Timber composites

Studies on structural aspects of aging are very limited in the number of samples and number of timber species examined. The results available today indicate that only minor changes occur in dry wood, even at the ultrastruc-tural level, after 3000-4000 years. However, there may be a variation in the effects of aging, depending on timber species. Chemical differences in timber composition (for instance, type and content of extractives) could possibly be important in the aging process. 

Timber is derived from a great number of botanical species, and has a wide range of properties. Variability also occurs within a single species and in order to achieve acceptable levels of uniformity, selection by grading is necessary. The timber trade differentiates between softwoods and hardwoods, and the latter are again separated into temperate and tropical types. Hardwoods are derived from broad-leaved and mainly deciduous trees, which are anatomically more complex and differ in chemical composition... 

All of the above environmental concerns are leading to restrictions being placed upon the use and composition of preservatives used to treat timber. Preservative systems of the future will therefore be selected not simply on the basis of criteria such as efficacy and cost, but also environmental impact, both during service and at the end of product lifetime. This will inevitably have economic implications. 

MRI is a versatile method and in addition to uses in diagnostic medicine, it is important to note that while MRI is best known as a medical tool, this technique has other useful scientific applications. As an example, geologists have used MRI to examine the composition of geological stmctures, and MRI has also been exploited in assessment of produce and timber quality. However, as noted earlier, MRI scanners cost millions to buy and thousands to run and maintain, so remain a luxury big-budget item. 

The formulation of a paint is a matter of the skill and experience of a paint technologist. It is largely determined by the ratios of the constituents in paints and the nature of the substrate to which the paint is to be applied. For example, a paint for use over concrete pavement will have very different properties from one intended for application to timber floors. Two paints may even be based on the same generic type of vehicle, but the formulation will be quite different in their final composition. 

Figure 1. Commercial timber is obtained from angiosperms (hardwoods) or from gymnosperms (softwoods). The wood tissue is made up largely of dead, hollow plant cells that are arranged to form a composite material of substantial void volume.

JL HE POLYMERIZATION OF VINYL MONOMERS in the void spaces of bulk wood results in wood—polymer composites of increased strength properties and dimensional stability see Chapter 6). Because the different environmental conditions expose in-service timber to attack by numerous wood-deteriorating microorganisms, it is desirable to enhance the biodegradation resistance of wood, with simultaneous improvements in mechanical behavior. This chapter summarizes the formation of bioactive wood-polymer composites (1-4). The basic approach is still in situ polymerization of vinyl monomers in wood, with the appropriate choice of a bioactive, toxic, functional group incorporated in the monomer, and with other modifications based on wood-polymer reactions. 

Blockboard, the original and still highly sueeessful composite, with a side-butted core of timber overlaid by veneer. 

There have been many intereshng approaches to overeome the shortage of high quality, large dimension hmber. Engineers have turned to trusses, I-beams, and space frames to achieve what had previously been aeeomplished by solid timber beams. Composites like glulam and the new produets diseussed below provide substitute elements that can be incorporated into the kinds of modem designs just alluded to. The thmst in the development of these new produets has been improved... 

Huang L-H, Qin T-F, and Ohira Tatsuro (2004) Studies on preparations and analysis of essential oil from Chinese fir. Journal of Forestry Research, 75(1) 80-2 Hudson MS and Henrrksson ST (1956) The oscillation pressure method of wood impregnation. Forest Products Journal, 6(10) 381-6 Hughes C (1982) The natural durability of untreated timbers. What s New in Forest Research No. 112. New Zealand Ministry of Forestry, Forest Research Institute, Rotorua Humphrey PE and Bolton AJ (1989) The hot pressing of dry-formed wood-hased composites. Part 2 A simulation model for heat and moisture transfer, and typical results. Holzforschung, 43 T) 199-206... 

Lehman WF (1986) Outline of a fast durability test for UF and PF adhesives in composite materials. In Maloney T (ed) Proceedings of the 20th Washington State University Particleboard Symposium, Pullman, Washington, 105-22 Leicester RH (1988) Timber engineering standards for tropical countries. Proceedings of 1988 International Conference of Timber Engineers, Seattle. Forest Products Society, Madison, Wisconsin, Vol. 1 177-85... 

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