Chapter 7
Loss of Antioxidants from High-Density Polyethylene
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Its Effect on Oatmeal Cereal Oxidation 1,2
1
1
J. Miltz , P. Hoojjat1, J. K. Han , J. R. Giacin1, B. R. Harte , and I. J. Gray 1
1School of Packaging, Michigan State University, East Lansing, MI 48824-1223 The loss of the antioxidants ΒHA and ΒHT from HDPE film was measured experimentally and analyzed theo retically. The volatilization of the antioxidant from the polymer surface was found to be the control ling parameter for mass transfer. Diffusion coefficients of the antioxidants evaluated from the experimental data and extrapolated to 100°C were found to be of the same order of magnitude as reported in the literature for BHT at that tempera ture. Oatmeal cereal packaged in a high level BHT impregnated HDPE had an extended shelf life when compared to a low level of BHT impregnated HDPE film, due to the adsorbtion, by the cereal, of the anti oxidant that had evaporated from the package. A n t i o x i d a n t s a r e w i d e l y used a s food a d d i t i v e s t o r e t a r d o x i d a t i o n o f l i p i d s and d e g r a d a t i o n o f o t h e r components. N o r m a l l y , t h e antioxidants a r e incorporated d i r e c t l y i n t o the food. This has p r o v e n t o be a v e r y s u c c e s s f u l and i n e x p e n s i v e method f o r p r o t e c t i n g oxygen s e n s i t i v e f o o d s . Antioxidants are also incorporated i n t o p l a s t i c f i l m si n o r d e r t o p r o t e c t them from d e g r a d a t i o n ( 1 - 2 ) . I t i s well e s t a b l i s h e d t h a t a n t i o x i d a n t s a r e l o s t from p o l y m e r i c f i l m s and s h e e t s d u r i n g s t o r a g e ( 3 - 4 ) . A r e l a t i v e l y s m a l l amount o f t h i s a n t i o x i d a n t i s l o s t t h r o u g h d e c o m p o s i t i o n r e a c t i o n s ( i f n o t exposed t o t h e o u t d o o r s environment) w h i l e t h e b u l k o f i t i s l o s t by what i s commonly assumed t o be a d i f f u s i o n c o n t r o l l e d p r o c e s s . The a c t u a l l o s s mode i s , however, more c o m p l i c a t e d . F o r an a n t i o x i d a n t t o be l o s t f r o m a p o l y m e r i c f i l m ( o r s h e e t ) i t h a s t o d i f f u s e t h r o u g h t h e b u l k o f t h e polymer towards i t s s u r f a c e and t h e n 2
Current address: Pillsbury Company, Research and Development Laboratories, Minneapolis, MN 55402; on leave from the Department of Food Engineering, Technion-Israel Institute of Technology, Haifa, Israel 0097-6156/88/0365-0083$06.00/0 © 1988 American Chemical Society
Hotchkiss; Food and Packaging Interactions ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
FOOD AND PACKAGING INTERACTIONS
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e v a p o r a t e from the s u r f a c e i n t o the s u r r o u n d i n g s . Depending on the n a t u r e and s t r u c t u r e of t h e polymer and on t h e p r o p e r t i e s of the a d d i t i v e , t o i n c l u d e i t s d i f f u s i v i t y and v o l a t i l i t y , t h e l o s s p r o c e s s can be c o n t r o l l e d e i t h e r by d i f f u s i o n or by v o l a t i l i z a t i o n o r by a combination of the two. The p r o c e s s o f t h e p h y s i c a l l o s s o f an a d d i t i v e which i s s o l u b l e i n t h e polymer t h u s i n v o l v e s two d i s t i n c t p r o c e s s e s : ( i ) the removal of a d d i t i v e from t h e s u r f a c e by e v a p o r a t i o n ; and ( i i ) the r e p l a c e m e n t of a d d i t i v e i n the s u r f a c e l a y e r by d i f f u s i o n from t h e b u l k polymer. A m a t h e m a t i c a l model d e s c r i b i n g t h e l o s s o f an a d d i t i v e f r o m the polymer t o a i r r e q u i r e s t h e r e f o r e two p a r a m e t e r s : a mass t r a n s f e r c o e f f i c i e n t c h a r a c t e r i z i n g t r a n s f e r a c r o s s the boundary o f polymer s u r f a c e - a i r i n t e r f a c e and a p a r a m e t e r c h a r a c t e r i z i n g mass t r a n s f e r w i t h i n t h e polymer b u l k p h a s e . Crank (3) has d e s c r i b e d a m a t h e m a t i c a l e x p r e s s i o n f o r a f i l m from which a d d i t i v e i s l o s t by s u r f a c e e v a p o r a t i o n w i t h f i n i t e boundary c o n d i t i o n s . A c c o r d i n g t o t h i s model, the t o t a l amount o f a d d i t i v e l e a v i n g t h e polymer i n t i m e (t) i s e x p r e s s i b l e as a f r a c t i o n of the c o r r e s p o n d i n g amount l o s t a f t e r i n f i n i t e t i m e by: M
-
t
1
where:
M
Τ L & t D α
3
n=l
= = = = = = = =
t
n
2L
2
exp
3^(3*
