Abstract
A fixture consisting of a bob and a special cup was developed to ease the charging of polymer melt to the gap of a concentric‐cylinder rheometer. Dynamic measurements with the improved rheometer for two polyolefins below melt temperatures were compared with results obtained on the Rheovibron and the torsion pendulum. Shear moduli were generated for polypropylene, polyethylene,and poly(vinyl chloride) melts by oscillating the bob in the axial mode at amplitudes effecting relatively large strain. Bob oscillations in the rotational mode were also investigated. The phase angles and complex shear moduli differed slightly for different modes of oscillation. At strains of 9%, the time‐temperature shift factor αT remained constant throughout the test‐frequency range for an isotactic polypropylene. However, αT increased with increasing frequency for strains of 98%. A time‐strain shift factor, αε, was found to satisfactorily superimpose polypropylene moduli data generated at high and low strain levels.
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