Percorrer por autor "Santos, Ricardo J."
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- Chestnut burrs as a sustainable source of cellulose for Pickering emulsion stabilisersPublication . Lains, Joana; Almeida, Heloísa H.S.; Barreiro, Filomena; Silva, Cláudia Gomes; Dias, Madalena M.; Santos, Ricardo J.; Ribeiro, Andreia; Martins, Isabel M.As the global population grows, increasing food consumption drives a significant rise in agri-food waste. In the northern Tras-os-Montes region of Portugal, one of the world's largest chestnut producers, this waste includes valuable by-products such as chestnut burrs, which are composed of 63% cellulose. This study aims to valorise chestnut burrs by extracting compounds for incorporation into high-added-value products. Cellulose was extracted through physical and chemical pre-treatments, alkali hydrolysis and bleaching. The process parameters were adjusted to enhance the extracted cellulose content and purity. Extracts were characterised by thermogravimetry and Fourier Transform Infrared Spectroscopy, and parameters such as particle size, zeta potential and wettability were also assessed and compared with commercial microcrystalline cellulose. Temperature was identified as the key parameter in alkali hydrolysis, with optimal conditions obtained for 10% NaOH at 100 degrees C for 1 h and a biomass-to-solvent ratio of 1:20 g/mL. Bleaching under optimal conditions (2% NaClO at 35 degrees C) removed an additional 7% lignin and enhanced the whiteness of the final product. The cellulose obtained has a purity of 72%, with a particle size of 55 mu m, a negative surface charge, hydrophilic behaviour, an estimated molecular weight of 13.2 kDa, and a crystallinity of 56.5%. When applied at 0.8 wt% of the aqueous phase in 20:80 oil-in-water emulsions, these particles stabilise Pickering emulsions with a 12 mm average droplet size, remaining stable for at least 30 days. These findings demonstrate that chestnut burrs are a viable and sustainable source of cellulose with high potential as a natural Pickering emulsion stabiliser for use in food, cosmetics, and pharmaceuticals.
- Literature Review on Single and Twin-Screw Extruders Design for Polymerization Using CFD SimulationPublication . Delvar, Elham; Oliveira, Inês; Brito, Margarida S. C. A.; Silva, Cláudia G.; Santamaria-Echart, Arantzazu; Barreiro, M.F.; Santos, Ricardo J.This work presents a comprehensive review of the evolution in modeling reactive extrusion (REx), tracing developments from early analytical models to advanced computational fluid dynamics (CFD) simulations. Additionally, it highlights the key challenges and future directions in this field. Analytical models to describe the velocity profiles were proposed in the 1950s, involving certain geometrical simplifications. However, numerical models of melt polymeric flow in extruders have proven to be crucial for optimizing screw design and predicting process characteristics. The state-of-the-art CFD models for single and twin-screw extruders design address the impact of geometry (type of mixing elements and geometrical simplifications of CFD geometries), pressure and temperature gradients, and quantification of mixing. Despite the extensive work conducted, modeling reactive extrusion using CFD remains challenging due to the intricate interplay of mixing, heat transfer, chemical reactions, and non-Newtonian fluid behavior under high shear and temperature gradients. These challenges are further intensified by the presence of multiphase flows and the complexity of extruder geometries. Future advancements should enhance simulation accuracy, incorporate multiphase flow models, and utilize real-time sensor data for adaptive modeling approaches.