| Rubberwood
(Parawood): Hevea Brasiliensis |
 In
1901 British planters introduced rubber trees into
the Malay Peninsula, where the soils and climatic
conditions were highly suited to rubber cultivation.
In Thailand early government restrictions on foreign
investment led to development of the industry by
local smallholders, usually subsistence rice farmers
who were able to start rubber tree stands on the
relatively abundant free land in the area. Land
under rubber cultivation expanded rapidly in the
1930s, consisting mainly of smallholdings controlled
by Chinese, Thai, and Thai Malays rather than large,
European-owned plantations, as in other Asian countries.
Thailand had about 1.6 million hectares in rubber
in the mid-1970s, of which about 10 percent were
located in an area along the Gulf of Thailand southeast
of Bangkok. Of the 500,000 holdings in the early
1980s, about 150,000 were under 2.5 hectares in
size, and another 300,000 were under 10 hectares.
The remaining larger holdings were operated more
as expanded smallholdings than as plantations. Production
was increasing in the early 1980s and had reached
about 830,000 tons in 1987. An extensive replanting
program, in which old tree stock was replaced with
new high-yield varieties, had reportedly been carried
out in about half the planted area by the mid-1980s,
significantly increasing the potential for expanded
production. |
| Tapping of rubber trees starts in
the fifth to seventh year after planting and then
continues for 25 to 30 years. A special knife is
used to incise the bark so as to wound the resin
canals without damaging the cambium. |
| After 30 years a decline in latex
production makes further tapping of the trees uneconomic.
The trees are then removed and replaced with new
seedlings. In the past, felled rubber trees were
either burnt on the spot or used as fuel for locomotive
engines, brick burning or latex curing. |
| A 30-year old cultivated rubber tree
is about 30 m tall with an average branch-free bole
of 3 m. The diameter at breast height (dbh) may
reach about 30 cm. The stem tends to taper. Young
rubber trees have a smooth brown-green bark. The
constantly tapped portions of the stem may develop,
with age, a latex-smeared cortex. |
| Rubberwood’s favourable woodworking
and timber properties make this medium-dense timber
suitable for a wide scope of applications. It can
be easily steam-bent, or stained to resemble any
other timber, depending on consumer demand. Its
favourable qualities and light colour make it a
good substitute for ramin, a timber known for its
quality in furniture making and other applications.
The natural colour of rubberwood is one of the principal
reasons for its popularity in Japan, where it is
increasingly used to replace more traditional timbers
in a wide variety of applications. |
 Rubberwood
has traditionally been used as a cheap source of
woodfuel in most of the countries where rubber plantations
are abundant, such as for industrial brick burning,
tobacco curing, or for fuelling of locomotive engines.
Due to lack of durability, rubberwood was rarely
used as utility timber except in timber-scarce countries.
After a number of problems had been overcome with
the help of applied research, particularly in connection
with wood seasoning and preservation but also related
to the small size of logs, rubberwood developed
as one of the most successful export timbers of
Southeast Asia.
It is reported that 61 different products are made
from rubberwood. The most important uses are: furniture
and furniture parts, parquet, panelling, wood-based
panels (particleboard, cement and gypsum-bonded
panels, medium-density fibreboard (MDF), kitchen
and novelty items, sawn timber for general utility
and fuel. Rubberwood has certain advantages over
conventional timbers from the natural forest. Because
it is a plantation by-product, it is available at
a relatively low cost. Thus in spite of its comparatively
low recovery rate, the production cost per cubic
meter of rubberwood is only about 30 percent of
the production cost of Meranti. Rubberwood is also
still used for charcoal manufacturing and woodfuel.
Timber availability, extensive research and aggressive
marketing have contributed towards making rubberwood
one of the most important export timbers in Southeast
Asia, a substitute for light tropical hardwoods
and one of the major timbers for the production
of furniture and indoor building components.
The main reasons for success are its favourable
timber and woodworking properties and the relatively
low cost of the raw material since rubberwood is
an agricultural by-product. This factor makes the
timber highly competitive in comparison with timber
from forest species that have comparatively high
raw material costs. An additional asset is its “green”
aspect: rubber trees have to be removed and the
areas replanted once the latex yield has declined
to uneconomic levels. The acceptance of rubberwood
as a sustainable, plantation-grown, “environmentally
friendly” timber has contributed to its universal
appeal. |
| It can be safely assumed that market
prospects for rubberwood will continue to be favourable.
This is also reflected by the increased overseas
investments in the Southeast Asian rubberwood industry.
Rubberwood now has a position no other single tropical
hardwood species can match in terms of available
volume. If we assumed that all plantations would
be available for wood production and that there
was a ‘normal’ distribution of age classes, then
the potential annual production could be up to 30
million m3 of rubberwood logs. |
| With the increase in plantation area
and research in improved hevea clones, which may
yield both high-quality latex and timber, prospects
for a continuous supply of rubberwood seem to be
good. |
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| PHYSICAL PROPERTIES |
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Colour: |
Pale cream to yellowish brown.
Oxidative discolouration can be limited by
rapid production sequence and vacuum drying. |
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Grain pattern: |
Mostly straight. A cross section of Rubberwood
shows few concentric markings reminiscent
of growth rings. These markings combined with
the large vessels in structure give an attractive
appearance with clear patterns on the longitudinal
surface. Many characteristics of Rubberwood
are similar to Ramin wood. |
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Structure: |
Uniform in structure with an excellent 'Timber'
feel |
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Green Density: |
800 kg/m2 |
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Density at 12% m.c.: |
600–620 kg/m2 (light) |
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Relative Density: |
0.63–0.66 (moderately heavy timber) |
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Volume Shrinkage: |
Negligible and comparable to Dark Red Meranti
Tangential 1.4%, Radial 1% |
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Compression Strength: |
Parallel to Grain 32 N/mm2
Perpendicular to Grain 4.69 N/mm2 |
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Bending Strength: |
Modulus of Rupture 66 N/mm2
Sheer Parallel to Grain 11 N/mm2
Modulus of Elasticity 9240 N/mm2 |
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| WORKING PROPERTIES |
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Durability: |
Resistant to many fungal, bacterial
and mould attacks can also be made resistant
to other specific susceptibilities. |
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Gluing: |
Good and compatible with almost all industrial
grade adhesives--its glue bond strength is
high |
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Machining: |
Easy to saw, machine, plane, turn and bore.
The resultant surfaces are fairly smooth |
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Nail holding: |
Average of Radial Tengential value
Average of end values 91 kg 53 kg |
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Screw holding: |
Average of Radial Tengential value
Average of end values 267 kg 164 kg |
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