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 degrees C due to the increased HS phase separation and crystallization mechanism in the presence of GMS and dissolved butane. (C) 2017 Elsevier Ltd. All rights reserved.