Polyurethane and silicone have their own specific benefits that tend to make them applicable in varying uses in business. TOGOHK’s today article will look at their characteristics, production, and differences to help you select the right one.
Polyurethane vs Silicone Rubber – At a Closer Look
What is Polyurethane? Understand the Material
Polyurethane has been defined as a polymer that is synthesized from organic species containing carbamate urethane functionality. Unlike such general polymers as polyethylene or polystyrene, polyurethane is, in fact, an entire class of polymers, also called polymers.
Unlike polyethylene and polystyrene, you can make polyurethanes from many monomers, leading to many types of them in one group.
This chemical variety makes polyurethanes with distinct chemical natures, which result in a wide range of uses. It is useful when you create foam products like rigid and flexible foams, coatings, adhesives, electrical potting compounds, and fibers used in the manufacture of apparel like spandex and polyurethane Laminate (PUL).
Properties of Polyurethane
Polyurethane is a polymer with numerous attributes of physical and chemical nature that enable it for multiple applications. Let’s find out:
A.Physical properties
- Density diversity: Can be performed with diverse densities, thus, offering additional freedom in the manufacturing of polyurethane products.
- Variety of hardness: Ranging from slightly to highly insoluble and hard, polyurethane is suitable for different uses.
- Elasticity: High and flexible material with a good recovery rate when subjected to stress or force.
- Thermal stability: It’s useful in a number of climatic conditions due to its stability at a range of temperatures.
- Abrasion resistance: Very hard-wearing material making it suitable for applications that require durability.
- Impact resistance: Administers and disperses force effectively for impact shielding.
- Tear strength: Good tear strength as it is almost impossible to rip the material once it has been pulled.
- Flexibility: It also can be customized for a different level of flexibility including foams to elastomers and with different hardness.
B.Chemical properties
- Chemical resistance: Standing up to a number of chemicals, inclusive of oil, solvent, acid, and alkali.
- Water resistance: Developed for waterproofing and having low moisture content compared to other blends.
- UV resistance: Some formulations are UV stabilized to avoid degrading with exposure to sunlight.
- Flame retardancy: It can be reformulated to avoid flammability, making safe use in certain circumstances possible.
- Compatibility: Able to interconnect with most surfaces and create strong bonding with different types of materials.
- Biocompatibility: There are some formulations that are considered biocompatible and can be used in medical and healthcare industries.
Polyurethane Manufacturing Process
The whole process of polyurethane synthesis has been simplified, from preparing the mixtures to using the final touches to achieve strength and elasticity. Now let’s take a look at what this process looks like!
- Preparation of polyols:
To start the synthesis, the polyols are made ready, and these can be produced from renewable or petrochemical routes. Polyols used can influence the properties of the resultant polyurethane, hence, manufacturers choose types most suited to the intended application.
- Preparation of isocyanates:
Following that, the preparation of isocyanates takes place. These are highly sensitive and can react at the sight of one another; therefore, they should be stored separately. The choice of which isocyanate to employ is essential for obtaining the planned characteristics of the material.
- Mixing and reaction:
Once the polyols and isocyanates are prepared, they are accurately weighed and blended under suitable conditions. This causes a process of cross-linking through a process that creates urethane linkages to create the polymer chains on which polyurethane is formed.
- Additives and modifiers:
Additives and modifiers are introduced to enhance specific properties:
- Catalysts: Speed up the reaction.
- Chain extenders: Regulate the size of the polymer chains.
- Cross-linking agents: Improve material strength.
- Fillers and pigments: How to change the look and how to polish the features.
- Curing and processing:
Processing of the polyurethane takes place after blending in line with the specific application needs of the polyurethane. It is possible to use such processes as extrusion or molding. Also, additional curing or crosslinking can be incorporated in order to improve the properties of the material.
- Post-processing and finishing:
After the formation of material alloys, post-processing is executed to improve mechanical properties and to fulfill prescribed product specifications. Formulation and processing must be done under strict conditions in order to produce a product with the required properties.
What is Silicone Rubber? Understand the Material
In the next section, you’ll learn everything about silicone rubber, from its properties to the manufacturing process.
Silicone rubber is a versatile elastomer obtained from silicone – a material derived from an inorganic polymer of silicon, carbon, hydrogen and also oxygen. At this point, it must be stressed that the available types of silicone rubber are high and vary in different segments of the industry.
The majority of silicone rubbers are one- or two-part polymers, and they also can contain fillers that raise their performance or lower their cost. Silicone rubber can be characterized as being stable, having low reactivity, and high temperatures.
Properties of Silicone Rubber
From flexibility to chemical resistance, silicone rubber brings a lot to the table—let’s take a closer look at its properties.
A. General properties
- Wide temperature range: Good thermal stability compounded by the performance of the material with temperatures ranging from -60°C to 230°C, depending on the exposure time.
- Resistance to oxygen, ozone, and sunlight: Preserves physical characteristics after exposure for a long time to environmental factors like sunlight, winds, and precipitation.
- Non-stick and non-adhesive: Organically non-stick, which means that it is appropriate in use that demands easy release or shedding.
- Low toxicity and biocompatibility: Usually used as medical devices or food contact surfaces because of its low toxicity and high biocompatibility.
- Flexibility at low temperatures: It also contains low glass transition temperature, thereby allowing the material to remain flexible even in freezing conditions.
B. Mechanical and chemical properties
- Excellent insulation: Better electrical insulating characteristics with an insulation resistance of 1TΩ.m to 100TΩ.m, volume resistivity of 0.01 Ω.m to 10 Ω.m
- Low chemical reactivity: Very chemically resistant, which makes it appropriate to use in extreme conditions.
- High tear strength and elongation: Has good mechanical strength, as can be seen from a minimum tear strength of 9.8 kN/m.
- Water vapor permeability: Resistivity to water vapor permeability and the values are reasonably moderate and range between 15 to 51 depending on the grade that is used.
- Optical transparency: Transparent grades with applied hardness allow for visibility or light transmittance purposes where needed.
C. Specific performance enhancements
- Thermal conductivity: Plastic with characteristics of thermal conductivity of 0.2 W/mΩ.K; ideal for moderate conduction of heat.
- Weather and abrasion resistance: Resistant to environmental wear and abrasion, hence, can last long, especially in outdoor and highly exposed places.
- Chemical stability and bio-compatibility: Because of its Si-O bond, silicone rubber keeps its stable shape even when it is used in chemically active conditions and is also used in health care products due to its biocompatibility.
Silicone Rubber Manufacturing Process
There are two aspects of the manufacturing process of silicone rubber, whereby chemistry is applied to create an object with high strength, flexibility, and tolerance to heat. Let’s discover the process.
- Synthesis of silicone polymer: It starts with the polymerization process, where atoms combine covalently to form the silicone polymer.
- Addition of modifiers (compounding): Silicone rubber is then added with various types of modifiers and additives to acquire set properties such as flexibility, color, or hardness.
- Uniform mixing: The compounded silicone rubber is uniformly mixed so that additives are distributed uniformly throughout the material so as to enhance quality.
- Curing or vulcanization process: This important step is the process of using chemical reactions to connect different polymer chains to boost flexibility, strength, and thermal stability. It cures can be done by heat, chemical or radiation curing.
- Shaping and molding: Silicone rubber is created in a manner to match the needs of a particular design for a certain application. For example, compression molding, injection molding, or extrusion.
- Post-curing (optional): In some cases, a final cure may be included to enhance characteristics. For instance, tear strength and tensile strength for the material to fit the high-performing purposes it is intended for.
- Quality assurance and testing: The final product also has to be tested for quality assurance purposes with regard to the level of performance as well as the resilience of the material.
Polyurethane vs Silicone Rubber – Pros & Cons of Each Material
| Polyurethane | Silicone Rubber | |
| Pros | – Versatile – Durable – High load capacity – Moldable – Broad Use | – High-temp resistant – Chemical resistant – Water resistant – Weather resistant – Electrical insulation |
| Cons | – Environmental impact – UV sensitivity – Complex processing – Recycling challenges | – Costly – Lower abrasion resistance – Lower tear strength |
| Applications | – Furniture/Bedding – Low-density foam for buildings – Footwear – Straps & Coatings | – Construction – Electronics – Seals for extreme conditions – Healthcare – Food |
1. Pros and Cons of Polyurethane
Pros of polyurethane
Here are the key benefits of polyurethane you will need to know before choosing this material for your products.
- Versatility in form: Polyurethane has the possibility of being modified to offer flexibility like that of a rubber or the hardness of metal. It can be produced in a soft, easily compressible foam, rubber-like material, or as a rigid adhesive.
- Durability and longevity: It does not wear out quickly and is not affected by pressure, friction, and abrasion without developing heat or stressing.
- High load-bearing capacity: Stronger and more durable than standard rubber. It is resistant to moisture, oils, and mildew; thus suitable for industrial use.
- Moldable into complex shapes: Polyurethane can be easily molded to produce very complex parts with particularly desired shapes and sizes.
- Broad industry use: Polyurethane provides applications such as thermal insulation, sound insulation, and structural reinforcement. Typical industries that can use this material are construction, automobile, furniture, agriculture, and renewable resources.
Cons of polyurethane
- Environmental impact: Both production and disposal could be dangerous, and many formulas include elements that are not good for human health. Polyurethane is conventional, it is a nonbiodegradable material and can last long for many years to decompose.
- Sensitivity to UV radiation: Easily degradable due to UV rays and may change colors and may need stabilizers or a protective layer.
- Complex processing: Must be accurately controlled in terms of mixing, temperature, and curing, hence increasing manufacturing difficulty.
- Recycling challenges: The main issues of recycling result from multifarious formulations and further complications in the segregation of such types.
Best for use cases
Below are the most commonly seen applications of polyurethane as following
- Furniture and bedding: This foam is highly valued due to the fact that the manufacturer is able to introduce it in a number of densities and hardness. Thus, polyurethane is a favorite in making mattresses, cushions, and car seats since they are very comfortable and strong.
- Thermal insulation: Polyurethane is used in the construction of the insulation because it has a low density and a long life span, which means low energy expenditure and frequent replacement.
- Elastomers: Companies apply it in uses such as gaskets, gel pads, and paint rollers; elastomeric polyurethane is flexible under pressure yet maintains its shape.
- Footwear: Polyurethane midsoles are hard-wearing, flexible, and anti-bacterial to enable natural foot movements.
- Straps: Durability and flexibility are characteristics of polyurethane that guarantee comfort while wearing watches and transporting loads.
- Coating: Many applications are coated with furniture polyurethane, such as floors and car bodies, to enhance durability as well as aesthetic look.
2. Pros and Cons of Silicone Rubber
Pros of silicone rubber
Here are the key pros of silicone rubber you might need to know when choosing material for your work, which are:
- High-temperature resistance: It has an inherent operating temperature of -60°C and 230°C, thus appropriate for aerospace and automotive applications.
- Chemical resistance: Outstanding resistance to many of the chemical, oil, and solvent products. It’s perfect for companies that deal with rough chemical products or organizations that are under FDA regulation.
- Water resistance: Some of the silicone grades have a closed-cell structure, which makes the material water repellent ideal for outer, marine, and sealing uses.
- Weathering resistance: Stable under sunlight, ozone, UV light, and radiation, it has enhanced durability and stability in the field.
- Electrical insulation: Affords excellent electrical conductivity and electrical insulation for use in EMI shielding instances or cable insulation in electronic gadgets.
- Longevity: Chemical, water, and weather resistance intrinsic to silicone rubber makes it sustain enduring performance necessary for high-velocity industries such as aerospace and automotive.
Cons of silicone rubber
- Higher cost: Silicone rubber is generally more expensive than polyurethane rubber. This can be a disadvantage when it comes to cost factors.
- Lower abrasion resistance: Silicone rubber, however, degrades faster under mechanical loading and therefore is not well suited for applications requiring high abrasion.
- Lower tear strength: They also discovered that silicone rubber has low tear strength, which allowed the material to become worn out in areas that expose it to tearing forces.
Best for use cases
Thanks to its durability and heat resistance, silicone rubber is suitable for various demanding applications, including
- Construction and restoration: Applied in combining substances such as glass, metal, and concrete to increase their structural strength and resistance to water, among other properties. Perfect for reviving structures without any need for a change of looks.
- Electronics: Safeguards electronics parts from heat, moisture, and corrosion by encapsulating inner circuits, as well as enhancing device durability.
- Aviation: A critical material in sealing applications such as doors, windows, and fuel tanks because of its high temperature and stress resistance.
- Healthcare: Due to its bacterial resistance, it is used for medical products; for instance, prosthetics, products for baby care, and most healthcare accessories.
- Domestic uses: A widely used in the construction of non-stick, heat resistant, and highly durable cook wares and other utilities.
- FDA compliance: Suitable for medical and food industry applications where products will come into direct contact with food products.
- Industrial production: Used in many production processes, it contributes to new technologies because of its versatility and resilience.
- Paints and adhesives: Commonly found in paints and sealants for adhesive properties, and for increased stain and weather resistance properties.
5 Key Differences of Polyurethane vs Silicone Rubber
1. Physical Properties
Polyurethane and silicone rubber are materials that vary in the essential characteristics that distinguish them for particular purposes.
Polyurethane is harder, rigid, or more brittle, with a hardness range of Shore A 50-95. Meanwhile, silicone rubber is softer, more flexible, and fluent with a hardness of Shore A 10-70.
Polyurethane tends to have better tensile strength, tear strength, and rather better abrasion and is ideal for heavy-duty uses. Nevertheless, silicone excels polyurethane in terms of heat endurance, operating between – 60°C to 230°C, and chemical and UV resistance. It is ideal for cutting-edge and outdoor conditions.
Lastly, polyurethane is more mechanically sound and has a better wear factor than other materials. Whereas, silicone material is best for high-temperature and chemical environments.
2. Mechanical & Chemical Properties
2.1. Mechanical Properties
The mechanical requisites of polyurethane and silicone rubber in the intended application are distinct from one another.
Polyurethane has a greater tensile strength (20-60 MPa) than silicone (5-12 MPa), and the latter is preferable for high-stress uses. Both materials can extend when stressed, but silicone has a slightly high elongation at a break of between 200 and 900% of its original length. At the same time, polyurethane is between 300 and 700% of its original length.
Polyurethane also has a higher tear strength of 20-100 KN/m and therefore is more suitable for wear applications compared to silicone, with a tear strength of 10-40 kN/m.
Comparing compression set ratios, silicone has 10-70%, while polyurethane is flexible for dealing with the value of 10-50% and has a definite shape when pressurized.
In abrasion resistance, polyurethane rate is also high, which makes it suitable for high friction while silicone has a moderate abrasion resistance.
2.2. Chemical Properties
It is recognized that silicone rubber and polyurethane present significantly different characteristics from the chemical point of view.
In the sense of resistance to chemical attacks, silicone costs more because it does not erode in either acids or base solutions or dissolve in solvents. Also, silicone can crystallize in contact with hydrocarbon fuels. Polyurethane, on the other hand, has a low resistance to acids and alkalis but a high resistance to oil and fuel.
Additionally, silicone works at high temperatures, while polyurethane tends to degrade when exposed to higher temperatures. Also, the use of silicone is more effective in terms of its UV and OZONE endurance than polyurethane, especially for outdoor applications. It is because UV is likely to reduce the life expectancy of polyurethane.
3. Heat Resistance
Polyurethane has a temperature range of operating temperature from -62°C to 93°C with some formulations supporting 150°C in limited terms. Nevertheless, it is preferable to avoid constant exposure to temperatures above 180°C.
Conversely, silicone rubber works between -60°C to 230°C and up to 300°C of the specialized formulation in high-temperature applications.
Looking at thermal stability, polyurethane has a tendency to decompose at high temperatures, compounded by the effect of moisture. Whereas, silicone chemical structure remains solid with high heat intensity.
4. Environmentally Impact
Polyurethane and silicone rubber both come with their environmental problems; they both are produced from petrochemicals and are not very recyclable.
Both materials are non-degradable; they have a long residual effect on the environment, provided they are not disposed of appropriately. Nevertheless, silicone rubber is slightly more environmentally friendly since it has better recyclability potential for the material. Moreover, it also generates less manufacturing scrap.
Polyurethane and silicone rubber are also long-lasting, meaning the frequency of replacement is low, and resource use should gradually decrease with time. However, they both might have production processes that emit hazardous substances into the environment and, therefore, call for control of the environmental impact.
In a nutshell, silicone rubber is slightly more eco-friendly than fluoro silicone rubber.
5. Cost
Polyurethane rubber is cheaper because of the availability of the raw materials, comparatively simple production process, and extensive use across different industries. These factors make polyurethane an economical product for manufacturers looking forward to cutting their unit costs.
However, the price situation indicates that polyurethane is considerably cheaper in most cases, yet silicone rubber is expensive. Due to specialized characteristics like heat resistance and electrical insulation, silicone becomes important when dealing with particular and strict applications.
Polyurethane vs Silicone Rubber – What Do You Choose?
There are differences between polyurethane and silicone rubber, and that is why a decision on which one to use has to be made. Polyurethane is very hard-wearing and economical, which makes it perfect for uses where strength is the primary need. Silicone rubber has excellent high-temperature properties and chemical resistance for medical applications.
Understanding the above properties helps you choose the right material that will suit your project. Moreover, TOGOHK offers a range of modified silicons as well. Feel free to contact us!