Preparación y caracterización de micropartículas de almidón de papa con acrilamida por irradiación de microondas

1 recurso en línea (páginas 149-159).In this study on decreasing the particle size of the potato starch, ultrasound and acid hydrolysis methods were carried out at the same time. The starch microparticles (SMP) obtained were modified with acrylamide(AM) monomer by microwave irradiation, employing a small concentration of chemical initiator. It was found that, with a low concentration of potassium persulfate (PPS) in aqueous medium and microwave assistance, starch microparticles grafted with acrylamide could be prepared quickly. Native starch, starch microparticles and grafted copolymers were characterized by various analytical techniques. The Fourier transform infrared spectroscopy (FT-IR) analysis demonstrates group acrylamide attachment to starch microparticles chains. X-ray diffraction (XRD) and scanning electron microscopy (SEM) demonstrate an increased amorphous region of starch microparticles and grafted copolymers, while the thermogravimetric analysis (TGA) highlighted the increase in thermal stability of the copolymers in comparison to potato starch microparticles.En este estudio para la disminución del tamaño de partícula del almidón de papa, se llevaron a cabo métodos de hidrólisis ácida y ultrasonidos al mismo tiempo. Las micropartículas de almidón (SMP) obtenidas se modificaron con monómero de acrilamida (AM) mediante irradiación de microondas, empleando una pequeña concentración de iniciador químico. Se encontró que, con una baja concentración de persulfato de potasio (PPS) en medio acuoso y asistencia de microondas, las micropartículas de almidón injertadas con acrilamida podrían prepararse rápidamente. El almidón nativo, las micropartículas de almidón y los copolímeros injertados se caracterizaron por diversas técnicas analíticas. El análisis por espectroscopía infrarroja de transformada de Fourier (FT-IR) demuestra la unión del grupo acrilamida a las cadenas de micropartículas de almidón. La difracción de rayos X (XRD) y la microscopía electrónica de barrido (SEM) demuestran un incremento en la región amorfa de las micropartículas de almidón y copolímeros injertados, mientras que el análisis termogravimétrico (TGA) destacó el aumento de la estabilidad térmica de los copolímeros en comparación con las micropartículas de almidón de papa.Bibliografía: páginas 157-159

Comparative Kinetic Study and Microwaves Non-Thermal Effects on the Formation of Poly(amic acid) 4,4′-(Hexafluoroisopropylidene)diphthalic Anhydride (6FDA) and 4,4′-(Hexafluoroisopropylidene)bis(p-phenyleneoxy)dianiline (BAPHF). Reaction Activated by Microwave, Ultrasound and Conventional Heating

Green chemistry is the design of chemical processes that reduce or eliminate negative environmental impacts. The use and production of chemicals involve the reduction of waste products, non-toxic components, and improved efficiency. Green chemistry applies innovative scientific solutions in the use of new reagents, catalysts and non-classical modes of activation such as ultrasounds or microwaves. Kinetic behavior and non-thermal effect of poly(amic acid) synthesized from (6FDA) dianhydride and (BAPHF) diamine in a low microwave absorbing p-dioxane solvent at low temperature of 30, 50, 70 °C were studied, under conventional heating (CH), microwave (MW) and ultrasound irradiation (US). Results show that the polycondensation rate decreases (MW > US > CH) and that the increased rates observed with US and MW are due to decreased activation energies of the Arrhenius equation. Rate constant for a chemical process activated by conventional heating declines proportionally as the induction time increases, however, this behavior is not observed under microwave and ultrasound activation. We can say that in addition to the thermal microwave effect, a non-thermal microwave effect is present in the system

Una experiencia con la estrategia de grupos cooperativos en la enseñanza de la Ingeniería Química

Desde 1995 la Universidad Nacional Autónoma de México ha venido desarrollando el Programa de Apoyo a Proyectos Institucionales de Mejoramiento de la Enseñanza (PAPIME), para financiar proyectos de docencia en todas las áreas buscando, al incentivar la investigación en esta temática, lograr una mejora sustancial en la formación impartida, El presente trabajo revisa antecedentes, estudia y analiza la estrategia de pequeños grupos cooperativos en cursos técnicos, la utiliza en la asignatura nuclear de Ingeniería Química, Fenómenos de Superficie, y formula conclusiones y recomendaciones

Preparation of an Adhesive in Emulsion for Maxillofacial Prosthetic

Maxillofacial prostheses is a dental medicine specialty aimed at restoring anatomical facial defects caused by cancer, trauma or congenital malformations through an artificial device, which is commonly attached to the skin with the help of an adhesive. The purpose of our research was to develop a pressure-sensitive adhesive (PSA) based on acrylic monomers, characterizing and determining its drying kinetics, that is to say the time it takes to lose 50 to 90% of its moisture. The adhesive synthesis was realized by means of emulsion polymerization; the composition of formulations was: (AA‑MMA‑EA) and (AA‑MMA‑2EHA) with different molar ratios. The formulation based on (AA‑MMA‑2EHA) with 50 w% of solids, presented good adhesive properties such as tack, bond strength, and short drying time. We propose this formulation as a PSA, because it offers an alternative for systemically compromised patients, by less irritation compared to organic solvent-based adhesives

Effect of the Acid Medium on the Synthesis of Polybenzimidazoles Using Eaton’s Reagent

The influence of trifluoromethanesulfonic (TFSA) superacid on conditions of the synthesis of polybenzimidazoles, such as OPBI and CF3PBI, was studied. It was shown that the polycondensations proceeded smoother and at lower temperatures in the presence of the TFSA in Eaton’s Reagent and that polymers of high molecular weights, and readily soluble in organic solvents, were obtained. The effect was more pronounced for CF3PBI, where the low reactivity monomer, 4,4′ (hexafluoroisoproylidene)bis (benzoic acid), was used. CF3PBI was obtained at a moderate temperature of 140 °C with no gel fraction and exhibited an inherent viscosity twice higher than the one obtained by the traditional method. In fact, the addition of TFSA allows the obtention of soluble N-phenyl substituted CF3PBI by direct synthesis, which had not been obtained otherwise. Thus, the use of TFSA is a good media for the synthesis of N-substituted PBIs under relatively mild conditions