Formation of PLA Stereocomplex Crystals through Homorecrystallization and Mesophase Growth Mechanisms

Hamid Ahmadi; Stan F S P Looijmans; Marc P F H L van Maris; Pauline Schmit; Siavash Maraghechi; Patrick D Anderson; Ruth Cardinaels

doi:10.1021/acs.macromol.4c02836

Formation of PLA Stereocomplex Crystals through Homorecrystallization and Mesophase Growth Mechanisms

Macromolecules. 2025 May 9;58(11):5651-5664. doi: 10.1021/acs.macromol.4c02836. eCollection 2025 Jun 10.

Authors

Hamid Ahmadi¹, Stan F S P Looijmans¹, Marc P F H L van Maris², Pauline Schmit³, Siavash Maraghechi⁴, Patrick D Anderson¹, Ruth Cardinaels^{1

5}

Affiliations

¹ Processing and Performance of Materials, Department of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, MB Eindhoven 5600, The Netherlands.
² Multi-Scale Lab, Mechanics of Materials, Department of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, MB Eindhoven 5600, The Netherlands.
³ Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P.O. Box 513, MB Eindhoven 5600, The Netherlands.
⁴ Applied Mechanics, Department of Built Environment, Eindhoven University of Technology, P.O. Box 513, MB Eindhoven 5600, The Netherlands.
⁵ Soft Matter, Rheology and Technology, Department of Chemical Engineering, KU Leuven, Celestijnenlaan 200J, Leuven 3001, Belgium.

Abstract

The present study systematically investigates the crystallization kinetics and crystal morphology of polylactic acid (PLA) stereocomplex (SC) crystallization from the cold state in 1/1 poly l-lactic acid (PLLA) and poly d-lactic acid (PDLA) mixtures, i.e., via homorecrystallization and mesophase growth mechanisms at two different temperatures (190 and 215 °C). Thereto, homocrystals and mesophase precursors are generated at temperatures of 80, 100, and 120 °C. For the characterization of the crystalline structures, a combination of wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and microscopy techniques is employed. The study reveals that homorecrystallization is much faster than crystallization via mesophase growth and can lead to the formation of either nodular-shaped stereocomplex crystals or coarser lamellar structures, depending on the crystallization temperature. The isothermal crystallization kinetics in a temperature jump stage is characterized via in situ WAXD and modeled with a modified Hillier-type model. The combination of thermal and structural characterization techniques allows to shed light on the factors that influence the crystalline structure of SC crystals, as well as the kinetics of their formation, which can be used for the development of high-performance PLA-based materials.