Fire research abstracts and reviews: Volume 13, 1971 (1971)

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THE CHEMISTRY OF FIRE RESISTANT MATERIALS AND SUPPRESSION I R V I N G N E I N H O R N College of Engineenng, University of Utah H I S T O R I C A L B A C K G R O U N D Durmg the past decade, we have witnessed a rapid and continued expansion of plastic products In this period the flammabihty characteristics of the predonunantly orgamc polymers have assumed great importance In the 1950's and 1960's plastics were considered for many applications due to theu- ease of fabrication, novelty, and other favorable physical properties in spite of undesirable flammabihty charac- teristics Nitrocellulose enjoyed a long era of extensive use m spite of its almost explosive character The gradual maturity of the plastics mdustry with a corre- spondmg mcrease m the variety and sophistication of its products resulted m a correspondmg demand by the consumer and by regulatory agencies for improved flammabihty characteristics At the present time, the lack of adequate fire retard- ance of most commercially available plastics appears to be one of the largest barriers to the opemng of extensive new markets for these materials m the buildmg and con- struction mdustry, in transportation apphcations, m household furmshmgs and furmture, m floor covermgs, and m clothmg The importance of fire-retardant chemicals and technology to the chemical and plastics mdustry has recently been the subject of several meetmgs whose proceed- mgs add greatly to the techmcal literature I n addition to reviewmg the current technology in fire retardation of polymeric matenals, it was pomted out at these meetmgs that the consumption of fire-retard- ant chemicals has risen from approximately 65 million pounds m 1960 to greater than 200 milhon pounds m 1969 Figure 1 illustrates the growth m sales of fire re- tardants m the Umted States for the period 1960 through 1969 The importance of fire retardance to the overall growth of the plastics mdustry has led to the mtroduction of many new fire-retardant compositions with mcreasmg frequency durmg the past five years Although this expandmg research mto the act of fire-retardant technology has uncovered many new facts about the mecha- nisms of fire retardation of polymeric materials, the technology of fire retardancy m polymer compositions still retams a high degree of empirical character Of the many empirical facts accumulated m the technology of fire-retardant plastics over the years, the followmg have been shown to be the most useful and commercially practical 1. The mcorporation of halogen atoms into a polymeric composition, either as an additive or by chemical reaction, decreases the flammability or mcreases the fire retardance of the composition 2 A combmation of antimony oxide and halogen is more efficient than either of the mdividual materials at the same total concentration In other words, 236

A B S T R A C T S A N D R E V I E W S 237 the combination of antimony and halogen displays an efficient s3Tiergism as a fire-retardant combination.' 3. The addition of some phosphorous compounds of specific structures retard the burning of many plastics.' 4. A combination of phosphorous and halogen also exhibits considerable synergism as a fire retardant. 5. The most efficient combination of fire-retardant materials varies consid- erably, depending upon the chemical structure of the plastic to which it is applied."" In the previous section, the general mechanisms of thermal and oxidative degra- dation of polymers were discussed. Some of those concepts are extended in this section to fire-retarded polymers. MECHANISM OF FLAME RETARDATION I N POLYMERS Many investigations""" have suggested mechamsms of polymer flame re- tardancy, but the general theories based on the decomposition of the flame re- T3 C 3 P 100 90 80 70 60 50 40 30 2 0 0 Co-Additive I I Additive Reactive 1 1 TP I 'A i 7/ \ 1960 1964 1965 1966 1967 F I G . 1. Sales of flame retardants. 1968

238 Radiant Heat F I R E B E S E A B C H Radiant Heat A i r Smoke Zone Flame Zone Carbonaceous Char Layer Pyrolys is Products Pyrolys is Zone Virgin Polymer Fia 2 Generalized model of burning polymer I [ Pyrolys i s Products tardants under burning conditions were summarized by Bel l ' ' as follows: 1 Gas theory large volumes of incombustible gases are produced, which dilute the oxygen supply. 2. Thermal theory the fire retardant decomposes endothermically and lowers the temperature of the flame. 3 Chemical theory decomposing polymers evolve smaller molecules or mon- omers and these m turn break down to give active high-energy free radicals dissipatmg their energy and thus extmgmshmg the flame 4 Coatmg theory the fire retardant fuses to form a protective layer which coats the combustible materials, thus preventmg the further access of oxygen to the substrate, or intumesces to give a carbonaceous foam which acts as a thermal insulator. A model of a burmng polymer, shown in Fig. 2, can be useful m discussing the role of halogens in flame-retarding polymers. Einhorn et aZ," and Riccitiello et aZ," studied the flammability characteristics of modified polyisocyanurate foams The isocyanurate rmg structure, found m these polymers, was formed by the cyclization of three isocyanurate groups Increased thermal stability and improved flamma- bi l i ty characteristics were obtamed by the incorporation of polyfunctional aromatic isocyanates such as 4,4'-diphenylmethanedusocyanate. The cyclization reaction

ABSTRACTS AND R E V I E W S 239 is shown in Eq. (1) 0) Isocyanurate Structure The highly aromatic structure of the isocyanurate polymer restricts motion in the polymer chain and produces brittleness Riccitiello, et ai,'° introduced urethane Imkages into the isocyanurate polymer to obtam the desired degree of flexibility The urethane linkages decompose f rom 180° to 275°C, wi th a char yield of 0 to 35% The isocyanurate rmg structure decomposes between 300° and 325°C, wi th an approximate char yield of 50% The polyol used to prepare these isocyanurate polymers was derived f rom glycerin and propylene oxide to which pendant mtrile groups were grafted. The polyol had the followmg structure- rCHz—0—R—OH I CH—0—R—OH L C H 2 - O - R - O H J M [ C H 2 - C H - C s N ] „ Acrylomtrile was selected as the graftmg monomer because nitrile Imkages cyclize to form a high-temperature-stable heterocyclic structure at temperatures

240 " ' ' F I H E R E S E A B C H below 200°C. The cyclization reaction of the nitrile groups is shown in Eq. (2 ) : ^ (2) N N N Thus, referring back to the generahzed model shown in Fig 2, we see the formation of stable-char structure developmg m the pyrolysis zone at approximately 180°- 200°C This precursor char structure, which forms m high yield serves as an efifec- tive diffusion barrier and thus retards the migration of volatile degradation species mto the gaseous phase The carbonaceous layer also provides an effective thermal msulation barrier to shield the underlymg substrate f rom the burmng region The volatile pyrolysis products were degraded into carbon and other products as they entered the combustion zone (700°—1000°C ) . For flame propagation, energy feedback from the flame envelope to the polymer (shown m Fig. 2) must be suf- ficient to sustam volatile fuel production This feedback of energy from the envelope to the polymer depends on a number of parameters which include the efficiency of combustion, the flame temperature, the carbon content and its radiation emis- smty , and the geometry of the flame. Volans" suggested the most effective approach to flammabihty control m a flame-retardant modified polymer might be 1 Limitation of the fuel supply to the flame by reduction of the pyrolysis reaction or modification of the fuel products, e g , production of more tars, coatmgs, and chars 2. Reduction of the energy hberation m the flame by modification of the com- bustion reaction, e g , allowmg more carbon to escape the flame 3 Reduction of energy feedback to the polymer surface by reducmg the flame temperature or eimssivity.^' 4. Increasmg the concentration of a flame inhibitor species above a concen- tration at which the combustion reaction fails to contmue. Fud Supply Control Design of the molecular structure of polymers wi l l permit the sjrnthesis of high- temperature resistant materials which give off li t t le or no volatile fuel Matenals such as the polyimides, benzimidozoles, and certain polyamides are examples of polymers which contain few hydrogen atoms and which are precursors for carbon or graphite Einhorn^ described several model urethane and isocyanurate polymers in which potassium fluoroborate was mcorporated to give rise to the formation of a protective layer of "glass" on the surface of the char and thus hmder gaseous fuel production Holmes and Shaw" and Grundfest''^ showed that phosphorous compounds would hmit the burmng of polymers only i f nonvolatile phosponc acid derivatives were formed upon pyrolysis

ABSTRACTS AND R E V I E W S 241 Role of Halogen %n the Fire Retardation of Polymers Rosser, Wise, and Miller,^^ and Wilson, O'Donovan, and Fnstrom^' showed that HBr , HCl , and CI2 prenuxed in hydrocarbon-air flames were active flame-inhibiting agents. I t appears that the prmciple action is the modification of radical concen- tration and/or distribution m the reaction zone Thus, mterference to the propa- gatmg and branchmg steps is produced Halogen compounds appear to act by sub- stitutmg a radical of low reactivity for the propagatmg radicals. Corrosion or toxicological considerations hmit practical extmguishments to halogenated hydro- carbons The chemistry of halogenated hydrocarbons mcludes that of the halogens and halogen acids The effectiveness of those inhibitors appears to be F < B r < C 1 < I and is proportional to the number of halogen atoms m the inhibitor molecule. Differences m halogen compounds are hkewise important, especially m regard to the nature of the attached hydrocarbon structiure. First, this may be saturated primary, secondary, or tertiary. Second, this could be unsaturated ally], benzyl, v inyl , or aryl structures The presence of nearby nonpolar or polar groups may markedly affect the behavior of the carbon-halogen bonds Knowmg that these differences i n chemical structure affect the thermal and hydrolytic stability of analogous smgle halogenated molecules, suggests that these structural differences very probably have an influence upon the effectiveness of halogens as fire re- tardants i n polymers Fristrom'" reported that all of the halogens, wi th the exception of iodine, can sustain hydrogen flames. The reactions for these systems are similar, as shown below. H+X2?±HX-|-X (3) X-|-H2?=>HX+X (4) X+X+M?=iX2-|-M* (5) H-l-H+M?:±H2- |-M* (6) H-|-X-|-M?=>HX-i-M*. (7) Halogen molecules and the halogen acids (excepting fluorine) react rapidly wi th both O atoms and • OH radicals to form the correspondmg halogen atoms. I n the case of Br and I , the atoms are unreactive wi th respect to hydrogen, molecular oxygen, and the common hydrocarbon fuels The result is the substitu- tion of a stable unreactive radical The CI atom reactivity is sufficient so that inhibition is less pronounced, and m some cases even a promotion of reaction can occur Reactions of halogen species wi th oxygen atoms and hydroxyl radicals are as follows: 0-|-X2?ziOX-hX* (8) 0H-|-X2?=±HX+X (OX-l-HX)* (9) 0-|-HX<=±OH+X ( O H + H ) * (10) 0H-|-HX?±H20-|-X. (11) Halogenated hydrocarbons are rapidly attacked under flame conditions to form halogen acids and halogen atoms This allows secondary inhibition reaction, as

242 shown below, to take place. F I R E R E S E A R C H R . X - | - H - * H X + R . (12) R - X + O H - ^ H s O - F - R X (13) R - X - l - O ^ O X - l - R . (14) Fluorocarbon molecules show inhibition properties m excess of that which would be predicted on the basis of the halogen atom substitution. F2 and H F do not inhibit flames This is probably associated wi th the stability of the fluorocarbon radicals under flame conditions A number of plausible reactions can be writ ten down, but httle reliable kmetic information is available at this time The principal reactions should be wi th hydrogen atoms Reactions w i t h oxygen atoms are thermodynamically favorable, but sterically improbable. The compound CF2 has been reported by Modica and LaGrafF" to react wi th molecular oxygen in a shock tube at 2000°K, but the elementary steps are not clear Possible reactions of CFj and CF2 m flames are CFa- | -X+H->HX-l -CF, (15) CF3-1-H-»CF2+HF (16) CF2 - | -H-*CF- | -H (17) CF2- | -0-»CO-|-2 F (18) CF2+02->CO+F2- |-0 (19) The above mechanisms may not apply directly to diffusion flames, where com- bustion mechamsms are different, due to the extreme concentration gradients and poor stability Halogen inhibitors were found to be more effective when added to air rather than to the fuel side of the diffusion flame However, the amount of i n - hibitor, added to the air side, required to extmguish the diffusion flame was of the same magmtude as that required for a premixed flame " Role of Halogens m the Condensed Polymer Many references are found in the hterature which discuss the action of halogens on vapor flames such as hydrocarbon-air flames But surprismgly l i t t le information has been published on the mechanism of flame suppression in sobd polymers Femmore and M a r t m adopted the hmitmg-oxygen mdex method to measure the flammabihty of sohd polymers. The l imiting oxygen index n of a material is defined as the percentage concentration of oxygen m a mixture of oxygen and nitrogen which wi l l just sustam combustion of the material n ( % ) = 100[O2/(O2+N2)] (20) For air, n = 2 1 Figure 3'* shows the effect of oxygen on the combustion of iso- cyanurate foam This method is simple and reproducible and has proven to be a useful tool for mechanistic studies of flame suppression m polymers One important characteristic of this test IS that the vertical sample burns downward, momtormg any convective heating of the burning material. A n important hmitation to this method is the fact that some materials melt too easily and abstract more heat f rom the surroimd-

ABSTRACTS AND R E V I E W S 243 ing diffusion flame than is required to pyrolyze the polymer. Recently, Stuetz"" reported on further modifications to the limiting-oxygen mdex test by usmg an upward burnmg flame as well as the downward flame to study fire retardancy mechanisms. Femmore and Jones" established that H C l or CI2 added to an O2-H2 atmosphere exerted only a very slight inhibition, whereas equivalent chlorme substituted m polyethylene gave a strong inhibition effect. This suggested that chlorme works i n I 1— 1 —1 1 1 — r - CB SE«L CB - CB Complete Burn - SE Self-extinguishing - - /-SE \ SE mi »SE \ \» - • A CB — / S E SE« - A » SE •yCB CB* VCB^CB \ ^ C B ^ 1 1 1 1 1 • 16 14 12 10 25 27 29 35 31 33 Per Cent Oxygen Fia. 3. Effect of oxygen on the combustion of isocyanurate foam, 37 39

244 F I B E R E S E A B C H the condensed phase of polyethylene. A fire retardant which is effective in the con- densed phase should remain effective when the polymer bums m an oxidizer other than oxygen Fenimore and Jones" proved this by showing the effective chlorine inhibition of polyethylene burmng m N2O-N2 as well as i n O2-N2 This mechamsm suggests that fire retardants which work well m one polymer may not perform in the same manner in another material. Fenimore and Jones'^ showed that tetrabromo bisphenol A in polyethylene is more effective than chlorme in O2-N2, but was less effective in a N2O-N2 atmos- phere. Similarly, (rts-(2,3-dibromopropyl) phosphate i n polyethylene is more effective than its chlorme analog m O2-N2, but not in N2O-N2 The above reactions suggest that bromme inhibits or poisons the flame rather than the condensed phase. During a transient igmtion period, the pyrolysis gas may change its composition, hence i t may be crucial to the flame retardancy of some halogenated fire-retardant polymers Eichhorn" reported that dicumyl peroxide and other free-radical generators m - creased the inhibitmg action of bromine m polystyrene, and he further stated that this mechanism operates largely outside the flame front but m the condensed phase. I t is believed that the peroxide and halogen radicals abstract hydrogen f rom the polymer, and the resultant poljTner radicals then react wi th halogen compounds or radicals. Those species wi th a lower vapor pressure decompose m a higher tem- perature range to cause the release of H B r when i t can be more effective. Ingram' ' proposed a similar mechanism when he used JV-chloro and JV-nitroso compounds as free-radical generators Gouinloch, Porter, and Hindersinn," however, offered a different explanation. They stated that the added peroxide degraded the hot polymer and gave a more flmd melt, therefore, requirmg more heat to sustain combustion of the fresh surface after the molten polymer dripped away. They showed that the peroxide was m- effective when drippmg was prevented by incorporation of glass fibers. Piechota'* reported that the concentration of chlorme alone was not the decisive factor for the effectiveness of a product. This phenomenon could only be mterpreted on a manifestation of the different trends toward intramolecular thermal hydrogen chloride elinunation as governed by the composition of the flame retardant. See Table 1. Chlormated ta l l oil ehmmated hydrogen chloride under relatively mild condi- tions, wi th 8 1 % of the chlorine being released as hydrogen chloride. I n this case, self-extmguishing urethane foams were prepared wi th only a 4 % level of chlorme. I n the case of chlorinated diphenyl, the release of hydrogen chloride was very difficult and self-extinguishmg characteristics could not be obtamed m similar urethane foams even at the 10% chlorine level. Tilley*' reported that neither sodium chloride nor sodium bromide contributed to the protection of urethane foams durmg fire exposure Presumably, neither halogen or hydrohahde was available f rom salts during combustion. Flame Retardance Conferred by a Halogen m a Reactive Intermediate Numerous investigators have reported on studies i n which the flameproofing elements such as a halogen or phosphorous or both are incorporated mto a reactive intermediate. L i " used pentaerythritol dichloride as the polyhydnc alcohol moiety

ABSTRACTS AND R E V I E W S 245 in preparing unsaturated polyester resins A chlorine content of at least 25% was considered essential to obtam a desired level of flame retardancy. Al'Shits ' ' and coworkers used a mixture of pentaerythritol dichloride and t r i - chloride to flame retard unsaturated polyester resins. The trichloride was used to form end groups m the Imear chains thus raising the molecular weight of the polymer (as compared to previous studies using only the dichloride) while also TABLE 1 Intramolecular elinunation of HCl from different chlorine compounds H — C — C — COOH I I H CI Chlorinated f a t ty acid — CH = CH - COOH + CHI unsaturated acid 3 C 1 — e — e— 3 CI Chlorinated diphenyl nonaromatic compound CI CI CI II . . . I C^ ^ - COOH CI- C -CI C - COOH I H CI HET Acid CI CI - C = C CI CI - C—C'^'^ ^ C l 1, Hexachi orocydopentadi ene + COOH COOH I H "H maleic acid NĤ C1 amnonium chloride NH3 + HCl

246 F I R E R E S E A R C H raismg the halogen level m the polyester. These polyester resms were prepared usmg a two-stage condensation reaction I n the first stage, excess maleic and phthalic anhydride were reacted with pentaerythritol dichloride Sufficient pentaerythritol trichloride was then added so that the total hydroxyl groups m the system would predommate and the condensation reaction would be completed. Resorcmol has been used as the startmg material to prepare halogen-containmg diols The resorcmol was epoxylated wi th ethylene or propylene oxide to yield l,3-5zs-(betahydroxyalkoxy) benzenes These were then brommated in a buffered solution to form 5,B'-(4,6-dibromo-l,3-phenylenedioxy) dialkanols which were used to prepare self extmgmshmg polyesters accordmg to the reactions: RCH-CH2 R Y HO CHCH2O ,^<:^0CH2CH-0H OCHoCHOH R HOCH CH 0 B r Other mterestmg halogen-containing diol structures were synthesized via a Diels-Alder reaction of hexahalocylopentadienes wi th unsaturated diols (such as 1,4-butenediol) used as the dienophiles ̂ ' '^ Replacement of some of the chlorine atoms by bromine m the diene mcreases the flame-retardance properties m poly- esters, while replacement of some of the chlorme atoms wi th fluorme yields poly- esters wi th enhanced agmg and heat resistant properties Recently, considerable interest has been shown m polyester resins based on tetrachlorophthalic anhydride and tetrabromophthahc anhydride Laboratory studies were conducted to evaluate the chemical and physical parameters which govern the flammability characteristics of these retardants m model unsaturated polyester resm systems The highest saturated-to-imsaturated molar ratio consistent w i th good resm properties was selected m order to permit synthesis of polyesters wi th the highest possible chlorme content A ratio of saturated-to-unsaturated acid of 1.1 to 1 0 was selected smce high ratios of tetrachlorophthalic anhydride to maleic anhydride would cause a rapid drop in heat-distortion temperature. This ratio was held con- stant i n all model systems by adjustmg the amount of phthahc anhydride used. Propylene glycol was selected as the glycol for this study and a 5% molar excess was used m all formulations The resins were prepared by a conventional fusion esterification wi th the reaction temperature bemg mamtamed at 190'*-195''C. The resms were processed to an acid number of 30, styrenated to a level of 25% or 30%, and inhibited wi th 125 ppm of hydroqumone Table 2 presents the formulations used to prepare resins based on tetrabromophthalic anhydride. Table 3 shows the formulations used to prepare resins based on tetrachlorophthahc anhydnde.

ABSTRACTS AND R E V I E W S 247 TABLE 2 Formulations for polyester resins based on tetrabromophthahc anhydride Calculated % bromine on dilution with Moles Moles Moles TBPA PA MA 25% styrene 30% styrene 0 80 0 30 1 0 30 4 0 60 0 60 1 0 22 0 20 5 0 30 0 80 1 0 14 8 13 8 0 25 0 85 1 0 12 7 11 8 0 23 0 87 1 0 11 8 11 0 0 20 0 90 1 0 10 5 9 8 0 07 1 03 1 0 5 0 — Figures 4 and 5 present the ideahzed structures of crosslinked polyester-based polymers contaimng the halogenated fire retardants The effect of fire retardants on the thermal characteristics of model polyester resm systems was deternuned usmg differential thermal analysis and thermo- gravimetric analysis Figures 6 and 7 illustrate the effect of fire-retardant concen- tration on the decomposition temperature for specimens fire retarded wi th the two anhydrides Relatively l i t t le difference was observed m the decomposition temperatures for the series contammg 25% styrene and the series contaimng 30% styrene The control samples contaimng only the halogenated fire retardant showed a shght lowermg of the decomposition temperature The mcorporation of triethylphosphate into these halogenated systems showed no marked synergistic effects Incorporation of antimony trioxide ( 2 % or 5% by weight) resulted m a substantial lowermg of the decomposition temperature wi th an observed minimum occurrmg at approx- imately 1 1 % bromme concentration or at approximately 21 7% chlorme content Two small-scale test methods were employed under controlled laboratory con- ditions to evaluate the relative effectiveness of the polyesters modified by the halogenated fire retardants. These tests were the A S T M D-757—Globar Test and the HLT-15—Intermittant Flame Test I n the A S T M D-757—Globar Test, at equal concentrations of halogen, the specimens based on tetrabromophthahc TABLE 3 Formulations for polyester resins based on tetrachlorophthabc anhydride Calculated % chlorme on dilution with Moles Moles Moles TCPA PA MA 25% styrene 30% styrene 1 0 0 0 1 0 21 7 20 3 1 0 0 1 1 0 10 2 18 9 0 9 0 2 1 0 18 7 17 4 0 8 0 3 1 0 17 0 15 8 0 5 0 6 1 0 11 6 — 0 2 0 9 1 0 6 0 —

248 y H wr—^ HC-C-OH " HC-C-OH F I R E R E S E A R C H HC=CH2 o Propylene Glycol Maleic Acid Phthalic Acid Tetrachloro Styrene Phthalic Anhydride H H ,0 ^ CI H 6 CH^ CI CI, c H ^ H FiQ 4 Idealized structure of a crosslinked polyester-based polymer containing tetrachlorophthalic anhydride

ABSTRACTS AND R E V I E W S H ^ HC-g-OH l^^^:;i^-OH ^""^W^g ^ 249 H5=CH2 -g-OH ^ Propylene Glycol Maleic Acid Phthalic Acid Tetrabromo Styrens Phthalic Anhydride H H HO^-C^Hj 0-C-CH C H , 0 6=0 O o Br, Q 0=0 H H H H Fia 5 Ideahzed structure of a crosslinked polyester-based polymer containmg tetrabromophthahc anhydnde

250 F I B E R E S E A B C H No Additive 3 percent TEP 2 percent SbzOa 5 percent SbaOa 368 h / / 25% S T Y R E N E MONOMER 0 4 8 12 16 20 24 28 WEIGHT PER CENT BROMINE FiQ 6 Effect of tetrabromophthalic anhydnde on polymer decomposition 32 anhydride had lower flame-propagation values than were observed for similar specimens based on tetrachlorophthalic anhydride The incorporation of tr iethyl phosphate reduced the burmng shghtly The mcorporation of antimony trioxide exhibited a strong synergistic effect and markedly improved the flame propagation characteristics of the test specimens The synergistic type of reaction wi l l be dis- cussed in greater detail later m this section. The HLT-15—Intermit tant Flame Test is more severe than the A S T M D-757 test because the specimen is suspended in a vertical position and heat f rom the flame is carried upward by convection along the length of the specimen I n addition, the specimen is igmted five times usmg mcreasmgly longer igmtion periods The brommated specimens obtamed a maximum ratmg without additional co-retardants Shght improvements were seen wi th the addition of t r iethyl phosphate. The chlo- rmated specimens were not able to exhibit burmng characteristics to obtam greater than a 40 ratmg by this test method Incorporation of antimony tnoxide improved the ratmgs of both the brommated and chlormated specimens, but the brommated specimens were more effectively fire retarded than the chlormated specimens.

ABSTRACTS AND R E V I E W S 251 Fire Retardance Conferred by a Halogen m a Nonreachve Intermediate Nonreactive fire retardants are generally used wi th thermoplastic polymeric systems where mcorporation of a reactive material would affect crystallmity, heat- distortion temperature, and resistance to ultraviolet light or humidity. Low- molecular-weight fire retardants have a tendency to migrate or outgas durmg processmg or while m actual use Thus, consideration should be given to those compounds having a molecular weight high enough to prevent subhmation, migra- tion, or volatilization S Y N E R G I S M D U R I N G F I R E EXPOSURE Synergism is the term applied to the observed ability of two materials to influence the properties or response of a material to a greater degree than equal amounts of the two materials used separately Antimony-Halogen Synergism Various antimony compounds have been used as flame retardants for material and synthetic polymers Antimony trioxide (SbaOj) and antimony oxychloride E 348 U 1— No ^dd1t^ve . 3 percent TEP 2 percent Sbzflj 5 percent SbjOs J_ J L -L 0 4 8 12 16 20 24 F I G 7. Effect of tetrachlorophthalic anhydride on polymer decomposition 28

252 F I R E R E S E A R C H (SbOCl) are the most commonly used antimony compounds for modifying the flam- mabihty characteristics of polymenc materials Schnudt" and Drake" reported that antimony trioxide by itself was a very poor flame retardant Little^' observed that the optimum flame retardancy occurred when the mole ratio of antimony, chlorme is 1:1. The H C l evolved f rom the decomposition of chlorinated organic compounds reacts wi th antimony oxide to produce the tnchloride (B.P. 223°C) or the oxy- chloride, which m turn decomposes to the trichloride. The strongly acidic t r i - chloride is thought to function as a dehydration catalyst for materials such as cellulose as well as a flame quencher for flammable gases. Equations (22)-(25) summarize the thermal reactions of antimony compoimds Sb203-^6 HCl->2 SbCl3+3 H2O (22) (B.P. 223°C) Sb203-|-2 HCl->2 SbOCH-HjO (23) 170°-280°C 5 SbOCl > SbCla+SbiOsCU (24) 320°-700°C 3 S b A C U > 2 SbCl3-l-5 SbjO, (25) Pitts, et a l , " found the thermal decomposition of SbOCl to proceed m four basic steps as illustrated m Eqs. (26)-(29) . 245°—280°C 5 SbOCl(s) > Sb406Cl2(3) -f-SbCl3(g)t (26) 410°-475°C 4 SbACl2(s) > 5 SbaOiCKs) +SbCl3(g)' (27) 475°-565°C 3 SbaOiCl » 4 Sb203+ShCh (g) ' (28) 658°C Sb203 > Sb203(1) (29) Einhorn et aP' have shown the effectiveness of the antimony-halogen synergistic reaction m reducmg the tendency for crack growth and enhancmg the development of a homogeneous char structure m unsaturated polyester resins through the use of infrared photographic techmques. Figure 8 shows the degradation of a polyester resm castmg fire retarded by the mcorporation of 11.5% by weight of tetrabro- mophthahc anhydride. Figure 8a illustrates the meltmg region, the region of char formation, and also shows flame propagation by burmng gases m the boundary region. Figure 8b shows the development of a crack which has started m the bound- ary region. Figure 8b shows the development of a crack which has started m the boundary region, char smtering, and after-flow (coohng). Figure 8c shows the

ABSTRACTS AND R E V I E W S 253 60 Seconds b) - 5 Seconds (d) - 90 Seconds F I G . 8. Flame propagation in a polyester resin casting fire retarded by tetrabromophthalic anhydride.

254 F I R E B E S E A R C H (a) - 1 Second (b) - 5 Seconds (c) - 50 Seconds (d) - 90 Seconds F I G . 9. Flame propagation in a polyester resin casting fire retarded by tetrabromophthalic anhydride and antimony oxide.

ABSTRACTS AND R E V I E W S 255 extension of the melting zone and further crack growth. Figure 8d shows char smtermg and flame propagation behmd the weak nonhomogeneous char front. A fire-retarded polyester resin castmg with 5% antimony oxide and 11.5% tetrabromophthahc anhydride was subjected to burmng as shown m Fig. 9. Figure 9a shows the development of a strong char structure m the flame front In contrast to the plastic having only the halogen-contaimng retardant, there is no evidence of flame propagation beyond that area m direct contact with the flame source by bum- mg gases m the boundary layer Figure 9b shows the gradual erosion of the strong homogeneous char structure m the area of actual flame contact. Figure 9c shows rapid extmgmshment of the flame front after travel beyond the imtial flame source Figure 9d illustrates the char structure after flameout Phosphorus-Halogen Synergism Mitchell et al ^ studied the effect on autoigmtion temperature and on char strength when urethane foams were fire retarded with phosphorous and halogen- containing fire retardants The results are summarized m Table 4. The foams retarded with halogen-contaming compounds were totally consumed without the development of char structure, while those retarded with phosphorous and halogen-contammg compounds showed both a quenching response to fire exposure and the development of a carbonaceous char structure. Hilado" explamed the mechanisms employed by phosphorous and bromme com- pounds as follows: "Without phosphorous, hydrogen bromide is believed to be the most active bromine compound Smce this compound boils in the combustion zone, when it participates in successive halogenation and dehydrohalogenation reactions The presence of phosphorous promotes the formation of char, which further restricts movement m the gaseous phase, and results m the formation of phosphorous tnbromide, phos- phorous pentabromide, and phosphorous oxybronude, which are less readily gasified and are heavier gases (molecular weights of 270 70, 430 52, and 286 70, respectively) Smce these bromides are continually regenerated m the halogenation- dehydrohalogenation process, their effectiveness mcreases with their residence time in the combustion regions, and keepmg them in effect control twice as long would tend to make them twice as effective." T A B L E 4 Effect of phosphorous and chlonde inhibitors on the autoigmtion temperature and char strength of a urethane foam Inhibitor Phosphorous Chloride Autoigmtion temp, Char content, % content, % °F strength 0 0 950 None 0 50 950 None 5 50 1000 Weak 10 0 1150 Strong

256 F I B E R E S E A R C H The fluxing action of phosphorous is probably hmited to the interface of the combustion and pyrolysis regions so that any excess over the amount needed to stabihze the char is meffective Since phosphorous oxides can effect only so much dehydration while the continually regenerated bromides can repeat the dehydro- halogenation process phosphorous/bromme combmations would be more effective than phosphorous oxides m promoting char formation The mechamsm of the phosphorous-chlorine synergism is similar to that of the phosphorous-bromme synergism It is more widely utilized because of the greater availabihty of chlorme-contaimng compounds The phosphorous-chlorine synergism is less effective than the phosphorous-bromine synergism to the same degree and for the same reasons that chlorme is not as effective, on an equal weight basis, as broimne The chlorides of phosphorous are lower boilmg and lighter gases than the correspondmg phosphorous bromides, and can be expected to have a shorter residence time in the combustion zone PHOSPHOROUS-BASED F I R E R E T A R D A N T S Phosphorous has an atomic number of 15, and an atomic weight, for the single natural-occurrmg isotope, of 30 98 The electromc structure is W2s'2p^Ss'Sp^ for a total of 15. Bonding m phosphorous compounds can mclude simple sharmg of the 3p orbitals or various 3s-3p orbitals The 3d orbitals are readily available, thus allowmg for spd hybrids Most phosphorous-ligand smgle bonds are now thought to be hybrids The PO smgle bonds m P O 4 ' - are sp' hybrids, the Cl-p bonds m P O C I 3 are a mixture of p' and sp' character The pentavalent and hexavalent compounds are spd hybrids as in PClsCsp'd) and PCl6-(ion-sp'tP) Many P-ligand bonds have considerable x bond character. Table 5 lists typical phosphorous-containmg compounds that are used as fire retardants Lyons" pomts out that almost all of the fire retardants that contain phosphorous are m odd oxidation states The behavior of phosphorous-based fire retardants has been studied m detail in several cellulosic systems Tang and Eichner*' reported that ammomum phosphates reduced the thermal decomposition temperature durmg pyrolysis of cellulose T A B L E 5 Fire retardants containing phosphorous Oxidation number Structure Name - 5 (H0)5P0 Phosphoric acid 0 0 0 1 1 1 +5 1 1 1 HO^P—(0—P—)xP—(OH), Polyphosphonc acid j [OH -1-5 POCU Phosphorous oxichlonde +3 PBr, Phosphorous tnbronude +1 HP(0)(OH) Hypophosphorous acid - 1 H J ' O H Phosphmous acid - 3 Phosphme

ABSTRACTS AND R E V I E W S 257 Similar findings were observed by Einhom" in the formation of chars and the effect of reaction and additive-type phosphorous-based fire retardants on urethane polymers Phosphorous compounds that can decompose to acids are effective fire retardants I t IS currently believed that phosphorous compoimds are acid precursors and further that the acids perform the key role in char formation and in the inhibition of afterglow. Equation (30) illustrates the formation of phosphorous acids dunng the thermal decomposition of a typical phosphorous compound" C H 3 C H , I I A I I H 3 C — C — O P >H3C—C = CH2+H0P—. (30) I I I C H , Equation (31) shows that the same reaction will occur in any alkyl ester when subjected to higher temperature I A I ROP * a lkene+HOP- . (31) Acid fragments will polymerize when subjected to heating to produce polyacids I A I I I HOPOH > HOPOP- • -0—P0H+H20(g)t . (32) I I I I The polyacids are strong mmeral acids, and also strong dehydratmg agents, which are capable of protonatmg other species The polyacids greatly enhance char forma- tions m polymers contaimng multihydroxyl grouped urethane, polyesters, and cellulose. The formation of a strong carbonaceous char is thought to proceed via ester formation or through an mtermediate carbomum ion 0 0 0 R C H 2 - C H 2 O H + POPOH RCH2CH2OPO3H2 + -P-OH (33) 0 0 H H I . OH RCH = C H 2 + HsPOij ESTERIFICATION AND DEHYDRATION R C H 2 - C H 2 O H ( R C H 2 C H 2 O H 2 * ) (34) RCH =• C H 2 + H2O SIMPLE CARBONIUM-ION MECHANISM

258 F I R E R E S E A R C H CHpOH - C H 2 OH .C— H I \—V 0 i n . Fia 10 Levoglucosan formation from cellulose Phosphoric acid is much more effective than sulfuric, sulfomc, and boric acids because it has sufficiently low volatility to remam m or near the site of combustion, is highly reactive, and is a mineral acid (pK, x ON). Figure 10 illustrates the formation of levoglucosan from cellulose Laible^ con- cluded that the major cause of cellulose flammability is the tarry products being vaporized and thermally cracked mto highly combustible gases The major con- stituent of the tar is levoglucosan, which is formed as mdicated in Fig. 10 I t is noted that all orgamc fibers give off gaseous products durmg combustion or pyrol- ysis Thus, if the textiles which are made from these fibers are to be fire retarded, the gaseous degradation products must be rendered nonflammable There are three general approaches used to impart fire retardancy to this class of materials (or too many other polymeric materials) 1 To add a reactive fire retardant which becomes part of the chemical struc- ture of the material, 2 To add an inert fire retardant which will function in a desned manner when required, but which is not part of the chemical structure of the material, 3. To deposit flame retardants or char precursors on the surface of the object to be protected. Whatever the method of application, the fire retardant can act through one of two methods In one the fire retardant causes the protective material to follow an abnormal course of decomposition, yieldmg less volatile and less combustible degradation products. In the second mechamsm, which is effective with fibers and many polymers, the additive decomposes to gaseous products which mix with the

ABSTRACTS AND R E V I E W S 259 normal gaseous products from the decomposing fiber to give a less-flammable gas mixture Phosphorous contaimng fire retardants which generate phosphoric acid may be added to prevent the formation of levoglucosan and form instead a char percursor during combustion R E T A R D A T I O N O F A F T E R G L O W The glowmg reaction is a solid-phase oxidation of carbon to oxides, CO and CO2 Phosphorous compounds are widely used to elimmate afterglow, but little informa- tion IS known about this mechanism Lyons^' summarizes the possible role of the phosphorous compound in retardation of afterglow by stating that the polyacid, formed durmg the decomposition of the phosphorous compound, forms a physical barrier or m some way alters the oxidation process Polyphosphoric acid is a very VISCOUS, film-formmg substance, which could coat the surface and retard oxygen diffusion into the reaction zone durmg combustion The greater tendency for phosphorous compounds to form a gummy film as compared to sulfur or boron may explam the superiority of phosphorous compounds as glow-mhibitors Al- ternative mechamsms such as favormg the production of CO2 because of some as yet unknown catalysis effect attributable to the phosphorous acids and not from other acids are not as easily argued. B O R O N F I R E R E T A R D A N T S The largest use of boron compounds as fire retardants is in wood and wood products Eickner'^ published a comprehensive review covering the performance characteristics of fire-retardant wood Borax, boric acid, and sodium borate are the most common boron compounds used in the treatment of wood McCluer" tested a number of morgamc boron salts as fire retardants for fabrics The most effective of those compounds evaluated was sodium fluoborate In general, organoboron derivatives (esters) are thought to be too hydrolytically unstable for general use as fire retardants Knaggs** found that solutions of triamyl borate in an orgamc solvent with tiitolyl phosphate and a fatty acid salt were effective m fire-retardmg fibrous materials Cyclic bono acid esters derived from diethanolamines are stabihzed towards hydrolysis by an mtramolecular, boron-nitrogen coordmate bond Rudner and Moores'^ utilized this structure to prepare direct polymers with cellulose that do not leach out on exposure to water. Cellulose fibers when treated with the followmg boron-contaimng compound were appreciably slower burmng than control fabrics.

260 F I R E R E S E A R C H Rudner and Moores assumed that the methoxy groups were displaced by the hydroxyl groups of the cellulose to give an integrally bound boron-contaimng crosslinkage. The mechamstic details of how bone acid and borate salts retard the combustion of cellulose are only partially understood Schwenker and Beck*" reported at least 37 products formed durmg the pyrolysis of cellulose The major volatile primary product IS thought to be levoglucosan (l,6-anhydro-/3-D-glucopyranose). Levo- glucosan is thought to arise by the thermal scission of the 1,4-glucoside bonds of cellulose. A free primary hydroxyl group at Ce is necessary for this depolymerization to occur. Levoglucosan is presumed to fragment to form the observed low molecular weight, volatile products A second pathway for cellulose decomposition is simple dehydration to give water and dehydrocellulose The dehydrocellulose is believed to be the principal source of char Woods etal" incorporated boron into the polyol moiety of rigid urethane foams Several boron-contaimng compounds were synthe- sized as shown in Eqs (35)-(38) B ( 0 H ) 3 + 3 C H 3 C H { 0 H ) C H 2 0 H * BOCHjCHCHa)^ + 3 H 2 O (35) I OH H 2 B ( 0 H ) 3 + 3HOCH2CHCH2OH + HO ( B - O C H 2 C - C H O H + 6 H 2 O (36) I I B ( 0 H ) 3 + 2HOCH2CHCH2OH + H O / ^ ° ) B - 0 C H 2 C H - C H 2 C H + 3 H 2 O ( 3 7 ) OH OH I I I B ( 0 H ) 3 + 3 H O C H 2 C H - C H 2 O H > B ( O C H 2 C H C H 2 O H ) + 3 H 2 O (38) OH OH I V Structures I - I V are idealized; the actual products are probably mixtures of boron- polyol polymers Prepolymers prepared with structures I , I V , or <ns-(hydroxy- propyl) glycerine and toluene diisocyanate produced foama of such poor quahty that their evaluation was discontmued. Foama were prepared using polymethylene polyphenylpolyisocyanate and the boron containmg polyols. Table 6 gives the formulations used by Woods in preparing these foams The formation of a complex (V) between the triethylenediamine catalysts and \

ABSTRACTS AND R E V I E W S 261 T A B L E 6 Polymethylene polyphenyl polyisocyanate boron-polyol foam formulations* Foam No PAPI (wt g) Polyol used Polyol (wt g) Catalyst System Catalyst (wt g) F-11 (wt g) 1 16 0 I 8 4 Triethylene diamine-hex- anetriolt 0 4 6 2 16 0 I I 19 1 Tnethylene diamme-hex- anetnol (CjH6)«H 0 4 0 2 6 3 16 0 I I I 12 6 Tnethylene diamine-hex- anetnol (CsH6)jN 0 4 0 2 6 4 13 1 IV 9 0 Tnethylene diamme-hex- anetriol 0 4 6 5 16 0 IV 9 3 Tnethylene diamme-hex- anetnol (C2H6)jN 0 4 0 2 6 6 15 5 IV 9 3 Triethylene diamme-hex- anetriol (CjH6)aN 0 4 0 2 6 7 21 5 e** 15 1 H,N,H\ AT'-tetramethyl- 1,3-butane diamine 0 2 5 *Each foam formulation contained 0 2 g of DC-113 sihcone surfactant (Dow Commg Company) t A 112 mixture of tnethylenediamine (DABCO-HOUDRY Process Company) and hexanetnol t Polymethylene polyphenylpolyisocyanate (Upjohn Corporation) § Tnchlorofiuoromethane •* A mixture of VORANOL RS 530 (Dow Chemical Company) and I . the acidic glycol borates resulted in retarded rates of rise during foam prepara- tions . 0 0 - Additional ainme catalyst was required to produce satisfactory foam specimens Table 7 presents the results of evaluations performed to determme the flam- mability characteristics of the boron modified foams Woods et aV^ prepared several brominated boric acid esters as potential non-

262 F I R E R E S E A R C H T A B L E 7 Flammability characteristics of boron-contammg foams Foam Density Bum rate,* No (pcf) % B (m /mm) Observations 1 2 96 1 4 10 1 ± 0 5 Shnnks 2 4 15 3 63 Immediate self-extinguishmg Melts 3 3 72 2 28 Self-extmguishmg (7-8ec) Chars 4 16 9 1 4 Self-extmguishing (1-6 sec) Chars, shght softenmg 5 3 54 1 26 Self-extmguishing (14:-8ec) Chars, shght meltmg 6 3 36 1 3 Self-extinguishmg (7-10 sec) Chars, sags 7 3 69 0 89 7 3 ± 0 3 Surface char, shnnks •Modified ASTM D 635-56T. reactive fire retardants Rigid foams were prepared from a polyhydroxylpropylated sucrose-TDI prepolymer and polyether polyols The additives were mtroduced at a level of 20 phr and the effect on burmng rate deternuned. Some reductions m burnmg rates were achieved, but no self-extmguishmg foams were obtained. N E W C O N C E P T S F O R T H E D E V E L O P M E N T O F F I R E - R E T A R D A N T P L A S T I C S The use of recently developed techmques of thermal analysis to match the chem- ical and physical properties of candidate fire retardants with that of the polymer to A > \ \ \\ \\ i \ 1 1 ^ C7> Temperature - C. F I G 11 Thermogram for a hypothetical polymer

ABSTRACTS AND R E V I E W S 263 be stabilized has been reported by Einhorn.'' Simultaneous differential thermal analysis ( D T A ) , thermogravimetric analysis ( T G A ) , and derivative thermogravi- metric analysis ( D T G ) are earned out under dynamic conditions of a heatmg rate of 10°C/mmute. Figure 11 presents the thermogram for a hypothetical polymer which exhibits a simple ummolecular degradation process Point A represents the region of mitial decomposition, pomt B represents the pomt of maximum degradation. I . - 312 M W. T n o l Tline - Minutes F I G 12 Sublmunation of fire retardant (vacuum). Fire retardants are screened so as to select a material having thermal charac- teristics similar to those illustrated in Figure 11 A greater degree of stabihty can be obtained if two fire retardants are used one fire retardant which changes state ap- proximately-60° to 75°C lower m temperature than pomt A, and a second fire re- tardant which changes state in the temperature range of point B. For polymers which degrade by means of a complex or autocatalytic process, this technique may be used to select a balanced fire-retardant system usmg a combmation of several retardants.

264 F I R E R E S E A R C H r 4 TGA T 1 1 -NCO NCO 312 M W Tr1ol -DIG .——Pressure (Vacuum) J _ 30 20 10 Tine - f'lnutes F I G 13 Degradation nonfire-retarded urethane polymer The choice of fire retardants, is of course, dependent on the nature of the polymer, the method of processing, the proposed service conditions, and economic considera- tions Generally, reactive fire retardants are more stable than mert systems Numerous mvestigations of materials exposed m actual fires have mdicated that the nonreactive retardants may sublime out of the polymer when exposed to the hot gases which normally proceed the flame front Figure 12 illustrates weight losses equivalent to the weight of fire retardant in urethane polymers when the nonreac- tive <m-2,3-dibromopropyl phosphate was used Further studies were carried out m a vacuum of 10~̂ torr. Figure 13 shows a smgle sharp weight-loss region when a nonfire-retarded urethane polymer was heated under dynamic conditions The change m pressure was due to the evolution of gaseous degradation products at the time of thermal decomposition of the polymer. Figure 14 shows a bimodal degradation process when the nonreactive fire-re- tardant im-2,3-dibromopropyl phosphate was added to the model urethane. The mitial weight loss (without an mcrease m pressure) was due to sublimation of the nonreactive fire retardant The material which was lost imtially was collected and identified by normal chemical analysis procedures as the fire retardant. In the process of selectmg fire retardants to improve the flammability charac- teristics of a polymer or plastic, consideration must be given to total fire response and not just a smgle parameter such as flame propagation, smoke development, or fire endurance The final product must be subjected to evaluation standards which approximates actual service life For example, it is not normally possible to fire- retard synthetic fibers, when they are produced, because of undesirable side effects

ABSTRACTS AND R E V I E W S 265 7^ t ' -1 1 — CH3 r NCO 312 H H Triol NCO 30% Fire Retardant Fire Retardant Sublimation (Vacuum) Pressure 30 20 10 0 Tine - 'linutes F I G 14 Degradation of fire-retarded urethane polymer during coloring, weavmg, or sizmg operations Nonreactive fire retardants may be added as an after treatment with only minor adverse effects to the process eco- nomics. Standardization tests usually are designed to rate the manufactured product I t IS necessary to perform use-oriented tests so as to predict with the desired degree of confidence the performance of the finished product. Thus, m the case of fabrics, a given number of cycles of washmg or dry cleamng may be used to evaluate the flammabihty characteristics after a preselected service life. F U T U R E T R E N D S I N F I R E R E T A R D A T I O N O F P O L Y M E R S Greater emphasis is now bemg directed toward modification of chemical structure m order to inhibit igmtion and flame propagation Einhorn has predicted that the second generation of fire retardants will not contain halogen atoms and thus reduce substantially the additional hazards to life support durmg the combustion of fire- retarded polymers. References 1 "Flammabihty Charactenatica of Polymenc Matenals," Proceedmgs of Polymer Conference Senea, Wayne State Umversity, Detroit, Michigan (June 1966). 2 "Symposium on Fire Retardant Plastics," 155th National Meetmg of Amencan Chemical Society—Orgamc Coatmgs and Plastics Chemistry, Vol 28, No 1 (Apnl 1968) 3. 'Tlammabihty Characteristics of Polymenc Matenals," Proceedmgs of Polymer Conference Senes, Umversity of Detroit, Detroit, Michigan (Jime 1969) 4. "Symposium on Textile Flammabihty and Consumer Safety," Gottheb Duttweiler Institute for Economic and Social Studies, Ruschlikon-Zunch (1969).

266 F I R E R E S E A R C H 5. 'Tlammabihty Characteristics of Polymeric Materials," Proceedmgs of Polymer Conference Senas, Umversity of Utah, Salt Lake City, Utah (June 1970) 6. "FlammabiLty Characteristics of Polymeric Materials," Proceedmgs of Polymer Conference Senes, Umversity of Detroit, Detroit, Michigan (June 1970). 7. "The Mechanisms of Pyrolysis, Oxidation, and Burning of Organic Matenals," Preprmta, 4th Materials Research Symposium, National Bureau of Standards, Gaithersburg, Maryland (October 1970) 8 P A B K T N , B Bntish Plastics 3^(1), 29 (1959) 9 B o T E R , N E AND VAJDN, A E SPE Trans 4(1), 45 (1969) 10 E i N H O R N , I N 'Tlammabihty Characteristics of Polymenc Matenals," Proceedmgs of Polymer Conference Series, Wayne State Umversity (June 1966) 11 H i L A D O , C J Flammabihty Handbook for Plastics, Technomic Pubhshmg Company, Stan- ford, Connecticut (1969). 12 CAQLIOSTRO, D E "Flammabihty Characteristics of Polymenc Matenals," Polymer Con- ference Senes, Umversity of Detroit (June 1969) 13. B E L L , K M . Trans J . Plastics Inst, Conf Suppl No 2, 27 (1967). 14 E i c H H O R N , J J Appl Polymer Sci 8, 2497 (1964) 15 B u R Q E , S . J AND T I P P E R , C F H Combust Flame IS, 495 (1969). 16 VOLONS, P Trans J Plastics Inst, Conf Suppl No 2, 47 (1967) 17 FENIMOHE, C . P Combust Flame IS, 155 (1968) 18 E i N H O H N , I N , SEADER, J D , D R A K E , W O , AND M I H L P E I T H , M 'Tlammabihty and Toxicological Characteristics of Isocyanurate Foams, Intumescent Coatmgs, and Fluorel," U T E C - M S E 70-006, Fmal Report NASA Contract NAS2-6063 (January 1971). 19 R i c c i T i E L L O , S R , F I S H , R H , P A R K E R , J A , AND GUSTAFON, E J "Development and Evaluation of Modified Polyisocyanurate Foams," 28th Annual Technical Conference, Soc of Plastics Eng , Inc, New York (May 1970) 20 E i N H O R N , I N "Thermal Degradation and Flammabihty Characteristics of Urethane Poly- mers," Proceedmgs of the Polymer Conference Series, Umversity of Utah (June 1970) 21 I B I B I C U , M M AND GAYDON, A S Combust Flame 8, 11 (1964) 22 E i N H O R N , I N 'Tlammabihty of Modified Urethane Polymers," Gordon Research Con- ference, Colby, New Hampshire (July 1970) 23. HOLMES, F . H AND SHAW, G J J A AppUed Chemistry 11, 200 (1961) 24 GRUNDFEST, I J Proc Div. of Orgamc Coatmgs and Plaatics, Am. Chem Soc SI, 113 (1961) 25. R o s s E R , W A , W I S E , H , AND M I L L E R , J Seventh Symposium (^Intemattonal) on Comhustvm, p 175, Butterworth (1959). 26. WILSON, W . E , O'DONOVAN, J T. , AND FRISTROM, R M Twelfth Symposium {International) on ComMstion, p 929, The Combustion Institute (1968) 27. FRISTROM, R M . "Kmetics and Mechanisms of Flames and Flame Suppression," Proceedmgs of the 4th Matenals Research Symposium, National Bureau of Standards, Gaithersburg, Maryland (October 1970). 28 MoDicu, A. AND L A G R A T F , J "Decomposition and Oxidation of C!F4 m Shock Waves," J . Chem Phys 43, 3383 (1965) 29 C R B r r z , B J J . Research, Natl Bur Std 65A, 389 (1961). 30 STUETZ, D . " 'Tlammabihty Characteristics of Polymenc Matenals," Proceedmgs of Polymer Conference Series, Umversity of Utah (June 1970). 31. F E N I M O R E , C . p . AND JONES, J W.: Combust Flame 10, 135 (1966). 32. FENIMORE, C P AND JONES, J . W. Combust Flame 10, 295 (1966) 33 INGRAM, A R J Appl. Polymer Sci 8, 2485 (1964). 34 G o u i N L O C H , E V , PORTER, J . F , AND HINDERSINN, R R Proceedmgs Div of Orgamc Coatmgs and Plastics, Am. Chem Soc, 28, (1), 275 (1968). 35 P i B C H O T A , H J . Cellular Plastics / ( I ) , 186 (1965) 36 T i L L B T , J . N 'Tlammabihty Characteristics of Polymenc Matenals," Proceedmgs of Polymer Conference Senes, Wayne State Umversity (June 1966) 37. L i , P Z et al Plaaticheskie Massy (5), 15-19 (1963)

ABSTRACTS AND R E V I E W S 267 38. A L ' S H I T S , I . M. Zhur Pnklad Khun S4, 468-469 (1961). 39 British Patent 924,323, Umted States Rubber Co (April 24, 1963) 40 Canadian Patent 681,805, Conumon Rubber Co , Ltd (March 10, 1964). 41 U S Patent 3,007,958, Hooker Chemical Corp (November 7, 1961) 42 U S Patent 3,113,933, Rutgerswerke, A G (December 10, 1963) 43 Bntish Patent 988,304, Michigan Chemical Corp (Aprd 7, 1965) 44 French Patent 1,294,986, Deutsche Akadimic der Wissenchafter zer Berhn (April 24, 1962) 45 Belgian Patent 655,793, Michigan Chemical Corp (November 16, 1964) 46 NAMETZ, R C AND N U L P H , R J • S P I Div of Remforced Plastics, 20th Annual Tech Conf, Chicago, Proceedmgs, Sec 11-C (1965) 47. NAMETZ, R C , D I P I E T B O , J , AND EINHOKN, I N Proc Div Organic Coatmgs and Plasties, Am Chem Soc 28, 291-310, San Francisco, Cahforma (March 1968) 48 R E A D , N J AND H E I G H W A T - B U R T , E G J Soc Dyers and Colorists 74, 823-830 (1958) 49. L I T T L E , R W . 'Tlameproofing Textile Fabncs," American Chemical Society Monograph Series No 104, Remhold Pubhshmg Corp, New York, N Y (1947) 50. Bntish Patent 924,945, Dow Chemical Co (1960) 51. P i J M P E L L Y , C T "Fire-Extmguishing and Fireproofing," Chapter 6, m Bromme and Its Compounds (Z E ZoUes, E d ), Academic Press, New York, N Y . (1966) 52. SCHMIDT, W G • Trans J Plashes Inst 247 ( D e c e m b e r 1965) 53 D R A K E , G L , J R : Fure-Resistant Textiles—Encyclopedia of Chemical Technology, 2nd ed , Vol. 9 (R E Kttk and D. F Othner, Eds ) , John Wiley & Sons, Inc, New York, N. Y (1966) 54 P I T T S , J , SCOTT, P H , AND P O W E L L , D S J Cell Plaat 6, No 1 (January/February 1970) 55 E i N H O R N , I N AND KANAKIA, M J Appl Polymer Sci (in Press). 56 M I T C H E L L , D W AND MURPHY, E M Proceedmgs of a Conference on Foamed Plastics, NAS Pubhcation PB 181576 (Apnl 1963) 57. LYONS, J . W • The Chemistry and Uses of Fire Retardants, Wiley-Interscience, New York, N Y . (1970). 58 T o N O , W K AND E i c K N E R , H W U. S Department of AgncuUure Forest Service Research Paper FPL 82 (1967) 59 E i N H O R N , I . N : "Flammabihty Characteristics of Polymenc Materials," Proceedmgs of Polymer Conference Senes, Umversity of Utah (1970) 60. L A I B L E , R C Am Dyestufif Reporter 47, 173-178 (1958) 61. LYONS, J W. • 'Tlammabihty Characteristics of Polymenc Materials," Proceedmgs of Polymer Conference Senes, Umversity of Utah (1970) 62 E i C H N E R , H W 'Tu:e Retardant Treated Wood," Amencan Society for Testmg Matenals, Seattle, Waahmgton (1965) 63 M C C L U E B , J D U S Patent 2,948,641, Thermoid Co (1960). 64 KNAGGS, J Bntish Patent 575,028 (1946) 65 R u D N B B , B AND MooRES, M S U S Patent 3,042,636, Koppers Co , Inc. (1962) 66 S c H W E N K E R , R F , J R AND B E C K , L R , J R J Polymer Sci, Part C, No 2,331 (1963) 67 WOODS, W G , BBNGELSDORP, I S , AND FARTTCCIA, D Flammabihty Characteristics of Polymenc Matenals, Wayne S t a t e Umversity (1966). 68. WOODS, W . G , BBNGELSDORF, I S , AND LASUCCIA, D . U S Patent 3,189,565, Umted States Borax and Chenucal Corporation (1965).