Process for enhancing the molecular weight of a polyester
The molecular weight of a semi-crystalline starting polyester comprising ethylene 2,5-furandicarboxylate units is enhanced by heating the semi-crystalline starting polyester, having a melting point Tm, at a temperature in the range of (Tm-40° C.) to Tm to obtain a solid stated polyester, where the semi-crystalline starting polyester has an intrinsic viscosity of at least 0.45 dL/g, and an amount of carboxylic acid end groups in the range of 15 to 122 meq/kg.
1. A process for enhancing the molecular weight of a semi-crystalline starting polyester comprising ethylene 2,5-furandicarboxylate units, by heating the semi-crystalline starting polyester, having a melting point Tm, at a temperature in the range of (Tm-40° C.) to Tm to obtain a solid stated polyester, wherein the semi-crystalline starting polyester has an intrinsic viscosity of at least 0.45 dL/g, and an amount of carboxylic acid end groups in the range of 15 to 122 meq/kg.
2. The process according to claim 1 , wherein the semi-crystalline starting polyester has a crystallinity of at least 25 J/g, measured by Differential Scanning Calorimetry (DSC).
3. The process according to claim 2 , wherein the semi-crystalline starting polyester has a maximum crystallinity of at most 80 J/g, measured by Differential Scanning Calorimetry (DSC).
4. The process according to claim 1 , wherein semi-crystalline starting polyester has a Tm of at least 200° C., as measured by Differential Scanning Calorimetry (DSC).
5. The process according to claim 1 , wherein the semi-crystalline starting polyester has an intrinsic viscosity in the range of 0.45 to 0.75 dL/g.
6. The process according to claim 1 , wherein the semi-crystalline starting polyester has been allowed to crystallize by having been kept at a temperature in the range of 90 to 200° C. before being heated to a temperature of at least (Tm-40° C.).
7. The process according to claim 6 , wherein the semi-crystalline starting polyester has been kept at a temperature in the range of 90 to 200° C. for a period of 2 to 48 hr.
8. The process according to claim 1 , wherein the semi-crystalline starting polyester having an amount of hydroxyl end groups in addition to carboxylic acid end groups, has a 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 0.7.
9. The process according to claim 8 , wherein the 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 is in the range of 0.14 to 0.65.
10. The process according to claim 1 , wherein the semi-crystalline starting polyester is contained in a composition that further comprises one or more esterification and/or polycondensation catalysts.
11. The process according to claim 10 , wherein the esterification and/or polycondensation catalysts have been selected from the esterification and polycondensation catalysts comprising a metal selected form the group consisting of titanium, tin, zinc, calcium, antimony, germanium, manganese, cobalt, lead, magnesium, aluminium, cerium, zirconium and hafnium.
12. The process according to claim 1 , wherein the semi-crystalline starting polyester is in the form of pellets having a mass of 2.8 to 28 mg.
13. The process according to claim 1 , wherein the semi-crystalline starting polyester is in the form of pellets having a particle size selected such that there are 40 to 350 particles per gram.
14. The process according to claim 1 , wherein the semi-crystalline starting polyester is heated at a temperature in the range of (Tm-40° C.) to Tm for a period of at most 120 hr.
15. The process according to claim 1 , wherein the semi-crystalline starting polyester is heated to a temperature in the range of 180 to 220° C. to obtain the solid stated polyester.
16. A polyester comprising ethylene-2,5-furandicarboxylate units, which polyester has an IV of at least 0.75 dL/g and an acetaldehyde content of at most 1 mg/kg.
17. The polyester according to claim 16 , which has an amount of carboxylic acid end groups in the range of 5 to 30 meq/kg.
18. The polyester according to claim 16 , which has a crystallinity of at least 40 J/g, measured by Differential Scanning Calorimetry (DSC).
19. The process according to claim 14 , wherein the semi-crystalline starting polyester is heated at a temperature in the range of (Tm-40° C.) to Tm for a period of from 2 to 60 hr.
20. The polyester according to claim 16 , which polyester has an acetaldehyde content of less than 0.5 mg/kg.