THE EFFECT OF WATER SOLUBLE EXTRACTIVES ON SOME PHYSICAL AND MECHANICAL PROPERTIES OF THREE TROPICAL HARDWOODS

Charles ANTWI-BOASIAKO
Dr., Head of Department of Wood Science &Technology - Faculty of Renewable Natural Resources
Kwame Nkrumah University of Science &Technology, Kumasi-Ghana
Tel: +233-243771376. Fax: +233-51-60137.
E-mail: cantwi-boasiako.frnr@knust.edu.gh

Jane ANTWIWAA BIMPONG
BSc. - Faculty of Renewable Natural Resources
Kwame Nkrumah University of Science &Technology, Kumasi-Ghana
Tel: +233-242153317. Fax: +233-51-60375. E-mail: preciouzjay@yahoo.com

Abstract: Wood's interaction with wet environment causes leaching of extractives, which influences its natural durability. This study also examines the influence of water-soluble extractives on some physico-mechanical properties of three economically important hardwoods (Milicia excelsa (Welw.) C. Berg., Sterculia rhinopetala K. Schum. and Piptadeniastrum africanum (Hook.f.) Brenan). Fifty heartwood stakes (2×2×2cm, 2×2×10cm and 2×2×6cm for specific gravity, shrinkage and compression strength tests respectively [BS 373, 1957]), selected from diameter at breast height of each timber, were boiled in water for 20 hours at 100°C (on water bath). Fifty unextracted stakes from each timber served as controls. Specific gravities for both extracted and unextracted stakes rank as: M. excelsa > S. rhinopetala > P. africanum, while those of their extractive-free stakes reduced. Shrinkages rate as: Volumetric > tangential > radial for each timber with an overall ranking as: S. rhinopetala > P. africanum > M. excelsa. Generally, the extracted stakes shrank more than unextracted. Tangential:Radial shrinkage ratio (T/R), usually employed to evaluate wood dimensional stability, range between 1.35 and 1.67 and fall between the accepted range of 1.4 - 2.0. However, extracted stakes have higher values and would be classified as more dimensionally unstable than the unextracted. Compression strength for the stakes also ranks as: P. africanum > S. rhinopetala > M. excelsa, with unextracted samples having greater values than those extracted. Removal of water-soluble extractives caused increased shrinkages in all stakes of each timber with decreased specific gravity and compression strength.

Key words: compression strength, dimensional stability, specific gravity, volumetric shrinkage, water-soluble extractives.

REFERENCES
ANDERSON, A. B. (1961). The Influence of Extractives on Tree Properties, California Redwood. Institute of Wood Science Nr. 8, pp.11-38.
ANON. (1956). Timber Design and Construction Handbook (TDCH). Prepared by Timber Engineering Company. Mc-Graw Hill Book Co. United States of America. Pp. 3-7.
ANON. (1957). Method of Testing Small Clear Specimen of Timber. British Standard Institution. BS 373.
ANON. (1994). The Tropical Timbers of Ghana. Timber Export Development Board.
ANTWI-BOASIAKO, C. (2004). Assessment of Anatomy, Durability and Treatability of two tropical lesser used species and two related primary species from Ghana. PhD Thesis. School of Plants Sciences, The University of Reading (UK). 319 pp.
AYARKWA, J. (2000). Ghana Journal of Forestry. Volume 9. Cold and Steam Bending Propeties of some Lesser Used Species in Ghana. Pp. 3-5.
BODIG, J. and JAYNE, B. A. (1982). Mechanics of Wood and Wood Composites. Van Nostrand Reinhold Company, New York. Pp. 712.
BOLZA, E and KEATING, W. G. (1972). African Timbers: The properties, Uses and Characteristics of 700 Species. Div. of Building Research, CSIRO, Melbourne, Australia. 710pp.
BROWNING, B. L. [Ed] (1963). The Chemistry of Wood 1963. Robert E. Krieger Publishing Company, Huntington, New York. Pp. 314-317.
DAVIS, E. (1999). Growth Performance of Ceiba Pentandra Bsc. Thesis, Faculty of Renewable Natural Resources, KNUST.
DESCH, H. E. (1986). Timber, its Structure, Properties and Utilization, 6th edition. McMillan Education Ltd. Houndmills,London. Pp. 410.
FINDLAY, W. K. P. (1985). Preservation of Timber in the Tropics. Crosby Lockwood Staples, London.
HAGGLUND, E. (1951). Chemistry of Wood. Swedish Forest Products Research Laboratory, Stockholm. Academic Press Incorporated Publishers, New York. Pp. 332-348.
HAYGREEN J. G. and BOWYER, J. C. (1982) Forest Products and Wood Science, 1st edition, An Introduction. IOWA State University Press, America. Pp. 164-199.
HAYGREEN J. G. and BOWYER, J. C. (1996) Forest Products and Wood Science, 3rd edition, An Introduction. IOWA State University Press, America. 484pp.
HSE, CHUNG-YUN; KUO, MON-LIN (1988). Influence of Extractives on Wood Gluing and Finishing- A Review. Forest Products Journal 38(1):52-56.
HILLIS, W. E. [Ed] (1962). Wood Extractives and their Significance to the Pulp and Paper Industry. Academic Press Incorporated (London) Limited. Pp. 47-63.
HILLIS, W. E. (1971). Distribution, Properties and Formation of some Wood Extractives. Wood Science and Technology Society. Number 26. Pp. 211-220.
HIGUCHI, T. [Ed] (1985). Biosynthesis and Biodegradation of Wood Components. Wood Research Institute, Kyoto University, Uji Kyoto, Japan. Academic Press Incorporated Pp. 209-213.
KOLLMAN, F. F. P. and COTE, W. A. Jr. (1968). Principles of Wood Science and Technology ?. Solid Wood. Springer -Verlag Berlin Heidelberg New York. Pp. 205-346.
KOLLMAN, F. F. P. and COTE, W. A. Jr. (1984). Principles of Wood Science and Technology ?. Solid Wood. Springer -Verlag Berlin Heidelberg New York. Pp. 592.
MACKAY, J. F. G. 1989. Kiln drying in lumber. In Second Growth Douglas-fir: It's Management and Conversion for Value. R.M. Kellogg (Ed.), Forintek Special Publication No. SP-32: 75-77.
MATTHEWS, S., ISABELLE, M., SCALBERT, A. and DONNELLY, D. M. (1997). Extractable and non extractable proanthocyanins in barks. Phytochemistry 45 (2):405-410.
NAULT, J. R. 1989. Longitudinal shrinkage. In Second Growth Douglas-fir: It's Management and Conversion for Value. R.M. Kellogg (Ed.), Forintek Special Publication No. SP-32: 39-43.
OFORI, J. and APPIAH, J. K. (1998). Some drying characteristics of five Ghanaian Lesser Known Wood Species. Ghana Journal of Forestry. Vol. 6. 22pp.
OTENG-AMOAKO, A. (2006). 100 Tropical African Timber Trees from Ghana. Tree Description & Wood Identification with Notes on Distribution, Ecology, Silviculture, Ethnobotany & Wood Uses. Printed by Graphic Packaging, Accra, Ghana. 304pp.
PANSHIN, A. J. and de ZEEUW, C. (1977). Textbook of Wood Technology. 4th edition. McGraw -Hill Book Co. New York. Pp. 722.
RAYMOND, C. A., HENSON, M., PELLETIER, M.-C., BOYTON, S., JOE, B., THOMAS, D., SMITH, H. and VANDCLAY, J. (2008). Improving Dimensional Stability in Plantation-grown Eucalyptus pilularis and E. dunnii. Resource Characterization & Improvement. Prepared for Forest and Wood Products Australia, Project No. PN06.3017.
TIEMANN, H. D. (1951). Wood Technology; its Constitution, Properties and Uses. 3rd edn. Pitman Publishing Corporation, New York, Toronto and London. Pp.1-385.
TSOUMIS, G. (1985). Science and Technology of Wood. Structure, Properties and Utilization. Pp. 36,145-149.
USTA, I. and GURAY, A. (2000). Comparison of the Swelling and Shrinkage of Corcisan Pine (Pinus nigra var. mantima). Turk J. Agric. For. 24. 461-464.
WAYNE, W. W., BOTSUE, E. E. and KUBLER, H. (1991). Wood as a Building Material: A Guide for Designers and Builders. Pp. 26-42.
WIKIPEDIA (2009). Moisture Meter - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Moisture_meter. Last modified:14 September, 2009. Wikimedia Foundation, Inc.)
WILSON, K and WHITE, D. J. B. (1986). The Anatomy of Wood. Stobart & Son Ltd, London.
WWPA. (1996). Douglas Fir and Western Larch Species. Western Wood Products Association (WWPA), January, 1996.