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

• Applicants: Professor Dr.-Ing. René Androsch; Dr.-Ing. Ines Kühnert
• Subject Area: Plastics Engineering
• Term: from 2014 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 261899164

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.

• DFG Programme: Research Grants