Inconsistencies in HDF production

Problems with production of high-density fiberboard with MUF adhesive. June 6, 2001

We produce high-density fiberboards with MUF adhesive. Recently, our product's elastic modules decreased by 25%, and linear expansion increased 50%, but the wood, adhesive and technology were unchanged. Why?

Forum Responses
Are you sure that everything was unchanged? How do you control the quality of your adhesive? Why do you use a melamine fortified UF-resin--stability or water resistance reasons? Or is it a real MUF-resin? Who is the producer of your adhesive? Or do you produce it on your own?

I don't have any obvious solutions for you, but it's important to point out that when dealing with wood (a natural substance), you are dealing with constant variations and change. Your process is never the same from day to day.

Jeff Pitcher, forum technical advisor

MUFs as well as UFs are very sensitive to pH conditions of the wood. If your MUF is added in the blowline, then the high temperature will aggravate the situation. It sounds like something is causing a pre-reaction in the blowline to cause properties to change that much. Or perhaps you did not change to a summer formulation for the MUF and hot weather is causing a problem during storage.

From the original questioner:
I produce hdf for laminating flooring and use MUF to increase the IB and water resistance. We prepare MUF by ourselves. The amount of F is about 7%. We got better results in January, February and March of this year. But the water resistance became worse since May. We add MUF in blowing line. How can I change to the summer formulation?

How does the climate change from winter to summer in your country? If you maybe have got problems with your formulation, I need more information (e.g. molar ratio at the beginning and end of condensation process, F quality, pH and temperature during condensation, viscosity, water solubility, condensation time).

From the original questioner
20 degrees in winter, 30s degree in summer. Molar ratio is 1.2. Which item of F quality influences the MUF property?

How can I get the article "Thermochemical analysis of wood/aminoplastic adhesives joints cross-linking-UF, MUF, PMUF" by Yin Suzhou, Deglis, Xavier Masson, Daniel.

The main items of the formaldehyde quality are the concentration (> 40%) and the methanol content (< 1% for best resins). The article you are looking for was published in "Holzforschung (1995)".