How Affine is the Entanglement Network of Molten Low-Density Polyethylene in Large Amplitude Oscillatory Shear?

1994 ◽  
Vol 116 (1) ◽  
pp. 14-18 ◽  
Author(s):  
A. J. Giacomin ◽  
R. S. Jeyaseelan
Keyword(s):  
Network Theory ◽  
Large Amplitude ◽  
Viscoelastic Behavior ◽  
Oscillatory Shear ◽  
Low Density Polyethylene ◽  
Low Density ◽  
Large Amplitude Oscillatory Shear ◽  
Chain Molecules ◽  
Oscillatory Shear Flow ◽  
Nonlinear Viscoelastic

The nonlinear viscoelastic behavior of molten plastics is often attributed to interactions between long-chain molecules. Entanglement theories model this behavior with a network of junctions. Whether this network deforms differently than the liquid is a question of considerable interest to polymer engineers since nonlinear viscoelasticity governs many plastics processing operations. In this paper, large amplitude oscillatory shear flow is used to measure how affine the network deformation is relative to the deforming melt. For a low-density polyethylene melt, a small amount of nonaffine network deformation is observed when the large amplitude oscillations are analyzed with a nonaffine structural network theory. Inaccurate predictions were obtained from both the nonaffine network theory due to Phan-Thien, and the nonaffine network strand theory due to Larson.

scholarly journals Viscoelastic Rheological Behaviors of Polypropylene and LMPP Blends

Polymers ◽  
2021 ◽  
Vol 13 (20) ◽  
pp. 3485
Author(s):  
Feichao Zhu ◽  
Sohail Yasin ◽  
Munir Hussain
Keyword(s):  
Large Amplitude ◽  
Viscoelastic Behavior ◽  
Nonlinear Behavior ◽  
Oscillatory Shear ◽  
Large Amplitude Oscillatory Shear ◽  
Mechanical Responses ◽  
Nonlinear Viscoelastic ◽  
Linear Viscoelastic ◽  
Viscoelastic Behaviors ◽  
Linear And Nonlinear

Dynamic oscillatory shear testing is used to investigate polymeric viscoelastic behaviors. Small and large amplitude oscillatory shear tests are the canonical method for characterizing the linear and nonlinear viscoelastic behaviors of any polymeric material. With prominent and abundant work on linear viscoelastic studies, the nonlinear behavior is evasive in terms of generating infinite higher harmonics in the nonlinear regime. For this reason, intrinsic nonlinearities from large amplitude oscillatory shear (LAOS) studies have recently been used for insights on microstructural behaviors. This study is carried out for linear and nonlinear viscoelastic behavior with a main focus on LAOS of isostatic polypropylene (iPP) and relatively new low molecular weight and low modulus polypropylene-based polyolefin (LMPP) blends. The morphological results showed reduced spherulitic crystal nucleus size and increased distribution in blends with increasing LMPP. The blends showed subtle linear viscoelastic responses with strong nonlinear mechanical responses to variant strain and stress compared to pure iPP. The intracycle strain thickening and intracycle strain stiffening of high-content LMPP blends were comparatively dominant at medium strain amplitudes.

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