Modeling flow and cell formation in foam sheet extrusion of polystyrene with CO 2 and co‐blowing agents. Part II : Process model

Prediction of the Bubble Growth Behavior by Means of the Time-, Temperature-, Pressure- and Blowing Agent Concentration-Dependent Transient Elongational Viscosity Function of Polymers

Bubble growth processes are highly complex processes, which are not only dependent on the foaming process parameters (temperature, pressure and blowing agent concentration) but also on the type and structure of the polymer used. Since the elongational viscosity at the bubble wall during bubble growth also depends on these influencing factors, the so-called transient elongational viscosity plays a key role in describing the gas bubble growth behavior in polymer melts. The model-based description of the transient elongational viscosity function is difficult due to its dependence on time, Hencky strain and strain rate. Therefore, representative viscosities or shear viscosity models are usually used in the literature to predict the bubble growth behavior. In this work, the transient equibiaxial elongational viscosity function at the bubble wall during bubble growth is described holistically for the first time. This is achieved by extending the so-called molecular stress function (MSF) model by superposition principles (temperature, pressure and blowing agent concentration) and by using the elongational deformation behavior (Hencky strain and strain rate) at the bubble wall during the initial, and thus viscosity-driven, bubble growth process. Therefore, transient uniaxial elongational viscosity measurements are performed and the non-linear MSF model parameters of the two investigated polymers PS (linear polymer chains) and PLA (long-chain branched polymer chains) are determined. By applying the superposition principles and by changing the strain mode parameter to the equibiaxial case in the MSF model, the transient equibiaxial viscosity master curve is obtained and used to describe the bubble growth process. The results show that the extended MSF model can fully predict the transient equibiaxial elongational viscosity function at the bubble wall during bubble growth processes. The bubble growth behavior over time can then be realistically described using the defined transient equibiaxial elongational viscosity function at the bubble wall. This is not possible, for example, with a representative viscosity and therefore clearly demonstrates the influence and importance of knowing the transient deformation behavior that prevails at the bubble wall during bubble growth processes.

Influence of Bacillus subtilis on the surface behavior and separation of talc and chlorite minerals

Bacillus subtilis was used as a bio-surface modifier to improve the floatability of talc mineral (Mg3Si4O10(OH)2) in the talc ore. The surface behavior of chlorite mineral as the main associated gangue with talc mineral was studied in the presence of B. subtilis using zeta potential, scanning electron microscopy, and Fourier-transform infrared spectroscopy techniques. The floatability of both minerals was investigated as a function of pH, contact time, and concentration of B. subtilis. The results showed that the zeta potential of the talc mineral was strongly influenced by the treatment with B. subtilis. The maximum separation efficiency of talc from chlorite was achieved at pH 4. A talc concentrate with 98% quality and about 95% recovery was prepared from a binary talc-chlorite mixture containing 85% talc under optimum conditions of 8 × 105 cells/mL B. subtilis, pH 4, 35°C, and a contact time of 10 min.