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Yuan Q.,University of Sichuan | Zhou T.,University of Sichuan | Li L.,Jiangsu Subute New Materials Co. | Zhang J.,University of Sichuan | And 3 more authors.
RSC Advances | Year: 2015

Hydrogen bond breaking of TPU based on 4,4′-methylenediphenyl diisocyanate (MDI)/1,4-butanediol (BDO) upon heating was studied and elucidated from molecular movements and enthalpy. Two temperature regions of hydrogen bond breaking, region I (80-133 °C) and region II (133-169°C), were determined via the combination of PCMW2D correlation with FTIR and DSC. The method of calculating the enthalpy of the hydrogen bond breaking was established via Van't Hoff plots. We also proposed a method of calculating the relative content of different hydrogen bonds. In region I, ΔHh = 58.8 ± 0.5 kJ mol-1 for N-H and CO, and ΔHh = 37.2 ± 0.4 kJ mol-1 for N-H and C-O-C groups. The content of hydrogen bonds generated by N-H and CO is 88.4%, and that of N-H and C-O-C is 11.6%. In region II, ΔHh = 65.0 ± 1.1 kJ mol-1 for N-H and CO, and ΔHh = 73.0 ± 3.9 kJ mol-1 for N-H and C-O-C groups. The contents of these two hydrogen bonds are 71.2% and 28.8%, respectively. The surprisingly high value of ΔHh = 73.0 ± 3.9 kJ mol-1 for N-H and C-O-C in region II is actually due to the stabilizing effect of the repulsion energy on hydrogen bonds at the interface. 2D correlation analysis was used to investigate the sequential order of the groups' movement involved in hydrogen bond breaking. In region I, the breaking of a small amount of hydrogen bonds between N-H and C-O-C at the interface first occurs, and then the breaking of irregular hydrogen bonds between N-H and CO in the TPU hard blocks dominates, resulting in the melting of the imperfect crystallinity in the hard blocks. In region II, the breaking of regular hydrogen bonds between N-H and CO in the perfect crystalline of the hard blocks first occurs, and is then followed by hydrogen bond breaking of N-H and C-O-C enhanced by the repulsion energy at the interface, leading to the order-disorder transition (ODT) of TPU. © The Royal Society of Chemistry.2015. Source


Li L.,Jiangsu Subute New Materials Co. | Li L.,University of Sichuan | Zhou T.,University of Sichuan | Liu J.,Jiangsu Subute New Materials Co. | And 7 more authors.
Polymers for Advanced Technologies | Year: 2015

Polyoxymethylene (POM) fiber was produced by melt spinning with a high take-up speed, which imposed a strong flow field. An unexpected formation of a shish-kebab morphology with multiple shish of POM fibers was reported for the first time. This morphology is a large-scale shish kebab with a diameter of 10.5μm. Further orientation of the POM fiber was obtained by hot stretching twice at 160°C. Two crystalline morphology evolution processes were also observed: (i) the process from the large-scale shish-kebab to the deformed small shish-kebab and (ii) the process from the deformed small shish-kebab to the perfect whiskers. Compared with the melt spinning fiber, fiber tensile strength with first and second hot stretching increased by 976% and 1705%, respectively. The crystalline melting behavior of fibers significantly changes after the first and second hot stretching. The flow field induces a large number of extended chain crystals. Copyright © 2014 John Wiley & Sons, Ltd. Source

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