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.

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The thermal degradation behavior of different types of cellulose before and after mechanical defibrillation and lyophilization was studied using isothermal and nonisothermal thermogravimetric analyses, followed by other characterization techniques, such as X-ray diffraction, Fourier transform infrared spectroscopy, degree of polymerization and scanning electron microscopy with field emission analysis. The thermogravimetric experiments were carried out in a nitrogen atmosphere at four different heating rates (5, 10, 20 and 40°C min -1 ) in a nonisothermal condition. Distinct thermal degradation behaviors were observed when the two types of cellulose were compared after defibrillation: (1) cellulose nanofibers tend to lose thermal stability and (2) cellulose nanowhiskers tend to gain thermal stability. The Flynn-Wall-Ozawa method results indicate that the apparent activation energies calculated for the cellulose fiber sample has higher values requiring more energy for the thermal decomposition. Criado curves indicated a degradation mechanism for the cellulose: one-dimensional diffusion.

Recycled polypropylene was reinforced with wood fibers that were non‐treated and treated with different natural oils (hexanoic, octanoic, decanoic and dodecanoic acids). The thermal properties, morphology, kinetics and thermodynamic parameters were investigated. The use of natural oils as coupling agents clearly improved the interfacial adhesion with the matrix and increased the thermal stability of the composites. Octanoic acid improved the thermal stability of the composite the most compared with the other evaluated natural oils. The improvement caused by this natural oil is similar to that promoted by the addition of PPgMA. The thermal stability of the composite was affected by the boiling temperature and the chain length of the acid used. POLYM. COMPOS., 35:1935–1942, 2014. © 2014 Society of Plastics Engineers

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.

Biodegradable polymeric foams have gained increasing attention as an alternative to conventional polymeric foams, whose recycling is economically unviable due to its low density. Based on this, this article discusses the development of poly(lactic acid) foams produced with the insertion of four and eight parts hundred resin (phr) of long and short cellulose fibers and nanofibers. Short fibers of nanocellulose were obtained by mechanical defibrillation and dried by lyophilization, and long fibers by CO 2 supercritical fluid extraction. The poly(lactic acid) foams were produced by adding a chemical blowing agent with a pressure-free expansion method. In general, short fibers of cellulose act as nucleating agents during the expansion of the foam, which is observed by its greater number of smaller-size cells than the non-reinforced poly(lactic acid) foams. The insertion of long fibers of cellulose restricts the mobility of the polymer matrix during the expansion, thus hindering the foam its growth and formation of bubbles.

The high PET consume, mainly as bottles, associated with rapid disposal and high resistance to ambient conditions and biological degradation lead to accumulation in the enviromental, constituting a worrying scenario in world level. Chemical recycle PET by glycolysis is an important alternative, once bis(hydroxiethyl)terephthalate (BHET), high added value monomer, can be obtained. In this context, this study approaches the use of titanate nanotubes (i.e. sodium/protonated titanate nanotubes) as catalyst for PET glycolysis. Reactional conditions, the origin and granulometry of PET flakes were evaluated (at 196 °C). Best results (BHET yield > 80%) were obtained for both catalyst in 3 h of reaction. The protonated titanate nanotubes catalyst were more efficient than sodium titanate nanotubes due to greater concentration of Brönsted and Lewis acid sites, indicated by TPD analyzes.