Surface deterioration of moso bamboo (Phyllostachys pubescens) induced by exposure to artificial sunlight

Abstract

The effect of ultraviolet-visible light irradiation on changes in surface chemistry and morphology of moso bamboo (Phyllostachys pubescens Mazel) was investigated. Fourier transform infrared (FT-IR) and FT-Raman spectroscopy were used in combination to study chemical changes induced by exposure to artificial sunlight (xenon lamp) for up to 160 h, and the resulting physical changes of cell walls of bamboo surfaces were examined by scanning electron microscopy (SEM). FT-IR results showed that significant changes occurred in the lignin component as indicated by considerable decreases in the intensities of the characteristic aromatic lignin peak at 1512 cm⁻¹ and other associated bands. This was accompanied by formation of new carbonyl groups at 1735 cm⁻¹, resulting in photooxidation of bamboo surfaces. The photosensitive nature of bamboo lignin was also demonstrated by FT-Raman analysis, in which obvious decreases in intensities of Raman bands at 1604 and 1630 cm⁻¹ mainly derived from lignin and free and esterified p-coumaric and ferulic acids were observed. SEM micrographs of the irradiated cross sections of bamboo revealed that significant damage occurred to the fiber walls, whereas the parenchyma cells exhibited slight distortion and some cracks occurred in the cell walls. The structures of cell corners and middle lamellae were nearly intact after irradiation.