The effect of cellulose nanocrystals (CNCs) on the reinforcing, cross-linking, and solvent barrier properties of lightly cross-linked natural rubber (NR) latex films for dipped goods applications were investigated. Predispersed CNCs, activating, and curing agents were mixed with natural rubber latex and allowed to mature for 2 h. Films were then prepared from the matured latex via dipping and solvent casting processes. The incorporation of CNCs in the NR latex led to remarkable improvement in tensile strength and modulus with progressively thinner films. An increase in the cross-linking density of the rubber films were observed as a result of the incorporation of CNCs, which was observed from proton nuclear magnetic resonance analysis, and toluene swelling studies. This was likely attributed to an enhanced dispersion of the zinc oxide (ZnO) used as a cross-linking activator as observed from electron dispersive X-ray spectroscopy (EDX). A possible mechanism for the improved dispersion of ZnO in the latex in the presence of CNCs was the formation of Zn–CNC complexes. Higher cross-linking densities also led to lower water absorption over a prolonged time period. The nanocomposite thin films showed low permeability to a nonpolar solvent vapor, such as tetrahydrofuran (THF), but increased permeability to water vapor. A practical application of the observed barrier properties in dipped rubber goods could be in gloves, where permeation of perspiration from hands, is allowed while preventing the passage of nonpolar solvents.

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The flow behavior of nanocrystalline cellulose (CNC) hydrogels in the presence of a monovalent electrolyte (NaCl) as a function of CNC and salt concentration is explored using a variety of linear and nonlinear rheological tests. We have first observed an apparent “slip yield stress” at small wall shear stress values that is mainly due to the onset of solidlike slippage of the hydrogels before their true yielding and deformation. This flow regime and the “slip yield stress” can be eliminated using a sandpaper of an optimum grit size. At higher wall shear stress values, two yielding points for the CNC/salt network are seen in strain sweep tests due to network disruption and cluster deformation that depend on the concentration of both CNC (1–5 wt. %) and electrolyte (0–100 mM). The first yield stress is due to yielding and flow of clusters, while the second one is due to breakage of clusters to small flocs and individual fibers. These yielding stresses were obtained by a variety of tests including strain amplitude sweep, creep, and steady shear, and their values are compared confirming their existence. Rheo-SALS (small angle light scattering) measurements confirmed structural changes as the scattering patterns change from isotropic to highly anisotropic with an increase of deformation and rate of deformation. Moreover, confocal laser scanning microscopy and polarized microscopy images confirm the gradual breakup of clusters to smaller ones and eventually to nearly individual fibers with an increase in the applied shear strain and rate.

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The rheological properties and yielding behavior of 1 wt. % aqueous sulfonated cellulose nanocrystals (CNCs) in the presence of monovalent (Na+) ions have been investigated. The introduction of more than 20 mM NaCl to the system causes aggregation of neutralized CNCs and leads to the formation of self-similar clusters, which grow in size until they form a three-dimensional network. In the present work, we report a comprehensive study of nonlinear rheology and yielding behavior of CNC/salt gels in steady shear and oscillatory experiments. Two yield stresses have been determined. The first yield stress at low shear rates is attributed to the disconnected CNC clusters as a result of bond breakage. The second yield point occurs at higher shear rates, and it is related to the deformation of clusters, where individual nanorods are nearly separated and dispersed. The existence of these two yield stresses has been identified in both steady-shear scans (high to low and low to high) as well as oscillatory experiments, resulting in consistent results.