Investigation of the influences of MMA on the skeletal reinforcement and mechanical properties of aerogel fibers with blue structural color

Nanofiber dispersions were prepared by fibrillating poly (p-phenylene terephthalamide) (PPTA) fibers, followed by wet spinning and supercritical fluid drying to produce aerogel fibers. These aerogel fibers exhibited a distinct blue structural color due to Rayleigh scattering, highlighting their promise as structurally colored materials. However, their high porosity and low density resulted in insufficient mechanical strength, limiting practical applications. In this study, after wet spinning in an acrylic acid coagulation bath, the resulting gel fibers were immersed in a polymerization solution using acetone as the solvent, methyl methacrylate (MMA) as the monomer, and 2,2-diethoxyacetophenone (DEAP) as the initiator. This solution was then irradiated with ultraviolet light to perform photoinitiated polymerization of methyl methacrylate (MMA) within a PPTA nanofiber network. This process formed a cross-linked reinforcing structure inside the aerogel fibers. Under optimal conditions (30 wt% MMA, 0.5 wt% initiator, 120 s UV irradiation at 100 % intensity), the reinforced aerogel fibers achieved a tensile strength of 1.68 cN/dtex while maintaining low density and enhancing the blue coloration. Compared with unreinforced fibers, the polymerized fibers exhibited suppressed shrinkage during supercritical drying, preserved fine microstructure, and maintained Rayleigh scattering centers, leading to increased blueness. The polymerization reinforced the fibrillar skeleton, resulting in higher breaking strength, greater strain at break, and lower Young's modulus. A clear trend was observed across parameters: higher tensile strength correlated with greater strain at break, lower density, and lower Young's modulus. Scanning electron microscopy after tensile testing suggested smaller microfibril diameters and increased crosslinking density. These results indicate that the reinforced aerogel fibers possess a hierarchical structure characterized by low initial density and Young's modulus, which allows progressive microfibril orientation and improved load transfer with increasing strain. This approach successfully achieved mechanical reinforcement while preserving the desirable structural color and low density of PPTA aerogel fibers.