Experimental works were carried out to produce high density fibreboard (HDF) using wood furnish with different wood species and geometries that are particularly used in Eastern Canada. The furnish included mixed softwood sawdust, mixed hardwood sawdust, aspen chips and mixed hardwood chips. The fibre refining was carried out with MDF pilot plant at the steam pressure of 6, 7.5 and 9 bars with retention time of 2.5 minutes and refining speed of 2500 rpm. Ten different types of wood fibres under different refining process conditions were produced and a total of 36 HDF panels were made.
Based on the results of this study, the following conclusions are made:
Under the same refining and hot pressing process conditions, different mechanical and physical properties of HDF panels were obtained with different raw materials. However, the properties of the panels were not consistently in favour of one particular type of the raw material.
With the same raw materials (60% softwood sawdust and 40% hardwood sawdust), the refining steam pressure had a strong impact on the panel properties. The properties studied were generally improved when the steam pressure was reduced from 9 bar down to 6 bar. This obvious difference in panel properties when using different refining steam pressures suggests that the required process conditions can be quite different for different raw materials and optimisation of the refining parameters are required for different types of raw materials.
There were no obvious differences in panel properties when using different sizes of raw materials with the same hardwood and softwood mixing ratio.
No obvious improvement in panel properties was observed with chemically pre-treated wood furnish under the process conditions used. However, speculation can be made that the UF resin was quite advanced and a higher degree of resin pre-cure occurred when using blowline resin blending and hot air drying with chemically pre-treated materials. That could be the major reason why we could not observe the improvement of the panel properties when using the pre-treatment or substantial reduction of IB and other properties when reducing hot pressing time.