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Effect of Chemical Pre-treatment of Sundry Wood Chips in Making Hardboard

Mr. M. S. Khan
Senior Research Officer
Pulp and paper Division, Bangladesh Forest Research Institute, P. O. Box 273, Chittagong-4000, Bangladesh

Dr. M. Shafi
Field investigator
Pulp and paper Division, Bangladesh Forest Research Institute, P. O. Box 273, Chittagong-4000, Bangladesh

Abstract/ Executive Summary:

Sundri wood chips were subjected to a mild chemical pre-treatment by soaking them in 1, 2 and 3% solutions of NaOH and Na₂SO₃, individually as well as in mixture, for 24 hours at atmospheric conditions. Hardboards made from pretreated chips were tested for determining their strength and water resistance properties. It was observed that the boards made from the chips pretreated with NaOH alone and in mixture with Na₂SO₃, were stronger than those made by simple steam softening of the chips prior to refining. Also the strength of the boards increased with an increase of the concentration of the pretreatment solutions. Pretreatment with NaOH alone produced stronger boards than with the mixtures. Any such effect on the strength property of the boards, however, was not obvious in the pretreatment with solutions. Na₂SO₃solutions. All the pretreatment methods adversely affected the water resisting properties of the boards.

Keywords: Chemical pre-treatment, Sundry wood, Hardboard. Water resistance properties, Steaming

Location: Bangladesh Forest Research Institute, Chittagong.

Start Date:

End Date:

Program Area: Postharvest and Agro-processing

Commodity: Wood

Objectives:

To investigate the contribution of a mild chemical pretreatment of sundry wood chips towards the fiber making characteristics of the species that might, in the long run, affect an improvement of the properties of the end product.

Methodology:

Sundri logs were chipped to produce 25 mm x 13 mm x 3 mm chips. The chips were then air dried.The chips were soaked in 1, 2 and 3% solutions of NaOH and Na₂SO₃ separately and in mixtures of both in equal proportions, for 24 hours under atmospheric conditions using 1:5 wood-liquor ratio in each case. The pre-treated chips were defiberized varying the plate clearance to obtain 3 pulps at different freeness levels ranging from 20 seconds to 60 seconds. For comparison, another set of 3 pulps were made from the chips softened by steaming only at 10 kg/cm² pressure.Thick mats were formed with the pulp slurries. The drainage time of each pulp was recorded. The mats were then cold pressed to lower the moisture content to about 60%. and then hot pressed in a single daylight hydraulic press. Pressing was carried out for the first 2 minutes at 35.5 kg/cm² followed by 1 minute’s breathing time at a low pressure of 7.5 kg/cm² for the escape of entrapped steam and then for another 3 minutes at 35.5 kg/cm² again, maintaining a constant temperature of 190°C although. Screen back S-1-S hardboard discs of 22.0 cm diameter and 0.35 cm nominal thickness were thus made.Five boards from each pulp were tested for determining their strength and water-resistance properties. Three test specimens of 12.7 cm x 5.10 cm size were prepared from each board and conditioned for 72 hours at 23 ±2°C temperature and (50 ±2)% relative humidity. The strength and water resistance properties of the boards were determined according to ASTM Standard (D 1037-52T, ASTM 1954).Water absorption tests were done by keeping the sample submerged under water at 23±2°C for 24 hours. Amount of water absorbed by the specimen and change in its thickness were measured.

Source of Information: Bano Biggyan Patrika Vol. 17 (1 &2) : 1-7, 1988

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

It may be concluded that pre-treatment of sundry wood chips, prior to mechanical refining, with NaOH and mixture of Na₂SO₃ and NaOH, would produce better pulps for making stronger hardboard than steam cooked chips. But the pre-treatment boards are less water resistant.

Knowledge Management: Journal