Importance of television in our life Essay

Natural condom, in any case called India inborn coat eraser or caoutchouc, as initially produced, consists of suitable polymers of the organic compound isoprene, with minor impurities of opposite organic compounds plus water. Forms of polyisoprene that argon use upful as natural no-goods argon classified aselastomers. Currently, rubber is harvested mainly in the form of the rubber-base paint from certain maneuvers.The latex paint paint is a sticky, milky colloid drawn off by making incisions into the bark and collecting the fluid in vessels in a mental process called tapping. The latex then is refined into rubber rig for commercial processing. Natural rubber is utilise extensively in many applications and products, either alone or in combination with other materials. In near of its useful forms, it has a large stretch ratio, high resilience, and is super waterproof.1VarietieseditThe major commercial source of natural rubber latex is the equating rubber tree ( rubber tree brasiliensis), a member of the spurge family, Euphorbiaceae. This species is widely utilize be beget it grows well infra cultivation and a properly managed tree responds to wounding by producing more latex for some(prenominal) years. Many other plants produce forms of latex rich in isoprene polymers, though not all produce usable forms of polymer as easily as the Par rubber tree does some of them require more elaborate processing to produce anything like usable rubber, and nigh atomic number 18 more difficult to tap. both(prenominal) produce other desirable materials, for example gutta-percha (Palaquium gutta)2 and chicle from Manilkara species.Others that have been commercially exploited, or at least have shown promise as sources of rubber, accommodate the rubber fig (Ficus elastica), Panama rubber tree (Castilla elastica), various spurges (Euphorbia spp.), lettuce (Lactuca species), the related Scorzonera tau-saghyz, various Taraxacum species, including common dandel ion (Taraxacum officinale) and Russian dandelion (Taraxacum kok-saghyz), and guayule (Parthenium argentatum). The term gum rubber is some time applied to the tree-obtained version of natural rubber in order to distinguish it from the celluloid version.1 Discovery of commercial potentialeditThe parity rubber tree is indigenous to South the States. Charles Marie de La Condamine is credited with introducing samples of rubber to the Acadmie Royale des Sciences of France in 1736.3 In 1751, he presented a paper by Franois Fresneau to the Acadmie (eventually make in 1755) which described many of the properties of rubber. This has been referred to as the runner scientific paper on rubber.3 In England, Joseph Priestley, in 1770, observed that a erect of the material was extremely good for rubbing off pencil marks on paper, hence the name rubber. Later, it s wiped out(p)ly made its way slightly England. South America remained the main source of the limited amounts of latex rubber used d uring much of the 19th century.In 1876, atomic number 1 Wickham gathered thousands of Para rubber tree seeds from Brazil, and these were germinated in Kew Gardens, England. The seedlings were then sent to India, Ceylon (Sri Lanka), Indonesia, Singapore, and British Malaya. Malaya (now Malaysia) was later to become the biggest producer of rubber. In the early 1900s, the Congo handsome State in Africa was also a crucial source of natural rubber latex, mostly gathered by force playd labor. Liberia and Nigeria also started production of rubber. In India, commercial cultivation of natural rubber was introduced by the British planters, although the experimental efforts to grow rubber on a commercial scale in India were initiated as early as 1873 at the Botanical Gardens, Calcutta. The first commercial Hevea plantations in India were established at Thattekadu in Kerala in 1902.In Singapore and Malaya, commercial production of rubber was heavily promoted by Sir Henry Nicholas Ridley, who served as the first Scientific Director of the Singapore Botanic Gardens from 1888 to 1911. He distributed rubber seeds to many planters and developed the first technique for tapping trees for latex without causing unsafe harm to the tree.4Because of his very fervent promotion of this crop, he is popularly remembered by the nickname Mad Ridley.5 PropertieseditRubber latex Rubber exhibits unique physical and chemic properties. Rubbers stress-strain behavior exhibits the Mullins effect and the Payne effect, and is often modeled as hyperelastic. Rubber strain crystallizes. Owing to the presence of a double bond in each repeat unit, natural rubber is susceptible to vulcanisation and sensitive to ozone cracking. The two main solvents for rubber are turpentine and naphtha (petroleum).The former has been in use since 1764 when Franois Fresnau made the discovery. Giovanni Fabbroni is credited with the discovery of naphtha as a rubber solvent in 1779. Because rubber does not dissolve easi ly, the material is finely divided by shredding prior to its immersion. An ammonia solution can be used to prevent the coagulation of raw latex piece of music it is being transported from its collection site. ElasticityeditIn most elastic materials, such as metals used in springs, the elastic behavior is caused by bond distortions. When force is applied, bond lengths deviate from the (minimum postal code) equilibrium and strain energy is stored electrostatically. Rubber is often assumed to behave in the same way, but this is a poor description. Rubber is a curious material because, unlike in metals, strain energy is stored thermally. In its relaxed state, rubber consists of long, coiled-up chains. When rubber is stretched, the chains are taut. Their kinetic energy is released as heat. The entropy and temperature increases during elongation but decreases during relaxation. This change in entropy is related to the changes in degrees of freedom.Relaxation of a stretched rubber bar is thus driven by a decrease in entropy and temperature, and the force experienced is a result of the cooling of the material being converted to potential energy. Rubber relaxation isendothermic, and for this reason the force exerted by a stretched piece of rubber increases with temperature. The material undergoes adiabatic cooling during contraction. This property of rubber can easily be verified by holding a stretched rubber band to ones lips and relaxing it. Stretching of a rubber band is in some ways opposite to compression(although both undergo higher levels of thermal energy of an ideal gas), and relaxation is opposed to gas expansion (Note rubber bands last longer in the cold).A compressed and heated gas also exhibits elastic properties, for instance inside an inflated car tire. The fact that stretching is equivalent to compression is counterintuitive, but it makes sense if rubber is viewed as a running(a) gas, plus it is attached to other molecules. Stretching and heat incr ease the space available to each section of chain, because the molecules are pulled apart.Vulcanization of rubber creates disulfide bonds between chains, so it limits the degrees of freedom. The result is that the chains tighten more quickly for a given strain, thereby increasing the elastic force constant and making rubber harder and little extensible. When cooled below the glass transition temperature, the quasifluid chain segments freeze into fixed geometries and the rubber abruptly loses its elastic properties, although the process is reversible. This property it shared by most elastomers. At very low temperatures, rubber is rather brittle. This critical temperature is the reason winter tires use a softer version of rubber than normal tires. The failing rubber o-ring seals that contributed to the cause of the Challenger disaster were thought to have cooled below their critical temperature the disaster happened on an unusually cold mean solar day.The gas molecules in the rubber were too determination to their bound solid molecules(a partial phase change that separated the rubber molecules may have occurred), allowing the rubber to take on a more solid shape(a partial phase change to a more liquid and molecularly separated form would not be good, either). Heated gas has a higher energy, and rubber must be kept at specific temperatures and probably should not be used on vehicles that undergo extreme temperature changes. chemical makeupeditLatex is the polymer cis-1,4-polyisoprene with a molecular weight of 100,000 to 1,000,000 dal heaps. Typically, a wasted percentage (up to 5% of ironical mass) of other materials, such as proteins, fatty acids, resins, and inorganic materials (salts) are found in natural rubber. Polyisoprene can also be created synthetically, producing what is sometimes referred to as synthetic natural rubber, but the synthetic and natural routes are completely different.1Chemical structure of cis-polyisoprene, the main constituent o f natural rubber Synthetic cis-polyisoprene and natural cis-polyisoprene are derived from different precursors. Some natural rubber sources, such as gutta-percha, are composed of trans-1,4-polyisoprene, a structural isomer that has similar, but not identical, properties. Natural rubber is an elastomer and a thermoplastic. Once the rubber is vulcanized, it lead turn into a thermoset. Most rubber in everyday use is vulcanized to a point where it shares properties of both i.e., if it is heated and cooled, it is degraded but not destroyed. The final properties of a rubber fact depend not just on the polymer, but also on modifiers and fillers, such as speed of light black, factice, whiting, and a host of others. BiosynthesiseditRubber particles are create in the cytoplasm of specialized latex-producing cells called laticifers within rubber plants.6 Rubber particles are surrounded by a single phospholipid membrane with hydrophobic tails pointed inward. The membrane allows biosyntheti c proteins to be sequestered at the surface of the growing rubber particle, which allows virgin monomeric units to be added from outside the biomembrane, but within the lacticifer. The rubber particle is an enzymatically spry entity that contains three layers of material, the rubber particle, a biomembrane, and free monomeric units. The biomembrane is held tightly to the rubber core due to the high negative charge along the double bonds of the rubber polymer backbone.7Free monomeric units and conjugated proteins make up the outer layer. The rubber precursor is isopentenyl pyrophosphate (an allylic compound), which elongates by Mg2+-dependent condensation by the action of rubber transferase. The monomer adds to the pyrophosphate end of the growing polymer.8 The process displaces the terminal high-energy pyrophosphate. The reaction produces a cis polymer. The initiation step is catalyzed by prenyltransferase, which converts three monomers of isopentenyl pyrophosphate into farnesyl p yrophosphate.9 The farnesyl pyrophosphate can bind to rubber transferase to elongate a new rubber polymer.The required isopentenyl pyrophosphate is obtained from the mevalonate pathway, which is derives from acetyl-CoA in the cytosol. In plants, isoprene pyrophosphate can also be obtained from 1-deox-D-xyulose-5-phosphate/2-C-methyl-D-erythritol-4-phosphate pathway within plasmids.10 The relative ratio of the farnesyl pyrophosphate initiator unit and isoprenyl pyrophosphate elongation monomer determines the rate of new particle synthesis versus elongation of existing particles. Though rubber is known to be produced by only one enzyme, extracts of latex have shown numerous small molecular weight proteins with unknown function. The proteins possibly serve as cofactors, as the synthetic rate decreases with complete removal.11 Current sourceseditClose to 21 million tons of rubber were produced in 2005, of which approximately 42% was natural. Since the bulk of the rubber produced is of t he synthetic variety, which is derived from petroleum, the price of natural rubber is determined, to a large extent, by the prevailing ball-shaped price of crude oil.1213 Today, Asia is the main source of natural rubber, accounting for about 94% of output in 2005. The three largest producing countries, Thailand, Indonesia (2.4m tons)14 and Malaysia, together account for around 72% of all natural rubber production. Natural rubber is not cultivated widely in its native continent of South America due to the conception of South American leaf blight, and other natural predators of the rubber tree. CultivationeditRubber is generally cultivated in large plantations. See the coconut shell used in collecting latex, in plantations in Kerala, India Rubber latex is extracted from rubber trees. The economic life period of rubber trees in plantations is around 32 years up to 7 years of immature phase and about 25 years of productive phase. The reproach requirement of the plant is generally we ll-drained, weathered soil consisting of laterite, lateritic types, sedimentary types, nonlateritic red, or alluvial soils. The climatic conditions for optimum growth of rubber trees are Rainfall of around 250 cm evenly distributed without any marked dry season and with at least 100 rainy days per year Temperature range of about 20 to 34C, with a monthly mean of 25 to 28C High atmospheric humidity of around 80%Bright sunshine amounting to about 2000 hours per year at the rate of six hours per day by means ofout the year Absence of strong winds Many high-yielding clones have been developed for commercial planting. These clones yield more than 2,000 kg of dry rubber per hectare per year, when grown under ideal conditions.Field coagulaeditMixed field coagulaSmallholders lump at a remilling factory There are four types of field coagula, cuplump, treelace, smallholders lump and solid ground scrap. Each has fundamentally different properties.15 Cuplump is the grumose material found in the collection cup when the tapper next visits the tree to tap it again. It arises from latex clinging to the walls of the cup after the latex was last poured into the bucket, and from late-dripping latex exuded before the latex-carrying vessels of the tree become blocked. It is of higher purity and of greater value than the other three types.Treelace is the clot strip that the tapper peels off the previous cut before making a new cut. It usually has higher copper and manganese contents than cuplump. both(prenominal) copper and manganese are pro-oxidants and can lower the physical properties of the dry rubber. Smallholders lump is produced by smallholders who collect rubber from trees a long way forward from the nearest factory. Many Indonesian smallholders, who grow paddy in remote areas, tap dispersed trees on their way to work in the paddy handle and collect the latex (or the coagulated latex) on their way home.As it is often impossible to preserve the latex sufficiently to g et it to a factory that processes latex in time for it to be used to make high quality products, and as the latex would anyway have coagulated by the time it reached the factory, the smallholder will coagulate it by any means available, in any container available. Some smallholders use small containers, buckets etc., but often the latex is coagulated in holes in the ground, which are usually (but not always) lined with plastic. Acidic materials and fermented fruit juices are used to coagulate the latex a form of assisted biological coagulation. small-minded care is taken to exclude twigs, leaves, and even bark from the lumps that are formed, which may also include treelace collected by the smallholder. Earth scrap is the material that gathers around the base of the tree.It arises from latex overflowing from the cut and running down the bark of the tree, from rain flooding a collection cup containing latex, and from spillage from tappers buckets during collection. It contains soil and other contaminants, and has variable rubber content depending on the amount of contaminants mixed with it. Earth scrap is collected by the field workers two or three times a year and may be cleaned in a scrap-washer to retrieve the rubber, or sold off to a contractor who will clean it and recover the rubber. It is of very low quality and under no circumstances should it be included in block rubber or brown crepe. ProcessingeditRemoving coagulum from coagulating troughsThe latex will coagulate in the cups if kept for long. The latex has to be collected before coagulation. The collected latex, field latex, is transferred into coagulation tanks for the preparation of dry rubber or transferred into air-tight containers with sieving for ammoniation. Ammoniation is necessary to preserve the latex in colloidal state for long. Latex is generally impact into either latex concentrate for make up of dipped goods or it can be coagulated under controlled, clean conditions using formic aci d.The coagulated latex can then be processed into the higher-grade, technically specified block rubbers such as SVR 3L or SVR CV or used to produce Ribbed Smoke Sheet grades. Naturally coagulated rubber (cup lump) is used in the manufacture of TSR10 and TSR20 grade rubbers. The processing of the rubber for these grades is a size reduction and cleaning process to remove contamination and wangle the material for the final stage of drying.16 The dried material is then baled and palletized for storage and shipment in various methods of transportation. TransportationeditNatural rubber latex is shipped from factories in southwestern Asia, South America, and North Africa to destinations around the world. As the cost of natural rubber has risen significantly, the shipping methods which offer the lowest cost per unit of weight are preferred. Depending on the destination, warehouse availability, and transportation conditions, some methods are more suitable to certain buyers than others. In international trade, latex rubber is mostly shipped in 20-foot marine containers. Inside the ocean container, various types of smaller containers are used by factories to store latex rubber.17 UseseditCompression molded (cured)rubber boots before the flashesare removed Contemporary manufacturingedit some 25 million tonnes of rubber is produced each year, of which 42 percent is natural rubber. The remainder is synthetic rubber derived from petrochemical sources. Around 70 percent of the worlds natural rubber is used in tires. The top end of latex production results in latex products such as surgeons gloves, condoms, balloons and other relatively high-value products.The mid-range which comes from the technically-specified natural rubber materials ends up largely in tires but also in conveyor belts, marine products and miscellaneous rubber goods. Natural rubber offers good elasticity, while synthetic materials tend to offer better resistance to environmental factors such as oils, temp erature, chemicals or ultraviolet light and suchlike. Cured rubber is rubber which has been compound and subjected to the vulcanisation process which creates cross-links within the rubber matrix. Prehistoric useseditThe first use of rubber was by the Olmecs, who centuries later passed on the knowledge of natural latex from the Hevea tree in 1600 BC to the ancient Mayans. They boiled the harvested latex to make a ball for a Mesoamerican ballgame.18 Pre-World War II manufacturingeditOther significant uses of rubber are door and window profiles, hoses, belts, gaskets, matting, flooring, and dampeners (antivibration mounts) for the automotive industry. Gloves (medical, household and industrial) and toy balloons are also large consumers of rubber, although the type of rubber used is concentrated latex. evidentiary tonnage of rubber is used as adhesives in many manufacturing industries and products, although the two most noticeable are thepaper and the carpet industries. Rubber is also commonly used to make rubber bands and pencil erasers. Pre-World War II textile applicationseditRubber produced as a fiber, sometimes called elastic, has significant value for use in the textile industry because of its excellent elongation and recovery properties. For these purposes, manufactured rubber fiber is made as either an extruded round fiber or orthogonal fibers that are cut into strips from extruded film. Because of its low dye acceptance, feel and appearance, the rubber fiber is either covered by yarn of another fiber or today woven with other yarns into the fabric. In the early 1900s, for example, rubber yarns were used in foundation garments.While rubber is still used in textile manufacturing, its low tenacity limits its use in lightweight garments because latex lacks resistance to oxidizing agents and is damaged by aging, sunlight, oil, and perspiration. Seeking a way to address these shortcomings, the textile industry has dark to neoprene (polymer of chloroprene), a type of synthetic rubber, as well as another more commonly used elastomer fiber, spandex (also known as elastane), because of their superiority to rubber in both strength and durability. VulcanizationeditMain article Vulcanization Natural rubber is often vulcanized, a process by which the rubber is heated and sulfur, peroxide or bisphenol are added to improve resistance and elasticity, and to prevent it from perishing. The development of vulcanization is most closely associated with Charles Goodyear in 1839.19 Before World War II era manufacturing, carbon black was often used as an additive to rubber to improve its strength, especially in vehicle tires. Today, all vehicle tires are made of synthetic rubbers. Allergic reactionseditMain article Latex allergy Some people have a serious latex allergy, and exposure to natural latex rubber products such as latex gloves can cause anaphylactic shock. The antigenic proteins found in Hevealatex may be deliberately reduced (though not elimina ted)20 through processing. Latex from non-Hevea sources, such as Guayule, can be used without allergic reaction by persons with an allergy to Hevea latex.21 Some allergic reactions are not to the latex itself, but from residues of chemicals used to accelerate the cross-linking process. Although this may be confused with an allergy to latex, it is distinct from it, typically taking the form of Type IV hypersensitivity in the presence of traces of specific processing chemicals.2022