CA2264003A1 - Heat stabilized, flame retardant thermoplastic polymer compositions - Google Patents

Abstract

Heat stabilized, flame retardant polymer compositions include a halogen based flame retardant such as hexabromocyclododecane, zeolite A heat stabilizer, and a transition metal compound such as a zinc stearate lubricant. The compositions are stable at high temperatures even when subjected to multiple heating processes and also have unique polymer foam forming properties when compared with compositions containing a different heat stabilizer.

Description

?10152025CA 02264003 1999-02-23W0 98/ 16579 PCT/U S97/ 16056EEAT STABILIZED, FLAME RETARDANTTHERMOPLASTIC POLYMER COMPOSITIONSThis invention relates generally to heat stabilized. ?ame retardant thermoplastic polymercompositions and more particularly to thermoplastic polymer compositions which include halogen-based ?ame retardants, such as cycloaliphatic bromine compounds, zeolite A heat stabilizers andtransition metal compounds such as zinc stearate,Halogen-containing materials, for example, cycloaliphatic organic compounds such ashexabromocyclododecane (HBCD) are widely used in thermoplastic polymer compositions to impart?ame retardant properties to the compositions. However, their presence in the thermoplasticpolymer-based compositions has the drawback of lowering thennal stability. This can cause seriouscolor and/or viscosity problems when the compositions are exposed to high processing temperatures.In order to improve their thermal stability, it is customary to add a stabilizing agent, such ashydrotalcite, tetrasodium pyrophosphate or dibutyl tin maleate. However, when these stabilizedcompositions are subjected to multiple heating processes, such as in attempting to re-use polymerscrap or when forming masterbatches which are reheated during their incorporation into the bulk ofthe heat-softened thermoplastic polymers, deterioration of the halogen-based ?ame retardants, as’ well as the polymer itself can occur. This is evidenced by discoloration of the compositions. Heatdeterioration is especially a problem when the polymer compositions contain even very smallportions of transition metal compounds such as zinc stearate, which is a preferred lubricant for manyextrusion and molding applications. Using lower processing temperatures may help, but this extendsprocessing times and lowers throughput.It has now been found that when zeolite A is added to thermoplastic polymer compositionswhich contain transition metal compounds and halogenated aliphatic compounds, they are heat stableeven when subjected to multiple heatings. It has also been found that when forming polymer foamsfrom such compositions, the zeolite A does not increase foam density to the extent that occurs whenusing other heat stabilizers.In accordance with this invention, there is provided a heat stabilized, ?ame retardant polymerformulation which comprises a thermoplastic polymer, a transition metal compound, a ?ameretardant amount of a halogen-based ?ame retardant, and a heat stabilizing amount of zeolite A.?1015202530CA 02264003 1999-02-23W0 98ll6579 PCT/US97/16056Also provided is a masterbatch composition which comprises from 10 to 90 weight percentthermoplastic polymer and from 10 to 90 weight percent of additives which include at least ahalogen-based ?ame retardant, zeolite A, and a transition metal compound.Additionally provided is a process for manufacturing a ?ame retardant article from athermoplastic polymer composition comprising the steps of (i) heating and mixing a firstthermoplastic polymer composition, said composition containing a transition metal compound andhaving been formed by combining a heat-plasti?ed thermoplastic polymer with a halogen-based?ame retardant, and zeolite A, with a second thermoplastic polymer composition to form a heat-plasti?ed polymer gel composition, (ii) either expressing the heat-plasti?ed thermoplastic polymergel composition from a die or injecting said gel composition into a mold so as to form a ?ameretardant article, and (iii) cooling the article to a temperature at which the article is self-supporting.The thermoplastic polymers and copolymers for use in the invention include those organicpolymers which are usually associated with ?ammability problems when formed into a broad rangeof plastic articles, both in the fonn of solid objects and foams. Non-limiting examples of suchpolymers include polyole?ns, polyesters, polyamides, polycarbonates, styrenic polymers, andpolyurethanes. Speci?c examples of such polymers include high and low density polyethylene,polypropylene, polystyrene, ethylene-propylene and ethylene-propylene-diene copolymers, nylon6 and polyethyleneterephthlate. The invention is particularly useful with styrenic polymers.Styrenic polymers are usually classi?ed as general-purpose polystyrene (GPPS) or as impactmodi?ed polystyrene (IPS). GPPS is a high molecular weight, clear polymer which is hard, rigidand free of odor and taste. It ?nds use in producing moldings and extrusions including foams and?lms. IPS is a rubber-modi?ed polystyrene which is characterized by its toughness and resistanceto abuse. The rubber is dispersed in the polystyrene matrix in the form of discrete particles. IPS isnot clear, but rather is either translucent or opaque depending upon the amount of rubber used. Theart recognizes two types of IPS, i.e., medium-impact polystyrene (MIPS) and high—impactpolystyrene (HIPS), the former containing less rubber than the latter. HIPS can be generallycharacterized as having an 8 to 18 wt% rubber content. In some instances, mixtures of IPS andGPPS are used to achieve certain blends of properties.For the purposes of this invention, the styrenic polymer can be GPPS, IPS or a mixture of thetwo. GPPS is generally used in making foams but GPPS-IPS mixtures are sometimes used. TheGPPS and IPS may be homopolymers, copolymers or block polymers and are formed from suchvinyl aromatic monomers as styrene, ring-substituted methyl or polymethylstyrenes, ring-substituted-2-?1015202530CA 02264003 1999-02-23W0 98/16579 PCT/US97/ 16056ethyl or polyethylstyrenes, ring—substituted propyl or polypropylstyrenes, ring-substituted butyl orpolybutyl styrenes, ring-substituted mixed polyalkylstyrenes wherein the alkyl groups differ fromeach other, alpha—methylstyrene, ring-substituted methyl— or polymethyl-alpha-methylstyrenes,propyl- or polypropyl-alpha-methyl-styrenes, butyl- or polybutyl—alpha-methylstyrenes, ring-substituted mixed polyalkyl-alpha-methylstyrenes wherein the alkyl groups differ from each other,ring-substituted alkyl- or polyalkylchlorostyrenes in which the alkyl group(s) contain(s) from oneto four carbon atoms, and similar polymerizable styrenic monomers--i.e., styrenic compoundscapable of being polymerized by means of peroxide or like catalysts into thermoplastic resins.Homopolymers and copolymers of simple styrenic monomers (e.g., styrene, p-methyl-styrene, 2,4-dimethylstyrene, alpha-methylstyrene, and p—chloro-styrene) are preferred from the standpoints ofcost and availability.The IPS may be either medium impact polystyrene (MIPS) or high-impact polystyrene(HIPS). The rubber used in effecting impact modi?cation is most often a butadiene rubber.The halogen-based ?ame retardants used in this invention may be any such ?ame retardantsthat are commonly used in this field and which are subject to heat stability problems, such asaliphatic, cycloaliphatic, and mixed aliphatic-aromatic organic halogen compounds in which thealiphatic groups contain halogen. Examples that may be cited include tetrabromoethane,tetrabromobutane, hexabromocyclododecane, acetylene tetrabromide, pentabromochlorocyclohexane,ethylene bis(dibromobomane dicarboximide) (BN 451), dibromoethyldibromocyclohexane (BCL462), tetrabromocyclooctane (BC-48), melamine hydrobromide, tris(2,3~dibromopropyl)isocyan-urate, tetrabromobisphenol A bis(2,3-dibromopropyl ether), 2,3-dibromopropylpentabromophenylether, tetrabromophthalic anhydride and esters thereof including RB-79 and PHT-4 diol, chlorinatedpolyethylenes, chlorinated paraffins, chlorendic anhydride and derivatives thereof. There is noparticular limit on the amount in which these halogen-based ?ame retardants are added, it beingsuitable to vary the amount as appropriate according to the desired degree of ?ame retardation. Itis generally preferable to use 1 - 35 parts by weight, per 100 parts by weight of thermoplasticpolymer, of one of these ?ame retardants alone or of two or more together. The invention isparticularly effective with cycloaliphatic ?ame retardants which are less heat stable, especially in thepresence of Lewis acids. A preferred ?ame retardant is a hexabromocyclododecane material. Thismaterial is a mixture of isomers.Both the low-melt and high-melt hexabromocyclododecane products having individualmelting point ranges within the general range of 170° C - 200° C can be used. A most highly-3-?1015202530CA 02264003 1999-02-23wo 93/15579 PCT/US97/16056preferred product is HBCD—LM ?ame retardant available from Albemarle Corporation. This HBCDmaterial has a melting point range of 178° C - 188° C and a minimum melt point of 175° C.The amount of ?ame retardant used is that amount which will render the formulation ?ameretardant. For the purposes of this invention, the term “?ame retardant” is to mean that the non-foamed formulations, when tested in accordance with UL 94, obtains a rating of at least V-2. TheUL 94 test is an Underwriters Laboratories Inc. test entitled “Test for Flammability of PlasticMaterials for Parts in Devices and Appliances” and for foam materials when tested in a SteinerTunnel in accordance with UL 723 and ASTME—84, obtains a Standard Building Code rating of atleast C (?ame spread index 76 - 200, smoke density 2 450) and, preferably, a rating of A or B (A =?ame spread index of 0 - 25, B = ?ame spread index of 26 — 75). For cycloaliphatic halogen-based?ame retardants such as HBCD, from 0.5 to 8 wt% is generally used, based on the total weight offormulation in order to obtain such ratings. Usually, highest ratings can be obtained in foams usingfrom 1.0 wt% HBCD at a foam thickness of 1.27 cm (0.5 ”) up to 3.0 wt% at a foam thickness of 5.08cm (2.0”).The zeolite A used in the practice of this invention can be represented by the generalizedformula for zeolite, M2,,,O-A1303-ySiO2-wH2O, wherein M is a group IA or IIA element, such assodium, potassium, magnesium and calcium. For a sodium zeolite, the formula isNaz-OAl203-xSiO2-yH2O. The value of x normally falls within the range of 1.85 i 0.5. The valuefor y can also be variant and can be any value up to 6. On average, the value of y will be 5.1. Fora sodium zeolite A the formula can be written as l.0:0.2Na3O-AIO3-1 8510.5 SiO2-yH2O, whereinthe value of y can be up to 6. An ideal zeolite A has the following formula, (NaAlSiO4),2-27H2O.Zeolite A is commercially available and can be purchased from Albemarle Corporation under thetrademark EZA. The zeolite A is not modified by reaction with compounds such as inorganichalides.The amount of zeolite A used is that amount which effects thermal stabilization of theformulation. Generally, for most formulations of the invention, the amount of zeolite A used willbe within the range of from 0.1 to 5 wt% based upon the total weight of the formulation. A preferredamount is within the range of from 0.6 to 1.5 wt%.Transition metal containing compounds, for example, lubricants, nucleating agents, dyes, orpigments are commonly present in the thermoplastic polymer compositions in amounts of from 0.005to 1.0 weight percent or more of the compositions. Non—limiting examples of these compoundsinclude lubricants such as zinc stearate and other Zn, Cu, and Fe, salts of fatty acids such as stearic,-4-?1015202530CA 02264003 1999-02-23wo 98116579 PCT/US97/16056tallow, and coco fatty acids and the dimer of oleic acid. Aryl carboxylate and sulfonate salts, i.e.,benzoate or terephthalate salts, are used as nucleators. It has been found that the transition metalcompounds have a destabilizing effect as they tend to cause serious degradation problems, especiallywith cycloaliphatic ?ame retardant containing polymer compositions, upon the achievement of hightemperatures and/or undergoing a heat history (masterbatch heat experience + processing heatexperience or other multiple heating processes such as scrap recycle). This can occur not only whenthe transition metal compound is present in functional (i.e., lubricating, nucleating, or colorant)amounts of 100 to 1,000 ppm or more of transition metal by weight of the polymer formulation, buteven when the transition metal is only incidentally present in amounts of less than 100 ppm (as smallas 10 ppm) by weight of the polymer formulation as a result, for example, of incorporating polymerscrap into the composition. The presence of the zeolite A stabilizer renders the compositionsexceptionally heat stable when they are subjected to such multiple heatings.In addition to the thermoplastic polymer, halogen-based ?ame retardant, transition metalcompound, and zeolite A, there can be present in the formulation other conventional additives in theirconventional amounts. Exemplary of such additives are: ?llers, pigments, dyes, impact modifiers,UV stabilizers, antioxidants, processing aids, nucleating agents, and lubricants.All of the constituents are blended in any conventional manner and can be blended in anyorder. For example, the constituents can ?rst be dry mixed and then fed to a Banbury or Herschellmixer or to a twin screw extruder such as a ZSK 30 Werner and P?eiderer extruder, to obtain ablended material for feed, for example, to an injection molding apparatus, such as a 500 kN Demagmachine. Blending temperatures will generally be within the range of from 180 to 200° C andinjection molding temperatures will generally be in the range of 180 to 250° C.A convenient way to add the ?ame retardant and stabilizer to the thermoplastic polymer isas a masterbatch which is a concentrated, heat blended or extruded mixture of the various additivesin the polymer. The concentration of additives usually ranges from 10 to 90 percent by weight ofthe total weight of masterbatch composition, with the balance of 10 to 90 weight percent beingpolymer. The masterbatch is then added to the bulk of the thermoplastic polymer material, whichmay already contain other additives such as a zinc stearate lubricant. The masterbatch is added inproportions to give the desired concentration of additives in the ?nal blended product and usuallyin proportions of from 1 to 50 percent by weight of total weight of the ?nal blended polymercomposition.?1015202530CA 02264003 1999-02-23wo 98/16579 PCT/US97ll6056In one embodiment of the article manufacturing process of the invention, thermoplasticpolymer foam materials, for example, rods or rectangular boards, are formed, as is known, by mixingthe additives, either individually or as a masterbatch, with the polymer, preferably a styrenicpolymer, and then feeding the mixture to an extruder along with a foaming agent and, optionally, anucleating agent, such as commercially available carbonate based materials, for example, thematerial sold under the trademark, Safoam - F P.Any of a wide variety of known foaming agents or blowing agents can be used in producingthe expanded or foamed ?ame resistant polymers. U.S. Patent No. 3,960,792 gives a listing of somesuitable materials. Generally speaking, volatile carbon—containing chemical substances are the mostwidely used for this purpose. They include, for example, such materials as aliphatic hydrocarbonsincluding ethane, ethylene, propane, propylene, butane, butylene, isobutane, pentane, neopentane,isopentane, hexane, heptane and mixtures thereof; volatile halocarbons and/or halohydrocarbons,such as methyl chloride, chloro?uoromethane, bromochlorodi?uoromethane, l,l,1—tri?uoroethane,1 ,1,1,2—tetra?uoroethane, dichloro?uoromethane, dichlorodi?uoromethane, chlorotri?uoromethane,1 ,2,2-trichloro-1,1,2-tri?uoroethane,trichloro?uoromethane, sym-tetrachlorodi?uoroethane,' symdichlorotetra?uoroethane; volatile tetraalkylsilanes, such as tetramethylsilane, ethyItrimethyl-silane, isopropyltrimethylsilane, and n-propyltrimethylsilane; and mixtures of such material. Onepreferred ?uorine-containing blowing agent is 1,1-di?uoroethane also known as HFC-152a(FORMACEL Z—2, E.I. duPont de Nemours and Co.) because of its reported desirable ecologicalproperties. Water-containing vegetable matter such as ?nely-divided corn cob can also be used asblowing agents. As described in U.S. Patent No. 4,559,367. such vegetable matter can also serve as?llers. Use of carbon dioxide as a foaming agent, or at least a component of the blowing agent, isparticularly preferred because of its innocuous nature vis-a-vis the environment and its low cost.Methods of using carbon dioxide as a blowing agent are described, for example, in U.S. Patent No.5,006,566 wherein the blowing agent is 80 to 100% by weight of carbon dioxide and from 0 to 20%by weight of one or more halohydrocarbons or hydrocarbons that are gaseous at room temperature,in U.S. Patents Nos. 5,189,071 and 5,189,072 wherein a preferred blowing agent is carbon dioxideand 1-chloro-1,1-di?uoroethane in weight ratios of 5/95 to 50/50, and in U.S. Patent No. 5,380,767wherein preferred blowing agents comprise combinations of water and carbon dioxide. Suchmaterials can be utilized with appropriate ?ame retarded thermoplastic polymer compositions of thisinvention.?1015202530CA 02264003 1999-02-23wo 93/15579 PCT/US97/16056The invention is further illustrated by, but is not intended to be limited to, the followingexamples.Masterbatgh EormationExample 1A masterbatch of polystyrene (Styron® 685D GPPS, Dow Chemical Co.), which polystyrenecontained 136 ppm by weight of zinc as zinc stearate lubricant, was formed by blending, at atemperature of 150° C - 180° C, with mechanical mixing (100 rpm) in a Werner and P?eiderer ZSK30 twin-screw, co—rotating extruder, 77 parts by weight of polystyrene with 23 parts by weight of amixture containing 75 wt% HBCD-LM ?ame retardant and 25 wt% zeolite A. The polymer and?ame retardant were gravimetrically fed from two separate feeders. Barrel zone temperatures were150 - 160 - 170 - 175, and 180° C and the throughput was 6 Kg/hour. The extruded strand waspelletized in line.ggpmparatjve ExampleA masterbatch was prepared using the same zinc containing polystyrene and ?ame retardant,but with dibutyl tin maleate and 2,2’-oxamidobisethyl—3-(3,5-di-t—butyl—4—hydroxyphenyl)propionate(Naugard XL—1) as the stabilizers. The proportions were 76 wt% polystyrene and 24 wt% of amixture containing 94 wt% HBCD-LM, 4 wt% dibutyl maleate, and 2 wt% Naugard XL-1 stabilizer.When an attempt was made to form a masterbatch which contained only the styrenic polymercomposition and HBCD with no stabilizer, it turned black and degraded and no useful product wasobtained. When a zinc free (< 1 ppm) polystyrene was used with HBCD, an amber coloredmasterbatch product could be obtained.Example 2-5A 3.175 cm (1.25 inch) segmented single screw extruder having a 40/ 1 length to diameterratio and a rod die was used for foaming several mixtures of the masterbatch prepared in Example1 with the same type of GPPS polystyrene used to make the masterbatch. The screw was designedto operate in three stages: a plasticization section, a gas injection section, and a metering and mixingsection. Several samples were prepared to provide different concentrations of additives in thepolymer. A small amount (0.05 wt% of composition) of Safoam - FP nucleating agent was also dryblended with the mixture. The mixtures were metered through a single screw feeder. CO2 gas wasused as a physical blowing agent for foaming the polystyrene blends. A description of the samplesis given in Table 1 and the melt temperatures and CO2 gas injection pressures are given in Table 2.The density of the foam products was also measured by the water displacement technique on samples-7-?10152025CA 02264003 1999-02-23wo 98/16579 PCT/US97/16056of the product and the results are reported in Table 1. The lowest density product was obtained ata gas injection pressure of 5515 - 5654 kPa (800 - 820 psi), a melt temperature of 143° C - 149° C(290° F — 300° F) and at melt pressures above 9653 pKa(1400 psi). Temperatures at the differentbarrel zones were typically, in degrees C, 38 - 149 - I77 - 177 - 166 — 149 - 149 - 149 - 149 - 143 —and 141 — 144 (melt) (in degrees F, 100 - 300 - 350 - 350 — 330 - 300 - 300 - 300 - 300 - 290 and 286- 292). As a comparison, several samples of foam were made in the same way but using themasterbatch composition from the first Comparative Example which contained a tin maleate andNaugard XL-l stabilizers.It was observed that the comparison samples appeared dark when extruded at a hightemperature, e.g., 204° C (400° F). The use of a lower processing temperature was needed.to reducethe color fonnation. In contrast, the foam samples prepared from the composition of the inventionhad much less color, even at high processing temperatures. It appears then, that even though the tinmaleate and Naugard XL-l stabilizers were adequate to reduce decomposition during masterbatchformation, signi?cant decomposition occurred as a result of the second heating step when themasterbatch was used in the foaming process. The compositions of the invention were stable duringthe second heating step even at high processing temperatures, despite the presence of the zinc stearatelubricant which otherwise would accelerate the decomposition of the bromine containing styrenicpolymer composition.TABLE 1Wt% Wt% Br Fresh Foam Aged FoamExample HBCD-Zeolite Theory Density g/cc Density g/cc*Control 0.00 0.00 0.10 0.0722A 0.50 0.28 0.10 0.083213 0.50 0.28 0.10 0.0753 0.70 0.38 0.11 0.0754 2.00 1.12 0.11 0.078Wt%Qgmparjsgn I-IBQD-Tin Maleate-Naugard XL-]1 0.50 0.35 0.10 0.072?10152025CA 02264003 1999-02-23wo 98116579 PCT/US97ll60562 1.50 1.05 0.12 0.0763 2.00 1.40 0.14 0.090*Measurements made 8 to 10 weeks after manufacture of the samples.TABLE 2Q2 E_xapm§ Melt Temp 1° C) Pressure (k?g)Control 141 (286° F) 5606 (813 psi)2A 142 (288° F) 5661 (821 psi)2B 143 (290 ° F) 5544 (804 psi)3 144 (292° F) 5654 (820 psi)4 142 (289° F) 5675 (823 psi)Comparison1 143 (290° F) 5626 (816 psi)2 141 (287° F) 5606 (813 psi)3 141 (286° F) 5681 (824 psi)As illustrated by the foam density data in Table 1, in addition to being more heat stable thanthe comparative materials, the combination of additives used in Example 4, at the higher brominelevel required to obtain adequate ?ame retardancy, such as when forming 5 to 7.6 cm (2 to 3 inch)thick building insulation panels, also had less effect on the foam density. A significant increase infoam density was observed at a bromine level of 1.4% in Comparison 3 when using the tin maleateand Naugard XL-1 stabilizers. In contrast, the foam density of the samples made according to theinvention remained about the same (within 10 - 15%) with increasing bromine levels besides havingimproved color and thermal stability in the presence of the zinc.Example 6Six general purpose polystyrene formulations (GPPS) were compounded in a Haake twin-screw extruder at 60 rpm by bag-mixing 3 weight percent of different mixtures of ?ame retardantsand zeolite A with 97 weight percent of GPPS and feeding the mixture from a single hopper into theextruder. The temperature pro?le was 190 - 220 - 240 - 252° C. The extruded strand was pelletized-9-?10152025CA 02264003 1999-02-23W0 98/ 16579 PCT/US97/16056in line. The pelletized composition was then injection molded into disks using a Battenfeld BSKM100/40 injection molding machine under the following process conditions:holding time = 10 secondscooling time = 15 secondsmold open time = 2 secondstemperature pro?le = 199 - 221 - 227° Cnozzle = 75%mold temperature = 45° Cinjection pressure = 8964 kPa (1300 psi) on ramholding pressure = 4827 kPa (700 psi) on ramThe color of the injection molded disks was measured using a HunterLab scale, D65 illuminant, 10°observer, and integrated-sphere geometry. The Melt Flow Index (ASTM D1238) procedure A, wasmeasured at 200° C/5 Kg. The formulations and results are given in Table 3.TABLE 3ln2r_Qc1i;2m.§ A B 2 6A D 5.13.97GPPS 97 97 97 97 \ 97For Mix 1 3 3For Mix 2 3 3For Mix 3 3 3Zn as Zn Stearate 0 50ppm 0 50ppm 0 50ppmggglor TestInitial ColorL 67.5 ---* 68.7 65.6 69.4 72.3a 5.8 ---* -0.5 0.7 -0.8 -0.4b 23.4 ---* 7.2 11.2 8 10.8Melt Flow(g/min) 12.4 NM 10.8 10.2 10 10.3200° C / 5kg-10-?10CA 02264003 1999-02-23wo 98/16579 PCT/US97/16056Mix 1 = 94% HBCD, 4% dibutyl tin maleate, 2 % Naugard XL-1 stabilizerMix 2 = 75% HBCD, 25% zeolite AMix 3 = 75% HBCD, 20% zeolite A, 2% dibutyl tin maleate, 1% Naugard XL-1 stabilizert,2% Ethanox 330 antioxidant* = sample was very dark after extrusion and was not injection moldedNM = not measured.The results given in Table 3 show that, after extrusion and molding, the zeolite A containingcompositions of the invention (Formulations 6A and 6B) had about the same stability asFormulations C and D which did not contain the zinc stearate. In contrast, the tin maleate stabilizedFormulation B had such poor stability in the presence of the zinc stearate that it turned very darkafter the initial extrusion. Such a ?ame retardant zinc containing polymer material would not beuseful in forming molded objects.-1]-

Claims

16. A process for manufacturing a flame retardant article from a thermoplastic polymer composition comprising the steps of (i) heating and mixing a first thermoplastic polymer composition, said composition containing a transition metal compound and having been formed by combining a heat-plastified thermoplastic polymer with a halogen-based flame retardant, and zeolite A, with a second thermoplastic polymer composition to form a heat-plastified polymer gel composition, (ii) either expressing the heat-plastified thermoplastic polymer gel composition from a die or injecting said gel composition into a mold so as to form a flame retardant article, and (iii) cooling the article to a temperature at which the article is self-supporting.
17. The process according to claim 16 wherein said first and second thermoplastic compositions comprise styrenic polymer, said halogen-based flame retardant is a cycloaliphatic bromine compound and said transition metal compound is a fatty acid salt.
18. The process according to claim 17 wherein said first thermoplastic polymer composition is a masterbatch.
19. The process according to claim 17 wherein said first thermoplastic polymer composition is polymer scrap or recycled polymer.
20. The process according to claim 17 wherein said flame retardant is HBCD and said transition metal compound is zinc stearate.
22. A process for manufacturing a flame retardant article from a thermoplastic polymer composition comprising the steps of (i) heating and mixing a first thermoplastic scrap polymer composition, said composition having been formed by combining a heat-plastified thermoplastic polymer with a halogen-based flame retardant, a transition metal compound, and zeolite A, with a second thermoplastic polymer composition to form a heat-plastified polymer gel composition, (ii) either expressing the heat-plastified thermoplastic polymer gel composition from a die or injecting said gel composition into a mold so as to form a flame retardant article, and (iii) cooling the article to a temperature at which the article is self-supporting.
23. The process according to claim 22 wherein the said first and second thermoplastic compositions comprise styrenic polymer, said halogen-based flame retardant is a cycloaliphatic bromine compound and said transition metal compound is a fatty acid salt.
24. The process according to claim 22 wherein said flame retardant is HBCD and said transition metal compound is zinc stearate.