MOISTURE RESISTANT PARTICLEBOARDS FROM SA PWOOD AND HEARTWOOD CHIPS OF LARCH (LARIX-DECIDUA), BONDED WITH DIFFERENT RESIN SYSTEMS

Chips from sap- and heartwood of 20, 40 and 102-year-old larch (Larix decidua) were prepared and chemically characterized. From the chips on e-layer boards of 20 mm thickness were prepared using melamine-urea-ph enolformaldehyde resin (MUPF-resin), phenolformaldehyde resin (PF-resi n), polymeric diisocyanate (PMDI), and tanninformaldehyde resin (TF-re sin). The physical and chemical properties of the boards were determin ed. Moreover, the influence of hot water extractives on the pH-value, viscosity and gelation time of the resins was assessed. Sap- and heart wood chips are different in their chemical properties as well as in bo nding behaviour. The age of the tree has also an influence on the bond ing characteristics of the chips. Thickness swelling, water absorption and equilibrium moisture content of heartwood boards were always lowe r than those of sapwood boards. Moreover, bending and internal bond st rength of heartwood boards made from 20- and 40-year-old trees are muc h higher than those produced from sapwood. The strength properties of the boards deteriorate, however, with increasing age of the tree. This applies for both heartwood and sapwood boards. The water extractives of heartwood boards are of lower pH-value and higher buffering capacit y than the corresponding boards from sapwood. Moreover, the emanation of acetic acid from heartwood boards is much higher than that of formi c acid. In addition, boards from heartwood are in general of lower for maldehyde release compared with boards from sapwood. The addition of h eartwood extractives to MUPF-resin increases the viscosity and gelatio n time of the resin and decreases its pH-value, whereas in case of PF- resin no such increase in the gelation time was registered. The extrac ts of heartwood increase the viscosity and gelation time of TF-resin.