High-Temperature Thermosetting Polyimide Nanocomposites Prepared with Reduced Charge Organoclay

Abstract

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.