On the formation of defects in drawn polypropylene fibres

Drawn polypropylene fibres were produced from as-spun fibres with a paracrystalline structure of low orientation. Drawing was carried out at 60 degrees C in order to prevent the transformation of the paracrystalline form into the monoclinic structure. The internal texture of the as-spun fibre and of a series of drawn fibres has been investigated by electron microscopy following permanganic etching. At draw ratios of 7 and above a series of transverse bands can be observed along the fibres. Homogeneous regions alternate with bands of defects which, after etching, appear as longitudinal cavities. Defect bands become more regular and increase in height with increasing draw ratio, lambda, occupying almost all the sample at lambda = 8.3. The nature of the defects, which are regions of reduced density, possibly voids, is discussed and a simplified model for their formation is suggested.