Abstract:

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 (0.01 N and 0.1 N 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.

Author affiliation: Mocchiutti, Paulina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Instituto de Tecnología Celulósica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina

Author affiliation: Schnell, Carla Natali. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Instituto de Tecnología Celulósica; Argentina

Author affiliation: Rossi, Gerardo Daniel. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Instituto de Tecnología Celulósica; Argentina

Author affiliation: Peresin, María Soledad. VTT Technical Research Centre of Finland; Finlandia

Author affiliation: Zanuttini, Miguel Angel Mario. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Instituto de Tecnología Celulósica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina

Author affiliation: Galván, María Verónica. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Instituto de Tecnología Celulósica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina

Abstract:

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.

Author affiliation: Mocchiutti, Paulina. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Instituto de Tecnología Celulosica; Argentina

Author affiliation: Galván, María Verónica. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Instituto de Tecnología Celulosica; Argentina

Author affiliation: Peresin, María S.. Technical Research Center Of Finland; Finlandia

Author affiliation: Schnell, Carla Natali. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Instituto de Tecnología Celulosica; Argentina

Author affiliation: Zanuttini, Miguel Angel Mario. Universidad Nacional del Litoral. Facultad de Ingeniería Química. Instituto de Tecnología Celulosica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentina

Abstract:

Se estudia la aplicación de tratamientos oxidativos enzimáticos y químicos sobre pulpas kraft no blanqueadas recicladas de coníferas con el objetivo de mejorar sus propiedades papeleras y ampliar sus posibilidades de aplicación. Para el tratamiento enzimático se utilizó el sistema lacasa-mediador (SLM). Las lacasas fueron aisladas del hongo Trametes hirsuta y el mediador usado fue 1-hidroxibenzotriazol. Se encontró que sobre la pulpa completa y sobre la fracción fibrosa produjo una leve reducción del número kappa en paralelo a un aumento en el coeficiente de absorción de luz que refleja el efecto oxidativo de las enzimas sobre este tipo de pulpas. Sobre la pulpa completa la drenabilidad aumentó, pero las propiedades de resistencia del papel no se modificaron o disminuyeron. Sobre la fracción fibrosa se encontró un aumento en el contenido de grupos carbonilos y ácidos carboxílicos en la lignina oxidada que quedó retenida en las fibras celulósicas y consecuentemente aumentó la resistencia a la tracción. Para el tratamiento oxidativo químico se utilizó ozono, el cual aumentó la resistencia a la tracción de la pulpa completa y la fracción fibrosa. Sin embargo, la drenabilidad disminuyó. El ozono redujo el número kappa y el contenido de lignina insoluble en medio ácido, indicando que la lignina oxidada es solubilizada. En esta Tesis también se optimizó el método de adsorción de polielectrolitos necesario para determinar el contenido de grupos ácidos superficiales de las fibras celulósicas. Se propuso una ecuación que ajusta las isotermas experimentales y que permitió obtener resultados más precisos.

The effects of the application of enzymatic and chemical oxidative treatments on unbleached recycled softwood kraft pulps were studied with the aim of improving their papermaking properties and extending their possibilities of application. For the enzymatic treatments, the laccase-mediator system (LMS) was used. The laccases were isolated from the Trametes hirsuta fungus and the mediator used was 1-hydroxybenzotriazole. It was found that the treatments produced a slight reduction in the kappa number in parallel to an increase in the light absorption coefficient showing the oxidative effect of the enzymes on this kind of pulps. The freeness of the whole pulp increased, but the papermaking properties were not modified or decreased. The amount of carbonyl and carboxylic acid groups in the oxidized lignin of the fibrous fraction increased and consequently the tensile strength also increased. Ozone was used for the oxidative chemical treatments, which increased the tensile strength of the whole pulp and the fibrous fraction. Nevertheless, the freeness decreased. Ozone reduced the kappa number and the amount of insoluble lignin in acid medium, indicating that the oxidized lignin was solubilized. In this work, the polyelectrolyte adsorption method, necessary to determine the content of the superficial acid groups of the cellulose fibers, was optimized. An equation was proposed that fits the experimental isotherms and allows obtaining more precise results.

Agencia Nacional de Promoción Científica y Tecnológica

Consejo Nacional de Investigaciones Científicas y Técnicas

Fundación Antorchas

Universidad Nacional del Litoral