The effect of polycaprolactone polyol molecular weight and chain extender type on the physico-mechanical properties and gas permeability of polyurethane thermoplastic elastomer membranes

ABSTRACT

In this study, polyurethane thermoplastic elastomers (TPU) were synthesized using isophorone diisocyanate (IPDI), 1,4-butanediol (BDO), and 1,6-hexanediol (HDO) as the chain extenders, and polycaprolactone diol (PCL-diol) with three different molecular weights (2000, 4000, and 10,000 g/mol) as polyols. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) patterns, and differential scanning calorimetry (DSC) were conducted to analyze the chemical microstructure and phase morphology of the prepared samples. The results showed that the change in the chain extender’s type (BDO and HDO) leads to a decrease in the hydrogen bonding index (HBI). Increasing the molecular weight of PCL-diol in BDO-based TPUs has led to an increase in their crystallinity, Young’s modulus, melting temperature, tensile strength, and a decrease in glass transition temperature and elongation at break. Moreover, the increase in the molecular weight of PCL-diol in HDO-based TPUs demonstrated an increase in the crystallinity and elongation at break and tensile strength up to the molecular weight 4000 in PCL-diol, after that, there was a decrease in those properties due to the increase of the soft segments content and change in the chain extender type. Permeability on TPU membranes was performed for N₂ and CO₂ at three different pressures 3, 6, and 9 atm at room temperature. An increase in pressure led to an increase in membrane permeability due to the increase in gas solubility in TPU based on Henry’s law. The permeability of CO₂ is higher than N₂ due to the proper interactions of CO₂ gas with the polar carbonyl groups of polyurethane. It is observed that the permeability increases in BDO-based samples with an increase in the molecular weight of PCL-diol, while the increase in permeability of HDO-based TPU is up to PCL-diol molecular weight 4000 and after that is decreased. The selectivity of CO₂ has decreased with increasing pressure due to the higher rate of dissolution of N₂ at higher pressures.

GRAPHICAL ABSTRACT

KEYWORDS:

• Crystallinity
• membrane
• permeability
• physico-mechanical properties
• polycaprolactone (PCL)
• polyurethane thermoplastic elastomer (TPU)

Author contributions

All authors affirm that this manuscript has not been previously published and is not being considered by another journal. All authors contributed to the conception, design, analysis, and interpretation of the data, as well as writing or rewriting the paper for key intellectual content and approving the final version. This paper has not been submitted to, or is currently being reviewed by, any other journal or publishing venue.

Disclosure statement

All authors contributed to the conceptualization, design, analysis, and interpretation of the data, as well as the drafting of the article. The authors are not affiliated with any entity that has a direct or indirect financial interest in the subject matter covered in this paper.

Data and code availability

Not Applicable

Ethical approval

There was no environmental damage of any living organisms during this investigation.

Additional information

Notes on contributors

Reza Abedi

Reza Abedi is a doctoral student in Chemical Engineering at Azad University, Ahar Branch. His area of expertise includes polymers, polymer composites, nanomaterials, and their applications in different types of polymers. He is currently working as a lecturer in the Chemical Industries field.

Behnaz Memar Maher

Dr. Behnaz Memar Maher is now an assistant professor at the Ahar branch of Islamic Azad University. Her research focuses on membrane science, specifically polymer membranes and their various types. She is presently mentoring multiple students in identical disciplines.

Leila Amirkhani

Dr. Leila Amirkhani is now an Islamic Azad University’s Ahar branch assistant professor. Her study focuses on various forms of polymer composites. She is presently mentoring multiple students in identical disciplines.

Mostafa Rezaei

Dr. Mostafa Rezaei has been a professor at Sahand University of Technology since 2005. His research focuses on the engineering properties of polymers, smart polymer composites, polymer thermodynamics, elastomer engineering, and engineering economics. He currently serves as a supervisor for multiple doctorate and master’s students who specialize in polymers.

Sona Jamshidi

Dr. Sona Jamshidi currently holds the position of assistant professor at the Tabriz branch of Islamic Azad University. She researches various types of membranes and examines their characteristics. She is presently mentoring multiple students in identical disciplines.