Which are the Best Injection Molding Materials?
Injection Molding materials selection is one of the most crucial parts for rapid and quality production. That becomes even more significant because injection molding processing needs supremely suitable materials to perform better. Having said that, selecting the best plastic material for the process is not rocket science.
With some research selecting the best injection molding material can become relatively easy.
But, a question might pop up in your mind. There are thousands of plastic materials out there, which one to choose?
Today, I will be sharing a list of 10 thermoplastics that can improve your injection molding productivity by many notches.
10 Best Injection Molding Materials –
- Polypropylene (PP)
- Acrylonitrile Butadiene Styrene (ABS)
- High-Density Polyethylene (HDPE)
- Polyoxymethylene (POM)
- Polycarbonate (PC)
- Polyethylene (PE)
- Thermoplastic Rubber (TPR)
- Polystyrene (PS)
#1 Polypropylene (PP):
Polypropylene is an “addition polymer” produced using polymerization and with the combination of propylene monomers.
High chemical and moisture resistance, flexibility, toughness, and excellent electrical insulation make polypropylene highly suitable for injection molding.
The common applications can be found in the food packaging industry. Washing and cleaning are also easy without degradation and damage chemicals. Mixing with foods is not a scenario with packaging made of PP. That’s why it is safe for human contact, and moisture resistance keeps the inside warm and fresh for a prolonged period of time.
Below is the table sharing the typical properties of polypropylene:
2 – 6 kJ/m2 at 20 °C
1.04 – 1.06 g/cm3
|Elastic Modulus||1.5 – 3 GPa|
0.41 W/(m.K) at 20 °C
|Flammability||UL 94 HB|
1*1013 – 1*1014 Ω.m at 20 °C
|Dielectric constant||2.8 at 20 °C|
|Specific heat capacity||
1520 J/(kg.K) at 20 °C
|Max. service temperature (short)||140°C|
|Coefficient of thermal expansion||
6*10-5 – 1*10-4 1/K at 20 °C
Nylon, also known as Polyamide, is a synthetic thermoplastic switch, a special structure where components are bound in some bond.
Nylon is made by filtration of hydrocarbon fuels into lighter groups of small molecules called “Fractions.”
Good chemical and thermal resistance, high melting temperature, high toughness, and brittleness make it one of the injection molding materials suitable for applications like mechanical parts, gears, bushing, bearings utilized mostly in automobile and electrical industries.
The only drawback one might face is the expansiveness of nylon. There’s a table below with general properties of typical variations of Nylon or polyamide
|Property||Units||ASTM Test||Extruded NYLON 6/6||Cast NYLON 6||
Oil-Filled Cast NYLON 6
|Flexural modulus||psi||D790||410,000||420,000 – 500,000||
375,000 – 475,000
|Tensile Strength||psi||D638||12,400||10,000 – 13,500||9,500 – 11,000|
|Heat deflection temperature – 264 psi||°F||D648||194||200 – 400||200 – 400|
|Water absorption (immersion 24 hours)||%||D570||1.2||0.60 – 1.20||0.50 – 0.60|
|Maximum continuous service temperature in air||°F||–||210||230||230|
|Coefficient of linear thermal expansion||in/in/°Fx10-5||D696||4.5||5||5|
|Izod Impact||ft-lbs/in of notch||D256||1.2||0.7 – 0.9||1.4 – 1.8|
Acrylic is a naturally transparent thermoplastic homopolymer better known by the trade name “Plexiglass.” Apart from being transparent, it also has scratch and impact resistance with high tensile strength.
It is often utilized as a suitable alternative for glass and even its alternative Polycarbonate for manufacturing windows, doors, transparent walls, display products lenses, fashion accessories, and even lighting equipment for the construction industry.
However, I would suggest using polycarbonate over acrylic for highly demanding applications.
|Melt Temperature||130°C (266°F)|
65 MPa (9400 PSI) ***
0.2 – 1% (.002 – .01 in/in) ***
90 MPa (13000 PSI) ***
Typical Injection Mold Temperature
79-107°C (175-225°F) ***
Water absorption (immersion 24 hours)
Heat deflection temprature
95°C (203°F) at 0.46 MPa (66 PSI) **
#4 Acrylonitrile Butadiene Styrene (ABS):
Acrylonitrile Butadiene Styrene is an opaque thermoplastic and amorphous polymer produced mainly by emulsion and mass polymerization methods; however, Emulsion is mostly preferred.
Key properties include toughness, scratch resistance, impact resistance, and good dimensional stability.
ABS is widely used in the electronics industry for manufacturing computer keyboards, power toll-housings, phone adapters, wall socket plastic guards, and even lego toys. It is one of the few injection molding materials with the strength and agility required to be utilized in electronics.
#5 High-Density Polyethylene (HDPE):
High-Density Polyethylene is durable and lightweight thermoplastic with variable structures. It is made by radical polymerization of ethylene monomers with Ziegler-Natta and Metallocene acting as catalysts.
HDPE has low-temperature resistance, high tensile strength, good chemical resistance, and excellent electrical insulating properties.
It is mostly used for food packaging applications like bottles of milk and juices, crates, trays, etc., and textile applications like ropes, decorative fabrics, fishing nets, etc.
#6 Polyoxymethylene (POM):
Polyoxymethylene is a formaldehyde-based, semi-crystalline engineering thermoplastic material containing the functional group of a carbon bonded to two -OR groups.
With excellent wear resistance, high crystallinity, and fantastic dimensional stability, good resistance to organic solvents makes POM one of the prime injection molding materials.
POM’s high-end properties make it suitable for applications in industries like automobiles, healthcare, and consumer goods.
Main products made from POM include ball bearings, knives, fasteners, pipe couplings, showerheads, automobile cushioning interior, etc.
Polyoxymethylene is inferior to hydrochloric acid and nitric acid.
#7 Polycarbonate (PC):
Polycarbonate is one of the most suitable injection molding materials used in industries like automobile, construction, consumer goods, electronics, and healthcare.
Polycarbonate is available in multiple grades and variations depending on the purpose.
Major properties include high impact strength, good abrasion resistance, excellent chemical resistance, great steam resistance (not affected by water or temperature), withstanding prolonged steam sterilization, etc.
Major products producing PC are coffee machines, food mixers, light housings, headlamp bezels, security windows, shelters, safety goggles, lenses, food storage containers, food processors, etc.
Polyethylene is one of the most produced plastic materisl in the world, with a variety of applications in multiple industries. Like PC, polycarbonate also boasts a variable crystalline structure.
There are three major variations within polyethylene. They are:
- Branched variation
- Linear variations
- Cross-linked polyethylene
Some of the major properties are phenomenal resistance to most solvents( except hydrocarbons), great electrical insulating properties, inexpensiveness, and decent water resistance.
Products made from PE include oil and liquid food containers, housewares, ice-boxes, toys, jerry cans, drums, pharmaceutical packaging, squeeze bottles, caps, pipes, garbage containers, etc.
#9 Thermoplastic Rubber (TPR):
Thermoplastic Rubber, or TPR, is sometimes called Thermoplastic elastomer (TPE), is a blend of rubber and plastic suitable for injection molding. It shows both rubber and plastic properties, which means it melts when heated and solidifies when cooled.
Like many other injection molding materials on the list, TPR is recyclable, which increases its applicability and helps manufacturers control their carbon footprint. Its boasts fantastic chemical and weather resistance coupled with high-impact strength.
Major products made from thermoplastic rubber are cable jacketing, footwear, automobile components, toys, soft handles and grips, window and door weather stripping, coated fabrics, household appliances, etc.
#10 Polystyrene (PS):
Polystyrene is a naturally transparent thermoplastic material that is available in both solid plastic and foam material forms. Amongst the foam form, there are two major variations 1) Expanded Polystyrene (EPS) and extruded polystyrene (XPS).
Talking about solid plastics, major variations are 1) General Purpose Polystyrene (GPPS) 2) High Impact Polystyrene (HIPS).
Major polystyrene properties are high chemical and heat resistance, high UV stability, and high dimensional stability. The most common applications are CD and DVD cases, food trays and containers, egg cartons, toys, automobile parts, gardening tools, equipment, etc.
53 MPa (7700 PSI)
210-249 °C (410-480 °F)
Heat Deflection Temperature (HDT)
95 °C (284 °F) at 0.46 MPa (66 PSI)
83 MPa (12000 PSI)
Typical Injection Molding Temperature
38 – 66 °C (100 – 150 °F)
Molecular Weight of Repeat unit
104.15 g mol-1
Molar Cohesive Energy
J mol-1 34200 – 37100
g mL-1 1.05 – 1.06
Entanglement Molecular Weight
g mol-1 13600 – 17500
18.5 – 19.4 MPa
1. What are the types of injection molding variations?
Ans. There are many variations associated with injection molding. Here are the most popular variations:
- Metal injection molding
- Micro-injection molding
- Cube molding
- Reaction injection molding
- Thin-walled injection molding
- Gas-assisted injection molding
- Liquid silicon rubber injection molding
2. Which is the strongest Injection molding plastic?
Ans. Polycarbonate is the strongest plastic material in the world. It is said to be 200 times stronger than glass.
3. How do I choose an injection molding machine?
Ans. There are four factors needed to be considered before the injection molding machine selection process. Here are they:
- Know the plastic parts to intend to mold
- Select machine type: Hydraulic, electric, or hybrid
- Calculate clamp weight requirements
- Calculate injection mold size
4. What are the stages of injection Moulding?
Ans. There are four stages in the injection molding cycle – Clamping, injection, cooling, ejection
5. Why does it take so much time to design and manufacture an injection mold?
Ans. It takes somewhere around a few weeks to a couple of months to design an injection mold. There are many factors contributing to the amount of time required. It can be anything from supplier inventory backlogs, available resources, the complexity of the molded part, the complexity of the desired mold, and even the number of cavities.
Fantastic Read – Top 10 Injection Molding Defects (And How To Prevent Them)
Final Thoughts –
Thus were my views on the top 10 injection molding materials. I have kept the piece brief and simple to understand. You can click on the detailed guide links to know more about the material.
In addition, always consult with your manufacturer regarding the properties and attributes of the polymer supposed to be used for manufacturing. Even the tiniest detail missed can have a significant effect on the production time and the quality of the produced part.
Kindly share your reviews in the comment box.