Orientation of polymer molecules during melt spinning. II. Orientation of crystals in as‐spun polyolefin fibers

Abstract

AbstractThree different polyolefins, a linear polyethylene, an isotactic polypropylene, and an isotactic polybutene‐1, were melt‐spun into filaments. The degree of orientation of the filaments was measured by polarized‐light microscopy, x‐ray diffraction, and a retraction technique, and the results were then related to the melt‐draw ratio. The increase in the elastic deformation ratio of polymer chains by spin‐stretching, estimated by thermal retraction at a temperature above Tm, was monotonic with respect to the melt‐draw ratio. On the other hand, as‐spun filaments of polyethylene and polypropylene were characterized by a plateau in birefringence over the range of melt‐draw ratios from 8 to 80. The change in orientation functions for crystals in these filaments was similar to the change of birefringence. On the other hand, the birefringence and the crystalline orientation functions for polybutene‐1 increased smoothly with increasing melt‐draw ratio. The most highly melt‐drawn filaments of these polymers had a strongly oriented structure, corresponding to that in highly cold‐drawn specimens.