Costas Tsioptsias

Development of micro- and nano-porous composite materials by processing cellulose with ionic liquids and supercritical CO2

Three lines of green chemistry were combined in this study, in order to produce porous materials with pore size distributions in the micro- and nano-scales. These lines are: (i) the renewable and biodegradable sources (cellulose), (ii) ionic liquids, and (iii) supercritical fluids. By dissolving cellulose in a room temperature ionic liquid and regenerating with water or methanol we obtained cellulose hydrogels and methanogels. The liquid mixtures were separated by vacuum distillation with high yield of recovery. The obtained gels were processed by supercritical carbon dioxide to give porous materials. A novel foaming procedure was applied to hydrogels in order to obtain microporous structures of cellulose and cellulose composites, while in alcogels the supercritical point drying method resulted in nanoporous aerogels. For elucidating physicochemical aspects involved in the two processes and for characterization of the produced materials, X-ray diffraction, sorption measurements (by a modified mass loss analysis and the BET method) and scanning electron microscopy were used. The role of various process parameters on the final porous structure was investigated.

Equation-of-state modeling of mixtures with ionic liquids

A non-electrolyte equation-of-state model was used to describe the phase behavior of binary systems containing alkyl-methyimidazolium bis(trifluoromethyl-sulfonyl)imide ionic liquids. A methodology is suggested for modeling this phase behavior by using the Non-Random Hydrogen-Bonding (NRHB) model. According to this methodology, the scaling constants of the ionic liquid are calculated using limited available experimental data on liquid densities and Hansens solubility parameters, while all electrostatic interactions (polar, hydrogen bonding and ionic) are treated as strong specific interactions. Using the aforementioned methodology, the model is applied to describe the vapor-liquid and the liquid-liquid equilibria in mixtures of ionic liquids with various polar or quadrupolar solvents at low and high pressures. In all cases, one temperature-independent binary interaction parameter was used. Accurate correlations were obtained for the majority of the systems, both, for vapor-liquid and liquid-liquid equilibria.

Thermal stability and hydrophobicity enhancement of wood through impregnation with aqueous solutions and supercritical carbon dioxide

A novel process for the thermal stability and hydrophobicity enhancement of wood is proposed. The process concerns the impregnation of wood with water-soluble and water-insoluble salts. The salts are synthesized in situ in wood through aqueous solutions and supercritical carbon dioxide treatment. To protect salt-treated wood from absorbing large amounts of humidity a polymer film is formed upon the surface of wood and depending on the inherent roughness of wood, superhydrophobicity can be obtained. Characterization of the materials was performed by infrared spectroscopy, thermogravimetry, calorimetry, density, color and contact angle measurements and ignition and visual observations. The fire retardation is achieved in both glowing and smolding combustion and may be due to different mechanisms as it was concluded from the thermogravimetric analysis and ignition.

Flame-retarded hydrophobic cellulose through impregnation with aqueous solutions and supercritical CO2

We have developed flame-retarded hydrophobic cellulose-based materials by producing in situ water-soluble and insoluble inorganic microparticles on various surfaces of native cellulose (filter paper and pure cotton textile). The nanoparticles were produced by simple impregnation of cellulose with two different aqueous solutions followed by a third impregnation with supercritical CO2. Finally, the composite cellulose materials were covered by a silicon-based polymer thin film, to turn it into hydrophobic and prevent the water-soluble particles from absorbing humidity. The obtained flame-retardant behaviour is due to a combination of mechanisms. The total treatment of cellulose has an impact on, both its surface morphology and its hydrophilicity. Thus, the hydrophobic nature of the silicon-based polymer film along with the roughness caused by the presence of the inorganic particles and the inherent roughness of native cellulose resulted in superhydrophobic behaviour. The same process-concept was also applied to regenerated (from newspaper) cellulose with ionic liquids. The produced materials were characterised by thermogravimetric analysis, differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy and water contact angle measurements.

Selective extraction of oxygenated compounds from oregano with sub‐critical water

BACKGROUND The essential oil of oregano is composed of numerous substances that exhibit various properties (e.g. antioxidants). The innovative and promising method of extraction with sub-critical water (subcH₂O) has been applied to the Greek oregano. RESULTS The sub-critical water extraction experiments were performed at various conditions of pressure, temperature and water flow rate. Extracts collected at different extraction times were examined by gas chromatography. The oil has been processed by super-critical carbon dioxide (scCO₂) followed by steam distillation or sub-critical water extraction. The conventional method of steam distillation was also performed. The main component of the plant is carvacrol. The favourable oxygenated compounds (carvacrol, thymol, borneol and thymoquinone) have been extracted preferentially and faster with sub-critical water. This method was selective for thymoquinone, which was not present in the oil from steam distillation. The oil yield obtained was much higher in the case of sub-critical water extraction compared to the one of super-critical carbon dioxide. The latter method resulted in oil with the highest concentration in carvacrol. CONCLUSION Compared to the classical steam distillation, the sub-critical water extraction is superior in terms of higher yields, less energy consumption (as it was a faster process), and better composition/selectivity of the extracts controlled by the extraction parameters.