NEW ROUTE TO HIGH MODULUS POLYETHYLENE BY LAMELLAR STRUCTURES NUCLEATED ONTO FIBROUS SUBSTRATES WITH GENERAL IMPLICATIONS FOR CRYSTALLIZATION BEHAVIOR

In the case of recent experiments with polyethylene involving nucleation of lamellar crystals along flow induced fibrous substrates unexpectedly high modulus (up to 1011 N/m2) filaments were obtained in spite of the fact that the samples consisted predominantly of lamellar material. This finding has led to reconsideration of the requirements for high moduli in general providing explanation for our observation and indicating new routes for the attainment of high moduli. In brief, the principle is that high modulus need not require complete chain extension and can be generated by lamellar crystals. We identify the following conditions as necessary: (1) the lamellae are all parallel; (2) the plane normals are along the tensile direction; (3) the straight chain segments within the lamellae are also parallel to the tensile direction (hence perpendicular to the lamellar surfaces); (4) the lateral extension of the lamellae in all directions is large compared to the lamellar thickness; (5) there is intimate and strong contact between consecutive lamellae piled onto each other; (6) there is interlocking between lamellae in lateral contact. It is shown how and why these conditions are fulfilled by our lamellar samples of ultra-high modulus while additional reasons for the observed stiffness are being looked for. It is noticeable that samples based on lamellar morphology have advantages over the more usual high modulus material of purely fibrous nature as obtained along more conventional routes. The issue of modulus apart, the lamellae of tapering thickness in our samples (the morphological feature meeting requirement 6) imply the presence of folds of unprecedently short stem lengths which raise new issues in crystallization studies, notably relating to crystallization of chains in confined spaces, and opens up avenues towards the visualization of space filling by lamellae in bulk samples in general. © 1978.