How Rubber is Made for Industrial Uses

EACH TYPE OF RUBBER HAS A DIFFERENT PRODUCTION PROCESS.

Humans began processing rubber as early as 1600 B.C.E after discovering that rubber is made from a natural byproduct of the rubber tree. 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. 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 begins 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 protects against wear and tear, such as abrasion, fatigue, and exposure to water and certain chemicals. Natural rubber also adheres well to other materials, ideal for making enforced products, such as tires.

Natural rubber has a decent service temperature range, but there may be better choices 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 products, from industrial components to everyday consumer items. These products may include hoses and belts, medical devices, protective gloves, and children’s toys.

The tire industry consumes a significant 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, heavy truck, and race car tires are often made from natural rubber.

The tire isn’t the only vehicle part that contains natural rubber. Brake pads, airbags, seals, and other automotive components also rely on rubber’s desirable properties to serve essential 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. An essential 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.

Industrial Applications of Natural Rubber

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.

How is rubber made? The first step of the natural rubber production process is harvesting. Rubber trees must be at least six years old before being 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 contain 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 a 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 critical differences between the two rubber formulas. Synthetic rubber is reasonably easy to produce and readily available. Synthetic rubber is more resistant to abrasion, grease, oil, and heat when compared to natural rubber. 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 proper 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 primarily 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) protects against environmental factors, making it a popular choice for weather stripping, roofing, and seals. Styrene butadiene rubber (SBR) is an excellent 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 which triggers the creation of monomers.
• Fillers, process aids, cure systems, anti-degradants, and other additives, depending on the product’s service environment.

HOW IS SYNTHETIC RUBBER MADE?

Regarding synthetics, the question is, “How is rubber produced?” Synthetic rubber production begins with a hydrocarbon mixture, usually from oil or coal. The refined mixture produces 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.

Different Types of Synthetic Rubber

EPDM

A remarkably diverse type of synthetic rubber is ethylene propylene diene monomer rubber, or EPDM rubber for short. EPDM is classified as an M-Class rubber composed of elastomers with a saturated polyethylene chain. Fillers like carbon black and calcium carbonate and various plasticizers are essential.

Common uses for EPDM rubbers are manufacturing that requires a solid resistance to outside heating, lighting, and ozone exposures. It can be utilized to create seals, respirators, and weatherstripping needs, to name a few.

SBR

Styrene-butadiene, more commonly known as SBR, are rubbers derived from styrene and butadiene. What makes this type of rubber particularly effective is abrasion resistance. It also possesses good aging stability.

It has many uses, such as waterproofing, speaker manufacturing, shoe production, gaskets, and even chewing gum.

NBR

Nitrile Rubber, or Nitrile Butadiene Rubber, more frequently known as NBR, is a unique synthetic resistant to fuel, oil, and other abrasive chemicals.

NBR has a wide variety of uses, ranging from the manufacturing of synthetic leather to disposable rubber gloves. It is arguably one of the simpler forms of synthetic rubbers to manufacture but also one of the most versatile.

SILICONE RUBBER

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

There are a variety of factors that will determine the type of rubber you need to accomplish your goals. As we have touched upon throughout this article, different types of rubber have different properties that make them better suited for other jobs. Depending on your task, you may need a rubber that is entirely flame resistant, or you need one that can withstand the use of oils and other liquids. That is why it is imperative that before you make your ultimate selection, you should conduct appropriate research to ensure that you will have optimum results for your industrial rubber.

According to the ASTM D2000 test, you need to consider these eight different components.

1. Standards
2. Year Last Revised
3. Units of Measure
4. Grade
5. Type
6. Class
7. Durometer Hardness and Tensile Strength
8. Suffixes

However, the research can continue once you have made your initial selection. Sometimes, there is no clear-cut answer, and you must make your best judgment with the data and facts presented. Before you begin mass production of your industrial applications of rubber, consider having the rubber tested at a professional testing facility, like those at ACE Laboratories.

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 and comprehensive, custom testing protocols. Whether you need industrial goods, to assess a raw material, or to investigate the failure of a whole product, our team can help. Get in touch >