(291a) Tuning Interactions Between Cellulose Nanocrystals With Adsorbing Polysaccharides and Surfactants

Cellulose nanocrystals (CNCs) are strong, light-weight, renewable, and highly crystalline rod-like nanoparticles of cellulose. CNCs from wood or cotton are nanorods of approximately 200 nm in length and 6-10 nm in width and are hydrophilic due to the presence of surface hydroxyl groups and charged sulfate ester groups. Because CNCs have recently become available in commercial scale quantities, they are being evaluated in a wide range of potential application. For example, CNCs have been incorporated into renewable polymer matrices to create sustainable, nanocomposites and assembled into optically active films that reflect specific wavelengths of light. We anticipate that because of the green, biocompatible nature of CNCs that they will be considered in formulated chemical products such as cosmetics. For these types of applications it is important to understand the influences of water-soluble polymers and surfactants on the colloidal stability and rheological properties of CNCs suspensions.

The aim of this paper is to investigate the structure formation and rheological properties of suspensions of in the presence of polymers and surfactants. Adsorption of hydroxyethyl cellulose (HEC), hydroxypropyl guar (HPG), locust bean gum (LBG), and dextran (Dex) onto cellulose nanocrystals- coated substrates was investigated. Measurements using the quartz crystal microbalance with dissipation (QCM-D) confirmed that all polysaccharides except dextran adsorbed onto cellulose nanocrystals and formed viscoelastic gel layers with water contents over 90%. Shear-thinning hydrogels were readily produced by mixing CNCs with adsorbing polysaccharides over the concentration range studied. Viscoelasticity measurements showed a larger linear elastic moduli than loss moduli, confirming gel formation. These results lead us to conclude that adsorbing polymer-induced bridging flocculation of cellulose nanocrystals causes gel formation. The stability of CNCs-polymer hydrogels was tailored by exposing the hydrogels to sodium dodecyl sulfate solutions. Complementary use of QCM-D and surface plasmon resonance (SPR) spectroscopy indicated that polymers desorb from the cellulose surface in the presence of sodium dodecyl sulfate. A depletion flocculation mechanism was suggested to explain the decrease in viscosity for cellulose nanocrystals-polymer hydrogels upon addition of anionic surfactants. We believe that the more detailed understanding of the network formation and rheology of CNCs suspensions in the presence of polymers and surfactants will aid in incorporating CNCs into various formulations extending the range of possible applications.