Influence of transpiration on discolouration of beech wood during kiln drying

Raziskovali smo učinek sečnje na suš in transpiracijskega sušenja na obarvanje bukovine (Fagus sylvatica L.) med postopkom konvekcijskega sušenja. Med 4 postopki sušenja (pri temperaturah 20 °C in 38 °C ter relativnih zračnih vlažnostih 33 % in 75 %) smo s sistemom CIE L a b spremljali spremembo barve po prerezu 25 mm in 50 mm debelih elementov. Primerjali smo obarvanje med takoj po poseku drevesa tehnično sušenimi elementi in tistimi, ki smo jih tehnično sušili po 16 dnevnem transpiracijskem sušenju. Les po sečnji na suš je imel nižjo in predvsem bolj enakomerno razporejeno vlažnost. Vpliva transpiracijskega sušenja na kinetiko sušenja nismo ugotovili, značilen pa je bil ugoden vpliv na obarvanje. Celotna barvna razlika in razlika svetlosti sta bili pri transpiracijsko sušenem lesu značilno manjši pri vseh postopkih tehničnega sušenja. Manjše tveganje obarvanja transpiracijsko sušenega lesa ostaja tudi, če poteka proces pri višji temperaturi in manjši ostrini.Effect of transpiration drying on discolouration of beech wood during convection drying procedure was studied. In 4 different drying procedures (at temperatures 20 °C and 38 °C, and at relative humidity 33 % and 75 %), colour changes were observed, using CIE L a b system within sections of 25 mm and 50 mm thick elements. The colour of elements, kiln dried immediately after tree felling, was compared to that of elements dried after 16 days transpiration drying. Beech wood after transpiration drying had lower and more homogeneously dispersed moisture. Influence of transpiration drying on drying kinetics was not detected, but it had advantageous effect on colour change. Whole difference in colour and lightness of transpiration dried wood was significantly smaller after all kiln drying procedures. Lower risk of discolouration remained at transpiration drying of beech wood, if the drying procedure had run at higher temperature and lower sharpness