The effect of molecular weight on the physical and mechanical properties of ultra-drawn high density polyethylene

A study has been made on the effects of molecular weight on the physical and mechanical properties of cold-extruded high density polyethylene. Prior data indicate that such ultra-drawn strands contain a significant fraction of extended-chain crystals. Four samples, spanning the molecular weight range of 59,000 to 147,000, were cold-extruded under the same conditions and were examined with respect to their melting point, degree of crystallinity, linear expansion coefficient, Young' modulus, strain to break, and tensile strength. The degree of crystallinity, linear expansion coefficient, and modulus did not change significantly with molecular weight. The melting point, strain to break, and tensile strength do increase with increasing molecular weight. This leads to the conclusion that the amount of extended-chain crystals is invariant with molecular weight. Higher molecular weight polymers are seen as providing a greater number of the chains, thus giving the fiber a higher tensile strength.

[1]  R. Stein.  Deformation mechanisms of polyethylene , 1972 .

[2]  R. H. Peters,et al.  Morphology of cold-drawn high-density polyethylene fibres , 1974 .

[3]  Roger S. Porter,et al.  Polyethylene crystallized under the orientation and pressure of a pressure capillary viscometer. Part I , 1970 .

[4]  M. Takayanagi,et al.  Crystal orientation and some properties of solid-state extrudate of linear polyethylene , 1971 .

[5]  P. Flory.  Thermodynamics of Crystallization in High Polymers. IV. A Theory of Crystalline States and Fusion in Polymers, Copolymers, and Their Mixtures with Diluents , 1949 .

[6]  N. E. Weeks,et al.  Unique polyethylene morphologies produced under extrusion conditions , 1972 .

[7]  A. Peterlin,et al.  Molecular model of drawing polyethylene and polypropylene , 1971 .

[8]  R. Porter,et al.  The properties of polyethylene crystallized under the orientation and pressure effects of a pressure capillary viscometer , 1970 .

[9]  L. A. Davis.  Hydrostatic extrusion of solid polyethylene , 1974 .

[10]  I. Ward,et al.  Preparation of ultra-high modulus linear polyethylenes; effect of molecular weight and molecular weight distribution on drawing behaviour and mechanical properties , 1974 .

[11]  N. Capiati,et al.  Tensile properties of ultradrawn polyethylene , 1975 .

[12]  I. Ward,et al.  The cold-drawing of high density polyethylene , 1970 .

[13]  F. E. Karasz,et al.  The Influence of Stereoregularity on the Glass Transition Temperatures of Vinyl Polymers , 1968 .

[14]  N. E. Weeks,et al.  Polymer modulus and morphology: The tensile properties of polyethylene , 1975 .

[15]  L. Scott,et al.  Superdrawn crystalline polymers: A new class of high‐strength fiber , 1974 .

[16]  I. Ward,et al.  Ultra-high-modulus linear polyethylene through controlled molecular weight and drawing , 1975 .

[17]  A. Peterlin.  Morphology and Properties of Crystalline Polymers with Fiber Structure , 1972 .