Formaldehyde emission behavior from phenolic foam insulation: Post-curing-driven internal retention independent of...

Formaldehyde, classified as a Group 1 human carcinogen by the International Agency for Research on Cancer (IARC), is continuously re-emitted from phenolic foam insulation through Post-curing reactions under ambient conditions. The combined influence of board storage period and thickness-direction position on Formaldehyde emission behavior has not been quantitatively elucidated. Specimens from the same production lot with varied board storage periods of 0-544 days (Cut-Point Series) and naturally aged samples spanning 1697-1932 days (Long-Term Series) were evaluated using three independent analytical methods, including the KS M 1998 small chamber method. The core section exhibited a non-monotonic emission pattern, peaking at the 105-day specimen (0.250 mg/m²·h) among tested time points, with a core-to-surface emission ratio reaching 9.6. Attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FT-IR) indices for methylol groups, ether bridges, and methylene bridges simultaneously peaked at the 105-day specimen, converging with the emission trend. This emission maximum diverged from the residual content maximum, which was found at the core section of the 544-day specimen (12.000 mg/L), indicating that low surface emission rates do not reflect internal Formaldehyde depletion. Two distinct aging trajectories were identified: the surface section showed oxidative resin degradation accompanied by spatial homogenization of residual content, whereas the core section retained elevated reactive group indices without signs of oxidative deterioration even after 1932 days. These results suggest that Formaldehyde exposure risk from phenolic foam insulation may persist across the full service life of the material, from installation through occupancy to demolition. All results are based on single-specimen (n = 1) measurements per condition and are intended to provide an experimental foundation for future reaction-diffusion coupled modeling.