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

Abstract

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.