Germán Quintana

Mixture Design Approach on the Physical Properties of Lignin-Resorcinol-Formaldehyde Xerogels

Organic xerogels were functionalized by incorporating sugarcane bagasse lignin from soda pulping black liquor, not used so far in this materials, with the aim of introducing new functional groups on traditional gels that could improve its adsorptive capacity. Two mixing designs were applied to identify the reactive combinations that allow a well gel formation and to adjust models that predict physical properties. The designs study five components: resorcinol (, 0.04–0.3), lignin (, 0.004–0.14), formaldehyde (, 0.08–0.17), water (, 0.45–0.8), and NaOH (, 0.0003–0.0035). The first experimental design was an extreme vertices design and its results showed shrinkage between 4.3 and 59.7 and a bulk density from 0.54 to 1.3; a mass ratio near 1.5 was required for gel formation. In the second design a D-Optimal was used to achieve better adjusted coefficients and incorporate the largest possible amount of lignin in the gels. Bulk density varies from 0.42 to 0.9, shrinkage varies from 3.42 to 25.35, and specific surface area reaches values of 451.86 m2/g with 13% lignin and 270 m2/g with 27% lignin. High catalyst content improves lignin dissolution and increase shrinkage and bulk density of xerogels and bulk density. Lignin contributes to reducing shrinkage and specific surface area due to his compact and rigid structure.

Polyelectrolyte Complexation versus Ionotropic Gelation for Chitosan-Based Hydrogels with Carboxymethylcellulose, Carboxymethyl Starch, and Alginic Acid

The preparation of gels by charge interaction methods has been extensively studied, but it is not yet clear how these methods influence gel characteristics. The objective of this work was to study differences in morphology and surface charge of hydrogels prepared by ionotropic gelation, polyelectrolyte complexation, and a combination of both methods. Thus, the anionic charge was provided by carboxymethylcellulose (CMC), carboxymethylated starch (CMS), and alginic acid (AA); calcium chloride (CaCl2) and chitosan (CS) were used for the ionotropic gelation and polyelectrolyte complexation, respectively. Those materials are commercially available, have low toxicity, and are widely used in the area. These compounds interact through physical crosslinks, which are affected by physical changes of the medium. Our results showed that these two methods produced changes in the morphology of the hydrogels. CMC gels exhibited larger pores in the presence of CaCl2. In polyelectrolyte complexation, CMS produced an increased agglomeration of particles, while the addition of CaCl2 to AA generated dispersed particles of size in the order of millimeters. Mixing both ionotropic gelation and polyelectrolyte complexation methods yielded gels of varied charge (568 mV for CMC, 502 mV for CMS, and 1713 mV for AA). FTIR spectra of the hydrogels showed interactions between the different polymeric compounds, being the greatest changes between 1250 and 1600 cm−1, due possibly to the replacement of Na by Ca at crosslinking points. Therefore, the method of gel preparation employed had a major influence on the size and pore distribution, parameters which in turn influence encapsulation and drug delivery in these systems.

EFECTO DE LA PRESIÓN DE PRENSADO Y LA ADICIÓN DE LIGNINA KRAFT EN LA PRODUCCIÓN DE TABLEROS AGLOMERADOS AUTOENLAZADOS A PARTIR DE Gynerium sagittatum PRETRATADA CON VAPOR

El Gynerium sagittatum es una graminea que presenta gran adaptabilidad ecologica lo cual la hace una fuente lignocelulosica ideal para la fabricacion de tableros aglomerados sin aditivos sinteticos. Se evalua el efecto de la presion de prensado y de la adicion de lignina kraft purificada sobre las propiedades fisicomecanicas de tableros de fibras de Gynerium sagittatum de alta densidad. La materia prima es pretratada en un reactor de steam explosion a severidad 4,1 y la temperatura de prensado se fija en 217°C. Se varia la presion de prensado entre 2 y 15 MPa. Se determina que la presion de prensado mas apropiada para obtener tableros de buena calidad es 2 MPa obteniendo valores para el modulo de elasticidad de 6000 MPa, modulo de ruptura de 47 MPa, enlace interno de 1,50 MPa, absorcion de agua durante 24 horas de 25% e hinchamiento en espesor durante 24 horas del 15%. Partiendo de estas condiciones de operacion, se evalua la inclusion de lignina entre 0 y 30%. Se determina que el aumento de lignina no afecta significativamente el desempeno mecanico de los tableros, pero si su estabilidad dimensional, dando como resultado una absorcion de agua durante 24 horas de 19% e hinchamiento en espesor durante 24 horas del 8,5%, a un valor optimo de 20% de inclusion de lignina.