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Plasticizing effect of water on poly(lactide-co-glycolide)
Paolo Blasi1, Susan S D'Souza, Francesca Selmin
1Dipartimento di Chimica e Tecnologia del Farmaco, Università degli Studi di Perugia, Via del Liceo, 1-06123 Perugia, Italy.
Summary
Water reversibly lowers the glass transition temperature (Tg) of poly(D,L-lactide-co-glycolide) (PLGA) by 15°C. This plasticizing effect is attributed to non-freezable water, which also accelerates PLGA degradation.
Area of Science:
- Materials Science
- Polymer Chemistry
- Physical Chemistry
Background:
- Poly(D,L-lactide-co-glycolide) (PLGA) is a biodegradable polymer widely used in biomedical applications.
- Understanding the influence of hydration on PLGA's thermal properties and degradation is crucial for predicting its in vivo performance.
- The physical state of water within polymers significantly affects their mechanical and chemical stability.
Purpose of the Study:
- To evaluate the effect of hydration on the glass transition temperature (Tg) of PLGA.
- To investigate the nature and physical state of water within PLGA during hygrothermal aging.
- To correlate water content with Tg and assess the impact on polymer degradation.
Main Methods:
- PLGA samples were incubated in water at various temperatures (23-55°C) and aged under controlled humidity using saturated salt solutions.
- Water content was quantified using Karl Fischer titration.
- Thermal behavior (Tg) was analyzed by modulated differential scanning calorimetry (mDSC), and degradation was monitored by gel permeation chromatography (GPC).
Main Results:
- Water reversibly depressed the Tg of PLGA by approximately 15°C, irrespective of incubation conditions.
- A linear correlation (r²=0.9837) was observed between Tg and moisture content (0.3-2.6% w/w).
- Non-freezable (bound) water was identified as the primary plasticizing agent, and its absorption at high humidity accelerated PLGA degradation, similar to bulk water aging.
Conclusions:
- Hydration significantly plasticizes PLGA, lowering its Tg via non-freezable water.
- The presence of bound water plays a critical role in both the thermal properties and degradation kinetics of PLGA.
- Findings suggest that hygrothermal aging conditions, particularly high relative humidity, can accelerate PLGA degradation through bound water absorption.