A quantitative model describing physical aging in isotactic polypropylenes |
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Authors: | S Hellinckx |
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Institution: | (1) Physique des Matériaux de Synthèse 194/8, Université Libre de Bruxelles, 50 avenue F. Roosevelt, 1050 Bruxelles, Belgium |
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Abstract: | Physical aging of isotactic polypropylenes (homopolymer and random ethylene-propylene copolymer) at room temperature is investigated by low-strain creep, damping measurements, differential scanning calorimetry, and infra-red spectroscopy. Examination of the results suggests that physical aging produces a decrease of the magnitude of the -relaxation (lower glass transition) and an increase of the magnitude and of the relaxation time of the -relaxation (upper glass transition). A model is proposed that accounts for the variations of the fractions of amorphous material which undergo these relaxations. In this model, deformation and increase in the -fraction at the expense of the -fraction are expected to be diffusion processes. The agreement with experimental data is good. Moreover, the -form is shown to be an amorphous phase rich in molecular segments having a helical conformation. |
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Keywords: | Isotactic PP physical aging low-strain creep magnitude of and gif" alt="beta" align="MIDDLE" BORDER="0"> and relaxations" target="_blank">gif" alt="agr" align="BASELINE" BORDER="0"> relaxations amorphous forms |
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