Lecture 22
Rubber

Hevea Rubber Tree: Hevea brasiliensis, Euphorbiaceae

 fig. 1

History

A latex yielding plant native to South America (Amazon region).

There are 9 species of Hevea, of which Hevea brasiliensis is the most important.

Seeds can be eaten when boiled, oil in seeds can be used for illumination.

The native Indian of the area used the product to make dolls and balls; also used it to waterproof moccasins!

The French called it caoutchouc.

 fig. 2

Oozing latex

  • 1763—French found caoutchouc could be dissolved in naphtha, suggested use in waterproofing clothing but it became tacky when warm.
  • 1770—Joseph Priestly discovered that the material would rub out paper marks, hence the name India rubber, and now simply "rubber."
  • 1823—Mackintosh manufactures waterproof raincoats by coating fabric with rubber dissolved in naphtha.
  • 1824—Hancock suggested plantation growing of rubber.
  • 1839—Goodyear and/or Hancock discovered vulcanization; when rubber was heated with sulfur, rubber retained physical properties from 0° to 100°C. This led to rubber boom.
  • Interest in rubber with vulcanization process led to increased demand and exploitation of wild Hevea trees (Hevea was the native word). Native tappers (seringuiros) hacked trees and spoiled them for later tapping.
  • 1870—Sir Clements Markham of India Office suggested that rubber along with cinchona (source of quinine) be obtained from tropical America and grown in Asia.
  • 1872—James Collins reviewed rubber producing plants, published monograph entitled Caoutchouc of Commerce.
  • 1873—Seeds from Brazil sent to Kew Botanical Gardens; 12 plants raised and sent to Calcutta, but failed.
  • 1875—Second consignment of seed failed to germinate.
  • 1876—Makham sends Robert Cross to Panama (for Castilla) to Para, Brazil where he obtained 1000 plants of Hevea, but no plants reach the East.
  • At this time H.A. Wickham, an Englishman residing at Manaus (center of the rubber boom in Brazil), sent 70,000 seed from Central Amazon basin (he received 10 £ /100 seed) in an arrangement financed by the government of India. This provided the basis for the world's rubber industry. The seeds were sent to Kew. Seed has short viability but produced 2899 plants. Seedlings were sent to Ceylon and 50 plants to Singapore, and a few to Java.
  • 1888—In Singapore there were 9 trees of the original introduction, 21 five-year-old trees and 1000 seedlings. Ceylon had 20,000 seed.
  • H.N. Ridley, scientific director of the Botanical gardens at Singapore developed the rubber industry. He demonstrated that Hevea was the superior rubber bearing plant, he discovered excision method of extracting latex, devised method for coagulating latex, time of tapping and retapping.
  • 1898—Dunlop redisovers pneumatic tires (Motor cars invented in 1885). Today, 70% of rubber involves transportation, 6% footwear, 4% wire and cable.
  • 1898—First planting in Malaysia by a Chinese grower named Tan Chan Yoy. At this time coffee prices slumped and there was interest in establishing a new industry.
  • 1910—Rubber boom; rubber reaches $3 a pound.
  • 1956—Ridley dies at the age of 101.

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    Ecology and Anatomy

  • Hevea is a tropical evergreen rainforest tree of the Amazon basin, grows in the flooded or drained plateau.
  • Rubber is planted 15ºN to 10ºS, temperature of 74–95ºF, with well distributed rainfall, 75–100 inches per year.
  • Tree is fast growing, about 24 m maximum height.
  • Latex vessels are modified sieve tubes of the phloem, run counterclockwise, 2-1/2 degrees to the vertical.
  • Thus tapped in clockwise direction

    		•

    World Production 1000 t Chief countries
    World 5636  
    Africa 281 Nigeria (105); Ivory Coast (97); Central Africa Republic (50)
    North America 20 El Salvador (20)
    South America 36 Brazil (30)
    Asia 5297 Thailand (1667); Indonesia (1312); Malaysia (1074)
    Oceania 3 Papua New Guinea (3)

    Propagation

  • Seed (used for rootstocks; seed tree can be identified by seed marking)
  • Budding
  • Cutting; only from young (juvenile trees) using mist propagation. Leafy cuttings can be used but root system is poor and trees blow over easily
  • Marcottage (air layering)

    • fig. 4 fig. 5
    fig. 6 fig. 7
    Budding Rubber Tree
    fig. 8
     
    Budding Nursery    		 fig. 9
    fig. 10

    In New World where South American leaf blight (Dothidella ulei) is a problem a three part tree may be produced with a seedling rootstock, a high yielding trunk, and a leaf blight resistant top.

  • Resistant top
  • High yielding trunk
  • Seedling rootstock

    		•  fig. 32
    fig. 12

    Planting

    Plantings are usually about 15 × 15 feet apart.

    Tapping

  • A jeboug knife is used, a knife with a V-shaped cutting edge which leaves a grooved channel for latex to flow.
  • Present method is a single spiral 1/2 diameter of the tree.
  • Cutting is repeated 1 to 3 days; 1/16 inch per cut, 7/8 inches per month, 10 inches per year.
  • There are different systems on the length of the spiral and frequency of cut.
  • The intensity of tapping is indicated by the formula: S/2 d/2 = 100%
  • S/1 is a full spiral
  • S/2 is a half spiral
  • d/1 is a daily tap
  • d/2 is a tap on alternate days.
    •
  • Trees are usually tapped for 6 months and rested for 3 months.
  • The herbicide 2,4-D or ethephon is used to stimulate flow.
  • These prevent sealing of the cut ends.

    		•
    fig. 14

    Tapping rubber tree

    		 fig. 15

    Tapping rubber tree

    Collecting Latex, Tamo Crumb Rubber factory, Indonesia

    		 fig. 16

    Processing

    There are three types of latex:

  • Liquid: Highest quality
  • Cup rubber: The cut-lump that sticks to the plastic cup
  • Scrap rubber: Strip of rubber from the cut surface
    •

    Coagulation

  • 10–25% ammonia can be added as an anticoagulant
  • Latex bulked and strained, rubber content 30–35%
  • Latex diluted with water, poured into coagulation tanks, with acetic or formic acid (l part 4% formic acid required for 100 parts 12% latex—more if ammonia is added).

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    Processing Rubber

    fig. 18

    Sawing cup rubber

    		 fig. 19

    Coagulation tanks

  • The "curd" is separated from the serum, and squeezed in rollers to 2-1/2 mm thickness, dried in smoke house, bailed for export.
  • Crepe rubber is compressed granular rubber from sheet rubber that is passes through rollers.
  • Crumbing is the operation that cuts up crepe and compresses into blocks.

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    Guayule Rubber

  • In the US there has been interest for many years in obtaining rubber from guayule encourages by the strategic need to have a local source of rubber. (Parthenium argentatum, Asteraceae)
  • Production areas would be the southwestern arid areas of the United States (particularly Arizona) and Mexico.
  • However guayule cannot be tapped and yields do not compete with Hevea rubber.
  • However this industry has recently had some encouragement because a number of people, particularly health workers, who use rubber gloves are allergic to Hevea rubber (due primarily to processing contaminants).
  • Guayule rubber does not impart this allergic reaction and a niche market for guayule rubber may develop.

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