The 10 common plastic injection molding materials

There are 10 commonly used injection molding materials:

● Acrylic (PMMA)

● ABS

● Nylon poly (PA)

● Polycarbonate (PC)

● Polyethylene (PE)

● Polyoxymethylene (POM)

● Polypropylene (PP)

● Polyethylene soft (PS)

● Thermoplastic Elastomer (TPE)

● Thermoplastic polyethylene oxide (TPU)

Advantage

Acrylics have high tensile strength, can hold loads, don't absorb odors, and can hold tight tolerances during injection molding.
The material is also resistant to sunlight and weather, making it suitable for outdoor use. Because it doesn't degrade when in contact with water, PMMA doesn't release bisphenol A (BPA), a chemical found in many plastics that can adversely affect human health.


Disadvantage

Acrylics have some important limitations. They are more expensive than glass and scratch more easily. They are also easily stained by grease and oil. In addition, PMMA is used at temperatures too low for some industrial applications. Injection molded acrylics lack strong solvent resistance and are prone to stress cracking under particularly heavy loads.


Application

Acrylics are used in windows, greenhouses, solar panels, bathroom enclosures and other transparent components for architectural and lighting applications.

Grade

General purpose acrylic is the least expensive type of PMMA and is used in commodity rather than engineering applications. Sign-grade acrylic is ten times stronger than general-purpose acrylic, providing excellent light transmission for outdoor signage. Marine-grade acrylic resists damage from constant exposure to water and is often used by boat builders.

Advantage

ABS is tough, relatively cheap, and has good resistance to heat, oil, acids, and alkalis. Its styrene content gives injection molded parts a glossy, aesthetic appearance, while its butadiene content provides excellent toughness even at low temperatures.

Disadvantage

Since ABS is not very resistant to sunlight or weather, it is not a good choice for outdoor applications. ABS also produces a lot of smoke when it burns, has poor resistance to high friction, and has little resistance to solvents such as water.

Application

Injection molded ABS is used in electronic components and keyboard keys, protective headgear, plastic wall panels for electrical outlets, and automotive components such as dashboards, wheel housings, and auto body parts. Other applications include consumer goods, sports equipment and industrial accessories.

Grade

ABS can also be combined with glass fillers for strength, or polycarbonate for low temperature impact resistance. Some suppliers make filled and unfilled ABS plastic.

Advantage

It has good toughness and high heat resistance. They also have high wear resistance, good fatigue resistance and noise dampening properties. With its low coefficient of friction, injection molded nylon is suitable for high friction and wear applications.

While nylon doesn't offer inherent flame resistance and can burn quickly, flame retardant versions are available. Also, while nylon is degraded by sunlight, UV stabilizers can be added to improve performance.

Disadvantage

The material is less resistant to strong acids and bases.

Application

Nylon is commonly used in strong mechanical components such as bearings, bushings, gears and slides. It is also ideal for housings and snap closures, threaded inserts, power snaps, jigs and fixtures. Other applications range from toothbrushes and wheels to medical implants and electrical connectors.

Grade

There are four main grades of nylon: Nylon 66, 11, 12 and 46. Each grade has slightly different mechanical properties.

Nylon 66

Has a higher melting point and greater acid resistance for use in chemical processing applications.

Nylon 11

Has higher resistance to dimensional changes due to its higher moisture resistance. It is used for outdoor applications.

Nylon 12

Has the lowest melting point and relatively good resistance to water absorption.

Nylon 46

It operates at higher temperatures than other grades of nylon. Applications include engines and transmissions.

Nylon grades can be glass filled for increased mechanical strength.

Advantage

Polycarbonate is extremely durable and is 250 times stronger than glass. With its predictable and uniform mold shrinkage, this injection molding material provides precise dimensional control. PC plastic is also lightweight and has excellent optical properties to support light transmission.

Disadvantage

Because it contains BPA, injection molded polycarbonate is not recommended for food preparation or storage. It also requires higher processing temperatures, which makes molding more expensive. Polycarbonate is also scratch-resistant.

Application

Polycarbonates are used in mechanical guards, clear or tinted windows, diffusers and light pipes for light-emitting diodes (LEDs) and clear pipes. This material can also be used to produce clear molds for polyurethane and silicone castings.

Grade

Polycarbonate can be filled with glass and compounded with ABS for improved impact resistance. Some grades contain relatively small percentages of stainless-steel fibers.

PE is the only commercial polymer that can be selected based on its density, so this measurement is important because it controls other material properties. Both HDPE and LDPE have useful properties such as chemical resistance, but they differ in their hardness, flexibility, melting point and optical clarity. PET plastic is not defined by density.

Advantage

HDPE, LDPE, and PET are all low-cost plastics that resist both moisture and chemicals. LDPE is softer and more flexible than HDPE, which is an opaque material. Like LDPE, PET can be as clear as glass. Engineers and designers love these materials because they offer a variety of options in terms of optical clarity and other properties.

Disadvantage

PE plastics are limited by poor UV resistance and cannot withstand high service temperatures. HDPE parts less than 0.020 inches thick are difficult to form. Tight tolerances are difficult to achieve with injection molded LDPE. PET absorbs a lot of water and requires the resin to dry, which increases production costs.

Application

PE plastic is best known for use in baby bottles (HDPE), plastic film (LDPE) and water bottles (PET); however, these products are not injection molded. They are made using a different type of molding called blow molding. Examples of injection molded PE include children's toys, tool boxes, wire and cable insulation, and medical device components.

Grade

PE plastics have numbered grades, with higher numbers generally indicating higher density. For example, HDPE 500 is denser than HDPE 300. Both grades are denser than LDPE, which also uses a grade numbering system.

Advantage

Injection molded POM combines excellent rigidity, thermal stability and low coefficient of friction. It also has low water absorption and good chemical resistance. There are two main types of POM plastics available: homopolymers and copolymers. This allows engineers and designers to choose acetal materials with different properties.

Disadvantage

In its pure form, POM has low impact strength and very high thermal expansion. Mold shrinkage is relatively high, and acetal is not resistant to UV rays. POM plastic as a homopolymer offers higher stiffness and tensile strength. However, all POM plastics (homopolymers and copolymers) are not fire rated according to standards such as UL 94.

Application

Due to its low coefficient of friction, injection molded POM is suitable for bearings, gears, conveyor belts and pulleys. Other applications include fasteners, eyeglass frames, knife and firearm parts, locking systems and high-performance engineered components.

Grade

POM comes in glass fiber or mineral reinforced grades for strength and stiffness. Compounds reinforced with these two materials offer an excellent balance of mechanical properties.

Advantage

Polypropylene plastic offers good chemical resistance and retains its shape after twisting or bending. PP also has a high melting point and will not degrade when exposed to moisture or water. Injection molded polypore, as this plastic is sometimes called, is also recyclable up to four times. Furthermore, recycled PP can be combined with other plastic materials.

Disadvantage

Injection molded polypropylene degrades under UV light and is extremely flammable. At temperatures above 100° C (212° F), it dissolves into aromatic hydrocarbons such as benzene and toluene, which are harmful to human health. PP is difficult to color because it is difficult to bond; however, pigments can be added to color the material.

Application

Injection molded polypropylene has a variety of consumer, commercial and industrial applications. Examples include children's toys, storage containers, sporting goods, packaging, appliances, and power tool bodies.

Grade

PP plastics can be filled with glass fibers for dimensional stability, stiffness, strength and resistance to warping. Grades include high crystalline polypropylene (HcPP), which has higher stiffness than ordinary polypropylene.

GPPS is brittle and has lower dimensional stability than HIPS, and HIPS is compounded with butadiene rubber to enhance its material properties. GPPS also has glass-like transparency, while HIPS is opaque. Both types of polystyrene are well suited for injection molding because of their predictable and uniform shrinkage.

Advantage

PS plastic is inexpensive, lightweight, and resistant to moisture and bacterial growth. They also have excellent resistance to gamma radiation and can be used to sterilize medical equipment. Injection molded polystyrene also has good chemical resistance to diluted acids and bases.

Disadvantage

Polystyrene is flammable, susceptible to UV degradation, and attacked by hydrocarbon solvents such as benzene and kerosene. Because it is brittle, GPPS cracks easily. Although injection molded polystyrene is recyclable, it is not biodegradable.

Application

Polystyrene is used in medical, optical, and electrical and electronic applications. Due to its higher impact strength, HIPS is often used with appliances and equipment. Injection molded GPPS is used in plastic toys, boxes, containers and trays.

Grade

Polystyrene can be glass-filled for strength or copolymerized with acrylic for clarity and improved chemical and UV stability.

Advantage

Thermoplastic elastomers can be stretched to moderate elongations. When this stress is removed, they almost return to their original shape. TPE also offers shorter molding cycles, supports overmolding options, and is easier and less expensive to mold than liquid silicone rubber (LSR).

Disadvantage

Under sustained stress, however, TPE is prone to creep, the tendency of a solid material to deform permanently. This material also tends to lose its rubbery properties at higher temperatures and is much more expensive than other injection molding materials.

Application

Injection molded TPEs are used in footwear, medical devices, auto parts and pet products. Automotive applications include weather sealing and shock and dust covers. Medical applications include breathing tubes, valves, catheters and ventilation masks.

Application

Injection molded TPU is used in footwear, gaskets, casters and sporting goods. Applications also include enclosures or enclosures for electronic and medical equipment. In medical applications, TPU is sometimes used in place of polyvinyl chloride (PVC), a plastic that can cause skin irritation.

Grade

TPU is available in commercial, medical and industrial grades. TPU materials are mainly divided into three categories: polyester, polyether and polycaprolactone.

Conclusion

By understanding the key differences between these materials, product designers, engineers, and manufacturers can make informed decisions and select the best material for their specific application. Whether you are producing consumer goods, automotive parts, medical devices, or any other type of product, the right material can help you achieve the desired performance, aesthetics, and cost-effectiveness.

Overall, plastic injection molding continues to be a widely used and practical manufacturing process, thanks to its versatility, efficiency, and ability to produce high-quality products. With the knowledge gained from this blog, you can confidently choose the right plastic material for your next injection molding project and bring your product to life.

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