Influence of Water Removal Techniques on the Main Characteristics of Nanofibrillated Cellulose Obtained from Different Lignocellulosic Materials.

CELLULOSE fibers; CELLULOSE; SURFACE chemistry; SCANNING electron microscopy; SURFACE morphology; SLURRY

Cellulose nanofibers are often available in aqueous suspensions (~90% water), and water removal becomes necessary to transportation, practical application, and characterization by specific instruments such as x-ray diffractometer or FTIR spectrometers. Since the water remotion interferes in some properties of nanocellulosic materials, the description of the applied technique is essential to the appropriate comparison and discussion of the published results. Aiming this issue at the present work, distinguished drying procedures were applied at eight different nanofibrils slurries. The products from the procedures were evaluated in terms of crystallinity degree, surface chemistry and morphology. The films or nanocellulosic paper obtained by casting were the result of a complex entangling of cellulose nanofibrils, and it resulted in a material with two specific properties: it could not be resuspended in water and had significantly lower crystallinity indexes (18.7–30.3%) in comparison to the powders obtained by atomization (26.6–43.3%) or the flakes by sublimation (29.5–45.2%). Even with the possibility of a resuspension, the thin and flow format of spray-dried powder lost its nanoscale after drying. The images obtained by scanning electron microscopy evidence the aggregation formed during the water removal. The results of the infrared diffractograms suggest that the drying procedure only affected the nanocellulose characteristics at the physical level. [ABSTRACT FROM AUTHOR]

纤维素纳米纤维通常存在于水悬浮液中(~90%的水), 水的去除对于运输、实际应用和特定仪器(如x射线衍射仪或FTIR光谱仪) 的表征是必要的. 由于水去除会干扰纳米纤维素材料的某些特, 因此对应用技术的描述对于适当比较和讨论已发表的结果至关重要. 针对这一问题, 在目前的工作中, 对08种不同的纳米纤维浆料采用了不同的干燥程序. 从结晶度、表面化学和形貌等方面对程序中的产物进行了评估. 通过浇铸获得的薄膜或纳米纤维素纸是纤维素纳米纤维复杂缠绕的结果, 它产生了一种具有两种特性的材料: 与通过雾化获得的粉末相比, 它不能在水中重新悬浮, 结晶指数显著降低 (18.7–30.3%)(26.6–43.3%) 或升华后的薄片(29.5–45.2%). 即使存在再悬浮的可能性, 喷雾干燥粉末的薄层和流动形式在干燥后也失去了其纳米级. 通过扫描电子显微镜获得的图像证明了在脱水过程中形成的聚集. 红外衍射图的结果表明, 干燥过程仅在物理水平上影响纳米纤维素的特性. [ABSTRACT FROM AUTHOR]

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