Effect Of Retarder On Properties Of Magnesium Oxychloride Inorganic Plywood

Magnesium oxychloride original gum was prepared by lightly burning magnesium oxide,magnesium chloride and self-made catalyst in laboratory.Magnesium oxychloride inorganic plywood was prepared by cold pressing process with different amounts of trisodium phosphate and phosphoric acid as retarder.The retarding effect of retarding agent on adhesive was studied by changing the amount of trisodium phosphate and phosphoric acid.The effect of retarder on the properties of magnesium oxychloride inorganic plywood was analyzed by crystal phase composition and crystal morphology.The feasibility of using trisodium phosphate and phosphoric acid to delay the initial setting time of magnesium oxychloride adhesive was investigated.The study mainly draws the following conclusions:（1）After the addition of trisodium phosphate,the initial setting time of magnesium oxychloride adhesive was delayed,and the maximum delay was 4h when the addition amount of trisodium phosphate was 1%;When the amount of trisodium phosphate was 0.8%,the bonding strength of plywood was the highest.The elastic modulus,static bending strength and flame retardancy of plywood decreased after adding trisodium phosphate.There was no defrosting phenomenon in the plywood.When the addition of sodium phosphate was 0.6%,the water resistance of plywood was the worst and the nail holding strength was the best.The content of phase 518 was the highest when the amount of sodium phosphate was 0.8%.The content of Mg（OH）₂ was relatively high when the dosage of trisodium phosphate was 0.6%and 1%.（2）After phosphoric acid was added,the initial setting time of magnesium oxychloride adhesive was delayed by 4.84 h at the highest level when phosphoric acid was added at 1%.The binding strength,elastic modulus,static bending strength and nail holding force of plywood are relatively higher when the phosphate content is 0.2%.The flame retardant property of plywood is the best when the amount of phosphoric acid is 1%.There was no defrosting phenomenon in the plywood.24 h water absorption and dip stripping of plywood increased to 23.9%and 15 mm,respectively,when the phosphate content was0.2%.After the addition of phosphoric acid,the phase transformation of magnesium oxychloride adhesive occurred,the content of 518 phase increased first and then decreased,and the content was the highest when the addition amount was 0.2%.The content of Mg（OH）₂ was the highest when the phosphate content was 0.4%.The content of Mg（OH）₂ increased significantly and the content of Mg O decreased at 0.4%phosphate.（3）After adding complex retarder,the initial setting time of magnesium oxychloride adhesive was significantly increased,and the maximum initial setting time was delayed 5.53 h when the amount of trisodium phosphate was 0.8%and the amount of phosphate was 0.6%.When the amount of trisodium phosphate is 0.2%and the amount of phosphoric acid is 0.2%,the internal bonding strength and other physical mechanics,flame retardant properties,water resistance of the plywood are relatively high,the reason is that the crystal structure of the adhesive is good,the plywood did not appear back halogen frost phenomenon,suitable for the actual production.