GROWTH OF POLYETHYLENE SINGLE-CRYSTALS FROM THE MELT - CHANGE IN LATERAL HABIT AND REGIME I-II-TRANSITION

Using the technique of extraction, single crystals have been obtained from polyethylene fractions isothermally crystallized from the melt at atmospheric pressure. It has been found that the lateral habit of single crystals changes in the vicinity of the transition temperature of growth regime (regime I-II): lenticular shape elongated in the direction of the b axis (type A) in the range of regime I and truncated lozenge with curved edges of {200} and {110} growth faces (type B) in that of regime II. The transition of lateral habit causes a drastic change in the width of {110} growth faces; {110} growth faces are well developed in type B crystals while they cannot be observed and must be very small in type-A crystals. It has been shown that the growth regime of the small {110} growth face of type-A crystals must be in regime I; hence, the regime I-II transition can be explained as the result of this change in lateral habit (width of the {110} growth face).