As alternatives to formaldehyde, further aldehydes are now available in principle for manufacturing formaldehyde-free amino polymer resins. Some alternative aldehydes have the disadvantage that they can cause discoloration, are to a certain extent toxic, volatile or not reactive enough, or that their solubility causes problems.
The results of the investigations so far show that there may be solutions to allow formaldehyde-free melamine glyoxylic acid / glyoxal resins to be used as adhesive for particle board, medium-density fiberboard (MDF) and plywood with very low formaldehyde emissions (caused by the wood particles). Melamine glyoxylic acid / glyoxal resin can also be used in cement-bound particle board to improve the workability of the cement bonding and the board’s mechanical properties. Further research is necessary to assess the potential and cost-effectiveness of formaldehyde-free melamine resins in industrial applications.
For reasons of cost, melamine and melamine resins are currently used only to a limited extent as reinforcing components in urea formaldehyde resins (UF resins) in industrial wood-based materials. The adhesive manufacturers therefore have to develop new, low-cost adhesives (particularly due to the current moves to reclassify formaldehyde as Class 1B) and the wood-based material manufacturers have to adapt their press conditions to these new adhesives. A cost-effective and technically acceptable formaldehyde-free adhesive alternative to UF resin is currently not available.
Initial tests on high-density fiberboard (HDF) show that melamine urea glyoxal resin can, in principle, achieve the properties of an HDF board made with UF resin.
Table 1: Mechanical and hygric properties of 8mm-thick HDF boards with melamine urea glyoxal resin (MHG) and UF resin as a reference
Resin |
Press duration |
Board characteristic |
Density |
Bending strength |
Bending modulus of elasticity |
Transverse tensile strength |
Thickness swelling 24h |
|
s/mm |
kg/m³ |
N/mm² |
N/mm² |
N/mm² |
% |
MHG-Harz |
22 |
722 |
16,3 |
1902 |
0,31 |
27,1 |
UF-Harz |
22 |
717 |
25,5 |
2472 |
0,5 |
16,5 |
DIN EN 622-2:2004 an Typ HB |
≥ 25 |
k.A. |
≥ 0,5 |
≥ 25 |
Fraunhofer Institute for Wood Research 
