Characterisation of the Rheological Properties of Melt-Spun Nylon 6 Fibres Produced for Industrial Applications in Kaduna State

Nylon 6 fibres produced by melt spinning are widely used in technical textile and industrial applications requiring high strength and chemical resistance. This study characterises the rheological properties of Nylon 6 polymer melt and the resultant fibre properties for industrially spun fibres manufactured in Kaduna State, North West Nigeria. Polymer samples were collected at different stages of the extrusion process and characterised using a capillary rheometer at shear rates ranging from 10 to 5000 s-1 and temperatures of 240, 260, and 280 degrees Celsius. Viscosity-shear rate relationships, die swell ratios, and activation energy of viscous flow were determined. Spun fibre samples were tested for linear density, tenacity, elongation at break, birefringence, and boiling water shrinkage to evaluate the relationship between melt rheology and fibre structural development. Results demonstrate that Nylon 6 melt exhibits pronounced shear-thinning behaviour, with apparent viscosity decreasing from 480 Pa.s at 10 s-1 to 32 Pa.s at 5000 s-1 at 260 degrees Celsius. Die swell ratio decreased with increasing shear rate, indicating elastic relaxation characteristics relevant to spinneret design. Fibres spun at higher take-up speeds showed improved tenacity and reduced elongation, consistent with greater molecular orientation. Boiling water shrinkage was highest at low draw ratios, suggesting incomplete orientation development. The study provides rheological reference data for optimising melt spinning conditions of Nylon 6 in North West Nigerian textile production facilities. Keywords: Nylon 6, melt spinning, rheology, fibre properties, Kaduna