Search

The influence of beech bark concentrations as filler in urea-formaldehyde (UF) adhesives was investigated relative to the composite forming process and selected properties of final 5-layer beech plywood. Beech bark was used as filler to lower the wood processing waste production and decrease formaldehyde emissions. A combination of UF adhesives filled with different beech bark concentrations as the adhesive was used. Three different concentrations of beech bark, 15 wt.%, 20 wt.%, and 25 wt.% were used in the experiment. Urea-formaldehyde adhesive filled with 20 wt.% technical flour was used as a reference sample. The effect of the filler was studied via its temperature profile during pressing, mechanical properties in bending, water absorption, thickness swelling, and formaldehyde emissions after pressing. The time needed to reach the temperature between the beech veneers, at least 105 °C, which was equal to the final temperature filler-adhesive-wood matrix cross-linking, was also investigated during the pressing process. The measurements of the free formaldehyde emissions showed that for samples with non-zero bark concentrations there was a decrease of formaldehyde emissions by at least 46%. [ABSTRACT FROM AUTHOR]

The results of research into utilizing grinded beech bark in order to substitute commonly used fillers in urea formaldehyde (UF) adhesive mixtures to bond plywood are presented in the present study. Four test groups of plywood with various adhesive mixtures were manufactured under laboratory conditions and used for experimentation. Plywood made using the same technology, with the common filler (technical flour), was used as a reference material. Three different concentrations of grinded beech bark were used. The thermal conductivity of the fillers used, viscosity and its time dependence, homogeneity and the dispersion performance of fillers were evaluated in the analysis of adhesive mixture. The time necessary for heating up the material during the pressing process was a further tested parameter. The produced plywood was analyzed in terms of its modulus of elasticity, bending strength, perpendicular tensile strength and free formaldehyde emissions. Following the research results, beech bark can be characterized as an ecologically friendly alternative to technical flour, shortening the time of pressing by up to 27%. At the same time, in terms of the statistics, the mechanical properties and stability of the material changed insignificantly, and the formaldehyde emissions reduced significantly, by up to 74%. The utilization of bark was in compliance with long-term sustainability, resulting in a decrease in the environmental impact of waste generated during the wood processing. [ABSTRACT FROM AUTHOR]