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Multistep Relaxation Pathway from Glass to Crystal Development in Poly(l‑lactide)
Lorenzo Augusto Rocchi1, Elisa Sturabotti1, Andrea Martinelli1
1Department of Chemistry, Sapienza University of Rome, P.le Aldo Moro 5, 00185 Rome, Italy.
Researchers discovered a new transformation in amorphous poly-(l-lactide) (PLLA) within the supercooled liquid (SCL) phase before crystallization. This SCL transformation involves conformational changes, leading to a more stable PLLA state via a hierarchical relaxation pathway.
Area of Science:
- Polymer Science
- Materials Science
- Physical Chemistry
Background:
- Amorphous poly-(l-lactide) (PLLA) exhibits complex thermal behavior.
- Understanding transitions in the supercooled liquid (SCL) state is crucial for polymer processing and stability.
Purpose of the Study:
- To investigate the thermal transitions of amorphous PLLA.
- To characterize the SCL transformation and its kinetics.
- To elucidate the relaxation mechanisms involved in PLLA.
Main Methods:
- Differential Scanning Calorimetry (DSC)
- Fast Scanning Calorimetry (FSC)
- Infrared Spectroscopy
- Sub-Tg and Supra-Tg Annealing Isotherms
Main Results:
- Identified a novel SCL transformation in amorphous PLLA occurring before crystallization.
- Assessed SCL transformation kinetics, revealing a hierarchical relaxation pathway.
- Observed conformational rearrangement from gg to gt conformers during SCL transformation.
- Proposed that SCL transformation is mediated by alpha-relaxation and non-alpha relaxation (Slow Arrhenius Process - SAP).
Conclusions:
- The SCL transformation provides a pathway for unstable PLLA-quenched liquid to relax to a more stable SCL state.
- This transformation is driven by conformational changes and involves complex relaxation dynamics.
- The findings offer insights into the hierarchical relaxation mechanisms governing amorphous PLLA dynamics.
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