Volume 11, Issue 1

The melt rheology of a low T g tin phosphate glass [Pglass] has been studied with oscillatory shear flow experiments to accelerate efforts to melt process the glass with different organic polymers. The w dependence of the complex viscosity η * of the Pglass is easily predicted by a modified Rouse model with two relaxation times. The complex viscosity of the glass at different temperatures and frequencies can be superposed and described by the Arrhenius equation. At higher temperatures, the melt viscosity of the Pglass increased monotonically with time. This viscosity rise is thought to be due to sample crystallization. The Pglass was melt-mixed with two different thermoplastic polymers (low-density polyethylene and polystyrene) to produce unique hybrid materials with interesting microstructures.

Laboratory-scale experiments were carried out to explore the influence of the composition of the fat phase on mechanical and rheological properties of processed model cheeses. Cheeses made from caseinates, emulsifying salts and a milk fat fraction liquid at 24°C, which was achieved by thermal separation, showed much lower moduli than processed model cheeses manufactured with a fat fraction solid at 30°C. Processed model cheeses made from caseinates, emulsifying salts and a hard butter with a low amount of unsaturated fatty acids were significantly higher in firmness than cheeses made with soft butter with a higher amount of unsaturated fatty acids. In experiments using mature Gruyère and emulsifying salts, processed cheeses made from summer Gruyère were less firm than processed winter Gruyère. The results indicate that fat composition strongly affects mechanical properties of processed cheese, and a model is provided to explain structural changes during deformation.

The different methods that can be used for measuring the effect of a hydrostatic pressure on the viscosity of polymer melts are evaluated. A linear low-density polyethylene is chosen as test material, as it can be expected to have a small pressure dependency. Special attention is given to methods employing capillary rheometry, as these methods yield a range of shear rates and pressures that are typically encountered under polymer processing conditions. The accuracy of the different techniques is evaluated considering also the complexity of the experimental devices. First it is investigated to which extent standard capillary rheometry can be used to extract information about the pressure dependency of the viscosity. Secondly, it is shown how the accuracy can be greatly increased by the simple addition of a pressure chamber below the exit of the capillary, with a needle valve to regulate the back pressure. The results from this device are compared with those from a more robust method using a pressurized double piston rheometer and with literature data. The experimental values for the pressure coefficient of the viscosity will also be compared with those predicted from PVT data using Utracki's method.