Search

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 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.

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.

Phenol-formaldehyde adhesives are in the wood industry most commonly used for bonding of structural wood composites where high strength and durability of the bond line is desired. Their curing is rather complicated due to the reactions that can occur simultaneously. Based on the acidity or alkalinity of added catalyst during the synthesis, these adhesives are divided into novolak and resol type of resins. In the study, the curing of different commercial resol type phenol-formaldehyde adhesives was analysed with differential scanning calorimetry (DSC). The influence of the addition of basic catalyst on the curing of the selected adhesive was examined, and a simulation of time required for the curing of the adhesive at isothermal conditions was also made. It was found that the curing processes of different adhesives varied. Because the examined phenol-formaldehyde adhesives were already optimised during the process of synthesis by means of optimal catalyst addition, the additional amount of catalyst into selected phenol-formaldehyde adhesive was unnecessary and has a negative impact on its curing.

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.

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.

Utekočinjanje lesa je proces solvolize lesa, pri katerem se ob prisotnosti topila in primernega katalizatorja osnovne komponente lesa degradirajo do stopnje monomerov in oligomerov. Ti v nadaljevanju medsebojno reagirajo oziroma reagirajo s topilom, pri čemer nastaja netopen produkt. V prispevku so podrobneje opisani mehanizmi in kinetika utekočinjanja lesa ter njegovih posameznih komponent (celuloza in lignin).

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.

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).

Abundant amounts of plants and their products can be found in the nature. They can be used as potential material to produce wood adhesives because of their ability to bond different materials. Furthermore, their environmental pollution is minimal, volatile organic compound emission is low, they are renewable and affordable in their basic form. Production of wood adhesives based on plants and their products is a sphere where many studies and attempts of industrial applications have already been done. Results of these studies and efforts to develop wood adhesives based on soy, carbohydrates fro mnatural sources and other plant materials are presented in this article. Rastline in njihovi produkti so v naravi dostopni v izdatnih količinah. Njihova sposobnost tvorjenja vezi med različnimi materiali je pomemben dejavnik, ki jih uvršča med potencialne surovine za izdelavo lepil za les. Poleg tega ti materiali minimalno onesnažujejo okolje, vsebnost hlapnih organskih spojin je nizka ali ničelna, so obnovljivi in v svoji prvotni obliki cenovno dostopni. Na področju izdelave lepil na osnovi rastlin in njihovih produktov je bilo opravljeno večje število raziskav in poskusov industrijske uporabe. V članku so predstavljeni rezultati teh raziskav in poskusov razvoja lepil za les na osnovi soje, ogljikovodikov iz naravnih virov in ostalih rastlinskih materialov.

Animal substances were important raw material for adhesive production until the middle of the 20th century, when animal adhesives were replaced by new and better synthetic adhesives. Good adhesive properties placed animal materials among the most important natural materials for production of adhesives. Animal adhesives have been a subject of many studies and attempts of industrial applications. Results of these studies and efforts to develop wood adhesives based on proteins derived from hides, bones, blood, sea-water and other organisms and adhesives from casein and shellac are presented in this article. Materiali živalskega izvora so bili vse do sredine 20. stoletja pomembna surovina za izdelavo lepil, nato pa so živalska lepila izpodrinila nova in boljša sintetična lepila. Dobre adhezijske lastnosti so materiale živalskega izvora uvrščale med najpomembnejše naravne materiale za izdelavo lepil. Lepila na osnovi materialov živalskega izvora so bila predmet številnih raziskav in poskusov industrijske uporabe. V članku so predstavljeni rezultati teh raziskav in poskusov razvoja lepil za les na osnovi proteinov, pridobljenih iz kosti, kož, krvi ter morskih in ostalih organizmov ter lepil iz kazeina in šelaka.

Zaradi čedalje večje okoljske osveščenosti, vse strožjih okoljevarstvenih zahtev, uvedbe uredb glede hlapnih organskih substanc (HOS) in višanja cen naftnih derivatov, na trg prodira vse več novih izdelkov iz naravnih materialov. Izdelava lepil za les na osnovi naravnih in obnovljivih virov je področje, na katerem je bilo opravljeno precejšnje število raziskav in poskusov uporabe v industrijske namene. V članku so predstavljeni rezultati teh raziskav in poskusov razvoja lepil za les na osnovi tanina, lignina in utekočinjenega lesa. Increasing ecological consciousness, strict environmental demands, introduction of volatile organic compound (VOC) ordinances and price rising of oil derivatives are main reasons for numerous new nature-based products. Production of wood adhesives based on natural and renewable sources is a sphere where many studies and attempts of industrial applications have already been done. Results of these studies and trials to develop wood adhesives based on tannin, lignin and liquefied wood are presented in this article.

Increasing ecological consciousness, strict environmental demands, introduction of volatile organic compound (VOC) ordinances and price rising of oil derivatives are main reasons for numerous new nature-based products. Production of wood adhesives based on natural and renewable sources is a sphere where many studies and attempts of industrial applications have already been done. Results of these studies and trials to develop wood adhesives based on tannin, lignin and liquefied wood are presented in this article. Zaradi čedalje večje okoljske osveščenosti, vse strožjih okoljevarstvenih zahtev, uvedbe uredb glede hlapnih organskih substanc (HOS) in višanja cen naftnih derivatov, na trg prodira vse več novih izdelkov iz naravnih materialov. Izdelava lepil za les na osnovi naravnih in obnovljivih virov je področje, na katerem je bilo opravljeno precejšnje število raziskav in poskusov uporabe v industrijske namene. V članku so predstavljeni rezultati teh raziskav in poskusov razvoja lepil za les na osnovi tanina, lignina in utekočinjenega lesa.

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.