Flexible electronics can be developed with a low-cost and simple fabrication process while being environmentally friendly. Conductive silver inks have been the most applied material in flexible substrates. This study evaluated the performance of different conductive ink formulations using silver nanoparticles by studying the material properties, the inkjet printing process, and application based on electrical impedance spectroscopy using a buffer solution. Silver nanoparticles synthesis was carried out through chemical reduction of silver nitrate; then, seven conductive ink formulations were produced. Properties such as resistivity, viscosity, surface tension, adhesion, inkjet printability of the inks, and electrical impedance of the printed electrodes were investigated. Curing temperature directly influenced the electrical properties of the inks. The resistivity obtained varied from 3.3 × 10 0 to 5.6 × 10 −06 Ω.cm. Viscosity ranged from 3.7 to 7.4 mPa.s, which is suitable for inkjet printing fabrication. By using a buffer solution as an analyte, the printed electrode pairs presented electrical impedance lower than 200 Ω for all the proposed designs, demonstrating the potential of the formulated inks for utilization in flexible electronic devices for biological sensing applications. Inkjet printing has been investigated as an alternative production tool for the fabrication of conductive elements and devices in the field of flexible electronics. This fabrication technique deposits particles of the material with desirable electrical properties onto a substrate, after which, the printed pattern is converted into conductive elements 1. There are benefits related to the inkjet printing, namely, a simple fabrication process, low cost, reduction of material waste, and excellent adequacy to several substrates 2-4. This printing process involves the storage of ink in a cartridge and the ejection of an exact amount of material through the nozzles 5. Therefore, the fabrication of flexible circuits, sensors, and other printed materials represents a great technological advancement compared with other standard methods, such as drop casting or stamping 6. Silver remains one of the best options for application as a conductive ink and adhesive, compared to other electrically conductive fillers. This is mainly due to its high electrical and thermal conductivity, chemical stability, relatively low cost (compared to gold or graphene, for example), and the ability of its oxide form to conduct electricity 2. Additionally, silver nanoparticles have a low melting point, which promotes the generation of conductive thin films in relatively low temperatures, this is vital to applications in flexible substrates, such polymers and papers 4,7,8. Different methods can be used for the synthesis and stabilization of silver nanoparticles. One of the most popular approaches is chemical reduction, using a variety of organic and inorganic reducing agents 7,9. Depending on the method used silver nanoparticles can be fabricated with different morpholo...

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As a byproduct of the combustion of rice husk to generate energy, rice husk ash (RHA) is formed by silica and carbon, apart from small amounts of other constituents. Several treatments can be used to increase the purity of the silica obtained, or even produce pure silica. The present study tested the efficiency of different techniques to obtain silica, characterizing and comparing the silicas obtained from RHA. A literature review was conducted, and then selected techniques were used to produce silica, which was characterized by XRF, XRD, particle sizing, specific weight, specific surface area, total carbon, and SEM. The literature review showed that most techniques include a pretreatment like acid or alkaline leaching followed by thermal treatment to increase the amount of silica produced by reduction of carbonaceous materials. The results showed that it is possible to produce silica from RHA using simple methods, and that these produced silica with purity above 98%. The treatments that afforded the best results were acid leaching followed by thermal treatment at 800ºC, and alkaline extraction at low temperature, with silica purity of 99.3% and 99.6%, respectively.

One of the consequences of industrial food production activities is the generation of high volumes of waste, whose disposal can be problematic, since it occupies large spaces, and when poorly managed can pose environmental and health risks for the population. The rice industry is an important activity and generates large quantities of waste. The main solid wastes generated in the rice production cycle include straw, husk, ash, bran and broken rice. As such, the aim of this article is to present a review of this cycle, the waste generated and the identification of opportunities to use them. Owing to impacts that can be minimised with the application of rice husk ash as a by-product, this work is focused on the recycling of the main wastes. In order to achieve that, we performed theoretical research about the rice production cycle and its wastes. The findings point to the existence of an environmentally suitable use for all wastes from the rice production cycle. As rice, bran and broken rice have their main use in the food industry, the other wastes are highly studied in order to find solutions instead of landfilling. Straw can be used for burning or animal feeding. The husk can be used for poultry farming, composting or burning. In the case of burning, it has been used as biomass to power reactors to generate thermal or electrical energy. This process generates rice husk ash, which shows potential to be used as a by-product in many different applications, but not yet consolidated.

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Since epoxy resins are used as composite matrix with excellent results, and silica is one of the fillers most often employed, this study compared the performance of rice husk ash (RHA) as filler in epoxy composites, in replacement for high-purity silica. Composites were molded containing 20%, 40%, and 60% (wt) silica or RHA. Viscosity analysis, infrared spectroscopy (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) as well as mechanical and water absorption tests were carried out to evaluate composites. Glass transition temperature after curing and thermal degradation temperature of all samples analyzed were approximately 140 ºC and 370 ºC, respectively. RHA and silica exhibited similar mechanical and water absorption characteristics, indicating that rice husk ash may be a suitable replacement for silica. SEM imaging showed good filler dispersion and distribution in the polymer matrix, highlighting the more effective adhesion interface between RHA particles and the matrix.

RESUMO A cinza de casca de arroz (CCA) é um resíduo proveniente da combustão da casca de arroz utilizada como biomassa na produção de energia. Esta cinza é gerada em grandes quantidades e possui baixa massa específica, o que dificulta o seu gerenciamento, pois demanda muito espaço para o devido armazenamento e descarte. A CCA possui um elevado teor de sílica em sua composição, fator este que pode torná-la um material atrativo para vários segmentos industriais. Neste contexto, este trabalho tem como objetivo avaliar a influência do beneficiamento físico da cinza de casca de arroz, por meio de processos de segregação granulométrica e moagem, com e sem o uso de aditivos, nas características deste material e na sua adequação como coproduto. A metodologia experimental utilizada para o desenvolvimento deste trabalho envolveu a segregação e moagem da CCA (com e sem aditivos de moagem), caracterização química, física e estrutural das amostras de CCA bruta, segregadas e moídas. Os resultados obtidos indicam que a segregação granulométrica se apresenta como fator determinante para a utilização da CCA como coproduto. Com relação à moagem, pode-se verificar que o diâmetro médio das partículas diminui e a massa específica das amostras aumenta, com o aumento do tempo de moagem. Entretanto, verifica-se que os aditivos usados neste trabalho, nas concentrações testadas, não influenciam significativamente na redução do diâmetro das partículas.

Resumo:Os óleos essenciais pertencem a um grupo importante de matérias-primas para diversas indústrias, no entanto, são compostos instáveis e sua aplicação pode ser limitada devido à elevada volatilidade e facilidade de oxidação. Sendo assim, a aplicação de técnicas de microencapsulamento pode contribuir para aumentar sua estabilidade. Este trabalho teve como objetivo produzir microcápsulas de alginato de sódio contendo óleo essencial de laranja e avaliar as microcápsulas obtidas. O processo de microencapsulamento foi realizado pela técnica de grãos de alginato. As microcápsulas foram avaliadas através de MEV, estabilidade térmica e determinação do teor de óleo essencial microencapsulado. Os resultados encontrados demostram que as microcápsulas foram produzidas com êxito, a técnica de microencapsulamento foi efetiva e o processo de síntese simples, verificou-se o aumento da estabilidade termo-oxidativa do óleo pelo microencapsulamento. As microcápsulas liberaram aproximadamente 88,3% do óleo essencial presente em 30 dias. Palavras-chave: óleos essenciais, microcápsulas, casca de laranja.Abstract: Essential oils belong to an important group of raw materials with several industrial applications. However, these substances are unstable, which may restrict applicability due to high volatility and high susceptibility to oxidation. Therefore, microencapsulation techniques may improve the stability of essential oils. The present study describes the production evaluates the performance of sodium alginate microcapsules containing orange peel essential oil. The production process was based on the alginate microencapsulation technology. Microcapsules were evaluated using scanning electron microscopy, thermal stability, and level of microencapsulated essential oil. The results showed that microcapsules were successfully produced, the microencapsulation technique was effective, and the synthesis process was simple. Also, it was observed that thermal and oxidative stability of essential oil