Polarization sensitive THz absorption spectroscopy for the evaluation of uniaxially deformed ultra-high molecular weight polyethylene

Mechanically extensional-deformation of ultra-high molecular weight polyethylene (UHMWPE) was examined by using polarization terahertz (THz) spectroscopy as well as X-ray diffraction (XRD) analysis. Due to the B_1u lattice translational mode, a THz absorption band was observed around 2.2 THz. The band intensity of the non-deformed UHMWPE is isotropic. For deformed UHMWPE, the dichroism appeared in the 2.2 THz band. The absorption intensity was smaller in spectra in which the THz wave electric polarization direction was parallel to the deformation direction than that in which the polarization was perpendicular. The intensities in each polarization direction are dependent on the amount of elongation strain. Based on the influences drawn from the THz and XRD results, THz non-destructive diagnosis of the tensile strain in deformed UHMWPE is proposed based on the dichroism of B_1u band intensities observed in polarization THz spectroscopy.