posted on 2021-10-04, 18:39authored byJean-Mathieu Pin, Andrew Anstey, Markus Schubnell, Patrick C. Lee
The bead foaming of semicrystalline
polymers is a complex thermal
process involving the formation of multiple crystalline populations,
which serve the dual purposes of ensuring the structural integrity
of beads while also allowing bead sintering at the interface. The
quality of this “double melting peak” structure is determined
by the temperature and duration of the isothermal treatment of the
beads as well as the quenching rate following the isotherm. Currently,
the intricacies of the quenching process are not very well-known due
to the challenge of replicating these rapid cooling rates in a laboratory
setting. Fast-scanning calorimetry was used to reproduce these conditions
for isotactic polypropylene (iPP), revealing optimal quenching rates
for the bead foaming of iPP. We further probed these thermal features
using two-dimensional correlation analysis as a tool to understand
the dynamics, interdependence, and relative contributions of multiple
thermal events such as glass transition, mesophase formation, cold
crystallization, and melting in response to the perturbation of the
quenching rate.