Most common injection moulding plastics

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Selecting a suitable material for injection moulded parts is one of the most important aspects of any engineering product design. It is vital to consider the injection moulding material selection at an early stage of product design as it impacts both part functionality and tooling cost.

Injection moulding is a method of producing plastic components. The process requires an injection moulding machine, mould, and raw material. The injection moulding machine melts the plastic, which cools inside the mould to take the shape of the finished product.

Injection moulded plastics

The consumption of plastic has increased unprecedentedly in recent years due to the global demand for consumer products. This demand has driven companies to find new and advanced polymers to withstand any application and environment, resulting in thousands of plastics and more than 45 polymer families.

According to the mat web database, there are over 70000 Thermoplastics and 18000 Thermosets available to choose from, highlighting the challenges faced by engineering product designers.




Narrowing down this vast selection of injection moulding material options is an overwhelming task, so finding a starting point is essential. The following material guide lists some of the most commonly used injection moulded materials and their benefits and properties.

Injection moulding material list

Most common Injection moulding materials
Acrylonitrile Butadiene Styrene (ABS)
Polycarbonate (PC)
Polycarbonate + Acrylonitrile Butadiene Styrene (PC/ABS)
High Impact Polystyrene (HIPS)
Polyphthalamide (PPA)
Polymethyl Methacrylate Acrylic (PMMA)
High-Density Polyethylene (HDPE)
Low-Density Polyethylene (LDPE)
Polypropylene (PP)
Polyoxymethylene (POM)

Acrylonitrile Butadiene Styrene (ABS)

Due to its flexible and diversified qualities, ABS is one of the most widely used injection moulding materials for engineering products. ABS offers the right combination of mechanical toughness, chemical resistance, and electrical insulating properties across a wide range of temperatures.

ABS hand console ( Source:ebay)

ABS is an opaque amorphous thermoplastic with a glass transition temperature of 105 degrees Celsius. Carbon black and UV stabilizers can be added to the base ABS to modify to avoid UV degradation for outdoor products.

Its mechanical properties, ability to add additives to change the composition to withstand the various application environments, and ease of colour change make ABS an attractive injection moulding material for consumer electronics.

It can be easily machined, relatively cheap and widely recycled, making it ideal for rapid prototyping at various new product development stages.

Common ABS brands – Polylac, Cycolac, LG ABS, Elix, Lustran, Novodur, Kumho, Magnum and Gebabs

Benefits and Limitations

BenefitsLimitations
It offers good impact resistance, toughness, and rigidityLow resistance against solvents
ABS surface is ideal for metal coatingsVulnerable against outside harsh weather
Excellent appearance and processabilityIt has low dielectric strength
Good resistance against chemicalsNot suitable for high-temperature application

Applications

  • Handheld consumer devices
  • Refrigerator vegetable boxes
  • Large photocopier panels
  • Interior and exterior automotive parts
  • Electrical toys

Properties

PropertyValueUnits
Density1140 - 1140Kg/m3
Young Modulus 2.20 - 2.50GPa
Elongation at Break50 - 120%
Elongation at Yield6.00 - 7.00%
Strength at Break (Tensile)55 - 77Mpa
Strength at Yield (Tensile)61 - 69Mpa
Toughness (Notched Izod Impact at Room Temperature)80 - 650J/m2
Flexibility-Stiffness (Flexural Modulus)2.2 - 2.5GPa
Hardness Shore D90 - 95
Shrinkage0.7 - 1.0%
Glass Transition Temperature160 - 200°C
UV Light ResistanceFair
Gamma Radiation ResistanceGood
Water Absorption 24 hours0.1 - 0.2%
Min. Continuous Service Temperature-20 to -15°C
Max. Continuous Service Temperature86 to 89°C
Coefficient of Linear Thermal Expansion7 - 1510-5 /°C

Further reading

Polycarbonate (PC)

Polycarbonate is an amorphous transparent thermoplastic polymer with excellent impact strength. Because of transparency and inherent UV filtering properties, it is frequently used as a substitute for glass such as lenses but is vulnerable to scratching.

Polycarbonate headlights (Source:calsak.com)

PC has exceptional mechanical properties and is highly suitable for moulding with tight tolerances. The compound has broad industrial and domestic applications.

They are less resistant to some solvents and petrochemical. The weather resistance of this polymer is not adequate, hence not recommended for outdoor applications without protective coatings, which will increase chemical and abrasion resistance.

PC is an excellent choice for injection moulding as it offers precise and predictable dimensional control in shrinkage.

Common Polycarbonate brands – Lexan Makrolon, Iupilon, Trirex, Lupoy, Carbotex and Ramtough

Benefits and Limitations

BenefitsLimitations
Possesses high strength and impact resistanceLess resistant to solvents
Less flammableCan crack in case of stress and susceptible to scratching
Dimensionally stable and able to keep tight moulding tolerancesDifficult to process because of the high temperature
It has good optical properties and a natural UV filterIt turns yellow if exposed to UV light for a long time without protection

Applications

  • Plastic eyewear lenses, CDs, and DVDs
  • Automotive parts such as headlights
  • Electrical insulators, connectors and lighting fixtures
  • Medical use and mechanical equipment

Properties

PropertyValueUnits
Density1140 - 1140Kg/m3
Young Modulus 2.20 - 2.50GPa
Elongation at Break50 - 120%
Elongation at Yield6.00 - 7.00%
Strength at Break (Tensile)55 - 77Mpa
Strength at Yield (Tensile)61 - 69Mpa
Toughness (Notched Izod Impact at Room Temperature)80 - 650J/m^2
Flexibility-Stiffness (Flexural Modulus)2.2 - 2.5GPa
Hardness Shore D90 - 95
Shrinkage0.7 - 1.0%
Glass Transition Temperature160 - 200°C
UV Light ResistanceFair
Gamma Radiation ResistanceGood
Water Absorption 24 hours0.1 - 0.2%
Min. Continuous Service Temperature-60 to -50°C
Max. Continuous Service Temperature100 to 140°C
Coefficient of Linear Thermal Expansion7 - 910-5 /°C

Further reading




Polycarbonate + Acrylonitrile Butadiene Styrene (PC/ABS)

Polycarbonate + acrylonitrile butadiene styrene (PC/ABS) is an engineering thermoplastic blend of PC and ABS. The properties of PC/ABS will depend on the ratio of the mix and any additives. PC/ABS is a high-impact engineering thermoplastic that is excellent for functional prototype and low-volume production.

PC/ABS Car dashboard (Source – polymer-compounders.com)

PC/ABS, like ABS, can be easily coloured and modified using modifiers such as flame retardants and impact modifiers. In addition, additives such as UV stabilizers and easy mould releases improve material characteristics to meet application requirements.

Also, reinforcing agents such as glass fibres and mineral fillers will improve the material for demanding applications. PC/ABS resins are suitable for applications requiring high toughness across a wide temperature range up to 110°C.

Common PC/ABS brands – Cycoloy, Pulse, Mablex, Emerge and Bayblend

Benefits and Limitations

BenefitsLimitations
Low overall shrinkagePoor insulator (Low dielectric strength)
Provides high strength, stiffness, and heat resistanceMedium impact performance& low continuous service temperature
Offers high toughness and dimensional accuracyPoor resistance against solvents
Printable and colourableLow fatigue endurance
Easy processing Poor resistance to outdoor weather exposure

Applications

  • Automotive components such as Glovebox, Knee bolsters, Blow moulded seatbacks.
  • Consumer electronics devices such as TV frames, Adapters and chargers
  • Mobile phone bodies and laptop monitors enclosures

Properties

PropertyValueUnits
Density1100 - 1150Kg/m3
Young Modulus 2.00 - 2.20GPa
Elongation at Break60 - 85%
Elongation at Yield3.00 - 5.00%
Strength at Break (Tensile)40 - 50Mpa
Strength at Yield (Tensile)45 -55Mpa
Toughness (Notched Izod Impact at Room Temperature)400 - 600J/m2
Flexibility-Stiffness (Flexural Modulus)2.0 - 2.3GPa
Hardness Shore D85 - 90
Shrinkage0.5 -0.7%
Glass Transition Temperature125°C
UV Light ResistanceFair
Gamma Radiation ResistanceGood
Water Absorption 24 hours0.2 - 0.3%
Min. Continuous Service Temperature-50 to -40°C
Max. Continuous Service Temperature70 to 110°C
Coefficient of Linear Thermal Expansion4 - 510-5 /°C

Further reading

High Impact Polystyrene (HIPS)

High impact polystyrene, widely known as HIPS, is an amorphous thermoplastic made from general-purpose polystyrene (GPPS) by adding rubber to increase its impact resistance and durability. Easy forming and properties such as low cost, high impact strength, and low density make HIPS ideal for model making applications.

HIPS Food Container
HIPS Food Container (Source: euroextrusions.com)

Due to its high pliable properties induced by the rubber, HIPS are widely vacuum formed. Although it is suited and commonly associated with vacuum or thermoforming, it is also an ideal material for injection moulding, especially for small parts in large quantities with high-level details.

Common HIPS brands – Ultratuf, Styron and Orfitrans™ Stiff​

Benefits and Limitations

BenefitsLimitations
Exceptional thermoforming properties Highly flammable
A recyclable and versatile material Poor resistance against organic solvents
Good rigidity and dimensional stability Recyclable, but uneconomical if recycled
Cost-effective
High impact strength
Lower surface friction

Applications

  • Used to make sports equipment and signage
  • Food packaging such as disposable trays, coffee cups and yoghurt cups.
  • Ideal material for creating ID cards

Properties

PropertyValueUnits
Density1030 - 1060Kg/m3
Young Modulus 1.5 - 3.0GPa
Elongation at Break10.00 - 50.00%
Elongation at Yield1.00 - 2.10%
Strength at Break (Tensile)20 - 45Mpa
Strength at Yield (Tensile)20 - 40Mpa
Toughness (Notched Izod Impact at Room Temperature)50 - 350J/m2
Flexibility-Stiffness (Flexural Modulus)1.5 - 3GPa
Hardness Shore D60 - 75
Shrinkage0.2 - 0.80%
Glass Transition Temperature88 - 92°C
UV Light ResistancePoor
Gamma Radiation ResistancePoor
Water Absorption 24 hours0.05 - 0.15%
Min. Continuous Service Temperature60 to 80°C
Max. Continuous Service Temperature-40 to-20°C
Coefficient of Linear Thermal Expansion5 - 2010-5 /°C

Further reading

Polyphthalamide (PPA)

Polyphthalamide, also known as PPA, is a high heat resistance polyamide. Compared to common polyamide types (PA6, PA66, PA11, PA12, PA46), it has very low moisture absorbent and excels in extreme temperature and chemical environments.

PPA gear
PPA gear(Source: wbsgear.com)

PPA is an excellent choice for metal replacement parts and parts with demanding requirements. PPA bridges the performance gap between nylons and polyesters and higher-priced, high-temperature materials such as PEI and PEEK.

Common PPA brands – Rilsan, Fortii, Amodel, Verton, Grivory, Zytel

Benefits and Limitations

BenefitsLimitations
Good dimensional stability and impact strengthSensitive to powerful oxidants, mineral acids, acetic acid and formic acid
Very low creep tendency & water absorptionNot flame-resistant
Good heat, chemical and fatigue resistanceRequires high processing temperatures
Good impact strength Special drying equipment required
Good chemical, heat and fatigue resistanceHigher cost compared to other common materials
High stiffness and strength compared to Nylon

Applications

  • Used for electrical connectors for high temperature
  • Extensive use in the automotive industry
  • Used to make combs, bearings, and spools
  • Used in cameras, structural parts

Properties

PropertyValueUnits
Density1110 - 1200Kg/m3
Young Modulus 3.7 - 3.7GPa
Elongation at Break2.60 - 3.0%
Elongation at Yield6.0 - 6.0%
Strength at Break (Tensile)80 - 90Mpa
Strength at Yield (Tensile)80 - 90Mpa
Toughness (Notched Izod Impact at Room Temperature)960 - 1065J/m2
Flexibility-Stiffness (Flexural Modulus)2.1 - 3.7GPa
Hardness Shore D60 - 95
Shrinkage1.50 - 2.20%
Glass Transition Temperature55 - 58°C
UV Light ResistancePoor
Gamma Radiation ResistanceFair
Water Absorption 24 hours0.36 - 0.75%
Min. Continuous Service Temperature-40 to -20°C
Max. Continuous Service Temperature60 to 80 °C
Coefficient of Linear Thermal Expansion5 - 610-5 /°C

Further reading

Polymethyl Methacrylate Acrylic (PMMA)

Polymethyl Methacrylate Acrylic, also known as Acrylic, is an amorphous transparent thermoplastic widely used as a glass replacement. Compared to other transparent polymers such as PC and Polystyrene, PMMA has a higher resistance to UV light, good weathering properties and superior light transmission.

Acrylic injection molding
Acrylic injection moulding (Source weetect.com)

When tensile strength, flexural strength, transparency, polishability, and UV tolerance are essential than impact strength, chemical resistance, and heat resistance, PMMA is a cost-effective alternative to polycarbonate (PC).

PMMA is also 100% recyclable, biocompatible and non-biodegradable.  Acrylic also can cope well with design without excessive shrinking or sinking due to irregular wall thicknesses. They are widely used to make light pipes, lenses, light shades, optical fibres and signs.

Common PMMA brands – Crylux, Plexiglas, Acrylite, Perspex

Benefits and Limitations

BenefitsLimitations
Offer extraordinary optical clarity Susceptible to organic solvents
Suitable for outdoor applicationsCracks under stress
Excellent scratch resistance compared with other polymers Melts easily
Offer sound transmission of light Absorbs moisture
Tough, durable and lightPoor impact resistance
High resistance to UV lightLow heat resistance (70oC - 90oC)

Applications

  • Transparent parts of automobiles like head and rear lenses
  • Covering of household lights
  • Used in making decorative materials
  • Used in Manufacturing safety materials and shields

Properties

PropertyValueUnits
Density1170 - 1200Kg/m3
Young Modulus 2.5 - 3.5GPa
Elongation at Break2.0 - 10.0%
Elongation at Yield2.0 - 10.0%
Strength at Break (Tensile)38 - 70Mpa
Strength at Yield (Tensile)38 - 70Mpa
Toughness (Notched Izod Impact at Room Temperature)10.0 - 25.0J/m2
Flexibility-Stiffness (Flexural Modulus)2.5 - 3.5GPa
Hardness Shore D90 - 99
Shrinkage0.2 - 0.8%
Glass Transition Temperature90 - 110°C
UV Light ResistanceGood
Gamma Radiation ResistanceGood
Water Absorption 24 hours0.1 - 0.4%
Min. Continuous Service Temperature-40 to -30°C
Max. Continuous Service Temperature70 to 90°C
Coefficient of Linear Thermal Expansion5 - 910-5 /°C

Further reading

High-Density Polyethylene (HDPE)

HDPE is a thermoplastic polymer with a linear structure and strong intermolecular forces, resulting in higher tensile strength compared to LDPE. Due to its high strength to density ratio, HDPE is used in a wide variety of applications, including corrosion-resistant pipelines, shampoo bottles, plastic lumber, plastic bottles, and cutting boards.

HDPE Injection Moulding cap
HDPE Injection Moulding cap(source: ampulla.co.uk)

They are light, have high toughness, strong chemical resistance, impermeability, and electrical insulating properties, making them one of the most versatile injection moulding materials available. Carbon black or UV additives will increase weather resistance.

Common HDPE brands – Marlex, Sabic, DOW and LG

Benefits and Limitations

BenefitsLimitations
Low cost and good processabilitySusceptible to stress cracking
Good impact resistance across a wide temperature range (-40oC to 90oC)Thermal expansion is high
FDA compliant and low water absorptionFlammable
Easily RecycledPoor temperature resistance
Excellent resistance to solvents Weather resistance is almost none
Good low-temperature resistanceHigh thermal expansion

Application

  • Excessive use in household usage
  • Used to make insulators for cables
  • Usage in Electronics and consumer products
  • Making of medical products

Properties

PropertyValueUnits
Density940 - 970Kg/m3
Young Modulus 0.5 - 1.1GPa
Elongation at Break500 - 700%
Elongation at Yield15.0 - 15.0%
Strength at Break (Tensile)30 - 40Mpa
Strength at Yield (Tensile)25 - 30Mpa
Toughness (Notched Izod Impact at Room Temperature)20 - 220J/m2
Flexibility-Stiffness (Flexural Modulus)0.75 - 1.575GPa
Hardness Shore D60 - 70
Shrinkage1.5 - 4.0%
Glass Transition Temperature-110°C
UV Light ResistancePoor
Gamma Radiation ResistanceFair
Water Absorption 24 hours0.005 - 0.01%
Min. Continuous Service Temperature-70 to -60°C
Max. Continuous Service Temperature100 to 120°C
Coefficient of Linear Thermal Expansion6 - 1110-5 /°C

Further reading

Low-Density Polyethylene (LDPE)

Low-density polyethylene is a semi-rigid and translucent polymer which belongs to the polyethylene family of thermoplastics.

LDPE Injection moulding bottles
LDPE Injection moulding bottles(Source: amirkhizplast.ir)

The wide range of properties of low-density polyethylene, such as soft, light, tough, and flexible making it an ideal choice for making containers, plastic bags, water pipes, and dispensing bottles. Plastic bags are the most common.

When subjected to stress, it can undergo permanent deformation; thus, making it not suitable for high-stress applications. LDPE also possess good electrical insulating properties and low water absorption but is very poor.

The ACC reports that LDPE has excellent resistance to acids, bases and vegetable oils. Its toughness, flexibility and relative transparency make it a good choice for packaging applications requiring heat-sealing.

Common LDPE brands – ExxonMobile, Nexxstar & Escorene Ultra

Benefits and Limitations

BenefitsLimitations
Excellent electrical insulating propertiesLow strength and stiffness
Low cost with easy processabilityVulnerable to stress cracking
Low moisture absorptionHighly flammable material
FDA graded materialShows high thermal expansion
High impact strength at low temperature Lower maximum service temperature
Excellent optical propertiesPoor UV resistance

Applications

  • Used to make diversified households
  • Used to make insulators for cables
  • Electronics products carry frequent use of this material
  • In the production of medical-related products

Properties

PropertyValueUnits
Density917 - 940Kg/m3
Young Modulus 0.13 - 0.3GPa
Elongation at Break200 - 600%
Elongation at Yield13.0 - 17.5%
Strength at Break (Tensile)10 - 20Mpa
Strength at Yield (Tensile)10 - 20Mpa
Toughness (Notched Izod Impact at Room Temperature)999 - 999J/m2
Flexibility-Stiffness (Flexural Modulus)0.245 - 0.335GPa
Hardness Shore D40 - 50
Shrinkage2.0 - 4.0%
Glass Transition Temperature-110°C
UV Light ResistanceFair
Gamma Radiation ResistanceFair
Water Absorption 24 hours0.005 - 0.015%
Min. Continuous Service Temperature-70 to - 60°C
Max. Continuous Service Temperature80 to 90°C
Coefficient of Linear Thermal Expansion10.0 - 2010-5 /°C

Further reading

Polypropylene (PP)

Polypropylene is a semi-crystalline light-weight thermoplastic and is one of the top three injection moulding material polymers used today to make varied products such as carpets, reusable water bottles and toys. It can be either homopolymers or copolymers with identical properties. They are tough and rigid and amongst the cheapest and lightest polymers available.

PP Rope
PP Rope

PP retains its mechanical and electrical properties even at elevated temperatures and in humid conditions. PP is also good at repelling water. Additives such as clarifiers, glass fibres, flame retardants, minerals, lubricants, conductive fillers, and pigments can improve physical and mechanical properties. Polypropylene has an identification code of 5 and is 100% recyclable.

Common polypropylene brands – Xyron, Ultrafuse, Torayca

Benefits and Limitations

BenefitsLimitations
Offer the best resistance against moistureErode if exposed to UV light
Better used as a food Graded materialHighly flammable
Excellent impact strength of the materialAffected by chlorinated hydrocarbons & solvents
Good resistance to environmental stress cracking and steam sterilizationPoor resistance to impact and scratches easily
Additives will improve propertiesBecome brittle below -20 oC
100% recyclableExtremely sensitive to highly oxidizing acids

Application

  • Polypropylene is used both as plastic and fibre.
  • Used in packaging material
  • Polypropylene fibres used in carpets
  • Making everyday usage products
  • Used in the automobile industry
  • Electrical components

Properties

PropertyValueUnits
Density900 - 910Kg/m3
Young Modulus 1.0 - 1.2GPa
Elongation at Break200 - 500%
Elongation at Yield6.00 - 250.0%
Strength at Break (Tensile)30 - 35Mpa
Strength at Yield (Tensile)20 - 35Mpa
Toughness (Notched Izod Impact at Room Temperature)60 - 500J/m2
Flexibility-Stiffness (Flexural Modulus)1.0 - 1.4GPa
Hardness Shore D70 - 80
Shrinkage2.0 - 3.0%
Glass Transition Temperature-20°C
UV Light ResistanceFair
Gamma Radiation ResistancePoor
Water Absorption 24 hours0.01 - 0.1%
Min. Continuous Service Temperature-20 to -10°C
Max. Continuous Service Temperature100 to 130°C
Coefficient of Linear Thermal Expansion7.0 – 17.010-5 /°C

Further reading

Polyoxymethylene (POM)

Polyoxymethylene, commonly known as Polyacetal or Acetal, is a semi-crystalline thermoplastic widely used for high precision engineering parts due to its high lubricity, excellent dimensional stability, good chemical resistance, and higher fatigue strength.

Acetal spur gear
Acetal spur gear (Source: 4plas.com)

POM has excellent mechanical properties across a wide range of temperatures ( -40oC to +140oC), such as high toughness, rigidity and tensile strength and low creep compared to some other plastic materials. Because of the above properties, Acetal is used as a metal alternative in engineering product design. Although they withstand a wide temperature range, it is worth noting that they are brittle at low temperatures and outgas at higher temperatures.

The use of this plastic material depends upon its grades; some of them are perfect for injection moulding, while some are not suitable.

Some grades of Acetal are also widely used in additive manufacturing due to their high lubricity, which makes them ideal for parts that are difficult to release.

Common Acetal brands – Delrin, Tecaform, Acetron and EMI

Benefits and Limitations

BenefitsLimitations
Wide temperature range -40oC to 140oC Poor resistance to strong acids, bases, and UV radiation
Excellent mechanical properties across wide temperature range – High toughness, tensile strength, and rigiditySensitive to the oxidising agents
High Impact resistance & dimensional stabilityMould shrinkage too high
Provides excellent solvent, chemical and wear resistance - except for phenolsDifficult to bond due to its low surface energy without any surface treatment
Glossy and low friction surface finishFlammable without any flame retardants due to high level of oxygen content
Very low creep and good resistance to environmental stress crackingThe processing temperature range is limited
Additives change the properties to suit the applicationPoor thermal stability without suitable stabilizer system

Applications

  • Extensive use in the automotive industry
  • Diversified applications in the making of everyday products
  • Mechanical components like bearings and cams
  • Limited role in the aviation industry

Properties

PropertyValueUnits
Density1410 - 1420Kg/m3
Young Modulus 2.8 - 3.7GPa
Elongation at Break15.0 - 75.0%
Elongation at Yield8.0 - 23.0%
Strength at Break (Tensile)60 - 70MPa
Yield Strength a (Tensile)54 -78MPa
Toughness (Notched Izod Impact at Room Temperature)60 - 120J/m2
Flexibility-Stiffness (Flexural Modulus)2.8 - 3.7GPa
Hardness Shore D80 - 95
Shrinkage1.8 - 2.5%
Glass Transition Temperature-60 to -50°C
UV Light ResistancePoor
Gamma Radiation ResistanceFair
Water Absorption 24 hours0.1 - 0.5%
Min. Continuous Service Temperature-40 to -30°C
Max. Continuous Service Temperature80 to 140°C
Coefficient of Linear Thermal Expansion10.0 – 15.010-5 /°C

Further reading

 

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