Study On Modification And Mechanism Of Wood Surface Flame Retardant

Wood is a natural macromolecular material,which has some inherent defects such as flammability,moisture absorption deformation,decay,etc.Unmodified wood cannot meet the needs of social development for wood products.Modification of wood to realize efficient utilization of wood has become a major issue in the field.In order to construct the flame retardant,hydrophobic coating on the wood surface,ultraviolet（UV）-assisted radical polymerization reaction,thiol-ene reaction,boronic acid self-coupling reaction and pyridine quaternary ammonium salt coupling reaction,layer-by-layer self-assembly（LBL）and other chemical modification methods were adopted in this paper,and the mechanism of different modification methods and systems in flame retardant wood was mainly revealed.The main contributions of the thesis are listed as follows:（1）Inspired by mussel adhesive behavior,we proposed a robust strategy for fabricating a halogen-free,flame retardant and good adhesive soybean oil-coating on the wood surface via a UV-assisted radical polymerization reaction,using AESO,DAPB and AAm as the reactive monomers.In all those samples,the results showed that the P-3 exhibited the highest LOI value of 27.3%and passed the UL 94 V-0 test.The adhesion and hydrogen-bond energy were systematically analyzed by cross-cut tape test and density functional theory（DFT）approach.The adhesion property could reach grade 4B from the cross-cut tape test and the corresponding maximum hydrogen-bond energy was 64.32 kcal?mol^-1.By the TG,TGA-FTIR and SEM tests,it can be concluded that flame retarded properties of the bio-coatings were improved through the combination of three reaction mechanisms,including scavenging of free radicals to interrupt the combustion process,dilution of flammable gas in gas phase and as a physical barrier to limit heat and mass transfer in the condense phase.（2）Transparent functional coatings consisting of allyl-functionalized phosphonitrile（HABP）,trimethylolpropane tris（3-mercaptopropionate）（TMMP）and1H,1H,2H,2H-perfluorodecanethiol（PFDT）were prepared via UV-induced thiol-ene reactions without photoinitiator.The effect of PFDT content in the coating formulations on the flame retardant and hydrophobic properties of the wood was investigated.The results showed that the flame retardant and hydrophobic properties of the coatings were improved with the increase of PFDT.The W-F-30 could pass the UL-94 V-0 test,especially after being immersed in water for 24 hours,the sample still maintained good flame retardant durability.The water contact angle of the W-F-30 reached 129.36°,and theγ_S^p was 0.02 m N·m^-1.The TG,TGA-FTIR and SEM results revealed that the flame retardant effect occurs by intumescence which formed a phospho-carbonaceous thermostable char layer in the condensed phase,but also in the gas phase by the release a large amount of the incombustible CO₂.（3）A porous aromatic frameworks（Zn-PAF-50）was synthesized in the wood structure by self-assembly strategy with in situ polymerization using 1,3,5-trichloro-2,4,6-triazine,4-pyridinylboronic acid and zinc nitrate as raw materials,which effectively realized wood fire prevention and anticorrosion.The results showed that the addition of Zn-PAF-50 reduced the activation energy by 26.3%in the pyrolysis process of the wood,the modified wood sample could pass the UL 94 V-0 test and showed good self-extinguishing performance.The char residue rate of Zn-PAF-50-wood at 800°C is36.5%,which is 112.2%higher than that of pure wood.The TG results showed that Zn-PAF-50 particles decomposed prior to the wood substrate,which played a key role in both gas phase and condensate phase flame retardant because of thermal insulation,oxygen and free radical depletion,nonflammable gas release and catalytic charring effects.The anti-corrosion tests show that the mass loss rate of the Zn-PAF-50-wood samples after brown-or white-rot fungus is less than 0.5%,and the variation of water absorption is about 0.8%,showing good corrosion resistance and dimensional stability.（4）A flame retardant and superhydrophobic coating made from chitosan（CH）,polyethylenimine（PEI）,ammonium polyphosphate（APP）,sodium alginate（SA）and Si O₂ nanoparticles was deposited on a wood surface by a layer-by-layer assembly（LBL）technique.The result of SEM-EDS confirmed that the thickness of the coating on the LBL-15-wood surface is about 12μm,and the weight gain rate（WGR）of the samples increased linearly with the growth of layer number.The LOI of the LBL-15-wood sample is 60.5%,which is 167.7%higher than that of pure wood,and passed the UL94 V-0 test.The surface of LBL-15-wood sample possessed superhydrophobicity with the water contact angle of 168°.The high-speed video system indicated that falling water droplets were able to bounce off the LBL-15-wood surface.Besides,the obtained wood sample has the advantages of self-cleaning capability,high separation efficiency,mechanical durability,well moisture resistance,and acid-proof alkalescence,leading to its greater usage value in oil-water separation.