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The primary objective of the research was to evaluate the rheology and thermal properties of silylated apophyllite–filled epoxy nanocomposite. Several n-octyldimethylsiloxy-apophyllite with different grafting degrees were synthesized by controlling the ratio of the apophyllite and n-octyldimethylchlorosilane. The thermal studies of silylated apophyllite have shown that the onset decomposition temperature of silylated apophyllite far exceeds the onset temperature of conventional organoclays (~260 °C). Chemorheological measurements of 1.8 wt% silylated apophyllite–filled tetra functional epoxy (MY720) and difunctional epoxy (DER661) resin mixture showed that the addition of the silylated apophyllite does not dramatically affect the cure profile of the epoxy resin with the availability of 40 min of processing window after the addition of apophyllite. Wide angle X-ray diffraction and transmission electron microscopy results of the shear mixed and cured nanocomposite suggest that the apophyllite was well dispersed in the epoxy matrix. The thermal studies of epoxy nanocomposite showed an increase in the char yield on the addition of silylated apophyllite to the epoxy resin. In addition, an improvement in the onset decomposition temperature of the cyanopropyldimethylsiloxy-apophyllite epoxy nanocomposite was observed compared with that of pure epoxy resin. Copyright © 2011 John Wiley & Sons, Ltd.

The residual stress that arises from processing and the mismatch of coefficient of the thermal expansion (CTE) between polymer and carbon fiber (or metal) could cause a crack initiation and de-lamination in the aircraft structural applications. In this study, bismaleimide composites with zirconium tungstate (−8.8 ppm/K) were successfully fabricated. A synergetic effect led to a significant improvement of the thermal stability of the composites due to the formation of the integrated structure in the zirconium tungstate (ZrW2O8)/Matrimid 5292 (Huntsman, the Woodlands, TX) composite at high temperature, which prevented and/or slowed the escape of the thermal decomposition by-products. The addition of zirconium tungstate into the Matrimid 5292 could also increase the storage modulus while keeping the glass transition temperature unchanged. The CTE of a 20 vol.% ZrW2O8/Matrimid 5292composite material can be reduced by 40% compared with that of the pure Matrimid 5292. The extent of reduction in the CTE is much greater than predicted from the rule of mixture. Micromechanical modeling shows that the Christensen model and the Schapery upper limit model gave a good prediction of CTEs for ZrW2O8/Matrimid 5292 composite. Published 2011. This article is a US Government work and is in the public domain in the USA.

Polymer/layered-silicate nanocomposites have unique and hierarchical structures that can provide improvements to the properties of polymeric materials. Controlling the dispersion of the nanomaterials through processing greatly influences the resulting morphology and the resulting properties of the nanocomposite. In this article, the dispersion behavior of organic layered silicates (OLS) as a function of the processing procedure is reported. The behavior of the OLS in all stages of processing—in the solvent, the epoxy prepolymer, and in the epoxy through cure—is discussed. On the basis of understanding of the dispersion behavior of the OLS in the epoxy resin at each stage of processing, a different processing procedure can be designed and used so that the morphology of the epoxy/layered-silicate nanocomposite can be regulated. Mild low-shear processing resulted in an intercalated nanocomposite with large-size aggregates (> 10 μm), and high-shear processing resulted in an intercalated nanocomposite with relatively small-size aggregates (0.5–3 μm), whereas the high-shear and ultrasonication processing procedures gave rise to an exfoliated nanocomposite. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

This research demonstrates that an epoxy nanocomposite can be made through electron beam (e-beam) curing. The nanofillers can be two-dimensional (layered-silicate) and zero-dimensional (spherical silica). Both the spherical silica epoxy nanocomposite and the layered-silicate epoxy nanocomposite can be cured to a high degree of curing. The transmission electron microscopy (TEM) and small-angle X-ray scattering of the e-beam-cured layered-silicate epoxy nanocomposites demonstrate the intercalated nanostructure or combination of exfoliated and intercalated nanostructure. The TEM images show that the spherical silica epoxy nanocomposite has the morphology of homogeneous dispersion of aggregates of silica nanoparticles. The aggregate size is ∼ 100 nm. The dynamic mechanical analysis shows that the storage modulus of the spherical silica nanocomposite has been improved, and the glass transition temperature can be very high (∼ 175°C). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

The objective of this study is to prepare layered organosilicates with enhanced thermal stability that can be used to formulate high-temperature polymer nanocomposites. Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray diffraction (WAXD), and thermal gravimetric analysis (TGA) characterization results of the modified silicates indicate that the organic pendant group has been chemically grafted on to the backbone of layered silicate and the organically modified apophyllite is thermally stable up to approximately 430°C. The organically modified apophyllite was mixed along with vinyl ester resin and styrene diluent in a sonic dismembrator and the mixture cured to form a nanocomposite specimen. Transmission electron microscopy (TEM) results of the nanocomposites showed mixed morphology with predominant fraction of organosilicates exhibiting an intercalated structure. Tapping mode atomic force microscopy (TMAFM) observation of the nanocomposite showed striated layered silicates dispersed in the resin matrix. The nanocomposites formulated with organosilicates containing reactive terminal pendant group were found to have a higher tensile strain than the nanocomposites formulated with organosilicates containing inert pendant group. Copyright © 2007 John Wiley & Sons, Ltd.

Fully exfoliated layered silicate epoxy nanocomposites are reported in this article. The processing route that resulted in these fully exfoliated layered silicate epoxies is based on a combination of high-shear mixing in the presence of acetone and ultrasonication. Homomogeneous and random dispersion of the individual silicate nanolayers in the epoxy is confirmed through transmission electron microscopy images spanning low to high magnification as well as by X-ray diffraction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3981–3986, 2004

Epoxy nanocomposites were prepared from the different organoclays with aerospace epoxy resin. A series of organoclays treated with alkylammonium chloride with different alkyl groups of different carbon chains were prepared, including SC4, SC6, SC8, SC10, SC12, SC16, SC18, and NC8, NC12, NC18. All of these organoclays, except for SC4, are very compatible with the aerospace Epon 862/curing agent W. The characterization from wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) confirms the exfoliated nanostructure. The six-carbon chain length of the ammonium cation is enough to wet the surface of the clay gallery to make the organoclay compatible with epoxy resin. The clay with lower cation exchange capacity is more favorable for the polymer penetration inside the gallery and is dispersed better in the polymer matrix. The structural evolution of the aerospace epoxy nanocomposite was monitored by in situ SAXS. The 3% SC18/Epon 862/W, 3 and 6% SC8/Epon 862/W showed exfoliated nanostructure, while there is no exfoliation taking place for 3% S30B/Epon 862/W and 3%S25A/Epon 862/W up to 200°C. The acidity from the pendent group in SC18 and SC8 has a catalytic effect for the polymerization inside the gallery, while the organic pendent group of S30B and S25A does not. The faster reaction of the intragallery epoxy resin produced extra thermal heat inside the gallery to expand the gallery and is favorable for the migration of epoxy resin outside the gallery into the gallery where exfoliation took place. The exothermal heat of curing inside the gallery is an important factor for nanosheets exfoliation. Although exfoliation took place for both 3% SC18/Epon 862/W and 3% SC8/Epon 862/W, the detailed morphology development during the curing is different. For 3% SC8/Epon 862/W, the interplanar spacing between the layers is increased gradually, while 3% SC18/Epon 862/W experienced the disappearance of the ordered structure of the layered silicate in the beginning of the curing process and reappearance of the ordered structure of the silicate later. The glassy and rubbery moduli of the polymer-silicate nanocomposites were found to be greater than the unmodified resin because of the high aspect ratio and high stiffness of the layered silicate filler. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2276–2287, 2003