The objective of this project was to help Forintek members to reduce formaldehyde and VOC emissions from MDF mills and increase resin efficiency.
Five novel blending methods were examined:
1. Post-dryer air-suspension blending with a PF powder resin (resol).
2. Post-dryer air-suspension blending with a PF powder resin and a liquid PF resin (resol).
3. Post-dryer air-suspension blending with a UF powder resin.
4. Post-dryer air-suspension blending with a UF powder resin and a liquid UF resin.
5. Refiner blending with a PF powder resin (novalac)
The following conclusions and recommendations are made:
It is feasible to produce MDF panels from blending powder PF resin (resol) with wood fibre at 8% MC & 5% wax using a post-dryer air-suspension blender. Combination of liquid and powder PF resins at a ratio of 1:1 appeared to work better. The thickness swell and water absorption were significantly lower than those obtained from panels bonded with liquid PF or powder PF alone.
It is feasible to produce MDF panels from blending powder UF resin with wood at 7% MC & 5% wax using a post-dryer air-suspension blender. Similar to the case of PF resin, the combination of liquid UF and powder UF at a ratio of 1:1 appeared to work better than liquid UF or powder UF alone. Unlike PF powder resin, however, UF powder was softened quickly by moisture, causing some blender build-up. There is room for improving UF powder resin performance by resin formula modification and the reduction of its water solubility.
It is feasible to produce MDF panels from blending a novalac resin with wood in a MDF refiner. Further exploration of this novel blending method in Forintek's MDF pilot plant is recommended.
Results from this project shoed that there are new possibilities for the next generation of MDF blending. These new methods will be able to overcome the disadvantages and preserve or even enhance the advantages of the existing blending methods. This project has demonstrated that, by changing the physical properties of a resin, it is possible to develop an improved MDF blending system. Using a powder resin in a post-dryer blending system may dramatically reduce resin consumption and formaldehyde emission from the MDF mills. The combination of a liquid resin with a powder resin is another possibility. In this case, perhaps a certain amount of liquid resin is delivered to a post-dryer mechanical blender or post-dryer air-suspension blender or via the blowline to produce some tack in the fibre while a powder resin is blended with the fibre in this post-dryer mechanical blender or post-dryer air-suspension blender. The powder resin may also be delivered at the end section of the tube dryer. Because the powder resin is blended after the dryer, the loss of resin efficiency can then be greatly reduced. The authors believe that there is great potential for technological advancement in this area.
In order to explore the full potential of powder resin blending in MDF manufacturing, joint research with a reputable blending equipment manufacturer is highly recommended.