Method for color stabilization of poly(butylene-co-adipate terephthalate

Abstract

Biodegradable compositions containing an aliphatic-aromatic copolyester derived from aromatic polyesters. Methods of making the compositions and articles made from the compositions.

1 .- 18 . (canceled) 
     
     
         19 . A method for making a copolyester, the process comprising
 (a) depolymerizing an aromatic polyester component, by reacting   (i) the aromatic polyester component with   (ii) a diol component selected from ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 2,3-butanediol, 1,4-butanediol, tetramethyl cyclobutanediol, isosorbide, 1,3-cyclohexanedimethanol isomers, 1,4-cyclohexanedimethanol isomers, hexylene glycol, bio-derived diols, and combinations thereof, and   (iii) an adipic acid component selected from adipic acid, adipic acid oligomers, and combinations thereof, in the presence of   (iv) a color reducing compound selected from a C 5-12  compound having at least three —OH groups and combinations thereof, and   (v) a titanium-containing catalyst,   wherein reaction is carried out in a reactor, at a pressure that is at least atmospheric pressure, at a temperature ranging from 170° C. to 250° C., under an inert atmosphere and with agitation, under conditions sufficient to depolymerize the aromatic polyester component into a molten mixture; and at a temperature from 160° C. to less than 250° C., to form a reaction mixture; and   b) subjecting the reaction mixture to vacuum distillation at a pressure of less than 2 Ton and a temperature of 220 to less than 260° C., to form molten copolyester;   wherein a copolyester polymer is obtained having a number average molecular weight of at least 20,000 Daltons and a polydispersity index from 2 to less than 6; and   wherein the copolyester composition obtains a whiteness of at least L*=70.0; a*=−8.0; b*=15.0 as determined using a colorimeter with D65 illumination.   
     
     
         20 . The method of  claim 19 , wherein the reaction mixture further comprises an epoxy compound selected from a glycidyl methacrylate copolymer, a bisphenol A epoxy, and combinations thereof. 
     
     
         21 . The method of  claim 19 , wherein no chain extender is present during the process. 
     
     
         22 . The method of  claim 19 , wherein the diol component comprises 1,4-butane diol. 
     
     
         23 . The method of  claim 19 , wherein
 the diol component comprises a diol selected from ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, and combinations thereof; and   the process further comprises adding 1,4-butane diol to the molten mixture.   
     
     
         24 . The method of  claim 19 , wherein the aromatic polyester component comprises a polymer selected from poly(trimethylene terephthalate)s derived from petroleum-derived 1,3-propanediol, poly(trimethylene terephthalate)s derived from bio-derived 1,3-propanediol, poly(butylene terephthalate)s derived from petroleum-derived 1,4-butanediol, poly(butylene terephthalate)s derived from bio-derived 1,4-butanediol, poly(trimethylene terephthalate)s derived from post-consumer poly(ethylene terephthalate)s, poly(butylene terephthalate)s derived from post-consumer poly(ethylene terephthalate)s, virgin poly(ethylene terephthalate)s, recycled poly(ethylene terephthalate)s, post-consumer poly(ethylene terephthalate)s, recycled poly(trimethylene terephthalate)s, recycled copolyesters of terephthalic acid with ethylene glycol and cyclohexane dimethanol, and combinations thereof. 
     
     
         25 . The method of  claim 19 , wherein the aromatic polyester component is poly(butylene terephthalate). 
     
     
         26 . The method of  claim 19 , wherein the aromatic polyester component is poly(ethylene terephthalate) homopolymer, copolymers of poly(ethylene terephthalate), or combinations thereof. 
     
     
         27 . The method of  claim 19 , wherein the color-reducing compound is selected from sorbitol, mannitol, xylitol, pentaerythritol, ascorbic acid, malic acid, and combinations thereof. 
     
     
         28 . The method of  claim 19 , wherein the color-reducing polyol is selected from sorbitol, mannitol, and combinations thereof. 
     
     
         29 . The method of  claim 19 , wherein the copolyester composition exhibits a T g  from −35° C. to 0° C. and a T m  from 90° C. to 160° C. 
     
     
         30 . A method for making a copolyester , the process comprising
 (a) depolymerizing an aromatic polyester component selected from poly(ethylene terephthalate), poly(butylene terephthalate), poly(trimethylene terephthalate), and combinations thereof, by reacting   (i) the aromatic polyester component with   (ii) a diol component selected from ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 2,3-butanediol, 1,4-butanediol, tetramethyl cyclobutanediol, isosorbide, 1,3-cyclohexanedimethanol isomers, 1,4-cyclohexanedimethanol isomers, hexylene glycol, bio-derived diols, and combinations thereof, and   (iii) an adipic acid component selected from adipic acid, adipic acid oligomers, and combinations thereof, in the presence of   (iv) a color reducing compound selected from a C 5-12  compound having at least three —OH groups and combinations thereof, and   (v) a titanium-containing catalyst,   wherein reaction is carried out in a reactor, at a pressure that is at least atmospheric pressure, at a temperature ranging from 170° C. to 250° C., under an inert atmosphere and with agitation, under conditions sufficient to depolymerize the aromatic polyester component into a molten mixture; and at a temperature from 160° C. to less than 250° C., to form a reaction mixture; and   b) subjecting the reaction mixture to vacuum distillation at a pressure of less than 2 Torr and a temperature of 220 to less than 260° C., to form molten copolyester;   wherein a copolyester polymer is obtained having a number average molecular weight of at least 20,000 Daltons and a polydispersity index from 2 to less than 6; and   wherein the copolyester composition obtains a whiteness of at least L*=70.0; a*=−8.0; b*=15.0 as determined using a colorimeter with D65 illumination.   
     
     
         31 . The method of  claim 30 , wherein said color reducing compound is combined with said copolyester in molten form to obtain a mixture and the mixture is subsequently cooled to obtain the copolyester composition, wherein the copolyester composition comprises a polymer consisting of said copolyester. 
     
     
         32 . The method of  claim 31 , wherein the color reducing compound is selected from the group consisting of mannitol, sorbitol, and combinations thereof. 
     
     
         33 . The method of  claim 32 , wherein the color reducing compound is present in an amount such that, compared to its absence, the copolyester composition obtains the whiteness of exhibits said whiteness of at least L*=70.0; a*=−8.0; and b*=15.0 as determined using a colorimeter with D65 illumination.