Blown films are often composed of blends of linear-low-density polyethylene (LLDPE) and low-density polyethylene (LDPE). The linear chains of the LLDPE component enhance the film solid-state performance while the nonlinear chains of the LDPE component enhance the blown-film fabrication performance. The compromise between solid-state and fabrication performance is dictated by the blend LDPE level. Often, LDPE is present as a minor component in order to optimize film mechanical performance while improving processability. The feasibility of using a melt rheology approach to assess the LDPE level in LLDPE+LDPE blends will be discussed. The approach focuses on the ability of the nonlinear chain architectures in LDPE, long-chain branches (LCB) in particular, to enhance the strain hardening material response during start-up of steady uniaxial extensional flow. The extensional strain hardening ratio (SHR), i.e., a measure of the deviation from linear viscoelastic (LVE) behavior capturing mainly the effect of LCB on the material response, is shown here to correlate with blend LDPE level for the selected set of LLDPEs and LDPEs. The observed trend is (i) monotonic, (ii) approximately linear, and (iii) with a slope that depends primarily on the LDPE component.

Assessment of a melt rheology approach to estimate composition in binary blends of linear-low-density polyethylene (LLDPE) and low-density polyethylene (LDPE)

ACS Spring 2022

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