Ghent University. Faculty of Bioscience Engineering
Abstract
Wood is very diverse and has specific features making it easily distinguishable from other materials. Due to its properties it can be applied both inside and outside, making it a rewarding material to work with. However, when applied outside it is liable to weathering, inducing changes to the wood, like i.e. surface discolouration, dimensional changes or even wood rot, which are not appreciated by end-users. Therefore wood constructors are looking for protection methods of wood, leading to longer service life of their wood products.
Since pressure is put on traditional wood preservation due to environmental and health considerations, new treatment technologies aiming at improved wood properties are launched. Besides wood modification technologies, treatments with organosilicon compounds were proposed. These chemicals proved to be suitable for the protection of other building materials like concrete and might therefore also be suited for wood.
To be able to optimise the treatment process and perform quality control afterwards, detection techniques of organosilicons in treated wood could be very helpful. Visualisation combining several scanning techniques proved to be suitable for this purpose and with new, more precise technologies being developed, the possibilities will only grow. However, before quantitative determination will be useful for these purposes obstacles related to the accuracy of the chemical analysis need to be overcome.
Since fungal attack is of major concern for the performance of a specific element, research was done to determine the fungal resistance of organosilicon treated wood and on methodology how to properly interpret the results. Furthermore care must be taken with the ecotoxicological consequences of the applied products. Therefore a study was devoted to developing a methodology determining on one hand the fungal efficacy of a certain treatment, while on the other hand the impact to the environment of this treatment was estimated. It was found that improving one parameter was often at the expense of the other parameter. Addition of a biocide improved fungal resistance, but increased the ecotoxicological risk of the leachates of the treated wood.
Organosilicons are known as water repellents and are assumed to interfere in the wood-water relationship. Whatever laboratory test performed, this assumption could not be corroborated when organosilicons were applied at concentrations supposed to be economically feasible. When evaluating high retentions to the envelope of the material, better performance was achieved and this both for solid wood and plywood. However, the efficacy was reduced due to weathering.
It can be stated that none of the laboratory tests was very hopeful for the application of organosilicons at economically feasible concentrations for wood used outdoors, out of ground contact. It was also demonstrated several times that the standard evaluation methods available are not really suitable for the evaluation of newly developed wood treatments. Therefore small-scaled wooden elements were constructed and exposed to accelerated natural weathering. This time organosilicon impregnated wood behaved much better than the untreated Scots pine sapwood reference material. Due to the treatment fungal discolouration, mass loss and moisture content could be reduced, without the application of a biocide. Further adding a biocide enhanced the first two parameters.
Concluding it can be said that organosilicons seem to have certain potential in improving wood characteristics like moisture balance and fungal resistance, as shown in field experiments. Nevertheless it remains doubtful whether that will be sufficient to protect wood in the long term. It is more likely that organosilicons will become one of the components in a more complex formulation than that they will be applied on their own
