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Gama N.V.,University of Aveiro | Soares B.,University of Aveiro | Freire C.S.R.,University of Aveiro | Silva R.,Sapec Quimica SA | And 3 more authors.
Materials and Design | Year: 2015

In this work the preparation of viscoelastic bio-based polyurethane foams (PUFs) using polyols obtained via acid liquefaction of coffee grounds wastes has been optimized. In a first stage, the effect of different ratios of isocyanate content to hydroxyl number (0.6, 0.7 and 0.8) and of three distinct percentages of catalyst (3%, 5% and 7%) on the extent of the polymerization reaction was studied by infrared spectroscopy. Next, different percentages of surfactant (14%, 16% and 18%) and blowing agent (12%, 14% and 16%) were used to assess their effect on the density, thermal conductivity and mechanical properties of the foams, including their recovery time. The mechanical properties of the ensuing foams proved to be very interesting due to their viscoelastic behavior. PUFs were also characterized by scanning electron microscopy (SEM) revealing a typical cellular structure and by thermogravimetric analysis (TGA) which proved that these materials are thermally stable up to 190. °C. These results suggest other potential applications for these materials beyond heat insulation in areas where damping properties can be an added value. © 2015 Elsevier Ltd. Source


Soares B.,University of Aveiro | Gama N.,University of Aveiro | Freire C.,University of Aveiro | Barros-Timmons A.,University of Aveiro | And 4 more authors.
ACS Sustainable Chemistry and Engineering | Year: 2014

Ecopolyol production from acid liquefaction of cork powder was studied for the first time using PEG 400 and glycerol as liquefaction solvents in the presence of sulfuric acid at moderate temperature and atmospheric pressure. The effect of the temperature, concentration of catalyst, and time on the liquefaction yield has been investigated using a fixed set of reaction conditions namely, a liquefaction solvent mixture/cork powder ratio of 5/1 and a solvent mixture PEG 400/glycerol ratio of 90/10. The full-factorial design of experiments (DOE) 23 was applied to obtain an optimized set of liquefaction conditions aiming at minimizing the residue content. The minimum residue contents experimentally obtained in this study were 29 wt %, related to cork powder, which were achieved at 150 °C, 4 wt % of sulfuric acid, and 60 min. This value corresponds to 5 wt % of residue per total mass of reaction product. The polyols obtained under optimal conditions present similar characteristics (hydroxyl number value 219 mgKOH/gpolyol and viscosity 2875 cP, at 25 °C) to those of petroleum-based polyols typically used in the polyurethane foam industry. © 2014 American Chemical Society. Source


Gama N.V.,University of Aveiro | Soares B.,University of Aveiro | Freire C.S.,University of Aveiro | Silva R.,Sapec Quimica SA | And 4 more authors.
Polymer International | Year: 2015

The aim of this study was to evaluate the possibility of using polyols derived from liquefied cork in the production of novel bio-based polyurethane foams (PUFs). For that purpose, different liquefaction conditions were used at atmospheric pressure and moderate temperature where poly(ethylene glycol) and glycerol were used as solvents and sulfuric acid as catalyst. The ensuing polyols were used to produce foams which were characterized using structural, morphological, thermal and mechanical analyses to demonstrate that liquefaction conditions play a crucial role in the properties of the foams. The resulting foams exhibited the typical cellular structure of PUFs with low densities (57.4-70.7 kgm-3) and low thermal conductivities (0.038-0.040 Wm-1K-1). However, the mechanical properties differed significantly depending on the liquefaction conditions. The best stress-strain results were obtained for PUFs prepared using the polyol with lowest IOH and water content (Young's modulus of 475.0 kPa, compressive stress (σ10%) of 34.6 kPa and toughness of 7397.1 Jm-3). This PUF was thermally stable up to 200 °C and presented a glass transition temperature of around 27 °C. The results obtained demonstrate that these polyols from liquefied cork yield PUFs that are adequate materials for insulation applications. © 2014 Society of Chemical Industry. Source


Soares B.,University of Aveiro | Gama N.,University of Aveiro | Freire C.S.R.,University of Aveiro | Barros-Timmons A.,University of Aveiro | And 4 more authors.
Journal of Chemical Technology and Biotechnology | Year: 2015

BACKGROUND: Based on the biorefinery concept, the main focus of this work was the increase in value of spent coffee grounds via an acid liquefaction process using polyhydric solvents in the presence of sulfuric acid, at moderate temperature. For that purpose the effect of temperature, sulfuric acid concentration and time on biomass conversion was studied using design of experiments combined with statistical analysis. RESULTS: The ANOVA results (95% confidence level) showed that temperature is the factor with most influence on biomass conversion, within the studied range, while reaction times above 40 min don't seem to bring significant advantages. The maximum conversion obtained in this study was 70 wt% which was achieved at 160°C, 4 wt % of catalyst and 80 min. The polyol obtained using these conditions presented a hydroxyl number value of 199 mg KOH/g polyol and a viscosity of 390 cP, at 25°C. CONCLUSION: This work showed that it is possible to convert spent coffee grounds into liquid polyols via an acid liquefaction process at moderate temperature and autogeneous pressure. These polyols have similar properties to those of petroleum-based polyols typically used in the polyurethane foam industry. © 2014 Society of Chemical Industry. Source

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