Rheo‐optical studies of the nature of the α mechanical loss mechanism of polyethylene

Abstract

Abstract Dynamic x‐ray diffraction and dynamic birefringence techniques are employed to determine the nature of the molecular motions associated with the α mechanical loss processes for low‐density polyethylene. The results indicate that the low‐temperature part of this loss (designated α 1 ) is associated with an interlammellar “grain boundary” slip process while the higher temperature process (α 2 ) involves intracrystalline motion and plasticity of the crystal itself. The activation energy for α 1 determined by x‐ray response is 25–30 kcal/mole, while that for α 2 is 30–60 kcal/mole. The findings are consistent with dynamic infrared and dynamic light‐scattering results which indicate that the motion of amorphous chains is closely correlated with that of the crystals. The relative contributions of amorphous and crystalline regions to the birefringence are dependent on the thermal treatment of the sample. The effect of static strain on the dynamic response indicates that crystal orientability is first increased with strain, probably because of splaying apart of lamellae, is subsequently decreased because of the restrictions of interlamellae tie chains, but then increases again as the spherulites are destroyed at high strain. The static strain reduces the orientability of amorphous regions.