Plastics Properties

Q: How do I find out what the properties of particular plastics are?

A: Our Resource Library contains the current edition of Plastics Digest, a publication of IPS D.A:T.A:. These volumes contain the detailed properties of plastics, including processing methods, process temperatures, melting point, and tensile strength. The volumes also contain common plastics acronyms, common terminology, and conversion factors.

Q: What are ASTM standards and how are they used?

A: The American Society for Testing and Standards (ASTM), organized in 1898, has grown into one of the largest voluntary standards development systems in the world. ASTM is a not-for-profit organization that provides a forum for producers, users, ultimate consumers, and others to meet on common ground and write standards for materials, products, systems, and services. From the work of 130 volunteer standards-writing committees comprised of 31,100 technically qualified ASTM members worldwide, ASTM publishes more than 10,700 standards each year. The standards are used throughout the world.

ASTM standards are used voluntarily and become legally binding only when a government body references them in regulations, or when they are cited in a contract. The standards are used by thousands of individuals, companies, and agencies. Purchasers and sellers incorporate standards into contracts, scientists and engineers use them in laboratories, architects use them in plans, government agencies reference them in codes, regulations, and laws, and many others refer to them for guidance.

Section 8 (plastics) of the ASTM Standards is available in the Automotive Learning Center Resource Library. Find out more about ASTM on their website, www.astm.org.

Q: What is the fatigue strength of some common plastics?

A: There are over 50-60 basic types of plastics, each having unique characteristics. The best way to search for fatigue life would be to narrow your application’s requirements (operating temperature, exposure to fluids, UV, cycle frequency, etc.), then investigate plastic resin properties by directly linking into the ACC's Plastics Division Member Company Websites. Each of our member companies would be happy to help you!

Q: What is the most basic hardness test that you use for plastics?

A: Since the family of plastics has over 50 to 60 basic types, not including elastomers (rubbers), there are a number of "basic hardness tests." Determining which test to use depends on the type of plastic you are evaluating. In general, two basic types of tests are used: Rockwell Hardness and Shore Hardness. Each of these test procedures has variations, again depending on what material you are measuring, such as Rockwell C, Shore A or Shore D. Rockwell hardness tests are described in ASTM D785, Volume 8.01 Plastics. ASTM, the American Society of Testing Materials, is one of the largest standards development systems in the world. Their website is www.astm.org.

Q: How does fiberglass compare to steel in strength?

A: Glass fibers are used to add tensile strength and stiffness (flexural modulus) to many plastics applications. Different lengths and diameters of glass fibers are used to impart the properties needed for particular applications. Consider, however, that you may be trying to compare "apples to oranges". Depending on size and configuration, or reinforcing plastics, glass fibers will have different properties. In general, the properties will be high in tensile strength and stiffness, but low in impact strength (brittleness). Fiberglass also weighs considerably less than steel.

Q: I am developing an electronic module to be sold as an aftermarket automotive product. What standards and safety regulations apply to plastics used to house an electric circuit?

A: All plastics used in automobiles must meet specifications to ensure that the particular part performs satisfactorily. There are specific materials specifications, usually ISO values, such as tensile strength, impact strength, flexural modulus, etc. There are also part specifications that most parts must meet, many of them established by the automotive OEM or their suppliers, or if the part/system is common enough, established as an SAE standard. All plastics must meet FMVSS (Federal Motor Vehicle Safety Standard) 302 flammability standard. Plastic boxes that hold electronic devices generally have special design criteria, particularly when it comes to electrical/electronic shielding, operating temperature, and dimensional stability.

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