High-modulus, high-strength, thick polypropylene monofilament production: Response surface analysis approach

Response surface analysis was used in optimizing spinning and drawing conditions for the production of a high-modulus, high-strength, thick polypropylene (PP) monofilament. Rotatable octagonal central composite design was adopted with two independent variables (take-up velocity and draw ratio), and variations in the diameter, tensile modulus, and tenacity of the PP monofilament were observed. Quadratic response surface functions described the variations in those properties with quite high correlation coefficients. Canonical analysis combined with contour plots revealed the variation sensitivity: the diameter varied more markedly with the take-up velocity, and the tensile modulus varied somewhat equally with the two variables, whereas the tenacity varied more markedly with the draw ratio. From such contour plots, the optimum processing conditions for desired properties were predicted without intensive structural analysis. Case studies showed that under the suggested processing conditions, the PP monofilament fulfilled the property requirements, such as a tensile modulus of 10.4 GPa and a tenacity of 672 MPa with a diameter still above 400 μm.