Dieter Eckstein, 1939-2021 and his rich legacy of dendrochronology in Slovenia and the world

Prof. Dr. Dieter Eckstein (1939-2021) was a leading scientist, teacher, mentor, leader, promoter and motivatorin the field of dendrochronology and wood biology. After graduating in wood science and receiving a PhD indendrochronology, he was professor of wood biology at the University of Hamburg. From 1995-2004, he was Director of the Department of Wood Biology, University of Hamburg, and of the Institute of Wood Biology and Wood Protection at the Federal Research Centre for Forestry and Forest Products in Hamburg, Germany. His work had a decisive influence on the development of wood anatomy, wood biology and dendrochronology and his laboratory was a reference point for dendrochronology worldwide. He supported dendrochronologists throughout Europe and around the world in their pioneering work to establish dendrochronology laboratories and develop dendrochronology in numerous countries, including Slovenia.

Uporaba lesno-plastičnih kompozitov v tehnologiji 4D tiska

Tridimenzionalni tisk (3D) z uporabo lesno-plastičnih filamentov je že dobro poznan, vse bolj pa se raziskuje tudi uporaba lesa v štiridimenzionalnem (4D) tisku. 4D tisk je razvijajoče se področje dodajalnih tehnologij, kjer s primerno zasnovo 3D tiskanja in uporabo ustreznih materialov naredimo izdelke, ki ob ustreznih zunanjih sprožilcih spreminjajo obliko in tvorijo dinamične strukture. Pri 4D tisku lahko higroskopnost lesa - običajno pojmovano kot njegovo pomanjkljivost - izkoristimo in zasnujemo izdelke, ki spremenijo obliko glede na spremembo klimatskih pogojev, predvsem vlažnost okolice. V raziskavi smo s FDM tehnologijo (modeliranje s spajanjem slojev) 3D tiska iz PLA (polimlečna kislina) in lesno-plastičnih filamentov (les-PLA) izdelali preizkušance z različnimi razmerji materialov, pri katerih smo spremljali odziv v spreminjajočih klimatskih pogojih. Za spremljanje spremembe oblike, kot je ukrivljanje, smo izdelali sestavljene preizkušance po principu bimetala (aktuatorje), kjer smo za pasivno plast (ob spremembi vlažnosti okolice ne spreminja svojih dimenzij) uporabili PLA, za aktivno plast (spreminja dimenzije ob spremembi vlažnosti okolice) pa les-PLA v različnih razmerjih debelin ter jih izpostavili laboratorijskim ter zunanjim pogojem. Rezultati so pokazali, da dodatek lesa pri lesno-plastičnih kompozitih v spreminjajoči se klimi povzroča dimenzijske spremembe in s tem spremembe oblike načrtovanih aktuatorjev. Sprememba oblike je odvisna od razmerja debelin slojev materialov v dvoslojnem aktuatorju, od sorpcije vodne pare ter od vsebnosti lesa v uporabljenem lesno-plastičnem kompozitu.

Motivacija za izobraževanje in usposabljanje generacij Y in Z v lesarstvu

Z industrijo 4.0 vstopamo v digitalno dobo, kjer se bodo tudi v lesnopredelovalnih podjetjih bistveno spremenile zahteve po znanjih in kompetencah zaposlenih. To vpliva tudi na izobraževanje na področju lesarstva. Cilj raziskave je bil ugotoviti, kateri načini poučevanja in učenja najbolj motivirajo predstavnike generacij Y in Z, na različnih nivojih izobraževanja (od poklicnega izobraževanja do magistrskega študijskega programa) v lesarstvu, kakšen način izvedbe izobraževanja je zanje najprimernejši in kaj menijo o študiju na daljavo. V ta namen smo izvedli anketiranje s pomočjo družabnih omrežij in e-učilnice. Rezultati so pokazali, da anketirane najbolj motivira okolje, naravnano k razvoju, je varno in stabilno ter delo v delovni skupini, medtem ko si ne želijo tekmovalnega okolja. Med skupinami na različnih ravneh in načinih izobraževanja (redno, vseživljenjsko) nismo opazili večjih razlik v motivacijskih dejavnikih. Sicer pa glavno motivacijo učečih se v lesarstvu ne glede na generacijo predstavljajo notranje spodbude posameznika, medtem ko se zunanje spodbude med generacijami bolj razlikujejo.

Odpornost premazov proti obarvanju zaradi grč v lesu

Po premazovanju lesa in izpostavitvi zunanjim klimatskim pogojem in/ali višjim temperaturam lahko namestih, kjer so prisotne grče, pride do obarvanja utrjenega filma, ki ga povzročajo hidrofilni in lipofilni ekstraktivi.Zaradi tega je odpornost premaznega sistema proti obarvanju zaradi grč v lesu zelo pomembna. V naši raziskavi smopreizkusili nekaj osnovnih tipov belo pigmentiranih sistemov. Pri tem smo metodo SIST EN 927-7:2020 ustrezno prilagodilinašim zmogljivostim, jo optimizirali in kritično presodili, ali so kje možne izboljšave standardizirane metode.Rezultati naše raziskave so pokazali, da je odpornost premaznih sistemov proti obarvanju zaradi grč v lesu povezana z vrsto topila v premazih, s prekrivnostjo sistema in njegovo slojnostjo oz. debelino suhega filma. Premazi na osnovi organskih topil so se izkazali za boljše, prav tako tisti, ki so vsebovali več pigmentov, in tisti z večjo debelino suhega filma. Prav tako smo dokazali, da lahko z vrednotenjem barvnih razlik na mestih z grčami in brez njih že pred izpostavitvijo in upoštevanjem te izhodiščne barvne razlike pri vrednotenju razlik po izpostavitvi premazne sisteme veliko bolj objektivno razvrstimo po njihovi učinkovitosti proti obarvanju zaradi grč v lesu. Na podlagi te ugotovitve menimo, da je standardizirano metodo potrebno ustrezno korigirati.

Wood analyses helped to determine the location and approximate construction period of the Roman bridge over the Drava River in ancient Poetovio (Ptuj, Slovenia)

We present the results of a dendrochronological study and radiocarbon dating of the wooden piles of the bridge over the Drava River in Ptuj. The piles, together with stone elements (a fragment of an imperial building inscription and parts of the architectural decoration) were retrieved from the riverbed in 1913 and are now in the Regional Museum Ptuj - Ormož. Using dendrochronology, radiocarbon dating of carefully selected annual rings in the wood and calibration with the wiggle-matching method, the date of the last (outermost) annual ring on the pile was determined to be 161 ± 27 cal AD (1σ) or 160 ± 32 cal AD (2σ). Since the pile contained no sapwood, the dating approximately agrees with the date of the building inscription on the stone slab, which attributes the commission for the reconstruction or construction of the bridge to Emperor Hadrian in the last years of his reign (117-138 AD). The dating of the wood has thus confirmed that the remains examined do indeed belong to a Roman bridge, probably built or renovated during the reconstruction of the road network in the area of the colony of Poetovio under Hadrian or one of his successors.

Anatomical and chemical characterization of Alstonia boonei for pulp and paper production

Alstonia boonei, an abundant lesser utilized species within the West African Subregion, was evaluated as an alternative raw material for pulp and paper production. The basic density (BD), fibre characteristics [fibre length (FL), fibre diameter (FD), lumen diameter (LD) and wall thickness (WT)], derived anatomical indices [Flexibility Ratio (FR), Slenderness Ratio (SR), Rigidity Coefficient (RC), Luce’s Shape Factor (LSF), Solids Factor (SF) and Runkel Ratio (RR)] and chemical composition (lignin, holocellulose, 1% NaOH solubility and ash contents) of A. boonei were studied to evaluate variation along the trunk (base, middle and top portions) and ascertain its suitability for pulp and paper production. Significant variations were observed in the density and fibre characteristics along the trunk of the tree. Although the FD was large, the observed adequate FL, thin-wall and large LD implied easy beating of fibres and manufacture of dense, smooth and strong papers. The favourable SF, RR, FR, RC, and LSF values obtained for the fibres would produce papers with suitable burst and tearing strengths and folding endurance. Chemically the lower lignin (< 30%), ash and 1% NaOH solubility and the high holocellulose contents of A. boonei, will generate a higher pulp yield. A. boonei although a low-density species, will be desirable for pulp and paper production.

Analysing the effect of thermal modification on the calorific values of Eucalyptus nitens wood

Gross and net calorific value of 13 samples of Eucalyptus nitens wood were determined at HAWK (Hochschule für Angewandte Wissenschaft und Kunst), Göttingen, Germany. Among 13 samples, 12 were thermally modified and one was unmodified. Calorific values of samples were determined by using a bomb calorimeter, and the wood components (cellulose, hemicellulose, lignin, and extractives) already analysed by Wentzel et al. (2019). After determination of the values, samples were statistically analysed by R studio to find the relations among the calorific value, temperature, and wood components. The gross calorific value and net calorific value of the untreated sample of Eucalyptus nitens were found to be 18.83 MJ/kg and 17.48 MJ/kg, and after thermal modification these increased up to 20.24 MJ/kg and 18.84 MJ/kg. Upon statistical analysis, the results for lignin showed a strong correlation with the temperature of thermal treatment and calorific value.

Comparison of mechanical properties of recent and 400-year-old European larch

Wood is considered the leading building material throughout the history of mankind. Wood has several advantages over other construction materials, which also makes it one of the most promising materials of the future. The environmental aspect also plays a major role today, as wood is a natural, renewable resource whose processing is very energy-intensive. Due to its repeated and widespread use in construction, the prediction of mechanical properties and their change over time is also very well known, as the overall safety of all buildings also depends on it. Therefore, we compared the mechanical properties of fresh European larch (Larix decidua) and 400-year-old larch found in the Ruard manor house on the Stara Sava in Jesenice, where the renovation of Upper Sava Museum is currently underway. In order to predict what will happen to the wood in the long term, it is necessary to expose the wood to the same conditions, i.e. to change it with dynamic loads or material fatigue. The effect of aging on flexural strength has not been confirmed. Fatigue results show that old wood withstood about 18 times fewer load cycles than recent larch wood.

Thermal conductivity of different bio-based insulation materials

To achieve the zero-waste goal as well as sustainability, the use of the raw materials, especially those from nature, and wood in particular, has to be smart, meaning that the resource has to be used to its full potential. Since wood-based industry is associated with high intensity and the generation of a relatively large amount of residues, those residues should be used for the production of useful products, otherwise they will easily be classified as waste and afterwards used as a source of energy. To present a possible solution for wood residues like wood chips, wood particles and bark, we investigated the possibility of using wood and bark residues as constituents for the production of single layer insulation panel with a target thickness of 40 mm and target density of 0.2 g·cm-3. Thermal conductivity was determined using the steady state principle at three different temperature settings. The average thermal conductivities were determined between 49 mW·m-1·K-1 and 74 mW·m-1·K-1. The highest values were determined at boards made from bark, which also had the highest density (0,291 g·cm-3), while the lowest thermal conductivity was observed for boards made from spruce wood particles.

Prof. dr. Katarina Čufar je prejela Jesenkovo nagrado za življenjsko delo

Prof. dr. Katarina Čufar je v marcu 2021 prejela Jesenkovo nagrado za življenjsko delo, ki je najprestižnejše priznanje Biotehniške fakultete Univerze v Ljubljani. To je tretja nagrada za Katarino Čufar v kratkem času, saj je konec leta 2020 prejela tudi Zlato plaketo Univerze v Ljubljani in Zoisovo priznanje Republike Slovenije za pomembne znanstvenoraziskovalne dosežke in uspešno pedagoško delo.