| Intumescent fire retardant coating is an important means of steel structure fire protection in modern society,but solvent fire retardant coating has the problems of high VOC content,low coating efficiency and uneven film thickness.In contrast,powder coating has the characteristics of environmental protection,convenient coating and economy,so the powdering of fire retardant coating is a very meaningful research direction.According to the classical foaming theory and cell growth mechanism,the expansion foaming performance of intumescent fire retardant coating is closely related to the melt strength of the matrix resin.At the same time,powder coating also has the requirements of easy melting,leveling and curing of the matrix resin.Therefore,how to regulate the matrix resin to meet the requirements of expansion foaming of fire retardant coating and powder coating has become a key problemIn this paper,from the perspective of in-situ curing,adjusting three-dimensional crosslinking network and branched chain modification,the powder fire retardant coatings of thermosetting and thermoplastic systems are prepared.The viscosity of matrix resin is adjusted by adjusting the crosslinking density of matrix resin,and the viscosity of matrix resin is adjusted by adjusting the degree of branched chain,so as to prepare expandable foaming powder coatings.The specific work is as follows:1.A thermosetting powder fire retardant coating was prepared by using solid boron phenolic resin(FB)and solid epoxy resin(E20)as matrix resin and expandable graphite(eg).The curing reaction of the coating at various temperatures was measured by infrared spectroscopy.By changing the ratio of matrix resin,the effects of crosslinking density on glass transition temperature,thermal stability,flame retardancy and foaming and thermal insulation properties were studied.The results show that the increase of FB resin in the matrix resin will improve the glass transition temperature,thermal stability and flame retardancy of the system.When EG is not added,the oxygen index reaches 29.5 and the vertical combustion grade reaches V-1.After EG is added,the oxygen index reaches 34.0 and the vertical combustion grade reaches V-0,but the addition of EG will increase the amount of flue gas.On the other hand,the increase of FB content in the matrix resin will increase the crosslinking density and then produce a certain resistance to EG foaming.When the same amount of EG is added,the higher the FB content in the matrix resin,the lower the expansion ratio.The maximum fire resistance of the prepared powder fire retardant coating is 41.7min and the maximum expansion ratio is4.0.When the proportion of matrix resin is the same,with the increase of EG content,the bubbles of the system gradually become smaller,and finally can not produce complete bubbles.2.Thermoplastic powder fire retardant coating was prepared by using PE resin as matrix resin and n-p-c ternary intumescent flame retardant.DCP,BPO and TBPB were used to modify the in-situ crosslinking of powder coatings.The effects of the type and amount of crosslinking agent on the melt strength,melt crystallization,mechanical properties and foaming and thermal insulation properties of matrix resin were investigated.The results show that the crosslinking agent can make the PE matrix resin produce more three-dimensional crosslinking network structure,destroy the crystallization process of PE and reduce the melting point.At the same time,it can improve the mechanical properties of the matrix resin.The maximum tensile strength is23.2MPa and the maximum elongation at break is 960.1%.The use of crosslinking agent improves the crosslinking density,thus improving the melt strength.The foaming resistance of intumescent flame retardant gradually increases.The maximum fire resistance is 34.55 min,the maximum expansion ratio is 8,the minimum fire resistance is 28.7min,and the minimum expansion ratio is 0.EVA,l9450 and Poe polymers with different branch chain lengths were used to improve the viscosity of the matrix resin and regulate the foaming process.The results showed that the compatibility of EVA with polar short branched chain and Poe with long branched chain with PE was poor,and the crystallization process of PE was destroyed after blending,and l9450 with short branched chain had the best compatibility with PE;After blending modification,the mechanical strength and elongation at break of the matrix resin were improved.The maximum tensile strength was 26.73 MPa and the maximum elongation at break was 1408.0%;Because the non-polar short branched chain can provide more free volume,the l9450 with the shortest branched chain length can greatly reduce the viscosity of the system and the foaming resistance after modifying PE.The maximum fire resistance and expansion ratio are 36.85 min and 19;The polar short branched chain in EVA increases the intermolecular force,improves the viscosity to a certain extent,and increases the expansion ratio and fire resistance limit,with the maximum of 38.67 min and 17 min respectively;Poe has the longest branched chain length,which leads to the enhancement of intermolecular entanglement and the improvement of viscosity to a certain extent.The maximum fire resistance and expansion ratio are 36.05 min and 19.5 min respectively. |
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