Origin, morphology and crystallography of transcrystallinity in polyethylene-based single-polymer composites

Polyethylene-based single-polymer microcomposites were prepared and a transcrystalline layer was grown on the fibre surface by using different processing conditions, i.e. liquid nitrogen or ice-water quenching, air cooling and isothermal crystallization. The morphology of the transcrystalline layer obtained under each of these conditions was found to be governed mainly by the crystalline morphology of the matrix, which in turn was governed by the processing conditions of the composite. A smooth and banded transcrystalline morphology developed under ice-water quenching and air cooling conditions, respectively, corresponding to smooth and banded spherulites in the matrix. Under isothermal conditions, an apparent rod-like morphology was observed to develop in the matrix. Accordingly, the transcrystalline layer obtained under the same conditions exhibited a similar morphology. X-ray diffraction studies have shown that the crystal structure of all the observed morphologies was orthorhombic. The X-ray diffraction patterns revealed a significantly oriented crystalline structure in the transcrystalline layer, in contrast with the isotropic bulk matrix. The predominant orientation observed is such that the a-axis makes an angle of approximately 39° with the fibre axis and the b-axis is directed radially outwards from the fibre surface. A model was suggested which may be used to explain these results.