Preparation And Properties Of Silica Mineralized Poplar Composites

This paper was inspired by the porous structure of wood and natural organic matrix-mediated silica mineralization.The study was based on the principle of biomimetic mineralization by following the natural method and using fast-growing poplar wood as the object of study.The vacuum-pressure impregnation process was used to combine the sol-gel method and layer self-assembly method.The mass ratio of ethyl orthosilicate to water,pH value and temperature were adjusted.Organic macromolecules were introduced to construct mineralized microenvironments in wood cell walls and wood pores.It induced silica nucleation and growth on wood cell walls to form organic-inorganic hybrid structures.In order to improve the physical and mechanical properties and flame retardant properties of fast-growing poplar,expand the application of wood resources.The compressive strength,flexural strength and flexural elastic modulus of mineralized wood were examined by universal mechanical testing machine.Fourier infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and X-ray diffractometer(XRD)were used to analyze the interfacial bonding mechanism and crystal structure of mineralized wood.Scanning microscopy(SEM-EDS)was used to observe the microstructure of mineralized wood.Thermogravimetric analysis(TG),microcalorimetry(MCC)and cone calorimetry(CONE)were used to evaluate the thermal stability and flame retardant properties of mineralized wood.The mechanism of action of silica-mimetic biomineralized wood was investigated.The following conclusions were obtained.(1)Organic matrix gelatin macromolecules were introduced during the wood mineralization process.The wood was impregnated with a silica precursor solution using the sol-gel method.Gelatin-silica mineralized poplar wood composites were prepared.SEM-EDX results showed that gelatin induced silica deposition on wood cell walls to form a uniform silica film layer,while filling the wood pores to change the wood from a porous structure to a dense "wall" structure.XRD and FTIR analysis showed that the silica generated by in situ mineralization entered the wood in an amorphous state,and the silica formed chemical cross-linkages with the wood components.The mechanical properties were significantly improved,with flexural strength(MOR)and modulus of elasticity(MOE)increasing by 52.2%and 46.2%,respectively.The CONE results showed that the peak heat release rate(pHRR)and total heat release(THR)of mineralized wood were reduced by 45.8%and 19.9%,respectively.However,their smoke suppression effects still needed further study.(2)After the wood was delignified,the gelatin hydrogel with biocompatible and mineral-inducing properties was vacuum impregnated into its interior.The silica was mineralized in situ on the gelatin hydrogel and wood pores using the sol-gel method.The interaction between silica and gelatin hydrogel solved the biocompatibility problem of wood and inorganic minerals,and silica mineralized wood hydrogel composites with efficient flame retardant properties were prepared.FTIR and SEM analyses showed that delignification treatment opened the nano-pores in the wood cell walls and increased the permeability of the wood.Simultaneous gelatin induced silica deposition on wood pores and wood cell walls and chemical bonding with wood components to form organic-inorganic hybrid structures.XRD analysis showed that delignification and mineralization treatment affected the structure of wood cell wall microfibrils to some extent,resulting in little improvement in the mechanical properties of mineralized wood hydrogel composites.The TG analysis and the combined analysis of MCC and CONE showed that the mineralized wood hydrogel composites had excellent thermal stability and good fire and smoke suppression,and their pHRR and THR were reduced by 63.0%and 47.0%,respectively,compared with the untreated wood.(3)The layer-by-layer self-assembly method combined with sol-gel method.Organic coating films were constructed in wood cell walls to provide sufficient nucleation sites for inorganic nanoparticles.Chitosan with good film-forming and biocompatible properties induced silica deposition on wood cell walls and wood pores to form chitosan-SiO2 film layers,which further improved the mechanical strength and flame retardant properties of wood.The FTIR,XRD and XPS analyses showed that silica generated in situ by the sol-gel method entered the wood interior in an amorphous form and chemically bonded with wood components,indicating that silica formed an organic-inorganic hybrid structure with the wood cell wall.The SEM analysis showed that chitosan synergized with silica to form chitosan-SiO2 film layers on the wood cell walls.The MOR and MOE of the layer self-assembled mineralized wood increased by 74.6%and 62.0%,respectively.The CONE results showed that the pHRR and THR gradually decreased with the increase of self-assembled layers,indicating that the chitosan-SiO2 film layer could effectively enhance the mechanical properties and flame retardant properties of wood.