Published on: Mar 3, 2016
Transcripts - Natural rubber-processing
1Natural RubberNatural rubber is obtained from the milky secretion (latex) of the tree Hevea brasiliensis.The only other plant under cultivation as a commercial rubber source is guayule(Parthenium argentatum), a shrub native to the arid regions of Mexico and the SWUnited States. To soften the rubber so that compounding ingredients can be added, thelong polymer chains must be partially broken by mastication, mechanical shearing forcesapplied by passing the rubber between rollers or rotating blades. Thus, for most purposes,the rubber is ground, dissolved in a suitable solvent, and compounded with otheringredients, e.g., fillers and pigments such as carbon black for strength and whiting forstiffening; antioxidants antioxidant, substance that prevents or slows the breakdown ofanother substance by oxygen. Synthetic and natural antioxidants are used to slow thedeterioration of gasoline and rubber, and such antioxidants as vitamin C (ascorbic acid),butylated hydroxytoluene (BHT), and butylated hydroxyanisole (BHA) are added tofoods (see food additives) to prevent them from becoming rancid or from discoloring;plasticizers, usually in the form of oils, waxes, or tars; accelerators; and vulcanizingagents. The compounded rubber is sheeted, extruded in special shapes, applied as coatingor molded, then vulcanized. Most Pará rubber is exported as crude rubber and preparedfor market by rolling slabs of latex coagulated with acid into thin sheets of crepe rubberor into heavier, firmly pressed sheets that are usually ribbed and smoked.An increasing quantity of latex, treated with alkali to prevent coagulation, is shippedfor processing in manufacturing centers. Much of it is used to make foam rubber bybeating air into it before pouring it into a vulcanizing mold. Other products are made bydipping a mold into latex (e.g., rubber gloves) or by casting latex. Sponge rubber isprepared by adding to ordinary rubber a powder that forms a gas during vulcanization.Most of the rubber imported into the United States is used in tires and tire products; otheritems that account for large quantities are belting, hose, tubing, insulators, valves,gaskets, and footwear. Uncoagulated latex, compounded with colloidal emulsions anddispersions, is extruded as thread, coated on other materials, or beaten to foam and usedas sponge rubber. Used and waste rubber may be reclaimed by grinding followed bydevulcanization with steam and chemicals, refining, and remanufacture.
2Story of Natural RubberNatural rubber is a solid product obtained through coagulating the latex produced bycertain plants, particularly the Brazilian rubber-tree (Hevea Brasiliensis). This rawmaterial is usually tapped from the rubber tree, which is native to Amazonia. Althoughthere a large number of species that exude secretions similar to latex when the bark is cut,only a few produce sufficient quantities of a quality adequate for exploitation oneconomic bases.The history of natural rubber in Brazil is a tale that is just as exciting as the Gold Rush inthe USA. For almost fifty years - during the second half of the XIX century through tothe second decade of the XX century - natural rubber underpinned one of the mostimportant development booms in Brazil. At that time, the Industrial Revolution wasexpanding rapidly as the world lived through a time of prosperity and discoveries thatwas reflected in all sectors. Automobiles, trams, telephones, electric light and otherinnovations changed the landscapes and customs of towns and cities. New marketsopened up. This was the Belle Époque period, whose splendor has been portrayed inliterature and film for subsequent generations.Thanks to its multiple applications, particularly in the expanding automobile industry,rubber produced from latex tapped from rubber-trees became a product in demandworldwide. And there was no lack of rubber-trees in the Brazilian Amazon. This broughta boom to Northern Brazil - which at that time was one of the poorest and least-inhabitedparts of the country. Eager to work the rubber-groves of Amazonia, leading foreign banksand companies set up shop in the towns of Belém and Manaus.The capital of Amazonas State become the economic heart of Brazil. It was equippedwith water and electricity supplies, in addition to telephones and large buildings such asthe Amazonas Theater, still today a symbol of the wealth brought in by Brazils rubberboom. Thousands of immigrants flowed in, mainly fleeing the drought that assailedNortheast Brazil during the 1870’s, invading the forest to tap the latex and turn it intorubber.The output of Amazonia reached 42,000 tons a year, with Brazil dominating the globalnatural rubber market. This euphoria lasted through to 1910, when the situation began to
3change: rubber exports began to appear on the market from British Colonies, and Brazilwas unable to withstand this fierce competition.In 1876, the British smuggled out rubber-tree seeds from Amazonia to the BotanicalGardens in London. Through grafting, they developed more resistant varieties that werelater sent to the Colonies in Asia where massive rubber plantations were established,particularly in Malaysia, Ceylon and Singapore.The difference between latex production techniques in Brazil and Asia was a significantfactor in the development of this business, due to these plantations. While the rubber treesof Asia were set only four meters apart, it was sometimes necessary to walk milesbetween one tree and the next in Amazonia, limiting the amount of latex collected andincreasing its price. Obviously, the well-organized plantations of the Far East resulted ina significant increase in productivity, making them more competitive.In Brazil, the Government was unwilling to change these methods. It believed thattapping these rubber trees would ensure the presence of Brazilians in the Amazon region,guaranteeing national sovereignty over this largely unpopulated area. It opted for geo-politics represented by human settlements instead of geo-economics that could haveproduced higher gains.This relative immobility cost Brazil dear; its exports shrank as they were unable towithstand the competition of Asian rubber, tapped at far lower prices. Consequently,production began to drop, bringing the decades of boom to an end for much of NorthernBrazil. The companies that had set up shop in Manaus and Belém left in search of othermore productive regions. The immigrants went home, and leading names in the world ofthe arts no longer performed at the Amazonas Theater. This golden age of opulenceslipped into history.In the late 1920s, Brazil was still attempting to catch up this lost ground with the help ofan unexpected partner: US industrialist Henry Ford, who had developed a new scheme -the production line - that was to change the face of industry for ever, and at that timeaccounted for 50% of the worlds vehicle output. In order to loosen the grip of the BritishColonies in Southeast Asia on the rubber market - the precious raw material for making
4tires - Ford planted no less than 70 million rubber tree seedlings in an area covering onemillion hectares in Para State.This ambitious project was soon christened Fordlândia by the local residents. It wasdesigned to produce 300,000 tons of natural rubber a year, accounting for one half ofglobal consumption. But the Ford Project succumbed to the hostile environment of theAmazon rainforest and was abandoned, posting huge losses.Within this context, Asia dominated global supplies of natural rubber with over 90% ofthe output. However, significant changes redistributed the production among the maincompetitors. Accounting for one-third of global output in 1985, Malaysia fell back due toalterations in its production profile, which began to stress non-agricultural investments.Its position as the worlds largest natural rubber producer went to Thailand. Based onadvantages in terms of available land and labor, Indonesia has maintained a significantshare in global output since the 1980s.Other countries have been successfully deploying their low-cost labor-forces and easily-available lands to expand in this sector, particularly India and China. By 2001, naturalrubber consumption accounted for some 40% of the total amount of rubber consumedworldwide.Synthetic RubberThe importance of the rubber industry ever since it first appeared and the decisive rolethat it has played in the development of modern civilization prompted much interest indiscovering its chemical composition in order to synthesize this product. Through theseresearch projects, the tire industry saw the possibility of breaking away from the grip ofthe worlds natural rubber plantations.The drop in natural rubber production in Brazil coincided with World War I (1914-1918),triggering the need for lower-cost products with steadier supplies in order to manufacturetires. The pressures imposed by the conquest of the plantations of Asia by the Japaneseprompted the development of a rubber that was able to meet the extraordinarily highdemands of the troops at that time, although its structure differed somewhat from itsnatural counterpart.
5This was how GR-S, Buna S, Hycar OS and SBR appeared, which are styrene andbutadiene copolymers. The launch-pad for the massive development of the syntheticrubber industry, this product could be vulcanized easily, and became the flagship of theworld rubber industry, although its properties did not correspond to all the qualities ofnatural rubber. But its costs and main characteristics made it into an unbeatablecompetitor. Although synthetic rubber had been known since 1875, its production hadbeen expensive and almost negligible.During World War II, a crucial historical episode altered the scenario for this market. OnDecember 7, 1941, the USA entered the War. Three months after the attack on PearlHarbor, the Japanese invaded Malaysia and the Dutch East Indies, desperate to take overnatural rubber production from the allies. This gave the Axis control over 95% of worldrubber supplies, plunging the USA into a crisis.Each Sherman tank contained twenty tons of steel and half a ton of rubber. Each warshipcontained 20,000 rubber parts. Rubber was used to coat every centimeter of wire used inevery factory, home, office and military facilities throughout the USA. There was nosynthetic alternative. Looking at all the possible sources, at normal consumption levels,the nation had stocks for around one year. And these reserves also had to supply thelargest and most critical industry in the history of the world during a time of rapidexpansion: the arms segment.The response of Washington was rapid and dramatic. Four days after Pearl Harbor, theuse of rubber in any product that was not essential to the war drive was banned. Thespeed limit on US highways fell to 35 miles an hour, in order to reduce wear and tear ontires countrywide. Rubber chips were sold a penny or more per pound weight at over400,000 depots all over the country. Even President Franklin Roosevelts pet dog Falasaw his rubber toys melted. This was the largest recycling campaign ever recorded inhistory, ensuring the success of the Allies through to 1942.Under these circumstances, an order was sent to all chemists and engineers to develop asynthetic rubber industry. In 1941, the total output of synthetic rubber barely topped8,000 tons, consisting largely of products not suitable for tires.
6The nations survival depended on its capacity to manufacture over 800,000 tons ofproducts that had barely begun to be developed. There were few detailed instructions onhow the factories should organize themselves to produce this vast amount. No facilitieshad been built, nor was there any way of producing enough raw materials to producerubber.The US industrial sector had never been called upon to shoulder such a massive task,achieving so much so quickly. The engineers were given just two years to reach thistarget. If the synthetic rubber program failed, the capacity of the USA to fight the warwould be blunted. This US drive was to help spread synthetic rubber throughout theworlds market, even in Brazil as it strove to consolidate its industrial park during thepost-War years.Although synthetic rubber may be obtained in many different ways, most of it isproduced through the system shown in the figure below:Main synthetic rubber production systemA wide variety of synthetic rubbers have been developed since this product was firstdiscovered. As massive investments were required to develop these different varieties,the production technology was heavily concentrated in long-established global
7enterprises such as DuPont, Bayer, Shell, Basf, Goodyear, Firestone, Michelin, EniChem,Dow, and Exxon.The use of rubber is widespread, as the characteristics and properties of these elastomersmake them useful in almost all economic sectors: automobiles, footwear, civilconstruction, plastics, hospital materials and others that are of crucial importance in thedaily life of society. As they are most widely used to produce tires, the SBR and BRvarieties are the most widely consumed type of synthetic rubber.*****
8Natural Rubber Research in India: Yesterday, Today and TomorrowDr. N.M. MathewResearch and development support is essential for the healthy growth of any industry.With the development of the rubber plantations in South East Asia, research on variousaspects of rubber cultivation started in most rubber producing countries, Malaysia andSri Lanka giving early leadership. Though rubber cultivation on a commercial scalestarted in India in 1902, R&D activities to support the growing plantation industry weremeager in the early phase of its growth. However, the institutional support provided bythe government through the establishment of the Rubber Board under the Rubber Act,1947 resulted in the spectacular growth of the industry during the second half of the lastcentury. There was phenomenal increase in the area under rubber as well as inproduction. More importantly productivity increased from a mere 300 kg/ha in the early1950s to 1576 kg/ha in 2000-01. The contribution of R&D and extension programmes ofthe Board to this remarkable progress needs no emphasis.1. HistoryEver since the beginning of commercial cultivation of natural rubber (NR) inIndia during the early 20th century, the planters in Travancore, Cochin and Malabarregions in Southern India had been experiencing the necessity for research on problemsof rubber planting and upkeep. Initially, the scientific department of the United PlantersAssociation of Southern India (UPASI) was largely responsible for the initiative inresearch on rubber. On their request, the Madras Government appointed a scientificofficer in 1909 to strengthen research activities on rubber. Subsequently, experimentstations were established in Mundakayam, Thenmalai and Moopley for addressingagronomic and mycological problems concerning rubber. Consequent to the rubberslump and falling revenue of rubber estates, Thenmalai and Moopley experimentstations were closed down in 1926 and the Mundakayam station in 1932. Since then, forover two decades, the Indian rubber plantation industry had been without any organisedresearch support.When the Indian Rubber Board was established on the 19th April 1947 to lookafter the rubber plantation industry in the country, its functions as defined under the
9Rubber Act, 1947 included the development of the NR industry by devising suitablepromotional measures, undertaking scientific, technological and economic research etc.Even after the establishment of the Rubber Board, there were only two scientific officersnamely, the Rubber Production Commissioner (RPC) and a Field Officer, and their workconfined mainly to advisory services and distribution of selected planting materials.The importance of research on rubber was recognized by the Rubber Board as early asin 1949, when the Board in its sixth meeting had resolved that it should establish its ownresearch stations at suitable places in the plantation districts of Travancore - Cochin.This meeting approved the appointment of Sri. K.N. Kaimal as the Rubber ProductionCommissioner. As per the request of the Rubber Board, the Indian Tariff Board whichwas entrusted by the Government of India in 1950 with the task of examining the cost ofproduction of raw rubber and determining the fair price of various grades, was asked toexamine the different aspects of protection necessary for the speedy development of theindustry. The Tariff Board in its report dated 28th March 1951 recommendedestablishment of an All India Rubber Research Institute on a scale comparable to theexisting research organizations in the main rubber producing countries. The schemeincluded the appointment of a Director, Rubber Production Commissioner, RubberChemist, Botanist, Pathologist, Soil Chemist and a few Assistant Chemists, AssistantPathologists etc.On the request of the Government of India, the Indian Council of AgriculturalResearch (ICAR) examined the recommendations of the Tariff Board and rejected thescheme as out of proportion with the requirements and suggested for a small laboratoryand essential staff (Pathologist, Junior chemist and Junior Botanist) to investigate localproblems. ICAR also recommended the establishment of a 100 acre experiment stationand also an isolated seed garden of 15 acres for the production of high yielding seeds.The Rubber Board also rejected the Tariff Boards proposals as unsuitable for therequirement and being beyond its resources. The Tariff Commission, in their reportdated 27th October 1952 recommended for the implementation of the revised scheme assuggested by the ICAR for the proposed research station.Meanwhile the Rubber Board on 27th March 1954 approved a research scheme
10prepared by the Rubber Production Commissioner for the establishment of a RubberResearch Institute with an Experiment Station, with a financial outlay of Rs.10 lakhs andthe Government approved the same in June 1954. According to the scheme, the newInstitute was to have four research divisions namely, Agronomy, Botany, Pathology andChemistry. Each Division was to have a research officer and a research assistant and asmall experiment station for field experiments. A beginning was made in 1955 byestablishing the Institute at the rented premises of Ancheril Buildings of the RubberBoard in Kottayam town with a temporary laboratory. The foundation stone of theRubber Research Institute of India (RRII) building was laid on 4th February 1956 in thesuburbs of Kottayam.During the early years, RRII had only three divisions namely, Agronomy, Botanyand Pathology. Agronomy and Botany divisions had senior officers only for shortperiods. Due to lack of enough laboratory space and supporting staff, the RubberResearch Scheme 1954 could not be implemented fully. The Agronomy and BotanyDivisions collected data pertaining to the response of clones to manuring and locationsrespectively. Subsequently the different Divisions were transferred to the RRI buildingin 1962, when its construction was completed. The Chemistry and Rubber Technology(C&RT) Division started functioning with the appointment of a Deputy Director on 1stJune 1963. Other senior officers of C&RT and Agronomy Divisions were also appointedduring June 1963.The Publicity Section of the Administration Department and the Extension Wing ofthe Development Department of the Rubber Board were put under the control of theDirector in 1964. The Library functioning under the Administration Department since itsbeginning was also transferred to the administrative control of the Director from 1st June1964.The Economic Research unit, which was functioning as part of the RRII since 1968 andlater as part of the Rubber Production (RP) and Rubber Processing Departments,became the Agricultural Economics Division of the RRII in September 1986. In 1976,the Biochemistry unit functioning under the C&RT Division was transferred to the PlantPhysiology unit of the Botany Division. The full-fledged Plant Physiology and
11Exploitation Division started functioning in 1978 and the Biotechnology Division inDecember 1985. The C&RT Division was renamed as Rubber Chemistry, Physics andTechnology (RCPT) Division in 1986. The Germplasm Division was established inFebruary 1989 and the posts created in the Botany Division during 1978 for germplasmwork were transferred to the new Division.When the research component of the World Bank Project was implemented in 1994,the organization set up of RRII has been changed with the creation of 28 new posts underthe scheme2. AchievementsProduction and productivity enhancement have been the major goals for researchactivities. This was achieved through improvements in planting material, estatemanagement practices, pest and disease control, crop harvesting and processing.Additional income generation from the rubber plantation also was given dueimportance. The major sources of additional income are intercrops, rubber wood,rubber honey and seeds.From the yield levels of 200-300 kg/ha of original Hevea during the early 20thcentury, systematic plant breeding efforts have raised this to the high levels of about 4000kg/ha. As a result of conventional breeding programmes with a judicial use of researchdata, RRII has been successful in evolving perhaps the highest yielding clone in theworld, namely RRII 105.The development of RRII 105 blending high yield potential with good tolerance toabnormal leaf fall disease has been instrumental in the significant leap that the countryhas made in production and productivity. This clone became so popular among rubbergrowers that it has covered more than 85 percent or the cultivated area in the traditionaltract. Rubber Research Institute of India (RRII) developed a few other clones, whichwere recommended for experimental planting. Though these clones did not perform wellin all the agroclimatic zones like RRII 105, some of these have performed extremely wellon certain areas. The potential and realized yield of a few of these clones are given inTable 1. Recently RRII has developed another set of eleven improved clones, which arein the final stages of experimentation. As some of these clones have significantly out
12yielded RRII 105 in experimental fields, limited quantities of bud wood of these clonesare being supplied to farmers for experimental planting and generation of more data priorto their release.Table 1. Performance of RRII clones (over 10 years)CloneYield (kg/ha)PotentialRealized (on-farm)RRII 5* 2797 1299RRII 105 3146 1710RRII 109 1699 1361RRII 116 2102 1490RRII 118* 2093 1246RRII 203 3272 1649RRII 208 3449 1743• For five years*****NATURAL RUBBER: TECHNICALNatural rubber is found in the latex of as many as 895 species of plants belonging to 311genera of 79 families. Among them, only a few species have proved to be fit forcommercial exploitation. Of these, Hevea brasilicnsis (Euphorbiaceac), the para-rubber-tree, is the most important commercial source of natural rubber. It is a native of Braziland was introduced into tropical Asia to 1876. The tree is now grown in the tropicalregions of Asia, Africa and America. It is a hardy, tall, quick-growing tree, reaching 18 to30 metres in height, with a straight trunk producing branches 3 to 5 m from above theground and forming a spreading or conical canopy. The other sources of natural rubberare Manihot glaziovii (Euphorbiaceae), Ficus clastica (Moraceae), Patheniumargentatum and Taraxacum kok-saghyz (Compositae). In addition, many other speciessuch as Euphoriba intisy (Euphoribaceae), Cryptostegia grandi-flora (Asclepiadaceae),
13and Landolphia sp. (apocynaceae) have been tried as possible minor sources of naturalrubber.India at present is the fourth largest producer of natural rubber in the world afterThailand, Malaysia and Indonesia. It is not however, a major player in the world naturalrubber market because it is also its major consumer with almost always, except in thevery recent years, production of rubber lagging behind its domestic demand by a smallmargin. The gap is being filled by import of small amount of natural rubber every year. Inthe past several years while the output of natural rubber in the country rose at an averagerate of about 7 per cent, its consumption went up by 8 per cent per annum. In the past twoyears. However, its production was above its consumption level. Worldwide, theautomobile industry is the single largest consumer of natural rubber in the form of autotyres and tubes and certain other parts and accessories.VarietiesNatural rubber is tapped from rubber trees in the form of a thick white viscous fluidcalled latex. The latex tends to oxidise and solidify, it cannot be stored for long in itsnatural state. It is either stabilized by mixing with liquid ammonia to produce latex, orcentrifuged to remove excess water and produce latex concentrate or converted intoribbed smoked sheets (RSS) or solid block rubber (Crumb rubber) or pale latex crepe.Approximately, 70-75 per cent of the natural rubber produced in India is converted intoRSS. There are 7 grades of RSS produced, called RSS1X, RSS1, RSS2, RSS3, RSS4,RSS5 and ungraded variety. The grades differ according to the content of some naturalimpurities or deficiencies, which are judged mostly by visual inspection. Out of theseRSS1X is the purest grade used in the manufacture medical rubber products. The RSS4 isthe most popular grade produced in largest quantity in India. it is used in the manufactureof automobile tyres. About 10 to 12 per cent of the rubber produced in India is in theform of rubber latex which is used in the manufacture of various dipped rubber goodslike balloons, gloves, condoms, feeding bottle nipples, etc. About 8 to 10 per cent of therubber in India is converted into crumb rubber. This is a technically specified rubber(TSR) with certain well-defined physical, mechanical and chemical characteristics and
14conforms to some BIS specifications. As against RSS rubbers, which are graded by amere visual inspection, the TSR is tested in laboratories for quality to certain standards.Varietal ImprovementNatural rubber is found in the latex of as many as 895 species of plants belonging to 311genera of 79 families. Among them, only a few species have proved to be fit forcommercial exploitation. Of these, Hevea brasilicnsis (Euphorbiaceac), the para-rubber-tree, is the most important commercial source of natural rubber. It is a native of Braziland was introduced into tropical Asia to 1876. The tree is now grown in the tropicalregions of Asia, Africa and America. It is a hardy, tall, quick-growing tree, reaching 18 to30 metres in height, with a straight trunk producing branches 3 to 5 m from above theground and forming a spreading or conical canopy. The other sources of natural rubberare Manihot glaziovii (Euphorbiaceae), Ficus clastica (Moraceae), Patheniumargentatum and Taraxacum kok-saghyz (Compositae). In addition, many other speciessuch as Euphoriba intisy (Euphoribaceae), Cryptostegia grandi-flora (Asclepiadaceae),and Landolphia sp. (apocynaceae) have been tried as possible minor sources of naturalrubber. The Rubber Research Institute of India, Kottayam has developed 10 new rubberclones, each with a potential to yield 20 per cent more rubber than RRII 105, the highestyielding commercial clone in the country. The clones are in various stages of finalevaluation. They have better disease tolerance level and good bark regeneration capacity.These clones are of importance not only because of their high yields, but also becausethey can save rubber industry from the threat of monoclone culture. At present about3,50,000 hectares of rubber plantations in India are based on one clone RRII 105. So anydisease afflicting this clone can devastate the entire rubber plantations in India. RRII 105has been a very important clone for India. It was developed and released for commercialplantation in 1975. It has given an average yield of 2,000 kg and a highest yield of 3,500kg per hectare in better managed plantations. Its use has raised the average yield ofrubber in India from 770 kg in 1995 to 1,500 kg in 1996 and the output from 1.35 lakhtonnes in 1975 to 5.40 lakh tonnes in 1996.
15Fertilizer and Nutrient ManagementRubber trees should be regularly manured with balanced fertilizer mixtures from the timeof planting to the age of economic production for ensuring maximum production. Therecommended dose varies according to the age of the plant. During the first year ofplanting, single dose of 225 g of 10:10:4:1.5 NPKMg mixture is applied to each plant.The dosage increases to 900 g and 1,100 g in two split doses during the second and thirdyears respectively. From the fourth year till the plants in the area become ready fortapping, the application of 900 g of the mixture per plant in two split doses, one in April-May and the other in September-October is recommended. For tree under tapping, NPK10:10:10 mixture at the rate of 900 g per tree is applied annually during April-may.TappingLatex is obtained from the bark of the rubber-tree by tapping. Tapping is a process ofcontrolled wounding, during which thin shavings of the bark are removed to induce theflow of latex. The bark of the rubber-tree has an outer hard portion and an inner zone,which is soft. The latex vessels are arranged in a series of concentric rings within thebats. Their number increases towards the cambium. They are disposed almost vertically,at a slight angle to the right. Tapping cuts extend to half the circumference of the tree(half spiral) and slope down to the right. The cut leads to a vertical groove, to the base ofwhich a zinc spout is fixed. Below the spout, a coconut-shell is placed to collect the latex.Tapping commences early in the morning when the latex-flow is high. A tapper insouthern India attends to 250-400 trees a day. After two or three hours, when the flowstops, the latex is collected in buckers and taken to the collection shed or factory. Toobtain the optimum yield, tapping should be deep, but care should be taken that thecambium is not cut. Tappings should be done plants and half spiral, once in three days(S/2 d/2) for bud-grafted plants and half spiral, once in three days (S/2 d/3) for clonalseedlings. A higher intensity of tapping often leads to `brown bast’, a physiologicaldisorder. However, on older trees, intensive tappings are practiced. Synthetic hormonesare also used to stimulate yield. A new yield-stimulant, known as `Ethrel’, when appliedhas almost doubled the yield of rubber. The yield of a rubber-tree varies according to thetype of the material planted, the age of the tree, the fertility of the soil, the climatic
16conditions and the skill of the tapper. During the south-westerly monsoon, many tappingdays are lost. However, by fixing polythene rain-guards, the non-tapping period can bereduced. During the wintering and re-foliation period, a rest of about four weeks is given.Thus the number of tapping days in a year may vary from 240 to 300. Normally, arubber-tree can be tapped economically for 25 to 30 years.ProcessingThe important forms in which the crop from rubber plantations is marked are thefollowing:Preserved latex and latex concentrateDry ribbed sheet rubberDry crepe rubberDry solid-block rubber.The crop collected in the form of liquid latex can be processed into any of the aboveforms. But the crop collected in the form of tree lace, shell scrap and earth scrap isprocessed only into crop or solid-block rubbers. Preserved latex concentrates aregenerally marketed in two concentrations-the latex between 36% and 50% drc and latexbetween 51% and 60% drc. Latex is concentrated either by creaming or by centrifuging.It is, however, to be preserved by adding ammonia and other chemicals to preventcoagulation and deterioration. The major quantity of natural rubber produced in thiscountry is marketed in the sheet form. When the latex reaches the factory, it is weighed,passed through sieves to remove impurities and the rubber content is estimated using ametrolac (hydrometer). The latex is then standardized by adding water, allowed to standand again sieved. Then it is poured into aluminum trays of standard size or into biggertanks, to which the required quantity of formic or acetic acid of a standard strength isadded to coagulate it into a soft whitish mass. This is taken out, washed in running waterand passed between smooth rollers to squeeze out the water. Finally, the sheets are passedthrough grooved marking-rollers. The wet sheets are hung on reapers in shade to get ridof the excess water and then moved into smoke houses for thorough drying. After dryingfor about 4 to 5 days at a temperature of 43° and 60°C, the sheets are graded and packedfor dispatch to manufacturers. Besides the smoked sheets, using different process also
17makes pale crepe and sole crepe. In order to improve the image of natural rubber in theworld market, new image of natural rubber in the world market, new methods ofprocessing and presentation are also adopted. As a result, processing of the crop fromestates into modern solid-block forms has been developed. This process involvescoagulation, size reduction, de-watering, and dirt removal, drying, baling and grading.Disease ManagementAbnormal leaf-fall caused by Phytophthora pulmivora and P. Meadii, the powderymildew caused by Odium keveae, and the pink disease caused by Corticium (Pelliculariasalmonicolor) are some of the major diseases affecting rubber in southern India. Thesediseases form a limiting factor in the growth of the trees and the yield of latex, and plant-protection methods have to be adopted in time. Prophylactic spraying with 1% Bordeauxmixture or the oil-based copper oxychloride is the control measure recommended againstabnormal leaf-fall. Powdery mildew is controlled by dusting with sulphur (70:30 sulphurtale mixture). Using Bordeaux paste in the early stages of infection checks the pinkdisease.******