We studied the effect of pressing temperature on hardening of urea-formaldehyde (UF) adhesives. We used two types of UF adhesives pre-prepared by manufacturer Basf: Kaurit 345 with a lower content of free formaldehyde and Kaurit 350 with a higher content. For testing of kinetics, we used ABES (Automated Bonding Evaluation System) instrument. To preform standard tests, we used maple veneers, with thickness of 0,6 mm. All veneer was prepared and then left for two day at room conditions of 23 °C and 55 % air humidity, to acclimate. Every test has constant adhesive mixture, consisted of 100 weight units of aqueous adhesive solution and 1,5 % catalyst (ammonium sulphate) (according to dry quantity of glue). Bonding strength was investigated at different pressing temperatures: 80, 100, 120, 150 and 170 °C. Times of gluing were adjusted according to feedback of shear strength. If ABES measured sear strength higher than 0 N/mm2, we carried out at least two more tests of strength. pH value of wood was measured. With usage of different veneers, we tested its influence on bond development. For this test, we used six different species (maple, beech, oak, walnut, spruce, elm). With use of thermocouple we investigated temperature changes in bond during gluing process. We found out that the pressing temperature had a significant influence on hardening time. Cooling specimens after gluing process did not have big effect on joint strength. Adhesive with more formaldehyde was curing faster.
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