Guide to plastics

Plastic’s versatility and affordability makes it a go-to choice for many manufacturing processes. Not all plastics, however, are created equal – and selecting the wrong type of plastic can result in poor product performance, increased production costs, and negative environmental impact.

In this guide, we will cover common types of plastics used in several manufacturing processes, taking a close look at their properties, characteristics, and other important information. This knowledge will help you make informed choices, leading to improved efficiency in terms of both cost and time – as well as increased overall success rates.

The focus here is predominantly on injection molding, although we will also briefly touch on plastics commonly used in 3D printing and CNC machining.

The injection molding process only uses plastic. One of its advantages, however, is its ability to be used with a wide range of plastics, including thermoplastics, thermosets, and elastomers. This allows manufacturers to choose the best material for the application based on factors such as impact resistance, wear resistance, and cost efficiency.

The following plastics are commonly used in injection molding. We have grouped them broadly, by category. Some plastics, of course, belong in multiple categories. In the interest of order and brevity, we have avoided listing a plastic multiple times for a specific manufacturing process, although we have done our best to include as many properties as possible in the material’s description.

Impact resistance refers to a material’s ability to resist damage or deformation when subjected to sudden, high-force impact or shock. A material with high impact resistance can absorb and distribute the energy from an impact, reducing the risk of cracking, denting, or breaking. It is important in many applications, such as manufacturing of safety equipment, construction of buildings, and production of consumer goods. The following plastics exhibit high degrees of impact resistance.

ABS (Acrylonitrile-butadiene-styrene) is widely used in the manufacturing of consumer goods and industrial products. It is known for its impact resistance, making it a popular choice for applications that require a material to withstand impact and shock. ABS also offers good dimensional stability and is easily machinable, which makes it suitable for applications that require tight tolerances. It is also resistant to chemicals, heat, and moisture, and exhibits a glossy and smooth surface finish.

PS (Polystyrene) offers good dimensional stability and impact resistance. It is commonly used in applications such as toys, packaging, and electronic housings. PS is a versatile material that can be easily molded into complex shapes. Its dimensional stability is due to its low coefficient of thermal expansion, which means it is less likely to warp or deform when exposed to temperature changes. PS is also lightweight, cost-effective – and exhibits a smooth, glossy surface finish.

PVC (Polyvinyl chloride) is widely used in the construction, healthcare, and packaging industries. PVC offers excellent impact resistance, making it a popular choice for applications that require durability and strength. It is also lightweight, weather-resistant, and flame-retardant, and therefore a good choice for use in outdoor applications and building materials. PVC can be easily molded, extruded, and fabricated, which makes it a cost-effective material for a variety of applications, including window frames, pipes, and medical tubing.

PE (Polyethylene) is a thermoplastic that is widely used in a variety of applications due to its excellent chemical resistance, low moisture absorption, and good impact resistance. PE is available in several different grades, including high-density polyethylene (HDPE) and low-density polyethylene (LDPE). HDPE is known for its excellent stiffness and impact resistance, making it a popular choice for applications that require a durable material. LDPE, on the other hand, is more flexible and has better impact resistance, making it suitable for applications such as plastic bags and packaging materials.

Polycarbonate (PC) is a durable and impact-resistant thermoplastic that is commonly used in applications that require high strength and optical clarity. PC offers excellent impact resistance, making it suitable for applications such as safety glasses, automotive parts, and electronic components. It is also lightweight and resistant to heat and chemicals, which makes it a popular choice for applications in the aerospace, automotive, and medical industries. Additionally, PC is easy to fabricate, can be molded into complex shapes, and exhibits a glossy, transparent surface finish.

Wear resistance in plastic refers to the ability of a plastic material to resist damage or deterioration due to friction or abrasion. Plastics with high wear resistance are ideal for applications where they will be subjected to constant wear, such as gears, bearings, and other mechanical components.

POM (Polyoxymethylene) is often used in applications that require stiffness, high durability and resistance to wear, such as gears, bearings, and other mechanical components. Due to its low friction coefficient, POM is also suitable for applications where high abrasion resistance is required, such as conveyor belts and sliding components. In addition to its excellent wear resistance, POM is also resistant to chemicals and moisture, and is therefore suited to industrial applications.

PEEK (Polyetheretherketone) has exceptional mechanical properties, including high strength, stiffness, and wear resistance. It is often used in applications such as bearings, bushings, and gears. Due to its high temperature resistance, PEEK is also suitable for use in high-temperature environments, such as aerospace and automotive applications. PEEK also exhibits excellent chemical resistance, as well as resistance to radiation and abrasion.

UHMW (Ultra-high molecular weight polyethylene) is known for its exceptional wear resistance and low coefficient of friction. UHMW is often used in applications that require high durability and resistance to wear, such as conveyor systems, chute liners, and gears. UHMW is also lightweight, impact-resistant, and self-lubricating, which makes it suitable for use in applications where low friction and noise are important. UHMW is also chemical- and moisture-resistant.

Dimensional stability refers to a material’s ability to maintain its shape and size when exposed to changes in temperature, humidity, and other environmental factors. Plastics with high dimensional stability are less likely to warp, deform, or shrink, making them ideal when precision and accuracy are essential, such as in the manufacturing of electronic components, medical devices, and automotive parts.

PBT (Polybutylene Terephthalate) is commonly used in electronic and automotive applications where tight tolerances and stability are crucial. PBT has a low coefficient of thermal expansion, which means it is less likely to warp or deform when exposed to temperature changes. It also has good electrical properties, and is often used to create electrical connectors and housings. It can withstand harsh environments and repeated stresses, making it a popular choice in industries such as aerospace, medical, and telecommunications.

PTFE (Polytetrafluoroethylene), commonly known by the brand name Teflon, is known for its excellent dimensional stability, as it has a low coefficient of thermal expansion. This means PTFE undergoes minimal dimensional changes with temperature fluctuations, making it highly resistant to warping, shrinking, or expanding under different temperature conditions. PTFE’s dimensional stability is advantageous in applications where precision and tight tolerances are required, such as in mechanical components, gaskets, and seals. It also exhibits good chemical resistance and non-stick characteristics – and as such is often used in the packaging and food processing industries.

PPS (Polyphenylene Sulfide) offers excellent dimensional stability. It is commonly used in applications where high temperatures and harsh environments are present, such as in automotive and aerospace parts. PPS has a low coefficient of thermal expansion, which means it is less likely to warp or deform when exposed to temperature changes. It also has excellent chemical resistance and is highly resistant to creep – the slow deformation of a plastic material over time under a constant load or stress – and is often used in situations in which other plastics would fail.

Chemical resistance refers to the ability of a material to resist the harmful effects of chemical substances, such as corrosion or degradation, when exposed to them. Materials with high chemical resistance are able to maintain their physical and chemical properties when in contact with these substances, without deteriorating or reacting with them.

PP (Polypropylene) is a cost-efficient plastic that offers good chemical resistance, making it ideal for use in chemical processing applications. It is also lightweight and has good mechanical properties, making it a popular choice for packaging and disposable products. Its moisture resistance, meanwhile, means it is suited for creating applications such as medical devices and outdoor equipment.

PE (Polyethylene) is widely used in packaging and disposable products due to its low cost and good chemical resistance. It is also lightweight and has good mechanical properties, making it a popular choice for outdoor equipment and toys. PE has a high resistance to moisture, and is often used in applications such as in medical devices and water pipes.

HDPE (High-density Polyethylene) is a thermoplastic polymer that offers good chemical resistance and is commonly used to make toys, food preparation products and durable packaging such as shampoo bottles. It is also lightweight, low-cost, and has good mechanical properties, making it a popular choice for outdoor equipment.

PA (Polyamide), commonly known as Nylon, offers good chemical resistance and mechanical properties – although chemical resistance will vary with the grade of Nylon used. It is widely used in applications where toughness and durability are needed, such as in automotive and industrial parts. It is also abrasion- and impact-resistant. Its chemical resistance, meanwhile, allows it to withstand exposure to harsh chemicals and solvents, making it ideal for use in chemical processing applications.

Rubber-like qualities refer to elasticity, flexibility, and resilience. Rubber-like materials can stretch and bend without breaking, and can also return to their original shape after being deformed.

TPE (Thermoplastic Elastomers) is a family of plastics that includes TPU, and exhibit rubber-like elasticity and flexibility. They are commonly used in applications where soft-touch and ergonomic features are important, such as in automotive interiors and medical devices. TPEs are also resistant to weathering and chemicals, and are thus often used in outdoor and chemical processing applications. They can also easily be molded into complex shapes and textures, making them a popular choice in the consumer products industry.

Silicone is a synthetic polymer commonly used in applications where durability and flexibility are important. Silicone is also resistant to heat, cold, and chemicals, and is often used in extreme environments. Its rubber-like qualities make it easy to mold into complex shapes. It is also non-toxic and hypoallergenic, making it safe for use in medical and food-related applications.

Cost efficiency in a plastic material refers to the ability of the material to deliver desired performance and quality at a reasonable cost. This includes factors such as raw material cost, processing costs, energy consumption, waste reduction, and product durability. A cost-efficient plastic material strikes a balance between these factors while meeting the desired application requirements.

In addition to being cost-efficient, PP offers good mechanical properties, making it a popular choice for packaging and disposable products. It is also lightweight and has good chemical resistance. PP has a low density, and is an affordable choice for products that require a large volume of material, such as bottles and containers.

HDPE (High-density Polyethylene) offers excellent chemical resistance and durability, and is suited to applications such as pipes, containers, and packaging. Its high strength-to-density ratio makes it a popular choice in the construction industry for products such as plastic lumber and decking. HDPE is also lightweight, making it a cost-effective option for products that require a large volume of material.

Many materials can be used in 3D printing, including plastic, metal, and ceramics. However, there are several key benefits to using plastic material.

• Versatility. Plastic can be used to create a wide range of shapes, sizes, and textures.
• Durability. Plastic materials used in 3D printing are often durable and can withstand various environmental conditions.
• Affordability. Plastic materials used in 3D printing are often less expensive than other materials such as metal or ceramic.
• Weight Plastic materials are often lightweight, making them ideal for creating parts that need to be lightweight or for applications that require mobility.
• Customizability. Plastic materials can be easily customized and modified to meet specific application requirements.

The following are five of the most commonly used plastics in 3D printing and their properties.

• PLA (Polylactic Acid). A biodegradable plastic made from renewable resources. It’s easy to print, has a low melting point, and produces minimal warping. However, it’s brittle and has low heat resistance.
• ABS. A strong and durable plastic with good heat resistance. It’s commonly used in automotive parts and household items. However, it produces strong fumes during printing and requires a heated print bed.
• PETG (Polyethylene Terephthalate Glycol). A strong and flexible plastic with good impact resistance. It’s food-safe and easy to print with. However, it can be prone to stringing and requires a higher printing temperature.
• Nylon. A strong and flexible plastic with high abrasion resistance. It’s commonly used in mechanical parts and gears. However, it’s difficult to print with and requires high temperatures and special printing conditions.
• TPU. A flexible and elastic plastic with good impact resistance. It’s commonly used in phone cases and shoe soles. However, it can be difficult to print with due to its tendency to warp and requires a slow print speed.

Like 3D printing, CNC machining is compatible with a range of materials. Here are a few of the benefits of using plastic with CNC machining.

• Versatility. Plastics can be machined into complex shapes and sizes, making them suitable for a wide range of applications.
• Weight. Plastics are often lighter than metals, which makes them a good choice for applications where weight is a concern.
• Cost-efficiency. Plastics are often less expensive than metals, making them a cost-effective option for manufacturing.
• Chemical resistance. Plastics are resistant to many chemicals, making them suitable for use in harsh environments.
• Electrical insulation. Some plastics have excellent electrical insulation properties, making them ideal for use in electrical and electronic applications.

The following are five of the most commonly used plastics in CNC machining and their properties.

• POM. Offering good dimensional stability, low friction, and excellent wear resistance, it is ideal for producing parts with tight tolerances, such as gears and bearings.
• PC. Transparent, with excellent impact resistance, high temperature resistance, and good electrical insulation. It is used in applications that require high transparency and durability, such as lenses and safety shields.
• PMMA (Acrylic). A transparent thermoplastic with good impact resistance, weather resistance, and optical clarity. It is commonly used in displays, signs, and lighting applications.
• PE. Offering excellent chemical resistance, low friction, and good electrical insulation. It is commonly used in applications such as packaging, tanks, and chemical processing equipment.
• PA (Nylon). Excellent strength, stiffness, and wear resistance. It is commonly used in applications that require high mechanical performance, such as gears, bearings, and bushings.

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You can learn more about injection molding, CNC machining with plastic and 3D printing with plastic on our website – or contact networksales@protolabs.com for personalized advice about your project.