TIT# Scattering of X-rays during melting and solidification of thermoplastic
     polyurethane. Graphite as nucleating agent and stabilizer of the
     colloidal melt
AUT# Stribeck, Almut; Dabbous, Raphaël; Eling, Berend; Pöselt, Elmar,
     Malfois, Marc; Schander, Edgar;
SOU# Polymer (2018), in print
DOI# 10.1016/j.polymer.2018.08.058
LOC# xv161
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ABS# Melting and solidification of thermoplastic polyurethanes (TPU) are 
     monitored by X-ray scattering. The colloidal character of the typical 
     material becomes unstable as soon as the hard domains (HD) are molten. Then 
     the scattered intensity fluctuates considerably and “lost” photons are 
     found at small scattering angles (Tyndall effect). In this temperature 
     regime the material is a fluid. Competing homogenization and segregation
     processes appear to take place, which modulate the materials colloidal 
     character. Monitored by SAXS and WAXS, TPU elastomers are melted and 
     re-solidified (heating rate: 20 K/min, temperatures Tmax: 220 °C, 190 °C). Strong fluctuations in scattering
     intensity due to varying Tyndall effect are observed in most of our 
     experiments. Here the typical effects are demonstrated on a polyether-based 
     TPU with a hard segment content of 30%, whose colloidal melt is stabilized 
     by adding 0.5% graphite. In the hot quiescent melt the morphology is 
     characterized by density undulations. HD arrangement does not grow late. 
     Graphite stabilizes the colloidal melt. It increases both the HD melting-
     temperature (from 185 °C to 210 °C) and the HD formation temperature
     (from 90 °C to 165 °C).