CA1102937A - Flame retarding agents containing zinc sulfide for synthetic organic polymers - Google Patents

Abstract

Abstract of the Disclosure - The flame retardancy imparted to synthetic organic polymers by a halogen source is significantly increased by the presence of zinc sulfide in the polymer composition. One or more specified basic compounds are optionally included to neutralize any acidic materials generated during pyrolysis of the polymer composition.

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Description

RS(~ ~ )MS
~ ~Z~3~7 FLAME RETARDING AGENTS AND POLYMER
COMPOSITIONS CONTAINING SAME
BACKGROUND OF THE INVENTION
This invention relates to decreasing the flammability Or halogen-containing polymer composltlons.
It is well known that the flammability of synthetic organic polymers can be slgnificantly reduced by including a halogen source in the pol~er composition. Among the p~ieferred halogen sources are halogen-containing hydrocarbons.
particularly bicyclic hydrocarbons such as perchloropenta-cyclodecane. Alternatively, the polymer itself can function as the halogen source. Examples of the latter are polyvinyl chloride and other polymers derived from halogen-contalning monomers.
In addition to reducing flammability of synthetic polymers it is also desirable to reduce the amount of smoke generated during combustion, since in many instances the dense,~
toxic smoke presents as much, if not more, of a h~zard than the f'ire itself.
A number of zinc compounds, including zinc oxide and zinc sulfate have been~proposed as flame retardants for various types of polymers, however these compounds are less than desirable because they adversely affect the heat stability of the polymers.
It ~s therefore an objec~ive cf this invention to define those zinc compounds whlch act as flame retardlng agents and smoke suppressants without adversely affecting the heat 25 ~ stability of halogen-containing polymers and polymer ¦ compositions contalning an or~sanic halogen source. Surprisingly lt has been round that zinc sulflde, a relatively inexpensive zinc compound, achleves this oh~ective.

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SUMMARY OF THE INVENTION
According to the present invention, there is provided a flame-retardiny agent for synthetic organic polymers comprising zinc sulf.ide, a basic compound in an amount sufficient to neutra-lize acidic by-products produced during pyrolysis of the agent together with the synthetic organic polymer, and an amount of halogen source equivalent to from 2 to 10 moles of halogen per mole of zinc sulfide.
In another aspect, the invention provides a method of imparting flame retardency to a synthetic organic polymer compo-sition wherein the polymer is selected from the group consisting of (a) polymers wherein at least a portion of the repeating units are derived from a halogen-containing monomer selected from -the group consisting of ethylenically unsaturated compounds, (b) halogen-containing polyesters derived from the reaction of at least one di.carboxylic acid containing from 4 to 20 carbon atoms with at least one diol containing from 2 to 20 carbon atoms, (c) non-halogen-containing polymers wherein the repeating units are derived from at least one ethylenically, unsaturated compound and (d) non-halogen-containing condensation polymers selected from the group consisting of polyesters, polyamides, polycarbonates, epoxide polymers and non-cellular polyurethanes, said method comprising adding a flame retarding agent to said polymer compo-sition wherein the flame retarding agent includes zinc sulfide, a basic compound in an amount sufficient to neutralize acidic by-; products produced during pyrolysis of the agent and said polymer composition and an amount of halogen source equivalent to from

2 to 10 moles of halogen per mole of zinc sulfide, the agent being : added in an amount such that 0.3 to 50~, based on the weigh~ of said polymer, of zinc sulfide is present in the polymer composi-tion~

3~7 Preferably, the flame retarded polymer composition comprises 1) a flame retarding agent as defined above together with 23 a polymer selected from the group consisting of (a) polymers wherein at least a portion of the repeating units are derived from a halogen-containing monomer selected from the group consisting oE ethylenically unsaturated compounds, (b) halogen-containing polyesters derived from the reaction of at least one dicarboxylic acid containing from 4 to 20 carbon atoms with at least one diol containing from 2 to 20 carbon atoms, (c) non-halogen containing polymers wherein the repeating units arede.rived from at least one ethylenically unsaturated compound~.and (d) non-halogen~containing condensation polymers selected from the group consisting of polyesters, polyamides, polycarbonates, epoxide polymers and non-cellular polyurethanes, said flame retarding agent being present in an amount such that 0.3 to 50%
based on the weight of said polymer, of zinc sulfide is present . -in the polymer composition. A basic compound such as magnesium hydroxide or barium sulfate is optionally included in the composition to neutralize any acid by-products formed during pyrolysis of the polymer composition.

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FLAME RETARDANT AGE;NTS AND POLYMER
_ CO~POSITIONS CONTAINING sAr~
DETAILED DESCRIPTIOM O~;' THE INVENTION
Zinc sulfide is unique among zinc compounds in that it is water insoluble, does not adversely affect the heat stability of the polymer composltion, and significantly improves the flame retardancy imparted to normally flammable polymeric materials by o.rganlc compounds containing chlorine or bromine.
Halogen-containing compounds suitable for use with ~ zinc sulfide include, but are not limited to the following ; classes: ¦ -1 Chlorinated and brominated hydrocarbons such as methylene chloride, chloroform, the isomeric brominated and/or chlorinated ekhanes, ethylenes, propanes, butanes and hexanes, halogenated cycloal~phatic hydrocarbons containing one or more rings which may be fused to form a bicyclic structure, halogenated aromatic hydrocarbons, including mono- and poly-halogenated benzene, toluene, xylene, naphthalene and anthracene. The compounds may contain one or more non-reactive substikuents in addition to halogen, such as ni~ro or ' ~`
.~ esterified acid or hydroxyl groups;
2. Chlo~inated and brominated organic compounds containing one or more f'unctional groups suc~l as carboxylic acid anhydride.s, amines, ketones and alcohols. Compounds containing two or more functional groups or a pokentially reactive carbon-carbon double bond can be employed to prepare halogen-containing polymers which are useful as addltives to render other polymers flame retardant in the presence of sodlum antimonate. ~lternatively the halogenated compounds can I~
., 1 lUZ937 be incorporated by copolymerization lnto the polymer which is to be rendered flame retardant or non-burning;
3. Organic compounds containing halogen in addition to other elements, such as phosphorus, which impar~
flame retardancy to synthetic organic polymers. Preferred embodlments of this class of compounds are the brominated trialkyl- or triaryl esters of phosphoric acid, including tris(2,3-di~romopropyl)phosphate ard tris(2 4,6-trihromopheny]), phosphate.
The amount of halogen-containing organic compound required to lmpart a given degree of flame retardancy to a particular polymer may vary somewhat depending upon the inherent flammability of the polymer, the halogen content of the organic compound and whether the halogen is chlorine or bromine. These ranges are sufficiently disclosed in the literature that a comprehensive discussion in this specification ls not required. Normally between 7 and 40$ of chlorine or I 3 to 20% of bromine, based on the weight of the polymer, provides acceptable levels of flame retardancy.
As disclosed hereinbefore, the organic polymer can also function as the halogen source lr the halogen content is ~i sufficiently high. Suitable halogen containing polymers include polyvinyl chloride, polyvinylidene chloride~ and -copolymers of vinyl chloride and/or vlnylidene chlorlde with ethylenically unsaturated monomers~ including ethylene, propylene and styrene. Polyesters and other condensation polymers wherein one or more of the precursors contain chlorine or bromine, i.e., tetrabromophthalic anhydride, are also useful as halogen sources.

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~ Z937 The comb1nation of zlnc sul~ide a~d one ~ the halogen sources described in the preceding paragraphs imparts an e~fective level of flame retardancy to practically all classes of halogen- and non-halogen-containing synthetic organlc polymers. If the polymer does not contain sufficient halogen, one of the chlorinated or brominated organic compounds described in a preceding section of this specification must be present in the final composition to obtain the deslred degree of flame retardancy. The present flame retarding agents can be combined with addition and condensation type polymers.
Examples of the former class include homopolymers and copolymers derived from organic compounds containing one or more double bonds between ad~acent carbon atoms. Representative compounds ;
of this class include mono- and diolefins such as ethylene, propylene, butylene, butadiene~ neoprene, isoprene, and the various halogen-containing derivatives thereof, such as chloroprene and tetrafluoroethylene; vinylic compounds, such as styrene, vinyl chloride, vinylidene chloride, vinyl esters such as vinyl acetate; unsaturated acids and derivatives thereof, such as maleic acid, acrylic acid, methacrylic acid and esters derived from reaction of these acids with alcohols containing between 1 and 12 carbon atoms, inclusive; and unsaturated compounds containing various substituer.ts, exemplified by acrylonitrlle and 2-vinylpyrldine.
~ondensation polymers are prepared from monomers containing 2 or more functional groups guch as carboxylic acid,;
hydroxyl, amine or isocyanate groups which can react intra-molecularly to form an ester, amide, carbonate, urethane or other radical which characterizes the repeatln~ unit of the polymer.
. ,, ~; . 'i iZ937 Addition polymers are prepared by bringing ~he monomer or monomers into contact ~ith a source of rree radicals, such as a peroxide, peroxy acid or compound containing an azo radical, i.eO, azo-bisisobutyronitrile. The polymerization is relati~lely rapid and often exothermic.
Condensation polymerization reactions are usually considerably slower than addition type polymerizations.
Elevated temperatures and the presence of acid or other type ¦l of catalyst are often required to achieve a useful reaction rate. Exceptions to this are the reaction of isocyanates with !
hydroxyl-containing compounds and the homopolymerization of epoxide radicals (-C~

which can be considered addition type reactions since no by-products, such as water, are generated. This is also true for the reaction of phenols, melamines or ureas with formaldehyde. Examples of condensation type polymers include polyesters such as polyethylene terephthalate, polybutylene sebacate and unsaturated polyesters derived from phthalic anhydride, maleic anhydride and ethylene glycol or other difunctional alcohol; polyamides, including poly(hexamethylene adipamide), poly(hexamethylene terephthalamide) and poly-caprolactam, the acetal resins and polysulfides.
Speclfic methods ~or preparing all of` the foregoing classes of polymers are described in textbooks, ~ournal a~ticles and are usually available upon request from many manufacturers of the monorners. A complete discussion of polymer preparation in the present specification is therefore ~ -6-~l~Z~37 not required, since the proced~res are kno~;n to those familiar with the art relating to synthetic organic polymers.
As stated in the preceding specification, it may be desirable to employ zinc sulfide in combination with a basic compound for the purpose of neutralizing any acidic materials generated as by-products during heating or combustion of the polymer composition. Preferred basic compounds include, but are not limited to, magnesium hydroxide, barium sulfate, calcium carbonate and hydrated alu.ina. ~lkali metal and alkaline earth metal hydroxides are also effective in some instances, however the use of these compounds should be limited to polymer compositions which are no~ adversely ', affected by the presence of these highly alkaline compounas.
In addition to polymer, halogen source and zinc sulfide the present compositions may also contain a plasticizer in an amount from 5 to 100%, based on the weight of the polymer. Many halogen-containing polymers, particularly polyvinyl chloride, are inherently rigid, brittle materials.
By combining the polymer with a suitable plasticizer it is possible to obtain a plastisol which is solid, semi-solid or liquid at ambient temperatures. Alternatively, an organic solvent can be added to the plasticized polymer to form an organosol. The resultant plastisol or organosol can readily be converted to sh~ped articles ~y casting or molding.
Plasticized halogen~containing polymers are employed as coating or encapsulating materials for a wide variety of metallic and non-metallic substrates. ~oatings for fabrics is only one of the many uses for these materials. ~he plasticized polymers ¦ are appl~ed to the fabric in liquid form by dippin~, spre~d ¦ coatin~ or sprayin~. Plasticized polymers in a finely dlvided -7~ `i I ~, ~ q~ 33~

soli~ form known es powder ooatings can be applied by suspendin~
the polymer particles in an air stream and dipping a heated substrate into the suspended particles. Some of the particles !
contact and are melted by the heated surface to form a coherent coating. Other known techniques for applying powder coatings, including electrostatic spraying, can also be employed. Regardless of the application method, the coated substrate is usually heated tG melt the polymer parcicies ~nd 3 form a coherent film.
Among the classes of known plasticizers for halogen- ' containing polymers are esters derived from aromakic or aliphatic dicarboxylic acids and monohydric alcohols, both of which contain between 6 and 20 carbon atoms. Representative plasticizers include dioctyl phthalate, diockyl adipate and 15 ~ dioctyl sebacate. Other plasticizers include alkyl, aryl and mixed alkyl-aryl triesters of phosphoric acid such as triphenyl phosphate; esters of benzoic acid with oligomers of alkylene diols~ such as dipropylene glycol dibenzoate, ' epoxidized esters of unsaturated acids such as bukyl epoxy stearate, lower alkyl esters of trimellitic acid, chlorinated paraffinic hydrocarbons containing bekween 30 and 70% by weight of chlorine and liquid polyesters derived from aliphatic dicarboxylic acids and diols.
Zinc sulfide is effective when employed in combination with a halogen source as the sole flame retarding agent for synthetic or~anic polymers. Alternatively, this comb-~nation can be used together with other known flame retardants.
Antlmony ioxide is paPtiCUlarly sui~ble, since ~ sm~

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i percentage of zinc sulfide has been shown to significantly increase the level of flame retardancy imparted by a given weight of antimony trioxide, even though zinc sulfide is a considerably less efficaclous flame retarding agent than antimony trioxide. Mixtures containing these two compounds are therefore highly advantageous for use with synthetic organic polymers, as will be demonstrated in the accompanying examples.
¦¦ The antimony trioxide is present at a concentration of from I 1 to about 10%, based on the weight of the polymer.
In addition to the present flame retarding compositions and~ optionally, a plasticizer, polymer compositions often incorporate one or more stabilizers which decrease the susceptability of the polymer to thermal i degradation. Numerous classes of compounds can be employed for this purpose. Stabilizers preferred for use in vinyl chloride polymers include diorganotin compounds and liquid mixtures containing barium and cadmium compounds. One unique feature o~ zinc sulfide relative to other water-insoluble zinc compounds is that it does not counteract the effect of the heat stabilizer.
Other additives which may be incorporated into the present polymer compositions include volatlle organic solvents such as ketones~ primary alcohols, and liquid hydro-carbons containing between 1 and 12 carbon atoms, pigments ~, such as titanium dioxide, antioxidants~ which include hindered phenols, among others, lubricating agents, including paraffin waxes, illers such as calcium carbonate or kaolin and viscosity control agen~s such as fused silica or polymeric glycols containing an average of between 2 and 5 repeating _9_ Z~37 ¦ unlts per molecule, The antioxidant prevents or delays degradation of the polymer or other constituent of the composition by oxidizing agents, such as the oxygen present in the air. Polyethylene glycols and polypropylene glycols are among the most useful viscosity control agents.
The following examples demonstrate preferred embodiments of the present flame retarding compositions, and '' should not be interpreted as limiting the scope of the invention as defined in the accompanying claims. In the examples all parts and percentages are by weight unless otherwise indicated.

EXA~PLE 1 The effect of various flame retarding compositions on f'lammability was evaluated using a plasticized vinyl chloride polymer composition containing the following I ingredients:
Vinyl chloride homopolymer 100 parts Dioctyl phthalate50 parts Epoxidized soybean oil3 parts Barium-cadmium stabilize~ 2.5 parts Stearic acid 0.5 part -i Flame retardantas specified ~A mixture of barium and cadmium soaps containing 5%
barium and 2.5% cadmium.
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The flame retarding compositions tested contained zinc sulfide alone and in combination with antimony trioxide.
The basic compounds present include magnesium hydroxide, barium sulfate (in combination with zinc sulfide as lithopone), calcium hydroxide and hydratcd alumina..
The polymer formulations were blended using a heated 2-roll mill and formed into sheets measuring 0.02Q inch ~0.05~ cm.) in thickness. ~ectangular samples measuring 6 x 18 inches (15 x 47 cm.) along the edges were cut from the sheets and evaluated using the American Society~for Test-ing and Ma~erials (AST~) Test E-162-67 ~reapproved in 1973~. The flame spread index ~IS? of asample is calcula.ted using the formula Is = ~`sQ
wherein Fs, the flame spread factor, is determined using the equation Fs = 1 + ~1/t3~ + Ll/~t6-t3~ + ~1/tg~t6] +

Ll/~tl2-tg) + Ll/~tl5-tl2~]

t3, t6, tg~ tl2 and tl5 correspond to the times in minutes from initial specimen exposure until the arrival of the flame front at the positions 3, 6, 9, 12 and 16 in. (76 .... 381 mm.~, respectively~ from the point of origin.
The term l!QI~, a direct measure of the heat evolved during burning of the sample, is defined by t~e equation Q _ O.l~T/~

where:
Q.l - an arbitrary constant, : T = the difference bet~een th.e observed maximum stack thermo-couple temperature rise in degrees Fahrenheit with the specimen present and the temperature rise observed in the absence of the specimen~ and - 11 -. -, X
.

B = th~ maximum stack thermocouple temperature rlse for unit heat input rate of the callbration burner in degrees Fahrenheit (per Btu per mln.). This is a constant for the apparatus.
The data obtained from an evaluation of the aforementioned film samples using the ASTM E162-67 test are I summarized in the accompanying Table I. These data demonstrate ¦ that the addition of zinc sulfide significantly reduces the flame spread and heat evolved during burning of a polymer containing a halogen source. Zinc sulfide also works effect;vely in combination with antimony trioxide. The flame spread of the sample containing a mixture of antimony trioxide and zinc sulfide is considerably less than a sample containing 1.5 parts of antimony trio~ide without zinc sulfide.

The evaluation for flammability described in the preceding Example 1 ~as repeated using a mixture containing ; antimony oxide and lithopone (a commercially available material containing 28% zinc sulfide and 72% barium sulfate). The polymer formulation employed to evaluate this flame retarding ; agent contained lOO parts by weight of a vinyl chloride homopolymer, 50 par~s of dioctyl phthalate, 20 parts of calcium carbonate, 0.5 part stearic acid, 0.2 part mineral oil, 1 part titanium dioxide~ 2.5 parts of ~he barium-cadmium stabilizer described in Example 1. One sample (Aj ; contained 3 parts of antimony trioxide and the second sample (B~
~ ~ contained .5 parts antimony trioxide and 1.5 parts lithopone.
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, , i The polymer compositlon was extruded to form a tube with an outside diameter of 3/4 inch (1.9 cm.) and a wall thickness of 0.055 inch (0.14 cm.).
When evaluated using AST~ test E162-67, Sample B, which contained both antimony trioxide and lithopone, T,~las considerably less flammable (Is = 50.2) than Sample A, which contained only antimony trioxiae and exhibited an Is value of ~4.1.

EXAMPLE 3 '. - '~
The 0.025 inch (0.063 cm.) thick film samples described in the preceding Example 1 were evaluated for smoke generation using a smoke density chamber available from the American Instrument Company~ Inc. as catalog no. 4-5800.
The.density (Dm) of the smoke generated by a heated or burning ~ 15 sample i9 measured photometrically and can be calculated using the equation Dm ~ 132 [loglO ( T )]

. ~ wherein T is the percent transmittance measured at a time . when the density of the smoke generated by the burning or l~

smoldering sample reaches a maximum. The constant 132 is determined by the volume of~ the combustion chamber and the .- dimenslons of the sample, which ls a square measuring 3 inches (7.6 cm.) along each side.

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~ ~3 7 For nonflaming (smoldering) exposures, the burner is moved away from the specimen exposure area. During ~laming exposures, the burner is positioned across the lower edge of the specimen. The premixed (air-methane) burner gas is ad~usted to produce controlled flows of o.80 ft./hr.
(375 cm. /min.) of air and 0.26 ft. /hr. (125 cm. /min.) of methane, for a total flow of 1 .o6 ft. /hr. (500 cm. /min.).
Before positioning the test specimen, the chamber I air starting temperature is measured using a thermocouple. I
This measurement is made with the chamber door and all dampers !
closed and sealed. A record is made of the temperature reached at 1.0+0.1 minute after the chamber is sealedO This temperature must be within the range of 100+10F. (38+5C.).
The chamber is flushed with air with the door and exhaust and inlet dampers open. The exhaust and inlet dampers are I then closed. The loaded specimen holder is placed on the bar supports in front of the furnace (burner for flaming exposures);
by displacing the "blank" holder. The chamber door is closed and the timer is started.
A record is made of the light transmittance and corresponding time, elther as a continuous plot with a recorder or in lntervals of not more than 15 seconds~ with a multi-range meter readout. ¦
~ The chamber pressure rise is monitored to determine 1~ 25 any leakage between tests. This pressure must be in the range of 4~2 inches tl0y cm.) of water.
~or flaming tests the lnlet damper must be closed at least five (5~ seconds a~ter the start of the test and pressure ln excess o~ one inch (2.5 cm.) is ven~ed so that the s ~as and air ~low rate to the ~lame will be un~form during the test.
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Periodic light transmittance readings are taken until minimum light transmittance is reached or untll the exposure time of the sample totals 2n minutes, whichever occurs first.
If desired, the test may be conducted for periods in excess of , 20 minutes, when a minimum transmittance level has not been attained during the 20-minute exposure.
The smoke density values obtained using the foregoing proce~ure must be corrected to co~pensate fcr 'he accumulation of soot and other combustion products on the windows of the photometer. This is accomplished using the formula corrected Dm = Dm ~ Dc = Dm-c wherein Dc represents the specific optical density equivalent I for the deposits on the windo-~s of the photometer.
The data from the smoke density evaluation onburning and non-burning (i.e. smoldering) samples are summarized in the following table. The mixture referred to in the table contained 1.5 part antimony trioxide (sb203), 0.3 part zinc sulfide and , 1~2 parts magnesium hydroxide. The,term Tgo re~ers to the time interval between initial exposure of the sampl~ to a M ame or radiant heat and an increase in the optical density , , ~alue to 90% of the maximum.
Flaming Formulation1.5 'Sb 2 33.0 Sb 2 33.0 Mixture ~' 25 Dm 269 309 245 Dc 6 6 5 Dm-c 263 303 240 T90 1.36 mln.1.42 min. 1.47 min.
. ~ ~
Dm 316 292 236 Dc 30 30 26 Dm-c 286 262 210 T90 8.65 min.9.40 min. 9,53 min.

;<Z937 The foregoing data demonstrate that the additlon ~
zinc sulfide decreases the amount of smoke generated by burning samples containing antimony trio:~ide as a flame retarding agent~.

_ The effect on the heat stability of polyvinyl chloride of zinc sulfideg zinc sulfate and zinc oxide was determined using the polymer formulation disclosed in Example 1.
Parts Added PVC Formulation (Ex. 1) 150 150 150 150 ¦ Sb2O3 1.51.5 1.5 1.5 Mg(OH)z ~ 1.2 1.2 1.2 ZnS 3 ZnO - .3 ZnSO 4 The five compositions were blended and formed into 0.020 inch (0.051 crn.)-thick films. The films were cuto into squares measurlng 1 inch (2.54 cm.) along each side. The squares were placed in an oven maintained at 400F. (204C.).
Samples were withdrawn every five minutes and evaluated for color. All samples were white prior to being heated in the oven. The results of the heat stability tests are summarized in the following table.
Heating Period (Minutes) @ 400F.
Sample No. Initial 5 10 15 20 25 30 35 40 #l (control) W W W OW OW Y BR BR BR
~2W W W W W- W Y Y BR
; . #3W W W OW OW BL BL BL BL
#4W W W OW OW Y BR BL BL
W = White OW = Off-white Y = Yellow BR = Brown ~ = }l~c~ -16-' ~ ~ . .
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;Z9137 Sample number 2, which contained a mixture of magnesium hydroxide and zinc sulfide, exhibited the highest level of heat stability. Zinc sulfate and zinc oxide adversely affected the long-term heat stability of the control (sample no. 1), which dld not contain any zinc compounds.

The flame retardancy imparted to a vinyl chloride polymer f`ormulatlon by zinc sulfide and antimony trioxide was evaluated using Limiting Oxygen Index (L.O.I.) values. The procedure for obtaining L.O.I. values is described in the November, 1966 issue of Modern Plastics at pages 141-148 and 192. The test samples are placed in a vertically oriented Pyrex glass tube, approximately 3.5 inches in diameter, which has a bed of glass beads located at the bottom thereof and a smaller Pyrex glass tube of approximately 7 mm. in diameter located concentrically with respect to the larger tube. ~he samples are suspended above the smaller tube. A known mixture of oxygen and nitrogen is introduced at the bottom of the larger tube and flows up through the glass beads. The flow of each gas is controlled~and monitored by means of valves and flow meters.
The sample is ignited and the minimum concentration of oxygen required to support combustion is noted. The Limiting ~ Oxygen Index is calculated using this m~nimum oxygen concentratlon and the formula [2] X 100 Lo~-~ lN2]
wherein ~Oz] and ~N23 represent the relative amounts of oxygen and nitrogen, respectively, expressed in any convlent unlts such as f'low rate in cubic centlmeters per minute.

oZ93 ~

Samples with an oxygen index of 21.0 or less will burn readily in air while oxygen indeces increasingly greater than 21.0 indicate that the sample would burn with greater difficulty, if at all, in air.
The composition of the two formulations evaluated together with the limitlng oxygen index values are summarized in the following table.

Vinyl chloride homopolymer ~parts) 100 100 Dioctyl phthalate (parts) 50 50 Epoxidized soybean oil (parts) 3 3 Stabilizer of Example 1 2.52.5 Stearic acid 0.50.5 Zinc sulfide -- 1.0 Limiting oxygen index 22.723.3 The data in the preceding table demonstrate that zinc sulfide imparts a useful level of flame retardancy to a plasticized vinyl chloride polymer in the absence of a base such as magnesium hydroxide. As previously disclosed the presence of a base is desirable, since it will react with 20 . any acidio materials generated during~pyrolysis of the polymer composition.
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¦ EXAMPLE 6 The flame retardancy of four polypropylene ¦
formulations was measured using Limiting Oxygen Index values l as described in Example 5. The composition of each formulation and the L.O.I. values are set forth in the following table.
Formulation Control 1 2 3 Polypropylene (Profax~ 6524) (parts) 10060 60 60 Perchloropentacyclodecane (parts) - 30 30 30 - ¦ Antimony trioxide (parts) - 10 5 5 I Zinc sulfide (partsj ! Magnesium h~Jdroxide (parts) ~ - 4 -Lithopone (ZnS-BaSO 4 mixture) (parts) - - - 5 L.O.I. 17.628.3 27.9 27.9 These data demonstrate the improvement in flame retardancy imparted by zinc sulfide to a non-halogen-containing polymer.

. . ~
The evaluation procedure described in Example 5 (L~O~ I. values) was repeated using a commercially available terpolymer of acrylonitrile~ butadiene and styrene. The composition and L~ O ~ I o value for each of the formulations ¦~ tested are sef forth in the following table. Flame retardant A
contalned 50% by weight of antimony trioxide, 10% zinc sulfide and 40% magnesium hydroxide. Flame retardant B contained 50%
antimony trioxide and 50% of lithopone (28% zinc sulfide and 72% barium sulfate~.
Formulation Control 1 2 3 ABS Terpolymer 80 80 80 80 l Halogen source* - 15 15 15 1 30 Antimony trioxide - 5 - -1~ Flame retardant A - - 5 Flame retardant B - - 5 L.O.I. value 18.3 31.4 28.0 30.6 *Halogen source - A condensation product of hexachloro-`
35 ~ cyclopentadiene and pentabromostyrene.
-19- , : ' 1~2~3~

The evaluation procedure described in Example 5 was employed using polystyrene with decabromobiphenyl oxide as the halogen source. The composition and limiting oxygen index (L.O.I.) values ror the three formulatlons tested are set forth in the following table.
Formulation Control 1 2 Polystyrene 100 85 85 I Halogen source - 10 10 Zinc sulfide - . - 5 L.O.I. value 18.0 21.4 22.6 These data and those disclosed in the preceding Example 7 clearly demonstrate the improved ~lame retardancy that can be achieved for non-halogenated polymers using ~ z1nc sulfL e in combination with a halogen eource.

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Claims (18)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A flame-retarding agent for synthetic organic polymers comprising zinc sulfide, a basic compound in an amount sufficient to neutralize acidic by-products produced during pyrolysis of the agent together with the synthetic organic polymer, and an amount of halogen source equivalent to from 2 to 10 moles of halogen per mole of zinc sulfide.

2. An agent according to claim 1 wherein the basic compound is selected from the group consisting of a hydroxide of an alkali or alkaline earth metal, barium sulfate, calcium carbonate and hydrated alumina.

3. An agent according to claim 1 wherein the halogen source is selected from the group consisting of halogen-containing hydrocarbons and halogen-containing esters of phosphoric and phosphorous acids and wherein said halogen is chlorine or bromine.

4. An agent according to claim 3 wherein the halogen source is a halogen-containing bicyclic hydrocarbon.

5. An agent according to claim 1 wherein said basic compound is barium sulfate present in combination with zinc sulfate as lithopane.

6. An agent according to claim 1 further comprising antimony trioxide.

7. A method of imparting flame retardency to a synthetic organic polymer composition wherein the polymer is selected from the group consisting of (a) polymers wherein at least a portion of the repeating units are derived from a halogen-containing monomer selected from the group consisting of ethylenically unsaturated compounds, (b) halogen-containing polyesters derived from the reaction of at least one dicarboxylic acid containing from 4 to 20 carbon atoms with at least one diol containing from 2 to 20 carbon atoms, (c) non-halogen-containing polymers wherein the repeating units are derived from at least one ethylenically, unsaturated compound and (d) non-halogen-containing condensation polymers selected from the group consisting of polyesters, polyamides, polycarbonates, epoxide polymers and non-cellular polyurethanes, said method comprising adding a flame retarding agent to said polymer composition wherein the flame retarding agent includes zinc sulfide, a basic compound in an amount sufficient to neutralize acidic by-products produced during pyrolysis of the agent and said polymer com-position, and an amount of halogen source equivalent to from 2 to 10 moles of halogen per mole of zinc sulfide, the agent being added in an amount such that 0.3 to 50%, based on the weight of said polymer, of zinc sulfide is present in the polymer composition.

8. A method according to claim 7 wherein said halogen containing ethylenically unsaturated compound is a vinyl halide.

9. A flame-retarded polymer composition comprising 1) a flame retard-ing agent according to claim 1 together with 2) a polymer selected from the group consisting of (a) polymers wherein at least a portion of the repeating units are derived from a halogen-containing monomer selected from the group consisting of ethylenically unsaturated compounds, (b) halogen-containing polyesters derived from the reaction of at least one dicarboxylic acid con-taining from 4 to 20 carbon atoms with at least one diol containing from 2 to 20 carbon atoms, (c) non-halogen containing polymers wherein the repeating units are derived from at least one ethylenically unsaturated compound and (d) non-halogen-containing condensation polymers selected from the group consisting of polyesters, polyamides, polycarbonates, epoxide polymers and non-cellular polyurethanes, said flame retarding agent being present in an amount such that 0.3 to 50%, based on the weight of said polymer, of zinc sulfide is present in the polymer composition.

10. A flame retarded composition as set forth in claim 9 wherein the polymer is derived at least in part from a halogen-containing ethylenically unsaturated compound.

11. A flame retarded composition as set forth in claim 10 wherein said ethylenically unsaturated compound is a vinyl halide.

12. A flame retarded composition as set forth in claim 11 wherein said vinyl halide is vinyl chloride.

13. A flame retarded polymer composition as set forth in claim 9 wherein said basic compound is selected from the group consisting of magnesium hydroxide, calcium hydroxide, barium sulfate and hydrated alumina.

14. A flame retarded composition as set forth in claim 9 wherein said composition contains antimony trioxide.

15. A flame retarded composition as set forth in claim 9 wherein the polymer does not contain halogen and is selected from the group consisting of polyolefins, polystryene and copolymers of acrylonitrile with at least one ethylenically unsaturated hydrocarbon.

16. A flame retarded composition as set forth in claim 15 wherein the polyolefin is polypropylene.

17. A flame retarded composition as set forth in claim 15 wherein the acrylonitrile copolymer is a terpolymer of acrylonitrile, butadiene and styrene.

18. A flame retarded composition as set forth in claim 9 wherein said composition is coated on a flammable substrate.