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Seasoning and Preservatio of RUBBER WOOD By N.KANAGARAJ BSF-06-007 BSC[FORESTRY]

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Rubber Wood belongs to refractoriness to seasoning class ‘B’ of IS:1141-1993 freshly cut, moisture content of the timber will be above 60 % . Rubber Wood contains tension wood , The final moisture content will be 10%. The drying time is dependent on the timber thickness. Rubber Wood Standard Name :Rubberwood Botanical Name :Hevea brasiliensis Family :Euphorbiaceae

Anatomy : 

Anatomy wood is fairly even with a moderately straight and slightly interlocking grain It is whitish yellow when freshly cut, but the wood turns to light brown during drying The wood is soft to moderately hard with an average weight of 515 kg m-3 at 12% moisture content. The length of the fibres is more than 1.0 mm

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The tension wood may vary from 15 to 65%. sapwood is not differentiated from the heartwood, which is pale cream in colour, often with a pink tinge. Fresh wood contains 1 to 2.3 percent free sugars and 7.5 to 10.2 percent starch.

Major problems : 

Major problems in rubber wood utilization is its low durability In natural state, rubber wood is highly susceptible to insect and fungal infestations due to its high starch content. Additionally, the moisture content of timber provides conductive conditions for the entry and establishment of the fungus

Processing of rubber wood : 

Processing of rubber wood Processing of rubber wood essentially include sawing, preservative treatment, seasoning and wood working operations. As received from field the logs are about 270 cm long with girth ranging from 80 to 100cm. Due to the absence of heart wood - the durable and usable part of the wood - rubber wood is susceptible to the attack of fungi and insects. Immediately after felling, to improve the durability of the wood, preservative treatment with suitable preservative chemical is carried out.

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It is important to say that preservative treatment is meant only for improving the durability. It dose'nt change the anatomical structure, strength, shape or any other property of wood.   The structure of the vessels in rubber wood permits easy and effective preservative treatment. Rubber wood belongs to the treatability class ‘b’ and durability class III

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Rubber Wood contains tension wood and hence seasoning is carried out with utmost care at controlled conditions of temperature & humidity so that the drying takes place uniformly throughout the entire charge. The final moisture content will be 10%. The drying time is dependent on the timber thickness.

Types of seasoning : 

Types of seasoning kiln drying Vacuum drying Air drying Super heated stream drying

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Planks about 25 mm thickness air drying- 55 to 60 days kiln drying -6 to 7 days solar kilns drying -15 days

Air drying : 

Air drying Air drying of green timber is done in the open: the timber is stacked under cover in a way that enables free air to pass through the stack. material above 10 cm in thickness must be air dried first to bring down the moisture content to about the fiber saturation point

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The treatment process will alter the color scheme to light straw or light brown The timber seasons fairly rapidly with bowing and springing as the main defects. 13 mm thick boards take 2.5 months to air dry while 38 mm thick boards take 3.5 months.

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Air drying

Vacuum drying : 

Vacuum drying This drying technique works on the principle of lowering of the boiling point of water and the subsequent generation of an over pressure within the wood. This pressure gradient causes an acceleration in the internal liquid migration rates, enabling water to be driven off efficiently from the wood.

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Vacuum drying


KILN-DRYING Kiln Schedule D is recommended.   25 mm thick boards can be dried in approximately 6 days. Main defects are bowing, springing and end-splitting. Radial shrinkage averages 0.8% ,tangential shrinkage averages 1.9%.

Wood drying kiln : 

Wood drying kiln

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Kiln Schedule D

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Fresh wood contains 1 to 2.3 percent free sugars and 7.5 to 10.2 percent starch.

Vacuum pressure impregnation : 

Vacuum pressure impregnation Treatment of seasoned timber on a regular basis for lyctine The levels of boron needed to control lyctines are relatively low green or partially seasoned hardwoods can be treated by VPI. Vessels usually empty of fluid soon after a tree is felled so can be filled with boron treating solution while the timber is still green, boron can then diffuse into the surrounding damp timber

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VPI is probably the most effective, easiest and most widely adopted method for shortening diffusion times (Lloyd and Manning,1995). It has been used extensively to treat rubber wood

Super heated stream drying : 

Super heated stream drying Drying conditions The drying temperatures tested were 60, 70, and80°C. Superheated steam at 110°C was injected prior to drying, after 4 hours of drying, and after 12 hours of vacuum drying. Since it takes about 10-15 minutes for the saturated steam to reach fully superheated condition, moisture is added to the wood surface which helps to relieve the stress and to keep the cell pores Open.

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Duration: 1 Superheated Steam at 110°C 1 hour 2 Vacuum at 67 cm Hg 4 hours 3 Superheated Steam at 110°C 1 hour 4 Vacuum at 67 cm Hg 8 hours 5 Superheated Steam at 110°C 1 hour 6 Vacuum at 67 cm Hg 8 hours *Temperatures for vacuum drying were 60, 70 and 80°C. Drying Rate: The drying rate for each condition was obtained by measuring the weight of the wood board after each period of drying. The initial moisture content of the wood was determined by cutting a small piece of the board and drying it in a 100°C oven for 48 hours

Superheated steam drying : 

Superheated steam drying Schematic of superheated steam drying operation Actual equipment setup

Lowry-empty cell pressure process : 

Lowry-empty cell pressure process Temperature : Room temperature (25-350c) Pressure : 10 kg/sq. cm 7 kg/sq. cm 5 kg/sq. cm Treating period: 1 hour Preservative chemicals: 5% copper- chrome - boron (2:2:1)

Degradability : 


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Ambrosia beetles attack the logs and Browne (1961) has recorded 16 species of ambrosia beetles attacking rubber logs. Timber from rubber logs, before or after seasoning, is attacked by 7 powder-post beetles and one scolytid

Fungal : 

Fungal Lenzites palisotti, Ganoderma applanatum, Tramates corrugata, Pollyporous zonzlis, Lentinus blapharods Schizophyllum commune Cerambycide, Bostrychidae, Lyctidae and Platypodidae Insects

Ambrosia beetle : 

Ambrosia beetle Sinoxylon cunigerum Powder post beetle




PRESERVATIVES CCA   --  Copper Sulphate, Potassium or Sodium Dichromate, Arsenic  pentoxide, CCB   --  Copper Sulphate, Potassium or Sodium Dichromate, Boric Acid, Boric Acid  --  Boric acid and Borax Equivalent, Cashew nut shell liquid(CSNL), Creosote oil.

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Preservative Requirement of Processed Rubber Wood

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CCA or CCB is suited for exterior use Boric Acid treatment is suitable only for interior use. Due to its high leachability ,boric acid retains the natural colour of the wood CCA gives an undesirable greenish yellow colour to the wood.

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Chemical preservatives by immersion treatment, brush coating or by pressure impregnation cashew nut shell liquid (CSNL) is easily available and is a low cost conventional treatment method. The specimens were brushed with CNSL and then hot dipped.

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CNSL being an oil based preservative restricts direct contact of specimen with water, but on prolonged exposure, is not very effective in resisting borer attack Specimens treated with Borax?Boric acid were completely destroyed. Borax?Boric acid is a leachable type of preservative and is thus completely washed away from the specimen rendering it prone to borer attack

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CCA first level and second level specimens were also found to be susceptible to borer attack Specimens treated with Creosote fuel oil mixture were found to be absolutely free from attack in specimens of both levels of impregnation.

Nature of wood to preservatives : 

Nature of wood to preservatives Rubber wood easily treatable by water soluble chemicals or even oil type preservatives. It can be treated by pressure process using a mild schedule 5 Kg/cm2 pressure and 1 hour period . Low cost Water- borne preservatives borax-boric acid and copper-chrome-boron can give adequate protection of rubber wood

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the required dry salt retention of CCB is 8- 16 Kg/m3 wood is more amenable to impregnation of preservative

chemical preservatives : 

chemical preservatives oil-based coal tar creosote, with or without admixture of fuel oil, for exterior use of rubber wood. The discoloration and unpleasant odour toxic to many types of organisms and also prevents any further splitting in wood

Water based : 

Water based preservatives contain toxic inorganic salts dissolved/dispersed in water. The leachable -are zinc chloride, boric acid or borax and sodium pentachlorophenate. Non -leachable water -include copper-chrome-arsenic (CCA), acid-cupric-chromate (ACC

CCA : 

CCA Rubber wood at all moisture contents could be easily pressure treated with CCA economical schedule of 15 minutes initial vacuum of 85 kPa a pressure of 1000 kPa for 15 minutes and a final vacuum of 85 kPa for 5 minutes. desired DSR (dry salt retention) range of 5.0-6.5 kg/m3 could be achieved by using CCA solution of 2-4%, depending on moisture content and thickness of the wood.

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The first stage of treatment involved steeping the planks in 7.5%CCA for ten days. On reaching moisture content of about 25% planks were kept immersed in creosote for 7 days. When treated with CCA and Creosote in combination it is observed that the compressive strength parallel to grain of the panels increased


MARINE PURPOSE The biocides used for treating the samples were 7.5% copper chrome arsenic solution and light creosote oil of 1.06 specific gravity. The experimental panels were treated by the full cell process (IS:401-1960) in a 400 litre pressure impregnation chamber . An initial vacuum of 56 cm Hg was 30 min.

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At the end a vacuum of 38cm Hg for 15 minutes was applied. An average retention of 16 kg/m3 of CCA and160kg/m3 of creosote was obtained after a dual treatment cycle with an intermittent drying period of nearly 15 days.

Processed Rubber wood – Attributes : 

Processed Rubber wood – Attributes Light colour Attractive grain structure Good strength properties Good working, machining and finishing properties Good staining properties These make the rubber wood a versatile woo


REFERENCE Rubber timber .asia

Slide 50: - 35 www.saw

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