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Research Papers

Processing and Characterization of Thermoplastic Polyurethane Nanocomposite Thin Films

[+] Author and Article Information
Anandh Balakrishnan

School of Aerospace and Mechanical Engineering, University of Oklahoma, Norman, OK 73019

Mrinal C. Saha1

School of Aerospace and Mechanical Engineering, University of Oklahoma, Norman, OK 73019msaha@ou.edu

1

Corresponding author.

J. Eng. Mater. Technol 133(1), 011012 (Dec 02, 2010) (7 pages) doi:10.1115/1.4002645 History: Received March 04, 2010; Revised August 30, 2010; Published December 02, 2010; Online December 02, 2010

In this article, we have set up protocols for fabricating thermoplastic polyurethane thin films of about 30μm (neat polyurethane and carbon nanofiber (CNF) containing polyurethane) via ultrasound assisted atomization at 20 kHz. From processing to thin film peel off, we have set up procedures for fabricating our samples. Using optical microscopy, we have examined the manufacturing of these films from a droplet diameter perspective. Our optical microscopy results indicate that the final film microstructure was directly dependent on the physical properties of the neat/CNF reinforced solution. Mechanical testing of these films was then carefully carried out using a dynamic mechanical analyzer (DMA) unit utilizing a specialized thin film test clamp fixture. These test results were compared with control cast films fabricated from the same solutions. For the similar extensions, we observed a drastic increase in the softness of the atomized film. We surmise that the ultrasound assisted droplet generation concurrent with secondary atomization and evaporation could have resulted in reduction of the molecular weight of the polyurethane in our atomized samples relative to the neat ones. Differential scanning calorimetry (DSC) scans have been conducted to confirm the changes in molecular weight. Although results were inconclusive there is evidence of exotherms at 49C in our atomized samples suggested of changes to molecular weight distribution.

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Figures

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Figure 2

Tensile test coupons (left) and tensile test setup (right) within the DMA furnace

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Figure 3

Tensile test trends for our control and atomized thin films

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Figure 4

SEM images of cast film samples: (a) TPU-neat and (b) TPU-CNF and atomized film samples (c) TPU-neat and (d) TPU-CNF

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Figure 5

DSC responses of all our thin film samples and pellet control

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Figure 6

Sample degradation plot of a neat TPU 30 μm sample

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Figure 7

Optical micrographs showing the microstructures in our atomized thin films: (a) and (b) refer to the neat TPU while (c) and (d) are the nanophased TPU films

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Figure 8

Isolated spray droplet image and corresponding binary images

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Figure 9

Droplet count and droplet diameter distributions

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Figure 10

Theoretical polymer diameter versus droplet number

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Figure 11

Real time solvent evaporation showing the drying time for complete solvent evaporation

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Figure 1

Ultrasonic atomization setup

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