Miguel A. Zanuttini

Cationic and anionic polyelectrolyte complexes of xylan and chitosan. Interaction with lignocellulosic surfaces

Cationic (CatPECs) and anionic (AnPECs) polyelectrolyte complexes from xylan and chitosan were formed, characterized and adsorbed onto unbleached fibers for improving the papermaking properties. They were prepared at a level of 30% of neutralization charge ratio by modifying the order of addition of polyelectrolytes and the ionic strength (0.01N and 0.1N NaCl). The charge density, colloidal stability and particle size of polyelectrolyte complexes (PECs) was measured using polyelectrolyte titration method, Turbiscan and Zetasizer Nano equipments, respectively. All the complexes were stable even after seven days from PEC formation. DRIFT spectra of complexes were also analyzed. The adsorption behavior of them onto cellulose nanofibrils model surfaces was studied using quartz crystal microbalance with dissipation monitoring, and surface plasmon resonance. It was found that the PEC layers were viscoelastic and highly hydrated. Finally, it is shown that the adsorbed PECs onto cellulosic fibers markedly improved the tensile and crushing strengths of paper.

Complexes of xylan and synthetic polyelectrolytes. Characterization and adsorption onto high quality unbleached fibres.

In this work, polyelectrolyte complexes (PECs) were formed by adding polyacrylic acid (PAA) or 4-O-methylglucuronoxylan (Xyl) on poly(allylamine hydrochloride) (PAH) solutions, at different ionic strength and neutral pH. Turbidity curves, charge densities of the cationic complexes determined by polyelectrolyte titration method, and z-potential values showed clear differences between both complexes. Stirring favourably reverses the effects of sedimentation of Xyl/PAH complexes, as demonstrated by colloidal stability tests. Adsorption studies on silica surfaces, performed by Quartz Crystal Microbalance with Dissipation (QCM-D) showed that PAA/PAH adsorbed complexes layers were rigid, while the corresponding Xyl/PAH layers were viscoelastic. Despite the different conformations, both complexes were adsorbed as spherical particles, as observed by Atomic Force Microscopy (AFM). Adsorption isotherms performed on fibre suspensions showed that the ionic strength of the liquid medium determines the amount of PEC retained. Finally, it was found that the papermaking properties were significantly increased due to the addition of these PECs.

Dynamics of the effective capillary cross-sectional area during the alkaline impregnation of eucalyptus wood

Abstract Wood diffusion is strongly affected by the effective capillary cross-sectional area (ECCSA), which is the area of paths available for diffusion. The ECCSA varies dynamically according to the conditions and progress of the alkaline action. The alkali diffusion in natural wood is a complex process in the course of which the local transport properties are modified by chemical reactions and swelling. A method was developed which allows the fast determination of ECCSA as a result of the dynamic process. It is based on measurements of the relative electrical conductivity through thin wood slices. It is assumed that restrictions in diffusion of thin slices can be neglected regardless of alkali action. The evolution of ECCSA was determined in transverse directions of eucalyptus wood. The influence of temperature, alkali concentration and time was established. As demonstrated earlier, alkalinity had a strong effect on the ECCSA at room temperature, which is dramatically increased when the pH is elevated from 12.5 to 13.5. At high temperatures, the steep increase in the ECCSA appears at pH 10.5. It was also demonstrated that the degree of the chemical action – indicated by the deacetylation level – is also very relevant, being even higher than the temperature effect.

Deacetylation consequences in pulping processes

When wood undergoes an acidic or alkaline chemical action or a moderate thermal action, acetyl groups are easily removed. As deacetylation favourably increases the accessibility of the cell wall and the fibre swelling, mechanical properties of wood and responses of wood to pulping are modified. In this paper, the importance of the deacetylation effects in alkaline pulping is highlighted. It is shown that it is very useful to analyse acetyl content profiles in eucalyptus wood for determining the level of alkali impregnation. Global deacetylation can be a parameter that can be practical for determination of the effectiveness of alkaline impregnation of chips. In alkaline chemi-mechanical pulping of poplar, the deacetylation level that takes place during pre-treatment can establish the bonding capacity of the pulp developed afterwards in the refiner. Acetyls can be very reactive under conditions of peroxide bleaching of chemi-mechanical pulps and, as a consequence of this reaction, alkali concentration in the process and final pulp properties can be notably affected.ZusammenfassungWenn Holz einer sauren oder alkalischen chemischen Behandlung oder einer gemäßigten thermischen Behandlung unterworfen wird, werden Acetylgruppen leicht abgespalten. Da eine Deacetylierung vorteilhaft die Zugänglichkeit der Zellwand und die Faserquellung erhöht, werden die mechanischen Eigenschaften des Holzes und das Verhaltung des Holzes beim Aufschluss verändert. In dieser Arbeit wird die Bedeutung der Deacetylierung beim alkalischen Zellstoffaufschluss hervorgehoben. Es wird gezeigt, dass es sehr nützlich ist, Profile des Gehalts an Acetylgruppen in Eukalyptusholz zum Bestimmen des Ausmaßes der Imprägnierung mit Alkali zu analysieren. Die Gesamt-Deacetylierung kann ein Parameter sein, der nützlich ist, die Wirksamkeit der alkalischen Imprägnierung der Späne festzulegen. Im alkalischen chemo-mechanischem Aufschluss von Pappelholz kann das Deacetylierungsniveau während der Vorbehandlung die spätere Bindungskapazität des Zellstoffs im Refiner bestimmen. Acetylgruppen können sehr reaktiv sein unter den Bedingungen der Peroxydbleiche des chemo-mechanischen Zellstoffs, und als Folge dieser Reaktion können die Alkalikonzentration im Prozess sowie die Eigenschaften des resultierenden Zellstoffs beeinflusst werden.

Profiles of alkali concentration and galactoglucomannan degradation in kraft impregnation of Scots pine wood: Experimental observations and modeling

Abstract A deep understanding of alkali impregnation including the profiles of alkali concentration and hemicellulose degradation is necessary to analyze the optimization of current and innovative processes. In this paper, the impregnation of Scots pine (Pinus sylvestris L.) wood is analyzed and modeled under consideration of deacetylation, reactions of acidic group, and galactoglucomannan (GGM) degradation. The immobile anionic groups activated by the ionization of lignin-derived OH groups are also considered for the assessment of the Donnan effect. Predicted profiles of sodium and hydroxide ions and acetyl group concentrations are compared to experimental results. The balance between impregnation and hemicellulose degradation levels is discussed based on the developed models. Expectedly, higher concentrations and temperatures speed up the impregnation process. Nevertheless, a higher OH-concentration has two benefits for the same impregnation front position – the alkali charge inside the chip is higher and the GGM degradation is lower.

The deacetylation reaction in Eucalyptus wood: kinetics and effects on the effective diffusion.

The removal of native acetyl groups from hardwood O-acetyl-glucuronoxylan has a strong effect on physical characteristics, accessibility and structure of this polymer. The removal also has effects on the swelling and ion transport capacity of the cell wall of hardwoods. In this work, a kinetic expression for Eucalyptus wood deacetylation is determined. Two liquid mediums are considered: a simple alkaline one and another with a higher sodium concentration. The kinetic expression is a power law for the acetyl content and the concentrations in the liquid medium dependence, and is an Arrhenius type expression for temperature dependence. The kinetic expression can be useful to predict the physical properties of wood since the analysis of deacetylation effects on effective capillarity (ECCSA) shows that the acetyl content is a determining factor of wood ionic transport capacity.

Polyelectrolyte complexes for assisting the application of lignocellulosic micro/nanofibers in papermaking

A novel procedure based on the addition of polyelectrolyte complexes (PECs) onto the pulp containing lignocellulosic micro/nanofibers (LCMNF) is presented. This procedure allows increasing paper strength avoiding an excessive loss in drainability. LCMNF were obtained from partially delignified kraft pine sawdust using a high-pressure homogenizer. Cationic complexes (CatPECs) were prepared by adding the anionic polyelectrolyte solution (polyacrylic acid) on the cationic polyelectrolyte solution (poly(allylamine hydrochloride)). According to turbidity and surface morphology changes, an interaction between CatPECs and LCMNF could be established. Different CatPEC dosages (from 0.3 to 1.0% on pulp) were added on a recycled unbleached softwood kraft pulp containing 3% of LCMNF. For a PEC dosage of 0.75% on pulp, an optimum balances between negatively and positively charged materials [near to zero value of the logarithm of the colloidal titration ratio (logCTR)] was found. Britt Dynamic Drainage Jar test showed a high retention of fines and LCMNF for all PEC dosages. A maximum in retention value was obtained for the addition of 0.75% of PECs on pulp, dosage that was suggested as optimum by the logCTR. In addition, the best drainability value (18°SR) was obtained for this PEC addition level. Papermaking properties were clearly improved for all dosage of PECs. Particularly for a dosage of 0.75% of PECs on pulp, tensile strength was noticeably increased (+48%) and both compressive resistance Concora Medium Test (CMT) and Short-span Compressive Test (SCT) were markedly increased (+64% and +39%, respectively). These results suggest that PECs are a possible alternative to assist the application of LCMNF in papermaking.

Deacetylation consequences in pulping processes@@@Konsequenzen der Deacetylierung in Zellstoffprozessen

When wood undergoes an acidic or alkaline chemical action or a moderate thermal action, acetyl groups are easily removed. As deacetylation favourably increases the accessibility of the cell wall and the fibre swelling, mechanical properties of wood and responses of wood to pulping are modified. In this paper, the importance of the deacetylation effects in alkaline pulping is highlighted. It is shown that it is very useful to analyse acetyl content profiles in eucalyptus wood for determining the level of alkali impregnation. Global deacetylation can be a parameter that can be practical for determination of the effectiveness of alkaline impregnation of chips. In alkaline chemi-mechanical pulping of poplar, the deacetylation level that takes place during pre-treatment can establish the bonding capacity of the pulp developed afterwards in the refiner. Acetyls can be very reactive under conditions of peroxide bleaching of chemi-mechanical pulps and, as a consequence of this reaction, alkali concentration in the process and final pulp properties can be notably affected.ZusammenfassungWenn Holz einer sauren oder alkalischen chemischen Behandlung oder einer gemäßigten thermischen Behandlung unterworfen wird, werden Acetylgruppen leicht abgespalten. Da eine Deacetylierung vorteilhaft die Zugänglichkeit der Zellwand und die Faserquellung erhöht, werden die mechanischen Eigenschaften des Holzes und das Verhaltung des Holzes beim Aufschluss verändert. In dieser Arbeit wird die Bedeutung der Deacetylierung beim alkalischen Zellstoffaufschluss hervorgehoben. Es wird gezeigt, dass es sehr nützlich ist, Profile des Gehalts an Acetylgruppen in Eukalyptusholz zum Bestimmen des Ausmaßes der Imprägnierung mit Alkali zu analysieren. Die Gesamt-Deacetylierung kann ein Parameter sein, der nützlich ist, die Wirksamkeit der alkalischen Imprägnierung der Späne festzulegen. Im alkalischen chemo-mechanischem Aufschluss von Pappelholz kann das Deacetylierungsniveau während der Vorbehandlung die spätere Bindungskapazität des Zellstoffs im Refiner bestimmen. Acetylgruppen können sehr reaktiv sein unter den Bedingungen der Peroxydbleiche des chemo-mechanischen Zellstoffs, und als Folge dieser Reaktion können die Alkalikonzentration im Prozess sowie die Eigenschaften des resultierenden Zellstoffs beeinflusst werden.

Deacetylation consequences in pulping processesKonsequenzen der Deacetylierung in Zellstoffprozessen

When wood undergoes an acidic or alkaline chemical action or a moderate thermal action, acetyl groups are easily removed. As deacetylation favourably increases the accessibility of the cell wall and the fibre swelling, mechanical properties of wood and responses of wood to pulping are modified. In this paper, the importance of the deacetylation effects in alkaline pulping is highlighted. It is shown that it is very useful to analyse acetyl content profiles in eucalyptus wood for determining the level of alkali impregnation. Global deacetylation can be a parameter that can be practical for determination of the effectiveness of alkaline impregnation of chips. In alkaline chemi-mechanical pulping of poplar, the deacetylation level that takes place during pre-treatment can establish the bonding capacity of the pulp developed afterwards in the refiner. Acetyls can be very reactive under conditions of peroxide bleaching of chemi-mechanical pulps and, as a consequence of this reaction, alkali concentration in the process and final pulp properties can be notably affected.ZusammenfassungWenn Holz einer sauren oder alkalischen chemischen Behandlung oder einer gemäßigten thermischen Behandlung unterworfen wird, werden Acetylgruppen leicht abgespalten. Da eine Deacetylierung vorteilhaft die Zugänglichkeit der Zellwand und die Faserquellung erhöht, werden die mechanischen Eigenschaften des Holzes und das Verhaltung des Holzes beim Aufschluss verändert. In dieser Arbeit wird die Bedeutung der Deacetylierung beim alkalischen Zellstoffaufschluss hervorgehoben. Es wird gezeigt, dass es sehr nützlich ist, Profile des Gehalts an Acetylgruppen in Eukalyptusholz zum Bestimmen des Ausmaßes der Imprägnierung mit Alkali zu analysieren. Die Gesamt-Deacetylierung kann ein Parameter sein, der nützlich ist, die Wirksamkeit der alkalischen Imprägnierung der Späne festzulegen. Im alkalischen chemo-mechanischem Aufschluss von Pappelholz kann das Deacetylierungsniveau während der Vorbehandlung die spätere Bindungskapazität des Zellstoffs im Refiner bestimmen. Acetylgruppen können sehr reaktiv sein unter den Bedingungen der Peroxydbleiche des chemo-mechanischen Zellstoffs, und als Folge dieser Reaktion können die Alkalikonzentration im Prozess sowie die Eigenschaften des resultierenden Zellstoffs beeinflusst werden.