| Wood/magnesium oxychloride cement(MOC)composite could solve the issues of the formaldehyde emission and fire hazards of traditional wood-based panels.However,the poor water resistance and the weak interface layer of wood/magnesium oxychloride cement composite caused the problems such as poor and unstable bonding performance.Usually,pores and cracks were introduced into the matrix after adding water resistance modifiers thus decreasing the Mechanical properties.In order to deal with these problems,this research intends to prepare wood/magnesium oxychloride cement composites with water resistance and high interfacial bonding by turning the structure and properties of MOC,constructing the“Mg O-Mg Cl2-H2O”stabilizing system,and pre-treating wood.The effects of the stabilizing system and the pre-treating methods on the components and structure of interface were explored.The wood/magnesium oxychloride cement bonding interface regulation and enhancement mechanism were clarified.The goal of this research is to solve the problem of weak interface layer of wood/magnesium oxychloride cement,and provide theoretical and technical support for developing high-performance wood/magnesium oxychloride cement composite and expanding the application field of wood.The main research conclusions are as follows:(1)As curing at 8?and 25?,with the increase molar ratio of H2O/Mg Cl2,the phase 5 content increased and the phase 3 decreased,Mg(OH)2 could not detected.What's more,the increase molar ratio of H2O/Mg Cl2 would reduce the compactness of microstructure.As curing at 40?and 55?,with the increase molar ratio of H2O/Mg Cl2,Mg(OH)2 significantly increased,phase 3 structure were appeared,and phase 5 decreased and even disappeared.Furthermore,the higher molar ratio of H2O/Mg Cl2,the looser microstructure as curing at high curing temperature.The MOC-wood shows the excellent flame resistance compared to SPI-wood and UF-wood.(2)To enhance the water resistance and mechanical properties by adding D-gluconate sodium salt or phytic acid.After adding D-gluconate sodium salt,the large pores porosity decreased and the water resistance and mechanical properties enhanced.The plywood prepared by the MOC that adding 1.2%of D-gluconate sodium salt shows dry bonding strength of 2.55 MPa and wet bonding strength of 1.54 MPa,which were increased by 4.51%and 21.26%in comparison with the unmodified MOC(2.44 MPa and1.27 MPa),respectively.After adding phytic acid into MOC,the generation of cracks was prevented.Additionally,the mechanical properties and water resistance of MOC-PA are significantly enhanced.The dry bonding strength and wet bonding strength of MOC-0.6 were 2.72MPa and 1.70MPa,which were16.24%and 24.09%higher than those of MOC-0,respectively.(3)Turning the structure and performance of the wood/magnesium oxychloride interface by constructing a“Mg O-Mg Cl2-H2O”stable system.Based on the phenol-amine synergy,the tannins(TA),amino-containing compounds(SPI and PAM),and PAAS were incorporated in order to enhance the properties of MOC system.Among them,the initial adhesion of the MOC composite which contained 2%TA,2%PAAS and 6%SPI were 12 folds higher than that of MOC-pure,and its dry bonding strength,and wet bonding strength 7.86%,and 21.67%higher than those of MOC-pure.The polyhydroxy and well-diffusion of polyvinyl alcohol(PVA),as well as the glutaraldehyde cross-linked the polyvinyl alcohol and wood could give the composites strong interaction(hydrogen-bonding and chemical bonding)between wood.Comparing to MOC-pure,the phase 5 content at bonding interface of MOC-PVA and wood(basswood)of MOC-5%2488xiao increased from 47.4%to 56.9%.The dry bonding strength and wet bonding strength increased by 18.26%and 28.57%,respectively.As for adhesion to cedarwood,the phase content at bonding interface were significantly increased,and the dry bonding strength increased by 24.03%in comparison with MOC-pure.(4)Inspired by oysters,the cornstarch and PAAS was added to prepare wood/MOC composites with high adhesion,stable components,water resistance and high strength.The phase 5 content at bonding interface of wood and MOC modified by 4%cornstarch and 1%PAAS increased from 48.5%to 53.0%,and the dry bonding strength and wet bonding strength increased by 20.00%and 39.82%,respectively.(5)Magnesium oxide(Mg O)pre-filled in wood can enhance the weak interface bonding that caused by filtration effect and can favor the phase 5 growth at the bonding interface.In comparison with the wood/MOC prepared by untreated wood flour,the wood/MOC composite prepared by Mg O pre-filled wood flour/alkali-treated wood flour showed more phase 5 growth on bonding interface and higher mechanical properties.The flexural strength of MOC composites prepared by Mg O pre-filled wood flour or Mg O pre-filled alkali-treated wood flour are 5.4 folds and 7.5 folds of flexural strength of MOC composites prepared by wood flour and alkali-treated wood flour,respectively.The synergistic effect between the carboxyl of the TEMPO-oxidized carboxylation wood flour and phase 5 could strengthen the interface bonding properties thus remarkable enhanced the toughness of composites.These results indicated that both Mg O pre-filled wood and TEMPO-oxidized carboxylation wood could enhance the phase 5 content of composites and could enhance the interface layer. |
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