Effect of Growing Crystalline Phase on Bubble Nucleation in Poly(L-Lactide)/CO2 Batch Foaming

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• 作者：Kentaro Taki ; Daisaku Kitano ; Masahiro Ohshima
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2011
• 出版时间：March 16, 2011
• 年：2011
• 卷：50
• 期：6
• 页码：3247-3252
• 全文大小：841K
• 年卷期：v.50,no.6(March 16, 2011)
• ISSN：1520-5045

文摘

Creating a high-efficiency bubble nucleation agent for a polymer foaming process is essential for increasing bubble density as well as decreasing bubble size. Spherulites (crystalline phase) grown in a semicrystalline poly(L-lactide) (PLLA) matrix enhanced carbon dioxide (CO₂) bubble nucleation in a batch foaming process. Several sites for PLLA spherulite formation were observed at a hold-temperature of 110 掳C after CO₂ saturation in molten PLLA, which was heated to 180 掳C at 11 MPa. By depressurizing the system from 11 MPa to atmospheric pressure, the dissolved CO₂ in the PLLA matrix became supersaturated, and CO₂ bubbles nucleated around growing PLLA spherulites. The number of nucleating bubbles increased as a function of increasing spherulite quantity and area. A faster linear spherulite growth rate and a lower hold-temperature created more bubbles around the spherulites. From these observations, it was concluded that the growing spherulites expelled CO₂ from the advancing spherulite鈭抋morphous phase interface and that CO₂ accumulated at the interface. Then, the increase in the concentration of CO₂ led to an increase in the nucleation of bubbles around the spherulites.