Papers

Chapter-2: Literature Review

2.1. Rubber Plant

2.1.1. Introduction

Common Name is rubber tree, English: Brazilian rubber tree, hevea, Para rubber tree, Fijian: rapa, French: arbre de Para, hévéa, Spanish: árbol del caucho, cauchotero de Pará, jebe, siringa (Duke. 1983). Scientific name of rubber is Hevea brasiliensis (Willd.) Muell.-Arg.

2.1.2. Classification of Rubber

Kingdom: Plantae

Division: Magnoliophyta

Class: Magnoliopsida

Order: Malpighiales

Family: Euphorbiaceae

Sub-family: Crotonoideae

Tribe: Micrandreae

Sub-tribe: Heaveinae

Genus: Hevea

Species: Hevea brasiliensis

2.1.3. Description of Rubber Plant

There are 11 species of Hevea. Hevea brasiliensis is a member of the Euphorbiaceae family (spurge family). Although not limited to the Euphorbiaceae, latex production is one of its distinguishing characteristics. The plants of the Euphorbiaceae family are mostly monoecious herbs, shrubs, and trees, sometimes succulent and cactus-like, and comprise one of the largest families of plants with about 300 genera and 7,500 species that are further characterized by the frequent occurrence of milky sap (Law, 1999).

Rubber Plant is a flowering plant belonging to Euphorbiaceae. The plant is a tall slender tree up to 40 m tall, with girth 2.6–3.3 m; stems smooth and straight; trunk un-branched up a long way and then with much-branched leafy canopy; bark grayish; taproot well-developed; leaves alternate, trifoliolate, stipulate, petioles 7.5–10(-70) cm long; leaflets obovate, apically acuminate, entire, basally acute, penninerved, 10–15(-50) cm long, 3–6(-15) cm broad, elliptic-lanceolate in outline; flowers numerous, monoecious, creamy, yellow or green, in axillary pubescent panicles, sweet-scented, small; female flowers apical, the more numerous male flowers lateral in the inflorescence; petals absent; fruit 3-lobed, 3-seeded ellipsoidal capsule, each carpel with 1 seed; seeds ellipsoidal, variable in size, 2.5–3 cm long, mottled brown, lustrous, weighing 2–4 g each. Seeds collected by July–September in India (Reed, 1976).

The flowering and pollination of the Hevea brasiliensis tree are also distinguishing characteristics of this plant. Hevea may undergo two flowerings. In Malaysia for example, flowering occurs in February to April and (a lesser flowering) in September and October with winterings in January and February, and August and September. The inflorescence is a panicle of separate staminate and pistillate flowers borne in the axils of basal leaves of new shoots that grow out after wintering. Pistillate flowers are terminal to the central stem and other major branches of the inflorescence. Smaller and more numerous staminate flowers make up the rest. Both flowers are shortly stalked and scented. Neither flower has petals but rather five triangular lobes. Staminate flowers have two rings of five stamens each borne on a stalk. Pistillate flowers have a compound ovary with three locules topped by three sticky, sessile stigmas. Within an inflorescence, a few staminate flowers open first and fall off after one day. Pistillate flowers then open for a period of three to five days after which the rest of the staminate flowers open. This mechanism ensures a high degree of cross-pollination (Law, 1999).

Pollination is primarily through insects, specifically midges and thrips. Wind appears to play no role. Fertilization occurs within 24 hours after pollination. Unfertilized pistillate flowers quickly wither and die. There appears to be no evidence of self-incompatibility although cross-pollination usually results in better fruit set. Hand-pollination for breeding purposes is customary. Stamens are removed from the seed parent to prevent selfing. A staminate flower from the pollen parent is then applied to the pistillate flower of the seed parent and secured with cotton (Law, 1999).

2.1.4. Distribution

Hot humid climate with plenty of sunshine is suitable for rubber plantations (Banglapedia, 2007). The rubber trees are Native to the Amazon region, Brazil, Venezuela, Ecuador, Colombia, Peru, and Bolivia and introduced to many other tropical regions of the world, as Indonesia, Malaysia, Liberia, India, Sri Lanka, Sarawak, and Thailand (Reed, 1976). However, plants of this species were also cultivated and domesticated elsewhere (Law, 1999).

2.1.5. Rubber

Rubber is an elastomer (an elastic hydrocarbon polymer) that was originally derived from a milky colloidal suspension, or latex, found in the sap of some plants. The purified form of natural rubber is the chemical polyisoprene which can also be produced synthetically. Natural rubber is used extensively in many applications and products.

The major commercial source of natural rubber latex is the Para rubber tree (Hevea brasiliensis), a member of the spurge family, Euphorbiaceae. This is largely because it responds to wounding by producing more latex.

Other plants containing latex include Gutta-Percha (Palaquium gutta), rubber fig (Ficus elastica), Panama rubber tree (Castilla elastica), spurges (Euphorbia spp.), lettuce, common dandelion (Taraxacum officinale), Russian dandelion (Taraxacum kok-saghyz), Scorzonera tau-saghyz, and Guayule (Parthenium argentatum).

Natural rubber is a polymer of isoprene - most often cis-1, 4-polyisoprene - with a molecular weight of 100,000 to 1,000,000. Typically, a few percent of other materials, such as proteins, fatty acids, resins and inorganic materials are found in natural rubber. Polyisoprene is also created synthetically, producing what is sometimes referred to as "synthetic natural rubber". (Anon, 2007)

2.1.6. Components of rubber

The chemical analysis of latex shows the following constituents of natural rubber;

a. Liquid materials (mentionable amount)

b. Solid materials: 22-48%, within this solid material we can get 25-40% rubber.

c. Resin: 2%

d. Water: 52-78%

e. Protein: 1.5%

f. Carbohydrate: 1%

g. Inorganic materials: 0.05%

h. Coagulates, phospholypase-D enzymes which helps to coagulate the latex within 48 hours normally. (Khisa, 1991)

2.1.7. Types of rubber

Natural Rubber: Natural rubber is a solid product obtained through coagulating the latex produced by certain plants, particularly the Brazilian rubber-tree (Hevea Brasiliensis). This raw material is usually tapped from the rubber tree, which is native to Amazonia. Although there 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 on economic bases. Chemical formula is (C₃H₈-)_n which is a hydrocarbon compound. It has elasticity, impermeability, vulcanization, stability and toughness. (Wikipedia)

Synthetic Rubber

Synthetic rubber is any type of artificially made polymer material, which acts as an elastomer. An elastomer is a material with the mechanical (or material) property that it can undergo much more elastic deformation under stress, than most materials and still return to its previous size without permanent deformation. Synthetic rubber can be made from the polymerization of a variety of monomers including isoprene (2-methyl-1,3-butadiene), 1,3-butadiene, chloroprene (2-chloro-1,3-butadiene), and isobutylene (methylpropene) with a small percentage of isoprene for cross-linking. (Wikipedia)

2.1.8. Species Which Produce Rubber

Rubber (cis polyisoprene) is a by-product of the cell metabolism of many species of plants, mostly belonging to the family Euphorbiaceae. Most rubber-containing plants are native to the tropics: Hevea spp., Castilla spp. and Manihot spp. in Tropical America, Funtumia elastica and Landolphia spp, in Africa, Ficus elastica in Asia. There are also some rubber-bearing species of Compositae: Parthenium argentatum (Central America), Taraxacum (USSR), Solidago spp. (USA).

With the exception of Parthenium (guayule), which remains a small-scale source for rubber in Mexico (and in Arizona), the only significant commercial source of natural rubber is Hevea brasiliensis, a forest tree which is indigenous to the tropical rain forests of Central and South America. In this and similar species, the rubber exists within the tree in the form of latex, a colloidal suspension of rubber particles. (Webster and Faardekooper, 1989).

In Brazil and other Latin American countries Hevea benthemiana including Hevea brasiliensis crossings are an important source of relatively SALB-free sources of rubber. Funtumia elastica is the rubber plant which is widely used as a decorative indoor plant in northern latitudes. It is also a source of wild rubber (that is non-planted) in some central African countries. (Anon, 2003)

2.1.9. Excellent Properties of Natural Rubber

Natural rubber, as fabricated in rubber products, combines high strength (tensile and tear) with outstanding resistance to fatigue. It has excellent green strength and tack (the ability to stick to itself and to other materials) which makes it simple to fabricate. The main weakness is its moderate resistance to environmental damage by heat, light and ozone, although this can be an advantage in disposable products like toy balloons and is not a problem in bulky products like bridge bearings where practical experience, that is length of time in service, has shown that degradation is a purely surface phenomenon and is not greater than, and is often less than, the surface damage to the concrete and metal parts of the structure. (IRRDB)

The technical strengths of natural rubber as a tyre material. These have been succinctly summarized by Baker as follows:

• High green strength, tack and cohesive properties: these are essential for maintaining green tyre uniformity and stability during building and shaping operations;
• Excellent adhesion to brass-plated steel cord;
• Low hysteresis which imparts low heat generation, which in turn maintains new tyre service integrity and extends retread ability;
• Low rolling resistance with enhanced fuel economy;
• Excellent snow and ice traction for winter tyres and all-season treads; and
• High resistance to cutting, chipping and tearing.

2.2. A scenario of world and Bangladesh rubber

2.2.1. Brief history of rubber

Rubber was known to the indigenous peoples of the Americas long before the arrival of European explorers. In 1525, Padre d'Anghieria reported that he had seen Mexican tribes people playing with elastic balls. The first scientific study of rubber was undertaken by Charles de la Condamine, when he encountered it during his trip to Peru in 1735. A French engineer that Condamine met in Guiana, Fresnau studied rubber on its home ground, reaching the conclusion that this was nothing more than a "type of condensed resinous oil".

The first use for rubber was an eraser. It was Magellan, a descendent of the famous Portuguese navigator, who suggested this use. In England, Priestley popularized it to the extent that it became known as India rubber. The word for rubber in Portuguese - borracha - originated from one of the first applications for this product, when it was used to make jars replacing the leather borrachas that the Portuguese used to ship wine.

Returning to the works of Condamine, Macquer suggested that rubber could be used to produce flexible tubes. Since then, countless craftsmen have become involved with rubber; goldsmith Bernard, herbalist Winch, Grossart, Landolles and others. In 1820, British industrialist Nadier produced rubber threads and attempted to use them in clothing accessories. This was the time when America was seized by rubber fever, and the waterproof footwear used by the indigenous peoples became a success. Waterproof fabrics and snow-boots were produced in New England.

In 1832, the Rosburg factory was set up. Unfortunately, cold weather affected goods made from non-vulcanized natural rubber, leaving them brittle and with a tendency to gum together if left in the sun, all discouraging consumers. After a long period attempting to develop a process to upgrade rubber qualities (such as including nitric acid) that almost ruined him, in 1840 Goodyear discovered vulcanization, quite by accident.

An interesting fact: in 1815, a humble sawyer - Hancock - became one of the leading manufacturers in the UK. He had invented a rubber mattress and through an association with MacIntosh he produced the famous waterproof coat known as the "macintosh". Furthermore, he discovered how to cut, roll and press rubber on an industrial scale. He also noted the importance of heat during the pressing process, and built a machine for this purpose.

MacIntosh discovered the use of benzene as a solvent, while Hancock discovered that prior chipping and heating were required in order to ensure that the rubber dissolved completely. Hancock also discovered how to manufacture elastic balls. Finally, in 1842, Hancock came into possession of vulcanized rubber produced by Goodyear, seeking and finding the secret of vulcanization that brought him a vast fortune.

In 1845, R.W. Thomson invented the pneumatic tire, the inner tube and even the textured tread. In 1850 rubber toys were being made, as well as solid and hollow balls for golf and tennis. The invention of the velocípede by Michaux in 1869 led to the invention of solid rubber, followed by hollow rubber and finally the re-invention of the tire, because Thomson's invention had been forgotten. The physical properties of rubber were studied by Payen, as well as Graham, Wiesner and Gérard.

Finally, Bouchardt discovered how to polymerize isoprene between 1879 and 1882, obtaining products with properties similar to rubber. The first bicycle tire dates back to 1830, and in 1895 Michelin had the daring idea of adapting the tire to the automobile. Since then, rubber has held an outstanding position on the global market.

As rubber is an important raw material that plays a leading role in modern civilization, chemists soon became curious to learn more about its composition in order to synthesize it. In the XIX century, work focused on this objective, soon discovering that rubber is an isoprene polymer.

The Russians and the Germans broke fresh ground in their efforts to synthesize rubber. But the resulting products were unable to compete with natural rubber. It was only during World War I that Germany - pressured by circumstances - had to develop the industrialized version of this synthetic product. This was the springboard for the massive development of the synthetic rubber industry all over the world, producing elastomers. (EH.NET)

2.2.2. Rubber plantation in Bangladesh

Rubber plantation is a highly land-intensive undertaking so that in Bangladesh which has severe land constraints, only those pieces of land which is not used for production of food can be made available for rubber cultivation. An attempt was made early in the 1960s to examine whether rubber plants would grow in the hilly regions of Chittagong district. Encouraged by the initial success of the trial, a more systematic cultivation project was undertaken as a pilot programme during the 1980s with experimental plantations having been established in Chittagong and Sylhet districts and in the Madhupur forest. Results of this particular study are yet to be fully evaluated. Commercial cultivation of rubber in Bangladesh as import substitute, therefore, still remains as an unresolved issue, but rapid depletion of arable land because of growing population pressure and resort of farmers to reclaim marginal land for food crop production, are the factors that have to be considered seriously in an objective assessment of the issue of whether rubber cultivation can be an economically viable undertaking for Bangladesh. (Banglapedia, BFIDC)

Rubber plantation a farm or large piece of land where rubber plants are grown. Usually rubber plants are cultivated as rubber plantations in specifically maintained rubber estates. The plant is a medium-sized tree with a slender trunk and thick green foliage. About 250 trees can be planted in one hectare of land. Yield of rubber varies with plant types the yearly average yield is about 500 kg rubber per hectare or 2 kg per tree, but there are high-yielding varieties of rubber plant that produce as much as 2,200 kg per hectare per year.

Rubber plantation attempts in Bangladesh are a story of mixed success. The tropical climatic conditions of Bangladesh, with high rainfall during the summer months, were thought to be congenial for rubber plantation. However, because rubber plantation is a relatively land-intensive undertaking, and Bangladesh does not have enough prime land to dedicate for this enterprise, it was decided during the Pakistan time to explore whether some of the marginal land available in hilly regions of the country, could be experimentally explored.

In parts of Chittagong forests, experimental rubber plantations were initiated in the early 1960s. The trial plants did grow well in local climatic conditions and the initial results were encouraging, but the activity could not be extended in more productive directions because of the intervening period of Bangladesh war of independence. Serious attempts towards rubber plantation were again undertaken after Bangladesh earned its independence in 1971. Thus, in 1980 the Government took the policy of producing rubber as import substitute for which the Asian Development Bank came forward with financial support. At this time there were already about 5,100 ha of rubber plantation in the country and the new programme included the creation of another 5,048 ha of rubber estate. These rubber plantations were managed by the state-owned Bangladesh forest industries development corporation (BFIDC). The operation of the project continued for about a decade largely as a pilot project to examine commercial feasibility of rubber production in Bangladesh. Results of this study are being evaluated and initial indications are that the project has failed to perform as per expectations. In the Madhupur forest area, out of a total plantation of 2.5 million saplings planted in 1987, only about 1.5 million survived as of 1999. The plants have now reached tapping stage, but the entire plantation area is so barren because of negligence in management and human interference that there is little incentive to go for tapping because very little output is expected.

It is believed that from well-managed rubber plantations comprising 11,000 ha of marginal land, about one m ton of dry rubber per hectare (total 11,000 m tons) could be produced per year in the country under optimum conditions. But the cost of good management of the rubber estates and the price of the product relative to international market price appear to negate any bright future for rubber production in Bangladesh. One factor which substantially contributes to this negative projection is that because of severe land constraints (currently 130 million people in a total land area of about 148,000 sq km), it is highly unlikely that the volume of rubber production could be increased substantially by increasing acreage for rubber plantations in order that the scaling up of the production might make the product more cost-effective and competitive. It is at present being seriously considered whether rubber cultivation can be a worthwhile economic activity for the country. (Banglapedia, BFIDC)

2.2.3. Rubber Estates under BFIDC: Lists of Rubber Estates under BFIDC with their total area, year of establishment and year of latex production are given below:

Table: 2.1. Rubber estates under BFIDC (Source: BFIBC)

Name and place	Total area (ha)	Year of establishment	Year of production
Rumu Rubber Estate, Rumu, Cox's Bazar.	850.20	1961	1968
Raojan Rubber Estate, Raojan, Chittagong.	546.15	1961	1968
Dauba Rubber Estate, Raojan, Chittagong.	855.47	1969	1976
Holudia Rubber Estate, Raojan, Chittagong.	901.21	1981	1990
Kanchannagor Rubber Estate, Ftikchachari, Chittagonj.	976.52	1982	1990
Tarakho Rubber Estate, Ftikchachari, Chittagonj.	986.23	1982	1990
Dantmara Rubber Estate, Ftikchachari, Chittagong.	1680.57	1968	1976
Rupichora Rubber Estate, Bahubol, Hobigonj.	786.23	1977	1988
Satgaon Rubber Estate, Srimongol, Moulovibazar.	789.07	1971	1979
Shajibazar Rubber Estate, Madhobpur, Hobigonj.	834.00	1979	1989
Bhatere Rubber Estate, Kulaura, Moulovibazar.	1045.34	1965	1972
Pirgacha Rubber Estate, Madhupur , Tangail.	1175.62	1987	1995
Chadpur Rubber Estate, Madhupur, Tangail.	962.75	1989	1997
Sontoshpur Rubber Estate, Madhupur, Tangail.	419.25	1994	2001
Komolapur Rubber Estate, Madhupur, Tangail.	402.26	1994	2001
Karnajhora Rubber Estate, Madhupur, Tangail.	250.90	1995	2002

2.2.4. International Natural Rubber Development Organizations

IRRDB=International Rubber Research and Development Board (England)

ANRPC=Association of Natural Rubber Producing Countries (Malaysia)

IRSG=International Rubber Study Group (England)

INRO=International Natural Rubber Organization (Malaysia)

IRQPC=International Rubber Quality and Packing Conference (USA)

2.2.5. Latest International Rubber Statistical Bulletin

International Rubber Study Group (IRSG) publishes data on production, consumption, trade and prices – covering both natural rubber (NR) and synthetic rubber (SR) – on a quarterly basis in its flagship documents, the Rubber Statistical Bulletin.
Table: 2.2. Natural rubber production (tons)

Region	Year
	2006	2007	2008
Latin America	202	228	241
Africa	423	445	443
Asia	9331	9386	9406
Total	9698	9707	9876

Table: 2.3. Natural rubber consumption (tons)

Region	Year
	2006	2007	2008
North America	1148	1157	1179
Latin America	528	565	562
European Union	1302	1377	1189
Other Europe	252	273	255
Africa	120	118	112
Asia/Oceania	5961	6391	6453
Total	9329	9884	9726
World stocks	2330	2154	2172

Table: 2.4. Natural rubber prices (tons)

Region	Year
	2006	2007	2008
Europe, TSR20 €/ton	1646	1619	1772
SICOM, RSS3, S$/ton	3344	3444	3685
New York, TSR20, US$/ton	2113	2321	2729

Source: International Rubber Statistical Bulletin, International Rubber Study Group (IRSG)

2.3. Prospects and Uses of Rubber

It should be mentioned here that, natural rubber is the raw material for tyres and tubes of automobiles, bi-cycle and rickshaw, footwear, belts and hoses, latex foam, cables and wires, battery boxes, gloves, coats and aprons, air bags, life jackets and life buoys, adhesives, balloons and toys etc. and it is also essential for processing synthetic rubber. Therefore, the future of rubber is very bright.

Besides rubber, rubber plants have many other uses e.g.:
1. Timber: After economic exploitation of rubber for about 30 years its timber will be a good source of furniture timber.
2. Rubber seed oil: Rubber seed kernel is used for extraction of oil, which is abundantly used as lubricant, and for soap and paint industries and the cake as a good fertilizes and poultry feed.
3. Honey: Mature rubber plantations are the potential source of honey. Honeybees collect large quantities of nectar from extra floral nectarines at the swollen tip of the petiole.
4. Affluent or latex processing wastes and residues can be used as fertilizer and making biogas for power.
5. Land improvement: Every year fallen leaves add 6 to 7 tons per hectare of biomass. Moreover, rubber roots make a very good net spreading in the top soil up to a depth 1 to 1.5 m and increase the porosity of the soil.
6. Carbon sink: Rubber is a very preferred fast growing multipurpose species for quick afforestation. It acts, as a good ‘carbon sink’ will be helpful in reducing global warming.
7. Ecofriendliness: Rubber plantations have a green image and are inherently environment friendly. Properly managed plantations are self-sustainable ecosystems and could maintain a fair degree of biodiversity. Rubber plantations do support different plant species.

8. Maximum utilization of land: Unproductive and marginal lands are taken into rubber cultivation. Barren lands as well as scrap forests are being put into rubber cultivation.

9. Maximum utilization of labour: A lot of people are required temporary or permanent basis. It helps to reduction of unemployment to a great extent and uplifting the socio-economic condition specially the rural people.

10. Aesthetic value: A rubber garden having a nice beauty may have aesthetic value which is enjoyable to the visitors. (Kamal, M.T. 2003)

2.4. Yield and productivity of rubber

A well-managed plantation in the traditional zone can produce 3 tons rubber per hectare. The average yield of rubber is about 1.6 tons in India. But in our non-traditional condition we have achieved about 0.5 ton/ha only. Unfortunately, the industry suffered badly in the last decade with the decreasing price in the international market, and import of low priced natural and synthetic rubber through free market economic policy. Moreover, low productivity due to lack of proper cultural practices and appropriate processing facilities aggravated the situation further more. New investment for extension of plantation and maintenance of existing plantations was becoming discouragious.

For development and expansion of rubber, systematic research and protection of market price were not done. As a result, the industry became a loosing concern and thousands of workers were not getting wages in time. Plantation investment, expertise and skillness, and dependency on the job were in a serious position. The rubber industry was facing destruction although there was a great demand for NR in Bangladesh. In this situation, the government should take necessary measures to save the plantation industry considering its contribution in land utilization, afforestation, and development of environment and in national economy. Nevertheless, a huge investment of foreign currency from Asian Development Bank (ADB) and World Bank was made for the industry.

However, the situation has been changed now, the price of rubber has been increased at least three-folds, at a very encouraging level. Now rubber is one of the most profitable commodities in the present market. Therefore, it is the right time to think forward for further development revising the policy and rectifying the faults through applied research and appropriate technology to achieve highest productivity and profit. (IRRDB,2009)

2.5. Future of rubber

A good day is waiting for rubber crop within a very near future. It is well-established fact that natural rubber is superior to synthetic rubber in all respects. In consideration to environment, health and safety, bio-degradation and waste disposal factors it is also more acceptable. The tyre industry is the largest consumer of natural rubber and its demand is increasing with the increase of wheeler vehicles. The demand of natural rubber is increasing at the rate of 3% annually (20 years average), and the gap between supply and demand will be widen more than 7% by 2005 and 19.2% by 2010 (Peyman, 2003). Moreover, the three major rubber-producing countries, Malaysia, Thailand and Indonesia are encouraging to replanting rubber areas with oil palm as the current low price of rubber in the world market. Effectively it would take 10 to 15 years of consistent replanting and new planting to enable supply to catch up with demand. Hence, it is predicted that rubber could see a decade of higher prices, which is estimated at least double of the present market price.

For sustained growth of a plantation industry the positive margin between the cost of production and the sale price of the products is mandatory. Otherwise the effect will be negative. It will also affect the national economy as the initial investment, maintenance before and after maturity and other cost in management of a garden e.g. in employment, disaster recovery, productivity etc. will be a poor show in such a loosing concern. Although price of rubber was very low in the international market, which influenced the domestic market price earlier but now the problem no more, exists; still there must be some sort of mechanism or regulation to control the domestic market price to protect the plantation industry. As a plantation crop, there is no permanent or continuous crisis, but thinking all other aspects: like timber, environment, soil and improvement etc. domestic price control by the government is essential to save the plantation industry and to fetch the good price of rubber in the coming days by improving the yield and quality, meeting the country demand and exporting quality rubber. (IRRDB,2009)

2.6. Potentiality of rubber production in Bangladesh

Bangladesh targets doubling its natural rubber production to 60,000 tones a year by 2020 to tap the growing potentials in its export market on meeting domestic demand, industry people said. Currently, the country has a capacity to produce about 30,000 tones of rubber a year, but some 10,000 tones were produced in 2007 because of the limited market demand. The production target has been set at 16,000 tones for 2008. There are 1,300 rubber gardens across the country. “We need to ensure quality to export the item to the developed market where the use of rubber is growing rapidly,” said Motahar Billah Chowdhury, vice president of Bangladesh Rubber Garden Owners' Association. He blamed negligence of the successive governments for not yet entering into the multi billion dollars export market. However, Commerce Adviser Dr Hossain Zillur Rahman said on Monday that Bangladesh had opened up rubber trade with Turkey, which is trying to get certificate for Bangladesh's rubber from renowned Japanese tyre maker Bridgestone. “Bridgestone's certification may take the Bangladeshi rubber industry to a new height,” Hossain Zillur said. Bangladeshi rubber is less costly than the imported one. One kilogram of locally produced rubber costs Tk 110-120, while it is Tk 200 for the imported rubber. Natural rubber is an elastic hydrocarbon polymer. It is used extensively in many applications and products. It can also be synthesized. The scientific name of the rubber tree is Hevea brasiliensis.
Around 25 million tones of rubber were produced in 2007, according to global statistics. Of which, around 42 percent was natural. The bulk of the rubber produced is the synthetic variety, which is derived from petroleum. Asia is the main source of natural rubber today, accounting for around 94 percent of output in 2005. The three largest producing countries are: Indonesia, Malaysia and Thailand -- together account for around 72 percent of all natural rubber production. Rubber garden owners said they are producing the item traditionally with layman farmers. They said the government has not done anything to develop the industry despite repeated requests.
“Government has neither set up any administrative wing to help the sector, nor formulated any policy for the industry,” Motahar Chowdhury said.
Garden owners have been pressing the government to formulate a policy since 1995. Rubber production in the private sector was allowed since 1980-81. Still the government owned forest department is the leading rubber producer in the country with annual production of over 3,500 tones on more than 32,000 acres of land. According to industry people, as many as 10 people are employed in every 25 acres of rubber land. (The Daily Star, 15/10/2008)

2.7. Rubber Cultivation

The rubber is propagated by seeds or vegetatively by budding or by a combination of both. Fruits burst open when ripe and the seeds are scattered up to 33 m from tree. Seeds gathered and sown fresh as they lose viability rapidly (only 7–10 days), extended to 4–6 weeks, if packed in charcoal powder or sawdust with 15–20% moisture in special containers. Buds collected from seedling trees used for budding. Area to be planted to rubber trees is cleared, then lined and marked for roads and drainage. Planting pits are dug, 75 x 75 x 75 cm, or 90 x 90 x 90 cm, and filled with surface soil and manure. Seedlings are raised in nurseries or directly in the field. Seeds germinate in 1–3 weeks, depending on climatic conditions and freshness of seed. Seedlings are 1–1.3 m tall in 6 months. About 100,000 plants/ha is average for a seedling plot, of which 60,000 to 70,000 should reach standard pulling size in 10–15 months. Then plants are uprooted, the stem cut back to 45–60 cm, the taproot 45–70 cm, and the lateral roots to 10 cm. Seedlings make good cuttings but rubber-bearing trees take very poorly or not at all. Transplanting to field is done during monsoon. Tapping stands of 250–300 trees per hectare are recommended, obtained by thinning bud wood densities of 375 to 450 or seedling densities of 500 to 600. Wider spacing might be used, intercropping coffee or cocoa, perhaps in conjunction with ipecac. A fodder crop such as Cajanus, might be tried for lac production, instead of the usually recommended cover crops (Centrosema, Calopogonium, Flemingia, Pueraria, Psophocarpus). After a few years under legumes, no N fertilizer may be needed, but phosphorus, magnesium, and potassium may be limiting in some areas. Potassium deficiency is frequent in Vietnam (Reed, 1976).

2.8. Plantation and Management

2.8.1. Factors of rubber plantation

There are two important factors which are considered for the plantation of rubber. These are;

1. Climatic factor
2. Edaphic factor

Climatic factor: This factor includes,

1. Rainfall
2. Temperature
3. Natural range

Rainfall: Hevea brasiliensis is a tropical tree, growing best at annual rainfall of 1,800-2,000 mm. Excessive rainfall interferes with tapping and collection. In case excessive rainfall, proper drainage facilities should be provided. Drought is also a serious problem, although it is probable that Hevea could be cultivated with irrigation.

Temperature: Hevea brasiliensis grows best at temperatures of 25-35°C and excessive temperature is unfavorable for its growth. The minimum survival temperature is 8-10°c. Prolonged periods of low temperature lengthen the time for trees to reach maturity. Some clones developed on Hainan Island are capable of surviving temperatures as low as -1°C. Tapping panels are sealed or dressed during winter.

Natural range: It grows satisfactorily up to 600 meters above sea level. Its required temperature and rainfall define its prime growing area as between the 10° latitudes on either side of the equator, but its actual extent is much greater.

Hevea is indigenous to the Amazon Basin where it grows within 5° of the equator. Thus the traditional rubber growing areas have tended to lie within 10° north or south of the equator, but various factors have extended this range to 29° north in China, India and Myanmar.

Edaphic factors: This factors includes,

1. Soil
2. Drainage system
3. Topography
4. Slope

Soil: Hevea is relatively insensitive to soil-type, but higher yields and disease resistance can be expected if it is grown on highly fertile soils. It does not grow in stony, snowy, desert soil. Well drained loamy soil in the low hill of 16-30° slopes is suitable. The soil must be of good aeration and water holding capacity and the p^H range4-6.5.

Drainage system: Good drainage system is required for rubber cultivation. The soil in which the water level is less than 1000cm or where the water logging is in permanent condition is not suitable for rubber plantation.

Topography: In south Asian countries, rubber can be found growing in granite, limestone and stone containing soil. It grows satisfactorily up to 600 meters above sea level and it can be grown on the plains near the sea level an up to an altitude of 1000ft.

Slope: Well drained loamy soil in the low hill of 16-30° slope is suitable and their should have terracing system. (Khisa, 1991).

2.8.2. Raising a rubber nursery

Various steps which are followed in raising a rubber nursery are given below:

Site selection:

The site should be well drained and more or less flat (0-3% slope) or undulated (3-8%) hilly land and it should be north-south facing and water table should not less than 75 cm. The soil should be fertile, loamy and rich of organic matter. The site should have perennial source of water such as lake, pond, stream etc, (Khisa, 1991).

Site preparation:

All the vegetation or weeds should be cut and allowed to dry up to 7 weeks and then burnt to ashes. Too make the soil granular all remaining stumps, debrises and roots of small plants should be uprooted and then ploughed two times and laddered one times. (Khisa, 1991).

Germination bed:

It is special type of bed where the seeds germinate first before putting the seeds in the nursery for getting a uniform stand in the nursery. Requirements for germination beds are,

The usual size of the bed is 40'-4'; it is the convenient size of the bed.

15000-16000 seeds are sown in a bed. (Khisa, 1991)

Sowing:

Seeds are sown in the germination bed 2"×2" apart. Seeds should be sown in such a way that the round portion of the seed at the upward and the plain portion at the downward and then a thin layer of sand should be spread over it so that the dorsal part of the seed is somewhat visible. Watering should be done and after watering again a thin layer of sand must be spreaded. Germination starts with in 7-10 days after sowing and maximum germination takes place within 14-21 days (Khisa, 1991)

2.8.3. Types of nursery: Generally there are tow types of nursery, these are;

1. Poly bag nursery
2. Ground nursery

Poly bag nursery:

At first collect the top soil and mix T.S.P and N.P.K with the soil. After some days filling of poly bag is done by these soil.

The size of the poly bag is 20 inch-12 inch and color of the bag is black. Each bag having at least 12pores at the bottom and filled with 9 kg fertile loamy or sandy loamy soil provided with 2-5 cm vacant at the upper side to make watering and fertilizing easily.

The seedlings are transplanted in the poly bag and manuring is done in a systematic way so that fertilizer is not contact directly with the stem. The task of applying fertilizer is done four times;

The ratio of fertilizer is, T.S.P:M.P: Urea is 3:2:4.

The time frame of applying fertilizer is;

1^st dose after 21 days,

2^nd dose after 42 days,

3^rd dose after 70 days.

After manuring a thin layer of soil should be added and watering is done twice a day.(Khisa, 1991)

Ground nursery:

In this case seedlings are directly raised in the nursery ground in stead of poly bag. Besides this there are many types of nurseries, these are:

• Bud bank or multiplication nursery,
• Budded stump nursery,
• Stump budding nursery.

2.8.4. Planting materials

1. Seeds
2. Green bud stick
3. Brown bud wood
4. Budded stump.

2.8.5. Protection:

For protection purpose fencing is done for protection against rats, squirrels, porcupines etc. A belt of one chain all around the nursery should be cleared by cutting the jungles to avoid harboring of insects. As a precautionary measure insecticides may be used on the beds drains before sowing the seeds in the germination bed. BHC powder 13% solution has given good result.

When the environment is very cold and heavy rain fall occurs, the seedlings are susceptible to attack by various pests, for that reason anti fungal can be used for the protection.

A mixture named Bordeau mixture, which gives better performance as an anti fungal treatment. For the preparation of this mixture Calcium sulphate and Copper sulphate are mixed in proportion of (2:1) .At first Copper sulphate is mixed with Calcium sulphate. This mixture shoes sky color and spray this solution for the better performance. (Khisa, 1991)

2.8.6. Maintenance:

To get sound and healthy seedlings the best possible maintenance is essential such as,

1. Regular inspection of nursery,
2. Watering during the dry season,
3. Weeding and clearing,
4. Proper management of pest and diseases and
5. Manuring and fertilizing

2.8.7. Plantation:

The plantation is done through some steps. These are:

Site selection: The selected site should have proper drainage system and water logged area should be avoided.

The selected area should at first surveyed carefully and a map showing the of natural drainage such as stream, nalla etc. All artificial drain should be connected with it and the site should away from public activities and soil is free from rock. (Khisa, 1991)

Site preparation: The selected area should be cleared at the last part of December and burnt within February to march. Burning should be done at noon. Burning is the first step in rising good plantation. After clearing the burnt debris it should be put as cover crops to protect the top soil for washing off and to maintain the normal temperature of the ground.

On flat or gently undulated ground square and rectangular planting is normally done. The planting line should be north and south so that the plants get maximum sunlight. (Khisa, 1991)

Contour lining: Contour lining is carried out in case of hilly site. This done in the following way;

• A base line is first fixed joining the pick and base of the hill.
• Guide poles are staked on this base line at 9m interval.
• Contour lines are determined with respect to the position of the guide pole.
• After contouring spacing stakes are fixed and
• Along with contour lines, hill slope is cut in the form of stairs and hoes are made for planting rubber seedlings. (Khisa, 1991)

Terracing: When the slope is comparatively more then terracing is necessary to protect the soil and to make easier the collection and carrying of latex. Width should be 100-180 cm and cut materials should be fixed down at the face of the terraces. (Khisa, 1991).

Holing: It is done before one month of the plantation of seedling. They should be in general 60cm×60cm×45cm. For budded stump and poly bag seedlings the size is 45cm×45cm×60cm and for large size stump budding seedlings the size is 60cm×60cm×60cm.

Half of the soil of the holes of the above layer should be kept on one side and the layer of the lower on the other side of the holes. During filling the holes, the soil of the above layer should be on the bottom of the holes while the other soil on the upper surface of the holes.

During plantation of seedlings in each hole 120gm of T.S.P should be applied with in 20cm depth.

2.8.8. Planting materials: The planting material varies from material to materials:

1. Planting seeds: Seeds must be already germinated and needle like sharp stick is used to make holes. Distance between two holes should be 15cm and in each hole 3 seeds should be planted and the roots of the germinated seeds must be downward. This system is no longer vogue now.
2. Planting of budded stump and stumped budding: In this stage hole is made by a wood made up sharp stick and depth of holes should be equal to the distance between the lower part of the patch and the root of the seedlings. Mulching is necessary in this stage and it should be 5cm away from the seedling base.
3. Plantation of poly bag seedlings: In this stage before planting the poly bag is cut off and removed .Depth of the hole should be equal or more than the patch length.
4. Planting of large size stump budding: The hole is not previously filled and on the contrary 15 cm more depth is cut for the penetration of the roots of the seedlings. Mulching is essential for making the seedlings alive and growing. (Khisa, 1991).

2.8.9. Raising cover crops: In context to the rubber plantation, cover crop can be defined as the lower class creeping that cover up the surface soil of the rubber estate and restore moisture and quality of the soil. (Khisa, 1991).

The cover crops which are generally used are given below:

1. Pueraria javancia
2. Pueraria phaseoloides
3. Calopogonium mucunoides
4. Calopogonium caerulium
5. Centrosema pubescences
6. Mucuna coccinsinensis

Cultivation procedure: Weeding should be done by using herbicide and V shaped canal should be prepared. Fertilizer should be used and then seeds are sown. If the sowing of cover crops starts at dry season then the seeds should be wetted.

2.8.10. Diseases of rubber trees and their remedial measures

Abnormal Leaf Fall

Causal organisms

Phytophthora palmivora (Butl.) Butl.; P. meadii McRae; P. botryosa Chee

Symptoms

Abnormal leaf fall affects mature leaves. The fungus attacks the petioles causing the leaves to shed while they are still green. The fallen leaves exhibit one or more dark brown lesions with one or two white spots of coagulated latex in the middle of each, usually towards the base of the petiole.

Disease control

The disease can be prevented by one spray of an oil-based copper fungicide before the onset of the rainy season. For aerial application, the application rate is 6kg i.e. copper oxychloride in 35 litres oil/ha. With minimicron sprayers, the rate is 3.5kg i.e. copper oxychloride in 25 litres oil/ha.

Black Stripe

Causal organisms

Several species of Phytophthora have been reported to be responsible for black stripe. The common species are: Phytophthora palmivora (Butl.) Butl., P. meadii Mc Rae, P. botryosa Chee.

Symptoms

The early symptoms of black stripe are not obvious: a series of sunken and slightly discoloured areas just above the cut. Later, vertical fissures appear in the renewing bark; when these are removed, dark vertical lines are visible. As the infection progresses, the stripes coalesce forming broad lesions, finally spreading the full width of the panel.

Disease control

Black stripe can be kept under control during continuation of tapping by regular applications of an effective fungicide provided the disease is detected before infection becomes severe. The recommended fungicides are 0.8% i.e. captafol alternate daily or 0.2% metalaxyl once every four days.

Brown Root Disease

Causal organism

Phellinus noxius (Corner) Cunn.

Symptoms

Brown rusty spots are visible .In addition, if the bark of roots infected with brown root disease is peeled off, the surface of the roots will be seen to be covered with honeycomb-like structures. These structures are also visible inside the infected roots. The fruiting bodies are smaller than is the case with the other root diseases and are hard with dark brown upper surfaces.

Disease control

Proper clearing of land of old rubber is recommended to reduce the incidence of brown root disease. Wounds resulting from wind damage or pruning must be treated with wound dressing especially in areas where brown root disease is known to be present. Collar protectant dressing containing tridemorph is recommended for treatment of infected trees.

Corynespora Leaf Fall Disease

Causal Organism

Corynespora cassiicola (Berk. and Curt.)

Symptoms (for greater detail)

On young yellowish green leaves, brownish small circular lesions with papery centres and surrounded by yellow halos are more prominent. The characteristic symptoms of the disease are seen on mature leaves whereby the lesions are large with dead papery centres often situated along or beside the main veins or smaller veins which are discoloured and form the railway track or fishbone appearance.

Control

In laboratory tests, several fungicides (benomyl, prochloraz, chlorothalonil, propineb, mancozeb, captan) have been reported to inhibit growth of C. cassiicola. Limited field trials indicate that benomyl is the most effective. Good control is achieved only if the weekly spraying is extended for several months, as leaves of all ages are susceptible to the disease.

The best strategy to manage the disease is to plant resistant clones. Clones which are known to be susceptible to the disease should not be planted in regions where the climate is suitable.

White Root Disease

Causal Organism

Rigidoporus lignosus (Imazeki) Klotzsch

Symptoms

R. lignosus infects and destroys the lateral and tap roots. The first visible symptom on the foliage is the change of colour of the leaves to off-green and yellowish. The leaves lack a bright waxy shine, appear leathery and curve downwards unlike boat-shaped healthy leaves.The entire canopies of trees with advanced disease turn yellowish-brown and eventually abscise.

The branches die back and the tree dies. These are white especially at the growing ends, possess many branches and are firmly attached to the surface of the roots.

Control

The incidence of white root disease is reduced if the cut surface of the stumps is covered with creosote to inhibit spore colonization.

Sulphur is applied at the time of planting rubber. Normally, about 150-200g of sulphur powder is mixed with the soil to be used to fill the planting hole or the sulphur can be sprinkled around the plant and immediately forked into the soil.

The trees are treated by pouring an aqueous mixture of the fungicide into a shallow furrow dug around the base of the tree. Triadimefon or propiconazole at 2.5% i.e. are recommended.

Red Root Disease

Causal Organism

Ganoderma philippii (Bres. and P. Henn) Bres.

Symptoms

The general appearance of the foliage of a tree infected by red root disease is similar to that of white root disease. Normally, the surface of roots infected by red root disease is coarse, as it is covered with a strongly attached layer of sandy soil particles. After washing, a layer of reddish-coloured mycelia is visible on the surface of the roots.

The fruiting bodies are large with dark-brown corrugated upper surfaces, whitish lower surfaces and creamy white edges.

Disease control

Cultural practices

Proper land clearing and planting of creeping legume covers as prescribed to reduce the incidence of white root disease are also beneficial in reducing the incidence of red root disease. Mechanical clearing is especially effective compared to with other clearing methods.

Chemical treatment

No fungicide has yet been recommended for application by soil drenching for the treatment of the disease. In Malaysia and several other countries, the disease is treated by applying collar protectant dressing containing tridemorph.

Pink Diseases

Causal organism: Corticium salmonicolor Berk. & Br.

Symptoms

The initial symptom is the exudation of drops of latex from infected bark which drip or run along the stem. Later, white silky threads of mycelium develop on the surface of the bark forming a "cobweb". Under favourable conditions, the lesions turn light pink in colour with more intense bleeding of latex. The infection may spread up the branches and down the main stem of the tree causing the foliage above the point of infection to wilt and die.

Disease control

Weekly spraying with Bordeaux mixture is recommended. The Bordeaux mixture is prepared by mixing 1kg of copper sulphate, 2kg of slaked lime and 100 litres of water. The mixture should be used immediately. Bordeaux mixture must be applied as long as the disease is apparent. Other fungicides which can be used against pink disease are chlorothalonil and thiram. Chlorothalonil at 3% can be sprayed fortnightly. Chlorothalonil and thiram can also be formulated in bitumen or other base and applied by brushing. (IRRDB,2009)

Brown bast diseases

It is a diseases or physiological disorder of the bark of the tapping panel or latex vessel which is caused by frequent tapping. It means the brown basting of latex vessel.

Symptoms: Latex production may increase suddenly but the amount of dry rubber content (DRC) is reduct. In some cases latex dripping takes place.

After a few days, only small portion of the tapping panel remains productive so latex production decreases considerably. If further tapping is done, the tapping cut becomes fully dried and ultimately no latex is produced. If the bark is pleed off brown discoloration is found. Ultimately tapping becomes difficult due to basting of tapping panel (Khisa , 1991)

Disease control: It may be prevented by two systems such as, per tapping separation system and post tapping separation system. These are effective methods to reduce the spreading this diseases along the panel (Khisa, 1991)

2.9. Production of rubber

2.9.1. Tapping

The method of collecting latex from a mature rubber tree by controlled cutting operation is called tapping.

It consists of paving off a small strip of bark just sufficient to open up the end of the latex vessels, which present in the inner part of the bark. If 75% trees are able to produce latex then this operation is being done. Latex production starts at the age of 7-8 years after plantation and continue up to 30 years. In another word tapping cut starts when the girth of the tree reaches to 18-20" at the height of 5 feet (75 cm) .Ultimately tapping becomes difficult due to basting of tapping the tapping cut, for this reason rubber tree is not tapped every day .(Khisa, 1991)

A tapper starts the trek around the plantation before dawn. At each tree a sharp knife is used to shave off the thinnest possible layer from the intact section of bark. The cut must be neither too deep, nor too thick. Either will reduce the productive life of the tree. This starts the latex flowing, and the tapper leaves a little cup underneath the cut.

2.9.2. Techniques followed during tapping

Direction and slope of tapping cut:

Cut: For the seedling originated and budded trees the cutting direction should be spiral cutting from the upward at the left hand side to the downward at the right hand side in a slanting manner. (Khisa, 1991).

Slope:

Foe the seedling originated trees tapping cut should be 25° angular with the horizontal stripe due to thicker bark. For the budded trees tapping cut should be 30° angular with the horizontal strip to get maximum latex due to thicker bark. (Khisa, 1991).

Height of the tapping cut:

For seedling originated tree 50cm-75cm or 20"-30" from the ground due to higher rate of tapping. But for the budded trees 125cm-150cm from the bud patch. Tapping starts when the girth of plant reaches minimum 18" at the height of 40-50". (Khisa, 1991).

Census of tapping ability:

For the seedling originated and budded trees generally tapping operation is not done in a rubber garden until the 70-80% trees are able to produce latex or attain the tapping ability. (Khisa, 1991).

Marking of tapping place:

To mark the tapping cut place at actual height and slope, a temp let should be made by placing a 5cm wide width metal foil at one end of a stick angularly and at the angular point the tapping cut should be made. (Khisa, 1991).

Depth of tapping cut:

Most of the latex vessels are present under the bark just near the cambium. So to collect the highest possible amount of latex, the depth of tapping cut should be as much as possible near the cambium and care should be taken not to disturb the cambium and for this it is better to not to cut 1mm bark out of cambium.(Khisa, 1991).

Tapping time:

The higher production is obtained when tapping is done at dawn. It is better before sunlight because at that time the transpiration remains stop and the cell of the tree remain fully turgid. Due to turgid pressure flow of latex remains high. (Khisa, 1991).

Tapping knife:

Tapping knife should be sharp enough to cut smooth and width should be such that it can remove the required amount of bark at a time.

2.9.3. Tapping procedure:

Generally there are two types tapping systems, these are:

For seedling originated trees the tapping system is,

½ S d/3 ↓

Where,

½ S =One half spiral tapping cut,

d/3=Tapping frequency every third day,

↓ =Downward tapping.

In this case 1.5 mm bark is removed.

For the budded trees the tapping system is,

½ S d/2 ↓

Where,

½ S =One half spiral tapping cut,

d/2=Tapping frequency every alternate day,

↓ =Downward tapping.

In this case 1.5 mm bark is removed. (Khisa, 1991).

2.9.4. Precaution in tapping

1. Remove the rubber chips from the tapping cut place and cup before tapping to avoid pollution of latex
2. Neat and clean tapping procedure should be maintained
3. To use anti coagulant to maintain the liquid condition before transferring the latex to the factory. (Khisa, 1991).

2.9.5. Sheet rubber manufacturing

After collection of latex the following steps are involved in converting the collected latex into dry rubber sheet:

First straining: straining is the process of filtering of unwanted materials such as coagulated latex, leaf, bark, insects etc. from the collected latex. For straining 1/6 perforated net are used which are spared from centre to centre. (Khisa, 1991).

Determination of DRC: The first requisite in standardizing the factory processing, is ti dilute the latex to a standard consistency. Two methods are used in determining the content of latex.

These are:

1. Chemical analysis
2. Hydrometer method. (Khisa, 1991).

Dilution and second straining:

Dilution: After calculating the dry rubber content latex is diluted to make 12-15% but it may be up to 20% concentration. This is done by adding water to the collected latex. The required amount of water is measured by using the formula:

Required water = (Volume of latex ×DRC)/Desired DRC

Second straining: After dilution the impurities are removed by second straining. (Khisa, 1991).

Coagulation: After dilution the diluted latex is then reserved in a tank called coagulation tank. The dimension of the tank is 6.5 ft in length, 3ft wide and 1ft height. It is also called pan. At first latex keep in a tank and water is mixed with the latex by maintain the same ratio.

To enhance the coagulation process different types of coagulants (acids) are added to the tank. The coagulants are generally acetic acid or formic acid. Solid acids are not used but they are used by making solution of 4% concentration. High concentrated acids are acids should not be used because it hardens the latex.

1.25 ml of formic acid is used /liter of latex. P^H paper is also used for the determination of ammonia level. If the level of ammonia is high the amount of formic acid will be high.

Then the latex is stirred by the partition plate. When acid is added on latex some forth appears at the top surface and coagulation it appears as bubbles on the upper surface. It reduces the quality of rubber. So forth should be removed. Then the partition plates are set in the tank.

The acid should be mixed with latex properly and thoroughly and after mixing it is generally coagulated within 6-8 hours.

Unsmoked sheet (USS) preparation: The thickness of each coagulated sheet will be the equal to the thickness to the thickness of the compartment, between two steel plates. After six hours this rubber sheet is obtained and passed through different rollers to prepare the rubber sheet. Rolling is done five times. Generally the thickness of the coagulated sheet is 8mm but when it is passed through rollers the thickness becomes 2.25mm. Rolling also ensures rapid drying of rubber. (Khisa, 1991).

Ribbed smoked sheet (RSS) preparation: The USS Sheets are then washed away by water and then these are hanging in trolly for natural drying for 2-4 hours. After natural drying the sheets are put in a closed smoke chamber for smoking for three days. The duration of temperature is;

35-40 for the first day

40-50 for the 2^nd day and

60-65 for the 3^rd day.

These sheets are called RSS sheet.

2.9.6. Grading and packing:

Grading of rubber refers to putting them into different strata or grades based on their qualities.

Grading of rubber or RSS is done on the basis of the following criteria of the sheets,

• External appearance
• Dust present on the exposed surface of rubber
• Bubbles present on the surface of sheet
• Presence of other substances such as sand, bark, fungi etc.

International grades:

On the basis of above criteria rubber mainly has 5 international grades.

• Grade-1: This grade holds the rubbers that have no defects.
• Grade-2: Bubbles present on this rubber surface.
• Grade-3: All the qualities of grade -2 and small bubbles along with the edges.
• Grade-4: All the qualities of grade-3 and small bubbles arranged in a cluster from through out the sheets.
• Grade-5: All the qualities of grade-4 and irregular small bubbles all over the sheet and large bubbles all over the surface. (Khisa, 1991).

2.9.7. Packing: Packing of rubber includes putting it into bundles in the form of bale. The size of the bale should be 53cm48cm48cm and weight ≤111.1o kg. Each bundle or bale should consist of the rubber belonging to more than one grade. In the same bundle different grades should be marked separately. (Khisa, 1991).