dc.description.abstract |
Wood is susceptible for insect and microorganism attack, though heartwood of some species is naturally
durable. Rubber is cultivating as a plantation species in Sri Lanka, and it is the second largest plantation
crop in the country (covers 124,000 ha). Rubber wood is less durable. Preservative application can make
rubber wood more durable. Several timber preservation methods are used in Sri Lanka, but rubber wood
treatment is mainly done using traditional boron diffusion treatment, which was invented in Sri Lanka in
1964. Vacuum pressure impregnation method for timber treatment is not very common for rubber wood
treatment in Sri Lanka. Boron is a better preservative compared to other preservative chemicals as it does
not cause discoloration of treated wood. Aim of this study is to investigate effectiveness of rubber wood
treatment by boron preservatives by different treatment methods.
40.63 cm * 10.16 cm * 1.60 cm (16 inches * 4 inches * 0.63 inches) size rubber wood samples were treated
by boron preservative by four different timber treatment methods. For each method, two moisture contents
of wood were tested (dry and green) and two boron solution strengths were used (8% and 12%). Timber
treatment methods used were dip diffusion, hot and cold open tank method, steam cold quench method and
vacuum pressure impregnation method.
In dip diffusion method, timber samples were dipped in boron solution for 24 hours and thereafter these
were block stacked for 1 hour. In hot and cold open tank method, timber samples were submerged in 80 ºC
hot boron solution and temperature was maintained for 4 hours and allows them to cool within the same
solution for 12 hours. In steam cold quench method, timber samples were steamed for 4 hours and
immediately transferred them in to cold boron solution and allow them to cool for 12 hours. Timber
samples were treated by vacuum pressure impregnation method as the 4th treatment method.
Effectiveness of each method was measured by chemical retention, chemical penetration and termite test.
Chemical retention was measured by the weight difference before and after the treatment, chemical
penetration was measured using Atomic Absorption Spectrometer and effectiveness against termite test was
measured by the sandwich method. Cost of treatment of one cubic meter of rubber wood was also
calculated for diffusion, hot and cold open tank method and vacuum pressure impregnation method.
Vacuum pressure impregnation method was found to be the best method for preservation of dry (12%
Moisture content) rubber wood, but it is less effective in green condition. Hot and cold open tank method
was the best method for preservation of green rubber wood. All treatment methods are more effective in dry
condition than green condition except dip diffusion method. Effectiveness increased with the solution
strength. Termite resistance was highest in Vacuum pressure impregnated dry timber. Cost of treatment of
one cubic meter of rubber wood by vacuum pressure impregnation was the highest then hot and cold open
tank method and diffusion method gave the lowest treatment cost. If high retention and penetration are
needed vacuum pressure impregnation method should be use for the dry rubber wood treatment. Although
retention and penetration is lower in Hot and cold open tank method and steam cold quench method
compared with vacuum pressure impregnation method, those methods can be recommended for low
hazardous situation of timber use such as indoor applications. |
en_US |