Furfurylated Superparamagnetic Poplar Wood: Morphological, Physical, and Mechanical Properties

Magnetic wood is one of the wood nanotechnology products with a wide range of potential industrial applications. Superparamagnetic wood is generally produced by in situ synthesis of magnetic nanoparticles in the wood structure. Among the various species of wood used for the production of magnetic wood, the fast-growing species are becoming increasingly important. On the other hand, the inherent properties of wood, such as its water absorption, dimensional instability, and susceptibility to biodegradation and weathering, may limit the potential of magnetic wood as an advanced engineering material. This study aimed to evaluate the effect of furfurylation on modifying the physical and mechanical properties of superparamagnetic poplar wood prepared by in situ synthesis of magnetic nanoparticles.

In situ synthesis of magnetite nanoparticles in poplar wood (Populus deltoides) was performed using iron II and III chloride solutions in a 2:1 molar ratio in a vacuum/pressure chamber. Then the treated wood was converted into magnetic wood by draining the solution of iron cations and replacing it with a one-molar solution of sodium hydroxide. After washing the excess alkali solution and drying, the magnetic poplar wood was treated with two different concentrations of a furfuryl alcohol solution under the vacuum/pressure system and converted into wood polymer after performing the necessary heat treatments. The specimens were characterized using a field emission scanning electron microscope, X-ray diffraction, vibrating sample magnetometry, a static bending test, and long-term water absorption and thickness swelling tests.

The conversion of poplar wood to magnetic wood reduced the weight percent gain (WPG) resulting from the furfurylation process. The saturation magnetization of the magnetic wood decreased significantly after furfurylation and conversion to the wood-polymer. Changing the concentration of the furfuryl alcohol solution had no significant effect on the saturation magnetization of the prepared magnetic wood polymers. The furfurylation treatment significantly reduced the specimens' flexural strength and flexural modulus. The flexural properties of magnetic and non-magnetic wood polymer specimens treated with the same concentration of furfuryl alcohol solution showed no significant difference. Microscopic examination of the fracture surface of the cell wall of the wood in the specimens subjected to the bending test showed the effect of furfurylation in transforming the behavior of the cell wall of the fibers from ductile to brittle, which was consistent with the results of the bending test. On the other hand, as the WPG increased, the specimens' long-term water absorption and thickness swelling decreased. Magnetic wood-polymer specimens had higher water absorption values and thickness swelling than non-magnetic wood-polymer specimens.

Based on the results of this study, it is recommended that magnetic poplar wood, if it must be used in high-humidity environments, be converted to magnetic wood-polymer with furfuryl alcohol, provided it has the required mechanical properties.