Processing, structure, and mechanical properties of as-spun polypropylene filaments - A systematic approach using factorial design and statistical analysis

Polypropylene filaments spun under a factorial experimental design were characterized with respect to filament tenacity, elongation, and specific secant modulus. These quantities were assessed quantitatively as responses to seven selected processing parameters using standard statistical methods. It was found that among all the significant factors identified, the draw-down ratio, which combines metering pump speed (MPS) and filament winding speed (WS), exerts the most significant effects on all the three responses. The grade of polypropylene used, as denoted by its melt flow index (MPI), also significantly influences tenacity and modulus. Spinning temperature, too, influences modulus. In addition, the significant influence of two interaction effects, MPS*WS and MFI*WS, is demonstrated. A further feature of the study is systematic correlation of physical properties with microscopic structure as well as processing conditions. The study has demonstrated that the statistical approach to the development of fiber process technology has the advantages of a one-step overall design, considerably reduced experimental size, and systematic analysis leading to concise models with known levels of confidence. © 2005 Wiley Periodicals, Inc.