Sarkar Plywood Rubber Wood
Rubber Wood
Wood has been used by us for a very long time for construction and other purposes. Forest’s were the main source of wood. As the global population increases so does the demand for wood. With the industrial revolution the demand went further up. The indiscriminate deforestation is showing signs of global warming, melting of polar ice, rising of sea water level, draught and consequent destruction.
As Science and Technology developed,several alternate materials like metals,plastics and composites with improved strength and working properties were developed. But none of them had the feel of wood and it was concluded that there is no true substitute for wood. The continued search for wood led to the utilization of secondary species of wood like rubber wood, a plantation timber.
Hevea Brasiliensis, the natural rubber tree, is the most important commercial source of natural rubber and it is grown in about 9 million hectares in the tropical regions of Asia, Africa and America. With over 5,30,000 ha under rubber, India is now the third largest producer of natural rubber in the world.
At the age of 22 to 29 years, latex production becomes uneconomic and the trees are then cut and replanted. Thus the rubber plantation is a sustainable source of rubber as well as timber, contributing positively to the environment.
In India rubber is predominantly a small holders’ crop and over 87% of the rubber is from this sector. A rubber tree from
small holdings will have about 0.57 m3 (20CFT) of timber and the per ha yield is about 150 m3 (5295 CFT). The stem wood has timber value of only 60%. Present total availability of rubber wood is estimated as 0.94 million m3/yr. and it is estimated to be 1.5 m3/yr times by the end of the decade.
Rubberwood is wood from the Pará rubber tree (Hevea brasiliensis), often called the rubber tree. Rubberwood, also called parawood, is used in high-end furniture. It is valued for its dense grain, minimal shrinkage, attractive colour and acceptance of different finishes. It is also prized as an "environmentally friendly" wood, as it makes use of trees that have been cut down at the end of their latexproducing cycle.
Rubberwood is often the most misunderstood species of wood in the furniture industry. The name rubberwood invokes a variety of misconceptions as to its features and to its durability. Rubberwood (also called Parawood in South East Asia) is the standard common name for the timber of Hevea brasiliensis.
In fact, rubberwood is one of the more durable lumbers used in the manufacturing of today's home furnishings. As a member of the maple family, rubberwood has a dense grain character that is easily controlled in the kiln drying process. Rubberwood has very ittle shrinkage making it one of the more stable construction materials availabe for furniture manufacturing.
Like maple, rubberwood is a sap producing species. In the case of maple, it is syrup; in the case of rubberwood, it is latex. Rubberwood produces all the latex used in the world for all rubber-based products.
There is one more feature of rubberwood that is very important in today's world. Rubberwood is the most ecologically "friendly" lumber used in today's furniture industry. After the economic life of the rubber tree, which is generally 26-30 years, the latex yields become extremely low and the planters then fell the rubber trees and plant new ones. So, unlike other woods that are cut down for the sole purpose of producing furniture, rubberwood is used only after it completes its latex producing cycle and dies. This wood is therefore eco-friendly in the sense that we are now using what was going as waste.
Properties of Rubber wood:
| Density(kg/M3 at 16%MC : | 560-640 |
| Tangential Shrinkage Coefficient (%) : | 1.2 |
| Radical Shrinkage Coefficient (%) : | 0.8 |
| Hardness(N) : | 4,350 |
| Static Bending, N/mm at 12% MC : | 66 |
| Modulus of elasticity,n/mm at 12%MC : | 9,700 |
Physical Properties:
Rubber wood is a light hardwood. The wood is whitish yellow or pale cream when freshly cut and seasons to light straw or light brown. It is a moderately hard and ‘light to moderately heavy’ timber with density ranging from 435 to 626 kg/m3 at 12% moisture content. It is a diffuse porous wood with medium texture and straight grain. Sapwood and heartwood are not distinct. Occurrence of tension wood seen as white lustrous zones when freshly cut is a characteristic feature of rubber wood.
Sub Topics
- Shrinkage of Rubber Wood From Green to Oven Dry Condition
- Weight and Specific Gravity of Rubber Wood
Shrinkage of Rubber Wood from Green to Oven Dry Condition
| Tangential | 5.7 to 6.5% |
| Radial | 2.6 to 3.1% |
| Longitudinal | 0.2 to 0.9% |
| Volumetric | 10.1 to 12.0% |
Weight and Specific Gravity of Rubber Wood
Most of the strength properties of wood are related to its specific gravity.
| Green | Dry | |
| Specific Gravity = Wt. Oven dry/ vol. at Test | 0.521 |
0.557 |
| Moisture content, % | 81.2 |
12 |
| Weight Kg/m3 at corresponding moisture | 944 |
624 |
Mechanical Properties
The mechanical properties determine the ultimate capacity of the wood to bear the forces in bending, tension, compression, shear etc. in the three directions or planes. The following tables give the properties under bending, compression, tension and shear as compared to teak wood. It is seen that under dynamic conditions in bending, the load bearing capacity increases.
Sub Topics
- Bending Properties
- Compressive Strength
- Tensile Strength
- Shear Strength
| Bending Properties | Units | Dry M. C.12% |
| STATIC CONDITION-Fibre stress at elastic limit | Kg / cm2 |
368 |
| Modulus of Elasticity | 1000kg / cm2 |
82 |
| Modulus of Rupture | Kg / cm2 |
756 |
| DYNAMIC CONDITION- Fibre stress at elastic limit | Kg / cm2 |
820 |
| Modulus of Elasticity | 1000kg / cm2 |
118.2 |
| Max height of drop of 25kg hammer | Cm |
43 |
| Compressive Strength | Units |
Dry M. C. 12% |
| PARALLEL TO GRAIN - Compressive stress at Elastic limit | Kg/cm2 |
187 |
| Max. Crushing Stress kg/cm2 | Kg/cm2 |
374 |
| Modulus of Elasticity in compression | 1000kg/cm2 |
99.3 |
| PERPENDICULAR TO GRAIN - Compressive stress at Elastic limit | Kg/cm2 |
101 |
| Tensile Strength | Unit |
M. C. 12% |
| Perpendicular to grainMax. tensile stress, radial | kg/cm2 |
56.7 |
| Max. tensile stress, tangential | kg/cm2 |
62.8 |
| Shear Strength | Maximum Shear Strength (kg / cm2) | ||
| Condition of material (M.C.%) | Radial | Tangential |
Average |
| Dry 12% | 107.7 |
119.5 |
113.1 |
Hardness on Different Surfaces
Hardness of the wood is very important for applications like flooring and decking where abrasion of surfaces is taking place. The table below gives the hardness as measured by indentation of a steel ball. It can be seen that dry rubber wood has better hardness than teak.
| Condition of material (M.C.%) | Indentation in Kg | |||
| Radial |
Tangential |
End |
Average | |
| Dry (12%) | 549 | 526 |
627 | 5 |
Note: Indentation is measured as load in kg required to embed a steel ball of diameter 1.28 cm to a depth equal to half its diameter
Sawing, Machining, Working and Finishing Properties
Rubber wood is easy to work in sawing and machining. Clogging of saw with latex can easily be eliminated by dabbing of saw blade with fuel oil. For best results in sawing, narrow gauge saw blade with teeth having top clearance angle of 15o and front rake of 20o should be used. Short length of sawn planks can be overcome by finger jointing.
Rubber wood has good machining and working qualities. A cutting angle of 30o gives very smooth surface on planing and stands well to further smoothening of the surface. It can be finished to a very glossy look on polishing and can be given ammonia fumigation cum bark extract -quenching treatment to obtain golden to dark brown hues and decorative figures. Rubber wood can be bent in steam or in ammonia to make curved items. It takes up stains well and being light in colour it can be stained to the shades of teak, rosewood, mahogani, beech, cherry etc.
Wood Working Properties
| Condition | Sawing | Planing | Boring | Turning | ||||
| Re-sawing | Cross cutting | Ease of planing | Quality of Finish |
Ease of Boring | Quality of Finish | Ease of Turning | Qualtiy of Finish |
|
| Green | Slightly difficult | Easy | Easy | Smooth | Easy | Rough | ||
| Dry | Moderately easy | Easy | Easy | Smooth | Easy | Rough | Easy | Rough |
Working Qualities
| Overall performance | Ease of working | Working quality index | Comparative performance in turning |
| 194 | 100 |
131 | 101 |
Nail and Screw Holding Strength
Rubber wood offers good resistance to Screw and Nail withdrawal forces as can be seen below.
| Rubber wood from Quilon, Kerala | Testing | Radial | Tangential | Average | End Surface |
| Standard nail withdrawal resistance in kg | |||||
| Green | 161 | 149 | 155 | 96 | |
| Dry | 126 | 116 | 121 | 113 | |
| Standard screw withdrawal resistance in kg | |||||
| Green | 248 | 256 |
252 |
154 |
|
| Dry | 328 | 263 |
296 |
176 |
|
Note:
- 1) Nail are 50mm long and 2.5mm shank diameter and screw No. 8 gauge, Penetration 25mm.
- 2) Rubber wood has superior nail holding power than Teak.
Comparative Suitability Indices of Rubber Wood with respect to Teak as 100
| Weight or Heaviness | 93 |
| Retention of Shape |
77 |
| Strength as a beam |
62 |
| Stiffness as a beam |
77 |
| Suitability as post |
52 |
| Shock resisting ability | 75 |
| Shear |
92 |
| Surface hardness | 74 |
| Splitting Coefficien |
75 |
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. 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.
Sub Topics
- Preservative Requirement of Processed Rubber Wood
- Seasoning of Rubber Wood
- Processed Rubber Wood - Availability
- Processed Rubber wood – Attributes
Preservative Requirement of Processed Rubber Wood
| Sl. No. | Service Condition Service Condition | CCA/CCB | Boric acid : Borax | Penetration |
| 1 | Interior protected from weather, painted | 5kg/m3 | 5kg/m3 | Throughout |
| 2 | Interior imtermittent wetting | 8kg/m3 | ||
| 3 | Exposed to weather not in ground contact | 12kg/m3 | ||
| 4 | In ground contact | 16kg/m3 |
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
CCA or CCB is suited for exterior use where as Boric Acid treatment is suitable only for interior use. Due to its high leachability boric acid retains the natural colour of the wood where as CCA gives an undesirable greenish yellow colour to the wood.
The preservation is generally carried out by impregnation under pressure and vacuum in cylinderical chambers. In vacuum pressure process, the timber is subjected to an initial vacuum followed by pressure treatment and a final vacuum. In the oscillating pressure and vacuum method the cycle is repeated 10 to 15 times
Seasoning of Rubber Wood
Rubber Wood belongs to refractoriness to seasoning class ‘B’ of IS:1141-1993. When freshly cut, moisture content of the timber will be above 60 %. For any use, the moisture content has to be reduced to the equilibrium moisture content (EMC) and this is about 12%. This is for dimensional stability and for obtaining good machining and finishing properties. 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.
Currently two types of seasoning techniques are employed; conventional kiln drying and vacuum drying. With vacuum drying, drying time can be saved and the wood will have less defects with better colour.
Processed Rubber Wood – Availibility
Processed rubber wood is available in the following forms.
* Rough Sawn Kiln Dried Timber (RSKD)
Width upto 150 mm.
Thickness from 25 to 75 mm.
Length upto 2400 mm
* Four Side Planed Sections (S4S)
Width upto 125 mm
Thickness from 25 to 50 mm
Length upto 2400 mm
* Finger Jointed Four Side Planed sections (FJS4S)
Width from 30 to 100 mm
Thickness from 20 to 65 mm
Length upto 2400 mm or more depending upon specific requirement
* Mouldings for furniture manufacture and interior work
* Panelling and flooring materials (tongue & groove, parquet etc.)
* Finger Jointed edge glued panels
Thickness 15, 18, 24, 30, 36, 42 and 48 mm
Length upto 2400 mm
Width upto 1200 mm
Other sizes on specific requirement
Processed Rubber Wood – Attributes
- 1. Light colour
- 2. Attractive grain structure
- 3. Good strength properties
- 4. Good working, machining and finishing properties
- 5. Good staining properties
These make the rubber wood a versatile wood.
Applications - Sub Topics
- 1. Furniture and Cabinet Making
- 2. Flooring
- 3. Packing Cases
- 4. Wood Carvings
- 5. Wooden Shuttle Block
- 6. Laminated Veneer Lumber
- 7. Veneer and Plywood
- 8. Block Board and Flush Doors
- 9. Fibre Boards-Medium Density Fibre Board and Hard Boards
- 10. Pulp and Paper
- 11. Bent Wood Articles
Furniture and Cabinet Making
Furniture suitability coefficient for rubber wood is evaluated as 69. Hence rubber wood is classified and standardized as a Group III species in IS 13622:1993. (Indian timbers for furniture and cabinets- classification.)
Interiors – Panelling, mouldings, beadings, skirtings, edging, parquet and strip flooring
Kitchen Wares, decorative and utility household items such as salad bowls, knife blocks, book shelves, trays, magazine racks etc.
Building Components – Rubber wood has been using for making doors, windows, steps, railings, balusters etc. Suitability coefficient of rubber wood for making door and window shutters and frames is evaluated as 77. Hence it has been included and classified as a Grade II timber in IS:12896-1990 (Indian timbers for door and window shutters and frames- classification) and in IS:1003-1991 (Timber paneled and glazed shutters-specification). CPWD has approved it as one of the species for government construction work. Rubber wood is suitable for structural purpose and is classified as
Group C timber according to its modulus of rupture and modulus of elasticity.
Flooring
Rubber wood has been successfully used for wooden flooring in offices, homes etc.
Packing Cases
Rubber wood is a widely used timber for making packing cases. It has a packing cases suitability figure of 89 and is classified as Grade II in IS: 6662-1993. (Timber species suitable for wooden packaging specification).
Wood Carvings
Rubber wood has been widely used for making carved, decorative and utility items like ornament boxes, utility boxes, lacquered items trays etc.
Wooden Shuttle Block
Rubber wood after being compressed to a density above 1000 kg/m3 is widely utilised for making compressed shuttle blocks and as compressed wood core in laminated shuttle blocks in the textile industry.
Laminated Veneer Lumber
Rubber wood is being used for making LVL, which is a new wood based panel product in India.
Veneer and Plywood
Rubber wood can easily be peeled into uniformly thick, smooth and tight veneers and is reportedly suitable for making commercial plywood. Rubber wood veneers after proper treatment with preservative is widely used as plywood core stock.
Block Board and Flush Doors
Rubber wood has been widely used for making the core stock of the block board and flush doors after proper preservative treatment. This species has been included in Grade I (Species suitable for core) in IS: 2202(part)-1999 (Wooden flush door shutters (solid core type)-specifications.
Fibre Boards-Medium Density Fibre Board and Hard Boards
Rubber wood finds extensive usage in the manufacture of fibre boards in countries like Malaysia. Since it is relatively a new product in India and the manufacturing facilities are away from the rubber wood growing areas, this potential raw material has not been utilised for making MDF so far. However rubber wood has been successfully utilizing for the manufacture of hard boards.
Pulp and Paper
Investigations on the suitability of rubber wood for making pulp and paper show that it is similar to other hard woods for making pulp. The problem of interference of latex during production can be overcome by different ways. One promising area in this sector is the mixing up of bamboo pulp with the pulp made of rubber wood for getting a superior quality paper.
Bent Wood Articles
Bending wood by employing ammonia plasticisation technique for making bent wood articles like walking sticks, stairs, trays, peg tables etc is a very promising area for the better utilization of rubber wood. Rubber wood can also be used for making many suitable curved components for the production of furniture, doors and other fancy, ornamental and utility items. Major rubber producing countries like Malaysia, Thailand and Indonesia are quite advanced in rubber wood processing and value addition. As an eco-friendly timber, it is well accepted in the world market. In India, rubber wood processing for value addition started in the ’80s and still it is in the infancy, consuming only about 17% of the available stem wood. With a gap of about 11 million m3/ year between the supply and demand, the domestic marketis also huge. We are also yet to tap fully the export potential. The country is importing wood and wood products worth about Rs 500 crores a year. Hence for the country it is a foreign exchange saver and earner. Development of the rubber wood processing industry in the country will help to generate employment, strengthen national economy, make rubber cultivation
sustainable and preserve the environment. This is quite relevant in the post liberalisation period in which trade barriers are disappearing across the world.
Rubber Wood Testing Laboratory
- 1. To improve the quality and acceptability of rubber wood and its products, a Laboratory has been set up in Kottayam to make available testing facilities to the processors and consumers. It will also train processors in testing and quality control.
- 2. To improve technology and skills through demonstration and training, a state of the art model rubber wood factory has been set up at Kottayam with equity participation of the Kerala State Industrial Development Corporation Ltd. (KSIDC) and private sector.
- 3. Promoting rubber wood and its products in the domestic and world markets.
- 4. Promoting processing and value addition through technical and financial assistance.
- 5. Demonstrating applications of rubber wood in furniture, interiors, doors etc.
It is hoped that through the above efforts rubber wood can meet partly the timber requirement of the country and improve the economy of the country in the coming years.
Testing Facility
The lab will provide facilities for conducting the following tests.
- 1. Identification of species.
- 2. Physical properties – density, specific gravity, moisture content, swelling,shrinkage.
- 3. Mechanical properties – bending, compression, shear, hardness, tension, nail/screw withdrawal resistance.
- 4. Durability tests on susceptibility to Biological agencies like fungi, termites and borers.
- 5. Qualitative and quantitative estimation of chemicals in the treated wood.
- 6. Gluing properties and strength of glues joints.
- 7. Strength of joints – carpentry/finger joint.
- 8. Finishing properties- abrasion, quality and type of finish.
- 9. Tests on frames and shutters of doors and windows.
- 10. Tests on finish and abrasion for flooring.
- 11.Tests in joints strength for furniture.
Sub Topics
- Selection and Preparation of Samples
- Testing Fee and Sample Size
Selection and Preparation of Samples
Convert logs in to scantlings/planks keeping an eye on the final dimension of the sample to be tested. After the chemical treatment dry them to a moisture content of 15%. Plane the surface and further rip them along the grain in to sections of 50 x 50 mm for further conversion in to specimens. Avoid areas of decay, defects like knots, stains, moulds and sloped grain more than 10o to the length. Cut specimen of required dimensions by exercising utmost care to see that the radial and tangential surfaces are exactly at right angles to the longitudinal surface. In case of qualitative and quantitative determination of preservatives in treated wood, the sample should be as representative as possible of the wood concerned. The area of wood selected should be free from end penetration.
Testing Fee and Sample Size
As an incentive for the various agencies for utilising the testing facility, a very nominal and affordable fee is levied.
