High modulus filaments of polyethylene with lamellar structure by melt processing; the role of the high molecular weight component

Abstract

In a previous work it was shown that, by appropriate melt processing, oriented filament polyethylene plugs could be produced such as possessed ultra-high modulus in spite of containing predominantly lamellar structures, the advantageous properties being due to the parallel and interlocking arrangement of the lamellae. In the present work it is demonstrated how the extreme high end of the molecular weight distribution is instrumental in the attainment of such structures. The longest chains, even if present in very small amounts, produce fibrous crystals during extrusion which are inadequate to influence the properties in themselves but by serving as nuclei for lamellar crystallization determine the detailed arrangements and hence the mechanical effectiveness of the lamellar texture. We show examples of how sensitively these structures and the resulting properties can be influenced by slight variations in the high molecular weight content of the material. In fact, materials which otherwise would not produce the desired effect can be made to do so through prior blending with a few percent of ultra high molecular weight material. By judicious creation of bimodal distributions, however, the previous batch production of high modulus plugs with lamellar structures can be turned into a continuous spinning process, thus for the first time achieving the production of oriented, high modulus filaments in the course of a single-step continuous extrusion.