Radical regulation and performance retention in functionalized UiO-66/epoxy nanocomposites under γ irradiation

High-dose γ irradiation induces radical-triggered oxidative chain reactions in epoxy resin (EP), leading to a progressive degradation of its thermo-mechanical properties. Here, EP nanocomposites containing hydroxylated and aminated metal-organic framework (MOF) fillers, UiO-66-(OH)₂ and UiO-66-NH₂, were prepared to regulate irradiation-induced radical buildup and improve property retention. The composites were evaluated before and after γ irradiation (1 MGy; at a dose rate of 10.8 kGy h^-1) using thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG), tensile testing, dynamic mechanical analysis (DMA), and spectroscopic characterizations including electron paramagnetic resonance (EPR), fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Prior to irradiation, both composite systems exhibited an overall strengthening tendency while maintaining ductility. After irradiation, the hydroxylated system showed better property retention. At 1 wt% loading, the tensile strength of UiO-66-(OH)₂/EP decreased from 72.41 to 67.09 MPa and the elongation at break from 6.4% to 6.1%, outperforming UiO-66-NH₂/EP (72.49 → 64.18 MPa; 6.8% → 5.5%). EPR indicated a pronounced increase in the paramagnetic signal of neat EP after irradiation (I _pp, peak-to-peak intensity, under identical settings: 0.174 → 14.23), whereas MOF incorporation attenuated the relative accumulation of paramagnetic centers, with UiO-66-(OH)₂/EP showing lower intensity at the same loading (1 wt%: 2.476 vs. 5.650 for UiO-66-NH₂/EP). FTIR/XPS revealed substantial buildup of oxygenated species on irradiated EP surfaces (Ox: 10.79% → 41.55%, ΔOx = 30.76). In contrast, 1 wt% UiO-66-(OH)₂/EP effectively suppressed oxidative accumulation (ΔOx = 13.53; Ox/C-C = 0.23 after irradiation), lower than UiO-66-NH₂/EP (ΔOx = 25.62; Ox/C-C = 0.45). Collectively, functionalized UiO-66 mitigates γ irradiation induced degradation by attenuating the relative accumulation of paramagnetic centers and inhibiting oxidation, thereby enhancing thermo-mechanical retention of EP; hydroxyl functionalization is more effective within a moderate loading window.