Monomer composition for synthesizing recycled plastic, preparation method thereof, and recycled plastic, molded product, plasticizer composition using the same

Abstract

The present disclosure relates to a monomer composition for synthesizing recycled plastic which is extremely reduced in the content of organic impurities such as formic acid and acetic acid while recovering from a (co)polymer synthesized from monomers containing terephthalic acid, a method for preparing the same, and a recycled plastic, molded product, and plasticizer composition using the same.

1 . A monomer composition for synthesizing recycled plastic, comprising:
 terephthalic acid; and   one or more organic impurities selected from the group consisting of formic acid and acetic acid,   wherein a weight ratio of the one or more organic impurities measured using a gas chromatography mass spectrometry is less than 5 μg relative to 1 g of the monomer composition, and   wherein the monomer composition is a recovered product from a (co)polymer synthesized from at least one monomer containing terephthalic acid.   
     
     
         2 . The monomer composition according to  claim 1 ,
 further comprising an isophthalic acid having a molar ratio of less than 0.85 mol % based on 100 mol % of a total monomer compounds contained in the monomer composition.   
     
     
         3 . The monomer composition according to  claim 1 , wherein the at least one monomer containing terephthalic acid further comprises aliphatic diols, polyalkylene oxides, fatty acids, fatty acid derivatives, or a combination thereof. 
     
     
         4 . The monomer composition according to  claim 1 , wherein
 the terephthalic acid has a molar ratio of more than 99.15 mol % based on 100 mol % of a total monomer compounds contained in the monomer composition.   
     
     
         5 . The monomer composition according to  claim 1 ,
 further comprising one or more aromatic impurities selected from the group consisting of 4-carboxybenzaldehyde, benzoic acid, and p-toluic acid,   wherein a weight ratio of the one or more aromatic impurities measured using a liquid chromatography (LC) is less than 100 μg relative to 1 g of the monomer composition.   
     
     
         6 . The monomer composition according to  claim 1 , wherein
 the (co)polymer comprises at least one (co)polymer selected from the group consisting of polyalkylene terephthalate, polyalkylene terephthalate-based copolymer, and thermoplastic polyester elastomer.   
     
     
         7 . A method for preparing a monomer composition for synthesizing recycled plastic, comprising the steps of:
 subjecting a (co)polymer synthesized from at least one monomer containing terephthalic acid to a depolymerization reaction and removing a diol component;   washing a depolymerization reaction product from which the diol component has been removed with a solvent at a temperature of 20° C. or more and 100° C. or less; and   dissolving the washed depolymerization reaction product in water and then recrystallizing the washed depolymerization reaction product dissolved in water,   wherein the dissolving and recrystallizing step comprises:
 dissolving the washed depolymerization reaction product in water at a temperature of 200° C. to 300° C.; and 
 cooling a solution in which the depolymerization reaction product is dissolved in water to a temperature lower by 50° C. to 200° C. than the solution temperature. 
   
     
     
         8 . The method for preparing a monomer composition according to  claim 7 , wherein
 the solvent is water.   
     
     
         9 . The method for preparing a monomer composition according to  claim 7 , wherein
 in the washing step, 1 part by weight to 50 parts by weight of the solvent is used based on 1 part by weight of the (co)polymer.   
     
     
         10 . The method for preparing a monomer composition according to  claim 7 , wherein
 in the step of dissolving the washed depolymerization reaction product in water at a temperature of 200° C. to 300° C.,   1 part by weight to 60 parts by weight of water is used based on 1 part by weight of the (co)polymer.   
     
     
         11 . The method for preparing a monomer composition according to  claim 7 , wherein
 the step of dissolving the washed depolymerization reaction product in water at a temperature of 200° C. to 300° C. comprises:   dissolving the washed depolymerization reaction product in water at a temperature of 200° C. to 220° C.,   wherein 30 parts by weight to 60 parts by weight of water is used based on 1 part by weight of the (co)polymer.   
     
     
         12 . The method for preparing a monomer composition according to  claim 7 , wherein
 the step of dissolving the washed depolymerization reaction product in water at a temperature of 200° C. to 300° C. comprises:   dissolving the washed depolymerization reaction product in water at a temperature of 240° C. to 300° C.,   wherein 1 part by weight to 20 parts by weight of water is used based on 1 part by weight of the (co)polymer.   
     
     
         13 . The method for preparing a monomer composition according to  claim 7 , wherein
 the depolymerization reaction of the (co)polymer is carried out by reacting a base and the (co)polymer with a molar ratio of the base in an amount of 2.3 moles or less relative to 1 mole of the (co)polymer.   
     
     
         14 . The method for preparing a monomer composition according to  claim 7 , wherein
 the depolymerization reaction of the (co)polymer is carried out in the presence of water or alkylene glycol solvent.   
     
     
         15 . The method for preparing a monomer composition according to  claim 7 , wherein
 before the washing step,   the method further comprises neutralizing the depolymerization reaction product from which the diol component has been removed with an acid.   
     
     
         16 . A recycled plastic, comprising:
 a reaction product of the monomer composition of  claim 1  and a comonomer.   
     
     
         17 . The recycled plastic according to  claim 16 , wherein
 the recycled plastic has a yellow index of 50 or less.   
     
     
         18 . The recycled plastic according to  claim 16 , wherein
 the recycled plastic has a color coordinate b* value of 3 or less.   
     
     
         19 . A molded product, comprising:
 the recycled plastic of  claim 16 .   
     
     
         20 . A plasticizer composition, comprising:
 a reaction product of the monomer composition of  claim 1  and an alcohol.