Effects of heat treatments on photoaging properties of Moso bamboo ( Phyllostachys pubescens Mazel)

Moso bamboos were heat-treated in three media separately: hot water, hot air and saturated steam, and then radiated by an ultraviolet (UV) 313 light for 56 days to imitate 1-year solar radiation in Southeast China. After heat treatments, the surface color of bamboos became darker and relative lignin contents increased. The darker color marked the color changes due to the formation of new compounds during UV radiation and showed higher color stability. Photochemical reaction was closely related to original chemical composition of bamboos. The saturated steam treatment led to higher color stability during UV radiation. However, lignin content analysis, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy showed heat treatment can delay but cannot prevent bamboo from photo-degradation. Color changes and C1/C2 analysis showed the photo-degradation was rapid at the initial UV radiation, then slowed down and almost stabilized after 14 days. Surface colors of both heat-treated and untreated bamboos all faded due to lignin degradation as the exposure time was extended to 56 days. XPS showed a decrease in C1/C2 and an increase in O/C ratio of heated bamboos during UV radiation, indicating the oxidation state of carbon increased and lignin content further reduced.