Feature of Coconut Timber

The coconut palm is a monocotyledon (similar to a grass) as opposed to a dicotyledon (a tree). Vascular growth of xylem and phloem is up the centre which, as it ages, is compressed to the outside. The hard wood is therefore found on the outside of the trunk. Coconut palms grow from the ‘heart’ at the top and have no annual rings, branches or knots. The wood is hard, durable and dense. The hardwood has a high resistance to indentation. Generally the hardwood is used for flooring, window frames, furniture and tool handles whilst the softer core timber is used internally for panelling, ceilings and less demanding uses.

Common Name: Coconut Palm

Botanical Name:Cocos Nucifera

Variety: Malaysian Tall Species

Biology:
The monocotyledonous coconut palm does not have a distinguishable separation of sapwood and heartwood as with dicotyledonous trees. It has vascular bundles that are spread throughout the cellulose structure of the palm, denser on the outside and continuous for the length of the palm. It is non-branching and free of knots. The older vascular bundles are located on the outer perimeter of the trunk and give the palm its high strength and elasticity.

Colour:
Colour varies from golden to deep chestnut. The colour is not necessarily related to hardness but a darker colour usually means a harder wood.

Density:
Coconut wood has three degrees of density:-
Soft : 250 -399 kg/m3
Core : 400 -599 kg/m3
Hard : 600 kg/m3 and above

Hardness Janka:
1600 psi. Load required to embed a 1.128 steel ball to 1/2 its diameter.
Side 524kg, End 488kg

Stress Grade:
F27 for seasoned high density wood

Notes:
1.Compressive stress at limit of proportionality.
2.Radial and tangential values differ insignificantly.
3.Combined maximum values of radial and tangential cleavage.

Density:
Coconut wood varies in density from 110kg/m3 at the centre of the top to 1000kg/m3 in the peripheral area at the base. Generally it is graded as:
Soft : 250 -399 kg/m3
Core : 400 -599 kg/m3
Hard : 600 kg/m3 and upwards.

Swelling and shrinkage:
Because coconut does not have any diametric growth, wood rays, branches or annual rings, the swelling and shrinkage properties hardly differ in the tangential or radial direction. Volumetric shrinkage is 5-7% for the soft and core wood and 10-12% for hard wood. Compared to other species of corresponding densities the volume shrinkages is mostly smaller.

Sorption properties:
The equilibrium wood moisture content in a state of balance with the air humidity and the temperature corresponds with the sorption properties of other wood species of similar density
At 20degC, 75% relative humidity = 12% equilibrium moisture content.

Drying rate is generally higher in the softer wood than the hard because of the higher initial moisture content. The high density wood, however, will under-step the fibre saturation point earlier. The equilibrium moisture content, around 17% in the tropics near the coast, is reached at the same time, 60-90 days.

Definitions:
Hardness gives an indication of a species’ resistance to indentation and abrasion. It is usually determined by a test called the Janka indentation test which measures the force required to embed a steel ball a certain depth into the wood. The higher the Janka rating the more resistant the timber to indentation.

Impact Strength is a measure of the energy needed to break a standard sized specimen.

Strength Group is mainly used by structural engineers to determine the size of structural timber. The strength groups are based on the following five strength properties:-
•Air Dry Density is the average density of the timber at a moisture content of 12%.
•Modulus of Rapture is a measure of the bending strength of the timber
•Modulus of elasticity is a measure of the timber’s stiffness and resistance to deflection.
•Maximum crushing strength in compression parallel to the grain
•Maximum shear strength parallel to the grain
A strength group rating from S1 to S7 is given to green timber and a rating from SD1 to SD8 is given to seasoned timber. The lower the number the stronger the timber..

References:
Bolza E. “Properties and uses from 175 timber species from Papua New Guinea and West Irian”. C.S.I.R.O. Division of Building Research Report 34., 1975
Bootle K.R., “Wood in Australia. Types, properties and uses”. McGraw-Hill Company Australia Pty Limited, 2004
Killmann, 1988
Kilian and Scharpenberg “Possibilities for the utilization of coconut palm wood in Tanzania” NCDP1993