A literature review of the chemical nature and toxicity of the decomposition products of polyethylenes

The literature on polyethylenes has been reviewed with an emphasis on the identification of gaseous products generated under various thermal decomposition conditions and the toxicity of those products. This review is limited to publications in English through 1984. The analytical chemical studies of the thermal decomposition products generated under vacuum, inert and oxidative experimental conditions are described. In oxidative atmosphere, which most closely simulate real fire conditions, carbon monoxide (CO) was found to be the predominant toxicant. Acrolein was another toxicant often noted in these reviewed studies. More acrolein was generated under non-flaming than under flaming conditions. Results from seven different test procedures were considered in assessing the acute inhalation toxicity of combustion products from various polyethylene formulations. The combustion products generated from the polyethylenes studied in the non-flaming mode appeared to be slightly more toxic than those produced in the flaming mode. In the non-flaming mode the LC₅₀ values ranged from 5 to 75 mg l^?1. In the flaming mode the LC₅₀ values ranged from 31 to 51 mg l^?1. The toxicity of the degradation products of polyethylenes appears to be similar to that found for other common materials designed for the same end uses.     

Toxicity of the pyrolysis and combustion products of poly(vinyl chlorides): A literature assessment

Poly(vinyl chlorides) (PVC) constitute a major class of synthetic plastics, Many surveys of the voluminous literature have been performed. This report reviews the literature published in English from 1969 through 1984 and endeavors to be more interpretive than comprehensive. PVC compounds, in general, are among the more fire resistant common organic polymers, natural or synthetic. The major products of thermal decomposition include hydrogen chloride, benzene and unsaturated hydrocarbons. In the presence of oxygen, carbon monoxide, carbon dioxide and water are included among the common combustion products. The main toxic products from PVC fires are hydrogen chloride (a sensory and pulmonary irritant) and carbon monoxide (an asphyxiant). The LC₅₀ value calculated for a series of natural and synthetic materials thermally decomposed according to the NBS toxicity test method ranged from 0.045 to 57 mg l^?1 in the flaming mode and from 0.045 to > 40 mg l^?1 in the non-flaming mode. The LC₅₀ results for a PVC resin decomposed under the same conditions were 17 mg l^?1 in the flaming mode and 20 mg l^?1 in the non-flaming mode. These results indicate that PVC decomposition products are not extremely toxic when compared with those from other common building materials. When the combustion toxicity (based on their HCI content) of PVC materials in compared with pure HCI experiments, it appears that much of the post-exposure toxicity can be explained by the HCI that is generated.     

Polystyrenes: A review of the literature on the products of thermal decomposition and toxicity

The current English literature through 1984 on the products of pyrolysis and combustion from polystyrenes and the toxicity of those products is reviewed. Among 57 compounds detected by chemical analyses of the thermal decomposition products produced under various atmospheric conditions (vacuum, inert and oxidative), the main volatile component is the styrene monomer, Evidence is provided that the mass fraction of styrene increases with furnace temperatures at least through 500°C. At 800°C and above, the concentration of styrene decreases. In oxidative atmospheres, carbon monoxide (CO), carbon dioxide (CO₂) and oxidative hydrocarbons are formed. The concentrations of CO and CO₂ are a function of temperature and combustion conditions, i.e. greater amounts are produced in the flaming than in the non-flaming mode. Eleven different test procedures were used to evaluate the toxicity of the pyrolysis and combustion atmospheres of polystyrenes. The more toxic environments produced under flaming conditions appear to be mainly attributed to CO and CO₂ but rather to some other toxicant, probably the styrene monomer. When compared with other common materials used in buildings and residences, polystyrenes, in general, are among the least toxic.     

Relationship between the thermal degradation chemistry and flammability of commercial flexible polyurethane foams

In this article, we report the use of a variety of analytical methods, in particular, solid‐state ¹H‐NMR and ¹³C‐NMR to characterize the relationship between the condensed‐phase chemistry and burning behavior as determined by a series of combustion tests for two commercially derived flexible polyurethane foams, one combustion‐modified. The combustion tests showed that the foams met several regulatory requirements in terms of their fire performance, whether or not they were combustion‐modified. Both foams passed the MV SS 302 and CAL 117 small‐flame tests. The nonmodified foam failed the Crib 5 test, but this test had a much larger ignition source. The particular problem with the nonmodified foam was melt drip into the flame zone. This led to a steady maintenance of the fuel feed and a rapid escalation of the fire. In contrast, the combustion‐modified foam showed little melt drip and self‐extinguished. Thermal analysis data for the two foams showed that melamine acted in part as an endothermic heat sink. This alone did not account for the much reduced melt flow and drip of the combustion‐modified foam, but the solid‐state ¹H‐NMR data clearly showed that the molecular mobility of the combustion char from combustion‐modified foam was lower than the unmodified foam char, which indicated that the flame‐retardant formulation in the combustion‐modified foam acted by a condensed‐phase mechanism. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3024–3033, 2006     

The incapacitative effects of exposure to the thermal decomposition products of polyurethane foams

The mechanisms of incapacitation resulting from exposures to the thermal decomposition products of flexible and rigid polyurethane foams (PUF) were studied over a range of different temperatures under pyrolytic or non-flaming oxidative decomposition conditions. Individual cynomolgus monkeys were exposed to atmospheres increasing in separate experiments from very low concentrations until early physiological signs of incapacitation were detected. When flexible PUF was pyrolysed at 900°C and rigid PUF was oxidized at 600°C, clear atmospheres containing CO and HCN were produced and the signs of toxicity were very similar to those produced by HCN gas alone, consisting of an episode of hyperventilation followed by a semi-conscious state. Pyrolysis of flexible PUF at 600°C and 300°C produced a dense yellow smoke but no HCN. The signs, consisting of hyperventilation throughout exposure and dyspnoea afterwards, were consistent with pulmonary irritation, Since TDI monmer is not present at 600⁰ C it is concluded that some as-yet unidentified but highly irritant chemical species is present in smoke from flexible PUF.     

Development of a rigid polyurethane foam from palm oil

The reactions between polymeric diphenyl methane diisocyanate (polymeric MDI) and conventional polyols to produce foamed polyurethane products are well documented and published. Current polyurethane foams are predominantly produced from these reactions whereby the polyol components are usually obtained from petrochemical processes. This article describes a new development in polyurethane foam technology whereby a renewable source of polyol derived from refined–bleached–deodorized (RBD) palm oil is used to produce polyurethane foams. Using very basic foam formulation, rigid polyurethane foams were produced with carbon dioxide as the blowing agent generated from the reaction between excess polymeric MDI with water. The foams produced from this derivatized RBD palm oil have densities in excess of 200 kg/m³ and with compression strengths greater than 1 MPa. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 509–515, 1998     

Generation of hydrogen cyanide from flexible polyurethane foam decomposed under different combustion conditions

Experimental thermal conditions conducive to the production of high levels of hydrogen cyanide (HCN) from flexible polyurethane foam were determined. In these experiments the material was exposed to relatively low-temperature non-flaming oxidative conditions for a short time period, during which a char was formed. Further heating of the char to temperature above 500°C generated the increased HCN levels. Upon exposure to this same two-step decomposition process, a fire-retarded flexible polyurethane foam produced twice as much char and twice as much HCN. Elemental analyses indicated that the HCN concentration was directly related to the amount of char formed and its nitrogen content. Room burns of slabs of flexible polyurethane foam and chairs containing flexible polyurethane foam indicated that this same phenomenon occurs in large-scale experiments. In these NBS tests, increased concentrations of HCN were produced when the material underwent flaming combustion following a period of smoldering, presumably from heating the char that was formed during smoldering. Investigation of the molecular mechanisms responsible for the increased HCN concentrations was attempted using ion chromatography, electron spectroscopy for chemical analysis (ESCA), Fourier transform infrared (FTIR), pyrolysis/mass spectrometry and ₁₃C solid-state nuclear magnetic resonance (NMR) techniques. While the molecular structures of the nitrogen-containing compounds in the char were not elucidated, these analyses provided evidence of multiple compounds containing amine, amide, imine and nitrile functional groups as the most likely sources of the observed HCN.     

Flexible‐elastic copolymerized polyurethane‐tannin foams

Open cell foams obtained by the simultaneous coreaction of condensed flavonoid tannins with an alkoxylated fatty amine and polymeric diphenylmethane isocyanate yielded highly flexible/elastic polyurethane foams. Copolymerized amine/isocyanate/tannin oligomers were identified by ¹³C NMR and MALDI‐TOF spectroscopy. In general, between 30% and 50% of natural tannins is added to the components used to obtain polymerisation of the polyurethane. The characteristic of these new, partially biosourced polyurethanes is that the tannin present slows down burning, some of them can be made flame self‐extinguishing and if burning they neither flow nor asperge flaming material around, contrary to what occurs with normal polyurethanes. This limits the possibility of transmitting fire to other materials in the same environment. Cyclic compression tests were carried out showing that after 50 cycles foam recovery was in excess of 80%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40499.     

Mechanical Properties and Flame Retardancy of Rigid Polyurethane Foams Containing SiO2 Nanospheres/Graphene Oxide Hybrid and Dimethyl Methylphosphonate

Halogen-free flame-retardant rigid polyurethane foams were prepared using the combination of SiO₂ nanospheres/graphene oxide hybrid and a phosphorus-containing flame retardant, dimethyl methylphosphonate. The flame retardancy, mechanical, and thermal properties of flame-retardant rigid polyurethane foams containing dimethyl methylphosphonate and SiO₂ nanospheres/graphene oxide were investigated. The results demonstrated that the combination of dimethyl methylphosphonate and SiO₂ nanospheres/graphene oxide enhanced flame retardant and mechanical properties of rigid polyurethane foam greatly compared with pure rigid polyurethane foam and dimethyl methylphosphonate-modified foam. Morphological study indicated that the partial substitution of dimethyl methylphosphonate with SiO₂ nanospheres/graphene oxide led to smaller cell sizes and more uniform cell sizes of dimethyl methylphosphonate-modified rigid polyurethane foams.     

Carbonyl sulphide in fire gases

The toxic gases released by combustion/pyrolysis of wool include CO, HCN and four compounds containing sulphur. Animal test data suggest that the toxicity of the sulphur compounds is significant. Wool was pyrolysed and the gases were analysed by GC-MS. SO² was the main sulphur-containing gas produced by flaming combustion in an oxygen-enriched atmosphere. In pyrolysis under various conditions COS was a major sulphur-containing product. Although it is a highly toxic gas, COS has not so far been reported by workers engaged in the toxicity of fire gases. It is suggested that analysis of COS be included in the analytical toxicology of sulphur-containing polymers.     

The Combustion of Rigid Polyurethane Foams

Abstract

The effect of the porous structure on the flammability characteristics of rigid polyurethane foams is studied. It is found that the velocity of the downward flame spread over the surface of foam slabs increases as the oxygen content into the ambient flow increases and the effective density of PU foams decreases.

The measurements of temperature profiles into the combustion wave made by Pt-PtRh thermocouples are used for the determination of the rate-controlling energy-transfer mechanisms.     

An experimental setup for observation of smoldering‐to‐flaming transition on flexible foam/fabric assemblies

Fires that involve upholstered furniture frequently begin as a smoldering combustion and, with time, transition to a flaming combustion, which sharply increases the level of hazard. Therefore, understanding how the compositions of the primary flammable components of the furniture, ie, flexible foam and upholstery fabric, affect this transition is important for fire safety considerations. In the current study, an experiment was designed to observe this transition using a sample consisting of 30 × 15 × 6 cm³ rectangular foam block covered with 30 × 15 cm² piece of fabric. For a representative system of 1.8 lb/ft³ (29 kg/m³) flexible polyurethane foam and 11 oz (0.37 kg/m²) cotton fabric, 0.69 transition probability was measured. This probability decreased by a factor of 4 when a small amount of phosphorus‐based flame retardant, Fyrol® HF‐9, was added to the foam. The transition to flaming was speculated to be associated with the formation of adjacent pyrolysis and smoldering regions within the foam. The pyrolysis region, dominated by anaerobic decomposition, provided gaseous fuel, the ignition of which resulted in the transition. The smoldering region, dominated by oxidation reactions at the solid‐gas interface, generated the heat necessary to maintain the pyrolysis process and ignite the gaseous fuel.     

The piloted transition to flaming in smoldering fire retarded and non‐fire retarded polyurethane foam

The piloted transition from smoldering to flaming, though a significant fire safety concern, has not been previously extensively studied. Experimental results are presented on the piloted transition from smoldering to flaming in non‐fire retarded (NFR) polyurethane foam and the fire retarded polyurethane foam Pyrell^®. The samples are small blocks, vertically placed in the wall of an upward wind tunnel. The free surface is exposed to an oxidizer flow and a radiant heat flux. The smolder product gases pass upwards through a pilot. The experiments on NFR foam show that the smolder velocity and peak smolder temperature, which increase with the oxygen concentration and heat flux, are strongly correlated to the transition to flaming event, in that there are minimum values of these parameters for transition to occur. The existence of a minimum smolder velocity for ignition supports the concept of a gaseous mixture reaching a lean flammability limit as the criterion for the transition to flaming. To compensate for the solid‐ and gas‐phase effects of the fire retardants on the piloted transition in Pyrell, it was necessary to increase the oxygen concentration and the power supplied to the smolder igniter and the pilot. The piloted transition is observed in oxygen concentrations above 17% in NFR foam and above 23% in Pyrell. The results show that although Pyrell is less flammable than NFR foam, it is still susceptible to smoldering and the piloted transition to flaming in oxygen‐enriched environments, which is of interest for special applications such as future space missions. Copyright © 2008 John Wiley & Sons, Ltd.     

The combustion products of polymeric materials. III: GC–MS Analysis of the combustion products of polyethylene,polypropylene, polystyrene and polyamide

A series of gas chromatographic–mass spectrometric analyses was carried out on polyethylene, polypropylene, polystyrene and polyamide in CAB 4.5 and CAB 650 chambers in the flaming and non-flaming combustion mode. The combustion products formed were identified and used to characterize the combustion process in both chambers; procedures were selected for testing polymeric materials for the dangerous effects of their combustion products.     

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     

Nylons: A review of the literature on products of combustion and toxicity

The literature on polyamides was reviewed to determine the nature and extent of information available on these materials which are commonly used in consumer and industrial applications. This review was limited to aliphatic polyamides normally called nylon and excludes aromatic polyamides such as Nomex and bicomponent polymers consisting of nylon and other polymers. The review was further limited to those publications in English through June 1984. Typical pyrolysis products from a broad range of nylons do not appear to differ greatly. Many of the decomposition products detected in vacuum pyrolysis experiments appear as products of thermal degradation in inert and air atmospheres. In air, a general reduction in the quantities of heavier hydrocarbons is noted along with an increase in the production of CO, CO₂, H₂O, NH₃, HCN and NO_x. The toxicity of the thermal degradation products from various types of nylon has been evaluated by nine different protocols. Reported LC₅₀ values range from 10.8 m l^?1 to 61.9 mg l^?1. Dyes apparently do not affect the materials' combustion products toxicity but an increase in the amount of backcoating on a nylon fabric increases toxicity. Time to death measurements show that volatile products from nylons are less toxic than those from rayons or cotton, while the blending of wool with nylon greatly increases the toxicity of the thermal decomposition products. In general, however, the overall toxicity of the thermal degradation products from nylon do not appear to be greatly different than those from many other polymeric materials. Large-scale test results are ambiguous, and it is difficult to interpret the results in terms of a single component in a multicomponent system.     

Combustion behaviour of polyurethane flexible foams under Cone Calorimetry test conditions

The first part of this study focuses on the effect of cone calorimeter test variables on polyurethane flexible foam properties such as ignitability, heat release rate, effective heat of combustion and mass loss. Three of the main commercial foam types were used, i.e. conventional slabstock foams, high-resilience slabstock foams and all-MDI (methylene diphenyldiisocyanate) moulded foams. A decrease in heat flux (down to 40%) with increasing distance from the conical heater was measured. As a consequence, results were found to depend to a large extent on the thickness and the melting behaviour of the foam samples. To achieve a sufficiently constant and uniform heat flux exposure, sample thickness had to be limited to 25 mm. In addition, repeatability was found to be good under various conditions, with percentage standard deviations for effective heat of combustion, peak rate of heat release and mass loss below 10%. Levels of radiant flux above 25 kW m^?2 were found to be very severe to test flexible polyurethane foams. Under such conditions, foams that show large differences in combustion performance in small-scale flammability tests performed almost identically in the cone calorimeter. In the second part of this study the effects of foam variables, such as foam type, density and melamine content, are defined. These effects were clearly pronounced at radiant flux levels of 15–25 kWm^?2. Density was found to be the key variable in controlling ignition resistance. In addition, high-resilience slabstock foams and all-MDI moulded foams performed better than conventional slabstock foams of the same density. Melamine addition resulted in a delay of ignition for all three foam types and an incomplete combustion, decreased heat release and effective heat of combustion in HR-slabstock and all MDI moulded foams. However, melamine is not effective as a heat sink in conventional slabstock foams. The different performance of the foam types under study can be explained by a different melting behaviour.     

Castor-oil derived nonhalogenated reactive flame-retardant-based polyurethane foams with significant reduced heat release rate

National Fire Protection Association encounters one structural fire every 66 s. Rigid polyurethane foam is one of the principal components used in constructional and household applications. In this work, a reactive flame retardant (FR) was synthesized using a facile one-step thiol–ene reaction by reacting mercaptenized castor oil (MCO) and diethyl allyl phosphonate (DEAP). The obtained MCO–DEAP polyol was used for the preparation of polyurethanes having different weight percentages of phosphorus (P). Addition of FR polyol showed no adverse effect on the cellular structure of the foams and maintained the compressive strength. All the foams showed closed cell content greater than 95%. Horizontal burning test (HBT) was performed before and after the migration test to understand the stability of the FR within the foams. Foams showed no relative weight loss before and after the migration test and maintained equivalent results for HBT. For 1.5 wt % P foams, low extinguishing time of 3 s and weight loss of 4% was observed. The cone calorimeter test showed a reduction in the peak heat release rate from 313 to 158 kW m⁻³, the total heat release from 18 to 8 MJ m⁻², and O₂ consumption from 12 to 6 g. Our results suggest that MCO–DEAP polyol could act as an essential FR for rigid PU foam ensuring fire safety. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47276.     

A summary of the NBS literature reviews on the chemical nature and toxicity of the pyrolysis and combustion products from seven plastics: Acrylonitrile–butadiene–styrenes (ABS), nylons,polyesters, polyethylenes,polystyrenes, poly(vinyl chlorides) and rigid polyurethane foams

A series of literature reviews was undertaken by the National Bureau of Standards to examine the toxicity and chemistry of the effluents produced when seven plastics were decomposed under various thermal and atmospheric condition. These plastics are: acrylonitrile–butadiene–styrenes, nylons, polyesters, polyethylenes, polystyrenes, poly(vinyl chlorides) and rigid polyurethane foams. The English-language literature on each of these was reviewed and published as a separate report of the National Bureau of Standards. Over 400 different thermal decomposition products, many common to more than one plastic, were identified. The toxicity of most of these individual products is products, many common to more than one plastic, were identified. The toxicity of most of these individual products is unknown and an assessment of the toxicity of the multitude of possible combinations is not feasible at this time. Therefore a variety of bioassay toxicity protocols have been used to assess the toxicity of the gaseous atmospheres generated by the thermal decomposition of these plastics. In general, these seven plastics did not produce unusually or extremely toxic pyrolysis or combustion products when compared with those of other synthetic or natural materials. In a few cases involving additives, toxic products of concern were produced.     

Investigation of fire behavior of rigid polyurethane foams containing fly ash and intumescent flame retardant by using a cone calorimeter

Cone calorimeter is one of the most useful bench‐scale equipment which can simulate real‐world fire conditions. Therefore, cone calorimeter tests have been the most important and widely used tests for research and development of fire behavior of polymeric materials. In this study, fire behavior of rigid polyurethane foams containing fly ash (up to 5 wt %) and intumescent flame retardant (up to 5 wt %) composed of ammonium polyphosphate/pentaerythritol was investigated by using a cone calorimeter. In addition, thermogravimetric analysis of the additives and the foams were also carried out to explain the effects of fly ash and intumescent flame retardant on fire behavior of the foams. Experimental results indicated that rigid polyurethane foam containing fly ash and the intumescent flame retardant in comparison with pure rigid polyurethane foam shows significantly enhanced fire resistance and thermal stability. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012