Oxygen-barrier properties of cold-drawn polyesters

The improvement of oxygen‐barrier properties of glassy polyesters by orientation was examined. Poly(ethylene terephthalate) (PET), poly(ethylene naphthalate), and a copolymer based on PET in which 55 mol % of the terephthalate was replaced with bibenzoate (PET‐BB55) were oriented by constrained unia...

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Bibliographic Details
Published in:Journal of polymer science. Part B, Polymer physics Polymer physics, 2002-05, Vol.40 (9), p.862-877
Main Authors: Liu, R. Y. F., Schiraldi, D. A., Hiltner, A., Baer, E.
Format: Article
Language:English
Subjects:
Applied sciences
cold drawing
Exact sciences and technology
free volume
gas barrier
glassy state
Miscellaneous
Organic polymers
orientation
oxygen diffusion
Physicochemistry of polymers
poly(ethylene naphthalate)
poly(ethylene terephthalate)
poly(ethylene terephthalate-co-bibenzoate)
polyesters
Properties and characterization
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Summary:The improvement of oxygen‐barrier properties of glassy polyesters by orientation was examined. Poly(ethylene terephthalate) (PET), poly(ethylene naphthalate), and a copolymer based on PET in which 55 mol % of the terephthalate was replaced with bibenzoate (PET‐BB55) were oriented by constrained uniaxial stretching. In a fairly narrow window of stretching conditions near the glass‐transition temperature, it was possible to achieve uniform extension of the polyesters without crystallization or stress whitening. The processes of orientation and densification correlated with the conformational transformation of glycol linkages from gauche to trans. Oxygen permeability, diffusivity, and solubility decreased with the amount of orientation. A linear relationship between the oxygen solubility and polymer specific volume suggested that the cold‐drawn polyester could be regarded as a one‐phase densified glass. This allowed an analysis of oxygen solubility in accordance with free‐volume concepts of gas permeability in glassy polymers. Orientation was seen as the process of decreasing the amount of excess‐hole free volume and bringing the nonequilibrium polymer glass closer to the equilibrium (zero‐solubility) condition. Cold drawing most effectively reduced the free volume of PET‐BB55. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 862–877, 2002
ISSN:0887-6266
1099-0488
DOI:10.1002/polb.10149