Article updated on 5 May 2020
Physical testing is an essential part of both research and production processes for polymers. Tests have been designed to assess the mechanical, physical, thermal, rheological, and other physical properties of various polymers.
Researchers conduct physical tests of polymers, or products with polymers, in development to determine if their materials meet the desired specifications on qualities like hardness or thermal tolerance. Manufacturers test polymers on these same qualities to ensure that raw materials or finished goods meet the established standards.
New polymers are constantly being developed and these novel materials are often compared to established polymers, including plastics. Plastics are a subset of polymers that are made from oil or petroleum, while the broader category of ‘polymers’ simply includes materials made from long chains of single molecules, also known as monomers.
When looking to compare new plastics or polymers to established ones, it is important to consider the following standard physical tests. During all of these tests, it is essential to replicate the environment in which the polymer will be applied, including atmospheric pressure, humidity, and other factors.
The hardness of a material refers to how easily it can be scratched or indented during static loading. The Vickers Hardness test, Brinell Hardness test, and Rockwell Hardness test are the three most common hardness tests for polymers. These tests all involve a small, hard indenter being used to place a predetermined load on a sample. After the load has been placed and removed, the depth and area of indentation is determined, with smaller depths and areas representing harder materials.
Shear tests are conducted to establish qualities such as shear strain and shear modulus.
Shear testing involves placing a specific, localized shear load on a specimen using a mechanical apparatus. The localized stress is typically increased until it generates failure at a weak spot, resulting in a deformation or tear that may progress through the material. Because specimens may vary, stress on any given sample can be highly complicated, and at times unpredictable outcomes can result from shear tests.
Polymers are often a material of choice due to their flexible qualities. Flexural tests can determine the limits of a material’s flexibility.
Often used to assess flexure, a three-point loading test involves placing a bar of material on two supports and a test load being placed on the sample midway between the two supports. A cantilever test determines flexure by clamping down a bar of test material at one end so that its suspended horizontally and then applying a load to the free end.
Most polymers are designed to be impact resistant and impact tests can not only indicate durability, they can also indicate the service life of a finished product. Drop weight testers and pendulum testers are both commonly used to perform impact tests. An impact test should be chosen based on the kind of impact a material is expected to be exposed to.
The thermal investigation of polymers provides data on thermal qualities and transitions to find out the material’s viability for its intended application.
Thermal testing of polymers and plastics is a robust way of gauging physical qualities, transitions, ageing, the impact of additives, and the effect of production conditions.
The four most common thermal tests are Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), Thermogravimetric Analysis (TGA) and Thermomechanical Analysis (TMA). DSC is typically used to assess chemical and physical transitions. DMA tests for qualities like elastics modulus and mechanical damping. TGA is often used to test for the amounts of plasticizers or filler materials. TMA is often to identify a material due to its unique thermal ‘fingerprint’.
Many polymers are designed to have adhesive qualities and adhesion tests are used to determine the degree of adhesion for a particular specimen. Establishing the failure point for a sample can be valuable for determining application viability. There are countless types of adhesive products that mandate multiple evaluation techniques to determine the qualities of a sample material.
Some shear testing methods may be able to determine adhesion qualities. Peel tests may also be used.
References and Further Reading