Vpliv temperature sušenja na lastnosti lesnih površin

This article deals with modifications of wood surface properties induced by different drying temperatures. The aim of the study was chemical and physical characterization of a wood surface concerning low and high temperature exposure. Additionally, the correlation between the chemical composition of a wood surface and its wetting capacity were investigated. X-ray photoelectron spectroscopy and contact angle measurements were conducted. Two wood species, yellow poplar (Liriodendron tulipifera) and southern pine (Pinus taeda) were studied. The results showed that the percentage of carbon increased with drying temperature, and consequently, the percentage of oxygen decreased. The samples exposed to high drying temperatures indicated a higher content of extractives on the wood surface. These samples exhibited the highest contact angle and the lowest wettabilityPovršina lesa, ki je izpostavljena visokim temperaturam, lahko postane neaktivna. Taka površina je težko lepljiva, zato je dosežena adhezija nezadostna. Neaktivnost lesne površine je povezana s kemičnimi in fizikalnimi spremembami. Cilj raziskave je bil ugotoviti razlike v kemični sestavi površine lesa, ki nastanejo pod vplivom nizkih oziroma visokih sušilnih temperatur. Raziskan je bil tudi vpliv sušenja na omočitev lesa in njena odvisnost od kemične sestave lesne površine. Uporabljena je bila rentgenska fotoelektronska spektroskopija in metoda merjenja kontaktnih kotov. Proučevani sta bili dve ameriški drevesni vrsti: tulipanovec in južni bor. Ugotovljeno je bilo, da se odstotek ogljika na površini lesa povečuje z naraščajočo temperaturo sušenja, medtem ko se odstotek kisika zmanjšuje. Površine lesa, ki so bile izpostavljene visoki sušilni temperaturi, so vsebovale višjo koncentracijo ekstraktivnih snovi kot običajno, kar je povzročilo visok kontaktni kot in slabo omočitev lesne površin

Zgoščevanje lesa

The paper treats the processes involved in wood densification and provides a summary of the state-of-the-art, as presented in the literature, with regard to densification as achieved by compression, accompanied by some form of hydrothermal treatment. The viscoelastic nature of wood is discussed, togetherwith its thermal softening and typical stress-strain relationships. The properties of densified wood products depend, apart from processing parameters, on various anatomical features such as density, the percentage of late wood material, ray volume and the loading direction. The problems associated with wood stabilization after densification are also treated. Relevant examples of wood densification from fundamental research, and the results of applied studies significant for everyday practice, are presented. Aspecial focus is given on the process of viscoelastic thermal compression (VTC) of wood.Članek obravnava procese, ki potekajo med postopkom zgoščevanja lesa, in podaja pregled dosežkov relevantnih raziskav, v katerih je bilo proučevano zgoščevanje lesa s kombiniranim postopkom hidrotermične obdelave in stiskanja.Predstavljena je viskoelastična narava lesa, skupaj s toplotnim mehčanjem oziroma plastifikacijo. Prikazane so značilne zveze med napetostjo in deformacijo lesa pri zgoščevanju. Pojasnjen je vpliv tehnoloških parametrovzgoščevanja in inherentnih značilnosti lesa, kot so gostota, odstotek kasnega lesa, delež trakovnega tkiva in smer obremenjevanja na končnelastnosti zgoščenega proizvoda. Članek obravnava tudi problem stabilizacije lesa po postopku zgoščevanja. Predstavljeni so relevantni primeri zgoščevanja lesa temeljnih raziskav in rezultati študij, ki so pomembni za aplikacijo. Podan je podroben opis procesa viskoelastične toplotnezgostitve (VTC) lesa

Križno lamelirani les – lastnosti in zahteve

Cross-laminated timber (CLT or X-Lam) is a modern building material used for load-bearing construction purposes in residential and non-residential buildings. CLT production has been increasing rapidly in recent years. CLT is suitable for wall, floor, ceiling and roof elements in the construction of houses, multi-family apartment buildings, industrial and storage halls and other buildings and bridges. Manufacturers demonstrate compliance with the essential requirements of the European Construction Products Regulation (CPR) on the basis of an initial type testing and the findings of a factory production control examination. In 2015, a harmonized European standard for CLT was adopted, which defines the requirements for built-in materials, the production and demonstration of constancy of performance, and the CE marking. The article presents the production technology and basic characteristics of CLT and the content of standard EN 16351

Influence of thermal treatment temperature on the dielectric properties of wood

V prispevku so predstavljeni rezultati vpliva temperature termične obdelave nadielektrične lastnosti bukovine (Fagus sylvatica L.) in smrekovine (Picea abies L.). V eksperimentu smo uporabili diskaste preskušance premera 45 mm in debeline 5 mm, ki smo jih termično obdelali pri sedmih različnih temperaturah (50 do 200 °C). Dielektrične lastnosti preskušancev smo ugotavljali pri devetih različnih frekvencah (2 do 10 MHz). Vse meritve smo opravili pri sobnitemperaturi z impedančnim analizatorjem HP 4191A RF po metodi z mikrometrom, na katerega sta bili pritrjeni diskasti aluminijasti elektrodi. Na osnovi dobljenih rezultatov smo ugotovili, da se dielektrična vrednost lesain izgubni kot zmanjšujeta z naraščajočo temperaturo obdelave, če je le-tavišja od 100 °C. Dielektrična vrednost lesa je nižja pri večji izgubi mase preskušanca.The effect of thermal treatment temperature on the dielectric properties of beech (Fagus sylvatica L.) and spruce (Picea abies L.) was investigated. Wood disks with a diameter of 45 mm and a thickness of 5 mm were thermally treated at seven different temperatures (50 to 200 °C) before measurements were performed. Dielectric properties of the wood disks were measured at nine various frequencies (2 to 10 MHz) at room temperature. The impedance analyzer HP 4191A RF and the micrometer screw method with circular aluminum electrodes were used. The results indicate that the dielectric constant and the loss tangent of wood decrease as the temperature of the thermal treatment increases, provided the temperature is higher than 100 °C. The dielectric constant also decreases with increasing weight loss of the specimen

Prof. Dr. Katarina Čufar received the Jesenko Lifetime Achievement Award

In March 2021, Prof. Dr. Katarina Čufar received the Jesenko Lifetime Achievement Award, the most prestigious prize of the Biotechnical Faculty, University of Ljubljana. This is the third award for Katarina Čufar within just a few months, as at the end of 2020 she also received the Golden Plaque from the University of Ljubljana and the Zois Prize of the Republic of Slovenia for significant scientific achievements and exemplary teaching

Prof. Dr. Katarina Čufar received the Zois Prize for important achievements and the Golden Plaque of the University of Ljubljana

At the end of 2020, Prof. Dr. Katarina Čufar received two prestigious awards: the Zois Prize for important scientific research achievements in the development of dendrochronology and wood science, which is a state award of the Republic of Slovenia, and Golden Plaque from the University of Ljubljana for outstanding scientific research, exemplary teaching and achievements in enhancing the university’s reputation. We briefly introduce the prize-winner and her work

Utjecaj količine otapala u utekućenom drvu i dodatka kondenziranog tanina na kvalitetu vezanja

Liquefied wood (LW) is a promising natural material that can be used as a part of the adhesive formulation. However, adhesive bonds made of LW only, have low durability. The aim of this study was, therefore, to increase the durability of adhesive bonds containing LW. LW was obtained with liquefaction of black poplar wood in ethylene glycol (EG) as the solvent and sulphuric acid (SA) as the catalyst. An optimal time of 120 minutes and a wood/EG mass ratio of 1:3 was defi ned for liquefaction at 180 °C. After liquefaction, the EG was evaporated in order to achieve a low solvent content LW with a fi nal mass ratio of 1:1. A hydroxyl number for 1:3 and 1:1 LW was determined in order to examine the reduction of hydroxyl groups. Four different adhesive mixtures were prepared: LW with a mass ratio of 1:1 (LW1:1 ), LW with a mass ratio of 1:3 (LW1:3 ), LW with a mass ratio of 1:1 and added condensed tannin (CT) (LW1:1 /CT), and LW with a mass ratio of 1:3 and added CT (LW1:3 /CT). The solid beech wood lamellas, which were bonded with these adhesive mixtures, were tested directly after bonding, and later on, after 7, 30 and 50 days. The test results indicated greater bonding shear strength in the case of LW1:1 compared to LW1:3. The addition of CT did not contribute to essentially higher shear strength values. The adhesive mixtures LW1:1 and LW1:1 /CT (uncured and cured) were analyzed using FT-IR spectroscopy. No significant differences were observed between the cured LW1:1 and the LW1:1 /CT samples.Utekućeno drvo (LW) perspektivan je prirodni materijal koji može biti upotrijebljen kao tvar za izradu ljepila. Međutim, vezivna ljepila napravljena samo od utekućenog drva imaju malu trajnost. Stoga je cilj provedenih istraživanja bio povećati trajnost vezivnih ljepila koja sadržavaju LW. U provedenim je istraživanjima LW dobiven utekućenjem drva topole u etilen glikolu (EG) kao otapalu i sumpornoj kiselini (SA) kao katalizatoru. Definirano je optimalno vrijeme utekućenja od 120 minuta i maseni omjer drvo:EG u iznosu 1:3 za utekućenje pri temperaturi 180 °C. Nakon utekućenja EG je ishlapljen da bi se postigao nizak sadržaj otapala u LW-u s konačnim masenim omjerom 1:1. Utvrđen je hidroksilni broj za LW s omjerom 1:3 i LW s omjerom 1:1 da bi se ispitalo smanjenje broja hidroksilnih skupina. Pripremljene su četiri različite mješavine ljepila: LW s masenim omjerom 1:1 (LW1:1 ), LW s masenim omjerom 1:3 (LW1:3 ), LW s masenim omjerom 1:1 te dodanim kondenziranim taninom (CT) (LW1:1 /CT), i LW s masenim omjerom 1:3 i dodanim CT-om (LW1:3 /CT). Lamele od bukovine lijepljene su navedenim mješavinama ljepila i ispitane odmah nakon lijepljenja, zatim nakon 7, 30 i 50 dana. Rezultati testa pokazali su veću smicajnu čvrstoću vezanja u slučaju LW1:1 u odnosu prema LW1:3 . Dodavanje CT-a nije znatno pridonijelo većoj smicajnoj čvrstoći. Mješavine ljepila LW1:1 i LW1:1 /CT (nesušene i osušene) analizirane su FT-IR spektroskopijom. Nisu zapažene signifi kantne razlike između osušenih uzoraka LW1:1 i LW1:1 /CT

High-frequency Heating of Wood with Moisture Content Gradient

The influence of moisture content (MC) gradient on the development of a temperature gradient in wood heated in a high-frequency (HF) electromagnetic field was investigated. Fifteen layers of 1.6-mm-thick beech veneer (Fagus sylvatica L.), with dimension 400 X 400 mm, were used to simulate a moisture content (MC) gradient. A uniform MC of 5, 10, 15, and 20%, and two MC gradient schemes ranging from 20% to 5%, were used in the experiment. The dielectric constant and loss tangent were measured before HF heating at 6.3 MHz. During HF heating of wood, the magnitude of the MC, the shape of the MC gradient, and the potential for thermal losses influence the development of the temperature gradient. An MC gradient in a laminated composite could be used to control the shape and severity of the temperature gradient during HF heating

Design and manufacturing of organic shape furniture

Wooden furniture of organic shapes was mostly handmade in the past, each piece was almost unique, since the manufacturing processes did not allow repeatability and larger quantity production of the same products. Today, modern 3D modelling software leads to completely different prospective in wooden furniture design and production. It enables modelling of any kind of shape, based on ideas, natural shapes, even 3D scanned existing shapes, etc. Furthermore, prototypes can be 3D printed. This enables that visual presentation of designed form is made in real. Based on the printed forms virtual models can be improved leading to the final sophisticated model. Additionally, during design process the best construction details can be made to improve material efficiency and manufacturing time. Final product can be than made on CNC machines, enabling reproduction of the same product of desired shape in chosen quantities

Kakovost lepilnega spoja med lesom in jeklom

The aim of the research was to determine the suitability of selected polyurethane and epoxy adhesives for structural bonding of wood and steel. We tested four polyurethane adhesives COSMO and two epoxy adhesives ERGO and XEPOX. The quality of the adhesive bond was evaluated by a shear strength test followed by one of the following exposure tests of the specimens: exposure to the standard climate with 65 % relative humidity and a temperature of 20 °C; exposure to humid climate with 87 % humidity and a temperature of 20 °C; and various exposures (soaking/cooking) in water. The results showed that the polyurethane adhesives studied in this work cannot compete with epoxy adhesives in terms of bonding quality. The epoxy adhesives provided excellent bonding properties in dry conditions, and proved to be potentially suitable for non-structural use in humid conditions. However, in order to use the selected adhesives in construction applications, it is recommended that the adhesive joint should be additionally reinforced with screws to ensure the reliability of the joint in the event of exceptional moisture or fire