Modification of Chinese fir (Cunninghamia lanceolata L.) wood by silicone oil heat treatment with micro-wave pretreatment

Chinese fir is traditionally used as a construction material in southern China. To enhance the wood properties of this species, silicone oil heat treatment was used in the modification of the wood. Chinese fir wood was silicone oil heat-treated (SOHT) in a preheated oil bath at 150, 180, or 210 °C for 2, 4 or 8 h, and the changes in the physical and chemical properties of the wood were examined. Prior to oil heat treatment of the samples, pre-treatment in a micro-wave oven for 5 min at 103 °C was conducted. The shrinkage, colour change, anti-swelling efficiency (ASE), density and changes in the chemical components including Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were determined. The results showed that the shrinkage of the wood decreased to 4.34%, 2.97% and 0.31%, and the ASE after 7 days of immersion in water increased to 58.68%, 49.38% and 61.81% along the tangential, radial and longitudinal directions, respectively, after oil heat treatment at 210 °C for 8 h. The colour change in wood increased significantly with heat treatment temperature increasing. Klason lignin increased by 50.54% while cellulose decreased by 35.66% after treatment at 210 °C for 8 h. Minor changes were observed in the FTIR spectra of the samples, and TGA analysis revealed that the oil heat-treated samples exhibited relatively high thermal stability. Hence, this study demonstrates that the SOHT with micro-wave pretreatment provides an economical and effective approach to wood modification.