Investigation of the relationship between surface colour, contact angle and chemical properties of heat-treated bamboo

The inherent relationships between the surface phenomena and chemical structures of thermally modified bamboo were investigated to predict the intrinsic properties of bamboo during the thermal modification through the surface phenomena effectively. Moso bamboo was firstly treated by vacuum treatment at 150°C, 170°C, 190°C and 210°C for 1, 2, 3 and 4 h, respectively. And then the surface colour, contact angle and chemical compositions of heat-treated bamboo and in-situ chemical properties of the heat-treated cell wall were analysed by using the colour metre, contact angle metre and confocal scanning microscope. Results showed that the surface colour became darker and the hydrophobicity was increased after heat treatment. As compared to the control, the lightness (L*) value carried out in accordance with CIELAB of heat-treated bamboo decreased by almost 54% and the maximum increase of contact angle was 160%. The surface colour and contact angle of bamboo were closely related to the lignin content. The darkened colour and increased hydrophobicity of the bamboo surface were caused by the crack of C–O–C and the decrease of C=O in lignin. Furthermore, fluorescence analysis indicated that the lignin distribution in the cell wall increased gradually after heat treatment, especially in the thick-walled cells and the corners of cells.