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Martins J.,University of Porto | Martins J.,Polytechnic Institute of Viseu | Pereira J.,University of Porto | Coelho C.,University of Porto | And 6 more authors.
International Journal of Adhesion and Adhesives | Year: 2013

This paper presents a new application of Automated Bonding Evaluation System (ABES) for studying the reactivity of adhesive-substrate combinations (adhesive-cork, impregnated paper-wood and laminate-wood); a new sample configuration and a new kinetic model are proposed. Isothermal bond strength development was plotted as a function of time for several platen temperatures and the kinetic parameters were computed from these plot families, for each type of adhesive and combinations. The methodology developed showed to have potential in quantitative screening of adhesives and operating conditions in industrial context (production of cork composites, melamine faced boards and high pressure laminates). © 2013 Elsevier Ltd.

Costa N.A.,University of Porto | Pereira J.,University of Porto | Ferra J.,EuroResinas Industrias Quimicas | Cruz P.,EuroResinas Industrias Quimicas | And 6 more authors.
Wood Science and Technology | Year: 2013

This work examines the performance of three formaldehyde scavengers in wood-based panels. Sodium metabisulfite, ammonium bisulfite and urea were applied in different physical forms during particleboard production, and the resulting physico-mechanical properties (internal bond strength, thickness swelling, density and moisture content) and formaldehyde emission levels were compared. Formaldehyde content was measured using the perforator method, and formaldehyde emission was evaluated both by desiccator and gas analysis methods. The chemical reactions involved in each formaldehyde scavenging process are proposed and discussed. The tested scavengers showed distinct performances under the different emission testing conditions, which were interpreted in terms of the stability of the chemical compounds formed upon formaldehyde capture. Sodium metabisulfite proved to be an excellent scavenger for all formaldehyde methods allowing the production of particleboard panels with zero formaldehyde emission. © 2013 Springer-Verlag Berlin Heidelberg.

Costa N.A.,University of Porto | Martins D.,University of Porto | Pereira J.,University of Porto | Martins J.,University of Porto | And 7 more authors.
Journal of Applied Polymer Science | Year: 2013

The chemical structure of amino adhesives produced by the strongly acid process was investigated by 13C Nuclear Magnetic Resonance spectroscopy. This technique allowed the identification of functional groups and its quantitative determination. Concentration of cyclic polymeric structures (urons) was shown to be related with adhesive performance and with particleboard physico-mechanical properties and formaldehyde content. Higher urons concentration presented lower viscosity and reactivity. Particleboards produced with resins with lower urons concentration presented lower formaldehyde content, but also lower internal bond strength. Wood-based panels produced fulfilled E1 class requirements for formaldehyde emissions, indicating that strongly acid process is an alternative to the conventional alkaline-acid process. Copyright © 2013 Wiley Periodicals, Inc.

Costa N.A.,University of Porto | Pereira J.,University of Porto | Ferra J.,EuroResinas Industrias Quimicas | Cruz P.,EuroResinas Industrias Quimicas | And 6 more authors.
International Wood Products Journal | Year: 2014

The influence of hexamine formed as byproduct during the UF cure was ignored in the past. However, with the increasing interest on low formaldehyde emission boards, this issue has become more pertinent. Formaldehyde release from hexamine degradation is extensive and could limit the success of the development of low formaldehyde emission adhesives if the conventional latent catalysts remain in use. In this study, formaldehyde released from recycled wood, hexamine and cured UF resin was assessed. Citric and oxalic acid, in solid form, were used as catalysts for UF resin in the production of particleboard. Mats with solid acids are less susceptible to resin pre-cure than with a latent catalyst. However, they can have higher formaldehyde emissions than latent catalyst. When both catalysts were used, combined with an ultra-low formaldehyde to urea molar ratio resin the internal bond was improved and formaldehyde content was below 4 mg per 100 g of oven dry board. © 2014 IWSc, the Wood Technology Society of the Institute of Materials, Minerals and Mining.

Costa N.A.,University of Porto | Pereira J.,University of Porto | Ferra J.,EuroResinas Industrias Quimicas | Cruz P.,EuroResinas Industrias Quimicas | And 6 more authors.
Journal of Adhesion | Year: 2014

In this paper, the use of Automated Bonding Evaluation System (ABES) for evaluation of bonding strength of wood adhesives is presented. A simple reactive model is proposed, which considers the phenomena involved during resin cure: formation of wood-resin-wood bonds. In the present study, experimental data of a standard urea-formaldehyde (UF) resin using different catalysts, phosphoric acid and ammonium sulphate, are presented and discussed. The proposed can be applied to wood adhesives, namely formaldehyde-based resins under different temperatures. The model fits well to experimental data, presenting high determination coefficient values. Copyright © Taylor & Francis Group, LLC.

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