Nonlinear Shear Relaxation Modulus for a Linear Low‐Density Polyethylene

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Abstract
The response of a polydisperse linear low‐density polyethylene to imposed step shear strains up to strains of 10 were measured. The measured stress is approximately factorable into a product of a time‐dependent term, which is just the linear relaxation modulus, and a strain‐dependent term, the damping function. The damping function can be fit by a simple analytic function derived from a molecular theory with a single ad hoc parameter ξ′; a larger value of ξ′ corresponds to more softening of the nonlinear modulus. A tabulation of ξ′ values from fits to experimental shear damping functions given here and published elsewhere indicates that ξ′ is decreased both by polydispersity and by long chain branching.

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