Shear Rheology of Varied Organosolv Lignin Samples

Lignin is an abundant natural, renewable, polymer that constitutes roughly 30 percent of lignocellulosic biomass. Lignin is a high volume byproduct of any cellulose based biorefinery and a potentially important revenue stream. However, lignin's chemical and structural complexity and variability has limited its processing ability, which restricts its use in fibers, films, and other products. Understanding the rheological properties of lignin is fundamental for its successful use in polymer melts and solution processing. In order to achieve this goal, the shear rheology of different lignin samples was studied by measuring the complex viscosity and dynamic moduli at different temperatures. The lignin samples used were an alkali 2-hydroxy-proply ether, acetate organosolv, aspen organosolv and other derivatives of organosolv lignin. Master curves were generated for complex viscosity and dynamic moduli by using Cross, Carreau and Sisko viscosity models to fit the variability of the experimental data. From the Arrhenius plots of the shift factors with respect to temperature, the activation energies for shear flow were determined. The complex viscosity curves showed typical and atypical shear thinning behavior indicating that the lignin samples had a wide range of rheological properties. At lower temperatures, all the lignins appeared to have normal shear thinning behavior; however at higher temperatures the aspen lignin and the organosolv lignin derivatives exhibited an increase in viscosity. This indicated that at a certain temperature threshold, the lignin underwent a shift in its rheological properties.