Study On Bonding Mechanism And Interface Enhancement Of Poplar Shavings And Magnesium Oxychloride Adhesive

There are some disadvantages of aldehyde and resin adhesive of wood-based panels,such as formaldehyde pollution,poor heat and water resistance,organic volatilization(VOC)and so on,magnesium oxychloride adhesive(MOA)is a kind of inorganic adhesive with high water resistance and flame retardation without no formaldehyde pollution and VOC.In this study,MOA and poplar shavings were used to prepare magnesium oxychloride adhesive particleboard(MOPB),fly ash(FA),soybean protein(SPI)and silane coupling agent(KH560)were used to modify and enhance the properties and interface of MOPB.Microscopic characterization was used to analyze the effect of microstructure and crystal content from modifier,in order to clarify the mechanism of bonding,modification and interface enhancement of MOPB.The results were as below:1.The hydration reaction of MOPB occurred during curing and maintenance,mainly produced crystallization as 5.1.8 phase and 3.1.8 phase,which filled and wrapped the pits of wood in the form of"glue nail"and formed"weak interface layer"at the bonding interface by mechanical extrusion force.The gelation action produced by dehydration condensation reaction from hydroxyl group-OH in MOA and the molecular chain of wood cellulose.When the molar ratio of Mg O/Mg Cl₂(M value)was 5,H₂O/Mg Cl₂molar ratio(H value)was 15,MOA addition rate(R)was 70wt%,cold pressing time(T)was 8h,curing days(D)was 28d,the modulus of rupture(MOR)of MOPB was 13.11MPa;the modulus of elasticity(MOE)was 2600MPa;the thickness swelling(TS)was 2.36%;heat release rate(HRR)was 24KW/m² at600?;the maximum value of total smoke produce(TSP)was 0.167m²,which reached the requirements of B1 type defined in national standard GB 8624-2012.2.Fly ash(FA)started a process as"break–depolymerization-compose"in Si-O and Al-O bonds and then polymerized into hydrated calcium silicate system C₁₃H₃₆Si₄(C-Si-H).This system was filled with whiskers of MOA and formed the structure like interweaved"skeleton",which was beneficial to the elastic recovery during the deformation.When the proportion of fly ash was 15wt%,the MOR of MOPB-FA was enhanced by 24.5%;the MOE was enhanced by 76.7%;TS decreased by 2.36%;HRR decreased by 61.8%;TSP decreased by 69.46%,THR decreased by 85.15%.3.The-NH group in protein peptide chain of soybean protein isolate(SPI)reacted with Cl^-from MOA to formed NH₄Cl crystal.SPI promoted the fully hydration of MOA and made the content of 5-phase crystal increase to 80%.MOR of MOPB-SPI was enhanced by 35.2%;MOE was enhanced by99.7%;TS decreased by 76.6%,HRR decreased by 61.8%;TSP decreased by 69.46%;THR decreased by 85.15%?4.Na OH(3wt%)was used to pretreat wood shavings,then KH560 was added to enhance the bonding interface after that.The siloxane Si-O group in KH560 decomposed into silanol in the hydration process.As the result,the reactivity and compatibility of the bonding interface were improved.The enhancement of MOPB was higher than MOPB-FA and MOPB-SPI.When the proportion of KH560 was 5wt%,MOE of MOPB-KH was enhanced by 63.5%,MOR was enhanced by 27%,TS increased by 71.4%,HRR decreased by 9.2%,TSP increased by 14.97%,THR decreased by 24.57%?...