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Top 5 Most Common Plastic Resins for Injection Molding

Posted by Jill Worth

7/12/16 6:30 AM

The job of a plastic injection molder involves helping the client select the best available plastic material given the application. The selection and availability of various polymers has exploded over the past 30 years. Today, it can be overwhelming to figure out what the best plastic material is for your project.

When clients come to us with their designs, they often suggest a particular material, due simply to their familiarity with it. However, at The Rodon Group, we feel it’s our duty, when applicable, to suggest alternatives when they exist.

The following article will give a brief discussion of our most commonly used resins. The discussion will look at impact strength, tensile strength, flexural modulus of elasticity (the amount a material can be bent, and still snap back to its original form,) and heat deflection qualities.

Materials Tensile Strength
(73° F)
(Units: psi)
Flexural Modulus of Elasticity
(73° F)
(Units: psi)
Izod Impact
(Notched)
(73° F)
(Units: ft-lbs/in)
Heat Deflection Temperature
(66 psi / 264 psi)
(Units: °F)
Water Absorption
(24 hr Immersion)
(Units: %)
ABS 4,100 304,000 7.7  200° / 177°  0.3
Acetal 10,000 420,000 1.5  336° / 257°  0.25
High Impact Polystyrene 3,500 310,000 2.8  - / 196°
LDPE 1,400 30,000 no break  122° / - 0.1 
Polypropylene 5,400 225,000 1.2  210° / - slight 

 

ABS 
Acrylonitrile Butadiene Styrene, or ABS, is a very common plastic material. First introduced in 1948, ABS was quickly adopted by a wide spectrum of industries from appliances, to piping, to automotive parts. It possesses outstanding impact and mechanical strength. Metal coatings have excellent adhesion to ABS, making it a great material for desktop phones, shower heads, faucets, handles, etc.

ABS should not be used in applications in which it will be required to resist chemical solvents, provide electrical insulation, or withstand UV exposure.

Celcon (Acetal)
Celcon.jpgCelcon is a common brand name for Acetal, a resin with great surface lubricity and creep resistance (memory). Unlike ABS, Acetal has good chemical solvent resistance and is frequently used in food and water applications. It’s also commonly found in mechanical &  automotive and household appliances in the form of slides, gears, cams, bushings, door handles, and seat belt parts. At Rodon, we use it to manufacture K’NEX toy parts, as well as gears and bearings.

Acetal should not be used for applications in high heat environments or where less expensive resins may be substituted.  It can also be difficult to bond, or glue.

Polypropylene 
Polypropylene (PP) is another very common plastic and is known for its flexibility. Impact-modified grades have  good impact strength and good cold-crack resistance. PP is a very dynamic plastic and has been compounded for a wide range of properties (at a wide range of costs.) It has good chemical solvent and electrical resistance. Common applications include packaging, industrial components for fluid processing, household goods, as well as some automotive components.

Note that most grades of PP are flammable and degraded by UV radiation. It can also be susceptible to chlorinated solvents.

HIPS 
HIPS.jpgHigh Impact Polystyrene is a popular low-cost and tough plastic that’s made from modifying crystal styrene with rubber. This gives it  many levels of impact resistance. HIPS is commonly found in point-of-purchase displays, printed graphics, thermoformed machine housings and parts, models, and prototypes. It can also be found in shelves, kiosks, and fixtures for its aesthetic qualities. It is easy to glue, or bond and can accept printing and decorating.

It is flammable, although flame retardant grades are available. It also has poor solvent resistance and is subject to stress and environmental cracking.

LDPE 
Low Density Polyethylene, as the name suggests, is the softest and most flexible version of the polyethylene family. It has excellent impact strength due to its physical properties, and is moisture resistant. Common applications include consumer products, houseware items, electronic wire/cable insulators, and medical products such as prosthetics.

LDPE should not be used for applications in high temperatures, and extreme weather. It is also flammable and can be difficult to bond.


Choosing the right material for your application can result in increased performance, manufacturability, and reduced cost. We strongly recommend researching your options and consulting with an experienced plastic injection molder to determine the best material for your specific application. 

If you’re interested in learning more about the resin selection process, we recommend reading our Plastic Injection Molding 101 post. For any other questions, feel free to visit our Contact Us page.

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Topics: Plastic Injection Molding, Plastic Manufacturing

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