Oxygen permeability in thermoplastic polyurethanes

Abstract

The thermal and oxygen transport properties of a series of thermoplastic polyurethanes (TPUs) based on 4,4 0methylene 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 polyetherbased 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 glasstransition and testing temperatures (i.e., the degree of super cooling) and decreases with the increased T g in polyesterbased TPUs. The intensity of low temperature gamma transi-tion 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. V C 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 50: 681-693, 2012

The influence of thermo-mechanical history on structure development of elastomeric and amorphous glass thermoplastic polyurethanes

“…Thermal as well as flow histories can greatly affect the micro-aggregation structure and properties of TPUs [2][3][4][5][6]. Much effort has been spent on investigating thermal transitions and morphological changes in TPUs using different experimental techniques such as differential scanning calorimetry (DSC) [2,4,5,[7][8][9], infrared spectroscopy [2,10], X-ray scattering [7,[10][11][12][13][14], and nuclear magnetic resonance spectroscopy [2,5,13]. Some relatively recent studies [4] have shown that rheology is also a very sensitive tool to investigate the microstructural changes taking place during the phase transition stages.…”

Influence of different β-nucleating agent on crystallization behavior, morphology, and melting characteristic of multiwalled carbon nanotube-filled isotactic polypropylene nanocomposites

“…Zhang et al [43] found the polymor-phic composition of MWCNT filled iPP nanocomposites nucleated by WBG was adjusted by varying the mass proportion of MWCNT/WBG. Wang et al [44] verified the enhanced nucleating ability of the MWCNT-supported b-nucleating agent, which greatly improved the impact toughness without significantly deteriorating the strength and stiffness of the iPP composites.…”

“…Therefore, the preparation, physical and mechanical property of b-nucleated iPP [18][19][20][21][22][23][24][25][26][27][28][29][30] and its composites [31][32][33][34][35][36][37][38][39][40][41][42] have been very active research fields over the last decade. Although some researchers observed that addition of CNT can induce the formation of a little b-form of crystalline iPP, the CNT filled b-iPP nanocomposites containing high content b-crystal have little been reported [43,44]. Zhang et al [43] found the polymor-phic composition of MWCNT filled iPP nanocomposites nucleated by WBG was adjusted by varying the mass proportion of MWCNT/WBG.…”

Polyurethane/clay nanocomposites with improved helium gas barrier and mechanical properties: Direct versus master‐batch melt mixing route

“…Generally, gas barrier property of TPU improves with increasing hard/soft segment ratio, crystallinity, glass‐transition temperature ( T g ), orientation and packing of polymer chains, and crosslinking density. Many literature discuss improvement in gas barrier property of TPU by changing its structure and morphology via changing the raw materials, their compositions and process conditions.…”

“…A good gas barrier property is needed for some special applications such as coated or laminated envelop for inflatables, transparent and flexible packaging, sport balls, biomimetic materials, pneumatic tires, corrosion resistant coatings, and many others, where polyurethane-based coatings or films are frequently used. [3][4][5][6] Therefore researchers have used many approaches for improving gas barrier property of polyurethane, like modifying structure-morphology [7][8][9][10][11][12] or incorporating nanoplatelets such as nano-clay 11,[13][14][15][16][17] or graphene 18,19 in TPU matrix. TPU/clay nanocomposites exhibit enhanced mechanical as well as gas barrier properties in comparison to neat polyurethane.…”