Drying of pine particles and the effect on the strength of particleboard

Increasing intensity of drying conditions lowered the pH-value, increased the buffering capacity towards alkali and enhanced the liberation of volatile acids from pine flakes. Drying exerted a pronounced influence on the strength properties of UF-bonded boards of pine flakes. The decrease of the flakes m.c. from 5.5% to 2.5% by drying led to an increase of the internal bond and to a decrease in theckness swelling. However, excessive drying to less than 1% m.c. adversely affects internal bond and thickness swelling. Drying, under the conditions investigated, seams to have no detectable influence, neither on the density profile of the boards, nor on the formaldehyde release when bonded with UF-resins of extremely low molar ratio. In contrast, drying chips below a moisture centent of 5.5% has a negative effect of the mechanical properties of MDI-bonded particleboards. Moreover, the swelling properties of MDI-boards deteriorate by decreasing the moisture content of the dried chips. In case of PF-bonded particleboards excessive drying of wood chips to a moisture content of about 1% positively affects the mechanical properties of the boards. The swelling properties upgrade in the same direction.