Oriented crystallization in fiber formation: Inferences from the structure and properties of melt spun syndiotactic polypropylene filaments

In processes, such as melt spinning, the crystallization behavior of syndiotactic polypropylene (sPP) is found to be substantially different from that of most other linear polymers. The anisotropic stress field in such processes leads invariably to extension as well as alignment (orientation) of the chains in the melt, both of which contribute usually to dramatic enhancement in the rate of crystallization. However, since the primary structure of the sPP chain in its most preferred crystal form is comprised of a “coiled helical,” (T₂G₂)₂, sequence, stress-induced chain extension can lead to conformational sequences that are not favorable for crystallization in this form. As a consequence, process conditions that generate higher stress levels can cause a diminution in the rate of crystallization of this polymer. Such conformation-related aspects of oriented crystallization of sPP have been addressed through an analysis of the structure and properties of melt-spun fibers, produced over a range of spinning speeds. The results serve to identify a refinement that is needed in current models of oriented crystallization and also a mechanism to promote the nucleation of crystallization of sPP. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2305–2317, 2001