Chemicals in Rubber Tires
When consumers think of a tire, they might imagine the inflated rubber ring which prevents their cars from scraping the road. However, tires play a critical role in many situations, from keeping shopping carts rolling along to supporting the weight of heavy machinery. Most consumers know tires are built to handle tough conditions, but they may wonder what exactly tires are made of.
Tires appear simple to the eye, but their composition is complex. The modern tire is made using advanced technology and is composed of dozens of chemicals to accomplish specific goals. Every component of a tire, from the tread to the inner liner, is carefully designed using chemistry, physics, and engineering. Rubber must be blended with as many as 200 different compounds to function as intended.
This piece looks at the materials tires are made of, how they are manufactured, and what the future holds for these critical everyday tools.
In this article you will learn:
The Raw Materials of a Tire
Tires begin with natural rubber – the primary raw material used to manufacture truck tires. Natural rubber comes from the milky sap of the Hevea brasiliensis tree. Although hundreds of plants produce rubbery liquids, the Hevea brasiliensis tree is the primary source of natural rubber used in commercial manufacturing.
Natural rubber is only part of a tire's makeup. For example, only about 19 percent of a car tire is made of natural rubber. Large truck tires, on the other hand, contain about 34 percent natural rubber. Natural rubber needs to be mixed with other compounds and heated to solidify and resist deterioration. Nevertheless, natural rubber is a useful ingredient regarding resistance to fatigue cracking.
Tires are also made with synthetic rubber polymers such as butadiene rubber (BR) and styrene-butadiene rubber (SBR). The synthetic polymers in a tire determine a tire's overall performance and its ability to resist wear, roll with ease, and gain traction. Halogenated polyisobutylene rubber, also called halobutyl rubber, is also an important synthetic rubber used in tires. This material helps to keep a tire inflated by strengthening the inner liner. About 24 percent of a regular car tire consists of synthetic polymers, whereas only about 11 percent of heavy truck tires are made of synthetic rubber. Carbon black, which is a fine black powder used as a pigment and filler, is another primary raw material found in tires. Most carbon black products are composed of elemental carbon.
Lastly, tire rubber must be blended with compounds such as silica and sulfur to improve strength and rolling resistance.
All of the specific chemicals available make tires perform in different ways. For example, race car tires need to be able to handle high friction. By adding specialty chemicals to tire rubber during the raw materials stage, a manufacturer can create a tire suitable for high speeds. We will look at a few of the different chemicals used in tires below.
CHEMICALS IN TIRES
Tire manufacturers choose chemicals depending on their needs and what their customers want. Once all of the raw materials are selected, they are mixed with natural and synthetic rubber. Chemicals used include vulcanizing agents, antidegradants, antioxidants, antiozonants, softners, waxes, oils, and various ingredients to improve tire performance and resistance to wear.
Here is a general overview of essential tire chemicals:
Antioxidants, along with antiozonants and curing systems, make up about 14 percent of a car tire. Antioxidants are needed to prevent rubber tires from breaking down. These chemicals protect tires from environmental factors, such as exposure to different temperatures and oxygen. Examples of rubber antioxidant products include:
- AMINOXⓇ stabilizer: AMINOX stabilizer is an antioxidant that
reacts at a low temperature and can be used with natural rubber and synthetic rubber polymers. It is used in the manufacturing of many rubber goods, including tires.
- BLEⓇ 65 stabilizer: BLE 65 is a high-temperature reaction product which works as an antioxidant and anti-flex cracking agent for natural and synthetic rubbers. It is recommended for use with tire tread and carcass compounds.
- NAUGARDⓇ DTDTDP thioester: NAUGARD DTDTDP thioester is used as a secondary antioxidant when mixed with phenolic antioxidants, and is appropriate for rubber applications. An advantage of this chemical is it easy to handle and store.
- LOWINOXⓇ CPL stabilizer: LOWINOX CPL stabilizer is a highly effective non-staining, non-discoloring phenolic antioxidant recommended for use with natural, and synthetic rubbers.
- WESTONⓇ 398 phosphite: WESTON 398 phosphite is a versatile phosphite stabilizer useful in a range of polymers. It improves color and processing stability as well as end use.
Antiozonants slow the effects of ozone exposure to a tire's surface. Antiozonants protect synthetic rubber
in the tire tread and sidewall from dynamic ozone cracking, and natural rubber compounds from various factors such as flex-cracking and heat degradation. Examples
of antiozonant chemical products include:
- FLEXZONEⓇ 11L antiozonant: FLEXZONE 11L antiozonant is used in combination with antiozonant waxes. This product provides excellent dynamic flex protection and protects rubber against ozone weathering, oxygen aging, and heat deterioration.
- FLEXZONEⓇ 4L antiozonant: FLEXZONE 4L antiozonant provides superior static protection, guards rubber against oxygen degradation, and is active in promoting the cure of compounds.
- FLEXZONEⓇ 3C antiozonant: FLEXZONE 3C antiozonant is unique because it functions as both an antiozonant and antioxidant, providing exceptional protection against heat, flex-fatigue, ozone, and oxygen.
Twenty-six percent of a passenger car tire is made of fillers like silica and carbon black to improve tensile strength, wear resistance, performance, and traction. Here are examples of fillers used to manufacture quality tires:
- ExCalⓇ CW calcium carbonate: ExCal CW calcium carbonate products are made from high-purity ore and processed to use in rubber, plastics, and other materials. Ground calcium carbonate is a low-cost filler used to improve many physical properties of rubber compounds.
- Micro Mica™ 105: Mica is used as a filler in molded rubber products and also as a dusting agent to provide a non-stick surface for rubber goods. For example, Micro Mica 105 is ultra-fine mica which makes a plastic or rubber surface more durable and crack resistant.
- CIMBAR™ barite products: CIMBAR barytes are made from the highest quality barium sulfate ore. They are used as a filler in many applications where low solubility and chemical inertness is needed.
Certain ingredients are critical in turning rubber into a solid object during the curing, or vulcanization, process. A manufacturer might add vulcanizing agents like elemental sulfur, vulcanization accelerators such as thiazoles, and vulcanization activators such as zinc oxide to aid the process. Curing systems shorten the amount of time needed to complete vulcanization and impact chemical reactions that occur. Here are just a few examples of essential products that may be used to assist vulcanization:
- HEPTEENⓇ Base curing agent: HEPTEEN Base curing agent is commonly used in cured natural rubber. It is a fast curing high-temperature accelerator with excellent processing safety.
- ZnO PRO: Zinc oxide, like ZnO PRO 1250, is used in rubber goods to activate the vulcanization process and increase tensile strength. The new ZnO PRO series offers optimized processibility, cost savings, and low heavy metal content for satisfaction with performance, price, and sustainability.
- BIKⓇ OT: BIK OT is an activator for accelerators such as thiuram, thiazole, and dithiocarbamate. It is relatively non-staining and non-discoloring, and also functions as an odor reducer when used with nitrosamine-type blowing agents.
We covered only a portion of the chemicals used in tires. Various other substances such as pigments and flame retardants may be necessary to create the desired tire characteristics.
The Manufacturing Process of a Tire
Once all the raw materials are selected, they are mixed together to start the tire manufacturing process. A large mixer blends the raw materials into a uniform batch of black substance with a gummy consistency. The mixing process is controlled by computers to ensure uniformity. The compounded materials are then sent to other machines to continue processing different tire components.
Once the different parts of the tire are created, the assembling process begins. Tire assembly first involves creating the inner liner on the tire building machine. The inner liner is made of a special rubber which is resistant to air and moisture penetration. The inner liner also preserves the inflation pressure inside the tire.
Next, the body plies and belts are built, usually from polyester and steel. The body ply is the structure of the tire and provides tire strength and flexibility. The belts provide stability and strength to the tread area. Belts are cut precisely to provide certain handling and riding characteristics designed by an engineer.
During this stage, beads are installed into tire sidewalls to make sure the tire forms an air-tight fit to the wheel. Tire beads are made of rubber-coated steel wire. Finally, the tread and sidewalls are positioned over the belt and body plies, and all pieces are pressed together. The tire product is now called a green or uncured tire.
The final step of the tire manufacturing process is vulcanization. During this stage, the green tire is placed inside of a mold and inflated with steam or hot water. The inflated tire presses against the mold to form the tread and the tire identification information on the sidewall. The tire is then heated at more than 300 degrees for 12 to 15 minutes – this is when many chemical reactions take place. Some chemicals are used to speed up the vulcanizing process, and waxes may be used as mold release agents. After a tire is cured, it is then carefully inspected for flaws such as bubbles or gaps.
Tires are thoroughly inspected and tested to ensure safety and quality performance. Random tires may be taken off the line to undergo X-rays or be cut apart and inspected for flaws. Other tires might be road tested to assess their performance regarding handling, mileage, and traction.
However, testing truly begins before the manufacturing process starts. Most manufacturers make sure to order chemicals from reliable distributors who test raw materials before they ship their products. To make sure the raw materials are safe for use, tire manufacturer chemists test raw materials randomly as they arrive at the plant. At Brenntag, we strive for excellence as a chemical distributor, and we work closely with manufacturers to ensure our products satisfy the industry's most strict technical, quality, and safety standards.
Rubber tires have come a long way since the days when rubber froze in the winter and melted in the summer. The tire industry is continuously making improvements, using modern technology to design and build safer, more efficient, and more reliable tires. Consumers want tires that help them save fuel and can perform well whether it is raining, snowing, or hot outside. New, quality tires, if properly maintained, can last up to 80,000 miles.
Tire industry chemists and engineers are also working hard to create tires which make less of an environmental impact. The main aspect of a tire that contributes to greenhouse gas emissions is related to the fuel needed to overcome a tire's resistance to rolling. By developing low rolling resistance tires, tire manufacturers can help consumers increase fuel economy by 4 to 8 percent. Manufacturers are also looking to use sustainable ingredients such as vegetable-based processing oils and non-petroleum versions of tire fillers. Also, companies are experimenting with the use of non-pneumatic tires which offer lowrolling resistance and cannot go flat — perhaps a safer option for consumers. As chemists and researchers continue to search for ways to make better, more environmentally-friendly tires, the tire industry is working to recycle millions of used tires.
The future of tires also addresses the health concerns of workers and consumers. For example, industry workers may be exposed to carcinogenic nitrosamines during the vulcanization process. However, companies have developed curing agents with health factors in mind. For instance, Brenntag distributes ROYALACⓇ 150 curing agent which is a rubber chemical used as an ultra accelerator for natural and synthetic rubbers. ROYALAC 150 does not emit nitrosamines.
Learn More About Brenntag's Rubber Solutions
Tire manufacturing is a complex process. Tire companies must develop relationships with chemical distributors they can trust to acquire the materials they need to build high-quality tires. These chemicals include antioxidants, antiozonants, curing agents, and protective waxes. Choosing the right chemicals from a knowledgeable distributor helps companies bring their designs to life, and get their tires on the market faster.
At Brenntag North America, we want to help you stay ahead of the curve. Our team of technicians and sales representatives are here to help you navigate recent product innovations and choose the chemicals you need to ensure safety, quality, and satisfaction. We are a top chemical distributor serving clients around the globe, and a leading source for rubber chemicals for all applications, whether you need fillers and additives for tires or pigments for wires and cables. To learn more about our rubber solutions, contact us today.
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