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

[Display omitted] •We have produced microcellular aramid films using ionic liquids and ScCO2.•Density has been diminished from 1.4 g cm−3 down to 0.3 g cm3.•Thermal degradation of microcellular aramids begins around 400 °C.•Relative Young’s moduli values are higher than 1.2 GPa (g cm−3)−1. 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 µm and cell densities between 109 and 1011 cells cm3. The density was lowered for the commercial poly(m-phenylene isophthalamide) (Nomex® and Teijin Conex®) from 1.43 to 0.62 g cm−3 and from 1.48 to 0.31 g cm3 for the aramid containing the azide group. Foams present the following thermal and mechanical properties: 5% weight loss observed at T > 400 °C and relative Young modulus and tensile strength of 1.2 GPa (g cm−3)−1 and 60 MPa (g cm−3)−1, respectively.