Hydrogel-Based Flexible Energy Storage Using Electrodes Based on Polypyrrole and Carbon Threads

Developing new flexible and electroactive materials is a significant challenge to producing safe, reliable, and environmentally friendly energy storage devices. This study introduces a promising electrolyte system that fulfills these requirements. First, polypyrrole (PPy) nanotubes are electropolymerized in graphite-thread electrodes using methyl orange (MO) templates in an acidic medium. The modification increases the conductivity and does not compromise the flexibility of the electrodes. Next, flexible supercapacitors are built using hydrogel prepared from poly(vinyl alcohol) (PVA)/sodium alginate (SA) obtained by freeze–thawing and swollen with ionic solutions as an electrolyte. The material exhibits a homogenous and porous hydrogel matrix allowing a high conductivity of 3.6 mS cm−1 as-prepared while displaying great versatility, changing its electrochemical and mechanical properties depending on the swollen electrolyte. Therefore, it allows its combination with modified graphite-thread electrodes into a quasi-solid electrochemical energy storage device, achieving a specific capacitance (Cs) value of 66 F g−1 at 0.5 A g−1. Finally, the flexible device exhibits specific energy and power values of 19.9 W kg−1 and 3.0 Wh kg−1, relying on the liquid phase in the hydrogel matrix produced from biodegradable polymers. This study shows an environment friendly, flexible, and tunable quasi-solid electrolyte, depending on a simple swell experiment to shape its properties according to its application

Envelhecimento físico de sistemas DGEBA/DDM investigado por análise térmica (DSC/DMA)

Neste trabalho, estudou-se o efeito do envelhecimento físico nas propriedades térmicas e mecânicas em sistemas diglicidil éter do bisfenol-A (DGEBA)/diaminodifenilmetano (DDM), em função do grau de conversão, induzido pela cura e do tempo de envelhecimento. A cura isotérmica foi realizada em uma etapa a 115°C por diversos tempos e o envelhecimento foi conduzido a 100°C por períodos de 240 a 4320 min. Considerando que o envelhecimento físico acarreta variações estruturais as quais afetam tanto o desempenho mecânico quanto as propriedades termodinâmicas do material, as técnicas de DSC e DMA são complementares. Através de Calorimetria Exploratória Diferencial (DSC), observou-se que o envelhecimento físico está associado ao pico endotérmico que ocorre na região da transição vítrea e que a entalpia de relaxação, calculada a partir da área deste pico, aumenta gradualmente com o tempo de envelhecimento. Os resultados obtidos por Análise Dinâmico-Mecânica (DMA) mostraram um aumento do módulo elástico E' com o tempo de envelhecimento. As velocidades de envelhecimento foram obtidas a partir da temperatura do pico endotérmico, a partir do módulo elástico E' e a partir da temperatura de transição vítrea e resultaram tanto menores quanto maior o grau de conversão da matriz. Os resultados salientam a importância da seleção adequada das condições de cura para que se possam obter as melhores propriedades destes materiais. A importância dos fenômenos observados é considerada, tendo-se em vista a grande utilização e aplicabilidade das resinas epóxi

Estudo da recuperação das propriedades de poliestireno de alto impacto (HIPS) através da incorporação de borracha termoplástica tipo estireno-butadieno-estireno (SBS) Recovering properties of recycled HIPS through incorporation of SBS triblock copolymer

A tenacificação de termoplásticos vítreos através da adição de partículas de borracha na matriz polimérica é um processo amplamente estudado. Neste trabalho foi avaliada a recuperação das propriedades de poliestireno de alto impacto (HIPS) reciclado através da incorporação de copolímeros estireno-butadieno-estireno (SBS) de estrutura linear e radial. As blendas foram processadas em uma extrusora dupla rosca. Os copolímeros foram adicionados em teores de 5, 10 e 15% em massa. As propriedades avaliadas foram o índice de fluidez, a morfologia e o comportamento frente a ensaios de tração, flexão e resistência ao impacto das blendas formuladas. Em todos os casos, o SBS radial foi mais eficiente na recuperação das propriedades do poliestireno de alto impacto que o SBS linear quando comparadas às propriedades do HIPS reciclado.Toughening glassy thermoplastics by blending a rubbery material to the polymeric matrix has been extensively studied. In this work, we evaluated the resulting properties of recycled high impact polystyrene (HIPS), after the incorporation of either radial or linear SBS triblock copolymers. The blends were melt mixed using a twin-screw extruder. The copolymers were added at 5, 10 and 15% weight percent. The investigated properties included the determination of the melt flow index, the morphology and the mechanical behavior according to standard tension, flexion and impact methods of all formulated blends. In all cases, the radial SBS was more efficient in recovering the HIPS properties than the linear SBS, when comparing the properties of the blends with the properties of recycled HIPS

Evaluation of Polyvinyl Alcohol/Pectin-Based Hydrogel Disks as Extraction Phase for Determination of Steroidal Hormones in Aqueous Samples by GC-MS/MS

A new extraction phase based on hydrogel disks of polyvinyl alcohol (PVOH) and pectin was proposed, characterized and evaluated for the extraction of six steroidal hormones (estriol, estrone, 17β-estradiol, 17α-ethinylestradiol, progesterone, and testosterone) in aqueous samples with subsequent determination by gas chromatography-tandem mass spectrometry (GC-MS/MS) after the derivatization procedure. The developed extraction procedure was based on the solid phase extraction (SPE) technique, but employed hydrogel as the sorbent phase. The effects of several parameters, including the amount and composition of the sorbent phase, pH, sample volume, flow rate, and gel swelling over the extraction efficiency, were evaluated. Gels with lower swelling indexes and larger amounts of sorbent ensured higher extraction yields of analytes. The main benefits of using the PVOH/pectin-based hydrogel as the extraction phase are the ease of synthesis, low-cost preparation, and the possibility of reusing the extraction disks. Limits of quantification of 0.5 μg L−1 for estrone and 17β-estradiol, and 1 μg L−1 for testosterone, 17α-ethinylestradiol, progesterone, and estriol were obtained. Accuracy values ranged from 80% to 110%, while the inter-assay precision ranged from 0.23% to 22.2% and the intra-assay from 0.55% to 12.3%. Since the sorbent phase has an amphiphilic character, the use of hydrogels is promising for the extraction of medium-to-high polarity compounds

Kinetic Approach to Elucidate Size Controllable Features in Nanocomposites of Gold Nanoparticles and Poly(3,4-ethylenedioxythiophene) in Aqueous Dispersion Stabilized by Gum Acacia

Research and development of conductive nanomaterials based on biocompatible matrices has been greatly rising in the past decade since synergistic properties can be achieved by combining metallic nanoparticles and natural/conductive polymers. Poly­(3,4-ethylenedioxythiophene) (PEDOT) is known to be an intrinsically conductive polymer, difficult to handle in aqueous medium. Therefore, in this work, we present a physical-chemical perspective in the development of novel aqueous dispersible nanocomposites of gold nanoparticles (AuNPs) and PEDOT, obtained through a one-pot synthesis, using the biopolymer gum acacia (GA) as stabilizer. A thorough kinetic study was carried out and correlated with microscopy analyses, evidencing that the concentration of GA influences the AuNP size by affecting their nucleation and growth stages. A quantitative detailing using kinetic models is shown, which to the best of our knowledge is the first report relating mechanism and rate constants with size controllable features of the stabilizer. Two distinct kinetic profiles were obtained and related to a critical concentration of GA (1%_w/v): (i) above, a characteristic nucleation–growth sigmoidal profile and (ii) below, an unexpected bilogistic profile, accounted to a two-step growth process. Indeed, the bilogistic kinetic model, usual in population growth studies, is presented herein for the first time regarding NP formation. These results incite the targeted design of novel nanomaterials, using kinetic studies as a promising tool to understand the mechanism of the size-controllable features of GA. Overall, we evidence that the nanocomposite characteristics can be optimized rationally. Also, considering the natural occurrence of GA, we contribute to the sustainable development of highly water-dispersible PEDOT-derived nanocomposites

Alginate/Polypyrrole Hydrogels as Potential Extraction Phase for Determination of Atrazine, Caffeine, and Progesterone in Aqueous Samples

Hydrogels are smart-swelling 3D structures capable of incorporating/expelling water while maintaining their structures. When combined with electroactive materials, such as conducting polymers, the resulting composite may present tunable properties. Herein, the preparation and characterization of alginate-polypyrrole composite hydrogels is described using chemical polymerization to form polypyrrole inside and around alginate beads, employing two simple protocols. These materials were qualitatively tested as extraction phases, using the solid-phase extraction technique, for the pre-concentration of contaminants of emerging concern (atrazine, caffeine, and progesterone). Compared to alginate alone, the composite materials showed a modified extraction capacity, especially for the extraction of progesterone. It was shown that the alginate matrix also contributes to the extraction, not only acting as a support but also as an active extraction media, evidencing a good combination of materials

Structure of Micelles Formed by Highly Asymmetric Polystyrene-b-Polydimethylsiloxane and Polystyrene-b-poly[5-(N,N-diethylamino)isoprene] Diblock Copolymers

The internal structure of polystyrene(PS)-shell micelles having core-forming blocks consisting of polydimethylsiloxane (PDMS) or poly[5-(N,N-diethylamino)isoprene] (PAI) was determined in detail by accessing the multilevel structural organization using static and dynamic light scattering and small-angle X-ray scattering techniques. Well-defined PS-b-PDMS and PS-b-PAI diblock copolymers with molar masses in the range of 12.0k-18.2k g/mol were dispersed in cyclohexane, dimethylacetamide, or dimethylformamide. Colloidal nanoparticles exhibiting either swollen core with a large surface area per corona chain that enables the PS chains to assume a random coil conformation with Gaussian statistics, or compact core and slightly stretched PS chains in the corona were obtained. Therefore, the results of this study provide an interesting alternative allowing for precise control of the core and corona properties of PS-b-PDMS and PS-b-PAI micelles in selective solvents. Admittedly, such differences in terms of micellar properties can dictate the potential of block copolymer micelles for generating thin films from preformed nano-objects, as well as the capability to function as nanoreactors in organic medium.Fil: Giacomelli, Fernando C.. Universidade Federal do ABC; BrasilFil: Riegel, Izabel C.. Universidade Federal do Paraná; BrasilFil: Stepanek, Petr. Institute of Macromolecular Chemistry; República ChecaFil: Petzhold, Cesar L.. Universidade Federal do Rio Grande do Sul; BrasilFil: Ninago, Mario Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentina. Universidade Federal do Rio Grande do Sul; BrasilFil: Satti, Angel Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentina. Universidade Federal do Rio Grande do Sul; BrasilFil: Ciolino, Andrés Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentina. Universidade Federal do Rio Grande do Sul; BrasilFil: Villar, Marcelo Armando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentina. Universidade Federal do Rio Grande do Sul; BrasilFil: Schmidt, Vanessa. Universidade Federal de Santa Maria; BrasilFil: Giacomelli, Cristiano. Universidade Federal de Santa Maria; Brasi

Alginate/Polypyrrole Hydrogels as Potential Extraction Phase for Determination of Atrazine, Caffeine, and Progesterone in Aqueous Samples

Hydrogels are smart-swelling 3D structures capable of incorporating/expelling water while maintaining their structures. When combined with electroactive materials, such as conducting polymers, the resulting composite may present tunable properties. Herein, the preparation and characterization of alginate-polypyrrole composite hydrogels is described using chemical polymerization to form polypyrrole inside and around alginate beads, employing two simple protocols. These materials were qualitatively tested as extraction phases, using the solid-phase extraction technique, for the pre-concentration of contaminants of emerging concern (atrazine, caffeine, and progesterone). Compared to alginate alone, the composite materials showed a modified extraction capacity, especially for the extraction of progesterone. It was shown that the alginate matrix also contributes to the extraction, not only acting as a support but also as an active extraction media, evidencing a good combination of materials

PYROLIGNEOUS LIQUOR PRODUCED FROM Acacia mearnsii DE WILD WOOD UNDER CONTROLLED CONDITIONS AS A RENEWABLE SOURCE OF CHEMICALS

Recebido em 07/04/2015; aceito em 02/06/2015; publicado na web em 13/07/2015 Acacia mearnsii de Wild (black wattle) is one of the most important trees planted in Southern Brazil for tannin extraction and charcoal production. The pyrolysis of the black wattle wood used for obtaining charcoal is performed in brick ovens, with the gas fraction being sent directly into the environment. The present study examines the condensable compounds present in the liquor produced from black wattle wood at different thermal degradation conditions, using gas chromatography coupled with mass spectrometry (GC/ MS). Branches of black wattle were thermally degraded at controlled ambient and temperature conditions. Overall, a higher variety of compounds were obtained under atmospheric air pressure than under synthetic air pressure. Most of the tentatively identified compounds, such as carboxylic acids, phenols, aldehydes, and low molecular mass lignin fragments, such as guayacol, syringol, and eugenol, were products of lignin thermoconversion. Substituted aromatic compounds, such as vanillin, ethyl vanillin, and 2-methoxy-4-propeny-phenol, were also identified. At temperatures above 200 °C, furan, 2-acetylfuran, methyl-2-furoate, and furfural, amongst others, were identified as polysaccharide derivatives from cellulose and hemicellulose depolymerization. This study evidences the need for adequate management of the condensable by-products of charcoal production, both for economic reasons and for controlling their potential environmental impact