Thermal properties
DSC curves of SMPU pellet and nanowebs show inflection
points at 25.3 and 29.3C, respectively (Figure 3),
corresponding to the Tg of their soft segments. Chung
et al.1 reported that the orientation of the soft segments
developed due to elongation during spinning so as to
increase the melting heat and Ttrans. Therefore SMPU
nanowebs showed slightly higher Ttrans than PU polymers
due to elongation. Table 1 lists the SMPU nanoweb
shape retentions at around the Ttrans. A wide
temperature range of changes was shown for fixing
and recovery around the Ttrans. Debdatta et al.10
reported an advantage of the Ttrans being the glass transition
temperature of the soft segments: energy can be
stored elastically. A disadvantage is that control of
Ttrans is not easy and the transition range is wide.
The range of changes during differential scanning
calorimetry was much wider than that of a material
with a Ttrans of the melting point of the soft segments
because the Ttrans of MM3520 was the glass transition
temperature of the soft segments. The SMPU nanowebs
showed wider ranging temperature changes than
MM3520.