Aggregate Morphology and Aqueous Dispersibility of Spray-Dried Powders of Cellulose Nanocrystals

Abstract

Spray drying is the most cost-efficient technology to produce bulk quantities of dry cellulose nanocrystals (CNCs) from acid hydrolyzed CNC suspensions. Spray drying results in the aggregation of CNC particles in granular material which is difficult to redisperse in water to individual particles. In this research, we investigated cospray drying of CNC suspensions with nonionic surfactant (10-mol ethoxylated octylphenol) at different concentrations and the role of this nonionic surfactant on the redispersion of spray-dried granular CNC particles. Dispersions of spray-dried CNC powder samples in water were investigated under static, mechanically stirred, and ultrasound-assisted mixing conditions. The granular morphology of spray-dried CNCs was affected by the concentration of nonionic surfactant. Overall, the formations of hollow and blistered particles in the presence of 5 and 10 mM OPE-100 were attributed to interactions between nonionic surfactant and CNCs which cause a reduction in the repulsion of nanoparticles during the shrinking of spray drying droplets. Higher light transmission properties, improved dispersion stability, and narrower particle size distribution of spray-dried CNC suspensions were achieved with the incorporation of nonionic surfactant at 5 and 10 mM prior to spray drying. These results are explained by the presence of hollow particles and by the increased interparticle interaction distance of CNCs due to weak and reversible adsorption of nonionic surfactant. Therefore, the addition of a nonionic surfactant is an attractive approach to control granular particle morphology and aqueous redispersion of CNC granular powder. Such results are of particular significance in the commercialization and process optimization for the manufacture of CNCs.