Plastic deformation of polypropylene

Abstract

In a wide range of drawing temperatures (20 to 150° C) and draw-ratiosλ (5 to 20) the axial long periodL T is a unique function of temperature. It is completely independent of the long period of the starting material which was varied within wide limits (125 to 350 A). The gradual transformation of the long period observed at small draw-ratio (λ between 1 and 5) from the valueL 0 of an undrawn sample to the limiting valueL T>L 0 of highly drawn polypropylene (λ ≥ 5) could be demonstrated on samples withL 0 larger thanL T. The change of long period is abrupt, indicating a discontinuous step in the transformation from the original microspherulitic into the fibre structure. These results may be interpreted in the same manner as in the case of polyethylene. During plastic deformation in the neck the lamellae are broken into small folded chain blocks which are then incorporated into the microfibrils, the basic building element of the fibre structure. The work of deformational forces must so mobilise the chains in the blocks that they get rearranged with a new long period, corresponding to the temperature of drawing.