On the release of volatile acids from wood-based panels – chemical aspects –

Abstract

Wood-based panels release different amounts of volatile organic acids, which depend, among other factors, on the binder used. The volatile acids released from the boards can be measured using the flask method following the principle of measuring the formaldehyde release according to EN 717-3. Particleboards bonded with alkaline curing phenol-formaldehyde resins (PF-boards) release higher amounts of acetic and lower amounts of formic acid compared to those boards bonded by acid curing urea-formaldehyde reins (UF-resins) or binders based on polymeric diphenylemethandiisocyanates (PMDI). This has been explained by the equilibrium reaction between sodium hydroxide in PF-resins and volatile acids, which leaves less free formic acid than free acetic acid to emanate from the boards. Increasing the binder content in the boards also leads to an increase in the over all amount of sodium hydroxide in the boards. Accordingly, less free acids are left, which could be released from the boards. Fibres made by the chemo-thermo-mechanical process (CTMP) using sodium hydroxide and sodium sulphite as pulping agents release less formic acid than those made by the thermo-mechanical pulping (TMP). This behaviour was also attributed to the equilibrium reaction between the alkali in CTMP-boards and the volatile acids.