Effects of superheated steam treatment on moisture adsorption and mechanical properties of pre-dried rubberwood

Abstract

Rubberwood (Hevea brasiliensis) was treated with superheated steam (140–160 °C) for 1–3 h and then its adsorption ability, mechanical properties, and color changes were investigated. The results of adsorption show decreased equilibrium moisture content (EMC) for all heat-treated cases throughout the hygroscopic range. The Hailwood–Horrobin model was used to analyze the sorption isotherms and determine the monolayer and polylayer moisture contents for untreated and heat-treated rubberwood. The monolayer moisture content clearly decreased with treatment temperature and duration, whereas the reduction in polylayer moisture was relatively smaller. Moreover, the least density of water adsorption sites was found in wood after treatment at 160 °C for 3 h, indicating this as the cause for reduced equilibrium adsorption. All treatment conditions had improved mechanical properties, including compression parallel-to-grain, hardness, and tensile strength. The total color difference of the wood surface increased with increasing temperature and treatment duration.

Keywords:

• Superheated steam
• adsorption
• H–H model
• rubberwood
• mechanical properties

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors would like to thank the PSU Graduate School Research Fund for providing financial support for this research. This research was also supported by the Natural Rubber Innovation Research Institute, Prince of Songkla University (Grant No. ENG5909315). In addition, sincere appreciation goes to the Department of Chemical Engineering, Faculty of Engineering, PSU, for the equipment and laboratory support. Finally, special thanks go to the PSU Research and Development Office (RDO) and Assoc. Prof. Seppo Karrila, Ph.D. (Chem Eng) for technical assessments of the manuscript.