What Are the Most Important Properties of a Polymer?

When assessing the performance of polymer materials, some properties have more weight than others. For example, properties such as strength and resilience are often prioritised when evaluating engineering polymers. Below, we take a closer look at the most important properties of a polymer and why they matter.

Tensile strength

Tensile strength is one of the most useful properties to assess the performance of polymers. This parameter evaluates how much one-directional force a polymer material can withstand before it breaks. Polymers are widely used in the construction and manufacturing industry, where products are required to endure a huge amount of stress. This makes tensile strength one of the most important properties of a polymer for both performance and safety.

Of all the synthetic polymers, polyamideimide (PAI) is one of the strongest. It boasts incredible tensile strength of 21,000 psi, making it one of the highest rated plastics. High tensile strength often comes with other desirable properties, such as radiation resistance, high thermal stability and low flammability.

A variety of methods are used to measure tensile strength, including the ASTM D5766/D5766M-95 Standard Test Method for Open Hole Tensile Strength of Polymer Matrix Composite Laminates. The method places test specimens in a universal tester equipped with grips. The specimen is then pulled apart until failure, usually at a typical test speed of 2 mm/min.

Refractive index

Optical properties are front and centre when designing and selecting polymer materials designed to replace glass. Refractive index is one of the most important as it determines how well a polymer material allows light to filter through. Polymethyl methacrylate (PMMA) is an example of a polymer with a brilliant refractive index. It’s often the material of choice for replacing glass for applications such as skylights, windows and screens.

Yellowness Index is another important optical property. Calculated using spectrophotometric data, it predicts how well a material resists taking on a yellow hue when exposed to elements such as water and UV rays. Other important optical properties include clarity, colour, haze and gloss.

Thermal expansion

Thermal expansion is another important polymer property and is usually dependent on the bond strength of the material. This property rates the tendency of a material to change shape and volume when exposed to temperature variations. Stronger molecular bonds generally correlate to lower thermal expansion ratings. Acetal (POM), Teflon (PTFE) and UHMW Polyethylene are all polymer materials with excellent thermal expansion.

Tensile strength, refractive index and thermal expansion are just some of the properties used to assess the performance and suitability of polymer materials. Find out more about other important properties in our complete guide, ‘Polymer Characterisation - Techniques, Types & Properties’.