Each Type of Rubber has a Different Production Process

Humans first began processing rubber as early as 1600 B.C.E. Evidence suggests that indigenous Mesoamerican cultures figured out how to stabilize natural rubber for containers, waterproofing, and even recreational items, such as balls and toys.

In 1839, Charles Goodyear discovered the rubber vulcanization process that set the groundwork for today’s natural rubber processing methods. As the story goes, in a moment of absent mindedness, Goodyear dropped a chunk of natural rubber on a hot stove. The heat caused the rubber to harden and stabilize—or vulcanize—which inspired Goodyear to experiment with a more controlled process for achieving the same outcome.

Goodyear’s discovery eventually led to a massive spike in demand for natural rubber, which continues to this day. In fact, global demand for rubber has long since surpassed the world’s production capacity for natural rubber, and many rubber products on the market are made with synthetic rubber instead. As of 2005, synthetic rubber is found in over 58% of rubber products.

While natural and synthetic rubber share many desirable qualities, the production process for each is quite different. For example, making natural rubber starts with a tree, whereas making synthetic rubber starts with a base of petrochemicals. Silicone rubber starts with massive quantities of quartz sand. All three products and processes are vital to many industries and everyday needs.

Natural Rubber

Natural rubber is strong and flexible and holds up well against wear and tear, such as abrasion, fatigue, and exposure to water and certain chemicals. Natural rubber also adheres well to other materials, which is ideal for making enforced products, such as tires.

Natural rubber has a decent service temperature range, but it may not be the ideal choice for extreme heat, harsh lighting, or ozone exposure. Additionally, natural rubber is not highly resistant to fuel, oil, and other substances.

What Is Natural Rubber Used For?

Natural rubber can be found in thousands of different products, from industrial components to everyday consumer items. This may include hoses and belts, medical devices, protective gloves, and children’s toys.

The tire industry consumes a large portion of the world’s natural rubber supply. Natural rubber is often found in high-performance vehicle tires because of its excellent tear strength, even at high temperatures caused by friction. Aircraft tries, heavy truck tries, and race car tires are often made from natural rubber.

The tire isn’t the only part of the vehicle that contains natural rubber. Brake pads, airbags, seals, and other automotive components also rely on rubber’s desirable properties to serve important functions while the vehicle is in service.

What Are the Ingredients Used to Make Natural Rubber?

Every natural rubber product will have a slightly different composition profile based on its service environment. A basic natural rubber recipe includes:

  • Latex, a milky white substance harvested from the rubber tree.
  • Acids, to trigger clumping of filtered latex.
  • Chemicals, for the prevulcanization process.
  • Additives, such as fillers, curing agents, antidegradants, and more.

How Is Natural Rubber Made?

Most of today’s natural rubber supply comes from a single species of rubber tree, Hevea brasiliensis. Hevea brasiliensis is native to South America, but Hevea brasiliensis plantations can be found all over southeast Asia. Some major companies are experimenting with making rubber from other plants, but Hevea brasiliensis remains the primary source.

The first step of the natural rubber production process is harvesting. Rubber trees must be at least six years old before they can be tapped. Once the tree reaches maturity, a tapper peels back a carefully cut section of the tree’s bark, which disrupts the plant ducts and releases latex, a milky white substance. The latex flows along the grooves of the peeled-back panel and is collected in cups or bags. Rubber tappers then collect all the harvested latex and transport it for processing.

The freshly harvested latex is filtered and packaged into drums. At this stage, acid is added to the latex, which forms clumps. This clumpy fluid is rolled into sheets at a mill, which removes water and prepares the material for drying and smoking.

Next, the latex sheets are treated with chemicals and low, gentle heating, a process called prevulcanization. Stabilizers and other ingredients may be introduced at this stage, depending on the desired final properties of the rubber. Further heating transforms the sheets into the firm, black material that most people recognize as rubber. At this stage, the rubber can be molded, shaped, or otherwise processed into a final product.

Synthetic Rubber

Synthetic rubber shares many of natural rubber’s most desirable qualities, but there are important differences between the two. Synthetic rubber is fairly easy to produce and readily available. Synthetic rubber is more resistant to abrasion, grease, oil, and heat when compared to natural rubber. In fact, some varieties of synthetic rubber are even flame resistant. Like natural rubber, synthetic rubber is highly flexible, but synthetic rubber maintains that flexibility even at low temperatures. With the right manufacturing methods, synthetic rubber can also be highly resistant to extreme temperatures and corrosion.

What Is Synthetic Rubber Used For?

There are many types of synthetic rubber, and their uses are largely informed by their unique properties. For example, polyisobutylene rubber, or “butyl,” has excellent damping properties and is commonly used to make massive seismic absorbers for skyscrapers in cities prone to earthquakes. Ethylene propylene diene rubber (EPDM) holds up well against environmental factors, making it a popular choice for weather stripping, roofing, and all kinds of seals. Styrene butadiene rubber (SBR) is a good all-purpose synthetic rubber and can be found in tires, shoe soles, and more. The applications for synthetic rubber are virtually unlimited.

What Are The Ingredients Used to Make Synthetic Rubber?

Synthetic rubber refers to a range of polymer materials created from petrochemicals. The exact ingredient breakdown for each synthetic rubber will differ. A basic synthetic rubber recipe includes:

  • A petrochemical base of hydrocarbons, such as oil or coal.
  • Natural gas, to trigger the creation of monomers.
  • Fillers, process aids, cure systems, antidegradants, and other additives, depending on the product’s service environment.

How Is Synthetic Rubber Made?

Synthetic rubber production begins with a hydrocarbon mixture, usually from oil or coal. This mixture is refined to produce naphtha, a flammable oil. The naphtha is combined with natural gas to create monomers, such as butadiene, styrene, isoprene, chloroprene, ethylene, and propylene. This substance is then polymerized using a catalyst and process steam, forming chains of polymers to create rubber. At this stage, the synthetic rubbers can be further vulcanized if needed.

Silicone Rubber

Silicone rubber, like natural rubber, is an elastomer. The difference between the two lies in their atomic structure. Most rubbers have backbones made of carbon-carbon bonds, but silicone’s backbone is made of silicon and oxygen.

Silicone is typically non-reactive, stable, and resistant to extreme environments. Silicone rubber holds up much better than natural rubber against heat, cold, chemicals, and ozone. Silicone also can handle long-term water exposure with very little absorption or other impact on mechanical properties. Other benefits include biocompatibility and radiation resistance.

What Is Silicone Rubber Used For?

Silicone rubber has many desirable properties and is commonly used in a wide range of products.

Silicone rubber doesn’t degrade in high temperatures and is food safe, making it a popular choice for cooking and baking tools. Silicone muffin tins, spatulas, and many other tools have become increasingly popular in recent years. Many other consumer products contain silicone, such as sportswear, storage containers, electronics, cosmetics, and footwear.

Industry uses for silicone include automotive products, sealants, and insulators. Silicone can also be found in many medical products, such as tubing, syringe components, fluid management components, and more.

What Are the Ingredients Used to Make Silicone Rubber

Silicone rubber is a highly customizable material and can be tailored to meet the requirements of a variety of service environments. A basic silicone rubber recipe includes:

  • Silica quartz, from which silica is extracted.
  • Methyl chloride, to create polydimethylsiloxane.
  • A curing agent.
  • Other additives, such as pigments, fillers, and others.

How Is Silicone Rubber Made?

Silicone rubber starts with silica, a silicone dioxide compound. Silica can be found throughout the natural world but is most easily extracted from quartz sand. Huge quantities of quartz sand are heated up to 1800°C to extract silicon atoms. The pure silicon is then combined with methyl chloride, exposed to heat, and distilled into polydimethylsiloxane. Final steps of the process include polymerization, molding or extrusion, and curing.

There are many different grades of silicone rubber, each offering a unique profile of performance properties, resilience levels, and other attributes. These grades are often achieved by various additives and other customization steps during the silicone rubber manufacturing process.

Rubber testing services from ACE Laboratories

The experts at ACE have years of experience working with natural, synthetic, and silicone rubber materials and products of all kinds. Our state-of-the-art ISO/IEC 17025 accredited laboratory is equipped to support industry standard testing as well as comprehensive, custom testing protocols. Whether you’re looking to assess a raw material or investigate failure of a whole product, our team can help. Get in touch > 

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