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Rubber and Other Latex Products



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                 Rubber    Hevea Rubber    Wild Rubber    Plantation Rubber (East)    Plantation Rubber (West)     Castilla Rubber   


       Ceara Rubber    Assam Rubber    Lagos Silk Rubber    Landolphia Rubber    Guayule Rubber    Dandelion Rubber   


            Minor Sources of Rubber    Other Latex Products    Gutta-Percha    Balata    Jelutong    Chicle






       Rubber is acquired from the milky fluid, or latex, of various erect or climbing woody plants of the tropics or subtropics.  Most of the rubber plants belong to the Moraceae, Euphorbiaceae, or Apocynaceae.  Although more than 50 species are available as sources, only a few have been important commercially, with Hevea brasiliensis being the most prominent.  Originally only wild trees were the source of rubber, but later cultivated Hevea trees, the “plantation rubber” furnished about 98 percent of the supply (Hill 1952).


       Rubber is the most recent of the major crops of the world.  The industry by 2003 was about 150 years old, but cultivation has been carried on only about 100 years.  The increase in the production of plantation rubber was from 800 long tons in 1900 to 305,000 tons in 1920 and 1,395,000 tons in 1940.  This development of the rubber-growing industry has not been without drawbacks.  Overproduction had seriously affected the industry financially by 1950, and many attempts have been made to regulate its supply.  The British and Dutch, in particular, tried to restrict production and exert other methods of control in Malaya, Java, Sumatra and other plantation rubber centers within their spheres of influence.  The successful development of synthetic substitutes for rubber, after many years of experimentation, further jeopardized the natural rubber industry.  Nevertheless, while these substitutes are superior for some purposes, such as the conduction of oil, natural rubber is still preferred for vehicle tires, which utilize about 3/4ths of the rubber output.


       Latex occurs in special cells or in a series of special vessels, which permeate the bark, leaves, and other soft parts of the tree.  Usually only the latex from the lower part of the trunk is of importance commercially.  Latex is a gummy white liquid full of minute globules.  It consists of a mixture of water, hydrocarbons, resins, oils, proteins, acids, salts, sugar and caoutchouc, the substance used as the source of rubber.  The significance of latex to the plant is obscure, but it is know to be of some value in the healing of wounds, and it may serve for protection, nutrition, and the transport of materials or as a fluid reservoir.


       The properties of rubber were known by primitive cultures in Central America and Peru.  Their word cauchuc has been changed to the present caoutchouc (caucho in Spanish).  Columbus was the first to report the existence of rubber to Europeans, but it was not introduced into Europe until 1735.  Priestley first applied the name “rubber” in 1770, due to the fact that caoutchouc could be used for removing pencil marks.  Mackintosh in 1823 developed a process for waterproofing cloth, but it was not until 1830 when Goodyear made the discovery of the vulcanizing process, that rubber really became popular.  From then on the rubber industry developed rapidly, and today rubber has a vast and constantly increasing number of uses and industrial applications.  The properties that make it so valuable include its plasticity and elasticity, its resistance to abrasion and to electrical currents, and the fact that it is impermeable to liquids and gasses.


     Hevea Rubber


       The Hevea or Para rubber tree (Hevea brasiliensis) is the normal source of 95-98% of the rubber produced throughout the world.  The tree is native to the hot damp forests of the southern affluents of the Amazon River in South America.  It was estimated in 1952 that that there are over 300-million trees in the vast area traversed by the Amazon and the Orinoco.  Within this region the optimum conditions for its development are found.  This includes a uniform climate with a temperature range from 75-90 deg. Fahrenheit and a rainfall of 80-120 inches.  The trees may reach an age of at least 200 years and may attain a height of 60-140 ft.  The leaves are 3-lobed, and the flowers are small and inconspicuous.  The fruits have three seeds, which contain 23-32 % of fatty oil.  This oil is sometimes extracted and used as a drying oil.  The resulting oil cake is rich in proteins and is used as a stock feed.  Although rubber trees are natives of swampy floodlands, they grow best on deep, fertile, well-drained upland soils at an elevation of 600-1500 ft. above sea level.  The latex occurs in a series of vessels in the cortex.  Several other species of Hevea are tapped, including Hevea benthamiana, which has high-quality latex, but their production is insignificant compared with H. brasiliensis.


     Wild Rubber


       In the beginning of the industry only wild rubber trees are available as a source of rubber.  The maximum production was reached in 1910 with an output of 83,000 long tons.  After that with the development of plantation rubber, wild rubber production steadily declined to as low as 8,500 tons in 1932.  Since that time the output has fluctuated, depending on price and demand.  During World War II wild rubber was again actively exploited.


       The methods employed in obtaining and preparing the latex have changed little over the years.  The collection of the latex is in the hands of local residents, called “seringuieros” who are usually in the employ of absentee owners (Hill 1952).  Each seringuiero is responsible for a single tapping circuit, which contains from 35-180 trees, about 2 or 3 to the acre.  When a new tree is located, it is tapped at a point about 3 ft. above the ground by cutting several short downward 30-degree panelike incisions in the bark with a special knife.  The cuts are deep enough to sever the latex vessels but do not extend far enough to injure the cambium.  Cups are placed below the incisions to receive the latex, which flows for several hours.  The seringuiero makes the round of his trees each day.  Successive tappings consist of entirely new incisions made slightly below the previous ones.  The latex is collected from the cups and carried to the camp for coagulation.  This is done by coating a pole with latex and suspending it over a fire made of palm seeds or special woods.  These yield a dense smoke containing acetic acid, creosote, and tars which coagulates the latex, forming a layer of crude rubber.  The process is repeated until balls weighing 125-200 lb. are obtained.  In some areas paddles are dipped in the latex and held in the smoke.  The balls are shipped to mills for processing.


     Plantation Rubber in the Eastern Hemisphere


       Henry Wickham transported 70,000 Hevea seeds from the Amazon to England in 1876.  These were grown at Kew, and enough seedlings were obtained to start a rubber industry in the eastern tropics, at first in British Malaya and Ceylon and later in Java, Sumatra and other areas (Hill 1952).  There had been earlier attempts at rubber cultivation, but plantation rubber did not become permanently established until the beginning of the 20th Century.  In 1910, when Amazon rubber production was at its peak, the East produced only 11,000 tons.  Four years later it had outstripped its rival, and by the outbreak of World War II, it was responsible for 98% of the world’s output of 1,500,00 tons, with nine million acres under cultivation.


       The rapid development of plantation rubber in the East may be attributed to a favorable climate, absence of diseases, low labor costs, and the extensive research program launched by the British.  Every step in the production of the crop was rigidly supervised, and the best methods of planting, cultivation, tapping and coagulation were discovered.  A selection and breeding program facilitated an increase in yield.  The discovery of bud grafting allowed that buds of high-yielding plants be grafted on ordinary seedlings.  The resulting clones differed greatly, and only those with the most desirable traits were retained.  Using such approved clones began in 1925.  By 1945 10% of the plantations had trees that were the result of grafting, and they obtained a yield of 1500 lb per acre.  The 90%, which still had a random mixture of trees, had a yield of only 450-500 lb/acre.  Where controlled crosses of high-yield clones were made, yields as much as 2000 lb. per acre were possible.  Not all plantation rubber was produced on the large estates.  The acreage devoted to rubber grown by small growers was produced in small family gardens and was actually more than that grown on estates.


     Plantation Rubber in the Western Hemisphere


       Following the imposition of export restrictions on eastern rubber in 1924, the United States favored the establishment of plantations in other parts of the world.  The Firestone Corporation selected Liberia, but Ford Motor Co. and Goodyear turned to tropical America, the native area of Hevea.  The 2,500,00-acre Fordlandia was started in Brazil in 1928, while Goodyear chose Panama and Costa Rica.  All the American efforts failed after a promising beginning, due primarily to the ravages of leaf blight, Dothidella ulei, to which plantation rubber in the Western Hemisphere was very susceptible.  It was obvious that rubber could not succeed as a crop in the American tropics without adequate disease control.  A research program did produce satisfactory results, however.  An effective spray, of copper and sulfur fungicides with various spreaders and stickers, was developed and could be used on seedlings.  Yield and resistance experiments were conducted on thousands of wild trees, with the most desirable being selected for propagation.  Fortunately there was a successful importation of approved eastern clones from a Goodyear plantation in the Philippines.  When these were budded on resistant stock from the jungles, desirable combinations of characters were obtained.  Double budding also proved satisfactory.  This involves budding a high-yielding eastern clone onto a native root as soon as the plant is large enough.  This is grown in a nursery under spray control until it is 6-10 ft. tall.  Then the top is budded with a disease-resistant strain.  The resulting rubber tree has a native root system, a high-yielding eastern clonal trunk, and a disease-resistant crown.  Long-term breeding programs were continued well into the mid 1900’s, as well as extensive explorations in the jungle, with the goal of obtaining strains that combined disease resistance and high yield and which would reduce the expensive spraying and double-budding practices.


       The cooperation of the United States with governments in Latin America resulted in rubber being grown successfully in many areas.  Emphasis was placed on small family plantings rather than on large plantations.  The rubber trees were usually set out at intervals of 12-24 ft. in tows 20 ft. apart.  Other crops were grown between the rows.  Thus, from 1/3rd to 1/2 of the acreage was resting; the balance was tapped on some alternating program.  At each successive tapping a thin shaving of bark was sliced off the original panel until it almost reached the ground.  One-third, 1/2 and full spirals were used.


       Following the collection of latex, a small amount of ammonia or some other anticoagulant was often added to keep it liquid until it reached the processing area, where it was concentrated and made into sheet rubber.  Cleaning the latex and pouring it into large pans accomplished this.  A coagulant, such as formic or acetic acid, was added, and in several hours a mass of soft rubber resulted.  Blocks of this were washed and run between rollers to form thin sheets.  These were smoked and baled for shipment.  Other types of crude rubber were also prepared.  “Worm rubber” consists of irregular wormlike pieces cut from sheets with a pair of shears.  “Crepe rubber” was made by passing washed and bleached coagulated latex through a creping machine, which turned out long, thin, perforated strips of rubber.  In the preparation of “sprayed rubber” latex was dropped on whirling disks and little particles of rubber were thrown off.  Any moisture quickly evaporated.  This kind of rubber was exceedingly pure and clean.   Also, steadily increasing amount of liquid latex was evaporated.  This required immediate processing in the field and was feasible only for large plantations


Castilla Rubber


     Panama or Castilla rubber is from Castilla elastica, a tall tree native to southern Mexico and Central America.  There are many names for this tree in the indigenous languages of the region.  It was the chief source of rubber from 1794-1850.  Other species of Castilla may also be used, among which are C. ulei of the Amazon, the source of caucho rubber. Castilla elastica is found in deep loamy soil on high ground and may reach a height of 150 ft.  It requires temperatures above 60 deg. F. and requires shade when young.  Often the natives cut these trees down in order to obtain the large possible yield of latex, which could ultimately lead to this species extinction.


       Trees are tapped when 8-10 years of age, with adult trees yielding a maximum of 50 lb. of latex.  This is coagulated with plant juices, alum and by boiling or exposure to the air.  The crude rubber is shipped in flat cakes.  Castilla rubber was once extensively cultivated in Central America in plantations, but it could not compete successfully with Hevea rubber.  The plantations were abandoned.  The surviving trees were the source of some of the emergency supply of Castilla rubber during World War II (Hill 1952).


Ceara Rubber


       Ceara or Manicoba rubber is obtained from Manihot glaziovii, a small tree native to drier regions in Brazil.  It grows well in dry rocky ground so that it may be utilized in areas unsuitable for other types of rubber.  The tree grows rapidly, reaching its maximum height of 30 ft. in a few years.  Ceara rubber is also grown in Ceylon, India and other tropical countries.  The trees are tapped when 4-5 years of age and yield a good grade of rubber.  The latex is coagulated by exposure to air or smoke.  The crude rubber is exported as blocks or flat cakes.


Assam Rubber


       Assam or India rubber as it is often called, is obtained from Ficus elastica, a native tree of northern India and Malaya.  The tree requires a hot climate and a high rainfall.  It often begins life as an epiphyte.  It grows to a great height, developing huge buttresses or prop roots.  The roots as well as the stem are tapped.  The latex is allowed to drip onto bamboo mats, where it coagulates.  A large amount coagulates on the trunk as well.  This crude rubber is scraped off, cleaned and dried.  The native procedures for tapping the wild trees have been very wasteful, so the tree is cultivated in some areas.  The yield is low and the trees do not mature until about 50 years of age.  Assam rubber is of low grade and has been of little or no commercial importance.


Lagos Silk Rubber


       Lagos silk rubber is from Futumia elastica, a large tree of tropical West Africa.  Discovered in 1894, it was immediately exploited to the point of near extermination.  In 1898 over 6 million pounds were exported.  The tree has been cultivated and an attempt made to reestablish the industry.  However, plantations of Hevea rubber are the chief source of rubber in West Africa.


Landolphia Rubber


       Other former sources of African rubber were several woody climbers in the genus Landolphia.  The most important were L. kirkii on the east coast and L. heudelotis and L. owariensis on the west coast.  The huge vines, sometimes 6 in. in diameter. Were pulled down and cut into small pieces.  The latex that exuded was coagulated with plant juices or the heat of the sun, sometimes even on the bodies of the native collectors (Hill 1952).  The most wasteful methods were employed, for a large immediate yield was desired.  There was very barbaric treatment of the natives involved in this harvest.  Operations in the Belgian Congo during the reign of Leopold II remain some of the most awful pages in history.  Although there is still a considerable amount of wild landolphia rubber, there is apparently no future commercial value for it.  Cultivation of this plant is not practical.


Guayule Rubber


       The guayule, Parthenium argentatum, a native of America, has been utilized sine 1910 as a minor source of rubber.  This low semi-shrubby plant grows in the arid regions of Mexico and the southern United States.  The early Amerindians who obtained the caoutchouc by chewing the plants knew it.  Unlike the other sources of rubber, there is no latex present in the guayule plant.  There are small granules of caoutchouc scattered all through the tissues.  These are extracted mechanically or by means of solvents.  The entire plant is pulled up and chopped up or ground with water.  The particles of caoutehouc float to the surface and are removed.  They are then dried and pressed into slabs.  If solvents remove the resinous materials the product is as good as the best Hevea rubber.  Guayule rubber is especially good for mixing with synthetic rubber substitutes.  Guayule has been adapted to plantation culture and it was extensively investigated as part of the Emergency Rubber Program during World War II.  The yield has been increased; the life cycle shortened, and improved cultural, harvesting, and processing machinery developed.  Production costs are still high so that it does not compete with Hevea rubber except in emergencies.  The importance of guayule for the future lies in the fact that it constitutes a living stockpile of rubber on land which otherwise would be idle (Hill 1952).


Dandelion Rubber


       The dandelion of Russia, Taraxacum kok-saghys, is a close relative of the common dandelion.  In 1931 Russian botanists discovered it while searching for new economic plants.  Rubber is present in considerable quantities in latex tubes in the long taproots.  The yield has been increased by selection and breeding, and the plant was grown on some 2 million acres during the time of the Soviet Union.  Seeds were brought to the United States in 1942 and planted experimentally in 42 states.  Vigorous plants with greater root weight and rubber content were segregated.  Hill (1952) believed that a yield of 400-500 lb. per acre could be achieved through continued research.  The plant is well adapted to the northern United States and Canada, where it can be harvested the year it is planted.  Under the most favorable conditions it might be profitable to grow this species as a minor source of rubber, and indeed was cultivated for this purpose in Argentina.


Minor Sources of Rubber


       Other species of plants have been considered as a possible source of rubber.  Among these are intisy (Euphorbia intisy).  This leafless shrub of arid regions of Madagascar contains latex that has had considerable use locally.  The rubber coagulates on the surface of the plant in long elastic strands and is of high grade.  Attempts have been made to cultivate intisy in the United States because of its adaptation to desert conditions.


       Cryptostegia grandiflora and C. madagascariensis are ornamental woody climbers from Madagascar.  They are now found in the tropics and subtropics of both hemispheres and were seriously considered during World War II as a new source of rubber.  Both species have been grown for many years in India as a source of high-grade palay rubber.  They are abundant in Mexico, occuring there in a wide variety of soils and climates.  They seem the hardiest and fastest growing of all rubber plants, attaining harvest age within six months.  They seem to offer considerable future promise, but attempts in Haiti to grow them on a large scale failed due to difficulties of extracting the rubber.


       Other rubber-bearing plants of local importance include the mangabeira (Hancornia speciosa), a shrub or small tree of Bolivia, Brazil and Paraguay; a species of Micrandra, which yields the caura rubber of Venezuela; and various species of Sapium in northern South America.  Also a few native North American plants have rubber-contining latex.  Among those, which have been given some attention, are the desert milkweed (Asclepias subulata); the Indian hemp (Apocynum scannabinum); several goldenrods, in particular Solidago leavenworthii, which was investigated by Thomas A. Edison; species of the rabbit brush (Chrysothamnus), the source of chrysil rubber; and species of Cnidoscolus from which chilte rubber is obtained.


Other Latex Products




       Gutta-percha is a nonelestic rubber obtained from the grayish-white latex of several members of the Sapolaceae.  It has been known since 1842.  The chief source is Palaguium gutta, a tree of Malayan origin, which has been grown in Borneo, Sumatra, the Philippines and other tropical countries. The latex is produced in sacs, which occur in the cortex, phloem, pith and leaves.  It is obtained by making incisions from which the milky juice runs out very slowly, or by felling the trees.  The latter is the usual method.  The bark is removed in strips one inch in with and one foot apart, and the latex is collected in coconut shells or in palm of plantain leaves.  The latex soon coagulates into grayish-yellow masses of a hard substance, which is odorless and heavier than water.  This crude product contains several resins and other impurities and is purified by washing in hot water.  The whole mass is boiled and then kneaded into blocks, or it is chopped or sliced up and the pieces are washed, strained and kneaded, and then rolled into thin sheets (Hill 1952).  The value of gutta-percha depends on the amount of a hydrocarbon, gutta that is present.


       Gutta-percha is hard at ordinary temperatures.  It deteriorates very rapidly when exposed to air through oxidation and should be kept under water.  It softens at 77 degrees Fahrenheit, can be kneaded at 122 deg. F., and melts at 248 deg. F.  Because it is an exceedingly poor conductor of electricity it has been used for insulation.  For many years no other material could replace gutta-percha and the similar balata in the construction of submarine cables, which require a substance that is resistant to salt water, pliable and with just the right amount of rigidity.  Other uses included splints, supports, pipes, golf balls, speakingtubes, telephone receivers, waterproofing and adhesives.  It has also been utilized for protecting wounds and in dentistry. 




       Balata is a nonelastic rubber that is obtained from the latex of Manilkara bidentata, formerly known as Mimusops balata, and other species of the genus.  It is a native of Trinidad and South America.  This magnificent tree grows to a height of over 100 ft.  When mature its purplish wood is very hard and durable and is much used for ties and building purposes under the name of bully wood or bulletwood.  The fruit is also edible.  The latex is obtained by tapping the trees three times each year.  It flows freely and readily coagulates in the air.  A tree 3 ft. in circumference will yield 50-100 lbs. of dry balata.  After coagulation it is cleaned and molded into cakes.  Balata contains about 50% gum.  It serves the same purpose in industry as gutta-percha.  It is particularly well adapted for machine beltings as it grips tightly and never stretches.  It is also used as a substitute for chicle.  Balata has been known since 1859, but unlike gutta-percha, it has never been cultivated.


       Several inferior types of balata are found in the Amazon region, chief of which is abiurana or coquilana obtained from Ecclinusa balata.




       Jelutong is obtained mainly from Dyera costulata and related species from Malaya.  These trees have a copious flow of latex, greater than all the other latex species combined.  From 1910-1015 this was exploited as a source of rubber.  However, the latex is combined with many gums, resins and other impurities, and it yielded a poor quality of rubber.  Jelutong has been used mainly as a substitute for chicle. 




       Sapodilla or naseberry (Achras zapota) is a tall evergreen tree native to the Yucatan Peninsula of Mexico.  It is cultivated in tropical America and Florida for its edible fruit.  The bark contains latex, 20-25% of which consists of a gum, or chicle, similar to that of gutta-percha.  It is the basis of the chewing-gum industry but is also used in making surgical tape and dental supplies.


       The primitive method of obtaining chicle involves tapping the trunk and then scraping the thickened exudates from the bark.  The crude or leaf chicle consists of pink or reddish-brown pieces mixed with 25-40% impurities.  In southeastern Mexico and British Honduras where the industry occurs most abundantly, the native collectors or chicleros are more careful.  Zigzag gashes are cut in the trunk with a machete, up to a height of 30 ft.  The latex runs to the base of the tree where it is collected in rubberized bags, leaves or even hollows in the earth.  This accounts for the grains of sand that are oftentimes found in chewing gum.  The flow of latex lasts for several hours and the yield may be as much as 55 liters.  In order to conserve the supply, plantations were established.  However, these were not practicable because the trees can be tapped only every 2-3 years.


       The hardened chicle is boiled; a process that requires considerable skill, for the chicle must be poured off when the moisture content reaches 33%.  It is then molded into blocks for shipment.  Raw chicle contains resin, gutta, arabin, calcium, sugar and various soluble salts.  Purification involves breaking the blocks into small pieces, washing in a strong alkali, neutralizing with sodium acid phosphate, washing again and finally drying and powdering.  The final product is an amorphous pale-pink powder, which is insoluble in water and forms a very sticky mass when heated.  Ageing partially oxidizes the mixture that then turns brown and becomes very brittle.  The final steps in the manufacture of chewing gum involves cleaning, filtering, sterilizing and compounding with various flavoring materials.  Thirteen pounds of the final product yields about 5000 pieces of chewing gum.  A piece of gum usually contains about 15% chicle, the remainder being chicle substitutes, sugar and flavoring substances.  Attempts to find substitutes have not been very successful, but inferior latex from other sapodillas, balata and jelutong are all utilized to some extent.  Sorva or leche caspi, obtained from Couma macrocarpa, a large tree of the upper Amazon, was exploited during World War II.  The tree, which has very abundant latex, is felled, ringed and the latex is collected in cups made from palm leaflets.  The latex is then coagulated by boiling and is shipped in the form of large blocks.  The white wood of this species is also used for furniture, and the fruits have a mucilaginous but edible pulp.


       By 1952 the United States was the greatest chewing-gum market and used about the entire output of chicle.  The supply was chiefly from Mexico, Guatemala and British Honduras.


     Rubber Plantation


<bot713>  Hevea brasiliensis plantation  {Brazil}

                       [CLICK to enlarge)]