FLAME-RETARDANT RECYCLED POLYESTER COMPOSITIONS

Abstract: A flame-retardant linear polyester comprising the product of recycled polyesters such as polyethylene terephthalate and a flame-retarding amount of a carboxy-phosphinic acid, a process for producing the polyester and products produced from the polyester are disclosed.

Description: FT.AMF RETARDANT RECYCLED POLYESTER COMPOSITIONS BACKGROUND OF THE INVENTION This invention relates to new flame retardant polyester compositions and a method for producing the polyester compositions. More particularly, this invention relates to new flame retardant copolyesters produced from recycled polyesters and to a method for producing the polyester compositions. More particularly this invention relates to new flame retardant copolyesters produced from recycled polyethylene terephthalate and carboxy- phosphinic acids, a process for producing the copolyesters and shaped articles produced from the copolyesters. DESCRIPTION OF THE PRIOR ART One of the major uses of polyesters is the production of shaped polyester articles and of woven and non-woven textiles such as fabrics, filaments, staples or yarn and of sheets. In recent years efforts to make textiles less flammable, to improve the safety characteristics of products such as apparel, bedding, home furnishings, aircraft and automobile interior fabrics and industrial fabrics, have increased. It is also recognized that the textiles may be blends, particularly blends of natural fibers, such as cotton, and synthetic fibers, such as polyesters. There are various methods known for flame retarding textiles. U.S. Patent 4,034,141 teaches the use of brominated phosphoramidates to treat combustible materials to impart fire retardant properties. The combustible materials are fabrics such as cotton, rayon and paper and synthetic fibers such as polyesters. The fire retardant composition is applied by treating the fabric with a solution of the composition, drying the fabric and curing the composition. U.S. Patent 3,969,437 teaches the use of a specific class of cyclic phosphorus esters to prepare a durable, flame retardant textile finish for cotton- polyester blends. The phosphorus ester used must contain at least one carbon-bonded primary alcohol group, and preferably two or more, plus a pentavalent phosphorus ester group. Surface treatment to impart flame retardant characteristics, and even the admixture of flame retardant compounds into hardenable shaped compositions, has disadvantages. Surface treatments may be removed by cleaning and admixed compounds may exude or migrate from the product. Therefore, attempts have been made to overcome these disadvantages by chemically building flame retardant compounds into the polyester. U.S. Patent 3,922,323 teaches a process for improving the flame resistance of polyesters, especially unsaturated polyesters, by chemically binding and/or admixing organic phosphorus compounds and, if desired, halogen compounds into the polyesters. Halogen containing, at least bicyclic phosphonic esters which are free from hydroxy and carboxylic groups are used. U.S. Patent 3,941,752 teaches a flame retarded, synthetic linear polyester modified with carboxy-phosphinic acids. The linear polyester is the polycondensation product of a dicarboxlyic acid, a diol and a flame-retarding carboxy-phosphinic acid monomer which may contain hetero atoms. As the environment has received greater attention, the need for a high value use for recycled polyester materials has grown. A need remains for flame retardant recycled polyethylene terephthalate materials, with properties equal to, or better than, the properties of virgin polyethylene terephthalate, which will maintain their flame retardant properties throughout their useful life and for a process to produce such a polyester. SUMMARY OF THE INVENTION It is an object of this invention to provide a flame retardant polyester material, a process to produce the polyester material and shaped articles produced from the polyester. It is another object of this invention to provide a flame retardant copolyester composition, produced from recycled polyester, in which the flame retardant material is chemically bound within the polymer structure. These and other objects are met by this invention which is directed to copolyesters of recycled polyethylene terephthalate and a carboxy- phosphinic acid monomer which have flame retardant properties. The copolyester is preferably a polyethylene dicarboxylate copolyester having from about 99.9% to about 90% by weight of recycled polyethylene terephthalate and from about 0.1% to about 10% by weight of the carboxy-phosphinic acid monomer. The copolyester is produced by placing the desired amounts of recycled polyethylene terephthalate and carboxy-phosphinic acid in a nitrogen filled reactor in the presence of ethylene glycol and a catalyst which is preferably based upon antimony such as, for example, antimony oxide. The reactor is heated to a temperature within the range of from about 263°C. to about 293°C. for a period of from about 1 hour to about 3 hours. A vacuum is applied slowly to reduce the pressure to a pressure within the range of from about 0.5 to about 1.0 mm of mercury. In addition to copolyesters of polyethylene terephthalate, the invention also includes copolyesters of other polyalkylene dicarboxylates such as polybutylene terephthalate and polyethylene naphthanate. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to copolyesters of recycled polyesters having flame retardant properties. The copolyesters of this invention have an intrinsic viscosity greater than about 0.7, and preferably within the range of from about 0.7 to about 1.2 and a glass transition temperature greater than about 65°C. The copolyesters of the preferred recycled polyethylene terephthalate are preferably a polyethylene dicarboxylate copolyester having from about 99.9% to about 90% by weight recycled polyethylene terephthalate and from about 0.1% to about 10% by weight of a flame retarding carboxy-phosphinic acid monomer having the general formula: 0 0 II II HO - P - R - C - OH R 1 wherein R is a saturated open-chain or cyclic alkylene radical having from one to about 15 carbon atoms, preferably from 2 to about 10 carbon atoms, or an arylene or aralkylene radical such as, for example, methyl, ethyl, propyl, isopropyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, 2-ethylhexyl, iso-octyl, decyl, isodecyl, dodecyl, tetradecyl, -C 6 H 4 -, -C 6 H 4 -CH 2 - , and -C 6 H 4 -CH 2 -CH 2 -, and R 1 is an alkyl radical having up to about 6 carbon atoms, an aryl radical or an alkaryl radical wherein the alkyl substituent has from 1 to about 6 carbon atoms such as, for example,methyl, ethyl and n- and i-propyl. The carboxy-phosphinic acid is preferably 2-carboxyethyl (phenyl)phosphinic acid, 2-carboxyethyl (methyl) phosphinic acid, the cyclic anhydride of 2-carboxyethyl (phenyl)phosphinic acid or the cyclic anhydride of 2-carboxyethyl (methyl)phosphinic acid. Polymerization of 90% by weight recycled polyethylene terephthalate and 10% by weight 2- carboxyethyl (phenyl)phosphinic acid produced a flame retardant polyester having an intrinsic viscosity of about 0.70. The polyester, however, had a slight drop in the glass transition temperature, the melting point and the crystallinity when compared to virgin polyethylene terephthalate, but the color of the polyester was improved. Recycling polyethylene terephthalate produces a polyester which has a lower molecular weight than virgin polyethylene terephthalate. The inclusion of the phosphinic acid moiety in the process of this invention promotes chain bonding to produce longer carbon chains and, thus, higher molecular weights. The inclusion of the phosphinic acid moiety is a complex process in which the intrinsic viscosity of the process fluid drops originally from the viscosity of the polyethylene terephthalate to as low as about 0.25 before it begins to rise and the intrinsic viscosity of the copolyester may reach as high as about 1.2 if the process is allowed to go to completion. The preferred acid, 2-carboxyethyl (phenyl) phosphinic acid, may be prepared in accordance with the teaching in U.S. Patent 4,081,463. The 2-carboxyethyl (phenyl)phosphinic acid is prepared in two stages by first reacting dichloro(phenyl)phosphine with acrylic acid employed at a molar excess of 25% to 45% to form a mixture of three intermediates, 3- (chlorophenylphosphinyl) propionyl chloride, the cyclic anhydride of 2-carboxyethyl (phenyl)phosphinic acid and the mixed anhydride of acrylic acid with 3- chlorocarbonylethyl (phenyl)phosphinic acid. The second stage of the process is the hydrolysis of the of the mixture of the three intermediates to obtain the desired product, 2-carboxyethyl (phenyl)phosphinic acid. The flame retardant copolyesters of recycled polyethylene terephthalate are preferably polyethylene dicarboxylate copolyesters having from about 99.9% to 90% by weight recycled polyethylene terephthalate and from about 0.1% to about 10% of the flame retarding 2- carboxyethyl (phenyl)phosphinic acid, or the cyclic anhydride thereof. The desired polyester of this invention may be produced by the polymerization of from about 99.9% to about 90% by weight recycled polyethylene terephthalate and from about 0.1% to about 10% by weight of 2-carboxyethyl (phenyl)phosphinic acid. The expected decrease in reactivity during the polymerization reaction, resulting from the addition of the phosphinic acid rather than another carbonyl acid group, was not observed. The high molecular weight of the product polyester indicated that the phosphinic acid group was highly reactive and the end- group analysis did not show terminal phosphinic acid groups in a high proportion. Further, the addition of phosphorus compounds usually creates additional observable color in the product. Surprisingly, the addition of the carboxy-phosphinic acid in this invention allowed the use of higher amounts of catalyst and still had less color in the product than polyesters produced without the included acid. The copolyesters were produced by placing the desired amounts of recycled polyethylene terephthalate and 2-carboxyethyl (phenyl)phosphinic acid in a nitrogen filled reactor in the presence of ethylene glycol and a catalyst which is preferably antimony oxide. The reactor was heated to a temperature within a range of from about 250°C. to about 293°C, preferably within a range of from about 263°C. to about 293°C. , for a period of from about 1 hour to about 3 hours. A vacuum was applied slowly to reduce the pressure to a pressure of from about 0.5 to about 1.0 mm of mercury. The reaction continued at those conditions for an additional 45 minutes before the heat and vacuum were removed. Ethylene glycol was used in the description of the process and it is the preferred diol. However, other aliphatic diols such as, for example, aliphatic diols having from 3 to about 7 carbon atoms, may also be used. The carboxy-phosphinic acid and its cyclic anhydride are not volatile under the process conditions for production of the polyesters so they can be incorporated in the polyester by inclusion in the condensation reaction. When incorporated into the molecule during the condensation reaction the phosphorus containing structural unit is randomly distributed in the linear polyester product. The polyesters of this invention may be made into shaped articles. They may be spun into filaments and fibers using well known processes and the standard additional treatments. The polyesters may also be extruded into sheets or formed into shaped articles which may be solid or hollow by press molding, injection molding and extrusion. All of these shaped articles (fibers, sheets and other shapes) are also an object of this invention. The fibers and filaments have very good and permanent flame retardant and self-extinguishing properties. Since they have a good degree of whiteness, they have very good dyeing properties for disperse dyestuffs and their receptivity includes acid dyestuffs in color shades of average to deep intensity. The tensile strength of the filaments and fibers, second order transition temperature and melting point approximately correspond to the values for polyesters which do not contain the flame retardant carboxy-phosphinic acid. The fibers and filaments are generally useful for applications where readily ignitable textiles cannot be tolerated and it is possible to use these fibers in combination with natural fibers, such as cotton, and other synthetic fibers. Sheets and shaped articles produced from the flame retardant polyester are generally used in locations where it is desired to reduce the possible serious risks if ignition and a fire occur. If the transparency of the shaped articles is not of concern, their solidity and flame retarding properties can be enhanced by the inclusion of inorganic fiber materials such as, for example, glass and quartz fibers and carbon in the usual quantities, in the polyester before molding. This invention will be explained in detail in accordance with the examples below, which are for illustrative purposes only and shall not limit the present invention. EXAMPLE 1 After the label was removed, a polyethylene terephthalate bottle, such as those which contain soft drinks, was washed with detergent and water, cut into pieces and dried at a temperature of about 60°C. for 7 hours in a vacuum oven. A mixture of 18 grams of recycled bottle polyethylene terephthalate, 2 grams of 2-carboxyethyl (phenyl)phosphinic acid, 3.2 grams of ethylene glycol and 0.02 grams of antimony oxide was placed within a 50 milliliter flask with a stainless steel stirrer. The flask had a nitrogen inlet and outlet and a provision for pulling a vacuum. The flask was evacuated and filled with nitrogen 3 times at room temperature and then a continuous, slow flow of nitrogen was maintained through the flask. The flask was placed in a salt bath which had been preheated to about 250°C. The temperature of the salt bath was raised from 250°C. to about 285°C. over a period of about 1.5 hours and ethylene glycol was distilled off. The pressure was then reduced to 150 millitorr over a period of about 1 hour. The pressure in the flask was further reduced to about 50 millitorr over a period of about 30 minutes and the reaction was continued at these conditions for an additional 45 minutes at which time the heat and vacuum were removed. The resulting copolymer had an intrinsic viscosity of 0.85 at a concentration of 0.5 grams/deciliter in a solution of 60% phenol/40% tetrachloroethane at 25°C. The glass transition temperature was determined to be 69°C. by differential scanning calorimeter. EXAMPLE 2 The reaction of Example 1 was modified. In this reaction, 19 grams of recycled bottle polyethylene terephthalate, 1 gram of 2- carboxyethyl (phenyl)phosphinic acid and 1.6 grams of ethylene glycol were reacted in the presence of 0.004 grams of antimony oxide. The conditions of the reaction were as set forth in Example 1 above. The resulting copolymer had an intrinsic viscosity of 0.83 at a concentration of 0.5 grams/deciliter in a solution of 60% phenol/40% tetrachloroethane at 25°C. The glass transition temperature was determined to be 69.8°C. by differential scanning calorimeter. EXAMPLE 3 In this reaction, 19.4 grams of recycled bottle polyethylene terephthalate, 0.6 grams of 2- carboxyethyl (phenyl)phosphinic acid and 0.41 grams of ethylene glycol were reacted in the presence of 0.004 grams of antimony oxide. The conditions of the reaction were as set forth in Example 1 above. The resulting copolymer had an intrinsic viscosity of 0.93 at a concentration of 0.5 grams/deciliter in a solution of 60% phenol/40% tetrachloroethane at 25°C. The glass transition temperature was determined to be 69.5°C. by differential scanning calorimeter. The polyesters produced in Examples 1 and 2 were tested for their flame retarding properties. The limiting oxygen index (LOI) was measured to be: 23.4 for recycled polyethylene terephthalate without additives; 26.9 for the flame retardant polyethylene terephthalate copolymer produced in Example 1; and 25.4 for the flame retardant polyethylene terephthalate copolymer produced in Example 2. These numbers are relative numbers which show the improvement in the flame retardant properties provided by the inclusion of the carboxy-phosphinic acid moiety in the polyethylene terephthalate copolymer. The numbers are not absolute numbers as the test was not performed in accordance with ASTM standard procedures. A strand of each material was tested instead of the molded tensile bars required by the ASTM procedures. Conforming to the ASTM requirements might change the numbers shown above; however, it is believed that the results of such a test would still indicate a similar improvement in the flame retardant properties. While certain preferred embodiments of the invention have been illustrated and described herein, it is to be understood that the invention is not limited thereby and that the invention may be variously practiced within the scope of the following claims.

Claims: I claim : 1. A flame retardant linear polyester comprising the product of recycled polyester and a flame-retarding amount of a carboxy-phosphinic acid. 2. The flame retardant linear polyester of claim 1 wherein the recycled polyester is recycled polyethylene terephthalate or recycled polybutylene terephthalate. 3. The flame retardant linear polyester of claim 2 wherein the carboxy-phosphinic acid monomer is present in an amount of from about 0.1% to about 10% by weight based upon the total weight of the polyester. 4. The flame retardant linear polyester of claim 3 wherein the carboxy-phosphinic acid monomer is selected from the group consisting of 2-carboxy¬ ethyl (phenyl)phosphinic acid, 2-carboxyethyl (methyl)phosphinic acid, the cyclic anhydride of 2- carboxyethyl (phenyl)phosphinic acid and the cyclic anhydride of 2-carboxyethyl(methyl) phosphinic acid. 5. The flame retardant linear polyester of claim 4 wherein the carboxy-phosphinic acid monomer is 2-carboxyethyl (phenyl)phosphinic acid. 6. The flame retardant linear polyester of claim 4 wherein the carboxy-phosphinic acid monomer is 2-carboxyethyl (methyl)phosphinic acid. 7. A process for the production of a flame retardant linear polyester comprising condensing a mixture of recycled polyester and a flame-retarding carboxy-phosphinic acid monomer, the carboxy- phosphinic acid monomer being present in an amount of from about 0.1% to about 10% by weight based upon the total weight of said polyester, in the presence of a catalyst at a temperature between about 250°C. and about 293°C. 8. The process of claim 7 wherein the recycled polyester is recycled polyethylene terephthalate or recycled polybutylene terephthalate. 9. The process of claim 7 wherein the carboxy-phosphinic acid monomer is selected from the group consisting of 2-carboxyethyl (phenyl)phosphinic acid, 2-carboxyethyl (methyl)phosphinic acid, the cyclic anhydride of 2-carboxyethyl (phenyl)phosphinic acid and the cyclic anhydride of 2-carboxyethyl (methyl)phosphinic acid. 10. The process of claim 9 wherein the carboxy-phosphinic acid monomer is 2-carboxyethyl (phenyl)phosphinic acid. 11. Shaped articles made from a flame retardant linear polyester comprising the product of recycled polyester and a flame-retarding amount of a carboxy-phosphinic acid. 12. The shaped articles of claim 11 wherein the recycled polyester is recycled polyethylene terephthalate or recycled polybutylene terephthalate. 13. The shaped articles of claim 12 wherein the recycled polyester is recycled polyethylene terephthalate. 14. The shaped articles of claim 11 wherein the carboxy-phosphinic acid is present in an amount of from about 0.1% to about 10% by weight based upon the total amount of the polyester. 15. The shaped articles of claim 14 wherein the carboxy-phosphinic acid monomer is selected from the group consisting of 2-carboxyethyl(phenyl) phosphinic acid, 2-carboxyethyl (methyl)phosphinic acid, the cyclic anhydride of 2-carboxyethyl (phenyl)phosphinic acid and the cyclic anhydride of 2-carboxyethyl(methyl)phosphinic acid. 16. The shaped articles of claim 15 wherein the carboxy-phosphinic acid monomer is 2- carboxyethyl (phenyl)phosphinic acid. 17. Fiber produced from a flame retardant linear polyester comprising the product of recycled polyester and a flame-retarding amount of carboxy- phosphinic acid. 18. The fiber of claim 17 wherein the recycled polyester is recycled polyethylene terephthalate or recycled polybutylene terephthalate. 19. The fiber of claim 18 wherein the recycled polyester is recycled polyethylene terephthalate. 20. The fiber of claim 17 wherein the carboxy-phosphinic acid is present in an amount of from about 0.1% to about 10% by weight based upon the total amount of the polyester. 21. The fiber of claim 20 wherein the carboxy-phosphinic acid monomer is selected from the group consisting of 2-carboxyethyl(phenyl)phosphinic acid, 2-carboxyethyl(methyl)phosphinic acid, the cyclic anhydride of 2-carboxyethyl (phenyl)phosphinic acid and the cyclic anhydride of 2-carboxyethyl (methyl)phosphinic acid. 22. The fiber of claim 21 wherein the carboxy-phosphinic acid monomer is 2-carboxy¬ ethyl(phenyl)phosphinic acid.

Inventors: ASRAR JAWED, ASRAR, JAWED
Applicants: MONSANTO CO, MONSANTO COMPANY
Application year: 1995
Main classification: C08K5
IPC codes: C08G63, C08K5, C08L67, D01F6