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Pressure Treatment of Teak Pole with Oil-borne Preservative.

M. A. Latif
Divisional Officer
Wood Preservation Division, Bangladesh Forest Terearch Institute, Chittagong.

B. C. De
Research Assistants
Wood Preservation Division, Bangladesh Forest Terearch Institute, Chittagong.

M. Younus-uzzaman
Research Assistants
Wood Preservation Division, Bangladesh Forest Terearch Institute, Chittagong.

Abstract/ Executive Summary:

Teak (Tectona grandis) pressure treated with an oil-borne preservative was investigated to find its usefulness as transmission poles. The pole size round Teak was found to contain an average of 45 percent sapwood which is readily perishable by wood destroying organisms. Teak poles were treated by the Bethel full-cell process using varying pressure and duration to evaluate their effect on the penetration and retention of the preservative mixture of 40:60 creosote light diesel oil. With the increase of both treating pressure and time the increase in penetration was not found to be statistically significant. The retention, however, significantly increased with the increase of pressure but the increase of time could not produce any significant effect.

Keywords: Teak, Oil borne preservative, Penetration, Retention, Pressure treatment.

Location: Wood Preservation Division, Bangladesh Forest Terearch Institute, Chittagong.

Start Date: 01-07-1976

End Date: 30-06-1977

Program Area: Postharvest and Agro-processing

Commodity: Teak

Objectives:

To determine the optimum treating schedule by pressure process

Methodology:

Fifty Teak poles were collected 33 t from the 20 year old plantation of Kasalong forests of Chittagong Hill Tracts District. Both the outer and the inner barks of the poles were removed before treatment. It was necessary to scrape the poles with a metal scraper to remove the inner bark (Hunt and Garratt 1967). The poles were then stacked for air drying in the open shed until the moisture content came down to 20-25 percent. Before treatment the poles were physically examined to determine the average thickness of sapwood which were given below .A 40:60 mixture of creosote and light diesel oil was used as preservative. The preservative stored in the Rueping tank was thoroughly mixed and heated to 84⁰C before use. The poles were then treated by Bethel full-cell process under three treating pressures and for three treating times. Three poles were treated at each charge under an initial vacuum of 50.80 cm of Hg for 60 minutes and a final vacuum of 50.80 cm of Hg for 15 minutes.The experiment was designed to establish treating schedules for 160.33 to 320.66 kg/m² retention with 1.27 cm penetration of preservative from the surface.Treatments were carried out in a pilot plant size treating cylinder. In a typical treatment three Teak poles were weighed individually. The poles were then placed in the treating cylinder and tied to an iron support so that they could not float on the preservative fluid during treatment. After required length of time the excess preservative was forced back to the Rueping tank with the help of existing air pressure in the treating cylinder. The pressure in the treating cylinder was then released and a vacuum of 50.8 cm of Hg was established and held for 15 minutes.After treatment the treated timbers were taken out of the treating cylinder and allowed to cool. These were then weighed. The difference between the final weight and the initial weight of a pole is the amount of preservative mixture retained in that pole. The retention value is expressed as the amount of preservative per cubic metre of pole.At least three boring cores were taken from each pole by increment borer and depth of penetration of preservative into the wood was measured.The results obtained were analyzed statistically to evaluate the significance of the effect of treating pressure and time on the penetration and retention of preservative in the Teak sapwood.

Source of Information: Bano Biggyan Patrika, A journal of Forest Science, Bangladesh Forest Terearch Institute, Chittagong. Jan-July 1981, 10(1 & 2): 27-32pp

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Both heartwood and sapwood of Teak are difficult to treat by pressure process. Difficulty in felt more when treatment is done with oil-borne preservative than done with water-borne ones. Since the protection of sapwood effects the protection of the pole itself it was felt necessary to ensure the minimum depth of penetration adequate to protect the sapwood.A substantial increase in the penetration was effected by increasing both the treating pressure and time simultaneously. But this increase is marred by the erratic and non-uniform penetration. However, it was found that treatment for longer time improved the uniformity of penetration. If higher penetration is desired it is the duration of treatment that should be increased rather than increasing the treatment pressure.The treating pressure has a significant effect on the retention of preservative. With increasing pressure retention increases. On the other hand, treating time does not have any significant effect on the retention.Retention of 115.44 kg/m³ to 272.56 kg/m³ in the treated sapwood could be obtained at 8.81 kg/m² treating pressure for 3 hours keeping all other schedules constant. Therefore, a more severe schedule is recommended to ensure better and uniform penetration and retention.

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