What Is SBR Rubber? – Its Properties, Applications, and Everything You Need to Know

There are various types of rubber. Each has its unique properties, applications, strengths and weaknesses. This is why you need to understand which one is the best for your needs.

Chances are that you’ve heard of SBR rubber. It’s the most popular synthetic rubber used across diverse industries.

So, what should you know about SBR rubber?

By the end of this post, you’ll have understood this synthetic rubber, its composition, and its applications.

What Is SBR Rubber?

Styrene-butadiene (SBR) rubber is a multi-purpose synthetic rubber. SBR and natural rubber share some characteristics. However,  the former is petroleum-based, while the latter is latex-based. Being synthetic, SBR is extracted as a result of oil refining. 

Chemically, it’s a copolymer comprising:

  • Styrene content (10-25%)- Makes SBR rubber cheaper while contributing to its good bonding and blending attributes. It also adds its strength, as well as wear and abrasion resistance to SBR.
  • Butadiene content– Comprises 60-70% of the trans unit, 15-20% of cis-1,4 units, and 15-20% 1,2 configurations for the polymer. These configurations happen at 50°C.

These polymers are polymerized in a controlled setting. Manufacturers then add curatives and fillers like Carbon black and Sulfur. They vulcanize or cure the material to give you SBR rubber.

Types of SBR Rubber

You can produce SBR rubber through emulsion and solution processes. These different methods contribute to different properties. 

Emulsion SBR

While emulsion SBR is the lesser-known type of SBR rubber, its popularity continues to grow. There are two different emulsion SBR production processes, which both contribute to different properties:

  • Hot Emulsion SBR (50-60°C)– Hot emulsion SBR has more of a branching polymer compared to cold emulsion SBR. It has exceptional processing attributes including good extrusion capabilities, good dimensional stability, and low mill shrinkage. These characteristics make hot emulsion SBR better for light-duty tires.
  • Cold Emulsion SBR (about 5°C)– The cold emulsion SBR process demonstrates superior tensile strength in comparison to the hot emulsion SBR process. Rubber grades produced in this process have dynamic properties and offer better tread wear. As such, these grades are preferred for high-performance tires.

Emulsion SBR is difficult to process. It also has low green strength and low resistance to oil, tear, ozone, and some hydrocarbon fluids. On the other hand, it has high abrasion resistance and good low-temperature properties.

Solution SBR

Solution SBR remains the most popular type of SBR rubber, maintaining about 75% of all SBR made. It has a smaller molecular weight distribution but a higher molecular weight.

Solution SBR is tougher compared to emulsion SBR. It has good resilience, better flexibility and performance, lower rolling resistance, and outstanding abrasion and fatigue resistance.

But just like emulsion SBR, Solution SBR has low resistance to oil, ozone, and some hydrocarbon fluids

While solution SBR is more expensive to produce than emulsion SBR, its features demonstrate why it’s the most used type of SBR rubber.

How Is SBR Rubber Made and Processed?

You might have noticed that rubber processing companies receive SBR rubber in large bale form. But how is it actually made?

The SBR rubber production process starts with mixing the elastomers with additives. The following step involves shaping the rubber using various processing methods.

That said, the compounding of SBR rubber additives occurs in two different processes:

  • Vulcanization
  • Reinforcing and non-reinforcing fillers

Vulcanization

In this process, you cross-link elastomer molecules to add strength and stiffness to the rubber. In addition, this process also retains the rubber’s extensibility.

All SBR rubber types share the same vulcanization agents as natural rubber. These agents include peroxides, sulfur, and sulfur donor systems. As for sulfur, it’s added in smaller quantities to vulcanize SBR rubber, compared to the amount used for natural rubber.

Reinforcing and Non-Reinforcing Fillers

There are many fillers and additives used in the SBR manufacturing and refining process. Let’s break down each of the additives to help you understand this process better.

Fillers

Without fillers, SBR becomes one of the weaker rubbers, due to its vulnerability to ozone, weathering, oxidation, solvent, and fatigue.

However, the use of fillers strengthens SBR.

One of the most significant fillers used is carbon black, which is the main reinforcing filler. You chemically obtain carbon black by thermally decomposing hydrocarbons. This is the process that boosts SBR’s abrasion and tear resistance while increasing its strength. It also gives SBR rubber ultraviolet radiation protection.

Due to these features, carbon black is used to make black SBR rubber suitable for tires.

Other important fillers you should note include china clays (mostly used for non-black rubber uses), Silica, calcium carbonate, filament reinforcement, fiberglass, recycled rubber, and steel.

Additives

Additives are used when manufacturing and refining SBR rubber to reduce aging, provide a stable bond, and offer protection during service. 

Additives used when manufacturing rubber include anti-degradants, antioxidants, processing aids, pigments, flame retardants, coupling agents, curatives, plasticizers, and mold-release compounds.

Once compounded, the rubber is shaped through calendaring, extrusion, compression molding, coating, casting, or injection molding.

What Are the Properties of SBR Rubber?

At this point, you might already tell some SBR rubber properties, based on the manufacturing and refining process. 

Some key properties that make it popular are its ability to withstand wear and tear, high durability, and high resistance to abrasion. These are the main characteristics that make many industries choose SBR for diverse applications.

SBR rubber has good tensile strength which helps it endure stretching and pulling. It’s highly flexible and doesn’t break easily. Due to this feature, manufacturers can shape and mold it into different forms.

It also has good resistance to heat, ozone, and weathering. This helps it maintain its condition when used in extreme weather and when exposed to sunlight and various outdoor elements.

SBR rubber also demonstrates good adhesion capabilities by adhering well to various materials. This property makes it suitable for adhesive application and as a binding agent for various products.

When it comes to the cost, SBR rubber is quite cost-effective and relatively cheaper compared to other synthetic rubbers. 

While it might not match up to some specialized rubber such as nitrile rubber, SBR rubber offers some fair oil resistance to some oils and fluids.

SBR is also a good electrical insulator. 

Applications of SBR Rubber

Due to the diverse properties we’ve just looked at, SBR rubber has a wide range of applications spreading across numerous industries. Let’s break down some popular SBR applications you should know:

Automotive Applications

SBR’s most prominent application in the automotive sector is tires used on passenger cars, trucks, and various vehicles. Due to the heat and wear resistance, as well as good traction and durability, tires made from SBR can be used on high-performance and heavy-duty vehicles.

Other than tires, SBR is also used in the production of other car parts including mounts, bushings, weather stripping, and grommets.

Industrial Applications

Remember, SBR has good resistance, flexibility, and tensile strength, making it great for heavy-duty use. This makes it suitable for use in power transmission and conveyor belts.

If you’ve been in the market for adhesives, you might have also seen SBR-based adhesives used in woodworking, paper, and construction industries.

Due to its resilience, SBR is also used to make gaskets, seals, and hoses that are then used in the automotive, plumbing, and industrial sectors.

Sports Applications

In the sports industry, SBR is used to manufacture rubber granules or SBR rubber sheets that are used in flooring applications, especially in playgrounds, gymnasiums, and sports surfaces. This is due to its anti-slip, durability, and shock absorption properties.

It’s also used for the manufacturing of sports equipment, particularly soccer balls, and basketballs.

Consumer Applications

SBR in the consumer industry is mainly used for the manufacturing of footwear, specifically soles for boots, sneakers, sandals, and sports shoes.

Advantages of SBR Rubber

Understanding SBR’s pros and cons will help you make a wise decision when selecting SBR for different applications, considering its different strengths and weaknesses.

SBR rubber has a long list of advantages, including:

  • Durability– With its resistance to wear, crack, and heat, SBR ages well and offers durability which makes manufacturers use it when longevity is important.
  • Tensile strength– Due to its tensile strength, SBR supports applications that require resistance and elasticity.
  • Versatility– As we’ve seen in the previous section, SBR is used in diverse industries since it can be easily shaped and molded.
  • Inexpensive– SBR is relatively cost-effective compared to many of its competitors. As such, it’s often used as an alternative to natural rubber due to its similar properties, but lower price tag.
  • Adhesion– SBR has good adhesive properties that help it create stronger and more durable bonds on materials such as metals, wood, plastics, and paper.
  • Availability– There’s a huge demand for SBR rubber all across the world due to its versatility and applications in various industries. Numerous manufacturers produce SBR in large quantities to meet this demand. It’s readily available through manufacturers, distributors, or suppliers.
  • Odor resistant– Generally, SBR tends to have a mild or less noticeable odor in comparison to natural rubber.

Potential Downsides of SBR Rubber

Due to their similarities, SBR and natural rubber share the same disadvantages. Some disadvantages to note include:

  • Low weather resistance– SBR has some moderate resistance to weathering. But when compared to other rubbers, its weather resistance is low. Extended exposure to extreme weather conditions often leads to degradation.
  • Low electrical insulation– While it has some electrical applications, SBR’s level of insulation may not be as high-performing as specialized insulation rubber.
  • Low oil resistance– SBR isn’t a good resistor when it comes to certain fluids and oils. It’s not suitable for applications that require high oil resistance compared to some rubbers like nitrile rubber.
  • Stiffness– SBR rubber’s stiffness may vary, which has a direct impact on its performance depending on its application.
  • Environment concerns– SBR rubber’s production process involves petrochemicals and emissions that are hazardous to the environment. It’s also not biodegradable and disposal has often posed some environmental challenges

ELT Vs. SBR Rubber

Some people often use ELT and SBR rubber interchangeably. But the two aren’t synonymous.

ELT is an acronym for end-of-life. ELT rubber therefore refers to rubber granules produced from end-of-life tires that are worn-down and can no longer be used for their original purpose.

ELT and SBR rubber aren’t a direct comparison since they’re both at different stages of their lifecycles.

Besides, ELT granules can be obtained from various types of rubber, regardless of the SBR percentage used originally in the manufacturing process.

ELT can be a good source of recycling rubber which can be repurposed for various applications, including processing new rubber products.

EPDM Vs. SBR Rubber

EPDM rubber is a different synthetic rubber from SBR. EPDM stands for Ethylene Propylene Diene Monomer which basically describes the monomers used to create it. It’s a versatile and durable synthetic rubber applied in diverse industries.

Some of its properties include good weather, heat, water, and steam resistance as well as excellent electrical insulation.

Just like SBR, EPDM is used to create some automotive parts, such as gaskets, seals, and hoses. It’s also used in the production of electrical insulation cables. 

EPDM demonstrates good weather resistance qualities. As such, it’s also used in roofing membranes.

SBR Rubber FAQs

Is SBR Rubber Recyclable?

Yes. SBR rubber can be recycled through various processes based on the intended purpose and condition of the rubber. These recycling processes include:

  • Mechanical recycling– This process involves physical processing and mechanically grinding or shredding SBR rubber into granules or powder which is then used as filler when producing new rubber products, such as playground surfaces, flooring, and mats.
  • Pyrolysis– This is a thermal decomposition procedure that involves breaking down SBR by heating it at high temperatures in the absence of Oxygen. This process leads to the formation of solid (char), gaseous, and liquid (oil) byproducts which can be used as fuel, chemical feedstock, or filler for new products.
  • Devulcanization– This process occurs during manufacturing when sulfur and other vulcanizing agents are added to boost SBR’s strength. Devulcanization reverses vulcanization to allow SBR to repossess its original characteristics. Devulcanized SBR can be mixed with virgin SBR and produce new rubber products.

Is SBR Rubber Safe or Toxic?

SBR rubber is non-toxic as a copolymer. However, the individual monomers can present some health risks when exposed in high concentrations and in some industrial settings. 

The risk is reduced once converted into solid SBR.

Can SBR Rubber Burn?

SBR typically burns. While the fire has to be extremely hot to burn the rubber, it can be hard to put out once SBr catches the fire. For this reason, large-scale fires in SBR factories and plants can be catastrophic.

The good thing is that manufacturers can add flame retardants when processing to make SBR fire-resistant.

Does SBR Rubber Harden?

SBR rubber hardens over time. But its hardening rate and its durability period depend on its manufacturing formulation and the end product’s application.

Does SBR Rubber Stretch?

SBR stretches depending on its hardness. The lower the density of SBR rubber, the more it stretches. Besides, manufacturers can formulate it to stretch.

Conclusion

Up to this point, you can see why SBR is the most widely used synthetic rubber across all industries. It has some superior qualities and properties that make it durable, versatile, and strong. Besides it’s relatively inexpensive compared to other synthetic rubbers. Now you’re well-informed to make wise decisions concerning SBR rubber.

 

More resources:

FFKM Rubber: Everything You Need to Know – Source: LEGENDAY

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