Structure, Types, Preparation, Vulcanization, and FAQs

Rubber is a natural product made by plants. Throughout the history of humanity and the rise of human civilizations, rubber has played a significant role. Today, we obtain 99% of the natural rubber we use from a tree known as Hevea brasiliensis. Hence, rubber is an elastic material produced from the emission of some tropical plants (natural rubber) or extracted from petroleum and natural gas (synthetic rubber). Rubber is an elastic, flexible, and tough substance therefore, it can be used to manufacture tires for vehicles, aircraft, bicycles, etc. 

What is Rubber? 

Rubber is a natural polymer that can stretch and shrink. It’s an elastomer that, after being deformed, may revert to its previous shape. Rubber is made by the polymerisation of Isoprene (2 methyl-1,3-butadiene). 

By cutting into the bark of a rubber tree and collecting the sticky fluid into containers attached to it, a polymer called Rubber is extracted from the tree. Brazil is where the rubber tree, Hevea brasiliensis, originated. The “Olmec people” were the first humans to use rubber some 3000 years ago. 

Types of Rubber

The two primary categories into which the various rubber types can be divided are Natural Rubber and Synthetic Rubber. Vulcanized rubber is sometimes considered to be a form of rubber as well. Let’s discuss these different types of Rubber:

• Natural Rubber – Natural rubber is the type of rubber obtained naturally from the milky liquid or latex obtained from the rubber tree. It is also known as India or gum rubber. Natural rubber can be vulcanized into many different types of rubber products
• Synthetic Rubber – Synthetic rubber is a man-made or artificial polymer. This rubber is an artificial elastomer obtained by synthesizing petroleum products under controlled conditions. An example of synthetic rubber is Neoprene which is made up of monomer unit chloroprene.
• Vulcanized Rubber – Vulcanized rubber is the substance that is obtained after the vulcanization of natural rubber. Vulcanization is the process that is done to improve the properties of natural rubber; so that, it can have more desirable properties.

What is Natural Rubber?

It’s a natural polymer derived from a rubber tree’s latex sap. Rubber’s elasticity makes it a popular material. Vulcanized natural rubber is used to make a variety of items. Polyisoprene is the chemical name for natural rubber. Natural rubber’s best feature is that it is biodegradable and renewable because it is extracted from trees. Thousands of items, including surgical gloves, medical gadgets, aircraft, and vehicle tires, mattresses, shoe soles, rubber boots, toys, and more, rely on it as basic material.

Isoprene (2-methyl, 13-butadiene) is the monomer of natural rubber. Natural rubber is the polymer of this isoprene, and its chemical name is ‘cis – 1,4 – polyisoprene.’

Preparation of Natural Rubber

The latex sap of the rubber tree is used to make natural rubber. The latex is harvested by affixing a container to the rubber tree, which is referred to as tapping.

After that, formic acid is used to coagulate the latex. They become a hard mass as a result of this process. These rubbers are now completely dried, either with a series of rollers or by allowing them to air dry for several days. These natural rubbers are now ready for processing and will be used to make a variety of products.

What is Synthetic Rubber?

Any artificial elastomer is referred to as synthetic rubber. Synthetic rubber is typically made up of additional polymers of polyene monomers, and laminates including such a layer will be categorized as additional polymers unless the synthetic rubber is disclosed as a polysulfide rubber. An elastomer is a material that has the mechanical property of being able to bend far more elastically under stress than most materials while still returning to its original size without permanent distortion. In many circumstances, synthetic rubber can be used in place of natural rubber, especially where better material qualities are required.

Preparation of Synthetic Rubber

Various synthetic rubbers are made using the polymerization process, such as neoprene by addition polymerization, Buna-S, and Buna-N through co-polymerization.

• Neoprene: Neoprene, commonly known as polychloroprene, is a homopolymer made from chloroprene polymerized by free radicals. It has a strong oil resistance and is used to make conveyor belts, hoses, and gaskets, among other things.
• Buna-S: Buna – S is formed by the copolymerization of 1,3-butadiene and styrene. It has a high tensile strength and can be used as a natural rubber alternative. It’s utilized to create car tires, footwear components, cable insulators, and other things.
• Buna-N: Buna – N is a copolymer made by polymerizing 1,3-butadiene with acrylonitrile in the presence of a peroxide catalyst. Oils, petrol, and some organic solvents won’t harm it. They’re typically utilized to make tank linings, oil seals, and other such things.

Vulcanization of Natural Rubber 

Vulcanization is a process of hardening rubbers. The term “Vulcanization” originally comes solely from the reaction of natural rubber with sulfur, which is the most common practice. It has also grown to include the hardening of other (synthetic) rubbers via various means. For example Silicone Rubber and chloroprene rubber (neoprene), etc.

A multi-step vulcanization method is used to create vulcanized rubber. The rubber is first immersed in a sulfur and additive-filled solution. Sulfur is the main component that promotes vulcanization, however, it is combined with additional chemicals. Both color-enhancing pigments and a process accelerator may be included in the bath.

The rubber is then shaped in the manner desired. Molding vulcanized rubber is difficult. Instead, because of its strength and flexibility, it is challenging to mold. As a result, the rubber is molded after being immersed in sulfur. An elastomer that has been strengthened by the biochemical process of vulcanization is known as vulcanized rubber. A curing agent, typically sulfur, is mixed with the milky latex from the rubber tree and heated under pressure.

What is Vulcanized Rubber?

An elastomer that has been strengthened by the biochemical process of vulcanization is known as vulcanized rubber. A curing agent, typically sulfur, is mixed with the milky latex from the rubber tree and heated under pressure.

Preparation of Rubber

After natural or synthetic rubber is made, it is delivered to processor plants to be processed into the final product, which may then be utilized to make a variety of goods. Compounding, mixing, shaping, and vulcanizing are the four processes in the rubber processing process.

1. Compounding: Rubber is fortified with additives and chemicals to improve its tensile strength and characteristics. Carbon black fillers, for example, are added to rubber to boost its tensile strength and protect it from ultraviolet radiation degradation.
2. Mixing: Rubber must be well mixed with the additives before use. The temperature is raised for this purpose, and the additives are thoroughly blended.
3. Shaping: Extrusion, calendering, molding or coating, and casting are four common methods for shaping rubber items. Extruders force a highly plastic rubber through a series of screw extruders to create rubbers. Calendering follows this phase, which involves passing the rubber through a series of smaller gaps between rollers. This roller-die method combines extrusion and calendering to create a superior result. The coating is the application of a rubber coat or the pushing of rubber into cloth or other materials. Rubber coatings are used to make tires, waterproof textile tents, raincoats, conveyor belts, and other items. Molds are used to make rubber products such as shoe soles and heels, seals, suction cups, and bottle stops.
4. Vulcanization: The rubber-processing process is finished with vulcanization. Sulfur cross-connections between rubber polymers are formed during vulcanization. Rubber that has fewer cross-connections between its polymers is softer. The elasticity of the rubber is reduced as the number of cross-connections increases, resulting in harder rubber. Rubber would be sticky when hot and brittle when cold if it wasn’t vulcanized.

Uses of Rubber

• One of the largest consumers of rubber is the tire and tube industry. To make natural rubber more durable, it is combined with synthetic rubber over time.
• Rubber is also employed in other areas of the vehicle industry. Seals and various types of cushioning for different car parts are made from natural rubber. For example, it’s used to make brake pads and window and windshield seals in automobiles.
• Rubber is used to produce airbags in automobiles, which protect passengers from damage caused by accidents.
• Clothing: Because natural rubber is elastic in its fibrous form, it is utilized to make clothing that is tight-fitting and expandable, such as swimwear and cycling shorts.
• Rubber is utilized to make flooring in a variety of business establishments, kitchens, and even playgrounds. It creates a cushioned surface that is also slip-resistant and waterproof. It’s simple to keep up with and lasts a long time.
• Gaskets: Gaskets are used to prevent leakage or fill uneven spaces between two or more mechanical parts.
• Erasers: This rubber device could “rub” away pencil marks on paper, earning it the name “eraser.”
• Natural rubber was used by ancient Mesoamerican civilizations to build waterproof shoes and bottles. Not only that but it was also utilized to make a sports ball for a game called football, which is comparable to modern-day basketball.
• Rubber is utilized as an adhesive and a protective layer for a variety of surfaces in its latex state.
• Rubber gloves are a well-known rubber product since they are frequently used to keep our hands safe and clean.
• Rubber is used to make soundproofing materials and a variety of children’s rubber toys.

FAQs on Rubber

Question 1: What is Rubber?

Answer:

Rubber is a natural polymer that can stretch and shrink. It’s an elastomer that, after being deformed, may revert to its previous shape. Rubber is made by the polymerisation of Isoprene (2 methyl-1,3-butadiene. 

Question 2: What is the vulcanization of the rubber?

Answer:

Vulcanization is a process of hardening rubbers. The term “Vulcanization” originally comes solely from the reaction of natural rubber with sulfur, which is the most common practice. It has also grown to include the hardening of other (synthetic) rubbers via various means. For example Silicone Rubber and chloroprene rubber (neoprene), etc.

Question 3: Dicarboxylic acids react with diols to form which type of copolymer?

Answer:

Dicarboxylic acids react with diols to form the alternating type of co-polymer type of copolymer. Polyesters obtained by them are glyptal, daozon, etc. 

Question 4: What are Rubber products?

Answer:

Commonly used rubber products are mattresses, shoe soles, hot water bottles, balloons, rubber boots, etc.

Question 5: What is the difference between natural and synthetic rubber?

Answer:

Natural rubber is defined as the type of rubber that are produced naturally from the rubber plant Hevea brasiliensis. However, the Synthetic rubber is defined as the type of rubber which is artificially produced from a variety of polymers which provides the rubber its properties.

Question 6: Why are rubbers called elastomers?

Answer:

An elastomer is a type of polymer that exhibits elasticity. Natural rubber is an elastomer manufactured from latex, the milky sap of the rubber tree. Petroleum is used to make synthetic elastomers. Rubber is frequently referred to as elastomers because of this feature.

Question 7: What is Neoprene?

Answer:

Neoprene, also known as polychloroprene, is a homopolymer formed by the polymerization of chloroprene by free radicals. It is used to create conveyor belts, hoses, and gaskets, among other things, and has a high oil resistance.

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15 Dec, 2022

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Humans have been using rubber to create products for hundreds of years. The earliest evidence of rubber use comes from the Olmec culture of Mesoamerica, who used natural rubber materials to create balls for ball games. Today, rubber is an incredibly common and versatile material that is used in the creation of thousands of products, ranging from cookware to rubber gloves to tires and more. While most rubber products today are made from synthetic rubber, natural rubber was considered the superior option for a significant time. 

In this two part series, we’ll be taking a look at how both natural and synthetic rubber are created and how they’re used. Read on for our discussion on the creation of natural rubber.

Uses Prior to World War II

Prior to World War II, significant uses of natural rubber included door and window profiles, hoses, belts, gaskets, matting, flooring, and automotive dampeners. The use of rubber in car tires consumed a significant amount of rubber, as did gloves and toy balloons. Rubber was used as an adhesive in many manufacturing industries and products, the two most significant of which were the paper and the carpet industries. Rubber was also commonly used to make rubber bands and pencil erasers.

The production of synthetic rubber greatly expanded during World War II, which we will discuss in the second part of this series. 

Where does natural rubber come from?

Natural rubber is made by extracting latex – the liquid sap – from certain types of trees and other plants. While most latex is sourced from the Hevea brasiliensis tree, aka the rubber tree, over 2,500 varieties of trees and plants (including dandelions) produce the right kind of sap.

Latex is harvested through a process called tapping. It is done by making a cut in the bark of a tree and collecting the runny sap that comes out in cups. In order to prevent the sap from solidifying, ammonia is added. Acid is then added to the mix to extract the rubber, in a process called coagulation.

This mixture is then passed through rollers to remove excess water. Once rolling is complete, the layers of rubber are hung over racks in smokehouses or left out to air dry. Several days later, they will be ready for processing.

Processing natural rubber

Even natural rubber needs to undergo a series of processes in order to turn it into a usable product.

Firstly, chemicals are added to the rubber to make it stable. These chemicals may vary depending on the intended use of the rubber. Without this process, the rubber would become brittle in cold or sticky in high heat. A carbon black filler is often added to the rubber mix at this stage to improve its strength and durability. The rubber is mixed, cooled, and shaped.

Vulcanization

In order to make rubber strong and durable, it goes through a heat-treatment phase known as vulcanization. Essentially, the rubber is cooked to create extra bonds or cross-links between the molecules of the rubber so they don’t easily fall apart. After vulcanization, the rubber is harder and more durable. The process of vulcanization was an accidental discovery of engineer Charles Goodyear in 1839. Having accidentally dropped a piece of sulfur-coated rubber onto a hot stove, causing it to char and metamorphose into a leather-like substance, the American inventor uncovered the secret to stabilizing the latex of the rubber tree.

Limitations

Natural rubber was considered superior to synthetic rubber alternatives for a significant part of history. However, developments during World War II, which we will discuss in more detail in part two of this series, changed this. It’s important to note that while natural rubber has a great many applications, like tires, and dampening applications, it is no longer considered a good option for the sealing industry, especially when there is a chance of oil contact. Natural rubber will absorb oil until the rubber itself has disintegrated, meaning that it cannot be used to seal against oil. Another consideration is ozone, which causes natural rubber to break down over time. 
For more information about rubber, natural or synthetic, contact the engineers at Apple Rubber!

How is Natural Rubber Made?

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