Freeze drying of wood

Sublimacijsko sušenje se uporablja za dehidracijo občutljivih in kemijsko nestabilnih snovi. V lesarstvu je ta tehnika uveljavljena pri sušenju zelo vlažnega arheološkega lesa. Presojali smo možnosti izvajanja sublimacijskega sušenja smrekovine, bukovine in hrastovine z zelo visoko začetno vlažnostjo. V laboratorijskem liofilizatorju smo ugotavljali čas in hitrost sušenja ter ocenili končno kakovost osušenega lesa. Časi sušenja smrekovine in hrastovine so bili krajši od konvencionalnega sušenja. Časi sušenja smrekovine in hrastovine so bili krajši od konvencionalnega sušenja, vendar zaradi zahtevnosti postopka niso izkazovali velike prednosti. Najugodnejši je bil čas sušenja bukovine. Tudi najvišja kakovost sušenja, ki smo jo ocenjevali z vlažnostnim gradientom, stopnjo zaskorjenosti ter pojavom razpok in veženja, je bila dosežena pri bukovini. Na nobeni proučevani lesni vrsti nismo zasledili vpliva postopka na obarvanje.Freeze or sublimation drying is used for dehydration of chemically sensitive and fragile materials. This technique has been established in the wood industry for drying waterlogged wood. We examined the possibillity of using sublimation drying for spruce, beech and oak with very high initial wood moisture content. In a laboratory lyophilizator, we observed the time and speed of drying and assessed the final quality of dried wood. The drying times of spruce and oak were shorter than with conventional drying, yet the complexity of the procedure did not show substantial benefits. The drying time proved optimum with beech. In addition to this, the quality of drying, which was evaluated with moisture gradient, case hardening, and the initiation of checks and wood twist, was also highest with beech. The impact of drying procedure on wood discoloration was not detected in any wood species studied