Das Projekt "Hybrid Wood Bond: Studies of the interactions between UF/pMDI hybrid adhesives and the final panel properties for the production of low formaldehyde emission wood based panels" wird vom Umweltbundesamt gefördert und von Haute ecole specialisee bernoise, Haute ecole d'architecture, de genie civil et du bois HSB durchgeführt. Combined mixtures of polymeric diphenyl-methane diisocyanates (pMDI) with Urea-formaldehyde (UF) - resins can provide alternative adhesives with improved properties. Although such adhesives are reportedly industrially used in some cases, a fundamental understanding of their influence on the panel properties is still lacking. The aim of this project is an investigation of the correlation of the colloidal appearance of such selected hybrids with the gluing, pressing and final panel properties. During the 1,5 years of study several formulations as well as the UF/pMDI hybrid adhesives-panel properties interactions have been experimented and tested in laboratory scale. This presented project reports on the results of (a) x-ray diffraction analysis (XRD) of the cured mixtures of pMDI with UF resin adhesives which present a certain percentage of microcrystallinity, this being due exclusively to the proportion of urea-formaldehyde resin present in the mix, (b) polarized light optical microscopy (PLOM) to present colloidal structures in which oligomers and colloidal structures of one resin have migrated within the colloidal structures of the other resin, and (c) solid state 13C nuclear magnetic resonance (NMR) spectroscopy of the hardened UF/pMDI resin systems showing that urethane bridges derived by the reaction of the isocyanate group with the hydroxymethyl group of urea do form, even at fast curing times, but they appear to form in lower proportions than what has already been shown to occur at much longer curing times. Also the simultaneous visualization of UF resin, pMDI and their combined mixtures on MDF fibre and panels is shown. Through the use of confocal laser scanning microscopy (CLSM) and dual fluo-rescent labels, the distribution and coverage of different UF resins, one emulsifiable and one non-emulsibiable pMDI and their mixtures have been quantified. Analysis of the UF resin, pMDI and their mixes gave resin coverage values generally in accord with the resin loading in the MDF panels. The resin distribution of the UF resins and pMDI was typical for dry-blending with some evidence of overlap of droplets at higher UF resin content. Substantial differences in coverage and distribution were obtained between the samples for UF resins. Some interactions of resin and pMDI on unpressed fibre and MDF were also determined by this image analysis method. Finally the panel proprieties as well as the formaldehyde emissions were evaluated. Best results concerning the improvement of the panel properties were obtained for gluemixes with low molar ratio UF 0,75:1 and emulsifiable pMDI. Starting from a ratio UF/pMDI of 70/30 all qualitative requirements of the international standards could be passed. However, lower Formaldehyde emissions, satisfying the requirements of F** (E1), were only reached using gluemixes with lower molar ratio UF. (abridged text)