Itziar Egüés

Effect of alkaline and autohydrolysis processes on the purity of obtained hemicelluloses from corn stalks

A study of the potential of autohydrolysis and alkaline extraction processes from corn stalks was performed for high purity hemicellulose extraction. The influence of process parameters on the purity of obtained hemicelluloses was analyzed. An experimental design was developed for the autohydrolysis treatments to determine the optimal conditions to solubilize the hemicelluloses with lowest content in contaminants. On the other hand, alkaline extraction, including raw material pretreatment (dewaxing and delignification step) was carried out analyzing the effectiveness of this processes for maximum pure hemicellulose recovery. The maximum yield (54% of the raw material hemicelluloses) and the best physicochemical properties (highest hemicellulose content free of lignin) were obtained with these pretreatments in alkaline extraction. Moreover, the effect of lignin removal by sulfuric acid from the autohydrolysis liquors before hemicellulose precipitation was studied. This purification step has allowed to obtain lignin-free autohydrolysis hemicellulose but with the presence of sulfur as predominant contaminant.

Autohydrolysis and organosolv process for recovery of hemicelluloses, phenolic compounds and lignin from grape stalks.

A combination of two environment-friend processes for hemicelluloses and lignin recovery from red grape stalks were investigated: an autohydrolysis pretreatment at 180°C for 30 min followed by a non-catalysed ethanol organosolv step at 180°C for 90 min. Hemicelluloses were precipitated by ethanol addition to autohydrolysis liquor, while lignin was tentatively precipitated by acidification of liquors from both the processes. Results suggest that stalks hemicelluloses can be easily hydrolysed requiring a milder treatment to reduce sugar degradation, while the organosolv process did not give a consistent delignification. Autohydrolysis allowed a recovery of 2% (on stalks d.m.) of total phenols in the liquor. Organosolv liquor had a higher concentration of phenols (corresponding to 0.72% of stalks d.m.) which almost completely precipitated with lignin.

Corncob arabinoxylan for new materials

Corncob agricultural waste was used as a source of arabinoxylan for preparation of films. Three arabinoxylan samples were prepared: crude extract (CCAX), purified by a washing step, and purified by bleaching CCAX. Films prepared with untreated CCAX were water soluble, yellowish in color and had poor mechanical properties. After the purification processes the Youngs modulus increased from ∼ 293 MPa to ∼ 1400-1600 MPa, and strength was improved from ∼ 9 MPa to around 53 MPa, while the strain at break was kept at ∼ 8% both in untreated and purified CCAX. The contact angle was increased from ∼ 21.3° to 67-74° after washing or bleaching CCAX. Acetylation of bleached CCAX showed the highest thermal resistance (325 °C), had low Tg (125°C) and a high contact angle (80°), and its films were stronger (strength ∼ 67 MPa; Youngs modulus ∼ 2241 MPa) and more flexible (∼ 13%). These characteristics make purified CCAX a suitable material to be used as a matrix for film applications.

Xylan-cellulose films: improvement of hydrophobicity, thermal and mechanical properties.

Xylan-rich hemicellulose from corn cob has been used for new material elaboration. Commercial cellulose was used as reinforcement in different percentages to improve properties of the films. Two types of composites were elaborated by solvent casting. Hydrophilic films, composed by bleached hemicellulose (BH), unmodified cellulose and glycerol as plasticizer, and hydrophobic films formed by acetylated bleached hemicellulose (BAH) and acetylated cellulose. The degree of substitution of BAH was 1.8 and acetylated cellulose presented a degree of substitution of 0.54. Thermal and mechanical properties of films were analyzed. A significant improvement was observed in the thermal behavior of hydrophobic films (Tmax ∼ 368 °C) respect to hydrophilic films (Tmax ∼ 300 °C). Although the addition of cellulose clearly increase the properties of both type of films, hydrophobic films (Youngs modulus ∼ 2300 MPa, strength ∼ 44.1MPa, strain at break ∼ 5.7%) showed better mechanical properties than hydrophilic films (Youngs modulus ∼ 3 MPa, strength ∼ 3.3 MPa, strain at break ∼ 5.3%).

Lignin-ester derivatives as novel thermoplastic materials

Spruce and eucalyptus lignins isolated by an organosolv process and lauroyl chloride were used as raw material for the synthesis of lignin-ester derivatives. The obtained products presented new and interesting properties suitable for use as thermoplastic materials. Esterification of the lignins was confirmed by FTIR, GPC, DSC and contact angle measurements. The modification of lignin –OH groups increased the molecular weight properties, changed its thermal behavior (reducing greatly Tg), and improved the hydrophobicity of the material. For composite elaboration, commercial cellulose acetate was used as reinforcement in different percentages (5%, 10%, 25% and 50%) to manufacture composites by press moulding. Thermal and mechanical tests as well as wetting behavior of the composites surface against water analysis were carried out. Surface morphology was analyzed by SEM. The mechanical test revealed tensile strength and Young modulus values of 130–900 kPa and 2–50 MPa respectively, with high elongation at break (5–130%) for eucalyptus lignin composites, while spruce lignin composites showed more a rigid (40–60 MPa) and tough (300–1400 kPa) behavior, but with the ability to deform only up to 6%.

The Biorefinery Concept for the Industrial Valorization of Grape Processing By-Products

The winemaking industry generates high amounts of underutilized by-products worldwide, which represent a significant economic potential and a great challenge. The main by-product of winemaking is grape marc, consisting of the stalks, skin, pulp (pomace), and seeds that remain after pressing the grapes. Other grape processing by-products include vine shoots (vine prunings), winery sludge (wine lees), effluents, and filtration residues. These residues have an interesting composition to be used as sources of high added-value products generated using environment friendly technologies within the biorefinery frame. Taking into account the problems induced by the disposal of these leftovers in the environment, this chapter describes the sustainable treatment of grape processing by-products within the integral biorefinery approach that promises potential economic benefits from the underutilized sources.