A model for the spherulite‐to‐fibril transformation

Based on an analogy with the growth of kink bands in oriented and annealed crystalline polymers, a mechanism is suggested for the deformation‐induced spherulite‐to‐fibril transformation. Oriented and annealed material was employed as a model because it has roughly the same structure as the lamellar bundle of the spherulite. Under conditions that minimize the fibrillar quality and maximize the lamellar bundle quality, oriented and annealed crystalline polymers deform with the formation and growth of kink bands. The characteristics of kink bands are the sharpness of the kinks, occurring within zones ca. 100 Å wide, and mirror symmetry of the fibrils about the kink‐zone planes. The spherulite‐fibril transformation is suggested by analogy, then, to occur in the narrow zones that indeed are often found and to result in mirror symmetry of the chain axes about the transformation‐zone planes, which may not exactly occur because of a tendency for the tie molecules to be pulled from the lamellae during drawing. The implications for the transformation are (a) that the microfibril backbones are derived from the tie molecules between lamellae and (b) though some unfolding occurs as blocks that were adjacent within the lamellae become separated, the crystals remain mostly intact during the transformation. The analog is supported by or at least is consistent with various other results, including those from morphological and small‐ and wide‐angle x‐ray studies.