Hydrophobization of Cellulose Nanocrystals for Aqueous Colloidal Suspensions and Gels (original) (raw)
Related papers
Mechanically Robust Gels Formed from Hydrophobized Cellulose Nanocrystals
ACS Applied Materials & Interfaces
Cellulose nanocrystals (CNCs) that bind to each other through associative hydrophobic interactions have been synthesized by modifying sulfated CNCs (sCNCs) with hydrophobic moieties. These octyl-CNCs form gels at significantly lower concentrations than parent sCNCs, producing extremely strong hydrogels. Unlike sCNCs, these octyl-CNCs do not form ordered liquid crystalline phases indicating a random association into a robust network driven by hydrophobic interactions. Furthermore, involvement of the octyl-CNCs into multicomponent supramolecular assembly was demonstrated in combination with starch. AFM studies confirm favorable interactions between starch and octyl-CNCs, which is thought to be the source of the dramatic increase in gel strength.
Ion-Mediated Gelation of Aqueous Suspensions of Cellulose Nanocrystals
Biomacromolecules, 2015
Nanofibrillar hydrogels are an important class of biomaterials with applications as catalytic scaffolds, artificial extracellular matrixes, coatings, and drug delivery materials. In the present work, we report the results of a comprehensive study of nanofibrillar hydrogels formed by cellulose nanocrystals (CNCs) in the presence of cations with various charge numbers and ionic radii. We examined sol−gel transitions in aqueous CNC suspensions and the rheological and structural properties of the CNC hydrogels. At a particular CNC concentration, with increasing charge and cation size, the dynamic shear moduli and mesh size in the hydrogel increased. These effects were ascribed to a stronger propensity of CNCs for side-by-side association. The resulting hydrogels had an isotropic nanofibrillar structure. A combination of complementary techniques offered insight into structure−property relationships of CNC hydrogels, which are important for their potential applications.
Physics of Fluids, 2019
This paper reports the surface modification of commercially available cellulose nanocrystals (CNCs) using polyethyleneimine (PEI) by means of non-covalent electrostatic interaction between the negatively charged sulfate groups of CNCs and positively charged amine functionalities of PEI. The modification, carried out in an aqueous medium, results in a stable CNC-PEI suspension with no phase separation that exhibits interesting rheological behavior due to bridging-type inter-particle interactions. The Newtonian 3% (w/w) CNC suspension evolves into a non-Newtonian gel system after modification with PEI with a consequent increase of almost three decades in complex viscosity. Pre-shearing of the 3% (w/w) CNC-PEI suspension resulted in the loss of the linear viscoelastic properties with increasing shear rate, as would be expected from the breaking of the inter-particle network. However, the system gradually re-established the inter-particle network in less than an hour to give the original rheological parameters. The effect of PEI on the rheological properties was attributed to the physical adsorption of PEI chains on the CNC particles, examined by dynamic light scattering, zeta potential, X-ray photoelectron spectroscopy, elemental analyses, and isothermal adsorption studies. The modified CNC-PEI particles did not show any significant change in the particle morphology compared to the unmodified CNCs, as observed from transmission electron microscope images.
Rheologica Acta, 2021
We investigated the gelation and microstructure of cellulose nanocrystals (CNCs) in nonionic hydroxyethyl cellulose (HEC) solutions. Cellulose nanocrystals (CNCs) with a particle length of 90 nm and width of 8 nm currently produced by acid hydrolysis of wood pulp were used in this study. The microstructures of CNCs/polymer suspensions were investigated by performing linear small amplitude oscillatory shear (SAOS) and nonlinear large amplitude oscillatory shear (LAOS), in addition to constructing CNCs phase diagrams and measuring steady-state shear viscosities. Significant viscosity increases at low shear rates coupled with high shear thinning behaviors were observed in CNCs in HEC solutions above the overlapping concentration of HEC. The physical strength of CNCs/HEC solution gels increased with the increase in CNCs concentration and resembled the weakly crosslinked gels according to the scaling of linear dynamic mechanical experiments. According to LAOS analysis, CNCs/HEC mixtures ...
Water-In-Water Emulsion Gels Stabilized by Cellulose Nanocrystals
Langmuir : the ACS journal of surfaces and colloids, 2018
Particle-stabilized water-in-water emulsions were prepared by mixing dextran and poly(ethylene oxide) (PEO) in water and adding cellulose nanocrystals (CNC). The CNC formed a layer at the surface of the dispersed droplets formed by the PEO-rich phase. Excess CNC partitioned to the continuous dextran phase. Aggregation of CNC at different rates was induced by adding NaCl between 10 and 100 mM. In the presence of more than 2 g/L CNC, fast aggregation led to the formation of an emulsion gel showing no signs of creaming. Confocal laser scanning microscopy showed that the emulgels were formed by a continuous network of CNC in which the randomly distributed droplets were embedded. The gel stiffness was measured with oscillatory shear rheology and found to increase strongly with increasing CNC concentration ( C). The dispersed droplets were elastically active and increased the gel stiffness at low C. However, up to C = 10 g/L, the yield stress was too small to inhibit the flow when the gel...
Cellulose
Utilization of reversible non-covalent interactions is a versatile design strategy for the development of stimuli responsive soft materials. In this study, hydrophobic interactions were harnessed to assemble water-soluble macromolecules and nanoparticles into a transient hybrid network forming thermosensitive hydrogels with tunable rheological properties. Hybrid hydrogels were built of biopolymer derived components: cellulose nanocrystals (CNCs), nanoparticles of high aspect ratio, and hydroxypropyl methylcellulose (HPMC). To enable polymer/CNC assembly via hydrophobic interactions, the surface of highly hydrophilic CNCs was modified by binding octyl moieties (octyl-CNCs). The amphiphilicity of Electronic supplementary material The online version of this article (
The Canadian Journal of Chemical Engineering, 2016
Non-Newtonian flow behaviours of dilute and semi-dilute carboxymethyl cellulose (CMC) solutions in the presence of spindle-shaped cellulose nanocrystal particles (CNC) were investigated. Scanning transmission electron microscopy, dynamic light scattering, polarized optical microscopy, and turbidity measurements of CNC suspensions in CMC solutions were also carried out. Adding CNC particles only within the range of 0.33-2.0 m 3 /m 3 into the dilute and semi-dilute CMC polymer solutions increased the viscosities at low shear rates between 10 3-10 5 times. The flow curves of CNC suspensions in CMC polymer solutions turned highly non-Newtonian, and their viscosities at high shear rates (> 10 3) still converged to the flow curves of CMC solutions. The viscosity increase comes from the nematic flocculation of CNC particles in the presence of a non-adsorbing CMC polymer which results in CNC flocs with water entrapped pockets.
Rheologica Acta, 2017
The rheological behavior of cellulose nanocrystal (CNC) and modified CNC (mCNC) suspensions in dimethyl sulfoxide (DMSO) was investigated. The efficiency of the surface modification of CNCs by grafting an organic acid chloride to produce hydrophobic CNCs has been verified by X-ray photoelectron spectroscopy (XPS). The thermal degradation temperature of the mCNCs was found to be 165 versus 275°C for CNCs. The CNC suspensions in DMSO at 70°C underwent gelation at very low concentration (1 wt%) after 1 day. The network formation was temperature sensitive and did not occur at room temperature. For gels containing 3 wt% CNCs, the complex viscosity at 70°C increased by almost four decades after 1 day. For the mCNCs in DMSO, a weak gel was formed from the first day and temperature did not affect the gelation. Finally, the effect of adding 10 wt% of polylactide (PLA) to the solvent on the rheological properties of CNC and mCNC suspensions was investigated. The properties of suspensions containing 1.9 wt% CNCs and mCNCs increased during the first and second days, and PLA did not prevent gel formation. However, the reduced viscosity and storage modulus of the CNC and mCNC gels with PLA were lower than those of samples without PLA.
Carbohydrate Polymers, 2020
Locust bean/xanthan gum (LBG/XG) synergistic networks have previously been well studied, with evidence that junction zones between the two polymers result in hydrophobic domains. Here we report on the effect of both hydrophilic and hydrophobic cellulose nanocrystals (CNCs) on the rheological properties of the individual gums, the gum networks, and emulsion gels consisting of the gum network and corn oil. We also take advantage of differences in the autofluorescent spectra for each of the components to map their distribution within the gel and emulsion gel systems. Whilst both types of CNC confer thermal stability to the systems, hydrophilic CNCs induce minor changes in rheological properties of synergistic gels and prove to be detrimental to the stability of the emulsion gels. In contrast, hydrophobic CNCs associate with the LBG/XG network, affecting the rheological response. Their inclusion in the emulsion gel system results in smaller, more homogeneously distributed oil droplets with a resultant increase in the storage modulus by an order of magnitude compared to the CNC-free and hydrophilic CNC systems. We conclude that hydrophobic CNCs play a critical role in stabilising LBG/XG network gels and emulsions.