Polyester and method for preparing such a polyester
A polyester, including ethylene 2,5-furandicarboxylate units, has an intrinsic viscosity of at least 0.45 d L/g, and has a relative content of carboxylic acid end groups, expressed as the fraction of the molar amount of carboxylic acid end groups divided by the sum of the molar amounts of hydroxyl end groups and carboxylic acid end groups in the range of 0.10 to 0.70. The polyester can be prepared with a method wherein a starting mixture comprising 2,5-furandicarboxylic acid and ethylene glycol is subjected to esterification and subsequent polycondensation at reduced pressure when the molar ratio of 2,5-furandicarboxylic acid to ethylene glycol in the starting mixture is 1:1.01 to 1:1.15, where water, that is formed during the reaction between 2,5-furandicarboxylic acid and ethylene glycol, and some ethylene glycol are removed in a distillation system, and where ethylene glycol that is removed with water, is separated from water and at least partly recycled.
1. A polyester comprising ethylene 2,5-furandicarboxylate units, which polyester has an intrinsic viscosity of at least 0.45 dL/g, and which polyester has a relative content of carboxylic acid end groups, expressed as the fraction of the molar amount of carboxylic acid end groups divided by the sum of the molar amounts of hydroxyl end groups and carboxylic acid end groups, in the range of 0.10 to 0.70.
2. The polyester according to claim 1 , which has an intrinsic viscosity of at most 1.0 dL/g.
3. The polyester according to claim 1 , wherein the relative content of carboxylic acid end groups is in the range of 0.14 to 0.65.
4. The polyester according to claim 1 , wherein the amount of carboxylic acid end groups is in the range of 15 to 122 meq/kg.
5. The polyester according to claim 1 , which has a light absorbance of at most 0.08, measured as a 30 mg/mL solution in a dichloromethane:hexafluoroisopropanol 8:2 (vol/vol) mixture at 400 nm.
6. The polyester according to claim 1 , which has a polydispersity index in the range of 1.9 to 2.6.
7. The polyester according to claim 1 , which has a crystallinity of at least 25 J/g, measured by Differential Scanning Calorimetry (DSC).
8. The polyester according to claim 7 , which has a melting point of at least 215° C.
9. A composition comprising the polyester according to claim 1 , which has a moisture content of at most 100 ppmw.
10. A method for the preparation of a polyester, wherein a starting mixture comprising 2,5-furandicarboxylic acid and ethylene glycol is subjected to esterification to form an ester composition, wherein the molar ratio of 2,5-furandicarboxylic acid to ethylene glycol in the starting mixture is 1:1.01 to 1:1.15; and
wherein the ester composition thus obtained is subjected to polycondensation at reduced pressure in the presence of a polycondensation catalyst to obtain a polycondensate, wherein water, that is formed during the reaction between 2,5-furandicarboxylic acid and ethylene glycol, and some ethylene glycol are removed in a distillation system, and wherein ethylene glycol that is removed with water is separated from water and at least partly recycled.
11. The method according to claim 10 , wherein the esterification reaction between 2,5-furandicarboxylic acid and ethylene glycol is carried out at a temperature of 160 to 240° C. and a pressure of 0.9 to 5 bar for a period of 0.5 to 4 hr.
12. The method according to claim 10 , wherein the polycondensation comprises a pre-polycondensation reaction conducted at a pressure of 20 to 700 mbar and a polycondensation reaction conducted at a pressure of 0.05 to 20 mbar.
13. The method according to claim 12 , wherein the combined period for the pre-polycondensation and the polycondensation reactions is in the range of 1.5 to 4 hours.
14. The method according to claim 10 , wherein during the polycondensation step ethylene glycol that is formed is removed from the ester composition that is subjected to polycondensation.
15. The method according to claim 10 , wherein the polycondensation step is carried out in the presence of a polycondensation catalyst.
16. The method according to claim 15 , wherein the polycondensation catalyst is selected from the catalysts comprising one or more elements selected from tin, zinc, titanium, antimony.
17. The method according to claim 10 , wherein the polycondensation is carried out at a temperature of 245 to 270° C. and a pressure of 0.05 to 5 mbar.
18. The method according to claim 10 , wherein the polycondensate is crystallized at a temperature in the range of 90 to 200° C.
19. The polyester according to claim 1 , which has an intrinsic viscosity in the range of 0.45 to 0.75 dL/g.