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Abstract Different semicrystalline polymers including poly(l‐lactic acid), poly(ethylene terephthalate), syndiotactic polystyrene, and polyamide 12 are studied in terms of their mechanical response to uniaxial compression deformation. Apparent decoupling of yielding of amorphous and crystalline phases is identified as separate peaks in the stress–strain curve in the vicinity of the glass transition temperature. The same feature is also observed for the uniaxial extension of predrawn semicrystalline poly(ethylene terephthalate). It is indicated that in absence of a strong amorphous phase a semicrystalline polymer is unable to yield and undergo plastic deformation and it fails in a brittle manner in the uniaxial compression. Treating a semicrystalline polymer as a composite of amorphous and crystalline phases, putting emphasis on the crucial role of amorphous phase in acting as connectors between crystalline domains and indicating that the yielding of amorphous phase is a prerequisite for yielding of crystalline phase, work toward a better understanding of the mechanical properties of semicrystalline polymers at the molecular level is done.
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Mechanical properties of polymeric microfiltration membranes
The influence of the pore topology and polymer properties on mechanical characteristics of asymmetric polyethersulfone (PES) and symmetric polyvinylidene fluoride (PVDF) microfiltration membranes was investigated by conducting elongation, creep, stress relaxation, small-amplitude oscillatory and bubble point pressure tests. The main aspects of the membrane stress-strain curves were found to be similar despite significant differences in the pore topology and polymer properties. While the Kelvin-Voigt model for solid polymers described the membrane viscoelastic response below the transition to ductile yielding, the stress-strain curves of membranes and solid polymers above the yield point appeared to be drastically different. All tested membranes demonstrated weak strain hardening, low sensitivity to strain rate, significant elastic recovery, stress relaxation and reduction of the bubble point pressure with accumulation of plastic deformation. Therefore, tensile stresses exerted on a membrane under assembling and process conditions should be smaller than the yield stress to assure that they will not impair filter performance. The novelty of our approach is the use of models for perforated plates to evaluate membrane mechanical properties as ductile yielding for both proceeds via localized plastic deformation around pores. Presented results provide a reliable framework for development of membranes with properties tailored to applications.
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- Award ID(s):
- 1822130
- PAR ID:
- 10162179
- Date Published:
- Journal Name:
- Journal of membrane science
- Volume:
- 591
- ISSN:
- 0376-7388
- Page Range / eLocation ID:
- 117351
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.memsci.2019.117351
