Characterization of hard-segment crystalline phase of thermoplastic polyurethane in the presence of butane and glycerol monosterate and its impact on mechanical property and microcellular morphology

The effects of glycerol monosterate (GMS) and high-pressure butane on the phase-separation and crystallization of the hard segment (HS) of thermoplastic polyurethane (TPU) were investigated. Small and wide angle x-ray diffraction, polarized optical microscopy and atomic force microscopy were used to characterize the crystalline morphology of TPU under various conditions. Overall, 60% higher HS crystallinity was observed in TPU-GMS samples annealed with butane compared to the neat-TPU samples. The toughness and Young Modulus in the TPU-GMS samples were increased due to the higher HS crystallinity compared to the neat-TPU samples. The HS crystallites were effectively utilized as heterogeneous bubble nucleation sites to induce microcellular morphologies in the TPU microstructure. Compared to neat-TPU, the TPU-GMS microcellular morphology showed higher cell density over the wide saturation temperature of 150–170 °C due to the increased HS phase separation and crystallization mechanism in the presence of GMS and dissolved butane. [Display omitted] •Hard segment (HS) crystallized faster in TPU with presence of GMS.•Plasticizing butane significantly induced a large number of HS crystals in TPU.•HS crystallization reduced activation energy for bubble nucleation in TPU microstructure.•Microcellular TPU foams was achieved with butane due to HS crystallization.