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Research Papers

Dispersion Characterization of Nanoclay in Molded Epoxy Disks by Combined Image Analysis and Wavelength Dispersive Spectrometry

[+] Author and Article Information
Levent Aktas, Youssef K. Hamidi

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

M. Cengiz Altan1

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

1

Corresponding author.

J. Eng. Mater. Technol 130(3), 031005 (Jun 10, 2008) (9 pages) doi:10.1115/1.2931140 History: Received May 12, 2004; Revised March 18, 2008; Published June 10, 2008

The state of nanoclay dispersion in a molded epoxy disk and its effects on the thermomechanical properties of the resulting nanocomposite are analyzed. A commercially available nanoclay, Cloisite® 25A, is mechanically mixed at 2wt% with EPON 815C epoxy resin. The epoxy∕clay compound is then mixed with EPI-CURE 3282 curing agent by a custom made molding setup and injected into a disk shaped mold cavity. Upon completion of curing, nanoclay dispersion is quantified on a sample cut along the radius of the composite disk. Dispersion of nanoclay clusters larger than 1.5μm are analyzed by digital image processing of scanning electron micrographs taken radially along the sample, whereas dispersion at smaller scales is quantified by compositional analysis of clay via wavelength dispersive spectrometry (WDS). Digital images of the microstructure indicate that amount of nanoclay clusters that are larger than 1.5μm remain approximately constant along the radius. However, size analysis of nanoclay clusters revealed that they are broken down into finer clusters along the radius, possibly due to the high shear deformation induced through the thickness during mold filling. Compositional analysis by WDS signified that approximately 0.4wt% of the nanoclay is dispersed to particles smaller than 1.5μm, which are not visible in micrographs. Tensile and three-point bending tests are conducted on additional samples cut from the molded disks. Except for slight reduction in flexural strength, up to 9.5% increase in tensile strength, stiffness, and flexural modulus are observed. Glass transition temperature is determined under oscillatory torsion and observed to increase by 4.5% by the addition of nanoclay.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Snap shots of epoxy drop spreading on compacted nanoclay surface. Images taken at t=0s, 0.6s, 1s, and 3600s. Initial drop diameter=1.2mm.

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Figure 2

Experimental molding setup used to fabricate pristine polymer and nanocomposite disks (31-33)

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Figure 3

Spatial distribution of samples cut from each disk. Dispersion analysis is performed on the through-the-thickness plane cut along the O-O section. Parts labeled 1 and 5 are for tensile testing and 2a, 2c, 4a, and 4c are for three-point bending tests.

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Figure 4

Clay clusters of various sizes are visible in SEM image taken at 2500× magnification

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Figure 5

SEM images are thresholded to discriminate the nanoclay from the matrix background. The depicted image is obtained after thresholding an SEM image captured at 50× magnification.

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Figure 6

EDXA spectra of Cloisite® 25A used to identify the constituent elements

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Figure 7

Temporal evolution of contact angle and penetration of resin drop into a nanoclay compact

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Figure 8

Radial distribution of nanoclay clusters dispersed in microscale

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Figure 9

Change in number of nanoclay clusters along the radius of the nanocomposite disk

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Figure 10

Percentage contribution of nanoclay clusters smaller than 3μm2 along the radius. Results indicate that the outer edges of the disk contain a higher percentage of finer clusters.

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Figure 11

Percentage contribution ratio of nanoclay clusters of different sizes along the flow direction calculated with respect to the inlet cluster size distribution

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Figure 12

Distribution of nanoclay dispersed in nanoscale. The data are obtained by WDS

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Figure 13

Effect of nanoclay reinforcement on the tensile properties

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Figure 14

Effect of nanoclay reinforcement on the flexural properties

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Figure 15

Evolution of storage and loss moduli for pristine polymer and nanocomposite as a function of temperature

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Figure 16

Glass transition temperature of pristine polymer and nanocomposite calculated by two different approaches

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