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Some Aspects of Thermal Stability and the Characteristics of Poly(ethylene terephthalate) (PET) under Stress
Author(s) -
Melinte Sofia,
Jeflea Alexandrina
Publication year - 2001
Publication title -
macromolecular materials and engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.913
H-Index - 96
eISSN - 1439-2054
pISSN - 1438-7492
DOI - 10.1002/1439-2054(20010301)286:3<196::aid-mame196>3.0.co;2-3
Subject(s) - materials science , birefringence , composite material , shrinkage , rheology , thermal stability , thermal , atmospheric temperature range , stress (linguistics) , thermodynamics , optics , chemical engineering , linguistics , philosophy , physics , engineering
In this work we use thermal shrinkage for estimating the internal stresses accumulated in a sample during a technological process. This can be a precious instrument available for every manufacturer interested in the thermal treatment efficiency. Based on the Kelvin‐Voight rheological model, we have established a correlation between the internal stresses appearing during the technological formation processes of yarns and their shrinkage at different temperatures. In this work (PET) fibers were used for study, with different birefringences ranging between 4.2×10 –3 –2.2×10 –3 . Thermal treatment was performed with warm air at temperatures between 333–453 K. The applied unitary stress changed within the range 5.09×10 10 –18.84×10 13 N·m –2 . From the examination of the curves obtained for free contraction Δ ε = f ( T ) for different birefringences Δ n for the preoriented PET fibers, contraction increases with increasing temperature up to a maximum situated at ≈ 353 K and then decreases to a constant value. From the examination of the curves, the dimensional change vs. contraction σ = f (Δ ε ), to a thermal treatment under stress for different birefringences Δ n , when an external stress σ is applied the thermal stability of the fibers already having on orientation, made evident by the birefringence magnitude, that in the case of a slight orientation, the retraction decreases with increasing temperature. Singular points registered for fibers with Δ n = 22×10 –3 for a temperature exceeding 393 K indicate that for the partially orientated fibers the sample is subjected to a stretching process during the thermal stability under stress. We established experimentally a correlation between the strain σ and Δ n , Δ n = ct. σ/T, i. e., a decrease of the birefringence with increasing temperature.