Plastic deformation of polyethylene. Mechanism and properties

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Abstract
Studies of single‐crystal deformation explain the small‐ and wide‐angle x‐ray observations of the cold drawing of PE, particularly the effects in the necking zone where the original spherulitic structure is transformed into a highly aligned fiber structure. Whole blocks of folded chains are broken out of the original crystals, which have undergone a substantial deformation by phase transformation, twinning, chain tilting, and slip, and are incorporated in the new fiber structure. The latter contains a great many highly strained tie molecules with an entropy and heat content lower than in a completely relaxed supercooled liquid. Melting experiments yield the heat content reduction which is a consequence of more extended chain conformation (intramolecular energy) and of closer chain packing (intermolecular energy). The entropy and enthalpy reduction explains the drastic decrease of sorption and diffusion of solvents first observed in wide‐line NMR experiments. Annealing at sufficiently high temperature (118°C.) lets the sample relax nearly instantaneously. The long period, heat content, diffusion, and sorption assume values corresponding to the temperature of annealing. If the plastic deformation is performed at so high a temperature that annealing effects are not more negligible (hot drawing), the drawn sample still consists of highly oriented crystals but the molecules in the amorphous regions are rather relaxed so that their density, entropy, and heat content do not appreciably differ from the values of a supercooled liquid.

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