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A study on the colloidal nature of urea-formaldehyde resins and its relation with adhesive performance

Authors

  • João M. M. Ferra,

    1. LEPAE -Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
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  • Adélio M. Mendes,

    1. LEPAE -Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
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  • Mário Rui N. Costa,

    1. LSRE -Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
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  • Luisa H. Carvalho,

    1. DEMad -Departamento de Engenharia de Madeiras, Instituto Politécnico de Viseu, Campus Politécnico de Repeses, Viseu 3504-510, Portugal
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  • Fernão D. Magalhães

    Corresponding author
    1. LEPAE -Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
    • LEPAE -Departamento de Engenharia Química, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
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Abstract

Urea-formaldehyde (UF) resins present a swollen colloidal phase dispersed within a continuous water phase containing soluble oligomers. The main goal of the present investigation is to clarify the physical and chemical nature of those two phases and elucidate their impact on the bonding process. Optical and electronic microscopy has provided information on the morphology of the colloidal phase, showing primary particles and particle agglomerates. Mechanisms are suggested for the colloidal stabilization and dilution-induced flocculation. Three commercial UF resins with different F/U molar ratios were studied using particle size distribution (PSD) analysis. The results showed the influence of the resin's degree of condensation and the aging status on the size of the colloidal structures. Gel permeation chromatography analysis was performed on samples of different resins and of the respective continuous and dispersed phases, separated by centrifugation. The quantified fraction of insoluble molecular aggregates present in the chromatograms was related to the resins synthesis conditions and age. Differential scanning calorimetry and tensile shear strength tests were performed to evaluate the reactivity and adhesive performance of each phase. It is suggested that the colloidal phase acts as a reactive filler at the wood joint interfaces, contributing for the resins bonding performance. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

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