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Percorrer por autor "Paiva, Diana"

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  • Formulation and Characterization of a Composite Coating Formulation Based on Acrylic Foam and Cork Granules
    Publication . Monteiro, Sandra; Ferreira, Nuno; Paiva, Diana; Silva, Susana P.; Martins, Jorge; Carvalho, Luisa; Magalhães, Fernão D.
    Cork, the bark of Quercus suber L., in addition to presenting several notable physicalmechanical properties, possesses a distinctive look and feel that make it attractive for interior surfaces, such as in furniture, wall paneling, or flooring. This work envisaged the development of a coating based on cork granules, a subproduct from the wine stopper industry, capable of creating a smooth surface similar to natural cork. In order to avoid the high rugosity that characterizes surfaces coated with paints that incorporate cork granules, a new solution was developed, based on a foamed acrylic binder, applied by knife coating. The foam formulation was successfully optimized, using appropriate additives and resorting to mechanical agitation to promote the generation of air bubbles. The addition of cork granules did not hinder foam stability, and the final coating displayed the intended visual and sensory characteristics. Dynamic Mechanical Analysis was performed on the pristine acrylic foam and on the composite foam showed a stiffening effect associated with the presence of cork granules, and a thermal transition centered at around −10 ◦C, associated with the acrylic binder’s glass transition. The surface has hardness slightly lower than cork, depending on the amount of particles incorporated. Pull-off testing consistently resulted in substrate failure, indicating that the coating’s cohesion and adhesion are excellent. The developed coating showed to have the intended functionality while being easily applicable on flat panel surfaces. The fact that a foam is used as a binder system allows for a smooth and soft surface, having excellent opacity with minimal usage of cork.
    2022-05-26Artigo de investigação Acesso aberto Ver mais
  • The Potential of Visible Spectroscopy as a Tool for the In-Line Monitoring of Lignin Methylolation
    Publication . Gonçalves, Sofia; Martins, Jorge Manuel; Paiva, Nádia T.; Paiva, Diana; Carvalho, Luisa; Magalhães, Fernão D.
    Out of the 50 to 70 million tons of lignin that are produced annually, only 1 to 2% are used for value-added products. Currently, 90% of the total market of this compound corresponds to lignosulphonates (LS). The most successful industrial attempts to use lignin for wood adhesives rely on using it as a partial substitute in phenol–formaldehyde or urea–formaldehyde resins. However, lignin’s aromatic ring presents a low number of reactive sites. Several methods have been proposed to improve its reactivity, such as prior methylolation with formaldehyde. Off-line methods are commonly applied to monitor this reaction’s progress, but this introduces a significant delay in the analysis. This study proposes a new method for in-line monitoring of the methylolation reaction using visible spectroscopy. In order to monitor the reaction progress, principal component analysis was applied to the spectra, and the obtained scores were analyzed. When these results were plotted against those obtained by the off-line methods, a satisfactory regression was obtained at 50 ◦C (R 2 = 0.97) and 60 ◦C (R 2 = 0.98) for two different LS samples. Therefore, it was concluded that visible spectroscopy is a promising technique for studying lignin methylolation.
    2022-12-30Artigo de investigação Acesso aberto Ver mais