Volume 21, Issue 4

Black liquor is the major by-product and biomass fuel of pulp mills, and the understanding of its thermophysical properties is essential for the improvement of the design and the operation of chemical recovery processes. In this work, the rheological behaviour of industrial samples of Eucalyptus globulus black liquor was investigated to study the influence of solids content ranging from 13 % for the white liquor sample, and from 30 to 65 % of dissolved solids for the black liquors, and of temperature from 298.15 to 338.15 K, covering shear rates from 0 to 1200 s -1 . The black liquor showed a complex non-Newtonian behaviour, presenting at low shear rates a pseudoplastic behaviour, followed by a viscosity Newtonian plateau. The modified Quemada model gives an expression applicable to all the shear rate range, which was used to describe the flow curves for the viscosity of E. globulus black liquors samples. Moreover, a correlation based on a VTF model with parameters dependent on solids content was successfully developed for the viscosity data of the Newtonian plateau.

An apparatus for small angle light scattering (SALS) and light transmission measurements under shear was built and tested at the University of Massachusetts Amherst. As a new development, the polarization direction can be rotated by a liquid crystal polarization rotator (LCPR) with a short response time of about 20 ms. The experiments were controlled and analyzed with a LabVIEW TM based code (LabVIEW TM 7.1) in real time. Quiescent and flow-induced crystallization experiments on isotactic poly-1-butene (iPB) were conducted to demonstrate the instrument and software capabilities. Software was designed with a modular approach, so that further modules can be added to investigate other systems such as polymer blends, colloidal suspensions, solutions with droplets etc. A replica of the SALS apparatus was custom built for ExxonMobil Research in Clinton NJ.

We report unprecedented non-Einstein-like viscosity decrease of polymer melts by special low glass transition, T g , inorganic tin fluorophosphate glass (Pglass) that is remarkably counter to widely accepted dispersions, suspensions, and composites theories. The well dispersed low-T g Pglass dramatically decrease the polymer melt viscosity while increasing its Young's modulus in the solid state at low loading (<2%) however decreasing with high loading (> 2 %), making the hybrid Pglass/polymer solid material stronger yet easier to process in the liquid state. Disruption of the Nylon 6 melt dynamics, strong physicochemical interactions, and submicrometer nanophase separation (proved by rheometry, FTIR, DSC, SEM, NMR and XRD) are thought to be responsible for this experimental fact. This finding should beneficially impact our ability to prepare lower viscosity, very highly filled Nylon 6 melts from already existing materials and polymer processing methods such as injection molding and extrusion, making the simple strategy potentially widely applicable in a number of applications such as thinner barrier resistant thin films, composites, and membranes for heterogeneous catalysis.

We have interpreted the results of shear creep data on samples of bread dough, tested in a parallel plate rheometer, by using a damage function model. Whilst the agreement between calculation and experimental results is satisfactory for the dough for stress levels less than 500 Pa, increasingly large deviations from the predictions occur for stress levels of 500 and 1000 Pa. This is in contrast with the behaviour in simple shearing, where agreement with the damage function model can be obtained up to shear stresses of several kPa. It is therefore of interest to see why the discrepancy between model predictions and experiments occurs in shear creep at such low stress levels. It is shown that edge fracture in a parallel-plate rheometer, due to the second normal stress difference, N 2 , is responsible for the deviations and the model behaves quite well for stress levels 300 Pa and below, where edge fracture is not important. Therefore the edge fracture instability, which depends on N 2 , limits the range of stress which can be applied in shear creep tests.