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

Abstract

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.

Keywords

• cnf
• nanocellulose
• bactris gasipaes
• agave tequilana weber
• cardboard fibers
• eucalyptus fibers
• oven-drying
• spray-drying
• freeze-drying