Supramolecular Structure Characterization of Cellulose II Nanowhiskers Produced by Acid Hydrolysis of Cellulose I Substrates

Abstract

Cellulose II nanowhiskers (CNW-II) were produced by treatment of microcrystalline cellulose with sulfuric acid by both controlling the amount of H(2)SO(4) introduced and the time of addition during the hydrolysis process. The crystalline structure was confirmed by both XRD and (13)C CP-MAS NMR spectroscopy. When observed between crossed polarizers, the cellulose II suspension displayed flow birefringence and was stable for several months. The CNW-II nanowhiskers were significantly smaller than the cellulose I nanowhiskers (CNW-I) and had a rounded shape at the tip. The CNW-II average length and height were estimated by AFM to be 153 ± 66 and 4.2 ± 1.5 nm, respectively. An average width of 6.3 ± 1.7 nm was found by TEM, suggesting a ribbon-shape morphology for these whiskers. The average dimensions of the CNW-II elementary crystallites were estimated from the XRD data, using Scherrer's equation. A tentative cross-sectional geometry consistent with both XRD and NMR data was then proposed and compared with the geometry of the CNW-I nanowhiskers.

Caracterização morfológica de nanocristais de celulose por microscopia de força atômica

“…[37] que caracterizaram fibras de mesocarpo de dendê por MEV e MET, hidrolisados sob as mesmas condições de concentração de H 2 SO 4 e temperatura, no entanto, sob maior tempo de exposição ao H 2 SO 4 (150 min). Tais variações nas condições podem ser responsáveis pela diferença na medida do comprimento dos CNCs [17].…”

“…A etapa de branqueamento com H 2 O 2 foi repetida, evidenciando que este processo promove a dissolução de gorduras, minerais, parte da hemicelulose e quebra da lignina, entre outros cromóforos, tornando a fibra mais clara. Posteriormente, as fibras foram submetidas à hidrólise ácida, utilizando ácido sulfúrico (H 2 SO 4 ) 64% m/v, durante 1h10 min, sob uma temperatura de 45°C, numa razão ácido-fibra de 12,5 mL.g -1 para obtenção dos CNCs conforme proposto por Sèbe et al (2012) [17]. Manga (NM).…”

“…CNCs apresentam uma razão de aspecto que pode variar de 1 a 100, sendo que quanto mais próximo de 100, considera-se uma alta razão de aspecto [15]. Outros fatores de interesse envolvem suas propriedades intrínsecas, como a área superficial maior, elevado módulo de elasticidade, baixa densidade para sua aplicabilidade em diversos meios, como indústrias de embalagens, automotivas e demais áreas [16,17,18,19,20].…”

Functionalized Polymers from Lignocellulosic Biomass: State of the Art

“…The dimensions and stiffness of CNW depend on cellulose source and conditions of hydrolysis such as time and temperature [117][118][119][120][121][122][123]. Several recent studies optimized the preparation conditions for pea hull fibers [117], coconut husk [118], kenaf bast fibers [119], grass (Zoysa japonica and Z. tenuifolia) [120], curauá (pineapple) fibers [121], rice straw [122] and microcrystalline cellulose [123].…”

Effect of Hydrolysis Treatment on Cellulose Nanowhiskers from Oil Palm (Elaeis guineesis) Fronds: Morphology, Chemical, Crystallinity, and Thermal Characteristics

“…CNW are highly crystalline needle-shaped cellulose particles with one of its dimensions equal to or less than 100 nm (Sebe et al 2012;Chen et al 2014;Xu et al 2014). Even a very low amount of CNW incorporation as reinforcement material in polymer has been found to significantly improve thermal, mechanical, and barrier properties of composite materials as compared to the conventional composites (OsorioMadrazo et al 2012;Chen et al 2014).…”