Preparation And Performance Study Of Transparent Intumescent Flame Retardant Coating Based On Amino Resin

Wood plastic composite material（WPC）has a broad development prospect because of its wide material source,environmental protection and recycling,excellent physical properties and high plasticity.However,WPC is mainly made of flammable wood materials and thermoplastic resins,which cannot be self-extinguished when it catches fire and is a flammable material,making the application of WPC greatly restricted.Although the additive flame retardant method has a good flame retardant effect,it often requires a large amount of additive,which not only affects the mechanical properties of WPC,but also increases the processing cost of WPC.To address the above problems,a transparent intumescent flame retardant coating was prepared and applied to the surface of WPC.Through the selection of WPC film-forming resin,optimization of flame retardant system,addition of graphene oxide（GO）and ammonium borate（ABT）flame retardant co-effectors,the effect of the coating on the flame retardant performance of WPC was studied and the flame retardant mechanism of the coating was analyzed.The main contents and results of the study are as follows:（1）The transparent intumescent flame retardant coating was synthesized by using melamine formaldehyde resin（MF）as the film-forming resin and phosphoric acid-pentaerythritol（H₃PO₄-PER）as the intumescent flame retardant system.When the quality ratio of each component of the flame retardant coating is MF:H₃PO₄:PER=8:10:10,the comprehensive performance is the best.This ratio was used as the control group for various tests.The results of the burning test on the large board showed that a layer of flame retardant coating on the surface of WPC could effectively protect the substrate,and the flame resistance time of the specimen reached 16 min;the thermogravimetric analysis showed that the flame retardant coating had good thermal stability,and the residual carbon amount was 20.5%at 700℃;the results of the cone calorimeter test showed that the flame retardant coating effectively reduced the heat release of WPC,and the total heat release（THR）of the control group was The total heat release（THR）of the control group was 103.99 MJ/m²,and the peak heat release rate（PHRR）was 238.58 k W/m²,which significantly improved the flame retardant performance.Combined with electron scanning microscopy and other analysis of the flame retardant mechanism of the coating is:when subjected to heat,the flame retardant coating first absorbs heat and releases inert gas to protect the substrate,and then expands to form a protective carbon layer,which isolates heat,blocks combustible gas and protects the substrate.（2）Keeping the mass ratio of MF:H₃PO₄:PER=8:10:10 unchanged,the flame retardant coating was synthesized by adding different proportions of GO as flame retardant co-efficient as the control group.The test results showed that the appropriate amount of GO did not affect the physical properties of the coating,and played a good flame retardant synergistic effect with MF-H₃PO₄-PER expansion system,and the comprehensive performance of the flame retardant coating was the best when the addition amount of GO was 0.2%.The results of large-plate burning test showed that the flame retardant performance of the flame retardant coating was further improved,and the flame resistance time of the specimen rose to 28 min;thermogravimetric analysis showed that the addition of GO could improve the stability of the expanded carbon layer,and the residual carbon amount of the flame retardant coating increased to 29.5%;cone calorimeter test showed that the addition of GO could effectively suppress the heat release and smoke release of the coating,and the THR and TSP of the coating were 103.99 MJ/m² and 10.49 m²/%,respectively.Combined with the scanning electron microscope analysis,it was found that the flake structure of GO became cross-linked points after the coating was expanded by heat,which improved the overall stability of the carbon layer and thus played the role of flame retardant co-efficient.（3）Keeping the mass ratio of MF:H₃PO₄:PER=8:10:10 unchanged,the flame retardant coatings were synthesized by adding different proportions of ABT as flame retardant co-effector as the control group.The test results showed that when the mass fraction of ABT was 4%,the comprehensive performance of the flame retardant coating was the best,and the overall light transmission rate of the flame retardant coating was kept above 80%.The burning time of the coating was 33 min measured by the large plate burning method;thermogravimetric analysis showed that the addition of ABT could improve the stability of the expanded carbon layer,and the residual carbon of the flame retardant coating increased to 37.9%when the ABT content was 4%;cone calorimeter test showed that the addition of 4%ABT could effectively suppress the heat and smoke release of the coating,and the THR and TSP of the specimen were 84.47 MJ/m² and 10.16m²,respectively.Combined with the analysis of electron scanning microscope,ABT will promote the carbonization of flame retardant system after heat,and at the same time form a layer of dense boron oxide on the surface of carbon layer,which will form a mixed carbon layer with excellent mechanical strength（boron-carbon）together with the expanded carbon layer.In turn,it plays the role of flame retardant co-efficient.（4）Keeping the mass ratio of MF:H₃PO₄:PER=8:10:10 unchanged,the flame retardant coating was synthesized by adding 0.2%mass fraction of GO and 4%mass fraction of ABT as the flame retardant co-effector as the control group.The test results showed that the physical properties of the coating were good,and the flame retardant and smoke suppression properties were excellent.The burning time of the coating was 37 min measured by the large plate burning method;the thermogravimetric analysis showed that the residual carbon amount of the specimen increased to 39.6%and the thermal stability of the coating improved significantly;the cone calorimeter test showed that the mixed flame retardant co-agent further reduced the heat release of the specimen and the THR of the specimen was 80.93 MJ/m².Combined with the SEM analysis,the addition of GO improved the stability of the carbon layer,and the addition of ABT improved the mechanical strength of the expanded carbon layer,which in turn improved the flame retardant and smoke suppressing effect of the coating.