POST-CONSUMER RECYCLED THERMOPLASTICS TREATED FOR MELT-PROCESSING WITH ENHANCED QUALITY
Post-consumer recycled polyethylene terephthalate (PCR-PET) flake is treated with chelant to reduce discoloration and generation of non-intentionally added substances (NIAS) upon melt-processing for use in making thermoplastic articles from the PCR-PET flake.
1 . A mixture comprising:
(a) post-consumer recycled polyethylene terephthalate (PCR-PET) flake; and
(b) chelant;
wherein the chelant is in physical contact with at least a portion of the PCR-PET flake.
2 . The mixture of claim 1 , wherein the PCR-PET flake has a surface and the chelant is present only at the surface of the PCR-PET flake.
3 . The mixture of claim 2 , wherein transition metal ions are present on the surface and the chelant is bonded to, and forms coordination complexes with, at least a portion of the transition metal ions.
4 . The mixture of claim 3 , wherein the chelant is bonded to, and forms coordination complexes with, substantially all of the transition metal ions.
5 . The mixture of claim 1 , wherein the chelant is present in an amount from about 1 to about 1000 ppm based on weight of the PCR-PET flake.
6 . The mixture of claim 1 , wherein the chelant is present in an amount from about 50 to about 500 ppm based on weight of the PCR-PET flake.
7 . The mixture of claim 1 , wherein the chelant is selected from the group consisting of carboxylic acids and salts thereof; phosphoric acids and salts thereof; phosphonic acids and salts thereof; and combinations thereof.
8 . The mixture of claim 1 , wherein the chelant is selected from the group consisting of ethylenediamine tetraacetic acid (EDTA); phosphoric acid; acetyldiphosphonic acid (ADPA); nitrilotris(methylenephosphonic acid) (NTMP); diethylenetriamine penta(methylene phosphonic acid) (DTPMP); and combinations thereof.
9 . A method of treating post-consumer recycled polyethylene terephthalate (PCR-PET) flake for its use in making a thermoplastic article by at least one subsequent melt-processing step, the method comprising the steps of:
(a) providing the PCR-PET flake;
(b) providing chelant;
(c) placing the chelant in physical contact with at least a portion of the PCR-PET flake; and
(d) optionally, removing at least a portion of the chelant from physical contact with the PCR-PET flake;
wherein steps (a), (b) (c), and optionally (d), each occurs prior to the at least one subsequent melt-processing step.
10 . The method of claim 9 , wherein the PCR-PET flake has a surface and the chelant is present only at the surface of the PCR-PET flake.
11 . The method of claim 10 , wherein transition metal ions are present on the surface and the chelant is bonded to, and forms coordination complexes with, at least a portion of the transition metal ions.
12 . The method of claim 11 , wherein the chelant is bonded to, and forms coordination complexes with, substantially all of the transition metal ions.
13 . The method of claim 9 , wherein the chelant is present in an amount from about 1 to about 1000 ppm based on weight of the PCR-PET flake.
14 . The method of claim 9 , wherein the chelant is present in an amount from about 50 to about 500 ppm based on weight of the PCR-PET flake.
15 . The method of claim 9 , wherein the chelant is selected from the group consisting of carboxylic acids and salts thereof; phosphoric acids and salts thereof; phosphonic acids and salts thereof; and combinations thereof.
16 . The method of any one of claims 9 to 15 claim 9 , wherein the chelant is selected from the group consisting of ethylenediamine tetraacetic acid (EDTA); phosphoric acid; acetyldiphosphonic acid (ADPA); nitrilotris(methylenephosphonic acid) (NTMP); diethylenetriamine penta(methyl ene phosphonic acid) (DTPMP); and combinations thereof.
17 . The method of claim 9 , wherein the physical contact of step (c) continues for a period of time ranging from about 1 second to about 25 minutes.
18 . The method of claim 9 , wherein the physical contact of step (c) continues for a period of time ranging from about 1 second to about 5 minutes.
19 . The method of claim 9 , wherein optional step (d) occurs and thereby at least a portion of the transition metal ions is removed from the surface of the PCR-PET flake prior to the melt-processing.
20 . The method of claim 9 , wherein optional step (d) does not occur and thereby at least a portion of the chelant is not removed from physical contact with the PCR-PET flake prior to the melt-processing.