High Pressure Capillary Rheometer Research Articles

Rheology of molten polystyrene with dissolved supercritical and near-critical gases

The viscosities of polystyrene melts containing three different dissolved gases, carbon dioxide, and the refrigerants R134a (1,1,1,2-tetrafluoroethane) and R152a (1,1-difluoroethane) are investigated at pressures up to 20 MPa. These pressures reach near-critical and supercritical conditions for the three gas components, and produce polymer-gas solutions containing up to 10 wt % gas. The measurements are performed in a sealed high-pressure capillary rheometer at 150 and 175°C, and at shear rates ranging from 1-2,000 s -1 . Very large reductions in melt viscosity are observed at high gas loading; at 150°C, 10 wt % R152a reduces the Newtonian viscosity by nearly three orders of magnitude relative to pure polystyrene. The viscosity data for all three polystyrene-gas systems follows ideal viscoelastic scaling, whereby the set of viscosity curves for a polymer-gas system can be scaled to a master curve of reduced viscosity vs. reduced shear rate identical to the viscosity curve for the pure polymer. The viscoelastic scaling factors representing the effect of dissolved gas content on rheological behavior are found to follow roughly the same variation with composition for all three polystyrene gas systems.

Modelling of packing behavior of irregularly shaped particles dispersed in a polymer matrix

The dependency of the rheological properties of highly concentrated suspensions on solid concentration and particle size distribution was investigated using a high pressure capillary rheometer. The maximum packing fractions estimated based on rheological measurements for irregular shaped particles were compared with the maximum packing fractions obtained for spherical particles having similar particle size and size distributions. This was done in order to understand the effect of sphericity on the packing behaviour of irregular particles. The maximum packing fractions of the spherical particulate systems were obtained by a mechanical vibration technique as well as by rheological measurements. The Ouchiyama and Tanaka model for spherical particles was modified to predict the maximum packing fractions of irregularity shaped particulate systems using the concept of packing diameter. The modified model was verified with experimental results obtained for bimodal irregularly shaped as well as spherical particles.

An automated high pressure capillary rheometer with hydraulic drive

AbstractA new capillary rheometer design is described, in which a hydraulic device is used to produce the pressure driving the sample fluid through capillaries. The device is fully automated and controlled by a PC unit. Various measuring modes can be preselected and are automatically executed. Some preliminary results with New tonian fluids and with polymer solutions show the functioning of the new rheometer.

Rheological characteristics of glass-fibre-filled polypropylene melts

The rheological properties of glass fibre-filled polypropylene melts have been investigated. A high pressure capillary rheometer has been used for the experimental study. The effect of shear rate, temperature, and fibre concentration on the melt viscosity and viscoelastic properties have been studied. An equation has been proposed to correlate the melt viscosity with shear rate, temperature and fibre content. A master curve relation on this basis has been brought out using the shift factora T .

Flow behavior of PVC in hot-die-face pelletizing: Die hole pattern optimization

Die hole pattern optimization can minimize the pressure loss across the die plate for a given set of products, while maintaining sufficient steel strength. Data will be presented from a high-pressure capillary rheometer to establish flow behavior and investigate the effects of die geometry on flow resistance. The influence of formulation parameters, degree of gelation and shear gradient will be considered. Finally a model will be developed for the optimization of the die hole pattern. Using this procedure, it will be possible to establish the data needed for optimal die hole pattern design by calculation and graphic presentation.

Rheological behaviour of mixtures of rubber and crumb from scrap pneumatic tyres

In continuation of earlier studies the flow behaviour of mixtures of rubber (SBR, EPDM) and crumb from scrap tyre treads was estimated at 120°C with the aid of a high-pressure capillary rheometer. The influence of the capillary dimension on the flow curves was studied. With narrow and short capillaries the flow behaviour proved to be independent of the filler concentration. At low shear rates a discrimination of the flow characteristics according to the filler loading was observed only with capillaries above a certain width and length. At high shear rates with such a capillary an inversion of the rating of the flow curves was found.