High-Temperature Thermosetting Polyimide Nanocomposites Prepared with Reduced Charge Organoclay

The naturally occurring sodium and calcium cations found in bentonite clay galleries were exchanged with lithium cations. Following the cation exchange, a series of reduced charge clays were prepared by heat treatment of the lithium bentonite at 130, 150, or 170°C. Inductively coupled plasma analysis showed that heating the lithium clay at elevated temperatures reduced its cation exchange capacity. Ion exchange of heat-treated clays with either a protonated alkyl amine or a protonated aromatic diamine resulted in decreasing amounts of the organic modifier incorporated into the lithium clay. The level of silicate dispersion in a thermosetting polyimide matrix was dependent upon the temperature of Li-clay heat treatment as well as the organic modification. In general, clays treated at 150 or 170°C, and exchanged with protonated octadecylamine or protonated 2,2′-dimethylbenzidine showed a higher degree of dispersion than clays treated at 130°C, or exchanged with protonated dodecylamine. Dynamic mechanical analysis showed little change in the storage modulus or T _g of the nanocomposites compared to the base resin. However, long-term isothermal aging of the samples showed a significant decrease in the resin oxidative weight loss. Nanocomposite samples aged in air for 1000 h at 288° C showed up to a 20% decrease in weight loss in comparison with that of the base resin. This again was dependent on the temperature at which the Li-clay was heated and the choice of organic modification.