Effects of additives on the particle morphology and aqueous dispersibility of foam-spray dried cellulose nanocrystal suspensions

Abstract

Cellulose nanocrystals (CNCs) are inherently hydrophilic; even so, their dispersions in water based applications such as rheology modifiers, coatings, and emulsion systems do not often produce perfect dispersions with a minimum energy input. Supplying the CNCs in dry granular powder form is needed in the industrial scale of production because of its easier handling, storage and transportation characteristics. Spray drying is the preferred industrial method for drying acid hydrolyzed CNC suspensions. However, spray drying often causes poor dispersion of dried CNC granules into individual nanoparticles in aqueous solutions if not mixed with high energy input. This study investigates foam-spray drying of CNC particles to enhance their dispersibility in water. Non-ionic 10-mole ethoxylated octylphenol surfactant (OPE-100) and methyl cellulose polymer (MC) were used as additives to assist the foaming of CNC suspensions. Foam-spray drying experiments were carried out under constant process conditions such as inlet and outlet temperatures, gas and liquid flow rates and concentrations of CNCs. We focus on the effects of 10-mole ethoxylated octylphenol surfactant (OPE-100) and methyl cellulose polymer (MC) as additives and foaming of CNCs suspension on the morphology of dried CNC aggregates and their dispersion in water. Our work also describes the molecular interaction mechanisms of CNCs with methyl cellulose and OPE-100 by means of isothermal titration calorimetry and surface charge of the coated CNCs. The addition of nonionic surfactant OPE-100 along with methyl cellulose polymer resulted in spray drying of CNC aggregates with the best water dispersion characteristics. While methyl cellulose generated foams, OPE-100 lowered the inverse thermal gelling of methyl cellulose in spray drying.