Thursday, June 26, 2008 - 1:30 PM
South American AB (Capital Hilton)
164

Phase Behavior and Rheological Analysis of Cellulose Nanocrystal Aqueous Suspensions

Esteban E. Ureña-Benavides and Christopher L. Kitchens. Clemson University, Clemson, SC

Cellulose nanocrystals (CNCs) have potential to become a renewable and cost effective alternative for biocompatible polymer nanocomposites with a high strength to weight ratio. However, these particles are usually very polydispersed and non-compatible with hydrophobic polymers. Aqueous suspensions of rod shaped CNC were prepared by sulfuric acid hydrolysis of ashless cellulose powder and kraft pulp from a local paper mill. The particles are less than 10 nm wide, and 20 to 300 nm long. The chiral nematic – isotropic phase behavior of aqueous CNC suspensions has been investigated by measuring the relative volume, concentration and particle size as a function of cellulose concentration, and temperature. Successive partition of both phases has been used to partially fractionate the particles by size into more uniform distributions with average lengths of 125 nm, 154 nm, and 207 nm. Transmission Electron Microscopy was used to measure the nanocrystals obtained from the isotropic and anisotropic phases to determine the effects of nanocrystal size on the phase behavior and degree of fractionation. Rheological analyses have been used to characterize the fluid behavior of the nanocrystal suspensions as a function of cellulose concentration, particle size, and nanocrystal ordering. This provides a fundamental understanding of the interactions between the particles, and the media in which they are dispersed. We are currently investigating the aqueous surface modification via esterification, and etherification of the nanocrystal's hydroxyl groups to make the particles hydrophobic. Nanocomposites filled with CNC have usually shown little improvement on their properties, presumably because of the poor compatibility with the polymeric matrix. The surface modification, as well as, size fractionation of the particles are intended to improve the dispersability and compatibility of the cellulose crystals within biodegradable and biocompatible polymers; leading to a new generation of green materials.