UV-triggered framework-confined strengthening of reprocessable aramid-nanofibre/polyurea nanocomposites

UV-induced mechanical degradation remains a major challenge to the long-term reliability of polymer composites used in harsh environments. Herein, we report a UV-triggered framework-confined strengthening (UV-FCS) strategy by integrating a rigid aramid nanofibre (ANF) skeleton with a UV-responsive photoinitiator, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide (BAPO), in a polyurea elastomer. The ANF skeleton provides nanoconfinement and hydrogen-bonding sites that immobilize polymer chain segments and restrict molecular mobility. Upon UV irradiation, BAPO anchored on the ANF framework generates initiating radicals, which promote localized free-radical polymerization of terminal C C groups in the confined interfacial region. This process reinforces the interfacial network while suppressing UV-induced structural deterioration. Before UV irradiation, the optimized nanocomposite exhibited a 93.4% higher tensile strength than the neat matrix, increasing from 19.98 to 38.64 MPa; after 24 h of UV irradiation, its tensile strength further increased to 45.94 MPa, corresponding to an 18.9% UV-induced increase, while the final value was 129.9% higher than that of the neat matrix, accompanied by a 122.07% enhancement in toughness and a high elongation at break of 850 ± 42%. SEM observations reveal a more compact fracture morphology after UV irradiation, and DMA analysis supports restricted chain relaxation after irradiation. The nanocomposite also shows improved damage tolerance and impact-protection performance, together with promising solvent-assisted reprocessability. This work provides a framework-confined interfacial reinforcement strategy for developing mechanically robust and UV-adaptive elastomeric nanocomposites for protective applications.