Investigation of the coloration and mechanical properties of polymer cross-linked para-aramid aerogel fibers with blue color derived from light scattering

The purpose of this study is to enhance the strength of aramid aerogel fibers, which display blue coloration from Rayleigh scattering. The strength of the aramid nanofibers' porous structure is promoted by the introduction of polymers into the aramid nanofiber dispersion, generating hydrogen bonds and metal ion bridges that result in stronger intermolecular forces than van der Waals interactions. Adding these polymers at 0.001–0.1 weight percentage has led to the production of aramid aerogel fibers with a better strength from 0.050 to 0.36 cN/dtex. These added polymers may align the aramid fibrils during stretching, resulting in increased strength and improved birefringence during extension. With the addition of polymer, aramid aerogel fibers go from rigid to more flexible, reducing their susceptibility to buckling. In addition, metal ionomers are used to further enhance the strength of aramid aerogel fibers. In this paper, polyacrylic acid (PAA) is added as a hydrogen-bonded polymer during the preparation of the aramid dispersion, and wet spinning is performed in a coagulation bath containing metal salts. This results in strong cross-linking that increases the maximum tensile strength from 2.4 to 4.9 MPa, from 0.51 to 0.84 cN/dtex facilitating better alignment of the fibril network during stretching. However, further increasing the amount of metal salt results in a decrease in tensile strength and strain. This may be due to increased cross-linking suppressing the alignment of fibrils during stretching, leading to fractures from weak points in the aramid-PAA and PAA-metal ion bridges.