Non-Isothermal Melt Crystallization of a Biodegradable Polymer Studied by Two-Dimensional Infrared Correlation...

Area of Science:

• Polymer Science
• Materials Science
• Spectroscopy

Background:

• Poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] (PHBHx) is a biodegradable polyester with tunable properties.
• Understanding its melt crystallization behavior is crucial for processing and applications.
• Non-isothermal crystallization kinetics influence material morphology and performance.

Purpose of the Study:

• To investigate the non-isothermal melt crystallization process of PHBHx.
• To elucidate the sequential formation and evolution of different crystalline phases.
• To correlate spectral changes with molecular ordering during crystallization.

Main Methods:

• Attenuated Total Reflection Infrared (ATR IR) spectroscopy was employed to monitor crystallization.
• Time- and temperature-dependent spectra were analyzed using Two-Dimensional Correlation Spectroscopy (2D-COS).
• Analysis focused on the C=O stretching, C-H stretching, and fingerprint regions.

Main Results:

• Distinct IR contributions were identified for amorphous, type I (well-ordered), and type II (less ordered) crystalline phases.
• Type I crystal formation initiated earlier and at higher temperatures than type II crystal growth.
• An early decrease in amorphous component suggested crystallization precursor species.
• C-H stretching and fingerprint band changes lagged behind carbonyl-based population dynamics.

Conclusions:

• The crystallization of PHBHx proceeds through distinct stages involving amorphous, type I, and type II crystalline phases.
• 2D-COS analysis successfully resolved the sequential evolution of these phases during non-isothermal melt processing.
• Spectral changes in C-H and fingerprint regions reflect the molecular evolution within crystalline structures rather than direct population changes.