Agglomeration of cellulose nanocrystals: the effect of secondary sulfates and their use in product separation

Abstract

This study was aimed at the development of a better understanding of the agglomeration behavior of sulfated cellulose nanocrystals (CNCs) in the presence of sulfates with monovalent (NH4+, K+, Na+) and divalent (Ca2+) cations, and to demonstrate their potential in simple and efficient product separation. Protonated CNCs were counterion-exchanged and their ionic strength was increased by adding sulfates of the respective cation to trigger agglomeration. The critical concentrations of agglomeration (CAC) and peptization (CPC) were determined. We found that the agglomeration behavior of CNCs could be attributed to matching affinities between the cations and the sulfate half-ester groups on the CNC surfaces. Based on these findings, a facile and efficient downstream process was designed to separate CNCs from neutralized reactant solutions using CAC and CPC. This method provides colloidally stable CNCs at high yield provided by centrifugation. When salt concentrations in the product are maintained below the CAC, as prepared CNCs from neutralized reactant solutions might be used in hydrogels and emulsions.

Effect of Ultrasonication on the Size Distribution and Stability of Cellulose Nanocrystals in Suspension: an Asymmetrical Flow Field-flow Fractionation Study

“…Colloidal suspensions of sulfated CNCs were prepared through the heterogeneous hydrolysis of cellulose with sulfuric acid, based on the method of Cranston and Gray (2006) and Metzger et al (2020). Cotton cellulose was dried at 105 °C for 30 min to remove adsorbed water.…”

“…Its high ionic strength causes agglomeration of CNCs (Phan-Xuan et al 2016, Metzger et al 2020. Peptization and the formation of a stable colloidal suspension is achieved by separating CNCs from acid and byproducts via sedimentation and filtration (Marchessault et al 1961, Rudie 2017, Gicquel et al 2019.…”

Effect of ultrasonication on the size distribution and stability of cellulose nanocrystals in suspension: an asymmetrical flow field-flow fractionation study

“…When the desired extent of hydrolysis of cellulose is approached during CNC production, the reactant solution-now containing CNCs, acid, and byproducts-is quenched with water. Its high ionic strength causes agglomeration of CNCs (Phan-Xuan et al 2016;Metzger et al 2020). Peptization and the formation of a stable colloidal suspension is achieved by separating CNCs from acid and byproducts via sedimentation and filtration (Marchessault et al 1961;Rudie 2017;Gicquel et al 2019).…”

Thermoplastic Starch Nanocomposites Reinforced with Cellulose Nanocrystal Suspensions Containing Residual Salt from Neutralization

“…[59] In this context, Metzger et al designed an economic separation process to produce colloidally stable CNCs from neutralized reactant solutions. [60] After hydrolysis, the reactant solution is neutralized with a base, such as sodium hydroxide, to form a secondary sulfate (Na 2 SO 4 ). Successive centrifugation steps remove excess ions and by-products until peptization occurs.…”

“…Hence, the amount of salt in the product can be controlled by adjusting the amount of water added before and after each washing step. [60,61] Eventually, a stable colloidal suspension is formed by diluting the product to a salt concentration below the critical agglomeration concentration.…”