Abstract:To further investigate the influence of organic modifiers (primary amine with catalytic hydrogen and quaternary alkylammonium salt) on exfoliation behavior of clay tactoids, high-speed emulsifying and homogeneous mixing(HEHM) and ball milling were used to exert external shearing force on two organic clay tactoids (termed as MMT_DDA and MMT_DBDA, respectively), which were organically modified with DoDecyl Amine(DDA) and Dodecyl Benzyl Dimethyl Ammonium chloride(DBDA), respectively. The effects of external shearing force on microstructure and properties of both resultant nanocomposites were investigated by X-ray diffractometry(XRD), transmission electron microscopy(TEM) and thermogravimetric analysis(TGA). The results show that whether the clay tactoids are organically modified with catalytic primary amine or quaternary alkylammonium salt, the large agglomerates will not be finely dispersed or exfoliated by conventional mixing (magnetic stirring). After being vigorously sheared by HEHM or ball milling, the dispersion and exfoliation of clay tactoids are increasingly promoted for both MMT_DDA and MMT_DBDA, and the mechanical properties of the high-performance epoxy/clay nanocomposites are enhanced. For epoxy/MMT_DDA nanocomposites, impact strength can be increased up to 44.5kJ/m² from 32.1kJ/m², which is about 39% higher than that of pristine matrix, and the flexural strength is enhanced by about 4%. A similar enhancement for epoxy/MMT_DBDA nanocomposites has also been achieved. Improvement on thermal stability of epoxy/clay nanocomposites is dependent on the exfoliation of clay layers and molecular structure of the modifiers. The onset temperature is increased with the clay loading decreasing from 5% or higher content to 3%(mass fraction), and the DBDA modifier with the heat-resistant benzyl may also improve the stability of epoxy/MMT_DBDA nanocomposites.

Key words: shearing force; exfoliation; nanocomposites; epoxy; clay