Static and dynamic deformation mechanisms of a high-density polyethylene having rownucleated crystalline texture of a-axis orientation as observed by orientation distribution function of crystallites

The rheo-optical properties of a high-density polyethylene having a row-nucleated crystalline texture of a-axis orientation were investigated in the machine direction (MD) and transverse direction (TD) of fabricating the specimen. The tensile complex dynamic compliance function $\text{J1}$ displays two dispersions designated as the α₂ and α₂ mechanical retardation processes with activation energies of about 21 and 35 kcal mol^?1, respectively, for both MD and TD specimens, and the complex dynamic stress-optical coefficient function $\text{M1}$ exhibits a single discrete dispersion designated as the α optical retardation process with an activation energy of about 24 kcal mol^?1 for both specimens over the same frequency and temperature ranges as those covered for the dynamic mechanical measurements. The real and imaginary components of $\text{M1}$ converge from positive values to almost zero at the highest frequencies and lowest temperatures covered for both specimens, with the exception of the real component of the MD specimen which converges to a small but definitely negative value. The analysis of this anomalous behaviour of the MD specimen in terms of the optical retardation time spectrum has ascribed the negative convergence to a negative form birefringence that arises from a dynamic lamellar splaying or bending process responding in phase with the dynamic bulk stress. The dynamic X-ray diffraction studies have revealed the α optical dispersion and possibly the α mechanical dispersion to be mostly attributed to the crystal orientation dispersions involving intralamellar shearing processes, i.e. detwisting and tilting processes of the lamellar segments for the MD and TD specimens, respectively. The optical dispersion, if any, associated with the lamellar splaying or bending process may be expected at higher frequencies or lower temperatures than those covered here to assign the β mechanical dispersion to the interlamellar shearing process.