EFFECT OF STORAGE OF RESIDUES FROM SAW MI LL PROCESSING OF PINE AND SPRUCE AND ITS SUITABILITY AS A RAW-MATERIAL FOR PARTICLEBOARDS AND MEDIUM DENSITY FIBERBOARDS (MDF) .5. CHEMICAL-PROPERTIES OF PARTICLES ANDFIBERS DERIVED FROM PINE AND SPRUCE WOOD FELLED IN SPRING AND THEIR INFLUENCE ON PROPERTIES OF PARTICLEBOARDS AND FIBERBOARDS PREPARED THEREFROM

Particles and fibres were prepared from saw mill wastes (chips) after different storage periods. The particles and fibres were chemically an alysed regarding the change in their pH-value, buffering capacity, ext ractive content, release of volatile acids and formaldehyde release. F urthermore, the physical-mechanical properties of UF- and PMDI-bonded particleboards and fibreboards prepared therefrom were assessed. The r esults reveal: 1. Storage leads to an improvement in the properties of UF-bonded particleboards prepared from pine chips as the internal bon d strength increases and the thickness swelling decreases. 2. Particle boards made from spruce prior to storage show in general better mechan ical properties and lower thickness swelling compared to those prepare d from pine wood. However the differences dwindle upon storage. 3. Sto rage seems to have almost no influence on bending properties of partic les bonded with PMDI, as no significant change in the properties of th e boards due to storage was detected. 4. Storage of chips from wood fe lled in spring has less impact on the properties of the boards than th at of chips from winterfelled wood (Schafer und Roffael, 1997). 5. The properties of MDF made from spruce using UF-resin as a binder show hi gher mechanical strength properties and less thickness swelling compar ed to those prepared from pine wood. However, after storage only subtl e differences between boards made from spruce and pine were detected. 6. On using PMDI asa binder no significant changes in the properties o f the MDF due to storage under the boundary conditions indicated in th e work were detected.