IJUP08 - Universidade do Porto

Characterization of Urea-Formaldehyde Resins
F. Silva 1, J. Ferra 2, L. Carvalho 2,3, J.P. Liberal 4 and F. D. Magalhães 2
1 RCP – Rede de Competência em Polímeros, Porto, Portugal
2 Department of Chemical Engineering, Faculty of Engineering, University of Porto, Portugal
3 DEMad – Department of Wood Engineering, Polytechnic Institute of Viseu, Viseu, Portugal
4 Euroresinas – Indústrias Químicas, S.A., Sines, Portugal
Urea-Formaldehyde (UF) resins are the most widely adhesives used in industry as binders for
the production of bonded wood products, particularly particleboards, because of their
versatility and low cost, despite of their vulnerability to moisture and water. This type of resins
is based in the reaction between the two principal monomers, urea and formaldehyde,
originating mixtures of several condensation products like simple methylolureas (mono-, diand
tri-) or insoluble high molecular weight compounds. Nowadays, the major problem to be
solved consists in the formaldehyde emission after the curing process, during the lifetime of
the material, namely in domestic furniture uses. The emission has to obey certain limits and all
efforts and research are directed towards reducing Formaldehyde/Urea (F/U) ratio, maintaining
the performance properties of a conventional UF resin. [1] The specific resins being studied in
this work are produced by Euroresinas – Indústrias Química, S.A.
Since the principal objective of this work is to implement methods of morphological and
physical-chemical characterization of the resins, we use two chromatographic methods, HPLC
(High Performance Liquid Chromatography) and SEC (Size Exclusion Cromatography),
calorimetric methods, DSC (Differential Scanning Calorimetry), and the measure of Particle
Size Distribution (PSD), Coulter-Counter.
With SEC, we can determine the molecular weight distribution of one resin, separating the
molecules according to their hydrodynamic volume which can be proportional to the molecular
weight. HPLC allow us to quantify urea and methylolureas (low molecular weight reaction
products) present in the resin. DSC studies directly the cure process of the resin, determining
the heat flow and the cure temperature, parameters that give an idea of the resin reactivity.
Finally, Coulter-Counter, give us the PSD of the insoluble fractions of the resins. The
compilation of all these methods also permits the study of the phenomena involved in the
resins ageing process. Table 1 shows the parameters range obtained for each one of the above
referred techniques.
Table 1. Parameters Range for the different techniques used in the resins characterization.
Techniques
SEC HPLC DSC PSD
Molecular Weight % Urea TCURE (ºC) (-ΔH) (J/g) Size (mm)
Parameters Range 100 - 10000 40 - 60 80 - 90 50 - 80 0.1 - 100
The final UF resins performance is evaluated by producing wood-based panels in a laboratory
hot-press. These will be then tested to evaluate several properties: density, moisture content,
internal bond, thickness swelling and formaldehyde content.
At this moment, all the methods are well implemented, making possible to distinguish different
types of resins. To improve the resin formulation, a Design of Experiment methodology will be
initiated.
References:
[1] Dunky, M. (1997), Urea-Formaldehyde (UF) adhesive Resins for wood, Int. J. Adhesion &
Adhesives, 18, 95-107.
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