Vulcanization or vulcanisation refers to a specific curing process of rubber Natural rubber is an elastomer that was originally derived from a milky colloidal suspension, or latex, found in the sap of some plants. The purified form of natural rubber is the chemical polyisoprene which can also be produced synthetically. Natural rubber is used extensively in many applications and products as is synthetic rubber. The entropy involving high heat and the addition of sulfur Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant, multivalent non-metal. Sulfur in its native form is a yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals. It is an essential element for life and is found in two or other equivalent curatives. It is a chemical process In a "scientific" sense, a chemical process is a method or means of somehow changing one or more chemicals or chemical compounds. Such a chemical process can occur by itself or be caused by somebody. Such a chemical process commonly involves a chemical reaction of some sort. In an "engineering" sense, a chemical process is a in which polymer A polymer is a large molecule (macromolecule) composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties molecules are linked to other polymer molecules by atomic bridges composed of sulfur atoms or carbon to carbon bonds. The end result is that the springy rubber molecules become cross-linked Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of cross-links to promote a difference in the to a greater or lesser extent. This makes the bulk material harder, much more durable and also more resistant to chemical attack. It also makes the surface of the material smoother and prevents it from sticking to metal or plastic chemical catalysts Catalysis is the process in which the rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. The catalyst may participate in multiple chemical transformations. Catalysts.

This heavily cross-linked polymer has strong covalent bonds A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds. In short, attraction-to-repulsion stability that forms between atoms when they share electrons is known as covalent bonding, with strong forces between the chains, and is therefore an insoluble and infusible, thermosetting polymer Thermosetting plastics are polymer materials that irreversibly cure. The cure may be done through heat (generally above 200 degrees Celsius), through a chemical reaction (two-part epoxy, for example), or irradiation such as electron beam processing. The vulcanization process is a progressive reaction and is therefore allowed for a specified time.

The process is named after Vulcan In ancient Roman religion and Hellenic neopaganism, Vulcan is the god of beneficial and hindering fire, including the fire of volcanoes. He is also called Mulciber in Roman mythology and Sethlans in Etruscan mythology. He was worshipped at an annual festival on August 23 known as the Volcanalia, Roman god of fire Fire is the rapid oxidation of a combustible material releasing heat, light, and various reaction products such as carbon dioxide and water. If hot enough, the gases may become ionized to produce plasma. Depending on the substances alight, and any impurities outside, the color of the flame and the fire's intensity might vary. Fire in its most.

A vast array of products are made with vulcanized rubber including ice hockey pucks, tires, shoe soles, hoses and many more.

Hard vulcanized rubber is known as ebonite Ebonite is a very hard rubber first obtained by Charles Goodyear by vulcanizing rubber for prolonged periods. It is about 30% to 40% sulfur. Its name comes from its intended use as an artificial substitute for ebony wood. Ebonite is a brand name — it is also known as vulcanite or hard rubber or vulcanite and is used to make bowling balls and clarinet mouth pieces.

Reason for vulcanizing

Uncured natural rubber Natural rubber is an elastomer that was originally derived from a milky colloidal suspension, or latex, found in the sap of some plants. The purified form of natural rubber is the chemical polyisoprene which can also be produced synthetically. Natural rubber is used extensively in many applications and products as is synthetic rubber. The entropy is sticky, can easily deform when warm, and is brittle when cold. In this state it cannot be used to make articles with a good level of elasticity In physics, elasticity is the physical property of a material when it deforms under stress , but returns to its original shape when the stress is removed. The relative amount of deformation is called the strain. The reason for inelastic deformation of unvulcanized rubber can be found in its chemical nature: rubber is made of long polymer A polymer is a large molecule (macromolecule) composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties chains. These polymer chains can move independently relative to each other, which results in a change of shape. By the process of vulcanization, crosslinks are formed between the polymer chains so the chains can no longer move independently. As a result, when stress is applied the vulcanized rubber will deform, but upon release of the stress, the rubber article will go back to its original shape.

Description

Vulcanization is generally considered to be an irreversible process (see below Vulcanization or vulcanisation refers to a specific curing process of rubber involving high heat and the addition of sulfur or other equivalent curatives. It is a chemical process in which polymer molecules are linked to other polymer molecules by atomic bridges composed of sulfur atoms or carbon to carbon bonds. The end result is that the springy), similar to other thermosets and must be contrasted strongly with thermoplastic A thermoplastic is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. Most thermoplastics are high-molecular-weight polymers whose chains associate through weak Van der Waals forces ; stronger dipole-dipole interactions and hydrogen bonding (nylon); or even stacking of aromatic rings ( processes (the melt-freeze process) which characterize the behavior of most modern polymers A polymer is a large molecule (macromolecule) composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties. This irreversible cure reaction defines cured rubber compounds as thermoset Thermosetting plastics are polymer materials that irreversibly cure. The cure may be done through heat (generally above 200 degrees Celsius), through a chemical reaction (two-part epoxy, for example), or irradiation such as electron beam processing materials, which do not melt on heating, and places them outside the class of thermoplastic A thermoplastic is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently. Most thermoplastics are high-molecular-weight polymers whose chains associate through weak Van der Waals forces ; stronger dipole-dipole interactions and hydrogen bonding (nylon); or even stacking of aromatic rings ( materials (like polyethylene Polyethylene or polythene (IUPAC name polyethene or poly) is a thermoplastic commodity heavily used in consumer products (notably the plastic shopping bag). Over 60 million tons of the material are produced worldwide every year and polypropylene Polypropylene or polypropene is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including packaging, textiles (e.g. ropes, thermal underwear and carpets), stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer). This is a fundamental difference between rubbers and thermoplastics, and sets the conditions for their applications in the real world, their costs, and the economics of their supply and demand Supply and demand is an economic model based on price, utility and quantity in a market. It concludes that in a competitive market, price will function to equalize the quantity demanded by consumers, and the quantity supplied by producers, resulting in an economic equilibrium of price and quantity. An increase in the quantity produced or supplied.

Usually, the actual chemical cross-linking Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of cross-links to promote a difference in the is done with sulfur Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant, multivalent non-metal. Sulfur in its native form is a yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals. It is an essential element for life and is found in two, but there are other technologies, including peroxide Organic peroxides are organic compounds containing the peroxide functional group . If the R' is hydrogen, the compound is called an organic hydroperoxide. Peresters have general structure RC(O)OOR-based systems. The combined cure package in a typical rubber Natural rubber is an elastomer that was originally derived from a milky colloidal suspension, or latex, found in the sap of some plants. The purified form of natural rubber is the chemical polyisoprene which can also be produced synthetically. Natural rubber is used extensively in many applications and products as is synthetic rubber. The entropy compound comprises the cure agent itself, (sulfur or peroxide), together with accelerators, activators like zinc oxide and stearic acid and antidegradants. Prevention of vulcanization starting too early is done by addition of retarding agents. Antidegradants are used to prevent degradation by heat, oxygen and ozone.

Along the rubber molecule In chemistry, a molecule is defined as a sufficiently stable, electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense. In organic chemistry and biochemistry, the term molecule is used less strictly and also is, there are a number of sites which are attractive to sulfur atoms. These are called cure sites, and are generally sites with an unsaturated carbon-carbon bond, like in polyisoprene, the basic material of natural rubber,and in styrene-butadiene Styrene-Butadiene or Styrene-Butadiene-Rubber is a synthetic rubber copolymer consisting of styrene and butadiene. It has good abrasion resistance and good aging stability when protected by additives, and is widely used in car tires, where it is blended with natural rubber. It was originally developed prior to World War II in Germany, but during rubber Natural rubber is an elastomer that was originally derived from a milky colloidal suspension, or latex, found in the sap of some plants. The purified form of natural rubber is the chemical polyisoprene which can also be produced synthetically. Natural rubber is used extensively in many applications and products as is synthetic rubber. The entropy (SBR), the basic material for passenger tires. The active sites are allylic hydrogen atoms; that means they are hydrogen atoms connected to the first saturated carbon atom connected to the carbon-carbon double bond. During vulcanization the eight-membered ring of sulfur breaks down in smaller parts with one to eight sulfur atoms. These small sulfur chains are quite reactive. At each cure site on the rubber molecule, such short sulfur chain can attach itself, and eventually reacts with a cure site of another rubber molecule, and so forming a bond between two chains. This is named a cross-link. These sulfur bridges are typically between two and eight atoms long. The number of sulfur atoms in a sulfur crosslink has a strong influence on the physical properties of the final rubber article. Short sulfur crosslinks, with just one or two sulfur atoms in the crosslink, give the rubber better heat resistance. Crosslinks with higher number of sulfur atoms, up to six or seven, give the rubber good dynamic properties but with lesser heat resistance. Dynamic properties are important for flexing movements of the rubber article, e.g., the movement of a side-wall of a running tire. Without good flexing properties these movements will rapidly lead to formation of cracks and, ultimately, to failure of the rubber article.

Vulcanization methods

There are various vulcanization methods. The economically most important method (the vulcanization of tires) uses increased pressure and temperature. A typical vulcanization temperature for a passenger tire is 10 minutes at 170 °C. This type of vulcanization is an example of the general vulcanization method named compression molding. The rubber article is intended to adopt the shape of the mold. Other methods for instance those used to make door profiles for cars use hot air vulcanization or microwave heated vulcanization (both continuous processes).

Four types of curing systems are in common use. They are:

1. Sulfur systems
2. Peroxides
3. Urethane crosslinkers
4. Metallic oxides

By far the most common vulcanizing methods are those dependent on sulfur.

Sulfur, by itself, is a slow vulcanizing agent. Large amounts of sulfur, as well as high temperatures and long heating periods are necessary and one obtains an unsatisfactory crosslinking efficiency with unsatisfactory strength and aging properties. Only with vulcanization accelerators can the quality corresponding to today's level of technology be achieved. The multiplicity of vulcanization effects demanded cannot be achieved with one universal substance, a large number of diverse materials is necessary.

Overview and history

Although vulcanization is a 19th century invention, the history of rubber cured by other means goes back to prehistoric Prehistory is a term used to describe the period before written history. Paul Tournal originally coined the term Pré-historique in describing the finds he had made in the caves of southern France.[citation needed] It came into use in French in the 1830s to describe the time before writing, and the word "prehistoric" was introduced into times. The name "Olmec The Olmec were an ancient Pre-Columbian people living in the tropical lowlands of south-central Mexico, in what are roughly the modern-day states of Veracruz and Tabasco" means "rubber people" in the Aztec Aztec is a term used to refer to certain ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl language and who achieved political and military dominance over large parts of Mesoamerica in the 14th, 15th and 16th centuries, a period referred to as the Late post-Classic period in Mesoamerican chronology language. Ancient Mesoamericans The term Mesoamerica—literally, "middle America" in Greek—was first used by the German ethnologist Paul Kirchhoff, who noted that similarities existed among the various pre-Columbian cultures within the region that included southern Mexico, Guatemala, Belize, El Salvador, western Honduras, and the Pacific lowlands of Nicaragua and, spanning from ancient Olmecs The Olmec were an ancient Pre-Columbian people living in the tropical lowlands of south-central Mexico, in what are roughly the modern-day states of Veracruz and Tabasco to Aztecs Aztec is a term used to refer to certain ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl language and who achieved political and military dominance over large parts of Mesoamerica in the 14th, 15th and 16th centuries, a period referred to as the Late post-Classic period in Mesoamerican chronology, extracted latex Latex refers generically to a stable dispersion of polymer microparticles in an aqueous medium. Latexes may be natural or synthetic. Latex as found in nature is the milky sap of many plants that coagulates on exposure to air. It is a complex emulsion in which proteins, alkaloids, starches, sugars, oils, tannins, resins and gums are found. In most from Castilla elastica Castilla elastica, the Panama rubber tree, is a tree native to the tropical areas of Mexico and Central America which was, in pre-Columbian times, the principal source of latex among the Mesoamerican peoples. The latex gathered from Castilla elastica was converted into usable rubber by mixing the latex sap with the juice of the morning glory, a type of rubber tree The Pará rubber tree , often simply called rubber tree, is a tree belonging to the family Euphorbiaceae and the most economically important member of the genus Hevea. It is of major economic importance because its sap-like extract (known as latex) can be collected and is the primary source of natural rubber in the area. The juice of a local vine, Ipomoea alba, was then mixed with this latex to create an ancient processed rubber Natural rubber is an elastomer that was originally derived from a milky colloidal suspension, or latex, found in the sap of some plants. The purified form of natural rubber is the chemical polyisoprene which can also be produced synthetically. Natural rubber is used extensively in many applications and products as is synthetic rubber. The entropy as early as 1600 BC ^[1] .

The first reference to rubber in Europe Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally divided from Asia to its east by the water divide of the Ural Mountains, the Ural River, the Caspian Sea, and by the Caucasus Mountains to the southeast. Europe is washed upon to the north by the Arctic Ocean and appears to be in 1770, when Edward Nairne was selling cubes of natural rubber from his shop at 20 Cornhill, London. The cubes, meant to be erasers An eraser or rubber is an article of stationery that is used for removing pencil and sometimes pen writings. Erasers have a rubbery consistency and are often white or pink, although modern materials allow them to be made in any color. Many pencils are equipped with an eraser on one end. Typical erasers are made from synthetic rubber, but more, sold for the astonishingly high price of 3 shillings The shilling is a unit of currency used in current and former Commonwealth countries, and continued to be used in countries that left the commonwealth, such as Ireland and Tanzania. The word shilling comes from schilling, an accounting term that dates back to Anglo-Saxon times where it was deemed to be the value of a cow in Kent or a sheep per half-inch cube.^{[citation needed]}

In the early 19th century rubber was a novelty material, but it did not find much application in the industrial world. It was used first as erasers, and then as medical devices for connecting tubes and for inhaling medicinal Medicine is the art and science of healing. It encompasses a range of health care practices evolved to maintain and restore health by the prevention and treatment of illness gases In physics, a gas is a state of matter, consisting of a collection of particles without a definite shape or volume that are in more or less random motion. With the discovery that rubber was soluble in ether Diethyl ether, also known as ether and ethoxyethane, is a clear, colorless, and highly flammable liquid with a low boiling point and a characteristic odor. It is the most common member of a class of chemical compounds known generically as ethers. It is an isomer of butanol. Diethyl ether has the formula CH3-CH2-O-CH2-CH3. It is used as a common, it found applications in waterproof coatings Waterproof or water-resistant describes objects unaffected by water or resisting water passage, or which are covered with a material that resists or does not allow water passage. Such items may be used in wet environments or under water. Waterproofing describes making an object waterproof or water-resistant, notably for shoes and soon after this, the rubberized Mackintosh coat became popular.

Nevertheless, most of these applications were in small volumes and the material did not last long. The reason for this lack of serious applications was the fact that the material was not durable, was sticky and often rotted and smelled bad because it remained in its uncured state.

Goodyear's contribution

Most textbooks point out that Charles Goodyear Charles Goodyear was the first American to vulcanize rubber, a process which he discovered in 1839 and patented on June 15, 1844. Although Goodyear is often credited with its invention, modern evidence has proven that the Mesoamericans used stabilized rubber for balls and other objects as early as 1600 BC (1800–1860) invented vulcanization of rubber Natural rubber is an elastomer that was originally derived from a milky colloidal suspension, or latex, found in the sap of some plants. The purified form of natural rubber is the chemical polyisoprene which can also be produced synthetically. Natural rubber is used extensively in many applications and products as is synthetic rubber. The entropy as used today by the addition of sulfur Sulfur or sulphur is the chemical element that has the atomic number 16. It is denoted with the symbol S. It is an abundant, multivalent non-metal. Sulfur in its native form is a yellow crystalline solid. In nature, it can be found as the pure element and as sulfide and sulfate minerals. It is an essential element for life and is found in two in high heat. Depending on what you read, the Goodyear story is one of either pure luck or careful research. Goodyear insisted that it was the latter, though many contemporaneous accounts indicate the former.

Goodyear claimed that he discovered vulcanization in 1839, but did not patent the invention until June 15, 1844, and did not write the story of the discovery until 1853 in his autobiographical book Gum-Elastica. Meanwhile, Thomas Hancock (1786-1865), a scientist A scientist, in the broadest sense, refers to any person that engages in a systematic activity to acquire knowledge or an individual that engages in such practices and traditions that are linked to schools of thought or philosophy. In a more restricted sense, scientist refers to individuals who use the scientific method. The person may be an and engineer, patented the process in the UK on November 21, 1843, eight weeks before Goodyear applied for his own UK patent.

Here is Goodyear's account of the invention, taken from Gum-Elastica. Although the book is an autobiography, Goodyear chose to write it in the third person, so that 'the inventor' and 'he' referred to in the text are in fact the author. He describes the scene in a rubber factory where his brother worked:

... The inventor made some experiments to ascertain the effect of heat on the same compound that had decomposed in the mail-bags and other articles. He was surprised to find that the specimen, being carelessly brought into contact with a hot stove, charred like leather.

Goodyear goes on to describe how he attempted to call the attention of his brother and other workers in the plant who were familiar with the behavior of dissolved rubber, but they dismissed his appeal as unworthy of their attention, believing it to be one of the many appeals he made to them on account of some strange experiment. Goodyear claims he tried to tell them that dissolved rubber usually melted when heated excessively, but they still ignored him.

He directly inferred that if the process of charring could be stopped at the right point, it might divest the gum of its native adhesiveness throughout, which would make it better than the native gum. Upon further trial with heat, he was further convinced of the correctness of this inference, by finding that the India rubber could not be melted in boiling sulfur at any heat ever so great, but always charred. He made another trial of heating a similar fabric before an open fire. The same effect, that of charring the gum, followed; but there were further indications of success in producing the desired result, as upon the edge of the charred portion appeared a line or border, that was not charred, but perfectly cured.

Goodyear then goes on to describe how he moved to Woburn, Massachusetts and carried out a series of systematic experiments to discover the right conditions for curing rubber.

... On ascertaining to a certainty that he had found the object of his search and much more, and that the new substance was proof against cold and the solvent of the native gum, he felt himself amply repaid for the past, and quite indifferent to the trials of the future.

Goodyear never made any money out of his invention. He pawned all his family's possessions in an effort to raise money, but on July 1, 1860, he died with debts of over $200,000.

Later developments

Whatever the true history, the discovery of the rubber-sulfur reaction revolutionized the use and applications of rubber, and changed the face of the industrial world.

Up to that time, the only way to seal a small gap between moving machine parts, such as between a piston and its cylinder in a steam engine, was to use leather soaked in oil. This was acceptable up to moderate pressures, but above a certain point, machine designers had to compromise between the extra friction generated by packing the leather more tightly and greater leakage of precious steam.

Vulcanized rubber offered the ideal solution. With vulcanized rubber, engineers had a material which could be shaped and formed to precise shapes and dimensions, and which would accept moderate to large deformations under load and recover quickly to its original dimensions once the load was removed. These, combined with good durability and lack of stickiness, are the critical requirements for an effective sealing material.

Further experiments in the processing and compounding of rubber were carried out, mostly in the UK by Hancock and his colleagues. These led to a more repeatable and stable process.

In 1905, however, George Oenslager discovered that a derivative of aniline called thiocarbanilide was able to accelerate the action of sulfur on the rubber, leading to much shorter cure times and reduced energy consumption. This work, though much less well-known, is almost as fundamental to the development of the rubber industry as that of Goodyear in discovering the sulfur cure. Accelerators made the cure process much more reliable and more repeatable. One year after his discovery, Oenslager had found hundreds of potential applications for his additive.

Thus, the science of accelerators and retarders was born. An accelerator speeds up the cure reaction, while a retarder delays it. In the subsequent century, various chemists have developed other accelerators, and so-called ultra-accelerators, that make the reaction extremely fast, and are used to make most modern rubber goods.

Devulcanization

The rubber industry has been researching the devulcanization of rubber for many years. The main difficulty in recycling rubber has been devulcanizing the rubber without compromising its desirable properties. The process of devulcanization involves treating rubber in granular form with heat and/or softening agents in order to restore its elastic qualities, in order to enable the rubber to be reused. Several experimental processes have achieved varying degrees of success in the laboratory, but have been less successful when scaled up to commercial production levels. Also, different processes result in different levels of devulcanization: for example, the use of a very fine granulate and a process that produces surface devulcanization will yield a product with some of the desired qualities of unrecycled rubber.

The rubber recycling process begins with the collection and shredding of discarded tires. This reduces the rubber to a granular material, and all the steel and reinforcing fibers are removed. After a secondary grinding, the resulting rubber powder is ready for product remanufacture. However, the manufacturing applications that can utilize this inert material are restricted to those which do not require its vulcanization.

In the rubber recycling process, devulcanization begins with the delinking of the sulfur molecules from the rubber molecules, thereby facilitating the formation of new cross-linkages. Two main rubber recycling processes have been developed: the modified oil process and the water-oil process. With each of these processes, oil and a reclaiming agent are added to the reclaimed rubber powder, which is subjected to high temperature and pressure for a long period (5-12 hours) in special equipment and also requires extensive mechanical post-processing. The reclaimed rubber from these processes has altered properties and is unsuitable for use in many products, including tires. Typically, these various devulcanization processes have failed to result in significant devulcanization, have failed to achieve consistent quality, or have been prohibitively expensive.

In the mid-1990s, researchers at the Guangzhou Research Institute for the Utilization of Reusable Resources in China patented a method for the reclamation and devulcanizing of recycled rubber. Their technology, known as the AMR Process, is claimed to produce a new polymer with consistent properties that are close to those of natural and synthetic rubber, and at a significantly lower potential cost.

The AMR Process exploits the molecular characteristics of vulcanized rubber powder in conjunction with the use of an activator, a modifier and an accelerator reacting homogeneously with particles of rubber. The chemical reaction that occurs in the mixing process facilitates the delinking of the sulfur molecules, thereby enabling the characteristics of either natural or synthetic rubber to be recreated. A mixture of chemical additives is added to the recycled rubber powder in a mixer for approximately five minutes, after which the powder passes through a cooling process and is then ready for packaging. The proponents of the process also claim that the process releases no toxins, by-products or contaminants. The reactivated rubber may then be compounded and processed to meet specific requirements.

Currently, Landstar Rubber, which holds the North American license for the AMR Process, has built a rubber reprocessing plant and research/quality control lab in Columbus, Ohio. The plant performs production runs on a demonstration basis or at small commercial levels. The recycled rubber from the Ohio plant is currently being tested by an independent lab to establish its physical and chemical properties.

Whether or not the AMR Process succeeds, the market for new raw rubber or equivalent remains enormous, with North America alone using over 10 billion pounds (circa 4.5 million tons) every year. The auto industry consumes approximately 79% of new rubber and 57% of synthetic rubber. To date, recycled rubber has not been used as a replacement for new or synthetic rubber in significant quantities, largely because the desired properties have not been achieved. Used tires are the most visible of the waste products made from rubber; it is estimated that North America alone generates approximately 300 million waste tires annually, with over half being added to stockpiles that are already huge. It is estimated that less than 10% of waste rubber is reused in any kind of new product. Furthermore, the United States, the European Union, Eastern Europe, Latin America, Japan and the Middle East collectively produce about one billion tires annually, with estimated accumulations of three billion in Europe and six billion in North America.

One company that has had commercial success with its devulcanisation technology is Green Rubber, based out of Malaysia. The company, which owns a patented mechano-chemical devulcanisation process called DeLink, recently signed a deal with Timberland, the footwear giant, to supply devulcanised compound made from tire waste. Timberland's Fall 09 range will contain boots with soles made from 50% Green Rubber compound. The company has two plants in Malaysia and one about to become operational in the US.

Recently a new method of devulcanization was developed by Coral GROUP, in Dnepropetrovsk, Ukraine. This method of devulcanization, includes impregnation of rubber with special solvent with additives of catalysts and reagents. In this process rubber is restructured, sulfuric "bridges are torn up, sulfur chemically connects, and rubber becomes plastic, suitable for molding. All that remains is to add 2-4% of sulfur, and new rubber products can be made. The quality of the obtained rubber compound is not worse than obtained from the initial materials, i.e. it is completely possible to make new automobile tires or other rubber products from the devulcanized rubber.

Room-temperature vulcanization

Room-temperature vulcanizing (RTV) silicone is constructed of reactive oil base polymers combined with strengthening mineral fillers. There are two types of room-temperature vulcanizing silicone:

RTV-1 (One-component systems)

RTV-1 hardens directly under the action of atmospheric humidity. The curing process begins on the outer surface and progresses through to its core. The product is packed in airtight cartridges and is either in a fluid or paste form. RTV-1 silicone has good adhesion, elasticity and durability characteristics. The Shore A hardness can be varied between 18 and 60. Elongation at break can range from 150% up to 700%. They have excellent aging resistance due to superior resistance to UV radiation and weathering. Industrial RTV-1 products are referred to as CAFs.

RTV-2 (Two-component systems)

RTV-2 elastomer are two-component products that, when mixed, cure at room-temperature to a solid elastomer, a gel, or a flexible foam. RTV-2 remains flexible from -80 °C to +250 °C. Break down occurs at temperatures above 350 °C leaving an inert silica deposit that is non-flammable and non-combustible. They can be used for electrical insulation due to their dielectric properties. Mechanical properties are satisfactory. RTV-2 is used to make flexible moulds, as well as many technical parts for industry and paramedical applications.

References

1. ^ D Hosler, SL Burkett and MJ Tarkanian (1999). "Prehistoric Polymers: Rubber Processing in Ancient Mesoamerica". Science 284: 1988–1991. doi:10.1126/science.284.5422.1988. PMID 10373117.

Categories: Chemical processes | Rubber | 1837 introductions

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• Vulcanization

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