TIT# Melting and solidification of thermoplastic polyurethanes as a function
     of nucleating agents
AUT# Stribeck, Almut; Eling, Berend; Pöselt, Elmar; Malfois, Marc; Schander, Edgar;
SOU# Nano Select (2022), 3(3), 673-687 
DOI# 10.1002/nano.202100219
LOC# xv163 @ xv163.pdf
CLA#
COM#
APP#
MAT#
ABS# The solidification of two thermoplastic polyurethanes (TPU) appears as a
     two-stage segregation (large-scale allocation of hard-phase entities, 
     short-scale granulation in the allocated entities). Following 
     consolidation may raise the hard-phase fraction. Mechanical stability 
     requires the granular morphology. Good nucleating agents (NA) raise the
     solidification temperature and shorten the lifetimes of allocation and
     granulation. They can suppress consolidation. Shorter allocation causes
     lower hard phase fraction, shorter granulation means earlier transition
     to the solid. Annealed materials have much higher hard phase contents and
     a morphology of more uniform hard domains in a more regular arrangement. 
     Both TPUs have a hard segment content of ≈30% but different soft segments
     (polyether, polyester). Samples are injection-molded and annealed. 
     Melting-and-solidification experiments ( |𝑇̇ |=20Kmin−1, 𝑇max=220∘C, Δ𝑇=1K) 
     are monitored by small-angle (SAXS) and wide-angle X-ray scattering. Three
     NAs contain resonating aromatic structures, the fourth is talc. NAs do not
     affect the melting of polyether TPU, but some NAs raise the melting point
     of polyester TPU considerably. SAXS chord-distribution analysis reveals 
     that the region of the melt is framed by segregation peaks. There, the mean
     chord lengths of the hard phase are the longest and the width of the
     distributions changes the fastest.