Barrier Polymers and Structures - American Chemical Society

Chapter 18

Diffusion and Sorption of Linear Esters in Selected Polymer Films 1

2

1

G.Strandburg ,P. T.DeLassus ,and B. A. Howell

Downloaded by TUFTS UNIV on November 27, 2015 | http://pubs.acs.org Publication Date: May 9, 1990 | doi: 10.1021/bk-1990-0423.ch018

1

Department of Chemistry, Central Michigan University, Mt. Pleasant, MI 48859 Barrier Resins and Fabrication Laboratory, The Dow Chemical Company, 1603 Building, Midland, MI 48674

2

Polymers are being used in more sophisticated food-packaging applications. These applications must do more than keep the food safe from oxygen damage. They must preserve the attractive flavor profile of the food. In short, the package must assist in flavor management. Permeation of flavor (and aroma) compounds in polymers can be part of flavor management in two general ways. First, unintended species can enter the food by permeation from the environment or by migration from the package itself. Second, the flavor and aroma molecules of the food may leave by permeation through the package or by simple sorption by the package. The flavor profile may be made unacceptable by broad diminution or by selective removal of a few components. This paper will describe experiments that concern this second area of flavor management. The experiments were directed toward the interactions between linear esters and some of the films that are important for food-packaging applications. The analysis of the data will focus on the important solution process with special attention for the thermodynamics. Framework f o r E x p e r i m e n t s

Aromas. Nine l i n e a r e s t e r s were i n c l u d e d i n t h i s s t u d y . They a r e l i s t e d i n T a b l e I . E s t e r s comprise an i m p o r t a n t f l a v o r g r o u p . Not a l l o f t h e s e e s t e r s a r e f o u n d i n f o o d . These s p e c i f i c e s t e r s p r o v i d e a s y s t e m a t i c approach t o a complex problem. They were p u r c h a s e d f r o m A l d r i c h C h e m i c a l Company as p a r t o f t h e " F l a v o r s and F r a g r a n c e s K i t #1: E s t e r s . " 0097-^6156/90/0423-0333$06.00/0 © 1990 American Chemical Society

In Barrier Polymers and Structures; Koros, W.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

334

BARRIER POLYMERS AND STRUCTURES

Table

I

L i n e a r E s t e r s f o r Permeation E s t e r Name

Number o f

Boiling

Carbons

5 5 6 7 7 8 9 10 10

Methylbutyrate Ethylpropionate Ethylbutyrate Propylbutyrate Ethylvalerate


Point

Ethylhexanoate Ethylheptanoate Ethyloctanoate Hexylbutyate

% Purity

102 99 120 142 144 168 188 206 208

98+ 97 + 98 + 98+ 98+ 98+ 98+ 98+ 98+

F i l m s . Three f i l m s were i n c l u d e d i n t h i s s t u d y . polyethylene i s not

(LDPE) was

considered

t o be

CAS

Number

*C

623- -42· -7 105- -37- -3 105- -54- -4 105- -66- -8 539- -82- -2 123- -66- -0 106- -30- -9 106- -32- -1 2639--63- -6

Low

density

i n c l u d e d as a r e p r e s e n t a t i v e p o l y o l e f i n . a b a r r i e r polymer.

It

I t has p e r m e a b i l i t i e s t o

s e l e c t e d aroma compounds s l i g h t l y h i g h e r t h a n the p e r m e a b i l i t i e s o f polypropylene

(1).

and h i g h d e n s i t y p o l y e t h y l e n e

c h l o r i d e copolymer

(co-VDC) f i l m was

A vinylidene

i n c l u d e d as an example o f a

b a r r i e r t h a t i s u s e f u l i n b o t h d r y and humid c o n d i t i o n s . was

made from a Dow

r e s i n which has

been d e s i g n e d

packaging a p p l i c a t i o n s . A hydrolyzed (EVOH) f i l m was humidity

ethylene-vinylacetate

o f 38

The

mole%

film

copolymer

polymer was

a blend of r e s i n s with

total

ethylene.

These f i l m s were t e s t e d as monolayers about 2.5 thick.

The

rigid

i n c l u d e d as an example o f a b a r r i e r f i l m t h a t i s

sensitive.

composition

for

χ

10~^m(=l m i l )

They would t y p i c a l l y be u s e d i n m u l t i l a y e r s t r u c t u r e s ;

however, t h e i n d i v i d u a l p e r m e a b i l i t i e s can be combined t o p r e d i c t the b e h a v i o r

of m u l t i l a y e r s .

Instrument.

The

a n a l y t i c a l instrument

shown s c h e m a t i c a l l y i n F i g u r e built

at The

f l a v o r and

Dow

f o r these

This instrument

aroma compounds t h r o u g h polymer f i l m s . instrument

solutions,

the e x p e r i m e n t a l

and

spectrometer.

The

was

designed

and

The

gas

handling

c o n t a i n s t h e plumbing, c o n t a i n e r s o f aroma film.

This enclosure

the temperature can be c o n t r o l l e d , + 1"C,

about 150"C.

experiments i s

C h e m i c a l Company f o r m e a s u r i n g t h e p e r m e a t i o n o f

s e c t i o n of the and

1.

i s insulated,

from subambient

d e t e c t o r i s a H e w l e t t - P a c k a r d 5970 mass

More d e t a i l s are a v a i l a b l e

(2).


to

18.

STRANDBURGETAL.

Diffusion and Sorption of Linear Esters

335

Film


©Κι

HP 5970

Control & Analysis

Mass

Computer

ΚΞ1 Display

Spectrometer Gas Handling

F i g u r e 1.

Schematic o f Instrument

T h i s i n s t r u m e n t i s u s e d i n two g e n e r a l ways. F i r s t , w i t h each new compound, a mass s p e c t r u m i s g e n e r a t e d t o i d e n t i f y t h e most p o p u l o u s and u n i q u e i o n f r a g m e n t s . Second, f o r a c t u a l p e r m e a t i o n e x p e r i m e n t s , t h e i n s t r u m e n t i s programmed t o m o n i t o r s e l e c t e d i o n fragments, t y p i c a l l y t h r e e , f o r each o f t h e aromas i n v o l v e d . When a s i n g l e permeant i s used, t h e t h r e e most p o p u l o u s i o n fragments may be chosen. However, when mixed permeants a r e used, s i g n i f i c a n t d e g e n e r a c i e s a r e a v o i d e d . A l l t h e e x p e r i m e n t s o f t h i s s t u d y were done w i t h a s i n g l e permeant. The r e s p o n s e o f t h e i n s t r u m e n t was d e t e r m i n e d t o be l i n e a r i n t h e o p e r a t i n g range and beyond, b o t h a t h i g h e r and lower c o n c e n t r a t i o n s . In a l l e x p e r i m e n t s , t h e f o l l o w i n g sequence was used. First, a c a l i b r a t i o n experiment was c o m p l e t e d by p r e p a r i n g a v e r y d i l u t e s o l u t i o n o f t h e permeant i n n i t r o g e n i n t h e one l i t e r f l a s k and i n t r o d u c i n g some o f t h e gaseous s o l u t i o n d i r e c t l y t o t h e mass spectrometer v i a a s p e c i a l l y designed i n t e r f a c e . A known c o n c e n t r a t i o n and a measured r e s p o n s e y i e l d a c a l i b r a t i o n c o n s t a n t . Then a p e r m e a t i o n experiment was c o m p l e t e d by p r e p a r i n g a d i l u t e s o l u t i o n o f t h e permeant i n n i t r o g e n i n t h e t h r e e l i t e r f l a s k and r o u t i n g t h i s gaseous s o l u t i o n p a s t t h e purged, e x p e r i m e n t a l f i l m . The d e t e c t o r r e s p o n s e was r e c o r d e d as a f u n c t i o n o f t i m e f o r subsequent a n a l y s i s .


336



The computer was u s e d t o program and c o n t r o l t h e mass s p e c t r o m e t e r and t o c o l l e c t and a n a l y z e t h e d a t a . The computer was e q u i p p e d w i t h a CRT and a p r i n t e r . The advantages o f t h i s i n s t r u m e n t a r e a) i t c a n be u s e d w i t h v e r y d i l u t e s o l u t i o n s o f permeants, b) m u l t i p l e permeants may be u s e d i n a s i n g l e experiment, c) h u m i d i t y may be u s e d by a d d i n g water or a s a t u r a t e d s a l t s o l u t i o n t o t h e t h r e e l i t e r f l a s k , d) t h e e n t i r e p r o g r e s s o f t h e experiment c a n be m o n i t o r e d as a f u n c t i o n o f t i m e , and e) a wide range o f t e m p e r a t u r e s c a n be used. V a r i a b l e s . A range o f t e m p e r a t u r e s was u s e d w i t h t h e b a r r i e r f i l m s — co-VDC and EVOH. Warm t e m p e r a t u r e s were u s e d because t h e s e b a r r i e r polymers had low p e r m e a b i l i t i e s and low d i f f u s i o n c o e f f i c i e n t s at c o o l e r temperatures. E x p e r i m e n t s a t lower t e m p e r a t u r e s would have t a k e n p r o h i b i t i v e l y l o n g and may have been below t h e d e t e c t i o n l i m i t o f t h e i n s t r u m e n t . Data a t s e v e r a l t e m p e r a t u r e s a l l o w a more s o p h i s t i c a t e d a n a l y s i s o f t h e p e r m e a t i o n process. The LDPE f i l m was t e s t e d a t a s i n g l e , low t e m p e r a t u r e . A s i n g l e c o n c e n t r a t i o n o f permeant was u s e d f o r a l l t h e experiments. A p p r o x i m a t e l y two m i c r o l i t e r s o f f l a v o r / a r o m a compound were u s e d i n t h e t h r e e l i t e r f l a s k . T h i s c o r r e s p o n d s t o about 150 ppm (molar) and v a r i e s from e s t e r t o e s t e r depending upon t h e m o l e c u l a r weight. P r e v i o u s e x p e r i m e n t s have shown t h a t , i n t h i s range o f c o n c e n t r a t i o n s , t h e p e r m e a t i o n p r o c e s s i s n o t a s t r o n g f u n c t i o n o f t h e permeant c o n c e n t r a t i o n (3,4). T a b l e I I l i s t s t h e p a r t i a l p r e s s u r e (Ρ ) a t the experimental temperatures f o r t h e f i v e c a r b o n e s t e r and t h e n i n e c a r b o n e s t e r . A l s o i n c l u d e d a r e the vapor p r e s s u r e s ( P ) a t t h e s e t e m p e r a t u r e s , and t h e r a t i o P / P . χ

Q

X

Q

Table IL Partial Pressure at the Experimental Temperature for Five-and Nine-Carbon Esters

Ester

C-5

T(C)

P

105

1,.1

0

(Pa)

X

10

5

1

Ρ

χ

p

x

19

1..7

X

(Pa)

2

/ p

o

ΙΟ"

4

4

C-5

95

8,.1

X

10

4

18

2..2

X

10"

C-5

85

5,.9

X

10

4

18

3..0

X

10~

4

C-5

25

4,.5

X

10

3

15

3..3

X

10"

3

C-9

105

7,.1

X

10

3

12

1,.7

X

10"

3

C-9

95

4,.5

10

3

12

2 .7

X

10"

3

C-9

85

2,.8

10

3

11

3,.9

X

10"

3

10

1

9

1,.1

X

ίο-

C-9

25

8,.3

X X X

1) From t h e A n t o i n e e q u a t i o n 5 2) F o r a 2/iL sample


1

18. STRANDBURGETAL.

337

Diffusion and Sorption ofLinear Esters

H u m i d i t y was t e s t e d o n l y q u a l i b a c i v e l y i n a s i n g l e e x p e r i m e n t . In an experiment w i t h t h e EVOH f i l m a n d e t h y l v a l e r a t e a t 110*C, 0.25 m i l l i l i t e r s o f water was i n j e c t e d i n t o t h e t h r e e l i t e r f l a s k a f t e r the p e r m e a t i o n experiment h a d r e a c h e d s t e a d y s t a t e . W i t h i n seconds, the p e r m e a t i o n r a t e i n c r e a s e d t o above the d e t e c t i o n l i m i t o f t h e mass s p e c t r o m e t e r . T h i s was c o n s i s t e n t w i t h p r i o r e x p e r i e n c e wherein the p e r m e a b i l i t y and t h e d i f f u s i v i t y i n an EVOH f i l m i n c r e a s e by a f a c t o r o f about 1000 i n t h e p r e s e n c e o f m o i s t u r e (6). No more e x p e r i m e n t s were done w i t h h u m i d i t y f o r t h i s s t u d y .


Framework f o r

Analysis.

F o r a t h o r o u g h a n a l y s i s o f aroma t r a n s p o r t i n f o o d p a c k a g i n g , t h e p e r m e a b i l i t y (P) and i t s component p a r t s - t h e s o l u b i l i t y c o e f f i c i e n t (S) and t h e d i f f u s i o n c o e f f i c i e n t o r d i f f u s i v i t y (D) a r e needed. These t h r e e p a r a m e t e r s a r e r e l a t e d as shown i n E q u a t i o n 1.

(1)

Ρ = D χ S

The p e r m e a b i l i t y i s u s e f u l f o r d e s c r i b i n g the t r a n s p o r t r a t e a t steady s t a t e . The s o l u b i l i t y c o e f f i c i e n t i s u s e f u l f o r d e s c r i b i n g t h e amount o f aroma t h a t w i l l be a b s o r b e d by t h e package w a l l . The d i f f u s i o n c o e f f i c i e n t i s u s e f u l f o r d e s c r i b i n g how q u i c k l y t h e permeant aroma m o l e c u l e s move i n the f i l m and how much time i s r e q u i r e d t o reach steady s t a t e . E q u a t i o n 2 d e s c r i b e s s t e a d y s t a t e p e r m e a t i o n where Δ Μ i s t h e χ

—χ At

=

p

A

Δ

Ρχ

(2)

L

q u a n t i t y o f permeant χ t h a t goes t h r o u g h a f i l m o f a r e a A and t h i c k n e s s L i n a time i n t e r v a l At. The d r i v i n g f o r c e f o r t h e p e r m e a t i o n i s g i v e n as t h e p r e s s u r e d i f f e r e n c e o f t h e permeant a c r o s s the b a r r i e r , Δ ρ . I n an e x p e r i m e n t , AM /At i s measured a t s t e a d y s t a t e w h i l e A a n d L a r e known and Δ ρ i s e i t h e r measured o r calculated separately. The d i f f u s i o n c o e f f i c i e n t c a n be d e t e r m i n e d from the t r a n s i e n t p o r t i o n o f a complete p e r m e a t i o n e x p e r i m e n t . F i g u r e 2 shows how t h e t r a n s p o r t r a t e o r d e t e c t o r r e s p o n s e v a r i e s w i t h time d u r i n g a complete e x p e r i m e n t . A t t h e b e g i n n i n g o f an e x p e r i m e n t , t = 0, a c l e a n f i l m i s exposed t o the permeant on the u p s t r e a m s i d e . I n i t i a l l y , the p e r m e a t i o n r a t e i s e f f e c t i v e l y z e r o . Then "break t h r o u g h " o c c u r s , and the t r a n s p o r t r a t e r i s e s t o s t e a d y s t a t e . The d i f f u s i o n c o e f f i c i e n t c a n be c a l c u l a t e d i n e i t h e r o f two ways. E q u a t i o n 3 uses t^^r time t o r e a c h a t r a n s p o r t r a t e t h a t i s one-half of the steady s t a t e rate (7). χ

X

χ

t

D

h

e

-

L

2

7.2 t

(3) 1

/

2


338


Equation

4 uses t h e

s l o p e i n t h e t r a n s i e n t p a r t o f t h e c u r v e and D

=

0.176

L

the

2

(slope) Rss

( 4 )


s t e a d y s t a t e r e s p o n s e Rss (8) . A f t e r Ρ has been d e t e r m i n e d w i t h E q u a t i o n 2 and D has been d e t e r m i n e d w i t h E q u a t i o n 3 (or 4 ) , and t h e n S can be d e t e r m i n e d w i t h E q u a t i o n 1.

Time Figure

2.

R e l a t i v e Transport

^-

Rate as a F u n c t i o n

o f Time

Many s e t s o f u n i t s are u s e d t o r e p o r t t h e p e r m e a b i l i t y i n t h e literature. T h i s p a p e r w i l l use SI u n i t s i n t h e f o l l o w i n g way. For E q u a t i o n 2 t o be v a l i d , the p e r m e a b i l i t y must have d i m e n s i o n s o f q u a n t i t y o f gas t i m e s t h i c k n e s s d i v i d e d by a r e a - t i m e - p r e s s u r e . If t h e k i l o g r a m i s u s e d t o d e s c r i b e t h e q u a n t i t y o f gas and t h e p a s c a l i s u s e d as t h e u n i t o f p r e s s u r e , t h e n u n i t s o f p e r m e a b i l i t y a r e kg-m/m «s«Pa. T h i s u n i t i s v e r y l a r g e and a cumbersome exponent often results. A more c o n v e n i e n t u n i t , t h e M o d i f i e d Z o b e l U n i t , (1 90 9 — —. » MZU = 10 * kg^m/itr* »s »Pa) , was d e v e l o p e d f o r f l a v o r p e r m e a t i o n . Z o b e l p r o p o s e d a s i m i l a r u n i t e a r l i e r (9) . The u n i t s o f t h e d i f f u s i o n c o e f f i c i e n t a r e m /s. The u n i t s o f t h e s o l u b i l i t y c o e f f i c i e n t are kg/m Pa. 2

υ

2

3


18. STRANDBURG ET AL·

339


E q u a t i o n s 1, 2, and 3 a r e working d e f i n i t i o n s o f P, D, and S. No c o r r e c t i o n s a r e made f o r t h e c r y s t a l l i n i t y i n any o f t h e e x p e r i m e n t a l samples o f t h i s s t u d y . F o r most s i m p l e c a s e s , P, D, and S a r e s i m p l e f u n c t i o n s o f temperature as g i v e n i n E q u a t i o n s 5, 6, and 7. (Τ) = P

D

(T) = D

S

(Τ) - S

0

Q

Q

exp (-Ep/RT)

(5)

exp (-E /RT)

(6)

exp (-AH /RT)

(7)

D

S

where, P , D , and S a r e c o n s t a n t s , Τ i s t h e a b s o l u t e t e m p e r a t u r e , and R i s t h e gas c o n s t a n t . Ε i s t h e a c t i v a t i o n energy f o r permeation. E i s t h e a c t i v a t i o n energy f o r d i f f u s i o n , and A H i s t h e heat o f s o l u t i o n . I f l o g Ρ d a t a a r e p l o t t e d on t h e v e r t i c a l a x i s o f a graph and T"" i s p l o t t e d on t h e h o r i z o n t a l a x i s , a straight line w i l l result. The s l o p e w i l l be -0.43 E /R. The d i f f u s i o n c o e f f i c i e n t and s o l u b i l i t y c o e f f i c i e n t behave s i m i l a r l y . E q u a t i o n s 1, 5, 6, and 7 c a n be m a n i p u l a t e d t o y i e l d e q u a t i o n 8 which r e l a t e s t h e a c t i v a t i o n e n e r g i e s and t h e heat o f s o l u t i o n . Q


Ρ

Q

Q

D

g

1

p

E

p

= E

+ ΔΗ

D

(8)

3

E q u a t i o n s 1-7 were d e v e l o p e d f o r gas p e r m e a t i o n t h r o u g h r u b b e r y polymers. They must be u s e d w i t h c a u t i o n w i t h g l a s s y polymers and/or o r g a n i c v a p o r s t h a t i n t e r a c t s t r o n g l y w i t h t h e b a r r i e r . The heat o f s o l u t i o n c a n be s e p a r a t e d i n t o two b a s i c p a r t s namely, t h e heat o f c o n d e n s a t i o n (AH ) and t h e heat o f m i x i n g ( A H ) . Equation 9 expresses the r e l a t i o n s h i p C

ΔΗ The h e a t s o f experiments, literature. 9. The heat relationship

3

=

ΔΗ

α

m

+

AH

m

(9)

s o l u t i o n can be d e t e r m i n e d e x p e r i m e n t a l l y i n t h e s e and t h e h e a t s o f c o n d e n s a t i o n a r e a v a i l a b l e i n t h e The heat o f m i x i n g can t h e n be c a l c u l a t e d w i t h E q u a t i o n o f m i x i n g d e s c r i b e s t h e b a s i c thermodynamic between t h e polymer and t h e p e n e t r a n t .

EXPERIMENTS T y p i c a l Experiment. F i g u r e 3 shows t h e r e s u l t s o f a t y p i c a l experiment w i t h t h e co-VDC f i l m . The permeant was e t h y l b u t y r a t e . The experiment was done a t 100'C. The warm t e m p e r a t u r e c a u s e d t h e experiment t o p r o g r e s s q u i c k l y . Three i o n s fragments, m/z = 60, 71, and 88 were m o n i t o r e d by t h e mass s p e c t r o m e t e r . The t o t a l i o n i n t e n s i t y o f t h e s e t h r e e i o n s i s shown h e r e . The f i r s t r e s p o n s e i n F i g u r e 3 i s due t o c a l i b r a t i o n . Here 2.4 u l o f a 0.5% s o l u t i o n o f e t h y l b u t y r a t e i n acetone was i n j e c t e d i n t o t h e 1 - l i t e r f l a s k and d i l u t e d with nitrogen. The r e s u l t i n g gaseous s o l u t i o n was i n t r o d u c e d i n t o t h e mass s p e c t r o m e t e r v i a t h e i n t e r f a c e .


340

BARRIER POLYMERS A N D STRUCTURES

A f t e r t h e b a s e l i n e was o b t a i n e d a g a i n a t 34 m i n u t e s i n t o t h e run, t h e p e r m e a t i o n experiment began. Here 2.5 u l o f e t h y l b u t y r a t e had been i n j e c t e d i n t o t h e 3 - l i t e r f l a s k and d i l u t e d w i t h n i t r o g e n b e f o r e b e i n g c i r c u l a t e d p a s t t h e upstream s i d e o f t h e f i l m . B r e a k t h r o u g h o c c u r r e d a t about 38 minutes, and s t e a d y s t a t e was r e a c h e d a t 90 t o 100 min.


TIC

of DRTR:EB/S100.D

ϋ 52.0E4

:

c j j 10000: (C

W » • • 1 · · · 1·· · 1 · • 20

40

60

80

100

120

F i g u r e 3 . P e r m e a t i o n Experiment o rηE. t h) ylbutyrate i n a Τ1 me (mf 1 V i n y l i d e n e C h l o r i d e Copolymer F i l m a t 100"C

Organized Results. Many c o m b i n a t i o n s o f permeant e s t e r , f i l m , and t e m p e r a t u r e were s t u d i e d . F i g u r e 4 shows t h e p e r m e a b i l i t y r e s u l t s f o r a s i n g l e e s t e r - f i l m combination at 5 d i f f e r e n t temperatures. S i m i l a r graphs were made f o r t h e o t h e r e s t e r - f i l m c o m b i n a t i o n s . F i g u r e 5 shows p e r m e a b i l i t i e s o f a l l t h e e s t e r s a t 85"C i n t h e co-VDC f i l m . These d a t a were t a k e n from graphs l i k e F i g u r e 4. F i g u r e 6 shows t h e d i f f u s i o n c o e f f i c i e n t s o f a l l t h e e s t e r s a t 85"C i n t h e co-VDC f i l m . F i g u r e 7 shows t h e s o l u b i l i t y c o e f f i c i e n t s o f a l l t h e e s t e r s i n t h e co-VDC f i l m . Figure 8 i s a r e - p l o t of the d a t a i n F i g u r e 7 w i t h t h e b o i l i n g p o i n t o f t h e e s t e r as t h e horizontal axis. The a c t i v a t i o n e n e r g i e s f o r p e r m e a t i o n i n t h e co-VDC f i l m were a l l positive. The a c t i v a t i o n e n e r g i e s f o r t h e d i f f u s i o n c o e f f i c i e n t a r e shown i n F i g u r e 9. The h e a t s o f s o l u t i o n f o r t h e e s t e r s a r e shown i n F i g u r e 1 0 . Fewer e s t e r s were u s e d i n e x p e r i m e n t s w i t h t h e EVOH because t h e t r e n d s o b s e r v e d w i t h t h e co-VDC f i l m were a p p a r e n t . Figures 11, 12, and 13 show t h e p e r m e a b i l i t i e s , d i f f u s i o n c o e f f i c i e n t s , and s o l u b i l i t y c o e f f i c i e n t s f o r t h e e s t e r s a t 85"C i n t h e EVOH f i l m . F i g u r e s 14 and 15 show t h e a c t i v a t i o n e n e r g i e s f o r d i f f u s i o n and t h e heats of s o l u t i o n .


18.

STRANDBURGETAL.


lOOOOOr

•H ιΗ


JJSS S ^ Pi Φ

10000+

α.

ιοοο

0.0030

0.0026

F i g u r e 4. P e r m e a b i l i t y o f E t h y l b u t y r a t e V i n y l i d e n e C h l o r i d e Copolymer F i l m

in a

lOOOOOr

o ο •H iH

10000+

8

OH

ο ο -4-

5

β

7

8

4-

θ

10

Number of Carbons i n B s t e r Figure

5. P e r m e a b i l i t y o f E s t e r s a t 85'C V i n y l i d e n e C h l o r i d e Copolymer

in a


341

342


4>

Ο

a

Φ

•Η

Ο

υ •rl «Η «Η

1β-14+

Φ

Ο

d α 0 ^

ο


3 «Η «Η •Η Ρ

le-15-

4-

5

4-

β

7

4-

8

9

10

Number of Carbons i n E s t e r F i g u r e 6. D i f f u s i o n C o e f f i c i e n t a t 85'C o f E s t e r s i n a V i n y l i d e n e C h l o r i d e Copolymer F i l m

Ο.ΙΟΟτ

8 α Φ

•Η

υ •Η *Η «Η

^

Φ οβ 0 Û4

ο2

0.010+

i

3 0

ο ο

CO

0.0015

4-

4-

6

7

4-

8

θ

10

Number of Carbons i n E s t e r Figure

7. S o l u b i l i t y C o e f f i c i e n t a t 85'C o f E s t e r s i n a V i n y l i d e n e C h l o r i d e Copolymer F i l m


18.

STRANDBURG ET A L


O.lOOr

43 α Φ

•Η

U

•Η «Η «Η

0

s i

°

ο

g 0.010+

* "Sa

Ο Ο


rH •Η ιΗ

Ο Ο

Ο CO

J

0.001

100

120

140

160

180

200

220

B o i l i n g Point Figure

8. S o l u b i l i t y C o e f f i c i e n t s o f E s t e r s a t 85*C i n a V i n y l i d e n e C h l o r i d e Copolymer F i l m

32

T

30f u

φ4 α

28+ Φ

§^

26+

•rl rH 4J (β

•Η

43

«3

Ο

O

24+

>X

Ο

Ο

^

22+ 20+

10 Number of Carbons i n E s t e r Figure

9. A c t i v a t i o n Energy f o r D i f f u s i o n o f E s t e r s i n a V i n y l i d e n e C h l o r i d e Copolymer F i l m


343

344

BARRIER P O L Y M E R S AND STRUCTURES

-4-r

-5-

-7--

Ο

o " - ^

°

-10»

ο


-11-

Ο

-12-13"

-14-1

1

1

1-

10 Number of Carbons

F i g u r e 10. Heats o f S o l u t i o n f o r E s t e r s i n a V i n y l i d e n e C h l o r i d e Copolymer F i l m

ΙΟΟΟτ

43 •rl rH

ri CSJ

0 ^

J

100

1

1

1

1

h

5

6

7

8

9

Number of Carbons Figure

11.

Permeability Coefficient of E s t e r s Through EVOH

a t 85'C


18.


STRANDBURGETAL.

α •Η

υ

10 •14 +

•Η «Η «Η

Ο ϋ

^
M


•H

^

43

30+

3

25-

+-

5

6

7

8

9

Number of Carbons F i g u r e 14. A c t i v a t i o n Energy o f D i f f u s i o n f o r E s t e r s Through EVOH

-1+ -2+

δ

el

-3+

% -4+

-5+ -6+ -7·

4-

1

6

7

f—

8

Number of Carbons F i g u r e 15. Heats o f S o l u t i o n f o r E s t e r s i n an EVOH Copolymer F i l m


18. STRANDBURG ET AL.

347


F i g u r e s 16 t h r o u g h 18 show the

results

f o r the

LDPE f i l m .

Discussion. In each f i l m the p e r m e a b i l i t i e s i n c r e a s e as t h e s i z e o f the e s t e r i n c r e a s e s . The d a t a show t h a t t h i s r e s u l t i s d r i v e n by the s o l u b i l i t y c o e f f i c i e n t . The d i f f u s i o n c o e f f i c i e n t s d e c r e a s e as the s i z e o f the e s t e r i n c r e a s e s ; however, t h e s o l u b i l i t y c o e f f i c i e n t s i n c r e a s e g r e a t l y as t h e s i z e o f t h e e s t e r i n c r e a s e s . The q u a l i t a t i v e e f f e c t o f permeant s i z e on the d i f f u s i o n c o e f f i c i e n t was e x p e c t e d . A r e c e n t s i m p l e a n a l y s i s q u a n t i f i e d the r e l a t i o n s h i p between D and permeant s i z e f o r s p h e r i c a l permeants up t o Cg i n s e v e r a l polymers ( 10) . That a n a l y s i s i s n o t d i r e c t l y a p p l i c a b l e h e r e s i n c e t h e s e permeants a r e l i n e a r and l a r g e r . A n o t h e r s t u d y q u a n t i f i e s t h e r e l a t i o n s h i p between D and permeant s i z e f o r l i n e a r a l k a n e s i n p o l y e t h y l e n e (11). The d i f f u s i o n c o e f f i c i e n t a t 25"C was o b s e r v e d t o d e c r e a s e from 3.9 χ 1 0 " m^/s f o r n-hexane t o 2.2 χ 10 m^/s f o r n-nonane. The d i f f u s i o n c o e f f i c i e n t s f o r the e s t e r s i n the p r e s e n t s t u d i e s seem t o change comparable amounts. A t 85"C i n co-VDC and EVOH, t h e d i f f u s i o n c o e f f i c i e n t s f o r the e s t e r s d e c r e a s e b y about 3x as t h e number o f atoms ( e x c l u d i n g hydrogen) i n the backbone i n c r e a s e s from 6 t o 9 (5 carbons p l u s one oxygen t o 8 carbons p l u s one oxygen). The d i f f e r e n c e would be g r e a t e r a t 25'C because t h e a c t i v a t i o n e n e r g i e s f o r d i f f u s i o n are l a r g e r f o r the l a r g e r e s t e r s . This i s c o n s i s t a n t w i t h the r e s u l t s o f L a n d o i s - G a r z a and H o t c h k i s s f o r an e s t e r s e r i e s i n p o l y v i n y l a l c o h o l (12). At 30"C i n LDPE, t h e d i f f u s i o n c o e f f i c i e n t s d e c r e a s e b y about 30% as t h e number o f atoms i n the backbone o f t h e e s t e r i n c r e a s e s f r o m 6 t o 9. S t u d i e s o f a l k a n e s i n low d e n s i t y p o l y e t h y l e n e show s i m i l a r t r e n d s (13).


11

_

1

1

8

io T

o ο ο

100 +

ο

5

6

7

8

9

10

Number o f Carbons F i g u r e 16.

P e r m e a b i l i t y a t 30 C f o r e

Library 115S 16tft St., N.W. In Barrier Polymers and Structures; Koros, W.; Washington, O.C. 20038 ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

348

BARRIER POLYMERS A N D STRUCTURES

43

10r l 2 4 0 1«

•H


CQ «H «H •H

Q

4

5

-+6

7

Number

8

9

10

o f Carbons

F i g u r e 17. D i f f u s i o n C o e f f i c i e n t o f E s t e r s i n a LDPE F i l m

a t 30'C

l.OOOr

0.100+

«Η «Η

ο +> μ •H rH •Η

w

0.010+

rH

0 CO

0.001

—I 100

1 120

1 140

Boiling

1 160 Point

F— 180

200

°C

F i g u r e 18. S o l u b i l i t y C o e f f i c i e n t a t 30*C v s . B o i l i n g P o i n t o f E s t e r i n a LDPE F i l m


18. STRANDBURG ET AL»

349



The a c t i v a t i o n e n e r g i e s f o r d i f f u s i o n i n t h e co-VDC and EVOH f i l m s i n c r e a s e as t h e s i z e o f t h e e s t e r i n c r e a s e s . T h i s i s e x p e c t e d s i n c e c o o p e r a t i v e m o t i o n o f l a r g e r zones o f t h e polymer m a t r i x a r e necessary t o c r e a t e l a r g e r holes f o r passage. The a c t i v a t i o n e n e r g i e s f o r d i f f u s i o n i n LDPE were n o t d e t e r m i n e d . The s o l u b i l i t y c o e f f i c i e n t s make i n t e r e s t i n g c o n t r i b u t i o n s t o the p e r m e a b i l i t i e s . The s o l u t i o n p r o c e s s o f t h e s e gas phase permeants c a n be s e p a r a t e d f o r a n a l y s i s i n t o two components c o n d e n s a t i o n and m i x i n g . Table I I I contains the heats of condensation f o r the experimental e s t e r s . Table I I I also contains t h e h e a t s o f s o l u t i o n i n t h e polymer f i l m s from l i n e a r f i t s o f t h e d a t a i n F i g u r e s 10 and 15. F i n a l l y , T a b l e I I I c o n t a i n s t h e h e a t s o f mixing f o r the e s t e r s i n the f i l m s . The h e a t s o f m i x i n g were c a l c u l a t e d u s i n g e q u a t i o n 9.

Table III Heats of Condensation and Solution for Experimental Esters Number o f

AH

ΔΗ

Q

Carbons

a)

1

3

ΔΗ

3

AH

m i x

AH

m i x

co-VDC

EVOH

co-VDC

EVOH

-8..4

-1..6

0..4

7.3

5

-8..88

6

-9..47

7

-10. .48

1

-9..7

-2..8

0..8

7.7

8

-11. ,20

2

-10, .3

-3,.5

0..9

7.7

9

-11. .92

-10, .9

-4,.1

1..0

7.9

10

-12, .87

-9..1

2

-11, .5

—— ——

0..4

1..4

kcal/mole

1) average

o f two v a l u e s

2) e x t r a p o l a t e d v a l u e s

The h e a t s o f c o n d e n s a t i o n a r e r e l i a b l e d a t a : On t h e o t h e r hand, there i s c o n s i d e r a b l e experimental u n c e r t a i n t y i n the heats of solution. The t r e n d s i n t h e heat o f s o l u t i o n a r e more c e r t a i n ; however, t h e a c t u a l v a l u e s a r e n o t so c e r t a i n . This uncertainty a r i s e s from two s o u r c e s . F i r s t , the s o l u b i l i t y c o e f f i c i e n t s are d e r i v e d from t h e p e r m e a b i l i t i e s and t h e d i f f u s i o n c o e f f i c i e n t s . Hence, t h e r e l a t i v e u n c e r t a i n t i e s o f b o t h Ρ and D t r a n s f e r t o S. The h e a t s o f s o l u t i o n a r e d e r i v e d by f i t t i n g e q u a t i o n 7 t o o n l y 3 o r 4 data. This i s not i d e a l . F u t u r e work w i l l expand t h e d a t a base to test t h i s preliminary analysis. Nevertheless, the trends f o r the heats of mixing a r e probably c o r r e c t as shown i n T a b l e I I . As t h e e s t e r s g e t l a r g e r , t h e m o l e c u l e becomes more l i k e an a l k a n e , and t h e p o l a r e s t e r group i s diluted. The t r e n d i n t h e h e a t s o f m i x i n g f o r t h e co-VDC f i l m i s interesting. As t h e e s t e r s become l a r g e r t h e h e a t s o f m i x i n g become l e s s f a v o r a b l e i n t h e co-VDC f i l m . This i s a r e f l e c t i o n of the


350


d i l u t i o n of the ester function. Esters are known to interact well with chlorine containing polymers. The heats of mixing f o r the esters i n the EVOH f i l m are unfavorable. They are more unfavorable than the heats of mixing i n the co-VDC f i l m . The heats of mixing i n the EVOH f i l m became more unfavorable as the size of the ester increases. This behavior may be predicted by s o l u b i l i t y parameters. Future work w i l l include a variety of functional groups to study the s p e c i f i c interactions of polymer and permeant. SUMMARY 1.


2. 3. 4. 5. 6. 7.

The d i f f u s i o n c o e f f i c i e n t decreases modestly as the ester size increases f o r low density polyethylene, EVOH and co-VDC f i l m s . The s o l u b i l i t y c o e f f i c i e n t undergoes a much greater change with increasing ester s i z e . Thus the permeability increases with increased ester s i z e . P l a s t i c i z i n g the polymer f i l m can result i n a dramatic increase i n the d i f f u s i o n c o e f f i c i e n t . Important flavor and aroma compounds can be l o s t to the food package by sorption. The amount of flavor loss to the package i s dependent on both d i f f u s i o n and s o l u b i l i t y c o e f f i c i e n t s . The heats of mixing are dependent on s p e c i f i c interactions between polymer and permeant.

LITERATURE CITED 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

DeLassus, P. T.; Hilker, B. L . , Proc. Future-Pak '85 (Ryder), 1985, p. 231. Tou, J. C.; Rulf, D. C.; DeLassus, P. T.; accepted for publiciation in Analytical Chemistry. DeLassus, P. T.; Tou, J. C.; Babinec, M. A.; Rulf, D. C.; Karp, Β. K.; Howell, B. A.; ACS Symposium Series 365, Food and Packaging Interactions (J. H. Hotchkiss, ed.) 1988, p. 11. Zobel, M. G. R., Polymer Testing 1989, 5, 153. Lange's Handbook of Chemistry 13th Edition, McGraw-Hill, N.Y., 1985, pp 10-28. DeLassus, P. T.; Strandburg, G., Howell, Β. Α., TAPPI Journal, 1988, 71(11), 177. Ziegel, K. D.; Frensdorff, Η. K.; Blair, D. E . , J. Polym. Sci., Part A-2, 1969, 7, 809. Pasternak, R. Α.; Schimscheimer, J. R.; Heller, J., J. Polym. Sci., Part A-2, 1970, 8, 467. Zobel, M. G. R., Polymer Testing 1982, 3, 133. Berens, A. R.; Hopfenberg, H. B., J. Membrane Sci., 1982, 10, 283. Peters, H.; Vanderstracten, P.; Verhoeye, L.; J. Chem. Tech. Biotech., 1979, 29, 581. Landois-Garza, J.; Hotchkiss, J. H., Food and Packaging Interactions, ACS Symposium Series 365, 1987, 53. Asfour, A. F. Α.; Saleem, M.; DeKee, D., Journal of Applied Polymer Science, 38, 1989, 1503.

RECEIVED January 31, 1990


Barrier Polymers and Structures - American Chemical Society

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