Interactions of Food, Drug, and Cosmetic Dyes with Nylon and Other

Chapter 4

Interactions of Food, Drug, and Cosmetic Dyes with Nylon and Other Polyamides 1,3

2

3

L.L.Oehrl ,C.P.Malone ,andR.W.Keown 1

Downloaded by PURDUE UNIV on November 29, 2016 | http://pubs.acs.org Publication Date: September 13, 1991 | doi: 10.1021/bk-1991-0473.ch004

Southern Testing and Research Laboratories, Inc., 3709 Airport Drive, Wilson,NC27893 2

Department of Textiles, Design, and Consumer Economics and Department of Food Science, University of Delaware, Newark, D E 19716

3

The Food, Drug and Cosmetic (FD&C) dyes are all low molecular weight acid dyes containing sulfonic acid salt auxochromes which result in interactions with polymer systems containing complementary functionalities capable of reacting to form chemical bonds. These include bonding between the amine in nylon and proteins and the group on the dye molecule. These interactions present problems in food systems using these dyes due to migration of the color between foodstuffs, packages and other non-food materials. The factors affecting the sorption of dyes from solutions encompassing concentration levels in processed foods by nylon and other polyamides are reported. This paper reports investigations into the mechanisms and kinetics of the interactions between the dyes and polymers. The effects of pH, time, temperature and dye concentration were examined. Adjuncts common to foods were investigated as to their ability to change the dye to substrate interactions.

T h e a p p e a r a n c e o f a f o o d p r o d u c t i s c o n s i d e r e d one o f t h e most c r u c i a l c o m p o n e n t s o f i t s a c c e p t a n c e b y t h e consumer. The c o l o r o f f o o d s t u f f s d e f i n e s t h e i r appearance. The importance o f p r e c o n c i e v e d i d e a s about t h e c o l o r s o f t h e s e m a t e r i a l s i s most n o t a b l e i n processed foods. T h e y may b e c o l o r e d w i t h n a t u r a l m a t e r i a l s b u t more o f t e n r e l y on s y n t h e t i c c o l o r s t o create the desired e f f e c t s . The u s e s o f t h e s e c o l o r s a r e p r i m a r i l y i n h i g h l y p r o c e s s e d foods such as s o f t d r i n k s , baked goods, 0097-6156/91AM73-0037S06.00/0 © 1991 American Chemical Society

Risch and Hotchkiss; Food and Packaging Interactions II ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

FOOD AND PACKAGING INTERACTIONS


38

c a n d i e s and d r y mixes f o r c a k e s , g e l a t i n s , p u d d i n g s and d r i n k s (1). The m a j o r i t y o f o t h e r t y p e s o f foods which r e q u i r e a l i m i t e d amount o f p r o c e s s i n g a r e n o t m a j o r users of these colors. I t i s these highly processed f o o d s w h i c h a l s o a r e most f r e q u e n t l y p a c k a g e d w i t h various types of p l a s t i c s . Due t o t h e f r e q u e n c y o f c o n t a c t s between s y n t h e t i c f o o d c o l o r s and p l a s t i c m a t e r i a l s , t h e problems o f t h e i r i n t e r a c t i o n s need t o be a d d r e s s e d . Due t o g o o d g a s b a r r i e r a n d g r e a s e r e s i s t a n c e p r o p e r t i e s , n y l o n and n y l o n c o n t a i n i n g f i l m s have been u s e d e x t e n s i v e l y f o r t h e vacuum p a c k a g i n g o f m e a t s a n d d a i r y products (2). I n a d d i t i o n t h e y have e x c e l l e n t toughness. They m a i n t a i n t h e s e good p r o p e r t i e s i n t h e p r e s e n c e o f a number o f e n v i r o n m e n t a l s t r e s s e s s u c h a s temperature. Some o b s e r v a t i o n s h a v e b e e n made t h a t when f o o d s c o n t a i n i n g d y e m a t e r i a l s a r e e x p o s e d t o polyamides, of the nylon 6 v a r i e t y , s c a l p i n g of the dyes can o c c u r . Consumer a c c e p t a n c e p l a y s a v i t a l r o l e i n t h e success o f a food product. B l e e d i n g o f c o l o r s between f o o d components c r e a t e s an u n a p p e t i z i n g a p p e a r a n c e . M i g r a t i o n o f c o l o r a n t s i n t o a package g i v e s a d i n g y and unsanitary looking product. S t a i n i n g of household m a t e r i a l s by p r o c e s s e d foods and b e v e r a g e s c o n t a i n i n g the s y n t h e t i c food dyes g e n e r a t e s c o m p l a i n t s by t h e i r u s e r s and l e a d s t o d e c r e a s e d p r o d u c t s a l e s . In order t o l i m i t s u c h p r o b l e m s , knowledge o f t h e i n t e r a c t i o n s between f o o d c o l o r a n t s and b o t h food and nonfood materials is essential. The p r e s e n t s c i e n t i f i c l i t e r a t u r e c o n t a i n s a l m o s t no i n f o r m a t i o n r e g a r d i n g t h e s e t y p e s o f s t u d i e s . Much o f t h e usage o f f o o d dyes i s e m p i r i c a l and t h e r e f o r e o r g a n i z e d d i s c u s s i o n on t h e s e i n t e r a c t i o n s i s l a c k i n g . T h e r e a r e e i g h t compounds t h a t c a r r y t h e F D a n d C designation (Table I)• Our i n i t i a l r e s p o n s e upon f i r s t e x a m i n i n g t h e d y e compounds was t o g r o u p them b a s e d o n t h e i r molecular structures. T h e r e a r e two t r i p h e n y l m e t h a n e s ( B l u e 1 a n d G r e e n 3 ) , one i n d i g o i d ( B l u e 2 ) , one x a n t h e n e (Red 3 ) , t h r e e monoazos (Red 4 , Red 4 0 , Y e l l o w 6) a n d one p y r o z o l o n e ( Y e l l o w 5 ) . Since Red number 4 i s no l o n g e r p e r m i t t e d i n f o o d m a t e r i a l s , and Red number 3 was f o u n d t o be c h e m i c a l l y v e r y d i f f e r e n t , t h e y were n o t p a r t o f t h i s s t u d y . A s t h e r e s e a r c h p r o g r e s s e d , i t was f o u n d t h a t t h e common m o i e t y b e t w e e n a l l t h e s e d y e s , t h e s u l f o n i c a c i d auxochrome a t t a c h e d i n e a c h c a s e t o a p h e n y l r i n g , was t h e most c r u c i a l e l e m e n t i n d y e t o p o l y m e r i n t e r a c t i o n s so t h a t s t r u c t u r e s a r e r e p r e s e n t e d g e n e r i c a l l y as seen here.

DYE

-


4.

OEHRL ET AL.

Interactions of FD&C Dyes with Polyamides Table I . FD&C COLORANTS

B r i l l i a n t B l u e (FD&C B l u e No 1.) F a s t G r e e n FDF (FD&C G r e e n N o . 3) Indigo

Disulfoacid

Erythrosine

(FD&C B l u e N o .

(FD&C Red N o .

3)


P o n c e a u SX (FD&C Red N o . 4) A l l u r a Red (FD&C Red N o . 40) S u n s e t Y e l l o w (FD&C Y e l l o w N o . Tartrazine

2)

(FD&C Y e l l o w N o .

6)

5)

The s u b s t r a t e s were c h o s e n b a s e d o n two c r i t e r i a (Table I I ) . The frequency o f t h e i r c o n t a c t w i t h F D and C d y e s a n d t h e p r e s e n c e o f p r o t o n a t a b l e amine g r o u p s on t h e m o l e c u l e . The p a c k a g i n g p o l y m e r was Nylon 6.6. F o r common h o u s e h o l d s u r f a c e s , m e l a m i n e f o r m a l d e h y d e r e s i n commonly known b y i t s t r a d e name F o r m i c a and t h e p r o t e i n s wool and s i l k were u s e d . As t h e f o o d m o d e l , t e x t u r i z e d s o y p r o t e i n was u s e d . The n y l o n , w o o l a n d s i l k s u b s t r a t e s were e x p o s e d t o d y e s o l u t i o n s i n t h e form o f f i b e r s k e i n s . Although there a r e c o m p a r i s o n p r o b l e m s b e t w e e n f i b e r s a n d f i l m s due t o d i f f e r e n c e s i n s u r f a c e t o volume r a t i o s , t h e s k e i n s were e a s i e r t o h a n d l e and a d e q u a t e l y s e r v e d t o d e m o n s t r a t e t h e e f f e c t s o f d y e s on t h e substrates.

Table I I . Substrates Nylon

6.6

Proteins

H-[-HN(CH ) NHCO(CH ) a

t

a

4

CO- ] -OH n

1

NH, "-Amino A c i d s - C O O

Melamine Formaldehyde Resin CHjOH NH

N

N

| NH

V

II N

iraCH^OCHa,

CNH NHC N N NH


39

40



METHODOLOGY• Colorants. Dyes b e a r i n g t h e F D a n d C d e s i g n a t i o n were p u r c h a s e d f r o m c o m m e r c i a l s o u r c e s i n t h e powder f o r m a s t h e i r sodium s a l t s . F D a n d C G r e e n N o . 3 was p u r c h a s e d f r o m T r i c o n C o l o r s (Elmwood, N J ) . The r e m a i n i n g c o l o r s were p u r c h a s e d f r o m W a r n e r J e n k i n s o n ( S t . L o u i s , M O ) . S t o c k s o l u t i o n s were p r e p a r e d i n d i s t i l l e d w a t e r a t c o n c e n t r a t i o n s o f 2000 p a r t s p e r m i l l i o n (ppm) d y e b a s e d o n t h e p e r c e n t a g e d y e ( o r p u r i t y o f t h e dye l i s t e d i n t h e p r o d u c t l i t e r a t u r e ) . New s o l u t i o n s were p r e p a r e d o n a m o n t h l y b a s i s a n d checked b e f o r e useage f o r d e g r a d a t i o n by v i s i b l e spectroscopy. Substrates. U s i n g s t a n d a r d f i v e gram s a m p l e s o f t h e f i b e r s c a l l e d s k e i n s , t h e s u b s t r a t e s were e x p o s e d t o s o l u t i o n s o f t h e d y e s u s i n g a n A h i b a WBRG 60 Texomat (Ahiba, I n c . , Charlotte, NC). This apparatus i s commonly u s e d i n t e x t i l e s c i e n c e a n d a l l o w s f o r t h e dyeing of f i b e r s under c o n t r o l l e d c o n d i t i o n s o f t e m p e r a t u r e and a g i t a t i o n . I t was a l s o u s e d f o r t h e F o r m i c a s u b s t r a t e by c u t t i n g t h e m a t e r i a l i n t o s t r i p s and a t t a c h i n g t h e s t r i p s t o t h e s k e i n h o l d e r s . The soy p r o t e i n u s e d was i n t h e f o r m o f lumps t h a t a p p r o x i m a t e a one i n c h d i c e n o r m a l l y s e e n i n m e a t s . After r e h y d r a t i n g the d r i e d p r o t e i n i n water, normal l a b o r a t o r y b e a k e r s a n d m a g n e t i c s t i r r e r s were u s e d t o expose t h i s m a t e r i a l t o the dye. pH V a r i a t i o n . F o r t h e s e s t u d i e s , 20 ppm s o l u t i o n s o f t h e d y e were p r e p a r e d . This concentration is similar t o t h e c o n c e n t r a t i o n o f c o l o r a n t s f o u n d when c o m m e r c i a l l y p r e p a r e d i n s t a n t beverage mixes a r e d i l u t e d f o r use a c c o r d i n g t o package i n s t r u c t i o n s . The pH o f t h e s o l u t i o n s was a d j u s t e d i n 1 u n i t i n c r e m e n t s o v e r a r a n g e o f 2 t o 8. T h i s i s t h e pH r a n g e o f a l m o s t a l l foodstuffs. T h e pH a d j u s t m e n t s were made u s i n g 1.0 & c i t r i c a c i d o r sodium h y d r o x i d e s o l u t i o n s . S u b s t r a t e s were e x p o s e d t o t h e s o l u t i o n s f o r a p e r i o d of 1 hour under c o n t r o l l e d temperatures. Concentration Variation. S o l u t i o n s o f t h e d y e s were p r e p a r e d by s e r i a l l y d i l u t i n g an aqueous s t o c k s o l u t i o n o f 2000 ppm d y e . The range o f c o n c e n t r a t i o n s e n c o m p a s s e d 0 . 2 ppm t o 2000 ppm w i t h a t l e a s t two p o i n t s i n each 1 0 - f o l d d i l u t i o n . A t o t a l of 5 c o n c e n t r a t i o n s were u s e d o v e r t h e r a n g e commonly s e e n i n powdered b e v e r a g e p r o d u c t s d i l u t e d t o t h e i r c o n s u m a b l e s t r e n g t h s (10 t o 50 p p m ) . The s o l u t i o n s were a d j u s t e d t o pH 3 . 0 w i t h 1.0 M c i t r i c a c i d . The s u b s t r a t e s were e x p o s e d f o r one h o u r t o t h e s e s o l u t i o n a t 25*C.


4.

OEHRLETAL.

Interactions of FD&C Dyes with Polyamides

41

Temperature E f f e c t s . S o l u t i o n s o f d y e were p r e p a r e d a s i n t h e pH v a r i a t i o n e x p e r i m e n t s . S u b s t r a t e s were e x p o s e d t o t h e s e s o l u t i o n s f o r 1 h o u r a t 2° , 25°, 50 and 1 0 0 C . c

C


Rate Determination. S o l u t i o n s o f t h e d y e s were p r e p a r e d a t c o n c e n t r a t i o n s o f 20 ppm and a d j u s t e d t o pH 3 . 0 w i t h 1.0 M c i t r i c a c i d . A s e r i e s o f n y l o n and wool s u b s t r a t e s were e x p o s e d t o t h e s o l u t i o n s a t 1 0 0 ° , 5 0 ° and 2 5 ° C f o r t i m e p e r i o d s r a n g i n g from 1 s e c o n d t o 1 hour. The a c t i o n o f t h e d y e a d s o r p t i o n was s t o p p e d b y plunging the substrates into ice baths. Mechanism Determination. F i v e s o l u t i o n s o f 20 ppm F D a n d C B l u e N o . 1 were p r e p a r e d f r o m t h e s t o c k s o l u t i o n . T h e pH o f e a c h s o l u t i o n was a d j u s t e d t o 3 . 0 w i t h one o f t h e s e a c i d s , t r i c h l o r o a c e t i c a c i d (pKa 0 . 5 2 ) , o x a l i c a c i d (pKa 1 . 2 7 ) , s u l f u r i c a c i d (pKa 3 . 0 0 ) , c i t r i c a c i d (pKa 3 . 1 3 ) a n d a c e t i c a c i d (pKa 4 . 7 6 ) . Nylon s u b s t r a t e s were e x p o s e d t o t h e s e s o l u t i o n s f o r 1 h o u r a t 25° C . Additive Effects. S o l u t i o n s o f 20 ppm d y e were p r e p a r e d f r o m s t o c k s o l u t i o n s and t h e pH o f e a c h s o l u t i o n was a d j u s t e d t o pH 3 . 0 w i t h 1.0 M c i t r i c a c i d . Sodium c h o r i d e o r sodium s u l f a t e c r y s t a l s were added t o g i v e a s e r i e s of s o l u t i o n s over a c o n c e n t r a t i o n range o f 1 juM t o 1.0 M s a l t . In another s e r i e s of experiments, c r y s t a l s of fructose, glucose or sucrose were added t o g i v e a s e r i e s o f s o l u t i o n s w i t h a r a n g e o f c o n c e n t r a t i o n o f 0 . 1 t o 1.0 g s u g a r . Quantitation. A f t e r t h e dye e x p o s u r e , t h e s u b s t r a t e s were r i n s e d w i t h w a t e r , a i r d r i e d and t h e c o l o r change was m e a s u r e d u s i n g a h a n d h e l d c o l o r i m e t e r . The r e s u l t i n g H u n t e r L * a * b * v a l u e s were g u a n t i t a t e d a s described i n the r e s u l t s s e c t i o n . U s i n g a v i s i b l e s p e c t r o p h o t o m e t e r , a measurement was made o f e a c h d y e s o l u t i o n b e f o r e i n t r o d u c t i o n o f t h e s u b s t r a t e a t t h e c h a r a c t e r i s t i c a b s o r b a n c e maximum for the i n d i v i d u a l c o l o r . A f t e r t h e t r i a l was c o m p l e t e , t h e maximum was a g a i n m e a s u r e d . The change i n a b s o r b a n c e o f t h e c o l o r a n t s o l u t i o n was g u a n t i t a t e d as d i s c u s s e d below.

RESULTS AND DISCUSSION pH V a r i a t i o n . The v a r i a t i o n s o f t h e pH o f t h e d y e s o l u t i o n s i n d i c a t e d (Figure 1), that the chemical c o m p o s i t i o n o f a f o o d i n r e g a r d s t o pH a n d p r o t o n a b l e amine c o n t e n t had a s i g n i f i c a n t e f f e c t on t h e c o l o r a t i o n o f t h e f o o d by t h e F D and C dyes and on m i g r a t i o n o f t h e dye from t h e food t o o t h e r m a t e r i a l s . W i t h t h e s y s t e m s o y p r o t e i n i n 20 ppm s o l u t i o n s o f B l u e



F i g u r e 1. Changes i n s u b s t r a t e s t a i n i n g ( A ) and dye b a t h d e p l e t i o n (B) w i t h pH v a r i a t i o n . T e x t u r i z e d soy p r o t e i n e x p o s e d f o r 1 h o u r t o 20 ppm B l u e 1 a t 2 5 ° C .



4.

OEHRLET AL.

Interactions ofFD&C Dyes with Polyamides

1, a t one h o u r e x p o s u r e t i m e s , t h e g r e a t e s t d y e u p t a k e b y t h e s u b s t r a t e o c c u r r e d b e t w e e n pH t h r e e a n d f o u r . T h i s c h a n g e was e x a m i n e d b y f o l l o w i n g two p a r a m e t e r s . T h e f i r s t was t o m o n i t o r t h e c o l o r c h a n g e o n t h e substrate (Figure 1A). U s i n g t h e H u n t e r L * a* b* s y s t e m , t h e v a r i a t i o n o f L * was f o l l o w e d a s t h i s measure. The o r d i n a t e s c a l e i s t h e n u m e r i c a l comparison o f L * v a l u e s f o r t h e s u b s t r a t e b e f o r e and a f t e r exposure t o a dye c o n t a i n i n g s o l u t i o n . T h e s e c o n d method was t o m o n i t o r t h e a b s o r b a n c e maximum o f t h e d y e s o l u t i o n i t s e l f u s i n g v i s i b l e spectroscopy. Each dye has a c h a r a c t e r i s t i c absorbance maximum v a l u e w h i c h i s d i r e c t l y r e l a t e d t o t h e c o n c e n t r a t i o n o f t h e dye i n s o l u t i o n . Comparison o f t h e dye r e m a i n i n g i n s o l u t i o n a f t e r exposure o f a s u b s t r a t e t o the o r i g i n a l c o n c e n t r a t i o n o f t h e dye i s seen i n F i g u r e IB. From t h i s , i t i s s e e n t h a t a t pH 3 . 0 , 65 p e r c e n t o f t h e d y e was removed f r o m t h e s o l u t i o n b u t a t pH 8, o n l y 5 p e r c e n t was a b s o r b e d . From e i t h e r o f t h e s e two m e a s u r e m e n t s , i t was o b s e r v e d t h a t a s t h e pH o f t h e s o l u t i o n i n c r e a s e d , t h e s t a i n i n g o f t h e s u b s t r a t e and t h e dye u p t a k e d e c r e a s e d . This p a t t e r n was f o u n d t o h o l d t r u e r e g a r d l e s s o f t h e F D a n d C d y e u s e d and t h e amine c o n t a i n i n g s u b s t r a t e monitored. I n a s y s t e m where t h e n y l o n p a c k a g e comes i n t o c o n t a c t w i t h d y e c o n t a i n i n g f o o d , t h i s phenomena c a n r e s u l t i n package s t a i n i n g . The system o f e x p o s i n g n y l o n t o dye c o n t a i n i n g s o l u t i o n m o d e l l e d t h a t o f c o l o r e d beverages packaged i n n y l o n b o t t l e s . T h e same p a t t e r n o f s t a i n i n g was s e e n b o t h i n d y e u p t a k e b y t h e n y l o n and i n c o l o r i n t e n s i t y o f t h e f i b e r s a f t e r exposure (Figure 2). Concentration V a r i a t i o n . By v a r y i n g t h e c o n c e n t r a t i o n o f t h e d y e s o l u t i o n , i t was f o u n d t h a t t h e d y e u p t a k e was d e p e n d e n t o n t h e number o f p r o t o n a t a b l e amine e n d s on t h e s u b s t r a t e . T h e v a r i a t i o n was i n e f f e c t , a t i t r a t i o n o f t h e end groups ( F i g u r e 3 ) . Dye u p t a k e c o n t i n u e d , d r o p p i n g r a p i d l y a s s a t u r a t i o n was approached. T h e s e t i t r a t i o n s were g u a n t i t a t e d i n t e r m s o f t h e l i t e r a t u r e v a l u e s o f t h e number o f amine e n d s o n t h e s u b s t r a t e s . The p a t t e r n o f t h e d a t a i n T a b l e I I I shows t h a t a s t h e number o f amine e n d s i n c r e a s e s , so d o e s t h e amount o f d y e d e p l e t e d f r o m t h e s o l u t i o n . From t h e same s t u d y , d y e u p t a k e was s e e n t o b e d e p e n d e n t on t h e number o f s u l f o n i c a c i d g r o u p s p r e s e n t on t h e d y e ( T a b l e I V ) . N y l o n bound l e s s B l u e 1 t h a n any o f t h e c o l o r s c o n t a i n i n g two s u l f o n i c s . Examination of microscopic cross sections of stained n y l o n and wool s u b s t r a t e s r e v e a l e d t h a t even a t t h e e a r l i e s t time p o i n t s , the c o l o r a n t s had m i g r a t e d completely through the f i b e r s . D i f f u s i o n through the w o o l s u b s t r a t e was f a s t e r t h a n t h r o u g h n y l o n due t o wool's greater moisture content. It w i l l reach e q u i l i b r i u m s w e l l i n g f a s t e r than nylon i n water


43


«

3

0.00

0.20 -

0.40

0.60

0.80

1.00

B

PH

F i g u r e 2. C h a n g e s i n s u b s t r a t e s t a i n i n g (A) a n d d y e b a t h d e p l e t i o n (B) w i t h pH v a r i a t i o n . N y l o n 6.6 e x p o s e d f o r 1 h o u r t o 20 ppm R e d 40 a t 2 5 * C .

PH A

100


i

25

c o

4.

OEHRL ET AL.


TABLE I I I . Blue 1 Uptake By 5 Grams F i b e r , 1 Hour, 50*C Substrate

M o l / 1 Dye D e p l e t e d

Nilli

Equivalents


Amine E n d s N y l o n 6.6

6.5

x 10-5

0.037

(3)

Silk

9.0

x 10-4

0.15

(4)

Wool

1.3

x 10-3

0.80

(5)

s o l u t i o n s due t o t h e p r e s e n c e o f h y d r o p h l i c amino a c i d side chains. Equilibrium absorption of colorant i s a c h i e v e d b y b o t h s u b s t r a t e s a f t e r a b o u t 15 m i n u t e s . A f t e r 1 h o u r , t h e d i f f e r e n c e s between t h e dye b i n d i n g w e r e a t t r i b u t e d t o more b i n d i n g s i t e s b e i n g o c c u p i e d b y t h e m o l e c u l e due t o t h e l a r g e r number o f s i t e s a b l e t o bind.

TABLE IV. Dye Uptake By 5 Grams Nylon F i b e r , 20ppm Dye, 1 Hour, 50 C 6

Color

S u l f o n i c Groups

M o l / 1 Dye D e p l e t e d

Blue 1

3

6.5

x

10-5

Blue 2

2

1.8

X

10-3

Red

2

4.5

x

10-4

2

1.9

x

10-4

40

Yellow 5

Temperature Effects. In the chemistry of t e x t i l e d y e i n g , i t h a s l o n g b e e n known t h a t t h e most e f f i c i e n t conditions for c o l o r a t i o n of f i b e r s are at b o i l i n g temperatures (5). T h i s r e s e a r c h has confirmed t h a t the i n t e n s i t y o f s t a i n i n g by food dyes i n c r e a s e d w i t h i n c r e a s i n g t e m p e r a t u r e s b u t s t a i n i n g was s t i l l v i s i b l e


45


46


a t l o w t e m p e r a t u r e s i f t h e pH c o n d i t i o n s w e r e l o w enough ( F i g u r e 4 ) . E v e n a t i c e t e m p e r a t u r e s , n y l o n was s e e n t o p i c k up 26 p e r c e n t o f t h e d y e i n s o l u t i o n , w h i l e a t room t e m p e r a t u r e , 87 p e r c e n t was r e m o v e d a t l o w pH v a l u e s . W h i l e t h e s m a l l d e c r e a s e i n t h e dye c o n t e n t o f t h e b a t h was n o t f o u n d t o be s t a t i s c a l l y s i g n i f i c a n t i n numerical terms, the o v e r a l l trend of the data i s followed at i c e temperatures. The c o r r e s p o n d i n g change o f c o l o r o f t h e n y l o n s u b s t r a t e is v i s i b l e t o t h e e y e , i n d i c a t i n g t h a t a low t e m p e r a t u r e does not o f f e r t o t a l p r o t e c t i o n from t h e exchange o f dye from t h e s o l u t i o n t o t h e n y l o n s u b s t r a t e . As the number o f a v a i l a b l e amine e n d s o n t h e s u b s t r a t e i n c r e a s e s , t h e amount o f d y e d e p l e t e d f r o m t h e s o l u t i o n i n c r e a s e s as o u t l i n e d i n T a b l e I I I . With wool, n e a r l y 90 p e r c e n t o f t h e d y e was removed f r o m a b a t h o f R e d 40 a t 2'c. A t t h e s e low t e m p e r a t u r e s , p l a s t i c p a c k a g i n g may be r e l a t i v e l y s a f e f r o m d y e m i g r a t i o n b u t e x c h a n g e o f c o l o r between o t h e r p r o t e i n s i n a food p r o d u c t o r between f o o d p r o d u c t and h o u s e h o l d s u r f a c e s w i l l be actively occurring. Rate Determination. T h e r a t e o f s t a i n i n g was a l s o found t o i n c r e a s e w i t h i n c r e a s i n g temperature. D i f f u s i o n o f the dyes i n t o a l l the polymers u s i n g the s y s t e m was v e r y f a s t w i t h t o t a l s a t u r a t i o n o c c u r r i n g i n most c a s e s b e t w e e n 5 a n d 10 m i n u t e s . U s i n g t h e wool s u b s t r a t e as an example, an A r r e n h i u s p l o t o f t h e t e m p e r a t u r e d e p e n d e n c e o f t h e r a t e c o n s t a n t s i s shown i n F i g u r e 5 f o r t h e two b l u e c o l o r s . From t h i s p l o t , t h e a c t i v a t i o n e n e r g i e s by dye d e p l e t i o n were c a l c u l a t e d t o be 42 k i l o j o u l e s p e r m o l e f o r B l u e 1 a n d 71 k i l o j o u l e s p e r m o l e f o r B l u e 2 . The r e l a t i v e c l o s e n e s s o f t h e s e v a l u e s i n d i c a t e d t h e mechanism o f c o l o r a d s o r p t i o n was t h e same d e s p i t e t h e differences i n c h e m i c a l s t r u c t u r e b e t w e e n t h e two c o l o r s . Mechanism D e t e r m i n a t i o n . I n c o n j u n c t i o n w i t h t h e pH s t u d i e s , t h e r e l a t i o n s h i p o f t h e pKa o f t h e a c i d used t o make t h e pH a d j u s t m e n t t o t h e c o l o r u p t a k e b y t h e n y l o n s u b s t r a t e was s t u d i e d i n o r d e r t o d e f i n e t h e mechanism. The s t r o n g e r t h e a c i d , t h e l e s s r e q u i r e d t o make t h e a p p r o p r i a t e pH c h a n g e t o t h r e e . This resulted i n l e s s p r o t o n s a v a i l a b l e t o i o n i z e t h e n y l o n amine e n d groups. A s t h e number o f p r o t o n s i n t h e b a t h i n c r e a s e d , more i o n i z a t i o n o c c u r r e d a n d more d y e a n i o n s w e r e removed f r o m t h e b a t h t o m a i n t a i n e l e c t r o n e u t r a l i t y on t h e f i b e r . This r e s u l t e d i n the g r e a t e s t d y e b a t h d e p l e t i o n when weak a c i d s w e r e u s e d (Figure 6). I t h a s b e e n p r o p o s e d t h e weak a c i d s a r e a b s o r b e d by n y l o n t o a g r e a t e r e x t e n t t h a n s t r o n g ones a t t h e same pH i n an u n d i s s o c i a t e d f o r m b y h y d r o g e n b o n d i n g t o t h e amide g r o u p s . T h i s would enable s i t e s o t h e r t h a n t e r m i n a l ones t o b i n d w i t h dye m o l e c u l e s (5).


OEHRL ET AL.

Interactions ofFD&C Dyes with Polyamides

47

Wool


Nylon

mol/1 Dye F i g u r e 3. Dye u p t a k e b y s u b s t r a t e s a s a f u n c t i o n dye b a t h c o n c e n t r a t i o n . S u b s t r a t e s exposed t o s o l u t i o n s o f Blue 1 f o r 1 hour a t 50*C.

of

100

/

80 -

/

2°C

// 25°C

60

50°C 40

/ 100°C /••

/ /

20

/ /

,

4

6

i

10

PH F i g u r e 4. Changes i n d y e b a t h d e p l e t i o n w i t h pH a t various temperatures. N y l o n 6 . 6 e x p o s e d t o 20 ppm Red f o r 1 h o u r . . m

American Chemical Societx Library

Risch and Hotchkiss;1155 Food and Packaging Interactions II 16th SU N.W. ACS Symposium Series; American Washington, DC, 1991. WtsMChemical oftML Society: OX. 20038


48


F i g u r e 5. A r r e n h i u s p l o t o f temperature dependence o f r a t e c o n s t a n t s o f dye b a t h d e p l e t i o n by wool e x p o s e d t o 20 ppm d y e s o l u t i o n s .

0

1

2

3

4

5

pKa F i g u r e 6. Changes i n dye b a t h d e p l e t i o n w i t h pKa variations. N y l o n 6 . 6 e x p o s e d f o r 1 h o u r t o 20 ppm Blue 1 at 2 5 ° C .


6


4.

OEHRL ET AL.


From t h e s e r e s u l t s , we h a v e e s t a b l i s h e d t h a t t h e mechanism o f t h e d y e t o amine e n d i n t e r a c t i o n i s one o f c h a r g e t o c h a r g e i n t e r a c t i o n between t h e dye a n i o n and t h e c a t i o n i c f u n c t i o n a l g r o u p on t h e s u b s t r a t e t o f o r m an e l e c t r o s t a t i c b o n d . A t h i g h a c i d c o n t e n t , t h e amine s i t e on t h e s u b s t r a t e i s i o n i z e d ( 6 ) . In the case of p r o t e i n s , s a l t l i n k a g e s b e t w e e n c h a i n s a r e b r o k e n due t o p r o t o n i z a t i o n o f c a r b o x y l ends l e a v i n g t h e p o s i t i v e l y c h a r g e d amine e n d s a v a i l a b l e f o r d y e binding. The v a l u e s o b t a i n e d from s t u d y i n g t h e dye u p t a k e b y n y l o n a n d w o o l a s a f u n c t i o n o f t i m e were u s e d t o c a l c u l a t e the r a t e constants. A p l o t of the decrease i n dye p r e s e n t i n the b a t h as a f u n c t i o n o f time t y p i c a l l y showed an i n i t i a l l i n e a r p o r t i o n u n t i l t h e d y e was e x h a u s t e d and t h e c u r v e l e v e l l e d o f f . T h i s was evidence that the s t a i n i n g followed f i r s t order kinetics. Linear regression f i t s of the l i n e a r p o r t i o n s o f t h e c u r v e s p r o d u c e d s l o p e v a l u e s w h i c h were the f i r s t order r e a c t i o n rate constants at 100°C (Table V). I t was f o u n d t h a t p r o t e i n s d e p l e t e d d y e b a t h s f a s t e r t h a n e q u i v a l e n t amounts o f n y l o n . T h i s was a c o n s e q u e n c e o f f a s t e r d i f f u s i o n o f dye due t o t h e h i g h e r m o i s t u r e c o n t e n t o f p r o t e i n s as w e l l as p r o t e i n s ' more i r r e g u l a r s u r f a c e b e i n g more c o n d u c t i v e to the r e t e n t i o n of h y d r o p h y l l i c molecules (7). This f a s t e r a t t a c h m e n t d o e s n o t mean p r o t e i n b o u n d d y e was more t i g h t l y h e l d . I t was f o u n d t h r o u g h some p r e l i m i n a r y s t u d i e s , t h a t m i g r a t i o n o f t h e dye o c c u r r e d b e t w e e n p r o t e i n s and n y l o n i n d i c a t i n g n y l o n h o l d s t h e dye m o l e c u l e s t i g h t e r . D i f f u s i o n o c c u r r e d from wool t o n y l o n b u t n o t from n y l o n t o w o o l . T h i s means t h a t c o l o r e d food p r o t e i n s are capable of s t a i n i n g nylon packages but t h a t c o l o r b l e e d from the package i n t o t h e food i s u n l i k e l y . TABLE V . k V a l u e s

(Min-1)

Color

Nylon

Wool

Blue 1 Red 40 Yellow 5

0.878 2.72 1.59

1.97 3.62 3.02

T h e number o f s u l f o n i c a c i d g r o u p s p r e s e n t o n t h e d y e h a d an e f f e c t on d e p l e t i o n r a t e s . The c a l c u l a t e d r a t e c o n s t a n t s p r o v e d t h a t t h e c o l o r s c o n t a i n i n g two a c i d g r o u p s , Red 40 a n d Y e l l o w 5, were d e p l e t e d f r o m t h e dye b a t h f a s t e r t h a n the B l u e 1 which has t h r e e (Table V ) . A d d i t i v e E f f e c t s . In the i n t e r e s t of p o s s i b l y m a n i p u l a t i n g dye m i g r a t i o n from f o o d t o o t h e r p o l y m e r s



50


P

•

*v

•

0.00 0.00

0.20

0.40

0.60

0.80

1.00

Interactions of Food, Drug, and Cosmetic Dyes with Nylon and Other

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