Size and orientation of cristallites in lightly cross‐linked polyethylene, crystallized from the melt under uniaxial compression

If lightly cross‐linked polyethylene films are crystallized from the melt under uniaxial compression, a very unique alignment of the molecular chains in the crystalline phase of the samples appears. The orientation of crystallites in which the (200) crystal plane is located parallel to the film surface first appears at a relatively low degree of compression, and subsequently the orientation in which the (110) crystal plane is located parallel to the film surface follows at higher degrees of compression. Despite the fact that the samples were crystallized from the melt rather rapidly, the unitcell density of the crystalline phase was very close to unity and the size of crystallites was very large. The dimensions of crystallites in the direction perpendicular to the film surface were in a range of 170—350 Å but they were as large as more than 1500 Å in the direction parallel to the film surface. Thus it is confirmed in addition by electron microscopic observation that these samples have a new type of lamellar structure in which the molecular alignments are quite different from those for the so‐called lamellar structure for polyethylene crystallized under isotropic conditions.