Structure of high-density polyethylene obtained by hydrostatic extrusion in solid state☆

A number of structural characteristics were calculated from X-ray diffraction patterns for high-density polyethylene obtained by hydrostatic extrusion at 393 and 353 K: dimensions of crystallites and X-ray long periods, the degree of crystallite orientation, total and fibrillar degrees of crystallinity (both volume and mass), weight fractions of intra- and inter-fibrillar amorphous interlayers. With increasing extrusion draw ratio the microfibrils become thinner and fuse, until alternating amorphous and crystalline lamellae oriented perpendicularly to the axis of extrusion are finally formed with a certain fraction of interlamellar interconnecting bridges. The observed increase of modulus with extrusion draw ratio at a given temperature is at first due to enhanced orientation of crystallites and increasing crystallinity, but in the later stages is connected with uniform distribution of load on all fibrils and interlamellar bridges.