Polyurethane vs Silicone Rubber: Material Differences, and Which Is Better For Your Application

If you’re a manufacturer, then you know that the success of your process will depend greatly on the quality of the products you use. Today, many manufacturers spend a lot of time going over material options and choices to ensure that they make the right choice based on their specifications. And over the years, polyurethane and silicone have become especially popular options. 

If you’re a manufacturer that develops products for different industries, then there’s a significant chance that you would have asked the silicone vs polyurethane question. So, we decided to look into this comparison to help understand the differences between the materials.

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Polyurethane vs Silicone Rubber: Comparisons & Material Differences

An Introduction To Polyurethane Rubber

Polyurethane rubber is a synthetic material that has gone through considerable development and innovation in the past few years. It is particularly popular for its ability to seemingly combine the properties of plastic and rubber, and this has been mostly due to its impressive formulation method and its general versatility. 

Whether it’s for making a urethane gasket or polyurethane rubber strips, this material is especially flexible. In most cases, it is formulated through a unique combination of isocyanates and polyols, with the reaction resulting in a polymer that offers a broad range of both mechanical and physical properties. 

So, to be clear, polyurethane rubber is made of two primary components: 

  • Polyols: A polyol is an organic compound that forms multiple hydroxyl functional groups. In polyurethane rubber, you have several of these components, all of which form the backbone of the material. Some of the most popular options for polyols include polyester and polyether polyols. 
  • Isocyanates: An isocyanate is a compound that contains an isocyanate functional group (-NCO). For the creation of a polyurethane primary product, the most common of these isocyanates being used include toluene diisocyanate and diphenylmethane diisocyanate. 

The seamless mixture of both components is what creates the general polyurethane reaction. First, you see the development of a polymer chain with different urethane linkages. From there, the properties unique to polyurethane rubber are formed, and the material is created.

However, it is also worth noting that these primary components don’t necessarily work alone. There are several modifiers, additives, and supporting elements that help polyurethane to achieve its distinct properties – from chain extenders to cross-linking agents to pigments and so much more. 

When conducting this manufacturing process, it is important to keep an eye on proportions and compositions, and to ensure that these properly match your desired characteristics for the rubber. 

How Polyurethane Rubber Is Made 

So, we already explained the different components that can make up a clear polyurethane caulk. Now, let’s examine ust how the product is made exactly: 

Preparation of Polyols:

The first step for most manufacturers is to prepare the polyols in the product. These components are usually gotten from renewable materials or petrochemical sources, and you can have different types. Choose which option will fit with your desired properties, and you’re good to go. 

Preparation of Isocyanates:

Next, you prepare the isocyanates as well. Like the polyols, you want to select an option that fits into your specific characteristics. Keep in mind that these components are very reactive and tend to be stored on their own. So, you want to exercise a lot of caution here. 

Mixing and Reaction:

With the two components ready, you can go ahead to measure and mix them together. This mixture is carried out in a controlled environment, initiating the polyurethane reaction. 

With urethane linkages being formed, you create the polymer chain that acts as a foundation for polyurethane to be created. 

Additives and Modifiers:

For the next step, you focus on throwing in a few modifiers and additives as part of the mixture. Some possible options include: 

  • Catalysts, which help improve the speed of the reaction
  • Chain extenders, which provide an avenue for you to control the length of the overall polymer chain.
  • Cross-linking agents, which optimize the overall strength of the material. 
  • Fillers and pigments, which help you to fine-tune the general appearance of the material. 

Curing and Processing:

Your mixture is now ready to go through additional processing to fit your requirements and application. Processes such as extrusion, molding, and other techniques are applied here, and you could even add some extra cross-linking or curing to the mix. 

Post-Processing and Finishing:

Finish things up with final post-processing steps like cutting and surface treatments, which help you to improve the product’s physical properties. As long as the formulation and processing conditions match your required product characteristics, you shouldn’t have a problem overall.

Key Characteristics Of Polyurethane Rubber

In order for it to work as expected, polyurethane rubber comes with several important characteristics. Some of those include: 

  • Formulation Flexibility: As a manufacturer, you would find that formulating polyurethane rubber is quite easy. You can formulate it to be stronger and more flexible, and you can even get a polyurethane liquid variant that flows seamlessly too.
  • Material Durability: Polyurethane rubber is also prominent for its impressive ability to resist tearing, abrasion, and even strong impact.
  • Elasticity: Formulations for polyurethane rubber make enough space for elasticity, with the material being able to go back to its original shape after enduring considerable stretching. 
  • Chemical Resistance: Polyurethane generally has a high level of chemical resistance. Whether it’s acids, oils, or solvents, the material doesn’t get affected when it comes in contact with them. However, keep in mind that the level of chemical resistance tends to vary based on the formulation you have. 
  • Temperature Resistance: The material can also be used across different temperature ranges without losing its properties or degrading.  
  • Water Resistance: Over the years, we’ve seen different forms of polyurethane that have also developed strong resistance to water. This is especially true for pourable polyurethane rubber, which has become popular for marine applications.

Understanding Silicone Rubber

Silicone is already one of the most popular materials used in the general manufacturing industry. Known for its versatility and impressive strength, this material is as reliable as it is effective. 

A synthetic elastomer, dura silicone is made through the vulcanization process, with cross-linking being incorporated to enhance its mechanical properties overall. In general, the building blocks of this material include: 

  • Silicon (Si): The central element used to make the rubber, silicone forms the foundation of the silicone polymer chain and offers optimal stability to the material.
  • Oxygen (O): Together with silicone, oxygen forms a siloxane polymer chain, which is strong and helps to improve overall flexibility. 
  • Carbon (C): You can usually also find carbon atoms in silicone rubber, although this is available in small portions.
  • Hydrogen (H): With their attachment to silicon atoms, hydrogen atoms generally contribute to the material’s overall structure. 

In its most basic form, a silicone rubber product consists of a silicon atom joined to two oxygen atoms. This structure forms the primary siloxane linkage, and when you have several of these links, you get the polymer chain that is responsible for the flexible, rubbery texture you get 

Manufacturers can take advantage of customization by adjusting the quantities and types of organic groups present in the silicone format, as well as the overall length of the siloxane chain. With these variations, you will have no issues tailoring the rubber to meet your performance requirements.

The Silicone Rubber Manufacturing Process 

The entire process of making silicone comes with several steps. And while many manufacturers tend to go with their unique options, we at Legenday can follow these processes: 

Silicone Polymer Synthesis:

The perfect process is to begin with synthesizing the silicone polymer itself. Essentially, you cause the constituent atoms to react with each other and be combined, thus creating the silicone compound. 

Compounding:

Following the synthesis, you compound the silicone with different modifiers and additives. This allows you to achieve the right characteristics and properties, so you can get the right properties. 

Mixing:

The next step will involve mixing the compounded silicone rubber. This ensures that you can evenly distribute all modifiers and additives as the need arises. 

Curing or Vulcanization:

In the curing or vulcanization step, you focus on cross-linking the polymer chains to give the rubber its texture and characteristics. This step is critical if you hope to optimize elasticity, durability, heat resistance, elasticity, and much more. 

You can generally achieve curing via different methods – from heat curing to chemical cuing and even radiation-enabled curing. 

Shaping and Molding:

You need your silicone rubber to take the perfect shape based on your specifications. So, it should come as no surprise that the shaping step will come in next. From compression molding to injection molding and more, this step can be as varied as possible. 

Post-Curing: 

Generally, this step isn’t so compulsory. However, in some cases, you might need to implement some post-curing for silicone rubber to optimize its overall chemical properties – tear resistance, tensile strength, etc. 

Quality Control and Testing:

Once you’re done with the manufacturing process, complete it all with quality control measures to ensure that your silicone meets the right standards and specifications. 

Packaging and Distribution:

Package and prepare your silicone rubber product, and send it out to the end users. 

Silicone Rubber’s Primary Features 

A synthetic elastomer, silicone rubber comes with different interesting properties that allow it to operate optimally. Some of these include: 

  • Heat Resistance: One of the primary features of silicone rubber is its ability to withstand a broad range of temperatures – from incredibly cold to extremely hot. Whether it’s a silicone spray foam rubber or some other rubber variant, rest assured that this feature is a lock.
  • Chemical Inertness: You get an incredible amount of resistance to chemicals from silicone rubber. It doesn’t get affected by bases or acids, and it also doesn’t react with most other substances. 
  • Electrical Insulation: Silicone rubber holds its own against electrical current. For meaning components that need to operate in the midst of electrical conduction, the material is perfect.
  • Flexibility and Elasticity: The material is elastic and flexible, so it deforms under pressure but easily returns to its original shape. 
  • Biocompatibility: Taking a cue from the original silicone, this rubber variant is also non-toxic and very biocompatible. It’s not harmful to the human system, so it works for things like kitchen utensils and medical applications. 
  • Water Resistance: Silicone rubber doesn’t allow moisture or water to come in. If you need to make components that work in wet environments, the material is quite ideal. 
  • Transparency: Some formulations of silicone rubber can be transparent or translucent. If you need to use the material to create containers, rest assured that their content will be visible.
  • Food-Grade Approval: Silicone rubber has also been approved for applications in food-related fields. While it might cause some allergies, it is generally non-toxic and good for making food equipment. 
  • Durability: Silicone rubber provides impressive resistance to weathering and aging. Regardless of the application, rest assured that the material will be able to last long.

Polyurethane vs Silicone Rubber: Material Applications and Use Cases

Next in the silicone vs polyurethane debate, let’s examine where they work.

Both polyurethane and silicone rubber can be incredibly flexible in how they operate. And, while they’d definitely have overlapping functionalities, some of those can be unique as well. Here’s an overview of the functionalities available in each product: 

Common Industries Where Polyurethane is Preferred

Automotive Components:

In the automotive industry, manufacturers make use of polyurethane rubber to make parts from suspension components to seals, and more. The material’s general durability helps here, as well as its ability to soak in shock. 

Rollers and Wheels:

The material is also used in making wheels and rollers that are functional in the industrial machinist development space. These components can also be used in making printing presses, vehicle conveyor systems, and more. 

Belts and Timing Components:

Drive belts, timing belts, and other components used in making machines tend to come with polyurethane rubber, capitalizing on the matria;’s abrasion resistance and dimensional stability. 

Seals and Gaskets:

As we all know, polyurethane gaskets and seals made of polyurethane rubber can be used across multiple industries – food processing, hydraulics, etc. The material’s operational flexibility comes in handy here, as well as its ability to maintain a seal across different temperature ranges.

Coatings and Linings:

Linings and coatings made of this material can help to protect surfaces from the effects of abrasion and prolonged exposure to harmful chemicals. 

Major Use Cases For Silicone Rubber

Medical Devices:

One of the defining points in comparing silicone rubber to polyurethane rubber is the former’s use in medical devices. Whether it’s making components like catheters and tubing or even developing prosthetics, the material is quite versatile across the board. 

This is mostly due to silicone rubber’s biocompatibility, which allows the material to easily be incorporated into the human body.

Electronics Encapsulation:

With silicone rubber, you can create capsules for different electronic components – connectors, sensors, and more. This way, they are protected from pollutants such as dust and moisture. 

Kitchenware and Bakeware:

Silicone rubber – particularly, the food-grade version – is used broadly in kitchens to create utensils, bakeware, and molds. The material resists high temperatures and doesn’t stick, making it perfect for use here. 

Sealing and Insulation:

Whether it is making seals or gaskets, you also get a lot of functionality from silicone rubber. The material doesn’t react to temperature changes, and it resists weathering over time as well. 

Automotive Applications:

In automotives, we see silicone rubber being used to make seals, hoses, and other components. Like polyurethane rubber, the material is excellent at handling high temperatures and several corrosive materials. 

Electronics and Electrical Components:

Cable insulation, connectors, and other small but critical components in electronics have a silicone rubber base. Manufacturers have been able to capitalize on the material’s electrical insulation properties for these.

Personal Care Products:

Thanks to its ability to interact well with human skin, this material has also been used in making cosmetics, personal care products, and more. It rarely causes allergies, and is generally considered to be healthy.

Mold Making:

Finally, we have seen developments in the use of silicone rubber for making molds in castings for different materials. Its flexibility and ability to work with different materials definitely comes in handy here. 

Polyurethane vs Silicone Rubber: How Do Their Physical Properties Compare? 

The table below provides a clear comparison of the physical properties in the silicone vs polyurethane rubber debate:

Mechanical Property  Polyurethane Rubber  Silicone Rubber 
Hardness (Shore A) 50 – 95 10 – 70
Tensile Strength (MPa)  20 – 60  5 – 12
Elongation at Break (%) 300 – 700  200 – 900 
Tear Strength (kN/m) 20 – 100  10 – 40 
Compression Set (%) 10 – 50  10 – 70 
Abrasion Resistance Impressive level of abrasive resistance  Between moderate and good levels, based on the formulation 
Flexural Strength (MPa)  30 – 90  5 – 10 
Modulus of Elasticity (MPa) 100 – 700  1 – 10 
Heat & Temperature Resistance  The polyurethane temperature resistance is generally less, with the material handling anything between -40°C (-40°F) to 90°C (194°F) On the other hand, the silicone temperature range is much broader. The material does well with anything ranging from  -60°C (-76°F) to 230°C (446°F)
Chemical Resistance  Good chemical resistance, but not as much as silicone rubber  Excellent resistance to a broad range of materials, from acids to solvents and more.
UV Resistance  Does well to resist exposure to UV rays  The silicone UV resistance is also quite impressive. 

 

It is important to note that these properties can vary based on the particular grade and specific formulation of the rubber options. Remember to consider these mechanical requirements when making a decision going forward.

Polyurethane vs Silicone Rubber: Comparing Their Mechanical Properties

 

Next, let’s take a look at the mechanical properties of both polyurethane vs silicone sealant and rubber variants to understand how they operate and where they stand. 

 

Mechanical Property  Polyurethane Rubber  Silicone Rubber 
Flexibility & Elasticity  Relatively flexible, with a strong, sleek body Very flexible and elastic, thanks to its impressive production process 
Durability & Resistance  Highly durable material that lasts considerably long Highly durable material that lasts considerably long
Impact Resistance     Impressive level of impact resistance  Does well to resist impact 
Fatigue Resistance    Fair level of fatigue resistance  Does well to resist fatigue, especially over time 
Operational Resilience  Very resilient to external factors   Also does well to resist external factors, improving its strength 

 

As you get with the physical properties, it is important to remember that these properties also depend on the formulation and variant of silicone or polyurethane rubber you’re working with. 

Polyurethane vs Silicone Rubber: Which Is Better For The Environment?

Today’s manufacturing industry has become especially curious about environmental impacts and the role of various materials in protecting the environment. 

So, if you’re considering polyurethane caulk vs silicone or even looking into which rubber material to use, it’s important to also consider their overall effects on the environment at large. To that end, here are a few things to note: 

Sustainability: 

Generally, both of these rubbers aren’t considered sustainable. They are gotten from petrochemical sources, so the process of manufacturing them might not be so eco-friendly. 

Recyclability: 

In the silicone urethane debate, silicone rubber generally comes as a more recyclable material. You can crush and recycle the material, while also using it to create new silicone products. And while you might not have many recycling processes available, silicone gets the edge here. 

Biodegradability: 

Both materials aren’t so highly biodegradable. They hold on in the environment for long periods, and without proper management, they might have considerable environmental impacts. 

Toxic Emissions: 

The process of creating both silicone vs polyurethane caulk can cause the release of certain emissions and chemicals. As such, it is important to take measures to properly minimize these outputs.

Durability and Lifespan: 

Both materials are known for their ability to last long. Technically, this can be good for the environment – silicone and polyurethane will help reduce the need for constant replacements, and as such, they cut down on resource consumption overall.

Waste Generation: 

This is another area of the polyurethane silicone debate where the latter takes hold. It usually produces less waste during manufacturing, especially in terms of scrap material and trimmings. 

At the end of the day, both materials have considerable effects on the environment. However, silicone can generally be better if you’re looking to have a clean and more eco-friendly production technique. Remember, however, that you need to also be very careful here. 

Polyurethane vs Silicone Rubber: Which Is Cheaper?

At the end of the day, every manufacturer wants to make – and save – money. As such, it is important to also choose the most cost-efficient option when considering the polyurethane sealant vs silicone debate. 

Generally, polyurethane rubber comes as a more cost-effective option for most applications. This lower cost is usually attributed to the increased availability of raw materials, the simpler manufacturing process, and the fact that polyurethane rubber is also more ideal for several applications. 

That said, factors such as abrasion, hardness, and more can easily affect the price of the product. 

At the end of the day, you also want to be mindful of your choice here. Look into the specific application requirements you have, so as to ensure that you’re getting the right formulation and product choice. 

For instance, if you need the specific properties of silicone rubber – such as optimal electrical insulation and heat resistance – then you might need to make a choice of using the product instead, even if it means paying an additional cost. 

Polyurethane vs Silicone Rubber: Understanding Their Pros & Cons 

To be fair, there are set benefits and drawbacks to both polyurethane rubber and silicone rubber. As you can imagine, understanding these will be critical if you hope to make the right choice between the two:

Polyurethane Rubber:

Pros:

  • Durability: Polyurethane rubber comes with impressive abrasion resistance and toughness. When used in harsh conditions, it does well to hold its own. 
  • Versatility: You can easily find the product in a broad range of hardness levels
  • Cost-Effective: Compared to silicone rubber, polyurethane rubber is more affordable and cost-effective across the board. 
  • Tear Strength: The material’s tear strength is also considerably higher – important if you hope to use it in applications that require a lot of mechanical stress. 

Cons:

  • Temperature Limitations: As the table above shows, the polyurethane temperature range isn’t necessarily broad. 
  • Inadequate Chemical Resistance: While chemical resistance for polyurethane rubber is decent, it might not necessarily have the same level of chemical inertness as silicone rubber in specific environments.

Silicone Rubber:

Pros:

  • High-Temperature Resistance: Compared to polyurethane rubber, silicone rubber does well to withstand a broad range of operational temperatures without degrading. 
  • Chemical Resistance: The material also resists different chemicals. 
  • UV Resistance: Just as you get with the original silicone UV resistance, this material holds its own when exposed to direct sunlight.
  • Flexibility at Low Temperatures: Silicone rubber maintains its pliability even when faced with incredibly low temperatures. As such, it is especially suitable for work in cold environments. 
  • Biocompatibility: One of the major benefits of silicone rubber is that you can also use it for food-related purposes and applications. It isn’t toxic, and it works well with the human body. 

Cons:

Higher Cost: Compared to polyurethane rubber, silicone rubber tends to be more expensive. As such, you want to think twice about it if cost-efficiency is your biggest requirement. 

Lower Abrasion Resistance: With silicone rubber, you admittedly don’t get as much abrasion resistance as you’d get with polyurethane rubber. This means that the material might wear out faster in applications that require it to sustain considerable mechanical wear.

Lower Tear Strength: As we pointed out earlier, tear strength isn’t where silicone rubber especially does well. 

Polyurethane vs Silicone Rubber: Which Do You Choose?

So, you understand the merits and demerits of each of these options and would need to make a decision going forward. Considering that they are both valuable and effective materials, how do you know which option to select? 

Temperature Range:

First, look into the temperature range of your application and how the product itself will need to work. If you need a material that can withstand some truly extreme temperatures, then we’d recommend using silicone rubber. 

Mechanical Requirements:

Hardness, tear resistance, and more are a few mechanical requirements you should consider. And, with the two materials being pretty even in this regard, you want to be as particular as possible when making a choice. 

Chemical Exposure:

If you’re using the materials in an environment where chemicals are present, then begin by determining the types of substances and chemicals that it will actually come in contact with. Generally, silicone rubber tends to take the prize here. But, remember to be as particular as possible. 

UV and Weather Resistance:

If the material will be used in outdoor locations, then consider its UV resistance as well. Once more, there’s a high likelihood that you’d select silicone rubber if this is your biggest consideration. 

Cost Considerations:

Consider your budget constraints. As we stated earlier, polyurethane rubber tends to be more affordable as an option. But, at the same time, keep in mind that cost shouldn’t necessarily be the only thing on your mind.

Environmental Impact:

As manufacturing processes turn greener these days, selecting a process that works for the environment is critical. There are already efforts being made to develop more eco-friendly formulations of each, but we recommend that you work so much as possible to keep your operations as green as they can be. 

Longevity and Maintenance:

Of course, remember to always consider the expected lifespan of the product based on your application requirements. Both materials exhibit impressive levels of durability, although this could differ based on the specific application conditions. 

Availability and Suppliers:

You want to verify that the product is available in your region. At Legenday, we’re experts in procurement and material sourcing. So, feel free to contact us with your material needs at any point. 

A careful consideration of these factors will go a long way in helping you to make the right choice and maintain a seamless manufacturing process overall. 

Conclusion

All in all, silicone rubber and polyurethane rubber are reliable products that should form valuable parts of your manufacturing process. As long as you’re able to make the right choice across the board, you shouldn’t have any issues. 

And, when you do, remember that you have the right partner at Legenday. We can help source the best in quality products, ensuring that you easily get what you need, when you need it.

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