Abstract
The role of processing conditions and intercalant chemistry in montmorillonite clays on the dispersion, morphology and mechanical properties of two epoxy/clay nanocomposite systems was investigated in this paper. This work highlights the importance of employing complementary techniques (X-ray diffraction, small angle X-ray scattering, optical microscopy and transmission electron microscopy) to correlate nanomorphology to macroscale properties. Materials were prepared using an out of autoclave manufacturing process equipped to generate rapid heating rates and mechanical vibration. The results suggested that the quaternary ammonium surfactant on C30B clay reacted with the epoxy during cure, while the primary ammonium surfactant (I.30E) catalysed the polymerisation reaction. These effects led to important differences in nanocomposite clay morphologies. The use of mechanical vibration at 4 Hz prior to matrix gelation was found to facilitate clay dispersion and to reduce the area fraction of I.30E clay agglomerates in addition to increasing flexural strength by over 40%.
Highlights
Amongst the various classes of nano-materials that have been reported over the past few decades, polymer/clay nanocomposites have undoubtedly been the most studied and have shown the greatest potential for property improvements [1,2,3,4,5,6,7,8,9]
By using the same high heating rate (10 °C/min) and sonication conditions that were previously reported [6], we extended the concept to investigate the effect that mechanical vibration and surfactant chemistry has on the dispersion of two commercial organoclays
This paper shows that sufficient evidence is required to characterise clay dispersion, where complementary diffraction, scattering and imaging techniques must be employed to characterise these morphologies
Summary
Amongst the various classes of nano-materials that have been reported over the past few decades, polymer/clay nanocomposites have undoubtedly been the most studied and have shown the greatest potential for property improvements [1,2,3,4,5,6,7,8,9]. The term, intercalated, refers to nanocomposites where penetration of the polymer chains into clay galleries only causes an expansion of the platelets on the order of 1 to 4 nm. Lou et al successfully used an electromagnetic vibration technique (80 μm amplitude) to disperse CaCO3 nanoparticles in high density polyethylene during extrusion [20] This process enhanced the shear flow field of the polymer, broke down agglomerate sizes and led to enhancements in both tensile and impact properties. The combination of a high amplitude sonication method combined with a heating rate of 10 °C/min was shown to reduce the viscosity, which, in turn, facilitated the penetration of polymer chains in between clay platelets (I.30E organoclays). The effect of surfactant chemistry on the epoxy-clay interface and the resulting differences in dispersion [in terms of clay d-spacing and the area fraction (%) of clay agglomerates] will be discussed
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