Study On Preparation And Performance Of Magnesium Adhesive For Wood Products

At present,wood composite materials made of aldehyde synthetic resin adhesive release formaldehyde during use to pollute the living environment,and their thermal stability and flame retardant effects are both poor.Therefore,there is an urgent need to develop wood-based adhesive that are functional superimposed and eco-friendly.Inorganic magnesium adhesive have the characteristics of high bonding strength,non-toxic and environmental friendly,good thermal stability,and not easy to burn.Comprehensive performance of magnesium adhesive is relatively outstanding,but there is a lack of relevant research on the use of magnesium adhesive for wood bonding,leading to its rarely use in the processing of wood products.?1?The bonding perfoemance of plywood prepared by magnesium adhesive is affected by factors such as molar ratio of raw materials,sizing amount,cold pressing time and curing days.Among them,the curing days have the most significant effect.The optimized formula and preparation process conditions are as following:n?Mg O?/n?Mg Cl₂?=6,n?H₂O?/n?Mg Cl₂?=16,sizing amount is 700g/m²?both sides?,cold pressing time is 28h,and curing days are 13d.Under the conditions,the dry bonding strength of the plywood prepared by the magnesium adhesive is 1.40MPa,and the wet bonding strength is 1.08MPa.The bonding mechanism between wood interface and magnesium adhesive that the magnesium adhesive wet the wood surface and diffuse into the wood pores.After curing,it forms a mechanical binding of glue nails to the glued wood.?2?The crystal phase composition and micro-morphology of the magnesium adhesive are the direct factors that affect its performance.The cured magnesium adhesive consists of a large amount of5Mg?OH?₂·Mg Cl₂·8H₂O?518 phase?,and a small amount of 3Mg?OH?₂·Mg Cl₂·8H₂O?318 phase?,Mg?OH?₂and Mg O.The microscopic morphology of the magnesium adhesive is dominated by staggered stacking of leaf-like crystals.After being immersed in water,the 518 phase crystals in the magnesia adhesive partially hydrolyzed leading to phase transformation.And the microscopic morphology of the magnesium adhensive being immersed in water is thin round crystals.?3?Adding proper amount of styrene-acrylic emulsion can improve the water resistance of magnesium adhesive.When the amount of styrene-acrylic emulsion added is 6wt%of the magnesium adhesive and the curing period is 13d,the water resistance of the plywood prepared by the styrene-acrylic emulsion modified magnesium adhesive is the best,the strength retention coefficient is increased by14.79%,and 24h water absorption rate was reduced by 18.56%.The modification mechanism is that the styrene-acrylic emulsion particles fill the voids of the magnesium adhesive structure and form a thin film on the surface of the crystal,which effectively inhibits the hydrolysis of the magnesium adhesive when it meets water.?4?Adding proper amount of soy protein can improve the bonding strength of magnesium adhesive.When the added amount of soy protein is 3wt%of the magnesium adhesive and the curing days are 13d,the bonding strength of the plywood prepared by the soy protein modified magnesium adhesive is the highest,the dry bonding strength increases by 18.57%,and the wet bonding increases by 18.52%.Its modification mechanism is that soybean protein and magnesium adhesive form an interpenetrating network structure,effectively improving the uniformity and compactness of magnesium adhesive structure.?5?Thermal stability of magnesium adhesive,styrene-acrylic emulsion modified magnesium adhesive and soybean protein modified magnesium adhesive are all good.And the flame retardant effect of the plywood prepared by them is excellent.The total mass loss rate of magnesium adhesive and modified adhesive in the range of 30-800?is 45%-50%.The total heat release amount and heat release rate of the plywood prepared by them during combustion are much less than that of phenolic synthetic resin adhesive.