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

Abstract

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.

Clarification of the effects of topological isomers on the mechanical strength of comb polyurethane

“…These changes in the mechanical properties are attributed to the polymer topology which could influence complex factors such as entanglement, crystallinity, and morphology. [13][14][15] Among branched polymers, comb polymers have recently attracted attention for helping the understanding of the mechanical and rheological properties of the branched topology by the quantification of the molecular structure defined by the backbone length, side chain length, and grafting density. 1,15,16 The unified scaling model beyond the chemical structure can describe the rheological properties, such as the entanglement plateau modulus, 15,17 zero shear viscosity, 18 strain hardening factor, 18 and relaxation time, allowing the prediction of mechanical properties 19 in soft materials.…”

Raman Spectroscopic Analyses of Structure–Mechanical Properties Relationship of Crystalline Polyolefin Materials

“…For high-density PE (HDPE) with a crystallinity of more than 60 vol%, the values of 〈P 2 〉 and 〈P 4 〉 during the yield deformation are in the region (iv): the values of 〈P 4 〉 decrease in the yield region, whereas 〈P 2 〉 increases monotonously with increasing strain. This result suggests that the crystalline chains orient to the oblique direction (θ = 30-50°) even during uniaxial stretching [38][39][40][41] . Oblique orientation of the crystalline chains has been observed in both PE and PP 43) , and is caused by the suppression of the molecular orientation due to the excluded volume effect of the rigid and bulky lamellar structure 44) .…”

“…The crystalline chains orient markedly to the stretching direction beyond the yield point, whereas the orientation function of the amorphous chains immediately increases in the elastic region and reaches an asymptotic value in the strain-hardening region 37) . Kida et al measured the strain dependences of both orientation parameters and the orientation distribution function of crystalline chains during the uniaxial elongation of various PE samples [38][39][40][41] at various temperatures 42) . For high-density PE (HDPE) with a crystallinity of more than 60 vol%, the values of 〈P 2 〉 and 〈P 4 〉 during the yield deformation are in the region (iv): the values of 〈P 4 〉 decrease in the yield region, whereas 〈P 2 〉 increases monotonously with increasing strain.…”

“…3(c) 42) . Considering that α 1 relaxation corresponding to the intercrystalline relaxation is observed at around 60 ºC for PE 42,45,46) , the size of the fragmented lamellar crystals above 60 ºC is smaller than that be- (a) M w dependence 40) , (b) M w /M n dependence 41) , (c) temperature dependence 42) , and (d) ultra-low-density polyethylene (ULDPE) and PE gels comprising various fractions of liquid paraffin (LP) 39,47) .…”

ANM 2017: 1st International Conference on Advanced Polymer Materials

“…Takumitsu Kida et al . highlight in situ Raman spectroscopy study of ultra‐low‐density polyethylene (ULDPE) and investigated the microscopic deformation behavior under uniaxial stretching . They found that the crystalline chains of ULDPE showed a bimodal molecular orientation parallel and perpendicular to the stretching direction beyond the elastic region.…”