Wood permeability and compressibility are affected by cell wall structure and chemical composition. These properties can be improved by appropriate wood pretreatments. Low-density poplar wood was converted to a more dense structure by the following steps: First, lignin and hemicellulose were removed using a mixture of NaOH and Na2SO3. Second they were impregnated with polyethylene glycol (PEG, mean molecular weight of 1200), nano-SiO2, and a silane coupling agent at atmospheric temperature and pressure. Finally, impregnated wood was compressed at 150 °C. Results showed that the tracheid lumens on the transverse section of the compressed wood almost vanished. Specifically, the lumens in the wood cells, especially those that were compressed, were almost completely filled with PEG. In FTIR, the asymmetric absorption peaks of Si–O–Si at 1078–1076 cm−1 were clearly observed, which confirms the existence of bonding between nano-SiO2 and wood. The highest melting enthalpy and crystallization enthalpy showed a heat storage capacity of modified wood, which were 20.7 and 9.8 J/g, respectively. Such phase change capabilities may have potential applications in regulating the rate of change of room temperature. In summary, the modified wood could be utilized as material for construction to conserve energy.

It is a novel idea to fabricate wood-inorganic composites by utilizing the transpiration of bionic trees to realize the self-assembly of inorganic precursors in wood formation. We selected a 10-year-old poplar and diffused the solvent or sol containing SiO2 precursor into the xylem via the slow-release drip method. In combination with the moisture in xylem, reactions such as hydrolysis, polycondensation and self-assembly were induced in order to form wood inorganic composites. It was found, through microscopic observation, that such inorganic substances were yellowish brown and widely existed in vessels, wood fibers and ray cells. For the new grown wood, the fiber–tissue ratio and cell wall thickness underwent an increase, while the vessel diameter and tissue ratio experienced a decline. Moreover, such change was related to the concentration of precursors. EDS analysis proved that the elemental composition of sediments in wood cells was C, O, Si, K and Ca. XPS confirmed that the newly formed wood contained silicon oxide, illustrating that the standing tree slow-release drip technology could induce wood to fabricate inorganic composites.