Aging-controlled crystallization of poly(lactic acid).Part 3: Control of crystallization, structure and properties of injection moldings of poly(lactic acid) by controlled crystal nucleation during and after the injection-molding process

在项目的第一部分中，聚乳酸晶体成核动力学考虑到热历史，量化了在静态熔体冷却以及在低于玻璃化转变温度的温度下退火/储存无定形样品期间的（L-乳酸）（PLLA）（冷却速率、退火温度和退火时间）和分子结构（摩尔质量、立体缺陷浓度）。结果发现，在预先定义的热处理后，在玻璃态下明显的晶核，其数量是可控的，在仅略高于玻璃化转变温度的温度下导致快速结晶，并产生对许多应用有利的细球晶半结晶形态。在项目的第二部分，关于PLLA中晶体成核的调查/研究旨在通过对熔体剪切变形的影响的附加评估来完成。熔体的变形以及由此产生的大分子的取向在许多聚合物的情况下导致晶核的产生，这加速了结晶。在PLLA的情况下，剪切诱导晶体成核的系统研究尚未进行。因此，在本项目中，将在模型实验中分析不同摩尔质量和不同D-异构体浓度的PLLA在剪切条件下形成的剪切诱导晶核和这种晶核的稳定性。结合该项目第一部分的结果，可以精确预测不同分子结构和热流变历史（冷却速率、剪切、低于玻璃化转变温度的老化）的PLLA的结晶。这样的信息然后可用于例如优化在真实的聚合物加工中否则仅缓慢结晶的PLLA的结晶过程。

In the first part of the project Aging-controlled crystallization of poly (lactic acid), the kinetics of crystal nucleation of poly (L-lactic acid) (PLLA) during both cooling of the quiescent melt as well as annealing/storage of amorphous samples at temperatures lower than the glass transition temperature was quantified, taking into account the thermal history (cooling rate, annealing temperature and annealing time) and the molecular architecture (molar mass, stereo defect concentration). It was found that the crystal nuclei, evident in the glassy state after a pre-defined thermal treatment and being controllable in their number, cause rapid crystallization at temperatures only slightly higher than the glass transition temperature and generation of a fine-spherulitic semicrystalline morphology which is advantageous for many applications.In the second part of the project, the investigations/research about crystal nucleation in PLLA is intended to be completed by additional evaluation of the influence of shear deformation of the melt. Deformation of the melt and, consequently, the resulting orientation of macromolecules lead in case of many polymers to generation of crystal nuclei, which accelerate crystallization. Systematic investigation of shear-induced crystal nucleation in case of PLLA was not performed yet. In this project, therefore, shear-induced crystal nucleation and the stability of such crystal nuclei formed under shear conditions will be analyzed for PLLA of different molar mass and different D-isomer concentration within model experiments. Together with the results obtained in the first part of the project, it will then be possible to precisely forecast crystallization of PLLA of different molecular architecture and thermo-rheological history (cooling rate, shear, aging below the glass transition temperature). Such information then can be used, for example, to optimize the crystallization process of otherwise only slowly crystallizing PLLA in real polymer processing.