Abstract
Cellulose nanocrystals (CNCs) are a biorenewable resource, which may be chemically modified to impart specific properties. Modified CNCs have found use in imaging applications, as rheology modifiers, polymer reinforcements, barrier and/or optical films, and nanocomposites. Nanoparticle dimensions of CNCs are typically 5–10 nm in width, with lengths of <100–300 nm. However, the physical properties are dependent upon the number and nature of the surface charge groups imparted during preparation. In the case of CNCs produced from sulfuric acid hydrolysis, the sulfated surface groups may be partially removed prior to further functionalization. This gives more available hydroxyls yet renders the CNCs less colloidally stable. Furthermore, conditions vary significantly and there is no consensus about the optimal conditions for partial removal of sulfate functionality or conditions developed to give specific surface charge. In the following, alkali hydrolysis of sulfate half-esters was quantified by conductometric titration of the strong acid groups, and using a design of experiments (DOE), optimal conditions were determined to produce CNCs with tailored surface charge.
Highlights
Cellulose nanocrystals (CNCs) are a biorenewable resource that is environmentally friendly, and possess unique physical properties such as high crystallinity and aspect ratio, large surface area, and a propensity to self-assemble into chiral nematic phases [1,2,3]
Wang et al developed a kinetic model, which indicated optimal conditions of 58 wt% H2SO4, 55 ◦C, 60 min based on constraints of maximal CNC yield at a given acid concentration and the minimal retention of cellulosic solid residues (CSR) and other decomposition products
The former was not quantified while the latter does not allow for tailored surface charge
Summary
Cellulose nanocrystals (CNCs) are a biorenewable resource that is environmentally friendly, and possess unique physical properties such as high crystallinity and aspect ratio, large surface area, and a propensity to self-assemble into chiral nematic phases [1,2,3]. Wang et al developed a kinetic model (for bleached Kraft eucalyptus pulp), which indicated optimal conditions of 58 wt% H2SO4, 55 ◦C, 60 min based on constraints of maximal CNC yield at a given acid concentration and the minimal retention of cellulosic solid residues (CSR) and other decomposition products (vide infra). Jiang et al observed that the acid-catalyzed desulfation of CNCs resulted in increased degradation products and the incomplete removal of surface –OSO3– groups, while solvolytic desulfation gives the CNC product as a pyridinium salt [32]. The former was not quantified while the latter does not allow for tailored surface charge.
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