Improving color stabilization in thermally modified wood by pretreatment with aluminum sulfate vacuum impregnation

The poor anti-weathering performance of thermally modified wood often influences the appearance and service life of wood exposed to an outdoor environment. In this study, wood samples exhibiting ultraviolet (UV) resistance were successfully fabricated by joint aluminum sulfate (Al 2 (SO 4 ) 3 ) impregnation and thermal modification, and the samples were subjected to accelerated weathering reaching 144 h. Time–dependent changes in the surface color of the control samples and treated samples during weathering were evaluated. Chemical and morphological alterations were analyzed by UV spectrophotometry, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The results showed that incorporating Al 2 (SO 4 ) 3 into the specimens helped prevent both the photooxidative degradation of lignin and the formation of degradation products. The anti-weathering performance of thermally modified wood pretreated by Al 2 (SO 4 ) 3 impregnation improved because the negative effects of ultraviolet light and water on the wood surface were controlled by the high temperature resistance and encapsulation of the hydrolyzed aluminum flocs. The thermal stability also improved in the impregnated–thermally modified samples, as confirmed by the TG results.