Latex (Rubber) Products PDF

**Biol 1300 Unit 10** **LATEX (RUBBER) PRODUCTS** Plant latex is a stable emulsion of polyterpenes (like polyisoprene) in water, with minor components such as proteins, alkaloids, resins, and gums. Polyterpenes are composed of carbon atoms attached to hydrogen atoms, and they feature both single a...

**Biol 1300 Unit 10** **LATEX (RUBBER) PRODUCTS** Plant latex is a stable emulsion of polyterpenes (like polyisoprene) in water, with minor components such as proteins, alkaloids, resins, and gums. Polyterpenes are composed of carbon atoms attached to hydrogen atoms, and they feature both single and double bonds. These compounds are polymers made up of repeating isoprene units, which are hydrocarbons with the formula C₅H₈. It is produced by specialized cells called lactifers, these may occur in the inner bark, taproot or leaves, depending on the species. Latex serves to protect plants from injury (e.g. inner tree bark latex seals wounds) and deter herbivores, pests, and pathogens (latex is bitter and may not be attractive). While many plants produce latex, only a few do so in economically significant quantities. The most important latex-producing plant is the Para rubber tree, whose latex is used to make tires and various commercial and household products. **PARA or COMMON RUBBER (Hevea brasilensis)** The Para rubber tree, native to the Amazon rain forests of South America, is frequently attacked by a fungal leaf blight (Microcyclus) in its native region. As a result, most natural rubber is now produced in plantations in Southeast Asia and Africa, where the disease is absent. The tree produces significant amounts of latex from lactifer vessels in the inner bark in response to wounding, arranged in right-handed spirals around the trunk. This latex is a milky colloidal suspension of hydrocarbon isoprene polymers with some natural impurities. Raw or "crude" rubber is an elastomer (a polymer with elastic properties) with thermoplastic properties, meaning it melts when heated and becomes brittle when cooled. Therefore, it is cured (thermoset) through vulcanization, which stabilizes rubber against temperature changes by cross-linking isoprene polymers with disulfide bonds (sulfide), making the rubber harder, more durable, elastic, and less thermoplastic. Vulcanization involves heating rubber with sulfur, peroxide, and bisphenol, and adding carbon black (amorphous carbon) to increase strength and durability. The sulfur stabilizes carbon and hydrogen. Cured natural rubber has unique physical and chemical properties, storing strain energy both electrostatically (like a spring) and thermally (causing it to cool as it contracts). In practical terms, this means that rubber can absorb and release energy efficiently, making it useful for applications like tires, elastic bands, and various other products where flexibility and resilience are important. Synthetic rubber, made through the polymerization of petroleum monomers (single or multiple), is often used as a substitute but is generally inferior and non-renewable compared to natural rubber. Approximately 40% (8.5-9 million tons) of the 21 million tons of rubber produced annually is naturally sourced from rubber trees. Most global production comes from plantations in Indonesia, Malaysia, and Thailand, with smaller contributions from India, Liberia, and Nigeria. Most natural rubber is used to manufacture various rubber goods like hoses, belts, matting, flooring, boots, and vehicle tires. In modern radial tires, the sidewalls are made of natural rubber for higher hysteresis, meaning better shock absorption while the treads are made from synthetic rubber for increased durability. Indigenous Mesoamericans used crude rubber latex to make balls for games, which astonished early European colonists, thinking they were possessed by evil spirits. The Mayans created rubber shoes by dipping their feet in liquid latex and then hardening it, and they also developed methods to enhance rubber's durability (e.g., adding morning glory sap). Indigenous peoples in Brazil's rainforests made water-resistant cloth and clothing with rubber coatings. Despite crude rubber's tendency to decompose and become foul-smelling, melt in heat, and become brittle in cold, it was exported to Europe in large quantities during the 1700s and 1800s. Rubber barons in Manaus, Brazil, profited greatly, while indigenous \"rubber tappers\" received little financial benefit. These tappers collected raw latex from wild trees and turned it on a stick over a fire, using smoke and ash as coagulants (thickeners), to form large balls weighing up to 100 kg each. These rubber balls were then floated down the Amazon River to Manaus, where they were shipped to Europe. Para rubber was used in the construction of the Amazonas Opera House in Manaus, Brazil. During the rubber boom from 1879 to 1912, Manaus became a wealthy and refined city, and the Amazonas Opera House was built as a symbol of its prosperity. The cobblestones at the entrance and porte-cochère were covered in a thick layer of rubber to muffle the horses\' steps, ensuring that guests arriving after performances had begun would not cause any disturbance. In 1823, Charles Macintosh patented a method for waterproofing cloth using a naphtha solvent of raw rubber between two layers of cloth. Although popular, this material was problematic as it became sticky in hot weather, brittle in cold, and tended to rot. Rubber's significance increased dramatically after American Charles Goodyear discovered vulcanization in 1839. Thomas Hancock, an Englishman, patented the vulcanization process in 1843, with Goodyear obtaining his patent a year later. Hancock acknowledged seeing vulcanized rubber from a sample sent by Goodyear but claimed to have independently invented the process. Until the 1870s, natural rubber was supplied from the Amazonian rainforest. In 1876, Henry Wickham smuggled 70,000 rubber tree seeds from Manaus to break the Brazilian rubber monopoly. These seeds were germinated at Kew Gardens, resulting in about 2,000 healthy seedlings sent to Sri Lanka and 22 to Singapore. The Singapore trees were propagated and distributed to British Malay (now Malaysia) and Dutch Java (now Indonesia) in 1883. By the late 1800s, large rubber plantations were established in Southeast Asia. In the early 1900s, King Leopold II of Belgium employed forced labour of native Africans to wild-harvest rubber from the Lagos rubber tree (Funtumia elastica) and other species. In 1911 almost one-third of the global supply of rubber was obtained by wild harvesting in Belgian Congo, but blatant over-exploitation (\"slaughter-tapping\") had depleted the supply by 1913. The labor conditions were inhumane with many deaths. In the early 1920s, Henry Ford bought large areas of land in Amazonian Brazil to create "Fordlandia," a huge rubber plantation with an American-style workers' community. He planned to establish an American monopoly with the goal to break the British and Dutch rubber monopolies. However, the project failed due to fungal disease, incompetence, lack of government cooperation, and Ford's unusual rules, such as banning alcohol and requiring workers to adopt American housing, culture, and food rather than accepting their culture. The demand for rubber surged with the invention of the pneumatic (air-filled) tire, which absorbs shocks more effectively than solid or foam-filled tires. Robert William Thompson patented pneumatic tires in 1846, but John Boyd Dunlop's 1888 patent marked the first practical application. Akron, Ohio, became the global hub for rubber tire manufacturing, with companies like B.F. Goodrich, Goodyear Tire, and Firestone dominating the market for bias-ply tires from the 1900s to the 1960s. However, these companies were slow to adopt new technologies, and by the late 1960s, safer and more reliable radial tires, developed by France's Michelin in 1946, were being produced in Europe. As a result, Akron's significance in tire production declined in the early 1970s. Rubber is harvested by making a careful incision/wound in the bark of a young tree (at least 5 years), following a downward spiral to \"tap\" into the lactifer vessels without damaging the conductive tissues. A skillfully tapped tree can produce latex for about 25-30 years. The latex runs down the spiral and collects in a cup. The raw latex is then mixed with formic acid in flat pans to form a coagulant called rubber "crump." The wet rubber sheets are wrung out and shipped for further processing, including vulcanization. **GUAYULE** (Parthenium argentatum) Guayule (pronounced 'why-YOU-lee'), a member of the Sunflower (Asteraceae) Family, is a shrub native to the southwestern United States and northern Mexico. It is used to produce hypoallergenic latex, unlike Para rubber, which can cause severe allergic reactions due to trace proteins. Guayule latex is used in medical products, especially surgical gloves, and consumer goods for people allergic to Para rubber (estimated in the millions in North America alone). It is preferred over synthetic rubber because it is stretchier. Guayule was first utilized for natural latex in the 1920s after leaf blight decimated the Brazilian Para rubber industry and again during World War II when Japan cut off Malaysian rubber supplies. By the late 1940s, large-scale guayule plantations were established in the southwestern United States but were mostly abandoned once cheaper Para rubber supplies resumed. Recently, the guayule industry has expanded rapidly in the last 20 years to meet the growing demand for hypoallergenic latex. **GUTTA-PERCHA** (Palaquium gutta) Gutta-percha is a large tropical tree species native to Southeast Asia that produces a non-elastic latex with unique and useful properties: it is bio-inert (does not provoke a significant biological response when introduced into the body), highly resilient, hypoallergenic, and a good electrical insulator. Unlike unvulcanized Para rubber, gutta-percha does not become brittle when cooled. In the 1800s, it was used to insulate telegraph wires and early trans-Atlantic telegraph cables due to its resistance to marine organisms. Additionally, gutta-percha was molded into furniture, kitchenware, and other household products, used as the core of golf balls, and as a dental filling material. **CHICLE** (Manilkara zapota) Chicle, a tropical tree species from Central and South America, was chewed by Indigenous Americans (including Aztecs and Mayans) for oral hygiene and pleasure. In 1850, Mexican General Santa Anna introduced chicle latex to American Thomas Adams, who initially tried to use it as a rubber substitute. When that failed, Adams marketed it as chewing gum or masticant in 1870 as used by Indigenous Americans. By the late 1800s, flavored chewing gums became popular in North America. Chicle latex, known for its sweet, subtle flavor, was the main ingredient in commercial chewing gums until the 1960s. Today, most chewing gums are butadiene-based synthetic rubbers with various additives (vinyl resins, waxes, and rosins). **BALATA** (Manilkara bidentata) Balata, a tropical tree native to northern South America, produces gutta-balata, a non-elastic latex like gutta-percha. This latex is used in the core of high-quality golf balls. Balata is also valued for its hard wood and is closely related to chicle (M. zapota) and gutta-percha (P. gutta). These species belong to the same family, Sapotaceae, and share similar characteristics, such as producing latex that can be used for various industrial purposes.