High modulus polypropylene fibers. I. Mechanical properties

Extensive studies concerning the spinning and drawing of polypropylene resulted in a method for production of high modulus fibers under industrially feasible conditions. The fibers were produced in a conventional melt spinning and drawing process that was optimized in order to increase the elastic modulus of fibers. By such optimization of the process, a tensile strength of around 8 cN/dtex, an elastic modulus up to 14.7 GPa, and a dynamic modulus up to 19 GPa were attained. In this study the mechanical properties of polypropylene fibers were investigated, which were spun from fiber grade controlled rheology (CR) polymers and from the blends of a fiber grade CR polymer with a molding grade polymer in the composition range of 10-50 wt %. The addition of the molding grade polymer to the fiber grade CR polymer resulted in lower tensile strength and moduli, with one exception. By blending a CR polymer with 10% of the molding grade polymer, maximization of the elastic and dynamic modulus was achieved. The predicted modulus of a two-phase blend, calculated from several representative equations, was compared with the elastic modulus of drawn fibers, determined from the specific stress versus strain curve, and the dynamic modulus, obtained from the sound velocity measurements. The best fit was achieved with the Kleiner simplex equation. (c) 2005 Wiley Periodicals, Inc.