Зменшення вмісту формальдегіду у фанері, склеєній карбамідоформальдегідними клеями з використанням деревинного волокнистого шламу [Formaldehyde content Reduction in plywood bonded with urea-formaldehyde adhesives filled by wood fiber sludge]
Journal Title: Наукові праці Лісівничої академії наук України - Year 2016, Vol 14, Issue
Abstract
Urea-formaldehyde adhesives were filled with wood fiber sludge in order to reduce the formaldehyde content of plywood. The dry milled wood fiber sludge, urea-formaldehyde resin, ammonium chloride and rotary-cut birch veneer sheets were used throughout the studies. Effects of bonding conditions (the amount of fiber sludge, the adhesive spread amount, the duration and temperature of pressing) on the formaldehyde content and shear strength of plywood were examined using the full factorial design of experiment technique. The formaldehyde emission was measured by WKI-flask method. The shear strength of plywood was measured according to the Ukrainian standards EN 314-1:2003 and ЕN 314-2:2006 (bonding class 1). Studies have shown that the adhesive spread amount and pressing temperature have the greatest influence on the formaldehyde content in plywood. Formaldehyde content in plywood increases with the adhesive spread amount in plywood, while the increase in pressing temperature reduces formaldehyde content. The findings are consistent with the conventional wisdom about the impact of adhesive spread amount and pressing temperature on the emission of formaldehyde from particle boards. Amount of fiber sludge in adhesive also influences the content of formaldehyde in plywood. The increase of its amount reduces formaldehyde content. The formaldehyde content in plywood decreases by 30-42 % with decreasing adhesive spread amount from 130 to 100 g/m2. When pressing temperature increases from 100 to 150˚C, formaldehyde content reduces by 34-41 %. If 4 parts by mass of fiber sludge is added to adhesive, the formaldehyde content reduces by 16-30 %. Adding filler to adhesive composition reduces the amount of urea-formaldehyde resin in adhesive composition, what accordingly reduces the content of formaldehyde in the adhesive composition. In addition, the fiber sludge is characterized by a high content of lignin, which interacts with formaldehyde in the resin and chemically binds it, which also leads to a reduction of free formaldehyde content in adhesive composition and, ac-cordingly, reduction of free formaldehyde content in the finished plywood. The amount of fiber sludge in adhesive and pressing temperature have little influence on the shear strength of plywood. When the amount of fiber sludge in adhesive increases, the shear strength of plywood decreases. If the pressing temperature increases, the shear strength also increases. The shear strength of plywood decreases by 11-12 % in the case of increasing of fiber sludge amount in adhesive. But even so, it shear strength is 2,3-2,5 times bigger compared with standard requirements. Reducing the adhesive bond strength when adding fiber sludge is possible through the deterioration of adhesive wetting ability because of an increasing in its viscosity, which reduces the contact area and causes the lack of a continuous adhesive layer. When pressing temperature increases, shear strength of plywood increases by 14-17 %. This is due to the fact that the thermal motion of molecules in the adhesive layer increases with temperature increasing, which reduces viscosity of adhesive and improves the contact between glue and wood. The adequate and reproducible regression dependences between the properties of plywood and the investigated factors were received. This enables to predict the content of formaldehyde in plywood and plywood shear strength according to the bonding conditions of veneer.
Authors and Affiliations
Pavlo Bekhta, Roman Salabay, Iryna Salabay, Gryhoriy Noshchenko
Keywords
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