Nanotechnology applied to cellulosic fibers has quickly become an interdisciplinary field with great interest in the application as reinforcement in polymer composites, mainly due to the abundance of these raw materials, and to their mechanical properties and multifunctionality. However, one of the critical points to obtain individualized cellulose nanofibers is the drying technique (dehydration), since most of the nanofiber processes are performed in the liquid phase. According to the methodology applied to the cellulose water dehydration process, various morphologies and properties can be obtained in the cellulose fibers. This review study aims to discuss the main processes used to obtain nanocellulose (chemical and mechanical) and the drying techniques applied to nanocellulose structures, such as conventional oven drying, freeze drying (lyophilization), supercritical extraction, and spray drying.
The use of natural fibers from renewable and biodegradable sources in oleophilic sorbents, such as cellulose, has become an interesting alternative due to their excellent properties and sustainability. In addition to that, the low density of the aerogels obtained from cellulose is favorable for their use as sorbents. In this context, the objective of this study is to develop hydrophobic aerogels of unbleached cellulose nanofibers of the Eucalyptus sp. and Pinus elliottii. Cellulose samples were submitted to mechanical fibrillation to obtain cellulose nanofiber suspensions, followed by a chemical treatment with methyltrimethoxysilane and dried by freeze-drying to prepare the aerogels. The aerogels presented hydrophobic and oleophilic characteristics, including a water contact angle of 134°, sorption capacities in a heterogeneous medium of above 21.0 g·g−1, and oil removal efficiency greater than 88.5%. The Pinus elliottii nanofiber aerogels showed higher compressive strength when compared to the nanofiber aerogels of Eucalyptus sp.
Wood is the main industrial source for obtaining cellulose. It is a natural composite, constituted by cellulose, polyoses, lignin, small amounts of extracts and mineral salts, wherein cellulose is the most abundant component. Many studies are being developed for obtaining materials based on natural fibers, which combine interesting properties such as renewability, biodegradability, low density and low cost. Aerogels are solid, lightweight materials with high porosity and high internal surface area. These features combined in one single material make the aerogels a differentiated product with potential for use as an adsorbent. In this context, aerogels made of cellulose nanofibers obtained from short-fiber cellulose of Eucalyptus sp. were made. The cellulose suspension was first disintegrated by a mechanical grinder, and the aerogels were undergone to freeze-drying. The characterization of the samples was performed by apparent density, porosity, scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analyses. According to the micrographs obtained by scanning electron microscopy and field emission gun scanning electron microscopy, it was observed the formation of pores formed by the interconnection of cellulose fibers. The apparent density of the starting cellulose fibers (pressed plates) was 0.6998 g.cm−3 and the aerogel density decreased to 0.0240 g.cm−3. The values for aerogel porosity were about 97%, which benefits the passage of liquids and gases from the external environment to the internal structure of the material. Fourier transform infrared spectroscopy and thermogravimetric analyses showed no change in the chemical composition or in the thermal stability of the obtained aerogels in comparison to their starting materials.
The membrane separation capacity allows the retention of the remaining organic matter that could not be removed by the biological process, increasing the treatment efficiency. The aim of this study was to evaluate the microfiltration (MF) process in a tertiary treatment system for landfill leachate from the Rincão das Flores, Caxias do Sul/RS/Brazil. The microfiltration system of commercial hollow fiber membrane poly(etherimide) was tested in oder to promote leachate treatment. The tests carried out were leachate permeation, concentration factor, determination of fouling and obtention of the values of the resitance to the flux. The resistance due to fouling and flux decline were evaluated to determine the best operating conditions. The potential for fouling was 53% and was evaluated by comparing the pure water permeability before and after the leachate filtration. It was observed that the resistance due to fouling express 32% of the total resistance. The results showed that the MF process allows the elimination of up to 43% of the organic matter measured as chemical oxygen demand (COD) and 63% of that measured as biological oxygen demand (BOD 5 ).
A utilização de adsorventes é uma maneira eficaz para a remoção do óleo em terra ou água. Os aerogéis são uma classe de adsorventes, que são caracterizados pela sua estrutura altamente porosa e o seu baixo teor de sólidos, o que confere ao material uma elevada capacidade de adsorção de petróleo. No presente trabalho, foi avaliada a influência da concentração de celulose e metiltrimetoxissilano (MTMS) na capacidade de adsorção de petróleo do aerogel. Os aerogéis produzidos apresentaram baixa massa específica (menor que 0,025 g cm-3) e elevada porosidade (maior que 95%). Pelas micrografias é possível visualizar alterações na superfície da fibras, com a formação de um filme, enquanto que na análise dos espectros obtidos, bandas características do silano foram identificadas nas amostras com tratamento químico. A hidrofobicidade dos aerogéis foram evidenciadas pelas medidas do ângulo de contato da superfície dos mesmos com a água, sendo obtidos valores superiores a 120°. A capacidade de adsorção dos aerogéis atingiu 78 g g-1 para o meio homogêneo e 53 g g-1 para o meio heterogêneo. Palavras-chave Aerogéis, celulose, adsorção, petróleo.
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