The Stability of Flowing Dispersions

Presented at the 13th Congress of the International Federation of Associations of Textile Chemists and Colourists in London on 20 September 1984. Within a package-dyeing machine the danger of dye agglomeration is always greatest in regions where the shear rate is high, i.e. where most of the mechanical energy of the pumps is dissipated. Therefore in modern circulation machines the dye tends to agglomerate mainly within the yarn package, thus hindering the throughput of dye liquor. However, the degree of hindrance to liquor throughput has only a very limited value as a criterion of dispersion stability. Liquor throughput is essentially dependent on the test conditions used. Reproducibility is less than satisfactory in most cases, and the significance of such test results for production conditions, which may vary greatly, can be severely downgraded. Provided certain precautionary measures are adhered to, the bath depletion due to coagulation during the heating phase is readily reproducible. From this it is possible to calculate the coagulation rate constant, i.e. a stability criterion independent of test conditions. Conversely, if a stability constant for a given product is available, then the bath exhaustion and thus the suitability of the product for any desired process can also be computed.