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

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

Treatment of recovered wood-based panels

Due to the increasing global production of wood based panels (particleboards, fiberboards, and plywood) problems with raw material and difficult treatment of recovered wood based panels after life cycle occur. Inorganic pollutants represent the main problem of raw material while treatment of recovered wood-based composites is aggravated due to the presence of synthetic adhesives. Latter and the release of methane during anaerobic decomposition are reasons for using alternative methods instead of sending these composites to landfills. The most promising methods of recovered wood-based panels treatment are: hydrothermal recycling, re-manufacturing of panels, combustion and pyrolysis, composting, re-use and some other less used methods for processing of new recycled products

Kinetics and mechanisms of wood liquefaction

Wood liquefaction is the process of wood solvolysis in which basic wood components are degraded to monomers and oligomers in the presence of a suitable solvent and catalyst. These later on react with each other or with the solvent, and insoluble product is produced. The paper describes the mechanisms and kinetics of wood liquefaction and liquefaction of its basic components (cellulose and lignin)

Influence of pH value of liquefied wood on shear strength and durability of bond lines

Liquefied wood is a product of wood solvolysis and can be used as a material for bonding of wood elements. The main problems of bond lines, prepared with liquefied wood, are their low shear strength and durability. This can be the consequence of low reactivity of liquefied wood or pH value, respectively. Curing of liquefied wood was elucidated using rheological measurements. Influence of different pH values of liquefied wood on shear strength value of bond lines and their durability was investigated in this work, as well

Monitoring of curing of liquefied wood and bonding of wood with liquefied wood

Liquefied wood is a potential alternative to the synthetic adhesives which are used for the bonding of wood. Despite the ability of liquefied wood to self-crosslink, bonds formed during the bonding of wood with liquefied wood do not achieve sufficient shear strength and have poor resistance to water. For this reason the process of the curing of liquefied wood, the influence of various parameters on the shear strength of bonds, and the structure of bonds formed during the bonding were analyzed. It was found that the chemical curing of liquefied wood started after water and solvent had been removed from it. When bonding wood, the curing of liquefied wood takes place faster because, in addition to evaporation, the transition of both vaporous components from the liquefied wood to the lamellas also occurs. During the bonding of 5 mm thick beech lamellas with liquefied wood having a negative pH, at optimal bonding conditions (180 °C, 12 min), a specific type of bond was formed. It consisted of a central part of carbonized wood cells of the bonded lamellas and the cured liquefied wood, and a narrow layer of partly delignified wood cells at the border between the central part and bonded lamella

Influence of biocides in glue line on mechanical and fungicidal properties of glued timber

Zaradi težav pri lepljenju impregniranega lesa in nezadostne zaščite lepljenega lesa s premazovanjem smo v lepilno mešanico pred lepljenjem dodali biocid. Biocid je difundiral iz lepilnega spoja v strukturo lesa in tako zaščitil lamele, pri tem pa je moral lepilni spoj ohraniti svoje mehanske lastnosti. Lesene lamele smo lepili z MUF in PU lepilom, ki smo jima dodali 0,5 in 0,1 % bora oz. bakra v obliki borove kisline oz. bakrovega hidroksid karbonata. Mehanske lastnosti lepilnih spojev smo preskušali s strižnim testom (SIST EN 392) in testom delaminacije (SIST EN 391). Pred tem smo utrjevanje lepil spremljali z dielektrično analizo, reološke lastnosti pa z reometrom. Difundiranje bora in bakra smo spremljali vizualno in z ICP ablacijo. Učinkovitost zaščite lepljenih vzorcev pred glivami smo preverjali s testom izpostavitve glivam (SIST EN 113). Ugotovili smo, da je utrjevanje hitreje potekalo pri lepilnih mešanicah z dodanimi biocidi, reološke lastnosti slednjih pa se niso bistveno poslabšale. Strižna trdnost se ob dodanem biocidu ni bistveno znižala oziroma se je v določenih primerih celo izboljšala. Podobno velja za delež delaminiranih spojev. Ugotovljena je bila povezava med vlažnostjo vzorcev in difundiranjem bora. Najhitreje in najintenzivneje so prodirale borove učinkovine iz spojev, ki smo jim dodali 0,5 % bora. Žal pa se je izkazalo, da je količina dodanih aktivnih učinkovin prenizka, da bi zaščitila lepljen les pred najpomembnejšimi glivami razkrojevalkami.Problems related to bonding of impregnated timber and insufficient protection of glued wood with surface treatment were the main reasons for adding biocides to adhesives before bonding. To protect lamellas biocide diffused from the glue line into the wood structure: at the same time the glue lines should have preserved their mechanical properties. Tested samples were glued with MUF and PU adhesives with addition of 0.5 or 0.1 % of boron or copper in form of boric acid and copper hydroxide carbonate. The shear test (SIST EN 392) and delamination test (SIST EN 291) were used to test the mechanical properties of glue lines and dielectric analysis was used to measure glue hardening, while the rheometer to test the rheological properties. Boron and copper diffusion was measured visually and by ICP ablasion. Fungal decay was tested according to SIST EN 113 standard. Results show that glue line hardening was more efficient when using adhesive with added biocidesč the rheological properties of the glues with addition of boric acid did not significantly differ from the glues without biocides. Shear strength prepared with the glues with biocides did not decrease, in contrary, in some cases it even increased. Similar influences of added biocides were observed at the delamination test of glue lines as well. Furthermore, there is a significant correlation between sample moisture content and boron diffusion. The quickest and most intensive diffusion of boron compounds was measured from glue lines with boron concentration of 0.5 %. Unfortunately, it turned out that the amount of added compounds was too low to protect glued timber against fungal decay

Treatment of recovered wood-based panels

Due to the increasing global production of wood based panels (particleboards, fiberboards, and plywood) problems with raw material and difficult treatment of recovered wood based panels after life cycle occur. Inorganic pollutants represent the main problem of raw material while treatment of recovered wood-based composites is aggravated due to the presence of synthetic adhesives. Latter and the release of methane during anaerobic decomposition are reasons for using alternative methods instead of sending these composites to landfills. The most promising methods of recovered wood-based panels treatment are: hydrothermal recycling, re-manufacturing of panels, combustion and pyrolysis, composting, re-use and some other less used methods for processing of new recycled products.Zaradi vse večje svetovne proizvodnje lesnih ploščnih kompozitov (iverne, vlaknene in furnirne plošče) prihaja do težav, povezanih z vhodno surovino in vprašanja ravnanja z odsluženimi lesnimi ploščnimi kompoziti po koncu življenjske dobe. Največje omejitve pri vhodni surovini predstavlja vsebnost anorganskih onesnažil, ravnanje z odsluženimi lesnimi kompoziti pa otežuje prisotnost sintetičnih lepil. Zaradi le-teh ter sproščanja metana med anaerobnim razkrojem na deponijah se države izogibajo odlaganju na odlagališčih in se poslužujejo drugih metod. Med najobetavnejšimi rešitvami so: recikliranje lesnih ploščnih kompozitov s pomočjo hidrotermične obdelave, ponovna izdelava plošč iz reciklirane surovine, sežiganje in piroliza, kompostiranje, ponovna uporaba ter še nekaj redkeje uporabljenih metod za predelavo lesnih kompozitov v reciklirane produkte