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A series of new flame retardants (FR) based on dibenzo[d,f][1,3,2]dioxaphosphepine 6-oxide (BPPO) incorporating acrylates and benzoquinone were developed previously. In this study, we examine the fire behavior of the new flame retardants in polyisocyanurate (PIR) foams. The foam characteristics, thermal decomposition, and fire behavior are investig...
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... study aims to investigate differences in phosphonate, phosphinate and phosphate (TPP) based FR in technically relevant PIR formulations. The synthesis of the novel BPPO compounds that are listed in Table 1 has been previously reported by our group [32]. We found that the synthesis of BPPO proceeds under significantly milder conditions than those reported for DOPO [33]. ...Context 2
... PIR foam preparation, a solution of 25 wt% potassium acetate in DEG (nOH: 793 mg KOH/g) was used as a catalyst. The synthesis of the BPPO-containing FRs according to Table 1 has been recently described [32]. The DOPO-derivative of dimethyl itaconate (DMI-DOPO) was synthesized according to Pospiech et al. [35]. ...Context 3
... 2 summarizes the general composition of the foams. The complete formulations are listed in Table S1 in the Supplementary Materials. ...Context 4
... the following, TPP was replaced by BPPO-and DOPO-based derivatives incorporating acrylates and benzoquinone. Table 1 provides the systematic structural variation. In case of the acrylate derivatives, the structure of the substituent was varied (methyl, ethyl, t-butyl, and phenyl). ...Context 5
... observations suggest that both TPP and TEP completely evaporate in the gas phase. Table S1 in the Supporting Information. Figure 5b illustrates the thermal decomposition of foams, where the acrylate-BPPO additives substituted TPP. ...Citations
A 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) derivative is prepared. At first, an intermediate 4,4'‐((triazole)bis(azaneylylidene)bis(2,6‐dimethoxyphenol)) (SGA) is obtained from the Schiff‐base reaction between syringaldehyde (S) and 3,5‐diamino‐1,2,4‐triazole (GA). The further product DOPO‐SGA is then introduced into epoxy by blending to improve flame retardancy and mechanical properties. The flammability evaluation is implemented by limited oxygen index (LOI), UL‐94, and cone calorimeter tests. The presence of 3wt.% DOPO‐SGA increases the LOI to 33.2%, upgrades the UL‐94 rating to V‐0, and reduces the release of smoke and heat of epoxy. The tensile strength and impact strength are also enhanced after the introduction of DOPO‐SGA. The addition of 5% DOPO‐SGA increases the tensile strength and impact strength by 47% and 42%, respectively, compared with that of the control EP sample. It is suggested that the mechanical strengthening is ascribed to the ternary cross‐linked network among epoxy monomer, curing agent, and DOPO‐SGA. This work provides a feasible solution to obtain flame‐retardant epoxy resin with enhanced mechanical performance. A DOPO derivative (DOPO‐SGA) is fabricated via a Schiff base addition reaction of DOPO, syringaldehyde, and 3,5‐diamino‐1,2,4‐triazole. The cured epoxy resin containing DOPO‐SGA exhibits improved flame retardancy. No dripping is produced in the burning, and the sample self‐extinguished after leaving the fire. The tensile strength and impact strength of the sample containing DOPO‐SGA are higher than the control EP sample.
Polyurethanes (PUs) are an important and versatile class of polymers that are applied in industry, building construction and in various consumer products. However, the rigid and complex structure of PU makes it challenging to deal with PU at end-of-life, while without appropriate waste treatment, disposed PU products may result in severe environmental pollution. Thermochemical recycling processes allow the production of valuable chemicals from PU waste streams and may enable circular recycling routes. This review focuses on pyrolysis of PUs studied by thermogravimetric methods as well as on experiments conducted in micro or bench-scale lab reactors, that allow to study the product distribution and the thermal decomposition chemistry relevant for pyrolysis and gasification processes. PUs typically decompose in multiple stages as function of the temperature, whereby generally the isocyanate linkers disassociate at lower temperatures and the high molecular weight polyol linkers decompose at higher temperatures. The product distributions were found to strongly depend on the composition of PU and the pyrolysis conditions, while the presence of fire retardants and other additives did hardly have an effect. By further development and optimization, it is expected that pyrolysis and gasification can be suitable alternatives to deal with growing amounts of PU waste.
Due to the high flammability and smoke toxicity of polyurethane foams (PUFs) during burning, distinct efficient combinations of flame retardants are demanded to improve the fire safety of PUFs in practical applications. This feature article focuses on one of the most impressive halogen-free combinations in PUFs: expandable graphite (EG) and phosphorus-based flame retardants (P-FRs). The synergistic effect of EG and P-FRs mainly superimposes the two modes of action, charring and maintaining a thermally insulating residue morphology, to bring effective flame retardancy to PUFs. Specific interactions between EG and P-FRs, including the agglutination of the fire residue consisting of expanded-graphite worms, yields an outstanding synergistic effect, making this approach the latest champion to fulfill the demanding requirements for flame-retarded PUFs. Current and future topics such as the increasing use of renewable feedstock are also discussed in this article.
In this study, a reactive flame-retardant diol (BEOPMS) was synthesized by the esterification reaction of 9,10-dihydro-10-[2,3-di(hydroxycarbonyl)propyl]-10- phospha-phenanthrene-10-oxide with diethylene glycol. The flame-retardant effect of it combined with polyaryl polymethylene isocyanate (PMDI) were tested for rigid polyisocyanurate-polyurethane foams (PIRs) fabricated via a one-step process. The higher limiting oxygen index (LOI) and char residue yield value of flame-retardant rigid polyurethane foam (FRPUF) (21.0 vol% and 21.9 wt%, respectively) at 3.5 wt% phosphorus content compared to those of the pure rigid polyurethane foam (RPUF) (17.0 vol% and 16.3 wt%, respectively), illustrating the great effect of BEOPMS on improving the flame retardancy of the foams. At a 3.5 molar ratio of NCO/OH and 3.5 wt% content of phosphorus, an even higher LOI value of PIR (28.0 vol%) with a highest char residue yield (44.7 wt%) was obtained. The flame-retardant mechanism was discussed according to the scanning electron microscope (SEM), energy dispersive spectrometer (EDS), cone calorimeter (CC) and thermal gravimetric analysis-Fourier-transform infrared analyses (TG-IR). It is recognized that the isocyanurate ring groups can improve the thermostability of resultant PIRs, and increase the char residue yield in combination with the higher content of PMDI. Meanwhile, the thermal degradation of BEOPMS produces phosphate in condensed phase and released PO and PO₂ free radicals, which inhibits the free radical chain reactions in the gas phase and thus enables a superior flame retardancy effect for polyurethane foams.
