Abstract
Differential scanning calorimetry (DSC) was used to evaluate the curing kinetics of two commercial urea-formaldehyde (UF) adhesives having different formaldehyde to urea (F/U) ratio of 1.112 (UF1) and 1.086 (UF2). DSC measurements were done in dynamic scanning regime with heating rates of 5, 10, 15 and 20?C?min-1 in order to determine the activation energy for each adhesive. Obtained data were analyzed using isoconversional methods with application of Ozawa-Flynn-Wall and Kissinger-Akahira-Sunose kinetic models. In addition, different catalyst levels were tested at the heating rate of 10?C/min. Results showed that the adhesive with higher F/U ratio achieved higher activation energy, while having lower peak temperature of curing reaction. It was also noticed that the increase of catalyst level influenced the increase of reaction enthalpy of the adhesive with lower F/U ratio.
Highlights
Differential scanning calorimetry (DSC) was used to evaluate the curing kinetics of two commercial urea-formaldehyde (UF) adhesives having different formaldehyde to urea (F/U) ratio of 1.112 (UF1) and 1.086 (UF2)
It is common practice to add monomeric urea acting as a scavenger of free or weakly bonded FA during adhesive cure. The problem with this approach lies in the fact that the properties of UF resin are significantly affected by F/U ratio [5]
Effects of catalyst addition on kinetic parameters obtained under dynamic DSC runs at the heating rate of 10 °C/min are given in Figures 2 and 3
Summary
Urea-formaldehyde (UF) resin presents the favorite adhesive system for the production of interior grade wood based panels, such as particleboards and medium density fiberboards used for furniture, cabinet making and interior construction elements. It is common practice to add monomeric urea acting as a scavenger of free or weakly bonded FA during adhesive cure The problem with this approach lies in the fact that the properties of UF resin are significantly affected by F/U ratio [5]. There are many phenomena that occur inside the panel, such as the heat and mass transfer, mechanical deformation of wood component and the chemical reaction of the resin Their intensity and interaction may significantly affect the properties of produced panels. The gel time tests at the temperature of boiling water (Figure 1) clearly show that the curing reaction of UF1 adhesive occurs faster than for the UF2 adhesive having lower F/U ratio
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