Abstract We studied poly(lactic acid)’s strain-induced crystallization behavior during a tandem extrusion process using visualization techniques. Our visualization results showed that, despite its inherently slow crystallization kinetics in the quiescent condition, PLA crystallites were quickly formed inside the die at a temperature even above the melting temperature (T m ), as the melt temperature was decreased. Their rapid formation at a high temperature above the T m peak, was due to the strain-induced crystallization. We also studied how the strain rate and the use of supercritical CO 2 affected PLA crystallization. A significant increase in the PLA crystallization kinetics was caused by a sudden increase in the screw speeds of the extruders with a fixed barrel temperature. The crystallization enhancement, which was caused by the increased flow rate, became more pronounced at lower temperatures due to the higher degree of molecular orientation. Adding the CO 2 shifted the crystallization temperature to a lower processing temperature due to its plasticization effect, but it accelerated the crystallization kinetics as well. We also observed a correlation between the content of the induced crystallites inside the extruder and the cellular structure of the extruded foams. This clearly explained the decrease in the optimal processing temperature for foaming with an increased CO 2 content.

中文翻译：

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PLA 结晶和结晶对挤出发泡的影响的原位可视化

摘要 我们使用可视化技术研究了串联挤出过程中聚乳酸的应变诱导结晶行为。我们的可视化结果表明，尽管在静止条件下其固有的结晶动力学缓慢，但随着熔体温度的降低，PLA 微晶在甚至高于熔化温度 (T m ) 的温度下在模具内迅速形成。它们在高于 T m 峰的高温下快速形成，是由于应变诱导结晶。我们还研究了应变速率和超临界 CO 2 的使用如何影响 PLA 结晶。PLA 结晶动力学的显着增加是由在固定机筒温度下挤出机的螺杆速度突然增加引起的。结晶增强，由于较高的分子取向度，这由流速增加引起，在较低温度下变得更加明显。由于其塑化作用，添加 CO 2 将结晶温度转移到较低的加工温度，但它也加速了结晶动力学。我们还观察到挤出机内诱导微晶的含量与挤出泡沫的多孔结构之间存在相关性。这清楚地解释了随着 CO 2 含量增加，发泡的最佳加工温度降低。但它也加速了结晶动力学。我们还观察到挤出机内诱导微晶的含量与挤出泡沫的多孔结构之间存在相关性。这清楚地解释了随着 CO 2 含量增加，发泡的最佳加工温度降低。但它也加速了结晶动力学。我们还观察到挤出机内诱导微晶的含量与挤出泡沫的多孔结构之间存在相关性。这清楚地解释了随着 CO 2 含量增加，发泡的最佳加工温度降低。