Polyurethane vs Silicone Rubber: Comparing Material Properties & Applications

Whether to choose polyurethane or silicone rubber entirely depends on a detailed understanding of these materials properties.

Through this, you will assess whether the materials meets specific needs of a project in terms of structural integrity, safety and reliability.  Therefore, before you choose polyurethane or silicone rubber for any application, let’s compare these two materials first.

What is Polyurethane?

Polyurethane is a versatile synthetic material that is durable, waterproof and is customizable for flexibility used in mattresses, cushions shoe soles and coatings. It is made from polyols and isocyanates hence when fully cured and properly used, its products are normally safe.

The raw chemicals can be harmful if inhaled or touched during manufacturing therefore safety precautions is vital.

What is Silicone Rubber?

Silicone rubber is a heat and chemical resistant durable rubber that is used in medical tubing implant, baking mats and automotive parts due to its long lasting and UV resistant.

It is made from a combination of hydrogen, silicon, oxygen and carbon. A combination of these elements give it a unique property, making it perfect for most industrial applications.

Comparing Polyurethane and Silicone Rubber

· Molecule Composition and Structure

Polyurethane has a structure that allows strong bonding hence it is a carbon based polymer made of organic chains linked by urethane groups [-NH-CO-O-]. Its structure also allows adjustable hardness thus giving good strength and abrasion resistance.

On the other hand, silicone rubber has a structure that makes it flexible, heat-resistant and chemically stable. This structure is an inorganic silicon-oxygen [-Si-O-Si-] backbone with organic side groups.

· Mechanical Properties

· Abrasion Resistance

Polyurethane has excellent abrasion resistance thus it’s commonly used for wheels, shoe soles, conveyor belts and industrial rollers. It resists wear and friction thus maintains shape under repeated rubbing or contact.

However, Silicone has low to moderate abrasion resistance therefore it’s better for seals, medical or food-grade uses. This is why you will not find silicone in high-wear applications since its soft surface will wear easily under friction.

· Flexibility

Here, polyurethane has moderate flexibility thus better for load-bearing parts than extreme bending. Whereas silicone has very high flexibility, thus excellent for seals, tubing and parts that move or flex repeatedly.

· Load-bearing Capacity

Polyurethane supports heavy load without permanent deformation thus is has high load-bearing capacity. Therefore, it is broadly used in wheels and structural components with high compressive strength and good shape retention.

However, silicone deforms more easily under sustained load therefore it has low to moderate load-bearing capacity. This implies, silicone rubber is best for sealing and cushioning because it does not fully recover after long pressure.

· Thermal Stability & Melting Point

Polyurethane has moderate thermal stability, which ranges from 150°C to 200°C. Therefore, this material works best at lower temperatures and softens or melts at high temperatures.

Whereas silicone rubber has an excellent thermal stability which can range from -60°C to 200°C. Therefore, you can use silicone rubber under a wide range of temperatures without worrying about the material melting or degrading.

· Chemical Inertness

Polyurethane has moderate chemical resistant thus can degrade when exposed to strong acids, bases or prolonged moisture. On the other hand, silicone rubber has highly chemically inert therefore does not easily react with acids, bases or biological fluids.

· Chemical Resistance

Polyurethane has good resistance to oils, greases, fuels and many solvents but can be attacked by strong acids, alkalis and long-term moisture. However, silicon has excellent resistance to watermelon and weak chemicals but poor resistance to oils, fuels and some solvents.

· Cost

Silicone is more expensive than polyurethane. In fact, there are instances where the price of silicone products is twice that of polyurethane products.

However, silicone has long term benefits. This material is highly durable.

· Environmental Safety

Polyurethane has greater environmental impact during production and disposal when using petrochemical raw materials and involving toxic chemicals. Whereas silicon rubber is more environmentally stable and has a longer lifespan when in use with fewer harmful release.

· Electrical Properties

Polyurethane performance can vary with heat and moisture, but it provides good electric insulation. Also, silicone is a good insulator. In fact silicone rubber provide better electrical insulation over a wide range of temperatures.

· Gas Permeability

Here, silicone rubber has high gas permeability, allowing gases to pass through easily while polyurethane has low to moderate gas permeability offering better gas barrier performance.

· Biocompatibility & FDA Compliance

Silicone rubber is highly biocompatible and widely FDA-approved for medical and food contact use. On the other hand, polyurethane has moderate biocompatibility with FDA approval only for specific medical grades.

· Common Application in Industries

FAQs

Is polyurethane better than silicone?

Both materials have strengths and weaknesses hence it depends on what you want to do with the material.

When it comes to strength and durability, choose polyurethane because it is very strong thus it is good for heavy duty and high-wear uses but less heat resistant.

However when it comes to flexibility, silicone is very elastic and is good for sealing medical/food uses and great heat and temperature resistant.

What are the disadvantages of polyurethane?

The following are the disadvantages of polyurethane rubber:

• Become brittle thus aging over time with long term use
• Polyurethane is tough and wear-resistant hence it is not ideal for food/medical use.
• It is not resistant to strong acids or some solvents therefore – it has limited chemical resistant.
• Degrades at high temperatures since it is poor heat resistant
• It can lose strength and cause cracking when prolonged to sunlight exposure
• It has less flexibility especially in extreme cold hence there is a high possibility of losing elasticity at very low temperatures

What is the lifespan of polyurethane?

Polyurethane can last longer with proper formulation, UV protection and controlled environments. It can last for 5-20 years if you avoid long-term water immersion and use UV stabilizers or protective coatings.

What are the limitations of silicone rubber?

Silicone rubber has the following main limitations:

• More expensive compared to other rubbers
• Low mechanical strength thus it tears and abrades more easily than polyurethane
• Requires special adhesives or surface treatment since it is difficult to bond
• It swells or degrades in fuel and some solvents because it is fuel resistant
• Poor abrasion resistance, thus not ideal for high-wear or friction applications.

Is polyurethane sealant better than silicone sealants?

Each sealant is best for certain applications. For instance polyurethane is strong and durable on tough surfaces while silicone is flexible and heat resistant.

What are the recommend ISO and ASTM testing standards for polyurethane and silicone rubber?

The standard testing varies with the specific applications requirements. Let’s have a summary of the various quality standards in the industry:

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