Melt Electrospinning of Shape Memory Polymer: An Initial Examination of the Morphological, Mechanical and Shape Memory Properties of Non-woven Melt-Electrospun Polyurethane Shape Memory Polymer Mats.

• Author / Creator

  White, Alan D

• Shape memory polymers (SMP) are a class of smart materials which are able to memorize a temporary shape and recall their original/permanent shape with the application of a stimulus. The electrospinning process has been utilized to produce fibrous SMP membranes from polymer solutions, but this process has the side effect of introducing toxic solvents into the materials particularly for biomedical applications. The melt-electrospinning process is a fiber production method that utilizes electrostatic forces in order to produce fibers with micro-diameters from a polymer melt. As such, it does not require use of solvents. In this thesis, I describe how the melt-electrospinning process was used to successfully produce fiber mats from polyurethane SMP (SMPU), and investigate the effect of varying the applied voltage and gap distance on the morphological, mechanical and shape memory properties of the non-woven mats.
  To examine the effect of varying the applied voltage and gap distance on the properties of the mats, four parameter cases were used to generate SMPU mats on an in-house built melt-electrospinning apparatus. The applied voltage was varied from 15 kV to 20 kV, and the spinning gap was varied from 5 cm to 10 cm in order to create the four cases.
  The morphology and fiber diameter of the mats were examined by SEM. It was found that all four cases produced smooth fibers. Over the investigated ranges, the variation of the spinning parameters caused a change in the structural layout of the mats if the change in the electrical field strength caused by the parameter variation was large enough. The diameter of the fibers ranged from 28.4 ± 6.8 µm to 73.6 ± 18.9 µm. Diameter was found to appear to increase when spinning distance was increased at both voltage levels, while diameter appeared to decreased when voltage was varied at a 5 cm gap distance, with no apparent change at a 10 cm gap distance. These apparent variations are attributed to the change in electrical field strength and thus the force on the polymer melt from increasing the voltage or gap distance respectively.
  The mechanical properties of SMPU mats at all four parameter cases were characterized. The Young’s modulus and tensile strength ranged from 8.38 ± 2.41 MPa to 14.2 ± 4.0 MPa and 2.13 ± 0.23 MPA to 4.27 ± 0.74 MPa respectively over the four investigated cases. No apparent variation in the Young’s modulus was found over the range of parameters investigated. This was attributed to the fiber diameters being above a critical diameter below which a change in diameter would affect the Young’s modulus due to polymer chain alignment. For the yield strength, no apparent change was found with varied voltage, but increasing the gap distance resulted in an apparent decrease. This is attributed to the decrease in complexity of mat structure due to decreased electrical field strength, resulting in straighter fibers, which result in the mat fully yielding before a more complex fiber structure would.
  Finally, the shape memory properties of the SMPU mats were determined by programming the materials and recovering them in order to determine the recovery ratio and recovery rate of the fibrous mats. The recovery ratio varied from 33.2 ± 2.2 % to 61.9 ± 6.1% with parameter variation. Variation of the applied voltage had no apparent impact on the recovery ratio, while increasing the gap distance produced an apparent decrease at both voltages. This apparent decrease was attributed to larger changes in the electrical field strength, which led to larger changes in the level of polymeric chain alignment in the polymer fibers. The recovery rate was found to vary from 0.00410 ± 0.00062 mm/s to 0.00723 ± 0.00129 mm/s, with the only change being an apparent decrease in the recovery rate when the gap distance was varied from 5 cm to 10 cm at 15 kV. This limited impact was attributed to only this case having a large enough change in electrical field strength / diameter in order to effect the polymer chain entanglement governing the recovery rate.
  This work shows that melt-electrospinning is a viable technique for SMPU, and that variation of spinning parameters results in variation of the morphological, mechanical and shape memory properties of the generated materials.

• Subjects / Keywords

  • Recovery Ratio
  • Morphological Properties
  • Shape Memory Properties
  • Yield Strength
  • Recovery Rate
  • Melt Electrospinning
  • Polyurethane
  • Young's Modulus
  • Mechanical Properties
  • Shape Memory Effect
  • Fiber Diameter
  • Shape Memory Polymer

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-f6mg-cs57

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.