S. Freire

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.

Effect of chemical modification of lignin on the gluebond performance of lignin-phenolic resins

Abstract Lignin obtained from eucalyptus wood by acetic acid pulping was methylolated or phenolated and used to prepare lignin-phenol-formaldehyde resins. The amount of formaldehyde consumed in the methylolation reaction, and supporting comparison of pre- and post-methylolation 1H and 13C NMR spectra, showed the reactivity of the crude acetosolv lignin with formaldehyde to be relatively high. Pine and eucalyptus plywood boards manufactured using the resins prepared with the modified lignins complied with European Standard EN 314-1:1993 for WBP quality boards and gave knife test results similar to those of boards manufactured with a commercial phenol-formaldehyde resin.

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=90u2009°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%) 90u2009°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.

The Influence of Pulping Conditions on the Structure of Acetosolv Eucalyptus Lignins

Abstract Acetosolv lignins obtained under a variety of pulping conditions as regards acetic acid concentration, catalyst concentration, temperature and pulping time were characterized structurally by elemental analysis, FTIR and 1H and 13C NMR spectroscopy, and determination of methoxyl group content. Increasing catalyst concentration and pulping time favours both the dissolution of lignin (by cleavage of α and β-O-4 bonds) and the occurrence of condensation reactions. Increasing temperature favours the degradation of syringyl units more than of guaiacyl units.

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.

Acetosolv pulping of pine wood. Kinetic modelling of lignin solubilization and condensation

Experiments of delignification of Pinus pinaster wood by acetic acid at atmospheric pressure showed that acetic acid concentration is a primary factor in the process and that high concentrations (90%) significantly improve the delignification degree. The kinetics of the process were satisfactorily explained by a model of consecutive first-order reactions corresponding to lignin solubilization followed by lignin condensation and reprecipitation onto the lignocellulosic matrix, hydrolysis of α-aryl ether bonds being the dominant reaction of the delignification process. The selectivity of the lignin dissolution was practically independent of operating conditions. When the degree of delignification reached a value around 90% the selectivity decreased considerably due to lignin condensation.

Structures, and Reactivities with Formaldehyde, of Some Acetosolv Pine Lignins

Abstract Lignins obtained from pine by the acetosolv process under various operating conditions were characterized structurally by elemental and methoxyl analyses, and FTIR. and NMR spectroscopy, and their reactivity with formaldehyde was determined. The reactivity results, including NMR quantification of the introduced methylol groups, suggest that the methylolated lignins are suitable for the formulation of adhesives.

Characterization of Pinus pinaster bark and its alkaline extracts by diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy

Pinus pinaster bark and of the raffinates obtained after an alkaline extraction, and also the Stiasny number of the corresponding extracts. By means of a stepwise regression analysis a selection of the DRIFT spectra bands which allow to correlate satisfactorily the experimental results has been made.

The influence of acetosolv pulping conditions on the enzymatic hydrolysis of Eucalyptus pulps

Eucalyptus globulus wood was subjected first to HCl–catalysed delignification with 70% acetic acid under conditions realizing an incomplete 3u2009×u20093u2009×u20093 factorial design (HCl concentration 0, 0.025 or 0.05%; temperature 120, 140 or 160u2009°C; reaction time 1, 2.5 or 4u2009h), and then to enzymatic hydrolysis. The hydrolysis kinetics conformed to both Ghoses empirical model and a biexponential equation. The biexponential fit implies the presence of both readily and reluctantly hydrolysed cellulose fractions, and the fitted coefficients show hydrolysis yield to depend largely on the digestibility of the latter. Multiple regression of performance variables on pulping conditions showed that neither the rate nor the extent of hydrolysis is greatest for pulps with minimum lignin or xylose contents; we attribute this circumstance to the condensation and precipitation of lignin under severe pulping conditions, which protects the cellulose of the pulp from enzymatic attack.