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V lesni industriji za lepljenje lesa večinoma uporabljajo sintetična lepila, ki so lahko človeku in okolju škodljiva. V diplomski nalogi smo primerjali uveljavljeno urea-formaldehidno lepilo z lepili na osnovi tanina. Taninskim lepilom smo dodali različne dodatke, s katerimi smo skušali izboljšali kakovost zlepljenosti. Uporabili smo 6 različnih lepil in z vsakim lepilom zlepili po dve trislojni vezani plošči iz 3 mm debelega bukovega luščenega furnirja. Lepilno mešanico smo pripravili za vsako vrsto plošč posebej. Nanos lepilne mešanice je znašal 250 g/m2. Vezane plošče smo stiskali 15 minut pri temperaturi 150 °C in specifičnem tlaku 18 barov. Vezane plošče smo nato razžagali na preizkušance standardnih dimenzij. Preizkušance smo testirali na upogibno trdnost in modul elastičnosti ter strižno trdnost. Iz preizkušancev za upogibno trdnost smo odvzeli preizkušance za ugotavljanje gostote in vlažnosti vezanih plošč. Pred testiranjem smo vse preizkušance klimatizirali v standardni klimi, polovico preizkušancev za testiranje strižne trdnosti pa smo dodatno za 24 ur potopili v vodo. Z raziskavo smo delno potrdili hipotezo pri kateri smo predvidevali, da lahko z lepili na osnovi tanina zlepimo furnirne vezane plošče, ki bodo po kakovosti zlepljenosti in po upogibnih lastnostih primerljive klasično izdelanim vezanim ploščam z urea-formaldehidnim lepilom. Vezane plošče lepljene s taninskim lepilom z dodatkom natrijevega hidroksida so pri vseh testiranjih razen pri strižni trdnosti imele najbolj primerljive lastnosti s ploščami lepljenimi z urea-formaldehidnim lepilom. The wood industry generally uses synthetic adhesives for bonding wood, although these can be harmful to both humans and the environment. In this thesis we compared well-known urea-formaldehyde adhesive with tannin-based adhesives. We added different additives to the tannin-based adhesives, with the aim of improving the quality of bonding. We used 6 different adhesives and with every adhesive we bonded two three-layered pieces of plywood made from 3 mm thick beech rotary cut veneer. The glue mixture was prepared separately for every type of board, and applied at the amount of 250 g/m2. The bonded plywood was compressed for 15 minutes at a temperature of 150 °C and specific pressure of 18 bars. The bonded plywood was then sawn into test specimens with standard dimensions, and these were tested for bending strength, modulus of elasticity and shear strength. The test specimens that were used to examine the bending strength were also used to examine the density and moisture content of the bonded plywood. Before testing we put all the test specimens in a standard air-conditioned climate, and the half of test specimens for examining the shear strength were additionally immersed in water for 24 hours. The results partially confirmed the hypothesis that tannin-based adhesives can bond veneer plywood to a comparable degree of quality and bending properties to those seen with traditional plywood bonded using urea-formaldehyde adhesives. The plywood bonded with tannin-based adhesive with the addition of sodium hydroxide had the best results with regard to shear strength in comparison to the boards bonded with urea-formaldehyde adhesive. |
