Thermoplastics, Elastomers and Thermosets: Understanding the Materials Around Us and Their Uses in the Operating Theatres.

Written By Thomas Ind

Modern healthcare and particularly the operating theatre, relies heavily on synthetic materials. Syringes, tubing, masks, packaging, and surgical instruments all depend on different polymers. However, not all polymer materials behave the same way. Broadly speaking, they fall into three categories:

  • Thermoplastics

  • Elastomers

  • Thermosets

Understanding the difference between these materials helps explain why some plastics are rigid, others behave like rubber, and why certain components cannot be melted or recycled.

1. Thermoplastics

Thermoplastics are what most people think of when they hear the word plastic. They consist of long polymer chains that are not permanently cross-linked, which means they soften or melt when heated and harden again when cooled.

The key characteristics of thermoplastics are:

  • Can be melted repeatedly

  • Are easily moulded

  • Range from flexible to rigid

  • Often carry recycling codes 1–7 (how to identify different plastics will appear in another blog)

In the operating theatre common thermoplastics include:

Polypropylene (PP) - Syringes, specimen containers, luer locks, vial caps

Polyethylene (PE) - Plastic drug bottles, Packaging films, drapes

PolyVinylChloride (PVC) - Tubing, oxygen masks. Can be rigid or soft

Polycarbonate (PC) - Instrument housings, visors

Polystyrene (PS) - Petri dishes, lab trays

 Acrylonitrile Butadiene Styrene (ABS) - Clip-on parts between robot drapes & robots

Polyethylene Terephthalate (PET) - Hard transparent packaging of single use instruments

Polyethylene (PE) can be High Density (HDPE) which is the harder denser form and often seen in large sterile fluid containers and Low Density (LDPE). which is seen in squeeze bottles and plastic drug and saline vials.

In everyday life the same materials appear in:

  • Food containers – PP

  • Yoghurt pots - PP

  • Drink bottles – PET

  • Plastic bags – LDPE

  • Milk containers – HDPE

  • Liquid detergent bottle, shampoo bottles, toothpaste tubes - HDPE

Other common plastics not commonly used in the operating room include;

Polylactic acid (PLA) which is often used in Filament Deposition Modelling (FDM) 3D printing and is made from corn oil. Under industrial conditions this can be biodegradable.

Nylon which is often used in machine parts for it’s sliding properties and can be spun into a cloth.

Polybutylene Terephthalate (PBT) which is hard and has excellent electric insulation properties and is commonly used in light switches.

Thermoplastic Polyurethane (TPU) which has some rubber–like propertied and is commonly found in phone cases and footwear.

2. Elastomers

Elastomers are materials that behave like rubber. Their polymer chains contain light cross-linkages, allowing them to stretch significantly and then return to their original shape. This gives elastomers their key property - elasticity.

In the operating theatre, common elastomers include:

Silicone rubber - Surgical drains, catheters

Latex rubber - Surgical gloves

Nitrile Butadiene Rubber (NBR) - Protective gloves & non-latex surgical gloves

Synthetic rubbers - Seals and tubing

In everyday life elastomers are also found in:

  • Elastic bands

  • Shoe soles

  • Seals and gaskets

  • Kitchen utensils made from silicone

Their key characteristics

·      Stretch easily

·      Return to their original shape

·      Feel soft and rubber-like

·      Are not usually recyclable by melting

3. Thermosets

Thermosets are polymers that undergo permanent chemical curing during manufacture. During this process, the polymer chains form extensive cross-links creating a rigid three-dimensional network. Once formed, thermosets cannot be melted again. Heating them simply causes degradation rather than softening.

In medical environments, Thermosets appear in:

  • Medical Adhesives

  • Composite components

  • Some instrument handles

  • Electronic components in medical equipment

In everyday life, Thermosets appear in:

  • Epoxy adhesives

  • Electrical plugs made from phenolic resin

  • Printed circuit boards

  • Composite materials

  • Resin moldeling

The key characteristics of thermosets are that they;

  • Are rigid and heat resistant

  • Cannot be remelted

  • Are difficult to recycle

  • Often have excellent chemical resistance

Summary

Understanding these categories helps explain why different materials are used for specific purposes in the operating theatre.

For example:

  • Thermoplastics allow inexpensive disposable devices.

  • Elastomers provide flexibility for tubing and seals.

  • Thermosets provide structural strength and heat resistance.

Each category has different implications for:

  • Sterilisation

  • Mechanical performance

  • Waste disposal

  • Recycling

A Simple Way to Remember

A useful way to summarise these materials is:

Thermoplastics - Melt and can be reshaped - Polypropylene syringe

Elastomers - Stretch like rubber - Silicone catheter

Thermosets - Permanently cured, cannot melt - Some instrument handles

Conclusion

Although hospitals may appear technologically specialised, the materials used in operating theatres are largely drawn from the same families of polymers found in everyday objects. By understanding the difference between thermoplastics, elastomers, and thermosets, it becomes much easier to recognise why a syringe is rigid, a catheter is flexible, and an adhesive becomes permanently solid.

In future posts, we will explore how to identify specific plastics used in surgical devices, and how they correspond to materials we encounter in daily life. We will also discuss the impact of plastic disposal in the operating theatre on the environment.

 

Thomas Ind