| Microcellular foams were successfully processed from several high-performance thermoplastics by a two-stage batch process using CO 2 as foaming agent. These microcellular foams had well-defined closed-cell structures with average cell sizes in the range 2--15 mum, and cell densities on the order of 109--1012 cells/cm 3. Compression and tension tests were performed on these foams to evaluate their mechanical properties. In order to improve the thermal stabilities and mechanical properties of these foams, composites were prepared by incorporation of rigid-rod polymers or nano-dispersed clay layers in the thermoplastics to form molecular composites, or nanocomposites. These composites were also processed into microcellular foams. The foaming behavior and morphologies of the resulting composite foams were much more complicated than those of the pure polymers. The thermal stabilities and some mechanical properties of the composite foams were significantly enhanced relative to those of the pure matrix polymers. These improvements could be due to nanoscale or even molecular dispersions of the rigid-rod chains in the polymer matrices, including having these chains aligned along the foam struts or within the foam walls in unique reinforcing arrangements. |
