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- Composite Films of Nanofibrillated Cellulose with Sepiolite: Effect of Preparation StrategyPublication . Alves, Luis; Ramos, Ana; Rasteiro, Maria G.; Vitorino, Carla; Ferraz, Eduardo; Ferreira, Paulo J. T.; Puertas, Maria L.; Gamelas, José A. F.Cellulose nanofibrils (CNFs) are nanomaterials with promising properties to be used in food packaging and printed electronics, thus being logical substitutes to petroleum-based polymers, specifically plastics. CNFs can be combined with other materials, such as clay minerals, to form composites, which are environmentally friendly materials, with acceptable costs and without compromising the final properties of the composite material. To produce composite films, two strategies can be used: solvent casting and filtration followed by hot pressing. The first approach is the simplest way to produce films, but the obtained films may present some limitations. In the present work, CNFs produced using enzymatic or TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidation pretreatments, followed by high-pressure homogenization, or only by mechanical treatment (homogenization), were used to produce films by both the available procedures. The films obtained by filtration + hot pressing presented higher tensile strength and Young’s modulus compared with those obtained by solvent casting. In general, a decrease in the values of these mechanical properties of the films and a decrease in elongation at break, with the addition of sepiolite, were also observed. However, for the TEMPO CNF-based films, an improvement in tensile strength could be observed for 10% of the sepiolite content. Furthermore, the time necessary to produce films was largely reduced by employing the filtration procedure. Finally, the water vapour barrier properties of the films obtained by filtration are comparable to the literature values of net CNF films. Thus, this technique demonstrates to be the most suitable to produce CNF-based composite films in a fast way and with improved mechanical properties and suitable gas barrier properties.
- Design of cellulose nanofibre-based composites with high barrier propertiesPublication . Alves, Luís; Ramos, Ana; Ferraz, Eduardo; J. T. Ferreira, Paulo; G. Rasteiro, Maria; A. F. Gamelas, JoséGas barrier properties are very relevant in composite materials for applications so diverse such as food packaging, electronics, or old document restoration. In the present work, four different types of cellulose nanofibres (CNFs), two types of clay minerals used individually (sepiolite) or combined (sepiolite + kaolinite), and the influence of pH, were explored in the production of composite films. Neat CNFs, only mechanically treated or prepared by enzymatic pre-treatment, gave films with good mechanical and barrier properties, but the addition of minerals led to a dramatic loss of these properties. Contrarily, the use of thin and functionalized fibrils (TEMPO-oxidised or cationized CNFs) gave composite films with good mechanical, thermal and barrier properties. Superior oxygen barrier properties (oxygen transmission rate (OTR) < 0.4 cm3 m−2 day−1) were obtained using TEMPO-oxidised CNF and 20% sepiolite, and, in general, for all the composite films containing the TEMPO CNF (OTR ≤ 1.8 cm3 m−2 day−1). The cationic CNF-based composites also showed a very good oxygen barrier (OTR ≤ 8.2 cm3 m−2 day−1). The high oxygen barrier could be explained by the compactness of the films and better entanglement of the more fibrillated nanocelluloses with the mineral particles. A decrease in the pH of the suspensions led to a decrease in the film preparation time, without a major negative impact on the composite film’s properties.
- Effect of the dispersion state of minerals on the properties of cellulose nanofiber-based composite filmsPublication . Alves, Luís; Ramos, Ana; Ferraz, Eduardo; Sanguino, Pedro; Santaren, Julio; Rasteiro, Maria Graça; Gamelas, José AFThe dispersion state and the efficiency of the mixture of the different components in a composite film have an important impact on its mechanical and optical properties. In the present work, the impacts of different dispersion treatments on the disaggregation state of fibrous clay particles in water, and on the properties of related cellulose nanofiber (CNF)-based composite films, were evaluated. X-ray diffraction studies, performed on samples of sepiolite and palygorskite, revealed only minor changes in the diffraction pattern when the minerals were subjected to ultrasonic treatment, with or without the addition of different chemical dispersing agents. Conversely, microscopic studies revealed important differences in the dispersion state of the samples, induced by the addition of the different dispersants, showing an improvement in the disaggregation of the mineral crystals. The composite films prepared with sepiolite (and carboxymethylcellulose, as chemical dispersant) dispersed using ultrasonic treatment, and different types of CNF, showed improved optical and mechanical properties when compared with composites of the same counterparts prepared with sepiolite dispersed using a high-speed shear disperser.
- Filmes de celulose nanofibrilada com incorporação de minerais: uma nova geração de materiais para embalagens alimentares e eletrónica impressaPublication . Alves, Luís; Aragão, António; Ferraz, Eduardo; Santarén, Júlio; Ferreira, Paulo J. T.; Ramos, Ana; Rasteiro, Maria G.; Gamelas, José A. F.
- Filmes de Celulose Nanofibrilada com Incorporação de Minerais como Substitutos de Plásticos em Embalagens Alimentares: Potencialidades e DificuldadesPublication . Alves, Luís; Ferraz, Eduardo; Santarén, Julio; J. T. Ferreira, Paulo; Ramos, Ana; Rasteiro, Maria G.; A. F. Gamelas, JoséCeluloses nanofibriladas (CNF) são nanomateriais com propriedades promissoras para produção de embalagens alimentares, sendo substitutos lógicos de polímeros de base petroquímica, especificamente plásticos. Contudo, estes materiais apresentam algumas limitações, como o seu elevado custo. A combinação de CNF com minerais argilosos representa uma excelente abordagem para a produção de materiais de elevado valor acrescentado com custos aceitáveis, possibilitando ainda a melhoria de algumas propriedades dos materiais, como por exemplo o efeito barreira a gases. Para a produção de filmes compósitos podem ser seguidas duas estratégias: evaporação de solvente ou filtração seguida de prensagem a quente. Os filmes obtidos por filtração apresentam propriedades mecânicas superiores às dos obtidos por evaporação de solvente e são preparados mais rapidamente. Assim, esta técnica apresentase como a mais apropriada e eficiente para a produção de filmes compósitos com boas propriedades mecânicas