Investigation of Crystallization Kinetics in Polyhydroxyalkanoates through Hyperthermal Cycles

Area of Science:

• Polymer Science
• Materials Science
• Sustainable Polymers

Background:

• Polyhydroxyalkanoates (PHAs) are sustainable, biodegradable polymers with potential to replace conventional plastics.
• PHAs are used in packaging, agriculture, cosmetics, and biomedical fields.
• Understanding PHA crystallization is crucial for optimizing their manufacturing and applications.

Purpose of the Study:

• Investigate the isothermal and nonisothermal crystallization behavior of polyhydroxybutyrate (PHB) and poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV).
• Analyze the impact of controlled hyperthermal cycles and cooling rates on PHA crystallization kinetics.
• Evaluate the predictive capability of common modeling techniques for PHA crystallization.

Main Methods:

• Utilized controlled hyperthermal cycles for isothermal and nonisothermal crystallization studies.
• Applied rapid hypercooling at 500 °C/min to isolate crystallization kinetics.
• Examined crystallization behavior at cooling rates up to 500 °C/min to simulate industrial processing.

Main Results:

• Isothermal activation energies were 91 kJ/mol for PHB and 139 kJ/mol for PHBV.
• Nonisothermal crystallization significantly decreased with increasing cooling rates for both PHB and PHBV.
• PHB crystallinity dropped from 48.6% to 10.9%, and PHBV from 45.9% to near zero at high cooling rates.
• Common crystallization models showed limited predictive power for nonisothermal kinetics based on isothermal data.

Conclusions:

• PHA crystallization is highly sensitive to processing conditions, particularly cooling rates.
• Current modeling approaches have limitations in predicting nonisothermal PHA crystallization.
• Novel insights into PHA crystallization mechanisms are provided, vital for optimizing sustainable polymer manufacturing.