Chapter 36
Food Packaging Made from Recycled Polymers Functional Barrier Considerations
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Timothy H. Begley and Henry C. Hollifield Division of Product Manufacture and Use, U.S. Food and Drug Administration, Washington, DC 20204
Over the past few years the c u r b s i d e c o l l e c t i o n of post-consumer r e c y c l a b l e products has c r e a t e d a supply o f raw m a t e r i a l s t h a t can easily be recycled into new products or packaging m a t e r i a l s . Recycled m a t e r i a l s used f o r food packaging r e q u i r e some s p e c i a l c o n s i d e r a t i o n s t o ensure that nonregulated chemicals or contaminants e i t h e r a r e not present i n t h e m a t e r i a l o r do not migrate i n t o t h e food. Because all chemicals d i f f u s e through polymers, a p o t e n t i a l f o r food contamination e x i s t s if unregulated chemicals o r contaminants a r e present i n the r e c y c l e d m a t e r i a l . The p o t e n t i a l f o r r e c y c l e d polymers t o contaminate food may be reduced by u s i n g a l t e r n a t i v e package designs. T h i s paper will d i s c u s s d i f f u s i o n c o n s i d e r a t i o n s f o r r e c y c l e d polymers and the f u n c t i o n a l b a r r i e r c h a r a c t e r i s t i c s o f polymers ( i . e . , p o l y e t h y l e n e terephthalate (PET)) as they apply t o food packages made from r e c y c l e d polymer r e s i n s . The f u n c t i o n a l b a r r i e r concept is d i s c u s s e d r e l a t i v e t o the Food and Drug A d m i n i s t r a t i o n ' s proposed Threshold o f Regulation Policy. Diffusion c o e f f i c i e n t s f o r a n o n v o l a t i l e plasticizer i n PET a t temperatures above 100°C were measured and used t o evaluate the b a r r i e r p r o p e r t i e s o f PET dual ovenable t r a y s p o t e n t i a l l y made from r e c y c l e d polymer.
Overview I t i s w e l l e s t a b l i s h e d t h a t polymers absorb chemicals from t h e i r surroundings as w e l l as g i v e o f f chemicals t o t h e i r surroundings. In t h e case o f food packaging, flavor This chapter not subject to U.S. copyright Published 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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446
PLASTICS, RUBBER, AND PAPER RECYCLING
components g e n e r a l l y d i f f u s e i n t o the package m a t e r i a l , and polymer oligomers and a d d i t i v e s d i f f u s e out of the package and migrate i n t o the food. From a r e g u l a t o r y food s a f e t y standpoint, i t i s this general type of behavior, a b s o r p t i o n / d e s o r p t i o n by p l a s t i c s , t h a t makes polymers d i f f i c u l t t o r e c y c l e d i r e c t l y i n t o new food packaging. The a b i l i t y t o demonstrate t h a t r e c y c l e d polymers and v i r g i n food-packaging polymers are of comparable p u r i t y and to s a t i s f y q u a l i t y assurance requirements (2) is a difficult a n a l y t i c a l chemistry problem. There i s no reasonable way t o assay a product when you don't know which contaminants you are l o o k i n g f o r , and the h i s t o r y of the product i s unknown and c o n s t a n t l y changing. T h i s q u a l i t y c o n t r o l problem can be s i m p l i f i e d somewhat by u s i n g only post-consumer c o l l e c t e d food packaging t o make new food packaging. T h i s does not e l i m i n a t e the p o t e n t i a l problem of consumer abuse before r e c y c l i n g , or the r e c y c l i n g of nonfood c o n t a i n e r s t h a t are s i m i l a r i n appearance i n t o food packaging. Once a package/polymer has left the manufacturing/converting f a c i l i t y , i t i s very d i f f i c u l t t o know i f the package has been contaminated with nonfoodr e l a t e d chemicals. Following post-consumer c o l l e c t i o n , the p l a s t i c t h a t i s t o be converted i n t o new food packaging can be subjected t o a d d i t i o n a l r e p r o c e s s i n g steps t o reduce or remove contaminants. Some of these more rigorous r e p r o c e s s i n g steps are expensive. Therefore, i t seems a p p r o p r i a t e t o consider a l t e r n a t i v e approaches t o ensure the s a f e use of r e c y c l e d polymers i n food a p p l i c a t i o n s . Instead of r i g o r o u s l y attempting t o reduce contaminant l e v e l s i n r e c y c l e d polymers t o those found i n v i r g i n m a t e r i a l s , an a l t e r n a t i v e approach may be t o use d i f f u s i o n theory t o estimate the amount of contamination l i k e l y t o migrate i n t o food. The maximum allowable m i g r a t i o n may be d e f i n e d by the Threshold of Regulation P o l i c y proposed by the Food and Drug A d m i n i s t r a t i o n (FDA) i n October 1993 (2) . T h i s t h r e s h o l d p o l i c y proposes a maximum s a f e d i e t a r y exposure of 0.5 ppb t o a noncarcinogenic chemical compound. T h i s same 0.5 ppb d i e t a r y exposure t h r e s h o l d may be used t o determine maximum p e r m i s s i b l e exposure t o a contaminant m i g r a t i n g from a package c o n s t r u c t i o n i n t o food. Therefore, f o r our d i s c u s s i o n s i n t h i s paper, a package c o n s t r u c t i o n w i l l be considered an i n s i g n i f i c a n t contaminant source i f the m i g r a t i o n of chemical/contaminant from a package c o n s t r u c t i o n t o food r e s u l t s i n a d i e t a r y exposure of 0.5 ppb or l e s s . The determination of theshold values i s d e s c r i b e d by FDA i n i t s "Points t o Consider f o r the Use of Recycled P l a s t i c s i n food Packaging: Chemistry Considerations" document (3) , i n which a 1 ppb d i e t a r y exposure was used t o determine t h r e s h o l d v a l u e s . Since t h i s document was published, FDA has decided t h a t a 0.5 ppb d i e t a r y exposure would be more a p p r o p r i a t e . By using the method d e s c r i b e d i n the "Points t o Consider" document and a 0.5 ppb d i e t a r y exposure, t h r e s h o l d values were c a l c u l a t e d and are l i s t e d
Rader et al.; Plastics, Rubber, and Paper Recycling ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
36.
BEGLEY & HOLLIFIELD
Food Packaging Made from Recycled Polymers 447
Table I . Threshold Values f o r Maximum R e s i d u a l Contamination and M i g r a t i o n Amounts Which R e s u l t i n a 0.5 ppb (ng/g) D i e t a r y Exposure t o a Contaminant
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Polymer Polyethylene t e r e p h t h a l a t e (PET) Polystyrene (PS) P o l y v i n y l c h l o r i d e (PVC) High-density polyethylene (HDPE) Polypropylene (PP) Low-density polyethylene (LDPE)
Residual Contamination (PP*>)'
Migration Amount (PPb) b
215 180 90
10 6 5
123 778
4 25
92
3
• I t i s assumed t h a t the base package t h i c k n e s s i s 20 m i l (0.0508 cm) and t h a t 100% o f the chemical migrates i n t o the food. The maximum t o l e r a b l e m i g r a t i o n from t h e polymer i n t o food t h a t r e s u l t s i n a 0.5 ppb d i e t a r y exposure.
b
i n Table I . The two columns o f numbers i n Table I r e f e r t o t h r e s h o l d s f o r the maximum r e s i d u a l contamination i n the package, assuming complete m i g r a t i o n t o t h e food, and t h e maximum amount of m i g r a t i o n t h a t c o u l d occur from a package i n t o a food and s t i l l y i e l d a d i e t a r y exposure o f
