| Summary: | Bead foam technology with a double crystal-melting peak structure has been well
established for polyolefins. The double crystal melting peak structure, which is required in the
molding stage of the bead foams, generates a strong sintering among the foamed beads and
maintains the overall foam structure. In this research, despite the PLA’s poor foaming behavior
and its slow crystallization kinetics, we successfully developed expanded PLA (EPLA) bead
foams with double crystal melting peak structure and the inter-bead sintering behavior was
verified through steam chest molding. For this purpose, the generation and evolution of double
crystal melting peak structure in different PLA materials is simulated in a high-pressure
differential scanning calorimeter (HP-DSC). The simulation results shows that the formation of
double crystal melting peak with different peak ratios can be controlled by varying the
processing parameters (i.e., saturation pressure, temperature, and time) during the saturation. The
PLA bead foams characterization showed that the high melting temperature crystals generated
during the saturation and the low melting temperature crystals formed during the cooling and
foaming can significantly affect the foaming behavior of PLA bead foams. Moreover, the
crystallization kinetics of different PLA materials are systematically investigated in presence of
dissolved gas. It is shown that the different crystallization kinetics (i.e., crystal nucleation and
growth rate) that can be induced at various gas pressures can significantly influence the PLA’s
foaming behavior (i.e., cell nucleation and expansion behavior).
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