Transport Properties of Commercial Cellulose Nanocrystals in Aqueous Suspension Prepared from Chemical Pulp via Sulfuric Acid Hydrolysis

Abstract

A cellulose nanocrystal (CNC) sample prepared from chemical pulp via sulfuric acid hydrolysis procedures has been supplied by InnoTech Alberta Inc. in the shape of white dry powder as a prototype product. Some transport coefficients were precisely investigated for the CNC sample in aqueous suspensions at the room temperature of 25 °C such as the average rotational and translational diffusion coefficients (Dr and Dt) and viscoelastic relaxation times (τv) at dilute conditions. The determined values, Dr ≈ 2.3 × 103 s-1 and Dt ≈ 1.0 × 10-11 m2 s-1, using depolarized and usual dynamic light scattering (DLS) techniques, respectively, proposed the consistent length and width of L ≈ 170 nm and W ≈ 7.6 nm via a theoretical model for monodisperse rigid rods dispersed in pure water. The viscoelastic behavior for aqueous CNC suspensions containing spherical probe particles was examined using DLS rheological techniques. The obtained value of τv = 1.0 × 10-4 s fairly agrees with that of (6Dr)-1 ≈ 7.4 × 10-5 s. Because the theoretical model for monodisperse rods denotes the relationship τv = (6Dr)-1, this observation strongly confirms that the CNC sample behaves as approximately monodisperse rigid rodlike particles. Transmission electron microscopy (TEM) images clearly demonstrated a bimodal distribution in rod length with major and small minor peaks at ca. 150 and 240 nm, respectively. Then, the reason for the observed disagreement between the L values resulted from the transport coefficients and the major peak in TEM images is the presence of the small minor component with L ≈ 240 nm. Consequently, individual nanosize rodlike crystalline particles in the CNC sample well disperse without forming large aggregations because of strong interactions and behave as isolated individual rods in dilute aqueous suspensions.