Лако-красочные материалы — производство

Extractives contained in wood can influence the gluing process in the physical as well as chemical sense. Several authors [391-393] have indicated that the chemical composition of a wood surface after processing might be different due to the concentration on it of polar and apolar substances coming from the wood itself. Even the fiber direction of the wood surface (longitudinal, radial, tangential) can influence this composition. Extractives solu­ble in water or steam can migrate during the drying process to the wood surface and can decrease its wettability. In particular fatty substances and waxes might cover the wood surface. As a consequence of this, chemical weak boundary layers (CWBLs) are formed [394,395]. A chemical-induced effect can also occur if the wood extractives have a strong acidic or alkaline behavior. This might cause acceleration or retardation of the hardening process of the adhesives based on polycondensation resins.

Different wood species can show great differences in pH as well as in the buffering capacity. Even within a single wood species differences might occur due to seasonal variations, position of origin within the tree log, pH of the soil, age of the tree, time span after cutting, and drying and processing parameters.