Research On High-Strength Environmental Flame Retardant Paper And Its Mechanism

Paper has received widespread attention because of its green and environmentally friendly characteristics,among others.However,the paper itself is easy to burn,so its application areas are limited.At present,paper flame retardant usually uses impregnation and coating method,but the resulting flame retardant paper does not have flame retardant durability or can only make the paper surface to achieve flame retardant effect,and easy to absorb moisture deformation,affecting the use of performance.Therefore,the use of the pulp addition method to achieve intrinsic flame retardant paper,with good prospects for development.Ammonium polyphosphate(APP),as a halogen-free flame retardant,is green,environmentally friendly and economical,and has been widely used in the fields of plastics,rubber and construction.However,so far,APP has not been reported for industrial application in paper making.Therefore,the present study investigated the preparation of flame retardant paper by APP in-pulp addition method,and the results of the study are as follows:APP particles were square in shape with an average particle size of 21.88μm,and the particle size decreased significantly after 24 h of impregnation in water at 25°C.After0.5 h of impregnation in water at 90°C,most of APP dissolved and the residue became irregular in form.the zeta potential,charge density and conductivity of APP were-64.1mv,-9.24 meq/g,and 208μs/cm,respectively,so that APP has a strong negative charge,and it will be partially ionized in water.When the temperature was 25℃,the solubility of APP was 0.18 g/100 ml.After the temperature was greater than 30℃,the solubility increased significantly,and when the temperature was 50℃,the solubility reached 1.24g/100 ml,which was 588.9%higher than that at 25℃.APP was used as a flame retardant to prepare flame retardant paper by in-pulp addition method.The tensile strength of the paper increased and then decreased with the increase of APP dosage,and the tensile index reached the maximum value when the amount of APP was 10%,and then began to decrease gradually,and the tensile index of the paper was 50.5 N·m/g when the amount of APP was 40%,which was lower than that of the paper without APP addition,When APP is added at 30%and CPAM is added at0.08%,the LOI(limiting oxygen index)value of flame retardant paper is 28.7%,which reaches the flame-retardant level.Epoxy resin microencapsulated APP(APP@EP)showed reduced negative electrical properties and enhanced water resistance.Compared with APP,its absolute zeta potential decreased from 64.10 mv to 53.0 mv,absolute charge density decreased from 9.24 meq/g to 8.64 meq/g,electrical conductivity decreased from 208μs/cm to 197μs/cm,water contact angle increased from 26.54 When 30%APP@EP was added to the pulp,the paper tensile index decreased from 56.43 N·m/g to 49.32 N·m/g,the LOI value increased from28.7%to 29.8%,and the total heat release rate(THR)increased from 7.828 MJ/m~2 to6.196 MJ/m~2,the exothermic rate(HRR)from 64.627 KW/m~2 to 62.486 KW/m~2,the effective heat of combustion(EHC)from 18.127 MJ/kg to 15.146 MJ/kg,and the char paper residue at 800°C from 22.089%to 29.196%.APP@EC was produced by microencapsulation of APP with ethyl cellulose(EC).The effect of APP@EC encapsulation was better when the percentage of EC shell layer was greater than 6%.APP@6 wt.%EC had very low negative surface charge and enhanced water resistance.Compared with APP,the absolute value of zeta potential was reduced from 64.10 mv to 31.30 mv,the absolute value of charge density was reduced from 9.24meq/g to 7.83 meq/g,conductivity from 208μs/cm to 153μs/cm,water contact angle from 26.54°to 101.52°,solubility in water at 75°C from 5.57 g/100 ml to 1.56 g/100 ml,and thermal decomposition residue at 800°C from 25.27%to 17.30%.DSC showed that the melt heat absorption of the shell layer EC caused APP@EC to appear as a heat absorption peak other than APP,thus improving the paper flame retardant effect.When30%APP@6 wt.%EC was added in the pulp,the tensile index of the paper decreased from 56.43 N·m/g to 49.98 N·m/g,the LOI value increased from 28.7%to 31.2%,the THR decreased from 7.828 MJ/m~2 to 6.126 MJ/m~2,the HRR decreased from 64.627KW/m~2 to 44.137 KW/m~2,EHC decreased from 18.127 MJ/kg to 13.478 MJ/kg,and carbon residue of 800°C paper increased from 22.089%to 31.805%.