Flame retardancy and thermal properties of rigid polyurethane foam conjugated with a phosphorus–nitrogen halogen-free intumescent flame retardant

Abstract

In this work, a halogen-free intumescent combining phosphorus and nitrogen, flame-retardant 2-((2-hydroxyphenyl)(phenylamino)methyl5,5-dimethyl-1,3,2-dioxaphosphinane 2-oxide (HAPO) was successfully synthesized. It had been synthesized by reaction of 5,5-dimethyl-1,3, 2-dioxphosphinane 2-oxide with Schiff base. Its chemical structure was characterized in detail by Fourier transform infrared spectroscopy, 1H NMR, and 31P NMR spectrum. The flame-retardant polyurethanes were prepared with different loadings of HAPO. The thermal properties, flame retardancy and combustion behavior of the pure polyurethane foam thermosets were investigated by a series of measurements involving thermogravimetric analysis, limited oxygen index measurement, UL-94 vertical burning test, and cone calorimeter test. The results of the aforementioned tests indicated that HAPO can significantly improve the flame retardancy as well as smoke inhibition performance of polyurethane foam. Compared with the PU-Neat, the limited oxygen index of flame-retardant polyurethanes (15%) thermoset was increased from 19.5% to 23.8% and its UL-94 reached V-0 rating. In addition, the cone test results showed that the heat release rate, total heat release, rate of smoke release, and total smoke production of flame-retardant polyurethanes (10%) were decreased obvious sly. The apparent morphology of carbon residue was characterized by scanning electron microscopy, and results revealed that the modified polyurethane foam can form dense carbon layer after combustion. Thermogravimetric analysis results also indicated that the char amount of flame-retardant polyurethanes was obviously increased compared with PU-Neat. Based on the above analysis, we can draw the conclusions which in the condensed phase, phosphorus-based acids from the degradation of HAPO, this could promote the formation of continuous and dense phosphorus-rich carbon layer. In the gas phase, the flame-retardant mechanism was ascribed to the quenching effect of phosphorus-based radicals and diluting effect by non-flammable gases.

Characterization and Properties of Water-Blown Rigid Polyurethane Foams Reinforced with Silane-Modified Nanosepiolites Functionalized with Graphite

“…However, they have a major drawback in that a large amount of toxic polluting gases are generated during their combustion. For this reason, the halogen-free FRs were developed from compounds based on phosphorus, nitrogen or silicon as substitutes for halogen-based FRs [ 4 , 5 , 6 , 7 ].…”

Acoustic Performance and Flame Retardancy of Ammonium Polyphosphate/Diethyl Ethylphosphonate Rigid Polyurethane Foams

“…Based on extensive research and practice, phosphorus is thought to be a crucial element exhibiting flame retardancy [ 19 ]. Reactive flame retardants containing phosphorus [ 20 , 21 , 22 , 23 , 24 , 25 , 26 ] have attracted much attention, yet their applications are limited since phosphorus is expensive and difficult to process. On the contrary, additive flame retardants are widely used for their versatility and availability.…”

Synergistic Flame Retardant Effect of Barium Phytate and Intumescent Flame Retardant for Epoxy Resin

“…In order to improve the flame retardancy of EP [ 6 , 7 , 8 , 9 ], there are several commonly used methods, such as surface modification [ 10 ], superrefining [ 11 , 12 , 13 ], complex cooperation [ 14 , 15 ], and cross-linking. A lot of research works have been carried out, and the direct addition of flame retardants has the advantages of convenience and economy, thus becoming the most chosen approach.…”