Investigation of hydro-thermal pretreatments effect on functional properties of densified wood

Background and objectives: Wood as a renewable material, with its various benefits, has always had different applications in human society. Wood as a natural and biodegradable material has always been considered by humans throughout the history. However, the fact that wood is a natural material originating from different trees, create limitations on its properties such as moisture absorption, dimensional changes, biodegradation, degradation by ultraviolet radiation and weathering, etc. Therefore, this natural product may need to be modified in order to achieve the desired functionality and application. There are different modification methods which can be improved the physical and mechanical properties of wood. Enhancement of light wood density by compression process is one of wood modification methods that often improve the mechanical properties. But springback is the main subject in this process. There have been done numerous studies in this field but no suitable method has been presented until now that can effectively control springback. Therefore, the aim of this study was improvement of physical and mechanical properties of poplar wood (Populus deltoides) by using hydro-thermal pretreatments; at the same time, springback assessment under this process.

Materials and methods: In current study, Poplar wood (Populous deltoids) was initially cut into timber in wood and paper laboratory of Alborz research complex and then change into the pieces with dimensions of 45×7×4.2 cm3 (longitudinal× tangential× radial). Afterwards, the wood specimens were hydrothermally treated at temperatures of 100°C for three times of 0, 60 and 120 minutes. In the next step, the second pretreatment and also densification process was carried out under a hot press in the radial direction with a compression set of 40 percent. The pretreated poplar wood specimens were immediately compressed by hot press at temperature of 160, 180 and 200°C for two times of 60 and 90 minutes. The press pressure was considered 50 kg/cm2. The specimens were then physically and mechanically tested as density gradient, springback after press and also conditioning, impact strength and compression parallel to grain. The results were analyzed based on complete randomized design (CRD) under a factorial experiment by SPSS software. The mean comparison was evaluated using Duncan's multiple range test.

Results: Results assessment in compared with other studies showed that acceptable physical and mechanical properties can be reached by this process such as uniform structure and less density gradient. Moreover, the results revealed reduction of springback after press and conditioning and also improvement of mechanical properties such as impact strength and compression parallel to grain.

Conclusion: The densification process of low-density wood species with hydro thermal pretreatments improve the physical and mechanical properties and expands their functional domain.