Residual Contaminants in Recycled Poly(ethylene ... - ACS Publications

Chapter 35

Residual Contaminants in Recycled Poly(ethylene terephthalate)

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 21, 2016 | http://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1995-0609.ch035

Effects of Washing and Drying 1,2

V. Komolprasert

2

and A. Lawson

1Division of Food Processing and Packaging, U.S. Food and Drug Administration, and National Center for Food Safety and Technology, 6502 South Archer Road, Summit-Argo, IL 60501 2

Because residual contaminants in recycled plastics intended for food packaging could be a risk to public health, the guidelines of the U.S. Food and Drug Administration suggest that the concentrations of any residual contaminants be determined after the recycling processes. This paper presents the results obtained from small-scale washing and drying experiments using polyethylene terephthalate (PETE) chips made from 2-L beverage bottles. The chips were individually contaminated with benzene, tetracosane, lindane, butyric acid, malathion and copper (II) 2-ethylhexanoate before they were washed and dried. The results show that washing significantly affected the removal of each contaminant from the PETE chips, but the effectiveness varied with the contaminant and washing conditions. Tetracosane was removed in the highest amount, followed by lindane, malathion, copper, butyric acid and benzene. After washing, the residues were present at 1 (tetracosane) to 90% (benzene) of their initial concentrations. Drying at 170°C also significantly affected the removal of the organic contaminants but not copper. After drying, the concentrations of the organic residues rangedfrom0.1 (benzene) to 21% (copper) of initial concentrations.

To detennine the efficacy of recycling process, the guidelines of the U.S. Food and Drug Administration (1) suggest that at least five different surrogates with various physical and chemical properties be used for testing the levels of potential contaminants that could conceivably be retained through recycling processes. In this study, benzene, tetracosane and lindane, butyric acid, malathion and copper (II) 2-ethylhexanoate were chosen to represent compounds that fall into the general categories of volatile, non-polar; non-volatile, non-polar; volatile, polar; nonvolatile, polar; and organically bound heavy metal, respectively. These surrogates

0097H5156/95/0609-0435$12.00/0 © 1995 American Chemical Society Rader et al.; Plastics, Rubber, and Paper Recycling ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

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PLASTICS, RUBBER, AND PAPER RECYCLING


were intentionally added to polyethylene terephthalate (PETE) chips prior to the recycling processes. In secondary or physical recycling, water-based washing and thermal drying are common procedures for recycling PETE. Therefore, the residual concentration of these surrogates were determined after washing and drying. The objective of this study was to evaluate the efficacy of washing and drying on the removal of these surrogates from the spiked PETE chips. Materials and Methods Chemicals Benzene -99% purity, reagent grade (Fisher Scientific, Pittsburgh, PA) Copper (II) 2-ethylhexanoate - (Aldrich Chemical Company, Inc., Milwaukee, WI) Tetracosane - 99% purity (Sigma Chemical Co., St. Louis, MO) Lindane - 99% purity (Supelco Inc., Beliefonte, PA) Butyric acid - purified (J.T. Baker Inc., Phillipsburg, NJ) Malathion - 57% purity, commercial grade (Platte Chemical Co., Inc., Fremont, NE) Sodium hydroxide (NaOH) - reagent grade (Fisher Scientific) Methylene chloride (MC) - HPLC grade (Fisher Scientific) 2-Propanol - reagent grade (Fisher Scientific) Hexane - HPLC grade (Fisher Scientific) Potassium acetate - 99.2% purity (Fisher Scientific) Copper reference solution - 1000 ppm (Fisher Scientific) Hexafluoroisopropanol (HFIP) - 100% purity (Eastman Kodak Company, Rochester, NY) Trifluoroacetic acid (TFA) - 97% purity (Fisher Scientific) n-Heptane - HPLC grade (Fisher Scientific) Triton X-100 - Union Carbide, Danbury, NJ Apparatus Perkin Elmer 3100 atomic absorption spectrometer, Tekmar LSC 2000 concentrator and Varian 3400 gas chromatograph system with flame ionization detector, flame photometric detector and electron capture detector were used. The Varian system was controlled by a 486 computer using STAR workstation software. PETE Material. Clean, blow-molded 2-L clear PETE bottles without caps and base cups were supplied by Eastman Chemical Co. (Kingsport, TN). They were pre-chipped by Eastman Chemical Co. (Kingsport, TN) before they were shipped to the test laboratory. Spiking Method. Clean PETE chips were soaked separately in each surrogate at the concentrations shown in Table I. A 950-mL glass jar containing a mixture of 270 g of chips and 600 mL of surrogate contaminant solution was sealed and placed in an incubator maintained at 40°C for 2 weeks. The mixture was periodically stirred to ensure uniform soaking. The chips were removed from the

Rader et al.; Plastics, Rubber, and Paper Recycling ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

35.

KOMOLPRASERT & LAWSON

Residual Contaminants in Recycled PET

spiking solution and allowed to air-dry for 2-3 h in a hood before washing and drying. Additional spiking experiments were conducted using 2-L PETE bottles which were filled with the surrogate solutions (Table II), capped and placed in the 40°C incubator. The bottles were cut in half and blotted twice with kimwipe and hexane prior to using.


Table I. Concentrations of Surrogates Used for Spiking PETE Chips Surrogate

Category

Concentration (w/v)

Benzene

volatile, non-polar

99% purity

Butyric acid

volatile, polar

1 % in hexane

Tetracosane

non-volatile, non-polar

1 % in hexane

Malathion

non-volatile, polar

5% commercial in water

Copper (II) 2ethylhexanoate

heavy metal

1 % in 2-propanol

Table II. Concentrations of Surrogates Used for Spiking 2-L PETE Bottles Surrogate

Category

Concentration (w/v)

Benzene

volatile, non-polar

10% in hexane

Butyric acid

volatile, polar

1 % in hexane

Lindane


0.1% in hexane

Tetracosane


1 % in hexane

Malathion

non-volatile, polar

5% commercial in water

Copper (II) 2ethylhexanoate

heavy metal

1 % in 2-propanol

Small-scale Washing Experiments. Small-scale washing experiments were performed using a 250-mL beaker containing 10 g of spiked PETE and 100 mL of washing solution consisting of 1 % Triton X-100 surfactant dissolved in deionized water or aqueous 4% NaOH. The washing solution was preheated to 90°C on a hot plate before the spiked PETE chips were added. The mixture was stirred with a 3.4 mm ID three-blade-propeller agitator equipped with a laboratory mixer


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(Lightnin Model DS 3014)(Mixing Equipment Co., Avon, NY) operated at 600 rpm for 20 min. These were optimum conditions as determined in previous experiments (2). The chips were removed from the washing solution and subsequently rinsed for 15 min with 200 mL of deionized water preheated to 8090°C. The chips were then removed with a sieve and dried using a sieve shaker and an IR lamp. Small-scale Drying Experiments. Drying experiments were performed with an electric laboratory muffle furnace (Eberbach Corp., Ann Arbor, MI). The washed, spiked PETE chips were contained in an aluminum foil dish (5 cm ID) and placed in the furnace, which was preheated and maintained at 160-170°C for 4 h. For test portions weighing more than 10 g, the chips were manually agitated periodically to ensure uniform heating. The chips were cooled to room temperature prior to quantitation. Benzene Determination. Concentrations of benzene in the spiked PETE chips were quantified using either dynamic or static headspace gas chromatography (HS/GC) with flame ionization detection (FID) as described by Komolprasert and co-workers (5, 4). In the dynamic headspace method, approximately 1 g of ground spiked PETE was loaded into a purge tube that was interfaced with the GC/FID system. In the static headspace method, 1 g of ground spiked PETE was loaded into a headspace vial, which was heated at 90°C to attain vapor equilibrium prior to GC/FID. The limits of detection (LOD) were 2 ppb for the dynamic HS/GC procedure and 100 ppb for the static HS/GC procedure. Recoveries ranged from 70 to 102% with repeatability of ±10% for PETE chips contaminated with benzene at concentrations of 0.1 to 120 ppm. Tetracosane Determination. Concentrations of tetracosane in spiked PETE were quantified using a procedure developed by Pierce and co-workers (Pierce and coworkers, Illinois Institute of Technology, unpublished data). Approximately 2 g of spiked PETE was dissolved in a mixture of 15 mL of TFA and 2 mL of deionized distilled water. Tetracosane was then extracted using 15 mL of nheptane and quantified by GC/FID. The LOD was 50 ppb in a standard solution. Recoveries ranged from 94 to 104% with repeatability of ±10% for PETE chips contaminated with tetracosane at concentrations of 1 to 500 ppm. Butyric acid Determination. Concentrations of butyric acid in spiked PETE were quantified using a procedure developed by Komolprasert and co-workers (5). Approximately 2 g of spiked PETE was dissolved in a mixture of 5 mL of HFIP and 10 mL of MC. The solution was diluted with an additional 60 mL of MC before polymer precipitation using 100 mL of acetone. The mixture was vacuumfiltered and the filtrate was subsequently concentrated by rotary evaporation to a final volume of 2-3 mL. The concentrated solution was diluted to 10 mL with acetone. The solution was filtered and butyric acid was quantified by GC/FID.


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The LOD was 50 ppb in a standard solution. Recoveries ranged from 85 to 95% with repeatability of ±5% for PETE chips contaminated with butyric acid at concentrations of 1 to 500 ppm. Malathion Determination. Concentrations of malathion in spiked PETE were quantified using the procedure developed by Komolprasert et al. (5). In the analysis, 2 g of spiked PETE was dissolved in a mixture of 5 mL of HFIP and 10 mL of MC. The solution was diluted with an additional 60 mL of MC before polymer precipitation using 100 mL of methanol instead of acetone as was used in the butyric acid determination. The mixture was vacuum-filtered and the filtrate was subsequently concentrated by rotary evaporation. The concentrate was dissolved in potassium acetate buffer solution (pH 5.3) and the mixture was filtered through C18 cartridge for cleanup using a C18 cartridge prior to determination of malathion by GC with flame photometric detection (FPD). The LOD was 50 ppb in a standard solution. Recoveries ranged from 72 to 93% with repeatability of ±8% for PETE chips contaminated with malathion at concentrations of 1 to 500 ppm. Lindane Determination. Concentrations of lindane in spiked PETE were quantified using the procedure used for malathion analysis with modifications. The modifications included the use of TFA instead of the HFIP, use of deionized distilled water instead of the buffer solution and determination of lindane by GC with electron capture detection (ECD) instead of the FPD. The LOD was 1 ppb in a standard solution. Recoveries of lindane are in a range of 70-80% with repeatability of ±5% for PETE chips spiked with lindane at concentrations of 15 ppb and 5 ppm. Copper Determination. Concentrations of copper in spiked PETE were quantified using AOAC method 969.32 (6) with slight modifications. Approximately 5 or 10 g of spiked PETE chips was ashed in an electric laboratory muffle furnace which was preheated to 300°C. The temperature of the furnace was raised to 400°C and then to 500°C. The ash was cooled, and copper was extracted and determined by atomic absorption spectrometry at 324.8 ran. The LOD was 100 ppb in a standard solution. Recoveries ranged from 95 to 105% with repeatability of ± 20% for PETE chips contaminated with copper at concentrations of 0.5 to 5 ppm. Results and Discussion The average initial concentrations and the coefficients of variation (CV) of these surrogates in PETE chips from several spiking experiments were determined and are shown in Table III. The results suggest that the initial concentrations obtained in the various runs were quite variable. This variability could be due to the different amounts of the surrogate adsorbed on the surface of the chips. It may also depend on how much of the surrogate diffuses or is absorbed into the polymer matrix. The variation in absorption may be affected by irregular size, shape and


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thickness of the chips. The variation in surface area may be a key parameter which dictates the amount of surrogate that diffuses into the PETE matrix. Table m. Initial Concentration of Surrogates in spiked PETE chips and in 2-L PETE Bottles Surrogate Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 21, 2016 | http://pubs.acs.org Publication Date: May 5, 1995 | doi: 10.1021/bk-1995-0609.ch035

Benzene

Spiked chips (ppm) s

7383 ± 270

2-L bottles (ppm) 310 ± 5

b

Butyric acid

755 ± 21

69 ± 6

Tetracosane

1928 ± 299

51 ± 2

Lindane Malathion

N/A

0.275 ± 0.021

5860 ± 2440

599 ± 524

Copper (II) - ethylhexanoate 636 ± 110 Obtained by using 99% purity benzene Obtained by using 10% benzene in hexane N/A : Not available

3.81 ± 0.05

a

b

Table III also shows that the initial concentrations of the surrogates in spiked bottle material are much lower than those in chips. This may result from the difference in surface area exposed to surrogates. These concentrations represent the actual amounts absorbed by the bottles and may simulate the incidental contamination that may occur in die commercial processes. Effects of Washing on Removal of Surrogate Contaminants from Spiked PETE Chips. The percentages of benzene, tetracosane, butyric acid, malathion and copper remaining in the spiked PETE chips after the washing experiments are summarized in Table IV. The results suggest that washing has a significant effect on removal of each surrogate from spiked PETE chips. In the absence of NaOH, 86% of the benzene remained while only 9% of the tetracosane was left. Even in the presence of NaOH, 70% of the benzene residue still remained and 11 % of the tetracosane was left. These results indicate that NaOH had a slight effect on the further reduction of benzene but no effect of on the further reduction of tetracosane. Washing appears to be more effective for removal of tetracosane than for removal of benzene. The other surrogates were intermediate in the amount of residue that remained after washing. The addition of NaOH appeared to have a significant effect on further reduction of the amount of surrogate residue. Regardless of the washing conditions, the level of the tetracosane residue was the lowest, followed by the levels of malathion, copper, butyric acid and benzene.


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Table IV. Initial Concentration and Percent of Residual Benzene, Tetracosane, Butyric acid, Malathion, and Copper in Spiked PETE Chips Washed with and without added NaOH at 90°C for 20 min % Residue after washing ( ± CV) Surrogate

Av. initial concn. (ppm) ± CV

Without addition of NaOH

With addition of NaOH

Benzene

7383 ± 270

86 ± 6

70 ± 1

Tetracosane

1928 ± 299

9±2

11 ± 4

Butyric acid

755 ± 21

44 ± 2

35 ± 4

5860 ± 2440

31 ± 5

16 ± 1

50 ± 5

21 ± 2


a

Malathion a

Copper (II) 636 ± 110 Determined from several experiments

Effect of Drying on Removal of Surrogate Contaminants from Spiked PETE Chips. The percentages of residual benzene, tetracosane, butyric acid, malathion and copper after small-scale drying experiments using the washed PETE chips were determined; the results are shown in Table V. The results indicate that drying for 4 h at 170 ± 5°C has a significant effect on removal of the organic contaminants, Table V. Initial Concentration and Percent of Residual Benzene, Tetracosane, Butyric acid, Malathion, and Copper in Spiked PETE Chips, Washed with and without added NaOH, and Dried at 160-170°C for 4 h % Residual after drying (± CV) a

Surrogate

Av. initial concn. (ppm) ± CV

Benzene

7383 ± 270

2.0 ± 1.0

ND

Tetracosane

1928 ± 299

1.0 ± 0.5

ND

Butyric acid

755 ± 2 1

0.3 ± 0.1

0.3 ± 0.1

5860 ± 2440

4.0 ± 1.0

1.0 ± 0.3

48.0 ± 5.0

22.0 ± 3.0

Malathion a

Copper (II) 636 ± 110 Determined from several experiments ND: Not determined

Without addition of NaOH

With addition of NaOH


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particularly benzene from the washed, spiked PETE chips. A combination of washing and drying removed 98% of the benzene from die spiked PETE. The drying was more effective than washing in removing benzene from PETE. Drying affected the volatile surrogates more than the non-volatile surrogates. The combination of washing and drying removed up to 99% of tetracosane, 99.7% of butyric acid and 99% of malathion (with NaOH) from the spiked PETE. Drying further reduced malathion from the washed chips by thermal decomposition. In contrast, drying has no effect on removal of copper from the washed, spiked PETE. Effects of Washing and Drying on Removal of Surrogate Contaminants from Spiked Bottle Material. The percentages of benzene, tetracosane, butyric acid, malathion, lindane and copper remaining in the spiked PETE chips after the smallscale washing experiments are summarized in Table VI. The results suggest that washing has a significant effect on removal of each surrogate from the spiked PETE bottle material. The effects appear to depend on surrogate and its initial concentration; the higher the initial concentration, the lower the percent removed. After washing, residual concentrations were 74% malathion, 55% benzene and 41% butyric acid, respectively. The other surrogate residues were lower, 35% copper, 1.5% lindane and < 0.6% tetracosane.

Table VI. Initial Concentration and Percent of Residual Benzene, Tetracosane, Lindane, Butyric acid, Malathion, and Copper in Spiked PETE Bottle Material, After Washing without added NaOH, and After Washing and Drying (160-170°C for 4 h) % Residual after (± CV) Initial concn. (ppm) ± CV

Washing

Surrogate

Washing and drying

Benzene

310 ± 5

55 ± 2

2.0 ± 0.6

51 ± 2

< 0.6

< 0.6

Lindane

0.275 ± 0.021

1.5 ± 0.1

< 0.1

Butyric acid

69 ± 6

41 ± 2

0.4 ± 0.1

Malathion

599 ± 524

74 ± 58

20 ± 16

Copper (II)

3.81 ± 0.05

30 ± 7

21 ± 2

Tetracosane

The results may also be because tetracosane and lindane which are nonpolar and non-volatile tend to diffuse so slowly that they were probably on the



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surface. Therefore, they were removed more rapidly than the other surrogates. On the other hand, malathion which is polar and non-volatile, and benzene which is non-polar and volatile diffuse so rapidly that it was probably present in the matrix of polymer and therefore was not removed easily by washing. The percentages of the surrogates in the spiked PETE after small-scale drying experiments are also shown in Table VI. The results indicate that drying further removed the surrogates to 21% or lower. Drying affected the volatile surrogates more than the non-volatile surrogates. Drying significantly reduced residual benzene and butyric acid from the washed PETE to 99% of tetracosane and lindane. Conclusions In this study, the uptake concentration of benzene, butyric acid, tetracosane, lindane, malathion and copper in 2-L PETE bottles was at least ten-fold lower than the initial concentrations observed by spiking the chips with the surrogate solutions. The results in this study indicate that washing alone significantly removed 10-90% of the surrogates from the spiked PETE chips and removed 26-99% of the surrogatesfromthe spiked PETE bottle material. The combination of washing and drying removed >99% of the organic surrogates from the spiked chips, regardless of how the spiked chips were prepared. Although the results in this study suggest that >99% of most organic contaminants can be removed by washing and drying, it is still not known whether the recommended levels of residual organic contaminants in the secondary recycled PETE can be attained. Future work will determine the effect of remelting on the removal of organic and inorganic surrogates as well as the potential migration of these surrogates into several food simulants. Acknowledgments This research was supported by Cooperative Agreement FD-000431 from the U.S. Food and Drug Administration and by the National Center for Food Safety and Technology. Literature cited (1) "Points to Consider for the Use of Recycled Plastics in Food Packaging: Chemistry Considerations." Chemistry Review Branch, U.S. Food and Drug Administration, Indirect Additives Branch, HFS-247, 200 C Street, S.W.,Washington, DC 20204, 1992. (2) Komolprasert, V. and Lawson, A. 1994. Effect of aqueous-based washing on removal of hydrocarbons from recycled polyethylene terephthalate (PETE). Proceedings of the annual SPE meeting, held on May 1-5, in San Francisco, CA.



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(3) Komolprasert, V . ; Hargraves, W.A.; Armstrong, D. Food Addit. Contam., 1994, vol. 11, pp 605-614. (4) Komolprasert, V . ; Hargraves, W.A.; Armstrong, D.J. and Sadler G. 1993. Determination of benzene in recycled polyethylene terephthalate (PETE) by dynamic and static headspace gas chromatography. Paper presented at the annual IFT meeting, held on July 11-14, in Chicago, IL. (5) Komolprasert, V . , Lawson, A. and Hargraves, W.A. 1994. An analytical method for quantifying polar contaminants in recycled polyethylene terephthalate (PETE). Paper presented at the annual ACS meeting, held on August 21-25, in Washington, DC. (6) Official Methods of Analysis of the Association of Analytical Chemists; Williams, S., Ed.; Association of Official Analytical Chemists, Inc.: Arlington, VA, 1990; 15th Ed., pp 272-273. RECEIVED March 8,

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