Toxic products from the combustion and pyrolysis of polyurethane foams

Products from the thermal decomposition of four polyurethane foams heated to temperatures in the range 220 to 400 °C, in atmospheres of nitrogen, of 6% oxygen in nitrogen and of air were examined for some of the anticipated toxic materials. When phosphorus-containing inhibitors were added to or chemically incorporated in the foams, phosphorus compounds were evolved under most of the conditions employed. Other materials detected were hydrogen cyanide, isocyanate, urea, halogenated compounds and alkenes. A brief discussion is given of the hazard presented by polyurethane foams decomposing under these conditions.     

Foamed polyurethane plastics of reduced flammability

In this study, modified foamed polyurethane materials were obtained with the use of new polyols. The polyols were synthesized by the reaction of N,N′‐bis(2‐hydroxyethyl)oxamide esterified with boric acid and various excesses of ethylene carbonate. Thus, poly(ethylene glycol)s with incorporated oxamide and borate groups containing different amounts of boron and nitrogen were obtained. On the basis of these new polyols, rigid polyurethane foams were produced. They contained 0.8–1.2 wt % boron and 7.9–8.5 wt % nitrogen. The resulting foams showed reduced flammability, as determined on the basis of the measurements of the oxygen index and horizontal and vertical flammability tests. The foams also exhibited improved thermal stabilities and mechanical strengths and good dimensional stabilities. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45748.     

A review of the literature on the gaseous products and toxicity generated from the pyrolysis and combustion of rigid polyurethane foams

The literature on rigid polyurethane foam has been reviewed with an emphasis on the gaseous products generated under various thermal decomposition conditions and the toxicity of those products. This review is limited to publications in English through 1984. Carbon monoxide (CO) and hydrogen cyanide (HCN) were the predominant toxicants found among more than a hundred other gaseous products. The generation of CO and HCN was found to increase with increasing combustion products from various rigid polyurethane foams. Lethality, incapacitation, physiological and biochemical parameters were employ as biological end points. In general, the combustion products generated from rigid polyurethane foam in the flaming mode appear from to be more toxic than those produced in the non-flaming mode. The LC₅₀ values for 30-min exposures ranged from 10 to 17 mg l^?1 in the flaming mode and were greater then 34 mg l^?1 in the non-flaming mode. With the exception of one case, in which a reactive type phosphorus containing fire retardant was used, the addition of fire retardants to rigid polyurethane foams does not appear to generate unusual toxic combustion products.     

Preparation and characterization of rigid polyurethane foams with carbamide and borate groups

The results of research on the application of hydroxyethyl urea derivatives modified with boron as polyol components to produce foamed polyurethane materials are presented. The obtained rigid polyurethane foams are characterized by good heat‐insulating parameters and decreased flammability. The decrease in flammability of the foams follows from the presence of boron and increased nitrogen content, resulting from the use of polyol with urea groups. The incorporation of boron into the foam structure also results in a substantial increase in the compression strength, compared to classic foams and to non‐boron‐modified ones. The self‐extinguishing foams of high mechanical strength can find application as heat‐insulating construction elements for the building industry. © 2016 Society of Chemical Industry     

Polyurethane foams with the contribution of products of hydroxyalkylation of N,N′‐bis(2‐hydroxyalkyl)oxamides with alkylene carbonates—obtaining and properties

In the reactions of N,N′‐bis(2‐hydroxyethyl)oxamide (BHEOD) with an excess of ethylene carbonate (EC) and N,N′‐bis(2‐hydroxypropyl)oxamide (BHPOD) with an excess of propylene carbonate (PC), the hydroxyethoxy and hydroxypropoxy derivatives of oxamide (OD) were obtained, respectively, distinguished by an increased thermal stability. First time, these derivatives were used as polyol components to obtain foamed polyurethane plastics with the contribution of 4,4′‐diisocyanate diphenylmethane (MDI). The rigid polyurethane foams of a slight water uptake, good stability of dimensions, enhanced thermal stability, and compression strength were obtained. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of surface chemistry on the reactive adsorption of hydrogen cyanide on activated carbons

Two activated carbons of different origins were modified by heating at 950 °C either with or without previous urea impregnation. The treatment causes changes in surface chemistry and porosity. The materials obtained were used as adsorbents for hydrogen cyanide in dry air at ambient conditions. The samples before and after adsorption were characterized using nitrogen adsorption, potentiometric titration, elemental analysis and thermal analysis. On selected samples extraction was carried out to identify surface reaction products soluble in alcohols. The results indicated differences in the amount adsorbed and the products of surface reactions on specific surface features. The presence of nitrogen incorporated in the carbon matrix leads to an enhanced performance owing to the basic environment and the ability of the surface to activate oxygen. These lead to complex surface reactions in which the derivatives of hydrogen cyanide form oxamide, and are incorporated in the carbon matrix, or are deposited as the bulky insoluble polymers of paracyanogen on the surface. The reactions mainly occur in pores with sizes between 10 and 20 Å where the functional groups can be present and HCN, or its derivatives, and water can take part in the reactions.     

Hydroxyalkoxy derivatives of oxamic acid: polyol substrates for polyurethane foams

BACKGROUND: The work reported aimed at obtaining hydroxyalkoxy derivatives containing oxalamidoester groups starting from oxamic acid (OA) substrate. These derivatives were then used for the synthesis of polyurethane foams. RESULTS: The hydroxyalkoxy derivatives were obtained by reaction of OA with 6 to 15 molar excess of ethylene carbonate (1,3‐dioxolane‐2‐one) or propylene carbonate (4‐methyl‐1,3‐dioxolane‐2‐one). The products obtained have good thermal stability and possess suitable physical properties for use as substrates for foamed polyurethanes. CONCLUSION: The rigid polyurethane foams obtained from the hydroxyalkoxy derivatives of OA possess enhanced thermal stability and good mechanical properties in comparison with traditional polyurethane foams. Copyright © 2009 Society of Chemical Industry     

聚氨酯/三聚氰胺甲醛树脂复合泡沫热降解动力学研究

三聚氰胺甲醛树脂脱水后和多元醇混合,然后用异氰酸酯与混合物进行交联反应,生成聚氨酯/三聚氰胺甲醛树脂复合泡沫.热重分析结果表明,复合泡沫失重分为3个阶段,二苯基甲烷二异氰酸酯(MDI)型三聚氰胺甲醛树脂复合泡沫的第2阶段的失重峰温比甲苯二异氰酸酯(TDI)型三聚氰胺甲醛树脂复合泡沫的高.采用Kissinger法研究了该...     

Reaction products of parabanic acid and alkylene carbonates as components of polyurethane foams

Esteramidoimidotetraols are obtained by reacting 8‐ and 12‐molar excess of ethylene carbonate or propylene carbonate with parabanic acid. The parabanic acid ring undergoes opening, and linear polymeric products are formed. The products can conveniently be used as polyols for polyurethane foams. The results of a study on thermal stability and on compressive strength of foams prepared from these tetraols, measured before and after thermal treatment, are reported. Copyright © 2007 Society of Chemical Industry     

The thermal decomposition of some tolylene bis-carbamates

In fires, flexible polyurethane foams can decompose to give smokes which are subsequently degraded with the generation of hydrogen cyanide. In order to understand the general nature of this hazard it is first necessary to obtain information about the decomposition mechanism of the polyurethane foams and the structures of the intermediate smokes. The complexity of this problem has required the use of suitable model compounds. The preparation is described of (i) the four bis-carbamates based on pure tolylene 2, 4-diisocyanate and pure tolylene 2,6-di-isocyanate, each in combination with 2-ethoxyethanol and with triethylene glycol monomethyl ether, and (ii) a urethane-carbodi-imide-urethane and a urethane-urea-urethane based on pure tolylene 2,6-di-isocyanate and 2-ethoxyethanol. All were decomposed by heating under nitrogen at temperatures near 300°C. The two di-2-ethoxyethyl bis-carbamates ( la and IIa ) gave volatile monoisocyanate-monourethanes and 2-ethoxyethanol. The two di-2-[2-(2-methoxyethoxy)ethoxy] ethyl bis-carbamates ( Ib and IIb ) gave corresponding products and residue which contained carbodi-imide functions. The urethane-carbodi-imide-urethane ( Va ) gave a volatile urethane-carbodi-imide-isocyanate ( Via ) and 2-ethoxyethanol. The urethane-urea-urethane ( VIIIa ) decomposed through isocyanate- and carbodi-imide-containing materials to a volatile polymeric urea, which was obtained as a smoke and appeared to be virtually identical with the smoke obtained in earlier work from a commercial polyurethane. These results suggest that poly-urethanes based on tolylene di-isocyanate and polyether polyols decompose, when heated under nitrogen at 300°C, by cleavage of urethane groups to regenerate isocyanate groups and liberate alcohols. The isocyanato groups may react either with other isocyanato groups to give carbodi-imides, which are then rapidly hydrated to ureas, or with water to give amines, which react with other isocyanato groups again to give ureas. Whether these processes occur separately or together, the ultimate product at 300°C, i.e. the smoke, will be a polymeric urea.     

新型硬质聚氨酯泡沫的热分解行为及动力学

利用热重分析法比较研究了新型硬质聚氨酯泡沫[超支化聚氨酯多元醇型(HBPU型)]和硬质聚氨酯泡沫(RPUF)在氮气中的热分解行为,探讨了HBPU型RPUF在不同升温速率下的热分解动力学,运用Kissinger最大失重率法和Flynn-Wall-Ozawa等失重百分率法计算获得了其热分解过程的活化能。研究结果表明,HBPU型RPUF的初始分解温度(T5%)为205℃,半寿温度(T50%)为361℃,略低于传统的RPUF。Kissinger法得到的HBPU型RPUF的热分解表观活化能为159.8 kJ/mol;Flynn-Wall-Ozawa法得到的热分解过程分为三个阶段:第一阶段的平均活化能为82.8 kJ/mol,第二阶段的平均活化能为140.7 kJ/mol,第三阶段的平均活化能为111.3 kJ/mol,HBPU型RPUF具有较好的热稳定性。     

Nitrogen-containing products from the thermal decomposition of flexible polyurethane foams

The thermal decomposition of a polyester and a polyether flexible foam in a nitrogen atmosphere has been studied by gas chromatography, mass spec-trometry and elemental ultramicroanalysis. It is shown that the decomposition behaviours of the two foams are similar. At low temperatures (200 to 300 °C) there is a rapid and complete loss of the tolylene diisocyanate unit of each foam as a volatile yellow smoke leaving a polyol residue. The smoke has been isolated as a yellow solid (common to both foams) which contains virtually all of the nitrogen of the original foams and, under the conditions of test, is stable at temperatures up to 750 °C. Nitrogen-containing products of low molecular weight (mainly hydrogen cyanide, acetonitrile, acrylonitrile, pyridine and benzonitrile) observed during the high temperature decomposition (over 800 °C) of the foams are shown to be derived from the yellow smokes. At 1000 °C, approximately 70% of the available nitrogen has been recovered as hydrogen cyanide.     

New foamed plastic based on polyetherols obtained from 6‐aminouracil,ethylene carbonate,and propylene oxide

Polyetherols with 1,3‐pyrimidine ring including both oxyethylene and oxypropylene groups were obtained in reactions of 6‐aminouracil with ethylene carbonate and propylene oxide. The structure of the products was analyzed by spectral methods. Some physical properties of polyetherols were investigated. The polyetherols were used as polyol components to obtain polyurethane foams. Some properties of the foams such as apparent density, absorption of water, linear dimensions stability, thermal resistance, and compression strength were investigated. The foams obtained show an improved thermal stability. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of the Additive Fire Retardants on the Properties of Rigid Polyurethane Foams,Obtained Using Hydroxyethyl Derivatives of Oxamide and Polymeric 4,4′-diphenylmethane Diisocyanate

The present work investigates the effect of polyol structure and physical addition of boric acid and N,N′-bis(2-hydroxyethyl)oxamide on the properties of rigid polyurethane foams. The product of hydroxyalkylation of oxamide by ethylene carbonate has been used as a polyol component. The new polyol has been foamed using polymeric 4,4′-diphenylmethane diisocyanate, water, and triethylamine. To decrease the flammability of the foams, boric acid, and N,N′-bis(2-hydroxyethyl)oxamide were used as the additive flame retardants. It has been found, that chemical modification of the foam structure by means of oxamide groups decreases their flammability only to a small extent, whereas physical addition of N,N′-bis(2-hydroxyethyl)oxamide does not influence the flammability. However, the addition of boric acid to the foam composition resulted in a distinct decrease of foam flammability, according to the amount of boric acid added. All the foams, modified and nonmodified by boron, have been categorized into flammability class HF-1, according to the applicable standard. The introduction of flame retardants had its impact on the properties of polyurethane foams obtained, as described in this work.     

Ignition,combustion, toxicity,and fire retardancy of polyurethane foams: A comprehensive review

This review provides insight into the ignition, combustion, smoke, toxicity, and fire‐retardant performance of flexible and rigid polyurethane foams. This review also covers various additive and reactive fire‐retardant approaches adopted to render polyurethane foams fire‐retardant. Literature sources are mostly technical publications, patents, and books published since 1961. It has been found by different workers that polyurethane foams are easily ignitable and highly flammable, support combustion, and burn quite rapidly. They are therefore required to be fire‐retardant for different applications. Polyurethane foams during combustion produce a large quantity of vision‐obscuring smoke. The toxicity of the combustion products is much higher than that of many other manmade polymers because of the high concentrations of hydrogen cyanide and carbon monoxide. Polyurethane foams have been rendered fire‐retardant by the incorporation of phosphorus‐containing compounds, halogen‐containing compounds, nitrogen‐containing additives, silicone‐containing products, and miscellaneous organic and inorganic additives. Some heat‐resistant groups such as carbodiimide‐, isocyanurate‐, and nitrogen‐containing heterocycles formed with polyurethane foams also render urethane foams fire‐retardant. Fire‐retardant additives reduce the flammability, smoke level, and toxicity of polyurethane foams with some degradation in other characteristics. It can be concluded that despite many significant attempts, no commercial solution to the fire retardancy of polyurethane foams without some loss of physical and mechanical properties is available. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Analysis of the reaction course of oxamide and N,N′‐bis(2‐hydroxypropyl)oxamide with propylene carbonate

Studies on obtaining and hydroxypropyl properties of oxamide (OD) derivatives with contribution of OD and N,N′‐bis(2‐hydroxypropyl)oxamide (BHPOD) were carried out. As a hydroxyalkylating agent, the propylene carbonate (PC) was used. Hydroxypropylating with OD proceeds with a partial preservation of carbonate groups in the structure of products, and during the reaction, a partial dimerization of hydroxypropoxylene derivatives of OD occurs. The obtained hydroxypropoxy derivatives of OD are distinguished by an increased thermal stability. Hydroxypropoxy derivatives of OD are expected to find application as polyol components for the manufacture of thermally stable foamed polyurethane plastics. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of the composition of rosin-based rigid polyurethane foams on their thermal stability

A series of rosin-based rigid polyurethane foams of different composition were synthesized directly from chemically modified gum rosin. The effect of the composition of these rosin-based rigid polyurethane foams on their thermal stability and compression strength was measured. It was shown that the onset temperature of weight loss and the dimensional stability at high temperature increased with increase of the molar ratio of NCO/OH. The TGA data further confirmed that the second stage weight loss in the two-stage weight loss process of these polyurethane foams was governed by thermal degradation of the isocyanate component. Although density had no significant influence on the TGA curves of the rosin-based rigid polyurethane foams, it had great influence on the dimensional stability at high temperature and compression strength of the foams. It has been shown that the inclusion of rosin in rigid polyurethane foams increases the strength and thermal stability compared with that of polyether-based ones. © 1996 John Wiley & Sons, Inc.     

The effects of intumescent flame retardant including ammonium polyphosphate/pentaerythritol and fly ash fillers on the physicomechanical properties of rigid polyurethane foams

In this study, rigid polyurethane foams that contain up to 5.0 wt % fly ash (FA) being a by‐product of thermal power stations and being cheap source were successfully produced using a polyurethane injection machine. The effects of FA content on the thermal conductivity, compressive strength, and flammability were investigated. The morphology of the cell was observed under a special microscope. The incorporation of FA in rigid polyurethane foams may dramatically decrease production costs and reduce environmental pollution. In addition, the effects of intumescent flame retardant composed of ammonium polyphosphate and pentaerythritol were examined in pure rigid polyurethane foams and FA‐rigid polyurethane foams. It was found that 5.0 and 7.5 wt % intumescent flame retardant loadings enhanced the thermal stability and improved the flammability resistance of the foams. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Reinforcement of soy polyol‐based rigid polyurethane foams by cellulose microfibers and nanoclays

Water‐blown rigid polyurethane foams from soy‐based polyol were prepared and their structure–property correlations investigated. Cellulose microfibers and nanoclays were added to the formulations to investigate their effect on morphology, mechanical, and thermal properties of polyurethane foams. Physical properties of foams, including density and compressive strength, were determined. The cellular morphologies of foams were analyzed by SEM and X‐ray micro‐CT and revealed that incorporation of microfibers and nanoclays into foam altered the cellular structure of the foams. Average cell size decreased, cell size distribution narrowed and number fractions of small cells increased with the incorporation of microfibers and nanoclays into the foam, thereby altering the foam mechanical properties. The morphology and properties of nanoclay reinforced polyurethane foams were also found to be dependent on the functional groups of the organic modifiers. Results showed that the compressive strengths of rigid foams were increased by addition of cellulose microfibers or nanoclays into the foams. Thermogravimetric analysis (TGA) was used to characterize the thermal decomposition properties of the foams. The thermal decomposition behavior of all soy‐based polyurethane foams was a three‐step process and while the addition of cellulose microfibers delayed the onset of degradation, incorporation of nanoclays seemed to have no significant influence on the thermal degradation properties of the foams as compared to the foams without reinforcements. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011