Expanded PLA Bead Foaming: Analysis of Crystallization Kinetics and Development of a Novel Technology

• Main Author: Nofar, Mohammadreza
• Other Authors: Park, Chul B.
• Language: en_ca
• Published: 2012
• Subjects: Polylactide; Foaming; 0495
• Online Access: http://hdl.handle.net/1807/43677

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).