Study Of Wood-Organic-Inorganic Hybrid Nanocomposites

Recently, organic-inorganic hybrid nanocomposites have attracted remarkable attention due to the synergistic effect of their components which contribute extraordinary properties such as mechanical properties, durability, and functional or smart properties stimulated by photoelectromagnetic effect to the composite. Inspired from this sort of composites, and on the basis of the dual structure of wood, this research put forward an idea that prepare novel wood-based composites, i.e., wood-organic-inorganic hybrid nanocomposites, by the in-situ hybrid synthesis of organic and inorganic compounds within the micor/nanometer containers, and synergistically endows wood with ultrahigh strength and excellent durability by controlling the uniform hybrid of organic and inorganic compounds and phase interface, to aim to overcome the drawbacks of lower thermal stability of wood-polymer composite and unsatisfactory mechanical properties of wood-inorganic (nano)composite. Such research is an positive exploration and has important research value for the value-added application of wood, especially low-quality wood.With this purpose, a novel functional monomer was first synthesized in terms of the molecular structure design, and then combined other functional monomer to establish a monomer system for the modification of wood. With the properties results of the prepared wood-polymer composite, the systematic construction law was further concluded and the functional monomer system was optimized for the following researches. On that basis, a series of cell lumen-impregnated and combined cell wall-lumen-impregnated wood-organic-inorganic hybrid nanocomposites were prepared with incorporating method and sol-gel method. The structure of each wood-based hybrid nanocomposite was characterized, and the properties, the reacting mechanism as well as the possible hybrid mode were also analyzed. Finally, the comprehensive performance of each wood-organic-inorganic hybrid nanocomposite was summarizely evaluated.1)①A novel functional monomer was first synthesized by glycidyl methacrylate (GMA) and polyethylene glycol (PEG-400) on the basis of the molecular structure design, and then combined GMA to prepare wood-polymer composite. The results from the structure characterization (SEM, FTIR) and properties evaluation indicated that the polymer with cross-linked structure grafted onto wood components, which strengthened the interface interaction, and remarkably improved the mechanical properties of wood.②On the basis of the above analysis, four wood-polymer composites were prepared by extendly building four types of functional monomer combination. The results from the structural characterization and properties analysis for the composites verified that all the polymers resulted from the four types of monomer combination formed well interface recombination with wood components, and their mechanical properties were also obviously improved. Resultantly, the monomer systematic construction law for wood-polymer composites with excellently comprehensive properties was concluded that monomer with combined unsaturated double bond and epoxy group or cyclic anhydride group, and monomer with combined double-terminal alkenyl group and soft ether chain can be optimally constructed into ideal aimed functional monomer system.③Directed by the constructional law, MAN (maleic anhydride), GMA and PEG200DMA (polyethelyeneglyco1200-dimethacrylae) were chosen to constitute the aimed functional monomer system. And the ratio of the monomers were further optimized into GMA: PEG200DMA=20:1(molar ratio) and6wt%of MAN accounting for the monomers, in the light of the surface bonding strength of decorative veneered wood-based panel that the veneer was modified by the monomer system.④The results from the structural characterization and properties analysis on the basis of veneer-based and solid wood-based polymer composites showed that the resulted polymer filled up cell lumen as an amorphous form, and formed chemical interface recombination with wood matrix, both which resulted in the obvious improvement of wood mechanical properties, thermal stability, dimensional stability and decay resistance. The mechanical properties values achieved those of high-quality wood from tree species in northeast area. All the results for the comprehensive properties verified the effectiveness and reasonability of the constituted and optimized monomer system.2) Based on the optimized functional monomer system, polymer-inorganic hybrid nanocomposites and the corresponding wood-organic-inorganic hybrid nanocomposites were prepared by incorporation of nano-SiO2, nano-clay and nano-POSS, respectively. The results from structural characterization, reaction mechanism and property analysis indicated that①the optimum content of nano-SiO2particle, nano-clay layed lattice and nano-POSS building block in the functional monomer (system) accounts for0.5wt%,0.1wt%and5wt%of the total monomers, respectively. Under such conditions, the maximum pyrolysis temperatures of the three polymer-inorganic hybrid nanocomposites were all improved10～12℃over the corresponding pure polymer. The nano-SiO2particles uniformly dispersed in the polymer matrix with<30nm sizes, and the nano-clay layed lattices dispersed in the polymer matrix as an exfoliated intercalation form, and the nano-POSS evenly dispersed in the polymer matrix with<10nm sizes. The three inorganic building blocks chemically bonded the polymer component, and the phase structure of the resulted nanocomposites was amorphous state for both SiO2and Clay, and crystal/amorphous two-phase structure for POSS, respectively.②Three kinds of wood-organic-inorganic hybrid nanocomposites were prepared at the optimum incorporating content of the three nanometer building blocks, respectively. The results from the characterization and analysis suggested that the SiO2particles heterogeneously aggregated in the polymer matrix within cell lumen at several decades to hundred nanometers, and the clay mainly dispersed in the polymer matrix with an intercalation hybrid form, and the POSS uniformally dispersed with10nm sizes in the polymer within wood cell lumen. The phase structures of the three wood-based hybrid naocomposites were mainly amorphous states. Organic polymer and the nanoscale inorganic moieties probably chemical bonded to wood components, resulting in satisfactory interface recombination. Their mechanical properties (bending strength, compression strength, impact toughness and hardness) were all improved than those of the corresponding wood-polymer composites, and were improved to achieve or even exceed those of high-quality wood obtained from the tree species in the northeast of China. Their dimensional stability and decay resistance in terms of anti-swelling efficiency after immersing in water for228h and weight loss by the fungi attack, respectively, almost equaled to those of the corresponding wood-polymer composite, and the decay resistance even better than those of typical inorganic boron preservative treated wood and organic IPBC treated wood. The Tmax were improved21℃,6℃(nano-SiO2) and25℃,10℃(nano-clay) than those of wood and the corresponding wood-polymer composite, respectively, and20℃(POSS) than untreated wood, indicating good thermal stability to a certain extent.3) The results from systematic studies on the polymer-inorganic hybrid nanocomposites and cell lumen-impregnated wood-organic-inorganic hybrid nanocomposites derived by sol-gel method indicated that①the optimum content of KH570was20wt%accounting for the total mass of monomers. Under this condition, the maximum pyrolysis temperature of the polymer-based hybrid nanocomposites was improved43℃over the pure polymer; and the initial decomposition temperature and maximum pyrolysis temperature of wood-based hybrid nanocomposites was improved55℃and53℃than those of untreated wood, respectively, and even improved40℃,32℃(nano-SiO2) and40℃,28℃(nano-clay) than those of wood-organic-inorganic hybrid nanocomposites prepared by the incorporating method, all of which indicates the excellent thermal stability of both the polymer-based and wood-based hybrid nanocomposites derived by the sol-gel method.②The inorganic moiety with size of smaller than50nm uniformly dispersed in the polymer matrix within cell lumen, and chemically bonded the polymer chains by Si-O bond. The resultant hybrid polymer also chemically grafted onto wood components.③The bending strength, compression strength, and hardness of the wood-based hybrid nanocomposite was increased by83%,156%and208%over those of untreated wood, respectively. Especially, the compression strength and hardness of the wood-based hybrid nanocomposite were even higher than those of wood modified by the incorporating method, while its impact toughness was not positively improved compared with untreated wood. Its anti-swelling efficiency was achieved47%after immersion in water for228h, and the weight loss was improved96%～97%compared with untreated wood, indicating satisfactory dimensional stability and decay resistance.4) on the basis of the natural dual structure of wood, cell wall-impregnated wood-SiC>2nanocomposite was prepared by sol-gel method, and combined cell wall-lumen-impregnated wood-organic-inorganic hybrid nanocomposites was further prepared following treatment of cell lumen with functional monomers impregnation. From the structural characterization and property analysis, the results indicated that①nano-SiO2moiety was uniformly produced within cell wall by hydrolysis-condensation reaction under the two different acid/basic catalyst conditions, which dispersed in an amorphous state and chemically bonded to wood components. The larger the moisture content, the higher the content of SiO2in cell wall.②The maximum pyrolysis temperature of the two cell wall-impregnated wood-SiO2nanocomposites (KH570or KH550as coupling agent) was improved15℃and27℃over unteated wood, respectively. Water contact angle of each wood-SiO2nanocomposite achieved105°～132°(KH570) and113°～143°(KH550), respectively, in terms of the initial moisture content of wood before treatment. Their wear resistance and decay resistance were also remarkably improved than those of untreated wood, and increased as the amount of produced nano-SiO2increased. Their weather resistances were improved, while mechanical properties were not obviously improved.③the polymer thermoformed within cell lumen as an amorphous state grafted onto the cell wall of the two wood-SiO2nanocomposites.④the maximum pyrolysis temperature of the two wood-organic-inorganic hybrid nanocomposites was respectively achieved390℃(KH570) and396℃(KH550), and improved25℃and31℃than that of untreated wood, respectively, and even more excellent than that of wood-organic-inorganic hybrid nanocomposite derived by incorporating method. Their bending strength, compression strength, impact toughness and hardness were all remarkably improved over untreated wood, and achieved or even exceeded those of high-quality wood from tree species in northeast of China. Their anti-swelling efficiency after immersion in water for228h achieved65%(KH570) and70%(KH550), respectively. The wear resistance achieved85.5%(KH570) and87.8%(KH550), respectively, and significantly higher than that of the corresponding wood-polymer composite. Their decay resistances were also more excellent than that of other wood-based hybrid nanocomposites and preservatives (boron compounds and IPBC) treated wood.