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

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

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

Sestava, lastnosti, uporaba in reciklaža Kerrocka

Kerrock is a solid surface composite material, which is composed of 40 wt.% of polymethylmethacrylate (PMMA) and 60 wt.% of aluminium trihydroxide (ATH) filler with silane as a coupling agent. Similar material is also called PMMA/ATH composite in the academic literature, while Kerrock is one of its commercial names. PMMA is a hard material that is water- and UV-resistant and easy to work with, although its characteristics depend on the degree and process of polymerization that occurs. ATH is a white, nontoxic material that is relatively soft and non-abrasive. It is widely used as an effective fire-retardant filler in polymer composites. Because of its composition, the machining of Kerrock is similar to the machining of wood. Moreover, it can also be thermoformed, like thermoplastics. Kerrock is widely used for work surfaces and cladding, with both indoor and outdoor applications. The material’s interfacial morphology, interfacial adhesion between the filler and polymer matrix, dispersion of ATH particles and concentration of adhesion promoting agent have the biggest impacts on the mechanical characteristics of Kerrock. While it is possible to chemically recycle Kerrock, the energy required for this is too high for this process to be practical. Another option for recycling this composite is to combine its particles in a hot press or to add MMA or polyester resin before pressing. However, there remains much work to be done with regard to effectively recycling Kerrock

Upogibna trdnost in togost slojnatega furnirnega lesa (LVL) iz termično modificirane in nemodificirane bukovine

The aim of the research was to define and develop a wooden composite with a thin cross-section and which could be used as reinforcement material in oversized wooden window profiles. An additional limitation was to bond the composite at room temperature. Based on a review of the literature, laminated veneer lumber (LVL) was chosen as the best option. The researched LVL samples were made of 0.5 mm thick, cut, beech (Fagus sylvatica L.) veneer, bonded with polyurethane adhesive (Purbond HB 440). Half of the samples were made of thermally modified veneers, and other half of unmodified. Bending strength and stiffness were determined with a three-point bending test. Thermally modified samples had on average 19 % lower bending strength compared to the unmodified samples, but the modulus of elasticity (stiffness) did not change significantly. The bending strength of up to 150 MPa was satisfactory, but the modulus of elasticity of 13 GPa was far below expectations. This is attributed to the selection of too thin veneer and too low bonding temperature, which does not enable densification of the composite