The Fibrillar Structure of Melt Spun and Drawn PP Filaments

Abstract

A basic study of fibrillation and void development during drawing of melt spun polypropylene filaments is presented. The filaments are characterized by small angle x-ray scattering (SAXS), density, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), wide angle x-ray diffraction (WAXS), and birefringence. The latter two methods were used to characterize the molecular orientation produced by processing while SEM studies of peeled filaments revealed, qualitatively, the development of the fibrillated internal superstructure. The volume fraction of microvoids was computed from the intensity of SAXS and from a combination of DSC and density measurements. The microvoid fractions determined by these two techniques were in good agreement. The volume per cent of microvoids varied from 0.04 to 2.8%. It was found that the fibrillation observed qualitatively by SEM and the measured volume fraction and number density of microvoids increased with (i) increase in draw ratio, (ii) decrease in draw temperature, (iii) increased orientation of melt spun filaments, and (iv) increased molecular weight of the polypropylene. Using Guinier analysis of the SAXS data it was found that the voids had dimensions of 25–40 nm, parallel to the fiber axis and of order 15 to 30 nm perpendicular to the fiber axis. As the drawing temperature increased the SAXS void size increased and void number density decreased. The longitudinal mechanical properties of the fibers were found to be mainly a function of the orientation and were not very much affected by changes in fibrillation or void structure per se.

Influence of molecular weight distribution on the structure and properties of melt‐spun polypropylene filaments

“…More recent articles of interest include Bodaghi et al, 4 Fan et al, 5 Kloos;and Andreassen et aL7 In particular,Fan et al did the first study indicating the major signifi-cance of MWD on the structure and properties of polypropylene spun and drawn filaments. Both Kloos and Andreassen et al added some additional insights.…”

Structure–property relationship studies in amine functionalized multiwall carbon nanotubes filled polypropylene composite fiber

“…PP fiber has been conventionally used in carpet, non‐woven fabrics, and netting. Melt‐spun PP/CNT composite fiber (as‐spun) would require significantly higher PP chains orientation [2, 7–12] and the CNT orientation [13, 14] in the fiber axis direction in order to translate the unique properties of CNT into the composite fiber. However, mechanical properties (4.0 GPa tensile modulus of PP/single wall carbon nanotubes (SWNT) composite fiber at 0.8 wt% SWNT versus 4.2 GPa for control PP fiber) of SWNT filled PP fiber has been reported to show any significant improvement [15] despite the presence of highly oriented SWNT (orientation factor of 0.95) along the fiber axis.…”

On the overdrawing of melt‐spun isotactic polypropylene tapes

“…However, obtaining fibers/tapes with mechanical properties suitable for advanced engineering applications requires extending and orienting the molecules in an additional solid-state post-drawing operation. [9][10][11][12][13][14] In many studies the dependence of mechanical properties on the applied draw ratio is described for solid-state drawn fibrous structures. It is commonly concluded that stiffness and strength increase with increasing draw ratio, while elongation at break decreases.…”