Characterization of highly oriented organoclay/ poly(methyl methacrylate) moulded nanocomposites

In the present paper, the effects of nanoparticles' content and orientation were studied on the structure, phase morphology and thermo-mechanical properties of highly oriented montmorillonite/ poly(methyl methacrylate) moulded nanocomposites. The nanocomposites were compounded using a co-rotating high-shear twin-screw extruder. Square plates were prepared by a two-stage compression-moulding process from the previously extruded materials, with the test specimens being directly machined in both parallel and perpendicular directions with respect to the plate's surface. Wide-angle X-ray diffraction (WAXD) revealed a highly-ordered structure of silicate platelets parallel to the plate's surface. Observations by transmission electron microscopy (TEM) supported this analysis, demonstrating the high anisotropy degree of the nanocomposites. Dynamic mechanical thermal analysis (DMTA) showed that the perpendicular specimens were stiffer than the parallel ones, with the presence of the oriented nanoparticles decreasing PMMA's mobility during the glass transition, although no significant differences were registered in the T(g) temperatures with increasing the amount of clay content or with orientation. Remarkable improvements regarding the fracture energy were observed for the perpendicular specimens, with the 20 wt% oMMT nanocomposite showing a fracture energy almost 10 times that of pure PMMA.