Three blocks of polyurethane.

Posted | Categorised in Manufacturing & Processes.

When most people hear ‘poly’ they think of plastic. So is polyurethane plastic? And if not, what is polyurethane? Whilst PU is part of a plastic family, thermoset polyurethanes are elastomers and not plastics.

This blog will highlight the differences between polyurethane and plastic, how it is formed, and its key features and benefits.

Did Polyurethane or Plastic Come First?

Polythene, (traditional plastic,) was first discovered in 1933 by a team of chemists at the ICI Wallerscote plant when an experiment went wrong; producing a white waxy substance which we now know as plastic. It took 5 years for ICI to consistently reproduce this chemistry.

Meanwhile, in 1937 at IG Farben in Leverkusen, Germany, Otto Bayer, Werner Siefken, Heinrich Rinke, L. Orthner and H. Schild discovered and patented the chemical process to make Polyurethanes.

In 1969, Otto Bayer displayed an all plastic car, a lot of which was made with the new process reaction injection moulding (RIM). This process is part of what makes polyurethane so uniquely versatile today.

What’s the Difference Between Polyurethane and Plastic?

Essentially, polyurethane is an elastomer, whereas plastic is a polymer; but what does this mean?

What is an elastomer?

Elastomers are characterised by their long flexible, chain-like, polymer molecules that allow elastomers to recover their original shape after being stretched. Elasticity is one of the key characteristics of elastomers, hence the name elastomer, or ‘elastic- polymer’. In-fact, natural rubber is an elastomer which has been made from latex.

How are plastics different?

Whilst plastics also have chain-like polymer molecules, they are not flexible like elastomers. Like polyurethane, plastics can be moulded into almost any shape, but are likely to be deformed or even break once they are stretched or under tension or force. Plastics need to be injection moulded, but elastomers are often cast moulded or reaction injection moulded.

The Benefits of Polyurethane Over Plastic

A PU star wheel.

  • Durability and flexibility. As a material, Polyurethane has an almost unique elastomeric ability. This means that it will maintain its shape even after force or pressure is applied.
  • Cost. Whilst it costs similar amounts to produce plastic as it does to produce polyurethane, urethane is more durable and has a longer lifespan; meaning they are more cost effective in the long run. In some cases, it can even prove to last longer than metal alternatives. The ways that polyurethane is used in the agricultural industry are a perfect example of this being the case; durable and microbial resistant polyurethane star wheels make a superior, (longer lasting, and more cost effective) choice over previous metal star wheels.
  • Load bearing. Urethanes are incredibly tolerant to heavy loads. They can resist an enormous amount of force before they break or lose their shape. This makes them excellent shock absorbers, great for things like packaging blocks, that are reusable and have a longer lifespan.
  • Abrasion resistance. Due to its flexible molecular structure, polyurethane does not break down due to friction as quickly as other materials. This makes them perfect for industrial wheels and tyres, or rollers, as the product lifespan is often a lot longer than other types of plastic.
  • Temperature and Friction. Polyurethane’s temperature limits are a massive benefit, they will continue to perform within the threshold of -62°C to 93°C, with some specific formulas able to reach temperatures of 150°C without losing shape. Polyurethane rollers can be made to have more or less friction; a great example of this is polyurethane rollers on a conveyor belt system. If the roller had less friction it would prevent it gripping to the surface, and would spin without moving the conveyor belt, and if it had too much friction it would simply not move at all.
  • Noise and sound. Polyurethane’s ability to absorb sound means that they can be used to dampen noise. This is especially true when custom made by specialist polyurethane services for your specific project, as this can provide the perfect density and fit. In the automotive industry, polyurethane foam is often injected into car doors to reduce the amount of road noise.

We hope we have answered your question, ‘is polyurethane plastic?’. Whilst both traditional plastics and polyurethane are both essential materials, they are effective for different types of products and different types of applications.

Polyurethanes allow more flexibility and durability, making them a cost effective alternative to other plastics, and in some places even metal. We recommend choosing a polyurethane product when you require a flexible and strong material that is resistant to wear and tear.