Dimensional stability wood products

R. M. RoweU and W. B. Banks, Water Kepelkng and Dimensional Stability of Wood, General Technical Report FPL 50, U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, Wise., 1985. 

Driers are used in the forest products industry to lower the moisture content of the wood product being processed. Drying of dimension lumber gives it dimensional stability. This type of drying is done in steam kilns and is a batch process. No appreciable pollutants are released. 

Analog-to-glass fibers silanes are used as coupling agents for natural fiber polymer composites. For example, the treatment of wood fibers with product A-175 improves wood dimensional stability [53]. In contrast, a decrease of mechanical properties was observed for coir-UP composites after a fiber modification with di-chloromethylvinyl silane [54]. The treatment of mercer-... 

Wood modification is a means of altering the material to overcome or ameliorate one or more of its disadvantages. The aim of a modification may be to bring about an improvement in decay resistance or dimensional stability, to reduce water sorption, to improve weathering performance and so on. The term wood modification applies to the application of a process that alters the properties of the material such that during the lifetime of a product no loss of the enhanced performance of the wood should occur. 

Goroyias, G.J. and Hale, M.D. (2002). Heat treatment of wood strands for OSB production effect on the mechanical properties, water absorption and dimensional stability. International Research Group on Wood Preservation, Doc. No. IRGAVP 02-40238. 

Kenaga, D.L. and Sproull, R.C. (1951). Further experiments on dimensional stabilization of wood by allylation. Journal of the Forest Products Research Society, 1, 28-32. 

McMillan, C.W. (1963). Chemical treatment of wood. Dimensional stabilization with polymerisable vapor of ethylene oxide. Forest Products Journal, 13(2), 56-61. 

Risi, 1. and Arseneau, D.F. (1957a). Dimensional stabilization of wood. Forest Products Journal, 7(6), 210-213. 

Seborg, R.M., Tarkow, H. and Stamm, A.J. (1953). Effect of heat upon the dimensional stabilization of wood. Journal of the Forest Products Research Society, 3(3), 59-67. 

Weaver, J.W., Nielson, J.F. and Goldstein, I.S. (1960). Dimensional stabilization of wood with aldehydes and related compounds. Forest Products Journal, 10(6), 306-310. 

D. Plastic Composites. Many different woods have been treated with organic monomers and the monomers catalytically polymerized within the wood structure. The subject of treating wood to form plastic composites is covered by Dr. John Meyer in another section of this publication. For the most part, these composites have been prepared and studied for their use in dimensional-stabilized products (for example, see 13-17). 

Chemical modification of wood does result in a treatment which is nontoxic, effective, and nonleachable. The high chemical treatment level required for effectiveness, however, results in a rather expensive treatment. Dimensional stability is also obtained at these high (17-25 WPG) substitution levels so, for those products where both rot resistance and dimensional stability are important, the present state of the technology is close to a viable industrial process. 

In an unpublished study at the U.S. Forest Products Laboratory, the moisture content of wood treated with two commercial formulations reached 48 to 58 percent (based on ovendry weight of treated sample) in 4 weeks1 exposure at 27°C and 90 percent relative humidity. Continuous exposure of wood treated with water-soluble salts to conditions above 80 percent relative humidity can result in loss of chemicals and in adverse effects on dimensional stability and paint coatings. Corrosion of some metals in contact with the wood will also occur. 

Fifteen years ago, when wood-plastic composites were first introduced many people predicted that this process would solve the problem of wood dimensional stability and great claims were made for its future use. Now that the physical properties of wood-polymer composites are better understood, specific commercial products are being produced which take advantage of the desirable aesthetic appearance, the high compression strength, increased hardness and abrasion resistance and improved dimensional stability. Future use of wood-polymer composites will depend upon the imagination of the producer and the market place. 

They have prepared some compressed wood samples which show, in addition to increased density and surface hardness, a lower moisture regain than untreated wood up to 80% relative humidity. Using materials such as these, they have experimented with the manufacture of parquet flooring, a rather severe test of dimensional stability. A variety of other finished products have been prepared, some on pilot plant scale. However, it is not known to what extent they have appeared as products in the open market. Their technology is available through licensure. 

A wood product of improved dimensional stability can be produced through heat treatment of wood at temperatures varying from 150 to 320°C. For good temperature control and to avoid strength loss the heat treatment preferably is performed under the surface of molten metal or a fused salt for exclusion of oxygen. The modified wood product is referred to as staybwood. 

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