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Shear-Induced Crystallization of Star and Linear Poly(L-lactide)s.
Joanna Bojda1, Ewa Piorkowska1, Grzegorz Lapienis1
1Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Lodz, Poland.
Molecules (Basel, Switzerland)
|November 13, 2021
Summary
Macromolecular architecture significantly impacts shear-induced crystallization in poly(L-lactide) (PLLA). Star PLLA showed stronger shear influence than linear PLLA at lower molecular weights, affecting crystallization temperature and degree.
Area of Science:
- Polymer Science and Engineering
- Materials Science
- Crystallization Phenomena
Background:
- Understanding polymer crystallization is crucial for material properties.
- Shear forces can induce or modify crystallization in polymers like poly(L-lactide) (PLLA).
- Macromolecular architecture, including branching and molecular weight, is known to influence polymer behavior.
Purpose of the Study:
- To investigate the effect of macromolecular architecture (linear vs. star) on shear-induced crystallization of poly(L-lactide).
- To compare the crystallization behavior of linear and star PLLA under various shearing and cooling conditions.
- To elucidate the role of molecular weight and architecture in shear-induced crystallization.
Main Methods:
- Synthesis of linear and star poly(L-lactide) with varying molecular weights.
- Application of controlled shear rates (5-20/s) at different temperatures (150-170 °C) followed by controlled cooling rates (10-30 °C/min).
- Analysis using light depolarization, Differential Scanning Calorimetry (DSC), 2D-Wide-Angle X-ray Scattering (WAXS), 2D-Small-Angle X-ray Scattering (SAXS), and Scanning Electron Microscopy (SEM).
Main Results:
- Shear-induced crystallization is dependent on shear conditions, cooling rate, molecular weight, and macromolecular architecture.
- Linear PLLA (240 kg/mol) exhibited more intense shear-induced crystallization than a 6-arm PLLA of similar molecular weight, potentially due to higher Mz.
- Star PLLA (around 120 kg/mol) showed a stronger response to shear than its linear counterpart, leading to higher crystallization temperatures and crystallinity.
Conclusions:
- Macromolecular architecture plays a significant role in modulating the shear-induced crystallization of PLLA.
- Star-branched PLLA can exhibit enhanced shear sensitivity compared to linear PLLA, particularly at lower molecular weights.
- The findings provide insights into controlling PLLA crystallization through processing conditions and molecular design.
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