Acetals-induced strength increase of melamine-urea-formaldehyde (MUF) polycondensation adhesives. II. Solubility and colloidal state disruption

The strength improvement induced by addition of acetals such as methylal and ethylal in melamine–urea–formaldehyde (MUF) resins could be mostly ascribed to the increased effectiveness and participation of the melamine to resin cross‐linking. This phenomenon has been shown here, by matrix‐assisted la...

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Bibliographic Details
Published in:Journal of applied polymer science 2002-11, Vol.86 (8), p.1855-1862
Main Authors: Zanetti, M., Pizzi, A., Beaujean, M., Pasch, H., Rode, K., Dalet, P.
Format: Article
Language:English
Subjects:
acetals
adhesives
Applied sciences
colloidal state
Compounding ingredients
ethylal
Exact sciences and technology
Fillers and reinforcing agents
melamine resins
methylal
performance improvement
polycondensation
Polymer industry, paints, wood
size distribution
strength improvement
Technology of polymers
wood panels
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Summary:The strength improvement induced by addition of acetals such as methylal and ethylal in melamine–urea–formaldehyde (MUF) resins could be mostly ascribed to the increased effectiveness and participation of the melamine to resin cross‐linking. This phenomenon has been shown here, by matrix‐assisted laser desorption/ionization time of flight (MALDI‐TOF) mass spectroscopy, resin aging time stability, and mainly by laser light scattering, to be due to the following: (i) the increased solubility in water afforded by the acetals cosolvents of both the unreacted melamine and of the normally very much lower solubility, higher molecular weight, lower methylolated oligomers fraction, this leading to preferentially homogeneous and hence more effective reaction rather than heterogeneous reactions; and (ii) the effect that such acetals have on the size distribution of the resin colloidal particles, with the presence of acetals such as methylals markedly decreasing the average colloidal particles diameter of the resin. This latter effect appears to be due to the disruption of the molecular clustering of the MUF resin colloidal particles, but rearrangements in the size of the colloidal particles due to the decrease in surface tension of the system, which has also been noted, cannot be excluded. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1855–1862, 2002
ISSN:0021-8995
1097-4628
DOI:10.1002/app.11105