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Ksilit je litotip lignita, ki ga poznamo predvsem kot kurivo. Les, iz katerega je nastal, je v obdobju skoraj dveh milijonov let doživel drastične spremembe, struktura lesa pa je delno še prepoznavna. Ksilit po videzu pogosto spominja na lesne vrste s temno jedrovino. Opravili smo karakterizacijo ksilita z vidika anatomije lesa, iz katerega je nastal, raziskali njegovo ohranjenost in določili osnovne fizikalne značilnosti. Prepoznali smo osnovno tkivo iz traheid, enoredno in homocelularno trakovno tkivo, taksodioidne piknje v križnih poljih in obilico aksialnega parenhima z vključki. To nakazuje, da je ksilit nastal iz lesa golosemenk (iglavcev) iz družine Taxodiaceae (taksodijevke) ali Cupressaceae (cipresovke). Barvnometrično je ksilit v sistemu CIELab* primerljiv z jedrovino lesa ebenovine ali wengeja. Proučeni ksilit je imel gostoto v absolutno suhem stanju 1216 kg/m3, zaradi velikega volumenskega skrčka (v povprečju 28.2 %) paje bila srednja osnovna gostota samo 873 kg/m3. Celotni linearni skrčki so veliki, kar se kot posledica kaže v neugodnih kazalnikih dimenzijske stabilnosti (qT = 0.65 %/%, qR = 0.30 %/%). Nadpovprečno visoke so tudi ravnovesne vlažnosti ksilita v procesu desorpcije, sorpcijska kapaciteta v procesu adsorpcije pa je podobna kot pri lesnih vrstah z visoko gostoto. Sorpcijski model GAB se je izkazal kot primeren za izravnavo sorpcijskih podatkov. Xylite is a lithotype of lignite, mainly used for fuel. The wood from which it was formed in a long term process (duration ca. 2 millions of years) was subjected to drastic changes. We conducted anatomical characterization of xylite, evaluated preservation of wood from which it was formed, defined its basic physical properties, and compared it with modern wood. We recognized ground tissue composed of tracheids, uniseriate and homocellular rays, taxodioid like cross-field pits, and abundant axial parenchyma with inclusions. The observed features are typical of coniferous wood species of the Taxodiaceae and Cupressaceae families. Colourimetric properties of xylite in CIELab* system are comparable to those of heartwood of ebony or wenge. The xylite had high oven dry density (1,216 kg/m3), but due to very high volumetric shrinkage (28.2 % on average), its basic density was much lower (873 kg/m3). Total linear shrinkage was considerable in all anatomical directions. Consequently it was characterized by low dimensional stability (qT= 0.65 %/%, qR = 0.30 %/%). The equilibrium moisture content (EMC) in desorption process was high, and that of adsorption was comparable to EMCs of high density wood species. GAB sorption model proved to be appropriate for fitting the data obtained in the sorption process.

Ksilit je litotip lignita, ki ga poznamo predvsem kot kurivo. Les, iz katerega je nastal, je v obdobju skoraj dveh milijonov let doživel drastične spremembe, struktura lesa pa je delno še prepoznavna. Ksilit po videzu pogosto spominja na lesne vrste s temno jedrovino. Opravili smo karakterizacijo ksilita z vidika anatomije lesa, iz katerega je nastal, raziskali njegovo ohranjenost in določili osnovne fizikalne značilnosti. Prepoznali smo osnovno tkivo iz traheid, enoredno in homocelularno trakovno tkivo, taksodioidne piknje v križnih poljih in obilico aksialnega parenhima z vključki. To nakazuje, da je ksilit nastal iz lesa golosemenk (iglavcev) iz družine Taxodiaceae (taksodijevke) ali Cupressaceae (cipresovke). Barvnometrično je ksilit v sistemu CIELab* primerljiv z jedrovino lesa ebenovine ali wengeja. Proučeni ksilit je imel gostoto v absolutno suhem stanju 1216 kg/m3, zaradi velikega volumenskega skrčka (v povprečju 28.2 %) paje bila srednja osnovna gostota samo 873 kg/m3. Celotni linearni skrčki so veliki, kar se kot posledica kaže v neugodnih kazalnikih dimenzijske stabilnosti (qT = 0.65 %/%, qR = 0.30 %/%). Nadpovprečno visoke so tudi ravnovesne vlažnosti ksilita v procesu desorpcije, sorpcijska kapaciteta v procesu adsorpcije pa je podobna kot pri lesnih vrstah z visoko gostoto. Sorpcijski model GAB se je izkazal kot primeren za izravnavo sorpcijskih podatkov. Xylite is a lithotype of lignite, mainly used for fuel. The wood from which it was formed in a long term process (duration ca. 2 millions of years) was subjected to drastic changes. We conducted anatomical characterization of xylite, evaluated preservation of wood from which it was formed, defined its basic physical properties, and compared it with modern wood. We recognized ground tissue composed of tracheids, uniseriate and homocellular rays, taxodioid like cross-field pits, and abundant axial parenchyma with inclusions. The observed features are typical of coniferous wood species of the Taxodiaceae and Cupressaceae families. Colourimetric properties of xylite in CIELab* system are comparable to those of heartwood of ebony or wenge. The xylite had high oven dry density (1,216 kg/m3), but due to very high volumetric shrinkage (28.2 % on average), its basic density was much lower (873 kg/m3). Total linear shrinkage was considerable in all anatomical directions. Consequently it was characterized by low dimensional stability (qT= 0.65 %/%, qR = 0.30 %/%). The equilibrium moisture content (EMC) in desorption process was high, and that of adsorption was comparable to EMCs of high density wood species. GAB sorption model proved to be appropriate for fitting the data obtained in the sorption process.

Kalorične lastnosti ksilita, litotipa lignita, so dobro raziskane, saj se pretežno uporablja kot gorivo. Natančnejše poznavanje njegove anatomske zgradbe ter fizikalnih in mehanskih lastnosti bi omogočilo izdelavo tudi uporabnejših izdelkov. Z mikroskopsko karakterizacijo zgradbe ksilita in proučevanjem osnovnih sorpcijskih in krčitvenih lastnosti smo določili sušilne parametre ter jih preverili v laboratorijskih pogojih. Gostota ksilita (ro=1229 kg/m3) je primerljiva z najgostejšimi listavci to povzroča močno krčenje. Na veliko nestabilnost kažejo tudi neugodno diferencialno nabrekanje, koeficient nabrekanja in sorpcijski kvocient. Sušilna krivulja izkazuje zelo kratek linearni odsek in velik difuzijski upor v 2. in 3. fazi sušenja. Zaradi različnih vključkov, deorientiranosti tkiva in velikih sušilnih napetosti je kohezivnost tkiva slaba, kar zmanjšuje kakovost in izkoristek osušenega ksilita. Calorific properties of xylite, litotype of lignite, are well researched, because it is used mainly as a fuel. If we knew the anatomical structure, physical and mechanical properties better, it would allow us to expand the use of xylite to some other areas. Using microscopic characterization drying parameters were defined and verified in laboratory conditions. Density of xylite (ro=1229 kg/m3) is comparable with highest densities of hardwoods. As a result xylite has high shrinking rate, differential shrinkage, shrinking and sorption coefficient. Drying curve has very short linear part and great diffusion resistance in 2nd and 3rd phase of drying. Poor cohesion of xylite tissues, caused by mineral inserts and deorientation of tissues, and great drying tensions are responsible for low efficiency of drying process.

Xylite very much has the appearance of precious wood species with dark heartwood and also has some physical and aesthetical properties of wood, required nowadays for making valuable products. Xylite, with well recognizable and preserved wood structure, was used for studying the drying kinetics and drying quality. The drying experiments were carried out at 20 °C and 40 °C using constant relative air humidity ranging from 34 % to 87 %, on elements 6 mm, 12 mm and 18 mm thick. The visual assessment of the drying quality was additionally made by light microscopy fracture analysis. The drying time increased with the increase of relative humidity and thickness of specimens. The yield of dry material decreased with the increase of drying time and with the increase of specimen thickness. End-splitting and bowing were the most common drying defects on tangentially oriented specimens. The failure usually occurred in collapsed earlywood, in disoriented tissue or in places with soil or mineral inclusions., Ksilit izgledom podsjeća na dragocjene vrste drva tamne srži i još posjeduje relevantna fizikalna i estetska svojstva drva koja su poželjna za izradu vrijednih proizvoda. Na uzorcima ksilita dobro vidljive i očuvane strukture drva istraživana je kinetika sušenja i kvaliteta osušenih elemenata. Eksperimenti sušenja izvedeni su s elementima ksilita debljine 6, 12 i 18 mm, pri temperaturama 20 i 40 °C u intervalu relativne vlažnosti zraka od 34 do 87 %. Vizualna procjena kvalitete dodatno je ispitana primjenom frakturne analize i svjetlosnog mikroskopa. Vrijeme sušenja produžavalo se s povećanjem relativne vlažnosti zraka i debljine elemenata, a kvalitativno iskorištenje materijala smanjivalo se s produljenjem vremena sušenja i s povećanjem debljine elemenata. Glavne greške sušenja bile su čeone pukotine i uzdužno zakrivljenje tangencijalno orijentiranih uzoraka. Najčešće mjesto grešaka sušenja bilo je kolabirano rano drvo, na mjestima velike dezorijentacije vlakanaca te tkiva s mineralnim i zemljanim inkluzijama. Savijanje osušenih uzoraka ksilita dodatno se pripisuje povećanju gustoće tog materijala.

The structure of xylite as lithotype of lignite indicates that it predominately originates from tree stems, from the family Taxodiaceae or Cupressaceae. Despite drastic changes in the long term process of its transformation, it retains some relevant properties of wood, nowadays applicable for specific products. The research examined the influence of moisture content and temperature on modulus of elasticity (MOE) and modulus of rupture (MOR) as well as shear strength and hardness. With decreasing of moisture content, the bending strength and stiffness of xylite increased and was best fitted by power regression model. The increasing of testing temperature from 20 °C to 80 °C had negative effect on stiffness and bending strength of xylite. The hardness was positively correlated with density of xylite, whereas shear strength had the opposite tendency., Građa ksilita, litotipa lignita, pokazuje da on većinom potječe iz stabala porodica Taxodiaceae i Cupressaceae. Usprkos drastičnim promjenama u dugotrajnim geološkim procesima transformacije, ksilit je zadržao neka važna svojstva drva. U istraživanju je ispitivan utjecaj sadržaja vode i temperature ksilita na njegov modul elastičnosti i modul loma pri savijanju, kao i na smicajnu čvrstoću te na tvrdoću. Sa smanjivanjem sadržaja vode u ksilitu posmična čvrstoća i modul elastičnosti poboljšavaju se. Ovisnost najbolje opisuje potencijski regresijski model. Podizanje temperature s 20 na 80 °C negativno je utjecalo na modul elastičnosti i čvrstoću savijanja ksilita. Tvrdoća ksilita bila je u pozitivnoj korelaciji s gustoćom, a smicajna čvrstoća se s povećanjem gustoće smanjila.