Study on die swell of cellulose diacetate spinning dope at the exit of regular triangular orifice

Abstract

Chemical fibers are typically spun with a spinneret, whose cross-sectional shape may be round, cross, trilobal, etc. On the contrary, cellulose diacetate (CDA) fibers used as cigarette tows are commonly spun with a regular triangular prism spinneret having a regular triangular cross-section because the cross-section of the spun cigarette tow is Y-shape owing to acetone solvent evaporation in the spinning column and the filter efficiency of the cigarette tow can reach the maximum value. However, previously CDA tows or fibers produced with such a regular triangular orifice were seldom reported. Many parameters influence the CDA tow spinning process with die swell being one of the most important factors. In this study, a model of a die swell was developed using rheological knowledge and second-type surface integrals. In order to confirm the validity of the model, the die swell of a CDA spinning dope at the exit of a regular triangular orifice was determined with a travelling microscope. Further, each parameter of die swell was studied. The apparent viscosity of the CDA spinning dopes was determined for different mass concentrations and temperatures with respect to shear rate and storage modulus and loss modulus with different mass concentrations and temperatures versus angular frequency were measured with a Physica MCR101 rheoviscometer. In addition, the flow rate was measured with a metering pump attached to the spinneret, and pressure drop was calculated from the above parameters. The results demonstrated that the die-swell ratio decreased when the dope temperatures were increased, but increasing trends were observed with dope concentrations and shearing rate. The experimental die-swell ratios were in good agreement with the calculated model results with less than ±6 % deviation. Therefore, this study can provide support for related CDA tows spinning studies.