Polyester compositions

1. A process for optimizing the crystallization behaviour of polyester moulding compositions or the crystallinity of products to be produced from the polyester moulding compositions, the process comprising producing a polyester moulding composition comprising polybutylene terephthalate (PBT) and polyethylene terephthalate (PET) at a PBT:PET ratio by weight of 5:1 to 0.2:1, wherein the polyethylene terephthalate has an alkali metal content of 1 to 10,000 ppm, and the polybutylene terephthalate and the polyethylene terephthalate each individually have an intrinsic viscosity of about 0.3 cm 3 /g to 1.5 cm 3 /g, measured in phenol/o-dichlorobenzene (1:1 parts by weight) at 25° C.

2. The process according to claim 1 , wherein the polyethylene terephthalate is otained from a process comprising:

washing polyethylene terephthalate with aqueous alkali metal hydroxide solution;

melting and mixing the polyethylene terephthalate to form a polyethylene terephthalate melt; and

removing contaminants, if present, from the polyethylene terephthalate melt.

3. The process according to claim 2 , wherein the aqueous alkali metal hydroxide solution comprises 1% to 10% alkali metal hydroxide.

4. The process according to claim 2 , wherein the process further comprises:

prior to washing, comminuting the polyethylene terephthalate;

melting and mixing the comminuted polyethylene terephthalate in a compounder; and

forming solidified portions of polyethylene terephthalate, wherein, if contaminants are present, the solidified portions are formed after removal of the contaminants.

5. The process according to claim 4 , wherein removing the contaminants comprises removing volatile contaminants by subjecting the melt to a vacuum.

6. The process according to claim 4 , wherein removing the contaminants comprises removing volatile contaminants by solid-phase post-condensation of the melt in vacuo, optionally with stripping and/or with passage of an inert gas, to remove residual contaminants and/or increase viscosity.

7. The process according to claim 6 , wherein after washing with aqueous alkali metal hydroxide solution, and prior to melting, the process further comprises additional cleaning by at least one of: steaming the polyethylene terephthalate, and washing the polyethylene terephthalate with water with admixed surfactant.

8. The process according to claim 6 , wherein the aqueous alkali metal hydroxide solution comprises at least one of: aqueous sodium hydroxide solution and aqueous potassium hydroxide solution, and the alkali metal content is correspondingly at least one of: sodium and potassium.

9. The process according to claim 7 , wherein:

the compounder comprises a plurality of screws;

the polyethylene terephthalate is previously used polyethylene terephthalate; and

the contaminants comprise aldehydes and oligomers.

10. The process according to claim 1 , wherein the alkali metal content is 3 to 5000 ppm.

11. The process according to claim 1 , wherein the alkali metal content is 7 to 1000 ppm.

12. A process for using recycled polyethylene terephthalate for optimizing the crystallization behaviour of polyester moulding compositions or the crystallinity of products to be produced from the polyester moulding compositions, the process comprising producing a polyester moulding composition comprising polybutylene terephthalate (PBT) and only recycled polyethylene terephthalate (PET) at a PBT:PET ratio by weight of 5:1 to 0.2:1, wherein the recycled polyethylene terephthalate has an alkali metal content of 1 to 10,000 ppm, and the polybutylene terephthalate and polyethylene terephthalate each individually have an intrinsic viscosity of about 0.3 cm 3 to 1.5 cm 3 /g, measured in phenol/o-dichlorobenzene (1:1 parts by weight) at 25° C.

13. The process according to claim 12 , wherein the recycled polyethylene terephthalate is prepared by a process comprising:

comminuting used polyethylene terephthalate;

washing the polyethylene terephthalate with aqueous alkali metal hydroxide solution;

melting and mixing the comminuted polyethylene terephthalate in a compounder to produce a polyethylene terephthalate melt;

removing contaminants, if present, from the polyethylene terephthalate melt; and

forming solidified portions of recycled polyethylene terephthalate.

14. The process according to claim 13 , wherein:

washing the polyethylene terephthalate comprises washing the polyethylene terephthalate with aqueous alkali metal hydroxide solution comprising 1% to 10% alkali metal hydroxide; and

the alkali metal content in the recycled polyethylene terephthalate is 3 to 5000 ppm.

15. The process according to claim 14 , wherein the aqueous alkali metal hydroxide solution comprises at least one of: aqueous sodium hydroxide solution and aqueous potassium hydroxide solution, and the alkali metal is correspondingly at least one of: sodium and potassium.

16. A method for optimizing crystallization behavior and processing behavior of polyester compositions in an injection molding process, the method comprising injection molding a composition comprising polybutylene terephthalate (PBT) and only recycled polyethylene terephthalate (PET) at a PBT:PET ratio by weight of 5:1 to 0.2:1, wherein the recycled polyethylene terephthalate has an alkali metal content of 1 to 10000 ppm, the polybutylene terephthalate and the polyethylene terephthalate each individually have an intrinsic viscosity of about 0.3 cm 3 /g to 1.5 cm 3 /g, measured in phenol/o-dichlorobenzene (1:1 parts by weight) at 25° C., and the composition is prepared by a process comprising:

comminuting used polyethylene terephthalate;

washing polyethylene terephthalate with aqueous alkali metal hydroxide solution to provide the alkali metal in the recycled polyethylene terephthalate;

melting and mixing the comminuted polyethylene terephthalate in a compounder to produce a polyethylene terephthalate melt:

removing contaminants, if present, from the polyethylene terephthalate melt; and

forming solidified portions of recycled polyethylene terephthalate comprising the alkali metal.