Treatability and dimensional stability of three hardwood species using different types of water-soluble impregnating agent

Abstract

The effectiveness of the impregnation process depends mostly on the treatability of wood species, along with the type and properties of impregnating agents. The treatability of wood is an essential factor, as it significantly affects the liquid flow path during the impregnation process. Unlike softwood, hardwood has more complexity concerning the liquid flow path due to the diversity of cells and their interconnections. Different impregnating agents result in different phenomena, which are interesting to investigate. Three hardwood species native to Indonesia, namely sepetir (Sindora spp.), pisang putih (Mezzettia spp.), and nyatoh (Palaquium spp.), were utilized and compared in an identical treatment. The impregnation process was carried out by vacuum-pressure and then followed by a hot immersion process in each water-soluble impregnating agent, namely the low molecular weight of phenol formaldehyde (LMW-PF), polyethylene glycol (PEG), and succinic anhydride (SA). Results showed that the treatability of wood during the impregnation process is more likely to be influenced by its oven-dry (OD) density. Sepetir, which has a lower OD density, takes up more impregnating agents and produces higher dimensional stability compared with other wood species. PEG and SA treatments result in higher treatability and dimensional stability; however, they are only suitable for short-term periods due to their weak bonding efficiency within the wood structure, causing some release of those compounds during the soaking-drying process. Even though LMW-PF treatment has lower treatability, as indicated by its lower impregnation uptakes, it can produce comparable dimensional stability with a lower leaching rate.