Effect of chemical pre-treatment of wood furnish on resin consumption and panel dimensional stability. Part II. Bio-treatment of wood fibre for the manufacture of MDF panels
Five fungal species were used to modify and activate natural binding agents from wood fibres for manufacturing MDF panels. Two different methods of the bio-treatment were carried out using these five different fungal species. In the first method, the fungi were inoculated to black spruce (Picea mariana) sawdust, incubated for 20 days at 25ºC, and then refined into wood fibres, with the UF resin loadings of 0% and 8%, respectively. The second method was carried out using normal fibres refined from fresh black spruce sawdust. The fibres were blended with the fungal filtrates in the rotary blender and incubated for 12 hours. MDF panels were made from these different fibres. The mechanical and physical properties were evaluated and compared with the normal MDF panels made of UF resin. Preliminary test results indicate that:
To some extent, the experimental work showed that the self-bonding ability existed after the bio-treatment of wood fibres using the fungal species studied in the project;
All the fungal treated fibres showed the improved bond quality in MDF. The fibres treated with Type-4 fungus yielded the highest bonding strength in the panels with the first treatment method while that with Type-3 had the best result using the second method;
The internal bond strength of all trialed panels without urea-formaldehyde (UF) resin was lower than that of the normal MDF with 8% or 12% UF resin and below the requirement of ANSI standard;
The results suggest that the fungal species studied behave different and no obvious correlation between IB and thickness swell or water absorption can be established;
No obvious consistent trend in MOR and MOE of the panels made with five bio-treatments between two different methods was observed;
Similar MOE and MOR were obtained in the second method among different treatments except T1. The MOE and MOR of T1 panels were lower than those of the rest panels and all of them were significantly lower than those of the control MDF;
This preliminary experiment showed that it is possible to produce MDF using bio-treated fibres with reduced UF resin content in the fibres and it was feasible to use crude extracts of fungi to replace high pure laccase. However, the experimental work was preliminary and further work is required to identify more suitable fungal species and better treatment and process conditions to substantially reduce the time of incubation and process cost to be compatible with the current resin systems used in the manufacture of MDF.