The influence of the anatomical structure of birch wood on its permeability to liquids

Birch is one of the most common hardwood trees in Russia. In addition to relatively high physical and mechanical properties, birch wood has a number of disadvantages. Wood modification and active compounds to be used to impregnate birch wood can neutralise such negative properties. According to available information, these impregnation compounds are not always uniformly localised along the width of an annual ring when wood is impregnated. To identify the causes of nonuniform localisation, we studied the anatomical structure of birch wood along the width of the annual ring. To do so, samples of 20×20×100 mm (the latter along the fibres) were impregnated with an acid dye in an autoclave. After impregnation, the samples were kept for 24 hours under normal conditions to redistribute the dye. After that, wood sections of 20×20×20 mm were cut out of the central part of the dyed samples. Based on the resulted samples nonuniformly dyed along the width of the annual ring, we used our standard method to make transverse wood microcuts, on which the distribution of the dye was studied using a microscope and a digital camera. To study the structural anatomical characteristics of birch wood elements localised in different parts along the width of the annual ring, the wood tissue taken from the «early» and «late» zones of the ring was macerated. The microstructure of the wood fibres obtained from various parts of the annual ring was studied in transmitted light using a microscope and a digital camera. In the course of microscopic studies, the ScopyFoto software product was used to measure anatomical parameters, such as length, cavity diameter, cell wall thickness, pore number and size. The data obtained were processed using Microsoft Excel and Statgraphics. As a result of the studies, it was established that fibrous tracheids located in the «late» zone of the annual layer, in comparison with tracheids of the «early» zone, have 26% larger cell cavities, 47% thicker cell walls, 11.1% more width of bordered pores, as well as 17% more number of pores. But as for their height, the fibre tracheid pores of the «early» zone exceed those of the «late» zone by almost 27.5%. The fibre tracheids of the «early» and «late» zones of the annual ring have no significant differences in the length. Based on the obtained data, one of the reasons for the uneven coloring of the annual birch wood layer across the width seems to be the difference in the filtration parameters of the impregnation solution due to the difference in the pore width of fibrous tracheids in the «early» and «late» zone of the annual layer.

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