Before you start designing your product, you must decide which thermoplastic you will use. Your material requirements may vary depending on the industry, the product’s environment, and the product’s intended life span. The two most common types of thermoplastics are commodity and engineering.
A thermoplastic resin becomes molten when heated above a certain point and solidifies when cooled. The process can easily be reversed without any impact on its properties. Engineering grades have a higher melting point than commodity plastics.
Before choosing your plastics, you need to you will need to answer questions about the product’s design and use. Examples include:
- Will the product be exposed to harsh environmental conditions?
- Will it be exposed to chemicals or solvents?
- Does it need to be compatible with other elements?
- Will it be exposed to very high or very low temperatures?
- Does it need to be strong or impact-resistant?
- How critical is the surface finish?
- What are acceptable tolerances?
- How complex is the shape?
Thermoplastics each have their own properties that may or may not be useful for your product. Working with an injection molder with vast material knowledge is critical to help you choose the correct thermoplastic for your project. Below is a brief overview of some commodity and engineering grades Greenleaf has experience with.
Commodity Thermoplastics for Injection Molding
Commodity thermoplastics are inexpensive and easy to process. They are used in various applications, including toys, interior automotive parts, and consumer products. Below are the pros, cons, and uses for five common commodity plastics used for injection molding.
Acrylonitrile Butadiene Styrene (ABS)
Pros
- Superior stiffness and strength
- Outstanding impact and abrasion resistance
- Excellent chemical resistance
- Low cost
Cons
- Not appropriate for high temperatures
- Poor solvent resistance
- High fatigue resistance
- Doesn’t stand up well to UV exposure and weathering
Some uses include:
- Toys (like LEGO® blocks)
- Consumer goods
- Machine housing
- Auto interiors
Poly (methyl methacrylate) (PMMA) – also known as acrylic
Pros
- Good strength and stiffness
- Optically clear
- Good dimensional stability
- Resistant to shrinkage and flash
- moderate cost
- Excellent insulation properties
- Good weathering
Cons
- Will crack under high pressure – not for structural use
Some uses include:
- Aquariums
- Casing
- LED diffusing light panels
- Glass replacement
Polypropylene (PP)
Pros
- High impact resistance
- Excellent durability
- Easily processed
- Food contact safe
- High chemical resistance
Cons
- Low strength
- Sensitive to UV light
- Not suitable for high-temperature applications
Some uses include:
- Consumer goods
- Living hinges
- Automotive components
Polyethylene (PE)
Pros
- Durability
- High impact strength
- Resistant to warpage and shrinkage
- Highly flexible
Cons
- Low strength
- High thermal expansion
- Poor weatherability
Some uses include:
- Tool handles
- Toys
- Bottle caps
- Packaging
Polystyrene (PS)
Pros
- Good rigidity
- Lightweight
- Easily molded
- Foods safe
Cons
- Poor impact strength
- Poor chemical and solvent resistance
Some uses include:
- Food packaging
- Automotive parts
- Plastic utensils
- Toys
- Product casing
Engineering Thermoplastics for Injection Molding
Engineering resins have better thermal and mechanical properties than commodity plastics. They offer high strength as well as heat, wear, and corrosive resistance. Engineering plastics are often used to replace other materials, such as metal, to reduce product weight.
Acetal
Pros
- Moderate strength and impact resistance
- Excellent chemical resistance
- Excellent wear and abrasion resistance properties
- Can maintain shape when exposed to heat and pressure
- Fair resistance to warpage and shrinkage
Cons
- Degrades when exposed to considerable UV light
- Poor resistance to acid
Some uses include:
- Valve parts
- Bearing
- Springs
Polycarbonate (PC)
Pros
- Good strength & impact resistance
- Heat resistant
- Excellent stiffness
- Dimensionally stable
- Good optical clarity
Cons
- Impact strength drops dramatically in freezing temperatures
- Poor scratch resistance
- Poor solvent resistance
Some uses include:
- Light covers
- Lenses
- Face shields
- Machine guards
Polyamide (PA) – common name is Nylon
Pros
- High strength and impact resistance
- Dimensional stability
- High abrasion resistance
- Good chemical resistance
- Filled grades offer additional properties.
Cons
- Water absorption
- Low resistance to acid and bases
- High shrinkage
Some uses include:
- Bearings
- Bushings
- Rollers
- Machinery parts
- Suited for structural parts
Thermoplastic Elastomer (TPE)
Pros
- Rubber-like characteristics – Returns to original shape when stretched to moderate elongation
- Good weatherability
- Good UV resistance
Cons
- Low strength
- Susceptible to creep
- Can lose rubbery properties at high temperatures
Some uses include:
- Seals
- Bushings
- Footwear
- Auto parts
Polybutylene Terephthalate (PBT)
Pros
- High resistance to solvents
- High strength
- Excellent dimensional stability
- Good heat resistance
- Good electrical resistance
Cons
- Poor resistance to acids, bases, and hydrocarbons
- Poor resistance to hydrolysis (sensitive to boiling water)
- Prone to warpage due to high differential shrinkage
Some uses include:
- Auto parts
- Electronic and electrical parts
- Mechanical gears
- Sporting goods
Let’s Create Something Great
The list above is just a few of the thermoplastics we have experience with at Greenleaf Industries. With so many thermoplastics available, knowing which is the best choice for your application and budget can be challenging. When you choose our plastic injection molding services, we can work with you to design and engineer your product and use efficient production processes to cut costs, reduce cycle time and offer 100 percent on-time delivery.
Contact us to learn how we can reduce your production costs.
