Urea-formaldehyde resins are mainly used for the production of wood-based materials, as they are inexpensive and easy to process and have high mechanical and technological properties. The disadvantages are the relatively low hydrolysis stability and the emission of formaldehyde, which is classified as carcinogenic. Since the legal guideline values for emissions have been decreasing for years, urea-formaldehyde resins with adapted molar ratios are produced to meet the requirements. The mechanical-technological properties decrease, so that reinforcing components such as melamine, phenols or isocyanates have to be used. If isocyanates are added to urea-formaldehyde resins, both adhesive systems accelerate the curing reaction. This effect has been known for some time and is used industrially; the underlying mechanism of this accelerated reaction is not yet fully understood. In the present work, the reaction mechanism between urea-formaldehyde resins and isocyanates was first investigated using laboratory methods. After identification of decisive factors, these were transferred to an acceleration of pure isocyanate adhesives, since such adhesives require relatively long pressing times in industry. In order to verify the results of the laboratory tests, wood-based materials (micro veneer bonding, veneer plywood, chipboard, fibreboard and insulation boards) were produced on a pilot scale and the resulting mechanical and technological properties investigated. In the first part, the relationship of mutual acceleration was investigated using established laboratory methods. Differential scanning calorimetry, gelation times, pot life, pH determination and scanning electron microscopy (SEM - ESEM) proved that a reaction between the adhesives is unlikely. The latent ammonium sulfate hardener was identified as the decisive factor. Due to its high nucleophilicity, the ammonia contained reacts earlier with the reactive groups of the isocyanate than with the free formaldehyde of the urea resin (formation of hexamethylenetetramine). The balance between ammonia and ammonium is shifted to the ammonia side and protons are released. These early generated protons catalyse the condensation reaction of the urea resin and cause a faster curing. The isocyanate also accelerates, since the reaction of ammonia with the functional groups is faster than the cross-linking via water as a nucleophilic agent typical in wood-based panel production. In the second step, seven selected ammonium salts were tested for their suitability for accelerating the curing of isocyanates. These were two thermally labile salts (ammonium VI carbonate and ammonium hydrogen carbonate) and five compounds based on the chemical equilibrium between ammonia and ammonium in aqueous solution (ammonium acetate, ammonium chloride, ammonium nitrate, ammonium sulphate, diammonium hydrogen phosphate). For the evaluation differential scanning calorimetry, gelation times, pot life, pH- value were used. It was shown that the carbonates react very quickly and have a high affinity to foaming. The effect of the other salts depended on the acid strength (pKa value) of the acid resorption. The higher the pKa value, the less the compounds contributed to a faster reaction. With solid-state NMR and isotope-labelled ammonia, its incooperation into the isocyanate polymer could be demonstrated. In order to test the practicability of the various salts, various wood-based materials were produced in the third step. Using the Automated Bonding Evaluation System, the general feasibility of the carbonates and micro veneer bonding was tested and positively evaluated. This was followed by the production of veneer plywood with all selected salts to validate the laboratory results. This confirmed the data already collected. Ammonium carbonates, ammonium acetate and diammonium hydrogen phosphate were selected for the production of fibreboards and chipboards. A wide variation of the pressing parameters (pressing time and pressing temperature) and the subsequent determination of the mechanical-technological properties of the plate-shaped materials could prove the postulated acceleration of the hardening reaction. The characterizing values were determined on the basis of bending strength and modulus of elasticity, transverse tensile strength and boiling transverse tensile strength, shear tensile strength and water absorption. The tests carried out in this study suggest, that urea-formaldehyde resins and isocyanates do not form common networks and that the mutual acceleration is based on the presence of latent ammonium hardeners. For the acceleration of pure isocyanates by different ammonium salts a theory could be developed and proved by numerous investigations. Ammonium acetate and diammonium hydrogen phosphate proved to be the most potent accelerators, the carbonates cannot be recommended due to their strong tendency to foam; special applications are conceivable. In the production of wood-based materials, a press time reduction of up to 35 % could be achieved with equivalent or better mechanical-technological properties compared to the reference. This enables energy savings that cannot be neglected and an increase in production capacity with relatively low financial investment.weiterlesen