Oxygen permeability in thermoplastic polyurethanes

• Published in: Journal of polymer science. Part B, Polymer physics Polymer physics, 2012-05, Vol.50 (10), p.681-693
• Main Authors: Wang, Yuxin, Gupta, Mohit, Schiraldi, David A.
• Format: Article
• Language: English
• Subjects: Annealing; Applied sciences; diffusion; Diisocyanates; Exact sciences and technology; Miscellaneous; Organic polymers; Permeability; Phase transformations; Physicochemistry of polymers; Polyurethane resins; polyurethanes; Properties and characterization; Segments; structure-property relations; Thermoplastic resins; Urethane thermoplastic elastomers
• ISSN: 0887-6266; 1099-0488
• DOI: 10.1002/polb.23053

The thermal and oxygen transport properties of a series of thermoplastic polyurethanes (TPUs) based on 4,4′‐methylene diisocyanate (MDI) and 1,4‐butanediol (BD) as hard segments, and poly(tetramethylene glycol) (PTMG) or poly(butylene adipate) (PA) as soft segments, are studied. Oxygen permeabilities (P) of both polyester‐based and polyether‐based TPUs increase with decreasing hard segment fractions. Oxygen solubility (S) and diffusivity (D) can be derived from permeation curves. S correlates with the amount of excess free volume as determined by the difference between glass‐transition and testing temperatures (i.e., the degree of super cooling) and decreases with the increased Tg in polyester‐based TPUs. The intensity of low temperature gamma transition reflects the activation energy for D; the higher the intensity is, the lower D is annealed TPU samples exhibited higher oxygen permeabilities as well as lower storage moduli at room temperature, despite modest increases in overall crystallinity. Dedensification of the soft segment phase during annealing/crystalline phase growth is the most likely explanation for loss of mechanical and barrier properties after annealing as partially confirmed by Fourier transform infrared spectroscopy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 The oxygen transport phenomenon of thermoplastic polyurethane (TPU) can be interpreted by studying its permeability, diffusivity, and solubility. Solubility is a quotient of permeability and diffusivity, which can be derived from the steady state and the nonsteady state of a typical permeation flux curve respectively. TPU oxygen permeability is related to its chemical structures. By varying the soft segment species and its ratio to hard segment, TPU with desired oxygen permeability can be achieved.