Rheo‐Raman spectroscopic study of microscopic deformation behavior for ultra‐low‐density polyethylene

In situ Raman spectroscopy was applied to ultra‐low‐density polyethylene (ULDPE) to investigate the microscopic deformation behavior under uniaxial stretching. It was found that the crystalline chains of ULDPE show a bimodal molecular orientation parallel and perpendicular to the stretching direction beyond the elastic region. The peak shifts of C − C stretching modes of the crystalline chains obviously depend on the polarization direction, suggesting that the microscopic load sharing is anisotropic. Whereas the stretching stress is applied on the crystalline chains oriented in the stretching direction, the compression stress is applied on those oriented perpendicular to the stretching direction. This anisotropic load sharing is caused by the Poisson shrinkage of the specimen owing to the rubber‐like properties of ULDPE. © 2018 Society of Chemical Industry The microscopic load sharing of ULDPE is anisotropic in the highly strained region, which results from Poisson shrinkage of the specimen owing to the rubber‐like properties of ULDPE.