Molecular mechanism of plastic deformation of polyethylene

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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 already undergone a substantial deformation by chain tilting and slip, and incorporated in the new fiber structure. In variance with drawing of single crystals, the plastic deformation of bulk samples adjusts the long period of folded chain blocks to the temperature of drawing so that the obtained value is a function of the latter, but very nearly independent of the long period of the sample before drawing. The amorphous regions of the drawn polyethylene contain a great many highly strained tie molecules with a lower entropy and heat content 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 experiment. Annealing lets the sample relax and return to thermodynamic equilibrium nearly instantaneously. The heat content, the diffusion, and sorption resume the values of the undrawn bulk material. The long period grows to the value which one would obtain if the original drawing were performed at the temperature of annealing.

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