Schlüsselwörter
(Englisch)
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Urea Formaldehyde; Isocyanate; Hybrid; Bonding; Colloidal; crystalline; amorphous structures; panes properties; Formaldehyde Emission; Confocal Laser Scanning Microscopy
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Forschungsprogramme
(Englisch)
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COST-Action E49 - Processes and performance of wood-based panels
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Kurzbeschreibung
(Englisch)
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Combined mixtures of polymeric diphenylmethane diisocyanates (pMDI) with Ureaformaldehyde (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.
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Weitere Hinweise und Angaben
(Englisch)
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Full name of research-institution/enterprise: Haute école spécialisée bernoise Haute école d'architecture, de génie civil et du bois HSB
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Partner und Internationale Organisationen
(Englisch)
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AT, BE, BG, CH, DE, DK, ES, FI, FR, GR, LV, MK, PL, PT, RO, SE, SI, TR, UK
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Abstract
(Englisch)
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Combined mixtures of polymeric diphenyl-methane diisocyanates (pMDI) with Urea-formaldehyde (UF) - resins can provide alterna-tive 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 lack-ing. The aim of this pro-ject is an investigation of the correlation of the colloidal appearance of such selected hy-brids with the gluing, pressing and final panel properties. During the 1,5 years of study several formulations as well as the UF/pMDI hybrid adhe-sives-panel properties interactions have been experimented and tested in laboratory scale. This presented project reports on the results of (a) x-ray diffrac-tion analysis (XRD) of the cured mixtures of pMDI with UF resin adhesives which present a certain percentage of mi-crocrystallinity, this being due exclusively to the proportion of urea-formaldehyde resin pre-sent in the mix, (b) polar-ized light optical microscopy (PLOM) to present colloidal struc-tures in which oligomers and colloi-dal structures of one resin have migrated within the col-loidal 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 gen-erally 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 evi-dence 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 for-maldehyde emissions were evaluated. Best re-sults concerning the improvement of the panel properties were obtained for glue-mixes with low molar ratio UF 0,75:1 and emulsifiable pMDI. Starting from a ra-tio UF/pMDI of 70/30 all qualita-tive requirements of the international standards could be passed. However, lower Formaldehyde emissions, satisfying the require-ments of F** (E1), were only reached using glue-mixes with lower molar ratio UF. Except for these glue-mixes high variations within the test series as well as an in-crease of the formaldehyde emission did occur. F**** emissions could be just reached using 100% MDI.
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Datenbankreferenzen
(Englisch)
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Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. +41 31 322 74 82 Swiss Project-Number: C05.0072
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