  • Transparency – among the clearest plastics available today
  • Weather Resistance – resists moisture and ultraviolet discoloration
  • Chemical Resistance – unaffected by water and weak acids and alkaline solutions
  • Surface Hardness – good impact strength and rigidity
  • Dimensional Stability – lends to a predictable final product

ABS plastic is one of the most commonly used plastics in injection molding due to its wide temperature range, good stability, and insulating properties. ABS is commonly found in plastic toys such as Lego bricks, but it’s also often used in many types of electronics, tools, and home repair equipment.

Advantages of ABS:

  • Impact Resistance – rubberlike formulations make ABS resilient to impact
  • Surface hardness – high rigidity in certain formulations
  • Chemical Resistance – not affected by alkalis, water, and most inorganic acids
  • Uniform Shrinkage – good dimensional stability
  • Wide Temperature Range – resists heat and won’t shatter in cold
  • Machinability – easy to form after cooling

When in need of rigid, heat-resistant plastic, HDPE is the best material to use. Since polyethylene is a food-grade plastic – meaning it is safe to use around food – this material is commonly manufactured in storage containers, kitchenware, and refrigerator shelving. HDPE is also a good plastic for holding chemical-based products such as cleaning agents, laundry detergent, bleach, and shampoo.

In commercial applications, HDPE falls under #2 (HDPE). 

Advantages of HDPE:

  • Sustainable – made of 100% recyclable material
  • Chemical Resistance – resistant to corrosion, rust, and other chemicals
  • Heat Resistance – doesn’t melt or corrode in high temperatures
  • Food Grade – safe to use as food packaging and equipment
  • Inexpensive – can be mass-produced at a low price

Nylon is one of the most versatile materials used in plastic injection molding. It’s commonly combined with a range of other materials to enhance its characteristics. Thanks to its high melting temperature and low friction properties, it’s useful for a wide range of products such as nylon rope, reinforced automotive parts, and even clothing.

Advantages of Nylon:

  • Low Friction – doesn’t heat up under high friction
  • Chemical Resistance – resistant to corrosion from chemicals
  • Abrasion Resistance – useful for elastic and clothing applications
  • Adaptable – can be combined with many other types of plastic materials

Polycarbonate is a useful plastic material for applications needing transparency or high impact resistance. For this reason, polycarbonate is most commonly used in eyewear applications, but it’s also used in pipes for LED lights, clear windows, and sporting equipment.

In commercial applications, polycarbonate falls under #7 (OTHER). This can include other types of plastics including acrylic, polylactic fibers, nylon, and fiberglass.

Advantages of Polycarbonate:

  • Impact Resistance – doesn’t scratch or dent under impact
  • UV Resistance – doesn’t corrode or discolor in ultraviolet light
  • Transparency – can be made into windows and eyewear lenses
  • Chemical Resistance – doesn’t corrode from chemicals
  • Rigidity – makes for good eyewear and window applications

Polyetherimide, also known as Ultem, is an amorphous material with extremely high heat resistance compared to other plastics. Due to its rigidity and high heat performance, polyetherimide is most commonly used in medical devices, electronics, and industrial plastic parts.

Advantages of Polyetherimide:

  • Rigidity – hard plastic useful for high-impact industrial applications
  • Heat Resistance – doesn’t melt or warp under high temperatures
  • High Tensile Strength – resists cracking or breaking in hard environmental conditions
  • Flame Resistance – isn’t flammable and generates low smoke

Also known as Acetal, polyoxymethylene is a semi-crystalline polymer which is very rigid and has a naturally glossy surface, making it a useful material for a wide range of industries. Acetal is most commonly found in automotive applications, household appliances, and electronics.

Advantages of Polyoxymethylene:

  • Rigidity – stays strong and doesn’t bend easily
  • Impact Resistance – strong and stable enough to resist strong impacts
  • Solvent Resistance – doesn’t corrode or rust due to chemicals and solvents
  • Glossy surface – smooth, reflective properties

Much like Acetal, polypropylene is a plastic with a naturally glossy surface when properly manufactured. Its chemical resistance and elastic properties make it useful for a wide variety of food-related applications, including plastic kitchenware, dishwasher-safe plates, and storage containers. Polypropylene is also commonly used to make toys, hard luggage containers, and even external car parts.

In commercial applications, polypropylene falls under #5 (PP).

Advantages of Polypropylene:

  • Chemical Resistance – doesn’t react with most bases and acids
  • Fatigue Resistance – retains its shape after a lot of bending and flexing
  • Electrical Resistance – strong insulation properties
  • Elasticity – can bend, flex and deform without actually breaking

Polystyrene is a polymer used in a wide variety of plastic and foam applications across a range of industries. Due to its bending and flexing properties, polystyrene is often used in hinged applications, such as disposable food containers and bottles. It’s also widely used to make rigid foam insulation and sheeting for laminate floors.

In commercial applications, polystyrene falls under #6 (PS). 

Advantages of Polystyrene:

  • Optical Clarity – transparent resin can be useful for see-through plastic products
  • FDA Grade – safe to use when packaging food and consumable materials
  • Stability – rigid material useful for packaging
  • Inexpensive – can be mass-produced at a low cost
Whatever type of molded plastic you need, the experts at Retlaw Industries can help! Contact us today to get a quote on our professional molding services.

Time to read: 9 min

Plastic materials for injection molding range from commonly used polymers to specialty plastics and polymer blends. There are hundreds of different plastic resins available, and they each have different end-use properties and processing requirements. Plus, there are different grades of the same plastic material, including resin types with fillers such as glass fibers or carbon fibers, and specific brand names.

With so many choices, it’s daunting to choose the right material for your project. Whether your project involves medical plastic injection molding, molded plastic components for the automotive industry, or something else, Fictiv experts are ready to help you go from design to production quickly.

And if you’re looking for help with your injection molding projects, check out our Guide to Injection Molding Production. This downloadable PDF explains what you need to know to make your next injection molding project a success.  

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Otherwise, keep reading to learn about the top 10 plastic injection molding materials.

The Top 10 Plastic Injection Molding Materials

These are 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)

This article discusses their properties, including comparisons to other materials, along with injection molding applications, grades, and brand names for each.

Injection molded acrylic

Acrylic (PMMA)

Acrylic is a strong, clear thermoplastic that provides a lightweight, shatter-resistant alternative to glass. This injection-molded material also offers excellent optical clarity so that a high percentage of light passes through. Acrylic resists ultraviolet (UV) light and weather, and is also known as PMMA, or by its full chemical name: poly(methyl methacrylate).  

Properties

Unlike some plastics, acrylic can withstand exposure to water and hold tight tolerances. PMMA won’t absorb odors, but it cannot resist solvents and is easily stained by greases and oils. Although injection-molded acrylic has high tensile strength, it’s prone to stress cracking under heavy loads.

Applications

Applications for acrylic injection molding include windows, greenhouses, solar panels, bathroom enclosures, and other transparent components for architectural, lighting, and outdoor applications. 

Grades and Brands

General-purpose and specialty grades of PMMA plastics are available, including:

  • 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 PLEXIGLAS®, which is available with high heat resistance, and DuPont LUCITE®, which has excellent optical clarity and transparency.

Injection molded ABS

Acrylonitrile Butadiene Styrene (ABS)

ABS has 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. Its butadiene content delivers exceptional toughness, even at low temperatures, and its styrene content imparts a shiny, attractive finish to plastic injection molded parts.

Properties

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.

Applications

ABS injection molding is used to produce many types of plastic parts, including:

  • keyboard keys
  • protective headgear
  • electrical outlet wall plates
  • automotive parts like wheel covers
  • consumer goods
  • sports equipment
  • industrial fittings

Grades and Brands

Well-known brands of ABS include Samsung Starex®, Toray Toyolac®, BASF Terluran®, and Ineos Lustran®.

Injection molded nylon

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.

Properties

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. Injection molding nylon is challenging because it’s prone to shrinkage and is subject to inadequate mold filling.

Applications

Applications for nylon injection molding include: 

  • strong mechanical parts such as bearings, bushings, gears, and slides
  • casings and snap-fit closures
  • threaded inserts and kinetic parts
  • jigs and fixtures 

With its low coefficient of friction, nylon is also well-suited for applications with high-friction and wear.

Grades and Brands

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.

Injection molded polycarbonate

Polycarbonate (PC)

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.

Properties

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, which can make it more expensive to mold. With its predictable and uniform shrinkage, however, polycarbonate offers precise dimensional control for tighter tolerances.

Applications

Applications for polycarbonate injection molding include:

  • machinery guards
  • clear and tinted windows
  • diffusers and light pipes for light-emitting diodes (LEDs)
  • clear molds for urethane and silicone casting 

Because it contains the chemical bisphenol A (BPA), polycarbonate is not recommended for food preparation or storage.

Grades and Brands

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.

There are several major categories of PE plastic

Polyethylene (PE)

Polyethylene is the most commonly used plastic in the world and is a 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.

Properties

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.  

Applications

Applications for polyethylene injection molding 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.  

Grades and Brands

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)

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 has low water absorption and good chemical resistance. In terms of appearance, POM plastics are naturally opaque and white in color.

Properties

In its pure form, acetals have low impact strength and a very high rate of thermal expansion. Yet, POM can be reinforced with fiberglass or minerals for improved strength and stiffness. Compounds that are reinforced with both provide an excellent balance of mechanical properties. Because injected molded POM lacks resistance to sunlight, its outdoor applications are limited.

Applications

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. 

Grades and Brands

There are two main types of acetal plastics: homopolymers, which 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. Popular brand names for POM plastics include DuPont Delrin® and Ensinger TECAFORM®.

Injection molded polypropylene

Polypropylene (PP)

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.

Properties

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

Applications for polypropylene injection molding include 

  • toys
  • storage containers
  • sporting goods
  • packaging
  • appliances
  • power tool bodies

Grades and Brands

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 (PS)

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.

Properties

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.

Applications

Applications for polystyrene injection molding include medical, optical, electrical, and electronic applications. With its higher impact strength, HIPS is often used with appliances and equipment, while injection-molded GPPS is used in plastic toys, cases, containers, and trays.

Both materials are flammable and susceptible to UV degradation.

Grades and Brands

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 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.

Properties

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 permanently deform. TPE also tends to lose its rubbery properties at higher temperatures and is significantly more expensive than other plastic injection molding materials.

Applications

Applications for TPE injection molding include: 

  • footwear
  • medical devices
  • auto parts
  • pet products 

Automotive applications include weather seals and shock dust boots. Medical applications include breathing tubes, valves, catheters, and ventilation masks. 

Grades and Brands 

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, and 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.

Properties

Compared to TPE, TPU has superior resistance to extreme temperatures and chemicals. TPUs may be too hard for some injection molded plastic parts, and tend to cost more, in part because drying is required before processing.

Applications

Applications for TPU injection molding include footwear, gaskets, caster wheels, and sporting goods along with 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.  

Grades and Brands

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 Injection Molding Materials

The plastics discussed in this article are the most common injection molding materials — including specialty plastics and polymer blends — that Fictiv can injection mold for you. 

With so many options, it helps to have an expert’s advice before choosing a plastic resin for your project. As part of our injection molding service, Fictiv has design and production experts ready to help you make the right choice, and you get design for manufacturing (DFM) feedback along with your quote.

So, create an account and upload your injection molding designs today!

Types of Plastic Materials Used in Injection Molding

Common Plastic Materials for Injection Molding