Optimizing Processing Conditions to Influence the Morphology of Nanocomposite
D. Raghavan, S. Balakrishnan, and Y. Gebrekristios
Howard University, US
Keywords: Materials, Surfaces and Interfaces
In recent years, the area of nanocomposites has received considerable attention with the expectation that nanotechnology can lead to lighter, better materials for engineering applications. For example, the attractiveness of polymer-clay nanocomposites resides in the potential of adding infinitesimally small clay platelets, to dramatically raise mechanical, thermal, barrier, and flame-retardant properties without increasing the specific gravity or reducing the transparency of the nanocomposite relative to the base material. Nanoclay reinforced composites garner their material improvements from interactions at molecular and macromolecular scale. To promote interactions at molecular scale between the clay platelets and polymeric resin, long chain surfactants are ion-exchanged to clay sheets. Many studies have addressed the role of long chain surfactants and the curing conditions on the morphology of clay platelets in polymer matrix. Although considerable progress has been made in understanding the kinetic and thermodynamic parameters that control clay platelet separation, many issues associated with the choice of interlayer surfactant, processing conditions, and control of morphology remain unresolved. Fabricating nanocomposites where the clay sheets are uniformly dispersed within the polymer matrix poses significant synthetic and processing challenges.
Of great current interest is the possibility to control the morphology development of organically modified clay-epoxy nanocomposites by influencing the processing parameters. We expect a wide variety of intercalated/exfoliated morphologies to be formulated by obtaining insight into the importance of processing parameters on clay platelet morphology. Some of the processing parameters that promote polymer precursor from diffusing into the clay interlayer are amount and type of swelling agent, duration of soaking in swelling agent, and ultrasonication conditions.
The organically modified montmorillinite clay and the epoxy resin were allowed to swell in a reactive diluent, glycidyl methacrylate (GMA). The mixture of swollen clay and epoxy resin was ultrasonicated, precured, and postcured to formulate epoxy nanocomposites. Wide angle X-ray diffraction studies of the epoxy nanocomposite were performed to relate the type of morphology development with swelling time, diluent amount, ultrasonication amplitude and combination thereof. By studying the breadth, position and intensity of the basal reflection of XRD, the relative extent of intercalation/exfoliation of the organoclay-polymer hybrid nanocomposite was determined. Figure 1 is the XRD pattern of nanocomposite for different processing parameters. As can be seen in Figure 1, minimal processing of nanocomposite yields a sharp peak at 2.3o. Soaking clay and polymer in a compatible reactive diluent reduces the intensity of peak, while ultrasonication in combination with soaking reduces the intensity of peak significantly. We noticed that the transparency (a measure of exfoliation) of epoxy nanocomposite with a loading of 3.5 wt% of organically modified clay can be significantly improved upon soaking the resin and clay in 50 phr GMA for 6h and ultrasonication for 30 minutes. Figure 2 is the XRD pattern of nanocomposite as it relates to the amount of diluent. The results indicate that exfoliation of the organically modified clay in epoxy matrix can be improved with use of reactive diluent. Studies are underway to establish clay structure/processing parameter/morphology and property relationship.
NSTI Nanotech 2003 Conference Technical Program Abstract