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.

Cellulose nanofibers are promising materials in the development of polymeric foams, because they act as heterogeneous nucleation sites for the growth of cells during foaming. In this research, we studied the incorporation of cellulose nanoparticles in poly(ethylene‐co‐vinyl acetate)‐EVA foams. The foams were produced with different fiber contents. We observed the effect of a chemical treatment by acetylation on the cellulose fibber, that is, we evaluated the use of hydrophilic and hydrophobic cellulose nanofibers in EVA foams. The main results indicate that with the addition of only 1% of cellulose nanofibers, cell density significantly reduces when compared with the pure EVA foams. On the other hand, by increasing the cellulose content, the agglomeration of nanofibers also increases, which results in heterogeneous cell sizes. The same phenomenon was observed in the foams produced with acetylated cellulose nanofibers, regardless of the fiber content used. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44760.

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Resumo: Neste trabalho foi avaliada a influência do tratamento alcalino na fibra de bananeira (FB) e seu uso como agente de reforço em compósitos expandidos de poli(etileno-co-acetato de vinila) -EVA. O processo de mistura dos compósitos ocorreu em um misturador de rolos aberto e após conformados e expandidos em uma prensa aquecida com moldes de volumes variáveis. Os compósitos foram avaliados por suas propriedades mecânicas, térmicas e morfológicas. Os resultados indicam que o tratamento alcalino promove a extração de componentes menos estáveis na FB, tais como a lignina, hemicelulose, ceras e óleos de baixo peso molecular. O uso da FB nos compósitos proporciona um decréscimo das propriedades mecânicas de resistência à tração e rasgo em relação ao EVA puro devido a moderadas propriedades de interface polímero-fibra. Nos compósitos expandidos, as propriedades mecânicas decrescem com a diminuição da densidade em função da maior presença de espaços vazios no interior dos compósitos, porém as propriedades mecânicas específicas de resistência ao rasgo apresentaram melhores resultados com 10 pcr de FB em todos os moldes utilizados. Palavras-chave: Fibra de bananeira, EVA, compósitos expandidos, tratamento químico. Influence of the Chemical Treatment of Banana Fiber on Poly(ethylene-co-vinyl acetate) Composites with and without a Blowing AgentAbstract: In this work the influence of alkaline treatment on banana fiber (BF) and its use as reinforcement agent in expanded composites of poly(ethylene-co-vinyl acetate) -EVA were assessed. The mixing process for the composite was performed in an open roll mill, with composites being then shaped and expanded in a thermal press using variable volume molds. The composites were evaluated as for their mechanical, thermal and morphological properties. The results indicate that the alkali treatment promotes the extraction of less stable BF components such as lignin, hemicellulose, waxes and low molecular weight oils. The use of BF in the composites imparts reduction in mechanical properties of tensile and tear strength compared to neat EVA, owing to the moderate properties of the polymer-fiber interface. In expanded composites, the mechanical properties decreased with the reduction in density due to a higher amount of void spaces within the composites. However, the specific mechanical properties of tear strength showed improved results with 10 phr BF in all molds.