A relationship between extrudate swell ratio and entry stored elastic strain energy during die flow of tyre compounds

The elastic strain energy stored in the channel entrance flow and the extrudate swell ratios are important characteristics of elasticity during channel extrusion of polymer materials. There should be some form of relationship between them, especially in the case of the use of a short or mid-length die. The viscoelastic behavior and mechanisms in capillary extrusion flow of rubber compounds were investigated in the present paper. Under the operation conditions with temperature of 90 degreesC and apparent shear rate range of 10-10(3) s(-1), the rheological properties of two tyre compounds, cavity stock and buffer stock, were measured. It was found that the shear flow of both the tyre compounds obeyed the power law. and the non-Newtonian index values were close to each other. The entry pressure drop (DeltaP(0)), entry elastic stored energy (e) and die-swell ratio (B) increased roughly linearly with increasing shear stress at the channel wall. The B value for cavity stock was greater than that for buffer stock, whereas it was the reverse for DeltaP(en). Also, the correlation between the die-swell ratio and entry elastic stored energy is discussed. The results showed that B was a linear function of e. (C) 2003 Elsevier Ltd. All rights reserved.