The 3-Phase Structure of Polyesters (PBT, PET) after Isothermal and Non-Isothermal Crystallization

Area of Science:

• Polymer Science
• Materials Science
• Physical Chemistry

Background:

• Semi-crystalline thermoplastics comprise mobile amorphous fraction (MAF), rigid amorphous fraction (RAF), and crystalline fraction (CF).
• Understanding phase composition is crucial for predicting polymer properties and performance.
• Polyesters like PBT and PET are widely used and their amorphous phase behavior requires detailed investigation.

Purpose of the Study:

• To investigate the phase composition (MAF, RAF, CF) of Polybutylene Terephthalate (PBT) and Polyethylene Terephthalate (PET).
• To explore how isothermal and non-isothermal conditions influence the amorphous and crystalline fractions.
• To determine the minimum achievable MAF and the formation mechanisms of the RAF.

Main Methods:

• Utilized Differential Scanning Calorimetry (DSC) for conventional thermal analysis.
• Employed Fast Scanning Calorimetry (FSC) to extend the accessible thermal conditions.
• Combined DSC and FSC to analyze phase composition under varied thermal histories.

Main Results:

• Both PBT and PET exhibit a significant rigid amorphous fraction (RAF).
• The RAF is primarily formed during primary and secondary crystallization processes.
• The mobile amorphous fraction (MAF) approaches a thermal history-independent minimum for both polymers.

Conclusions:

• The rigid amorphous phase (RAF) plays a dominant role in the structure of PBT and PET.
• Crystallization temperature significantly impacts the formation of RAF and the final MAF.
• The minimum MAF suggests a limit to amorphous phase mobility in these polyesters.