Deformation mechanism of high-density polyethylene probed by in situ Raman spectroscopy

The microscopic mechanism of high-density polyethylene under uniaxial drawing is investigated using in situ Raman spectroscopy. From the peak shifts of the symmetric and anti-symmetric C–C stretching modes, it is found that the load sharing on the polymer chain in the yielding region is anisotropic with stretching along the chain and compression perpendicular to the chain. The orientation functions (〈P2〉 and 〈P4〉) as well as the orientation distribution function (N(θ)) are determined from the polarized Raman spectra. The molecular orientation with cold drawing is found to proceed more effectively for lower crystallinity specimens. In the yielding region, it is also found that N(θ) has a maximum at the polar angle θ = 30–70°. This peculiar behavior in the microscopic scale is explained by the preferential collapse of spherulites and the existence of lamellar clusters as the bulky mobile units. [Display omitted] •In situ Raman spectroscopy is applied to investigate the deformation mechanism of the uniaxial cold drawing of HDPE.•The load sharing in the yielding region is anisotropic with stretching along the polymer chain and compression perpendicular to the chain.•In the yielding region, orientation distribution function shows a broad maximum in the intermediate direction (30–70°).