Study on phase separation of PET/PEN blends by dynamic rheology

• Published in: Journal of applied polymer science Vol. 110; no. 1; pp. 177 - 182
• Main Authors: Wagner, M.H, Wu, W, Liu, Y, Qian, Q, Zhang, Y, Mielke, W
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 05.10.2008; Wiley
• Subjects: Applied sciences; bi-oriented films; dynamic rheology; Exact sciences and technology; Organic polymers; PET/PEN blends; phase separation; Physicochemistry of polymers; Properties and characterization; Rheology and viscoelasticity; surface tension; time-temperature superposition; Ethylene terephthalate polymer; Viscoelasticity; Polymer blends; Molten state; Property composition relationship; Ester polymer; Biaxial drawing; Transesterification; dynamic rheology; Experimental study; surface tension; Heterogeneous mixture; Biaxial orientation; Interface properties; PET/PEN blends; Oriented polymer; Naphthalate polymer; Phase separation; Temperature time superposition; bi-oriented films; Rheological properties; time-temperature superposition
• ISSN: 0021-8995; 1097-4628
• DOI: 10.1002/app.28156

Blends of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) were processed into biaxially drawn films, and samples taken from the bi-oriented films were then investigated by dynamic rheology experiments in the melt state. Storage modulus G' and loss modulus G" were determined in the frequency range of 10⁻²-10² rad/s at temperatures between 260 and 300°C. Although the time-temperature superposition (TTS) principle was found to hold in the high frequency regime, a breakdown of TTS was observed at low frequencies, and the terminal behavior of the storage modulus G' of the blends departs drastically from the terminal behavior observed for the blend components. This is caused by interfacial surface tension effects. The results indicate that despite the effect of transesterification reactions, the PET/PEN blend systems investigated consist of a microseparate phase of PEN platelets in a matrix of PET. This morphology is produced when the blends are processed into biaxially oriented PET/PEN films, and droplets of PEN are deformed into a lamellar structure consisting of parallel and extended, separate layers. The large interfacial surface area of the bi-oriented PET/PEN blends leads to remarkably strong interfacial tension effects in dynamic rheology measurements.