Rheological characterization of the die swell phenomenon of rubber compounds

The die swell phenomenon of rubber compounds in capillary experiments with various ratios of length to diameter of capillaries is investigated. This knowledge is important for the design of injection heads for the extrusion of rubber profiles. The die swell of viscoelastic rubber compounds depends on the geometry of the capillary dies, on the melt temperature and on the shear strain rate. One empirical relationship will consider all these dependencies. Usage of this equation and identification of only one new material parameter enables the comparison and assessment of the die swell of different materials, independently of the corresponding geometry of the capillary die used. Furthermore, the influence of melt temperature, molecular structure and extrusion process on the die swell can be identified. The investigation was performed with various rubber compounds as well as rubber blends used in industry, mainly EPDM and carbon black in different compositions.