Stress Relaxation in Polymer Melts Following Equibiaxial Step Strain

Abstract

The nonlinear equibiaxial relaxation modulus for two polymer melts, one with linear and one with branched structure, were measured using the technique of lubricated squeezing flow. The experimental technique was validated for Hencky strains up to ∼1.6 by demonstrating that results are independent of the lubricant viscosity and thickness. Time−strain factorability of the relaxation modulus was observed for both materials. The measured damping functions were compared with tube model (Doi−Edwards) and pom-pom model (McLeish−Larson) predictions. Damping function data for the linear polymer showed reasonably good agreement with the tube model predictions. The relaxation modulus and the damping function of the branched polymer showed significant differences from the pom-pom model predictions.

Improvement of Poly(ethylene terephthalate) Melt-Foamability by Long-Chain Branching with the Combination of Pyromellitic Dianhydride and Triglycidyl Isocyanurate

“…For the three PET samples with typical LCB-dominated rheological properties, FPET, PET-P1T5, and PET-P5T5, tensile-hardening behavior appeared. This behavior is well-known for its treelike branch-on-branch structure in LDPE, , confirming that PET-P1T5 and PET-P5T5 have a high degree of branching. By using a combination of PMDA and TGIC, the modified PET (PET-P1T5) without a cross-linked structure showed a strong strain-hardening behavior, which was expected for the continuous melt-foaming processes.…”

“…Molecular slippage was constrained by strong entanglements corresponding to the recoverable deformation, which led to a strong rubbery elasticity. 49 It was no longer able to rapidly relieve stress when sufficient branches were present, and slower events, such as arm retraction, occurred. The strong entanglements of FPET arose from its high molecular mass.…”

Equibiaxial elongational viscosity measurements of commercial polymer melts

“…The experiments have been performed on two different rheometer platforms. For the RSA3 (TA Instruments), which was used in previous studies , plate separation was governed by an input function such that the sample thickness decreased as h = h 0 exp(−2 t ). For the MCR 301 (Anton Paar), plate separation was specified by setting / h = 2 to a constant where = dh / dt .…”

Assessing 1,9-Decadiene/Ethylene Copolymerization with Ziegler–Natta Catalyst to Access Long Chain-Branched Polyethylene

“…Among them, free radical polymerization-produced PE resins, commercially dubbed low-density PE (LDPE), contain significant amounts of short- and long-chain branches (SCBs and LCBs) . The LCBs render LDPE resins with high melt strength and enhanced shear-thinning behavior and thus good processability . On the other hand, chromium (Cr)-based Philips catalysts and titanium (Ti)-based Ziegler–Natta catalysts produce high-density PE (HDPE) under much milder conditions (much lower temperature and pressure) .…”