This work focused on the determination of crystallization kinetics of neat polylactide (PLA) and a plasticized grade of PLA obtained by reactive extrusion (pPLA), as a function of thermomechanical recycling. In particular, the materials were submitted to repeated extrusion and injection procedures to simulate recycling. Prior reprocessing, spherulitic growth rate determined by polarized light optical microscopy indicated that pPLA crystallized into much smaller spherulites as compared to PLA. This finding was explained by a lower nucleation energy barrier promoted by the plasticization of pPLA. Isothermal overall crystallization kinetics were determined by differential scanning calorimetry measurements. It was found that pPLA crystallized much faster than neat PLA due to the plasticization effect. With increasing the number of processing cycles up to 5, PLA crystallization rate gradually increased, while at the same time that of pPLA remained constant. This result was explained by more important degradation mechanisms in PLA as compared to pPLA that enhanced chain mobility, as shown by molecular weight measurements. Moreover, pPLA had a very high initial chain mobility that is maintained regardless of the number of processing cycles. However, the final crystallinity degree was lower in reprocessed pPLAs, as grafting and cross-linking reactions produced during reactive extrusion interrupt crystallizable linear crystallizable sequences and reduced the amount of crystals formed.

这项工作的重点是确定纯聚丙交酯（PLA）和通过反应挤出（pPLA）获得的增塑级PLA的结晶动力学，这是热机械循环的函数。特别是，将材料进行了重复的挤出和注射程序以模拟回收。在再加工之前，通过偏光光学显微镜确定的球晶生长速率表明，与PLA相比，pPLA结晶为小得多的球晶。pPLA的塑化促进了较低的成核能垒，从而解释了这一发现。等温总结晶动力学通过差示扫描量热法测量来确定。发现由于增塑作用，pPLA的结晶比纯PLA结晶快得多。随着增加至5个处理循环数，PLA结晶速率逐渐提高，而pPLA的结晶速率保持恒定。与分子量测量所显示的相比，与提高链移动性的pPLA相比，PLA中更重要的降解机理解释了这一结果。此外，pPLA具有非常高的初始链迁移率，无论处理周期数如何，都可以维持。但是，在再加工的pPLAs中，最终的结晶度较低，因为在反应挤出过程中发生的接枝和交联反应中断了可结晶的线性可结晶序列，并减少了形成的晶体数量。与分子量测量所显示的相比，与提高链移动性的pPLA相比，PLA中更重要的降解机理解释了这一结果。此外，pPLA具有非常高的初始链迁移率，无论处理周期数如何，都可以维持。但是，在再加工的pPLAs中，最终的结晶度较低，因为在反应挤出过程中发生的接枝和交联反应中断了可结晶的线性可结晶序列，并减少了形成的晶体数量。与分子量测量所显示的相比，与提高链移动性的pPLA相比，PLA中更重要的降解机理解释了这一结果。此外，pPLA具有非常高的初始链迁移率，无论处理周期数如何，都可以维持。但是，在再加工的pPLAs中，最终的结晶度较低，因为在反应挤出过程中发生的接枝和交联反应中断了可结晶的线性可结晶序列，并减少了形成的晶体数量。