A carregar...
6 resultados
Resultados da pesquisa
A mostrar 1 - 6 de 6
- The Potential of Visible Spectroscopy as a Tool for the In-Line Monitoring of Lignin MethylolationPublication . 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.
- High-value compounds obtained from grape canes (Vitis vinifera L.) by steam pressure alkali extractionPublication . Santos, Jorge; Escobar-Avello, Danilo; Magalhães, Pedro; Magalhães, Fernão; Martins, Jorge Manuel; González-Álvarez, Julia; Carvalho, LuisaThe main by-product generated by the wine industry is the grape canes derived from the pruning process. The aim of the current work was the valorisation of this highly polyphenolic lignocellulosic material, by alkali extraction methodology avoiding alcoholic solvents use. In lignocellulosic by-products valorisation, it is important to take into account the variability of the raw material. In the case of vine pruning this may be due to the different varieties used, the geographical area, the climate, or the processing. It is, however, important to develop a global strategy for valorisation, from a biorefinery and circular economy point of view. In this work, the grape canes were characterised, before and after the extraction process, by Fourier transform infrared spectroscopy – attenuated total reflectance (FTIR-ATR) spectroscopy. Changes in cellulose crystallinity, hemicellulose content and structural conformation of proteins, due to the alkali thermal extraction process were identified and evaluated. For the first time, a steam pressure alkali extraction method was used on this material. The products were characterised by FTIR-ATR and Matrix Assisted Laser Desorption Ionisation-Time of Flight (MALDI-TOF) mass spectrometry. The presence of high-value compounds such as stilbene oligomers and condensed tannins was demonstrated in the extracts. The work shows the viability of the steam pressure alkali extraction, a simple and environmentally friendly method, for grape cane valorisation
- Water resistance evaluation of a MFU resins with different molar ratio catalyzed with citric acidPublication . Santos, J.; Pereira, J.; Paiva, N.; Ferra, J.; Magalhães, F.D.; Martins, Jorge Manuel; Carvalho, LuisaUrea, in either solid form or in solution, is an additive commonly used to control the viscosity or act as a scavenger in MF (melamine-formaldehyde) and MUF (melamine-urea-formaldehyde) resins for particleboard production. The aim of this work was to evaluate the influence of adding urea to MF (melamine-formaldehyde) resin in terms of the water-resistance of the final particleboards. FTIR-ATR spectroscopy, adhesive bonding evaluation system (ABES) and gravimetric techniques were used. MF and MFU (melamine-formaldehyde-urea) resins were prepared. Urea was introduced as an additive, in different percentages (0, 10, 20, and 30% (on adhesive, dry basis), and citric acid was used as catalyst. Beech veneer strips were bonded together with these formulations and then tested in dry conditions and after immersion in water for 24 h. The effect of urea load on the resin curing reaction in dry and humid joints was studied. Particleboards were produced with MF and MFU (melamine formaldehyde urea) resins with different urea loads and using industrial recycled wood particles as raw material. Particleboard evaluation indicated that the water resistance of the final particleboards decreased linearly with urea addition
- Grape Canes (Vitis vinifera L.) Applications on Packaging and Particleboard Industry: New Bioadhesive Based on Grape Extracts and Citric AcidPublication . Santos, Jorge; Pereira, João; Escobar-Avello, Danilo; Ferreira, Irene; Vieira, Carlos; Magalhães, Fernão D.; Martins, Jorge Manuel; Carvalho, LuisaThe main by-product generated in the wine industry are the grape canes, derived from the pruning process. In order to increase the valorisation possibilities of this highly polyphenolic lignocellulosic material, this work focuses on its applicability in the materials industry. As a first step, we demonstrate the viability of using grape cane particles as raw material for particleboard production, combined with a melamine formaldehyde urea (MFU) binder. In addition, looking for the application of these particleboards in the food packaging industry, particleboards based on grape canes were also produced using a new bioadhesive, obtained from the grape cane extract and citric acid. The self-condensation reaction of the grape cane extracts, and the curing reaction with citric acid, were studied by FTIR-ATR and ABES showing the feasibility of this new bioadhesive formulation. Looking for a zero-waste process, the effect of the type of raw material (fresh grape cane, solid by-product of the extraction) and of the extract used on the properties of particleboard were also studied. Citric acid was demonstrated to be a good crosslinking agent for grape cane extract. This work shows that it is possible to produce a new lignocellulosic product based only on grape cane particles using a binder based on grape cane extracts and citric acid. The implemented methodology allowed producing particleboards with applicability in the food-packaging industry, minimizing the waste generated in the process
- Prediction of formaldehyde and residual methanol concentration in formalin using near infrared spectroscopyPublication . Magalhães, Roberto; Paiva, Nádia; Ferra, João M; Magalhães, Fernão D; Martins, Jorge Manuel; Carvalho, LuisaAmino resins are produced by two main processes: the strong acid process and the alkaline-acid process. Both use formaldehyde and a base (e.g. sodium hydroxide) in their formulation. In this work, Forward Interval Partial Least Squares methodology was applied to create prediction models for the determination of the concentration of formaldehyde and residual methanol (that is present in the formaldehyde solution) used in the production of amino resins. Near infrared (NIR) spectra were acquired at two different temperatures: 18 and 35°C. A Partial Least Squares calibration models were established with the measured values from reference methods: namely, sodium sulfite (formaldehyde) and gas chromatography (methanol). The performances of the best models were compared using the root mean square error of cross validation (RMSECV) and coefficient of determination for prediction (r2 ). The best results obtained a r2 above 0.994. The RMSECV values obtained were 0.063% (m/m) and 0.031% (m/m) for the formaldehyde and methanol concentration, respectively. External validation was performed using different formaldehyde solution samples. The NIR methodology presented in this work proved to be effective and enables a significant time reduction, when compared to the reference methods, in the measurement of formaldehyde and methanol concentrations.
- Antioxidant Particleboards Produced from Forest By-Products with Application in the Food Packaging IndustryPublication . Raquel A. Fernandes; Nuno Ferreira; Sandro Lopes; Beatriz Freitas; Jorge Santos; Martins, Jorge Manuel; Carvalho, LuisaThe food packaging industry is one of the fastest growing sectors of our economy, with a large contribution to environmental concerns due to the extensive use of fossilderived materials. Combining wood-based materials, such as particleboards, with bioadhesives may offer a great opportunity to develop sustainable packaging solutions with active antioxidant properties. In the present work, a phenolic extract of poplar bark was produced and bio-adhesives were formulated using citric acid as a cross-linker. The impact of citric acid content on the chemical and bonding properties of bio-adhesives was evaluated. Additionally, the impact of the temperature of curing on their antioxidant capacity was also accessed. The bio-adhesives were applied in the production of particleboards, using poplar veneer particles as raw material. The composite materials exhibit high mechanical resistance, fulfilling the requirement of PB type P1, with remarkable antioxidant activity, opening a possibility to be employed in an active packaging solution.