Influence of reaction wood (compression wood) and normal wood of Norway spruce on the properties of medium density fibreboards (MDF).

摘要

The main objective of the conducted research work was to study the performance of compression and normal wood as a raw material for medium density fibreboards (MDF). For this purpose stems from Norway spruce (Picea abies [L.] Karst.) with a high content of compression wood were selected, separated in compression wood and normal wood and finally chipped. Thermomechanical pulps (TMP) were prepared from both types of chips. Morphological, physical and chemical investigations were carried out on both wood samples as well as on TMP prepared therefrom. Moreover, medium density fibreboards (MDF) were made at pilot scale using a melamine modified urea formaldehyde resin (MUF-resin) as a binder. The results can be summarized as follows: Native compression wood fibres showed lower average fibre length (<15%) than fibres derived from normal wood. Furthermore, TMP from compression wood had a higher content of fine fibres. As anticipated, the lignin content of TMP from compression wood was relatively higher (>15%) compared to TMP from normal wood. Possibly due to the higher lignin content the water retention value (WRV-value) of TMP from compression wood was lower (10%) in comparison to normal wood fibres. Cold water extracts of TMP from normal and compression wood showed the same pH-value, the buffering capacity of cold water extracts was more or less at the same level. Moreover, the formaldehyde release of TMP from compression wood fibres was lower in comparison to normal wood fibres. Concerning the physical-mechanical properties of MDF the following results were found: MDF, prepared from compression wood TMP, showed lower thickness swelling values (20...30%) compared to MDF from TMP of normal wood. Also the water absorption value from compression wood MDF was at a relatively lower level. Moreover, MDF prepared from compression wood TMP showed in comparison to MDF from normal wood TMP both a higher internal bond strength (>35%) as well as a higher surface hardness (Brinell-hardness) (25%). The higher surface hardness may be due to the higher lignin content of compression wood fibres. In contrast, the bending strength of compression wood MDF was on a slightly lower level. This may be due to the shorter fibre length of compression wood TMP..