Julia González-Álvarez

Removal of cadmium and mercury ions from aqueous solution by sorption on treated Pinus pinaster bark: kinetics and isotherms.

Formaldehyde pretreated Pinus pinaster bark was used to sorb Cd2+ and Hg2+ from aqueous solutions. The sorption kinetics showed hyperbolic dependence of the proportion of cation adsorbed on time, and the sorption isotherms were satisfactorily fitted by Freundlich equations, with k and n values showing Hg2+ to be more efficiently sorbed than Cd2+. Except for low cation concentrations, for which sorption was practically total at all initial pH > or = 6, sorption increased in this range, in keeping with a mechanism based on ion exchange with the hydroxyl protons of ring B of the procyanidin units of the tannins in the bark.

Chestnut shell as heavy metal adsorbent: optimization study of lead, copper and zinc cations removal.

The influence of initial cation concentration, temperature and pH was investigated to optimize Pb(2+), Cu(2+) and Zn(2+) removal from aqueous solutions using acid formaldehyde pre-treated chestnut shell as adsorbent. Experiments were planned according to an incomplete 3(3) factorial experimental design. Under the optimal conditions selected, the metal ion adsorption equilibrium was satisfactorily described by the Langmuir isotherm model. The maximum pre-treated chestnut shell adsorption capacity was obtained for Pb(2+) ions, 8.5 mg g(-1), and the order of cation affinity was Pb(2+)>Cu(2+)>Zn(2+). A model that considered the effect of axial dispersion was successfully used to describe the fixed-bed adsorption behaviour of Pb(2+), Cu(2+) and Zn(2+) ions at the flow rates essayed. Fourier transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies showed that the functional groups involved in metal ions binding included carboxyl, hydroxyl, ether, alcoholic and amino groups.

Acetosolv pine lignin as copolymer in resins for manufacture of exterior grade plywoods

Abstract Plywood boards were prepared from pine and eucalyptus woods using resins obtained by copolymerization of phenol, formaldehyde and pre-methylolated acetosolv pine lignin. The influence of the lignin:phenol, formaldehyde:phenol and soda:phenol ratios on the properties of the resins and the quality of the boards was determined. Several formulations produced resins with knife-test results better than those obtained with a commercial phenol–formaldehyde resin.

Characteristics of Pinus pinaster bark extracts obtained under various extraction conditions

Pinus pinaster bark extracts obtained by lixiviation with water or alkaline solutions followed by spray drying. Extract yield was 2.5- to 6-fold higher with alkaline extractant solutions than with water. Within the ranges of temperature (T), NaOH dose (NaOH) and solid/liquid ratio (S/L) that were studied, the formaldehyde-condensable polyphenols content of spray-dried extracts obtained with NaOH as extractant was highest (27.3%) at T=90 °C, NaOH=5%, S/L=1/6. Polyphenols content fell with increasing particle size due to both diffusion limitations and the variation of particle composition with size, which is attributable to the dependence of both the chemical composition of the bark and its response to grinding on its anatomical origin. All the spray-dried extracts had Stiasny numbers high enough to allow their use in adhesives, although this application may require prior chemical modification to reduce the rapid rise in the viscosity of their aqueous solutions with increasing solids content. The reactivity of the extracts with formaldehyde is readily controlled by varying pH.P. pinaster wurden durch Auslaugen mit Wasser und Alkalien gewonnen. Nach Sprühtrocknen wurden ihre Eigenschaften bestimmt. Mit Alkalien ergaben sich 2,5- bis 6-fach höhere Ausbeuten als mit Wasser. Der Einfluß der Temperatur, des NaOH-Anteils und des Verhältnisses Festkörper zur Flüssigkeit (S/L) wurde untersucht. Der Anteil an Polyphenolen, die mit Formaldehyd kondensierbar sind, war am höchsten (27,3%) 90 °C, 5% NaOH und S/L=1/6. Der Polyphenolanteil wird niedriger mit steigender Partikelgröße. Die Gründe dafür sind die Begrenzung der Diffusion sowie die Variation der chemischen Zusammensetzung der Partikel, die sich entsprechend der anatomischen Herkunft beim Zerkleinern bilden. Die Stiasyn-Zahlen aller Extrakte waren ausreichend hoch für ihre Verwendung als Klebstoffe. Allerdings ist dafür eine chemische Modifizierung nötig, um den starken Anstieg der Viskosität der wässrigen Lösungen bei erhöhtem Feststoffgehalt zu verhindern. Die Reaktivität gegenüber Formaldehyd ist über den pH-Wert leicht einstellbar.

CURING KINETICS OF TANNIN-PHENOL-FORMAL- DEHYDE ADHESIVES AS DETERMINED BY DSC

Differential scanning calorimetry (DSC) was used to compare the thermal curing of two adhesives suitable for using in the manufacture of exterior-grade plywood boards: a commercial phenol-formaldehyde (PF) resin, and a tannin-phenol-formaldehyde (TPF) resin developed in our laboratory. The experimental curves were well simulated by means of the Model Free Kinetics isoconversional method incorporated in the Mettler-Toledo STARe software package. The corresponding kinetic calculations predict that the TPF resin cures faster than the PF resin. This finding implies the possibility that the TPF resin may allow the achievement of higher productivity by permitting the use of shorter press times than with conventional PF resins.

Effect of veneer side wettability on bonding quality of Eucalyptus globulus plywoods prepared using a tannin–phenol–formaldehyde adhesive

The influence of rotary peeling on the different behaviour of tight and loose sides of Eucalyptus globulus veneers has been studied. The presence of lathe checks on the loose sides favours wettability, the contact angle decreasing more rapidly on these sides than on tight sides. Additionally, pine bark tannins improved wettability due to their surfactant character. Bonding quality tests carried out on plywoods prepared using a tannin-phenol-formaldehyde adhesive showed that fracture almost invariably occurred in a glue line with at least one loose side, where wood failure appeared. This behaviour, confirmed by analysing the glue lines by means of fluorescence microscopy, was due to the large surface alterations of the loose sides which reduced mechanical strength but allowed greater penetration of the adhesive giving rise to high wood failure.

Rheology of tannin-added phenol formaldehyde adhesives for plywood

2 adhesive consumption in double glue line, which is significantly lower than the aprox. 400 g/m2 allowed by commercially available phenol-formaldehyde adhesives. The adhesives prepared with resols containing 36% reactive solids, the tannins representing aprox. 20%, has permitted the preparation of eucalyptus plywood boards exceeding the requirements of the European norm for exterior grade plywood.2 je doppelter Klebeline erlaubt. Dies ist bedeutend niedriger als die etwa 400 g/m2, die bei kommerziell erhältlichen Harzen nötig sind. Die hier hergestellten Harze enthalten etwa 36% reaktive Harze, wovon ca. 20% Tannine darstellen. Mit diesen Harzen konnten Eukalyptus-Sperrhölzer hergestellt werden, welche die Anforderungen der europäischen Normen für Außenverwendung übersteigen.

Effect of the Extraction Technique and Operational Conditions on the Recovery of Bioactive Compounds from Chestnut (Castanea sativa) Bur and Shell

The aim of this work was to study the extraction of phenolic compounds from chestnut bur and shell, both waste products of chestnut processing in the food industry. Two extraction techniques were compared—maceration with solvents and microwave-assisted extraction. The influence of the solvent used (water, 50% MeOH or 50% EtOH) and temperature (25-50-75°C) on extraction yield and extract total phenols content and FRAP, DPPH, and ABTS antioxidant activities was studied. In the conventional extraction, the yield was significantly higher for the bur (8.54–19.58%) than for the shell (2.91–13.27%); however, the shell extracts showed substantially greater properties. The best extract properties were achieved at 75°C using 50% MeOH for the bur and water for the shell and phenolic compounds with demonstrated antioxidant properties, as gallic acid esters of glucose and ellagic acid, were identified in these extracts by RP-HPLC-ESI-TOF. In addition, the aqueous extracts showed ability to inhibit the growth of gram positive and negative bacteria but not fungi. The kinetic of the extraction process was well fitted by the Pelegs model. The non-conventional microwave-assisted extraction slightly improved the chestnut bur extraction by reducing the extraction time.

Outstanding electrochemical performance of highly N- and O-doped carbons derived from pine tannin

Highly N- and O-doped carbons were prepared from pine tannins by hydrothermal carbonisation (HTC) and subsequently applied as materials for supercapacitor electrodes. Pine tannins were transformed into carbon materials by using environment-friendly solvents (water or ammonia) without applying any activation or functionalisation post-treatment. Depending on the solution used for extracting tannins and on the HTC method, carbons with different physicochemical and electrochemical properties were obtained. The material prepared from the water-extracted tannin and subjected to HTC in ammonia displayed a porous texture composed of: (a) low ultramicroporosity and well-developed mesoporosity; (b) a hydrophilic surface with a high density of surface functionalities; and (c) a high nanotextural order. These features accounted for the excellent electrochemical performance of the resultant carbon electrode in terms of high rate capability up to 1 V s−1, high energy density up to ∼1500 mA g−1, low cell resistance and fast frequency response, making it a suitable material for practical supercapacitors.

Environmentally friendly wood adhesives based on chestnut (Castanea sativa) shell tannins

The aim of this work was the formulation of adhesives for particleboards based on tannins extracted from industrial lignocellulosic wastes, namely chestnut shell, chestnut bur and eucalyptus bark. The interest was centred on the possibility of completely removing formaldehyde from adhesive formulations. For this, hardener alternatives to formaldehyde were used: tris(hydroxymethyl)nitromethane (TRIS), glyoxal (GLY) and hexametilentetramine (HEX). The influence of the type and concentration of the hardener and pH on adhesive gel time and pot-life were studied. A comparative structural characterization of the adhesives was performed by 13C-NMR spectroscopy. Thermomechanical analyses (TMA) tests were carried out as an indication of the final strength of the adhesive systems. Particleboards type 2 of interior use (EN 312) were manufactured with adhesives based on chestnut shell tannins alone or mixed with chestnut bur/or eucalyptus bark tannins. Free-formaldehyde was determined, and boards were prepared with TRIS, GLY and HEX tannin adhesives were classified as E0.