Spray-drying Cellulose Nanofibrils: Effect of Drying Process Parameters on Particle Morphology and Size Distribution

Spray-drying was chosen as an appropriately scalable manufacturing method to dry cellulose nanofibril (CNF) suspensions. Spray-drying of two different types of CNF suspensions—nanofibrillated cellulose (NFC) and cellulose nanocrystals (CNC)—was carried out using a laboratory-scale spray dryer. Effects of three spray-drying process parameters on particle morphology and particle size distribution were evaluated: 1) gas flow rate; 2) liquid feed rate; and 3) suspension solids concentration. Particle morphology was characterized by scanning electron microscopy (SEM) and a morphology analyzer. SEM showed that spray-drying of NFC formed fibrous particles and fibrous agglomerates, whereas spray-drying CNCs produced spherical and mushroom cap (or donut)-shaped particles. Particle morphology formation mechanisms are proposed for spray-drying nanocellulose suspensions. The effect of the three spray-drying process parameters on particle size distribution depended on the drying nature of the materials. The three parameters interacted to significantly affect particle size of CNC suspensions, whereas they did not interact to affect particle size of NFC suspensions. For the CNC suspension, a higher gas flow rate produced smaller particle sizes. The gas flow rate did not affect particle size for NFC suspensions. The effect of liquid feed rate and solids concentration on CNF particle size was negligible in this study. The smallest mean circle equivalent diameters produced in this study were 3.95 mm for NFC and 3.64 mm for CNC.