Spreminjanje pH-vrednosti jesenovine pri konvektivnem sušenju

Changes of pH of sawn wood during conventional drying were studied. Green ashwood boards (Fraxinus excelsior L.), 25.4 mm in thickness, were exposed to 1 month air drying and to kiln drying using 7 schedules, reached by varying temperature (20°C, 30°C and 65°C) and relative air humidity (33% to 90%). Wood samples for pH and moisture content (MC) determination were taken in successive time interval at 3 board`s depths (1/10, 1/3 and 1/2 of thickness).MC was established gravimetrically. pH-value determination of solid wood water system by suspending wood dust into distilled water was used. The lowest used temperature and duration of drying procedure had not significant influence on wood pH. Wood acidification was confirmed at higher drying temperatures (30°C and 65°C), particularly with lower drying rates and prolongation of the procedure. Among all the factors, drying temperature had the greatest impact on the pH-value of wood.Raziskovano je bilo spreminjanje pH-vrednosti lesa med procesom naravnega in komorskega sušenja žaganega lesa. Les velikega jesena (Fraxinus excelsior L.), debeline 25 mm, je bil sušen pod sedmimi konstantnimi sušilnimi režimi, z uporabo 3 temperatur (20°C, 30°C in 65°C) in relativnih zračnih vlažnosti med 33% in 90%. Vzporedno je potekalo zračno sušenje jesenovine v spomladanskih kontinentalnih klimatskih razmerah. Določanje pH vrednosti in lesne vlažnosti je potekalo z odvzemanjem vzorcev v zaporednih časovnih intervalih na 3 globinah žaganic (1/10, 1/3 in 1/2 debeline). Lesna vlažnost je bila določena gravimetrično, pH-vrednost lesa pa z vodno ekstrakcijsko metodo. Vrednosti pH jesenovine se pri sušenju z najnižjo temperaturo niso spremenile. Z višanjem temperature sušenja (30°C in 65°C) se je pH jesenovine značilno zmanjšala, še posebej pri daljšem sušenju in ob uporabi vlažnejših klimatskih razmer v komori. Temperatura sušenja je imela med vsemi dejavniki najbolj izrazit vpliv na pH lesa