No abstract

The structure-property relationship of highly oriented polypropylene (PP) blends were investigated. The as prepared blends consist of very thin sandwiched layers of both the components. After annealing the blends above the melting point of polyethylene (PE) and cooling them to room temperature, an increase in mechanical properties (Young's modulus, fracture stress) is observed. The synergisms of the mechanical properties are explained by a structural model based on transmission electron micrographs.

The relationship between the structural defects present in crystalline polymers and the molecular structure of the drawn material is studied by drawing fibers from irradiated polyethylene single crystals. Irradiation introduces a structural defect in the crystal lattice since it generates crosslinks preferentially, the density of which is controlled by the radiation dose. Observations by means of transmission electron microscopy and electron diffraction indicate that fiber drawing occurs by breaking off of single blocks of folded chains and by subsequent thermally activated rearrangement of the molecules in the drawn material. With increasing crosslink density the size of the blocks decreases, and the fibers become increasingly interconnected so that a network of fibers is formed. If the dose is about 10 Mrad, the crosslinks present in the crystals result in the formation of bundles of fibers. Above 35 Mrad the formation of fibers (single fibers as well as bundles) ceases, and the drawn material forms a thin (15 Å), continuous film. The observed change in morphology with increasing dose (crosslink density) is interpreted in terms of the additional bonding forces between adjacent chains due to crosslinks.