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Small strain Young's moduli of natural rubber (NR)/organoclay nanocomposites were estimated using the Guth-Gold, Halpin-Tsai (HT), and Krieger-Dougherty (KD) models, and compared with experimental measurements of NR vulcanizates containing organo-montmorillonite (OM) or organo-sepiolite (OS). To account for the effect on modulus of the NR matrix of the vulcanization-active modifier in the organoclay, a matrix modulus correction (MMC) term was derived from the vulcanization parameters of the nanocomposites. The KD model gave a better empirical fit with the experimental data than the Guth-Gold model, with both giving good agreement with particle shape factors estimated from transmission electron microscope (TEM) images. The HT model gave the best fit with experiment for both types of nanocomposite, and use of the MMC term meant that the empirical shape factor was sufficiently close to that estimated from TEM images that the model could potentially be used to accurately predict the Young's moduli of NR/OM and NR/OS nanocomposites. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1621-1627, 2011 [ABSTRACT FROM AUTHOR]

The effect of silica nanofiller surface chemistry on compounded particle size and high strain particle dewetting in a semitransparent nanosilica-filled elastomer composite was determined using backscattered visible light and transmitted light, respectively. The integrated intensities of backscattered light from the samples were collected at various visible wavelengths for thin-film composites using ultraviolet-visible spectrometer with an integrating sphere. The data revealed strong Rayleigh-type scattering from compounded filler particles. Size information was extracted and found to broadly correlate with scanning electron microscopy image analysis of fracture surface. Incorporation of a siloxane surface treatment chemical during compounding resulted in a reduced average filler particle size in the cured composite. On extension of the samples, an optical transition was observed only in the filled composites. At high strains, the semi transparent samples displayed an abrupt drop in transparency becoming opaque. This was quantified using a simple light transmission-sample extension technique. Strain-induced crystallization was discounted as the cause for the transition by X-ray diffraction analysis. The onset yield stress for the optical transition was found to be filler surface-chemistry-dependent with the siloxane-treated filler exhibiting a greatly increased onset stress value. These observations were discussed and rationalized in terms of filler particle-matrix dewetting and cavitation at high strains. Matrix-filler dewetting was distinguished from matrix cavitation by comparison with Beer-Lambert behavior derived from unstrained samples. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011. [ABSTRACT FROM AUTHOR]