Microcellular foamed aromatic polyamides (aramids). Structure, thermal and mechanical properties

We have deeply diminished the density of high performance aromatic polyamides or aramids. Thus, we have prepared microcellular films that at the same time maintain the outstanding thermal and mechanical properties characteristic of these high performance materials. Two different cellular aramids were produced, based on commercial poly(m-phenylene isophthalamide), one of them with an additional azide group. Microcellular structures have been obtained by adding ionic liquids combined to ScCO2 foaming process, with cell sizes between 0.6 and 4.7 mu m and cell densities between 10(9) and 10(11) cells cm(3). The density was lowered for the commercial poly(m-phenylene isophthalamide) (Nomex (R) and Teijin Conex (R)) from 1.43 to 0.62 g cm(-3) and from 1.48 to 0.31 g cm(3) for the aramid containing the azide group. Foams present the following thermal and mechanical properties: 5% weight loss observed at T > 400 degrees C and relative Young modulus and tensile strength of 1.2 GPa (g cm(-3))(-1) and 60 MPa (g cm(-3))(-1), respectively.