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Proučevali smo vpliv temperature stiskanja in deleža dodanega katalizatorja na rast strižne trdnosti urea-formaldehidnega (UF) lepilnega spoja med utrjevanjem. Preskušance iz bukovega furnirja (Fagus sylvatica L.) smo lepili z lepilom LENDUR-200. Debelina furnirja je bila 1.1 mm, vlažnost 7 % in nanos lepila 200 g/m2. Testiranje preskušancev smo opravili z univerzalnim testirnim strojem Zwick Z100 po metodi "dinamika graditve strižne trdnosti" (DGST), prilagojeni po metodi "Automated Bonding Evalution System" (ABES). Stroj je imel montirano manjšo vročo stiskalnico, v kateri smo preskušance lepili pri tlaku stiskanja 1,2 MPa. Utrjevanje UF lepilne mešanice, ki je vsebovala 100 delov UF lepila in 1 del suhega katalizatorja NH4Cl, smo proučevali pri štirih različnih temperaturah stiskanja: 90, 100, 110 in 120 °C. Nato smo pri temperaturi stiskanja 100 °C proučevali utrjevanje štirih različnih UF lepilnih mešanic z enako količino UF lepila (100 delov), spreminjali pa smo delež dodanega katalizatorja: 0,1 del, 0,5 dela, 1 del, 2 dela. Čas stiskanja je bil od 20 do 180 s, pri eni lepilni mešanici pa do 600 s. Rezultati raziskave so pokazali, da se je strižna trdnost UF lepilnega spoja pri višjih temperaturah gradila hitreje kot pri nižjih temperaturah. Z naraščanjem deleža dodanega katalizatorja UF lepilni mešanici je naraščala tudi hitrost utrjevanja in graditve trdnosti lepilnega spoja. Lom po lesu se je pojavil, ko je adhezija med lepljencem in lepilom presegla kohezijo lesa. Influence of press temperature and proportion of added catalyst on growth shear strength of urea-formaldehyde (UF) adhesive bond during cure was investigated. Specimens of beech veneer (Fagus sylvatica L.) were glued with adhesive LENDUR-200. Thickness of veneer was 1.1 mm, moisture content 7 %, and adhesive coating 200 g/m2. Specimens were tested with Zwick Z100 universal testing machine, by method "Dynamics of the Bond Strength Development" (DBSD), on a modified "Automated Bonding Evaluation System" (ABES) method. The machine had a mounted small hot-press, gluing specimens at compression pressure 1.2 MPa. Curing of UF adhesive mixture, which contained 100 parts of UF adhesive and 1 part of dry catalyst NH4Cl, was investigated at 4 different pressing temperatures: 90, 100, 110, 120 °C. At pressing temperature 100 °C, curing of 4 different UF adhesive mixture having the same quantity of UF adhesive (100 parts), was investigated. The proportions of added catalyst: 0,1 part, 0,5 part, 1 part, 2 part were different. Pressing time was from 20 to 180 s, by one adhesive mixture to 600 s. Results showed that the strength development of UF adhesive bond developed quicker at higher temperatures than at lower ones. Increasing the proportion of added catalyst to the UF adhesive mixture, the strength of curing increased, so as the speed of the strength development of adhesive bond. Wood failure appeared, when adhesion between adherent and glue surpassed cohesion of wood. |
