Analytical chemistry is important to industry because the accurate measurement of quantities, composition, and properties is critical to the market success of products. These measurements are usually performed on highly sophisticated and complex instruments that are not available in the high school laboratory, however many of the mechanical properties of plastics can be tested using simple apparatuses. A large number of standard tests have been developed to test these properties. Tensile strength is measured by clamping a test sample of uniform cross-section and stretching it until it breaks. Tensile strength is defined as the stress force necessary to break the sample at a constant rate of stretching.
Elongation is the increase in length of a sample at the breaking point.
Elongation is associated with the uncoiling of polymer molecules and their movement relative to other molecules. Highly crosslinked polymers have a low elongation relative to linear polymers. Elongation can vary widely among polymers and is usually expressed as a percent of the original length of the sample. Flexural strength is measured by supporting a sample test bar of uniform cross-section at each end, in a horizontal position. The sample is then subjected to a vertical stress until it yields or breaks.