Low-molecular weight sugars and nitrogenous compounds in Scots pine. Contents in the stem, redistribution during drying of lumber and practical consequences.
1996
Terziev N.
The study deals with the content and distribution of low-molecular weight (LMW) sugars and nitrogenous compounds in the stem of Scots pine, their subsequent redistribution during kiln and air drying of lumber, as well as their effect on mould susceptibility and colour of the dried material, and on coatings. Seasonal fluctuations are more important to the sugar and nitrogen contents than the effects of growth conditions and age of trees. The outer pine sapwood contained a higher content of LMW sugars and nitrogen during autumn and winter than during spring and summer. The contents of soluble sugars and nitrogen increased towards the cambium on all sampling occasions. The fast kiln drying schedules led always to greatest sugar enrichment at the lumber surface. The kiln drying enriched the lumber surface (0-3 mm zone) with LMW sugars and nitrogen, whereas the deeper zones had a constant content of soluble substances. The contents of sugars and nitrogen increased at the surfaces of the planks after air drying, but considerably less than after kiln drying. The content of accumulated soluble substances in the 0-3 mm zone after drying seemed to be proportional to their content in similarly located wood at the time of felling. The most important practical consequence of the redistribution of LMW sugars and nitrogen is the increased lumber susceptibility to mould. The original surfaces of fast kiln-dried lumber were more susceptible to mould growth than those of slow kiln-dried lumber. Planing of kiln-dried lumber is recommended as a simple and applicable means for improving the surface durability of the lumber used in exterior and interior joinery. The resistance of air-dried material to mould was not improved by planning, since the zone richest in nutrients is located deeper below the original surface than in kiln-dried material. The measured contents of LMW sugars and nitrogen at the dried lumber surfaces had no significant effect on the discolouration of coatings. High variation in the content of LMW sugars and nitrogen may influence the natural surface colour of lumber.
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