Preparation And Expansion Mechanisms Of UV Curable Phosphorus-nitrogen Intumescent Flame Retardant Coatings

In this paper, triazinyl tetraacrylate (FAT) and phosphate heterocyclic acrylate(PHA) were synthesized as flame retardant reactive monomer for UV curable resin.Polyacrylate (PEA) was synthesized by modifying epoxy side group polyacrylate withacrylic acid. FAT, PHA, pentaerythritol triacrylate (PETA), PEA were blended indifferent ratios to prepare UV curable phosphorus-nitrogen intumescent flame retardantcoatings.The limiting oxygen index (LOI), physical properties, thermal stability,thermal degradation mechanism and expansion properties of the cured films werestudied, and the expansion mechanism were further investigated. The details of thedissertation are as follows:The FAT was synthesized with cyanuric chloride, hexamethylenediamine andhydroxypropyl acrylate; PHA was synthesized with phosphorus oxychloride, neopentylglycol and methyl glycidyl acrylate; and characterized by Fourier transform infraredspectrometer (FTIR) and1H Nuclear Magnetic Resonance (1HNMR).A series of UV-cured intumescent flame retardant system were obtained by mixingof FAT, PHA and PETA in different proportions. The intumescent flame retardantproperties of the cured films were tested by LOI and unidirectional intumescentdegrees (UID). The results showed that the cured films had better performance of LOI29, UID22times, when the mass ratio of the FAT and PHA was1:2.The thermal degradation mechanisms of the cured films of FAT, PHA and theirblends were studied by Thermal Gravimetric Analysis (TGA) and FTIR. The resultsindicated that the degradation of cured FAT film could be divided into two steps. From250oC to350oC, the degradation was mainly attributed to the degradation of estergroup. From350oC to500oC, alkyl decomposed and triazinyl decomposed to formnon-combustible gases. The degradation of the cured PHA film could also be dividedinto two steps. From200oC to320oC, phosphate and esterdepredated and generatedphosphoric acid which catalyzed the resin charring at higher temperature. From500oCto750oC, the degradation attributed to the further degradation of the char layer. Thedegradation of FAT-PHA cured film included four steps. From200oC to350oC, thedegradation was mainly due tothe fast degradation of the ester group and phosphate toform poly(phosphoric acid). From350oC to470oC, poly(phosphoric acid) further catalyzed the degradation of the material to form char with the emission of nitrogenvolatiles from the decomposition of triazine rings, leading to the formation ofexpanding char. The formed char was further dehydrogenationin the range of470oC to600oC. When raising the temperature over650oC, the decomposition was mainlyattribute to the further oxidative and decomposition of the residue char layer.The flame retardant property of FAT-PEA and PHA-PEA cured films was studiedby LOI. The results showed that the addition of FAT and PHA could effectivelyimprove the retardant property of PEA, with the LOI values increasing from19to to23.2and28respectively.The phosphorus-nitrogen compound flame retardant (PN) by mixingFAT and PHAin1:2mass ratio was blended with PEA resin in different p roportions to obtain a seriesof UV curable intumescent flame retardant resin.The physical properties, LOI,expansion properties and thermal stability of the cured films were studied. The resultsshowed that the sample with the40wt.%content of PN has the best comprehensiveproperties among all samples: pencil hardness of2H, the adhesion of level0, flexibilityof2mm, the LOI of28.5, UED of13times, the char residue at550oC of25.3%.