Structural Basis for the Mechanical Properties of Polyethylenes.
Annual rept. Dec 81-Nov 82,
GAS RESEARCH INST CHICAGO IL
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The physical properties of polyethylene, the material used in gas transmission pipes, are ultimately determined by the nature of the polymeric molecules in the resin used in pipe manufacture. This relation between molecular structure and properties is based on the morphology formed in the polyethylene by a particular processing history. Model polyethylenes having very narrow molecular weight distributions and well defined levels of short chain branching and long chain branching have been used to quantify the effects of molecular structure on mechanical behavior. This first stage of the program has concentrated on true stress-true strain tensile properties and in the fracture toughness of single edge notched samples. It has been demonstrated that a critical molecular weight is required for the attainment of good ductility and fracture toughness. This critical molecular weight is increased by short chain branching and by long chain branching. The J-Integral method of analyzing fracture mechanics has been shown to be the best technique for inherently ductile polyethylenes. Measurements show 2.5-fold increase in fracture toughness over precisely the same molecular weight range at which tensile ductility is achieved. Further work will extend our studies to lower short chain branch concentrations with model polyethylenes directly analogous to the most satisfactory resins for gas pipe applications. jg p3
- Polymer Chemistry
- Atomic and Molecular Physics and Spectroscopy