Rheology of Lignin and Lignin/PET Blends

Lignin is the second most abundant biomass resource on the planet. It results in industrial quantities as a byproduct of pulping industry and is mostly used as fuel in the pulping chemicals recovery process. Due to the high content of carbon and hydrogen, it can be also used for making carbon fibers. In this thesis some rheological characteristics of the lignin/polyester blends are presented. Polyesters are added to enhance the process ability of the lignin for manufacturing carbon fiber precursors by melt spinning. The effect of polyester addition on viscosity and dynamic moduli of different lignins (organosolv, washed kraft, and kraft mixed wood) is studied. All blends and pure lignins show a shear thinning behavior, except mixed wood lignins at low angular velocities, where a short range of shear thickening is recorded. Organosolv and washed kraft lignins have viscosity comparable with that of some melt blowing grade PPs, suggesting that these lignins and their blends may be used to manufacture nonwovens by the melt blowing process. Mixed wood lignin viscosity is much higher and the shear thickening at low angular velocities could be explained by crosslinking or condensation of different types of lignins, from softwood and hardwood species used in pulping. All lignins and their blends with PET behave as viscous or viscoelastic fluids, depending on temperature and composition, as shown by the dynamic moduli curves versus angular velocity. Mixed wood lignin features a broader range of viscoelastic behavior at low angular velocities.