Barrier Polymers and Structures - American Chemical Society

Chapter 14

Improvement in Barrier Properties of Polymers via Sulfonation and Reductive Metallization 1

W. E. Walles

Downloaded by UNIV LAVAL on May 8, 2016 | http://pubs.acs.org Publication Date: May 9, 1990 | doi: 10.1021/bk-1990-0423.ch014

Central Research, The Dow Chemical Company, 1702 Building, Midland, MI 48674

This paper considers various methods to create a thin diffusion barrier at the surface of a plastic article such as a packaging film or container after i t has been given its intended shape. Such an approach permits one to choose the optimum polymer type based on strength, processability, cost, etc. without being constrained by barrier properties. The advantages of surface sulfonated containers are presented for barrier applications such as polyethylene drums and tanks for solvents and automotive gasoline. The improvement of barrier properties for c r i t i c a l gases such as oxygen are also treated. The barrier treatment can be applied during blow molding as an integrated process or as a separate step afterwards. For very demanding future applications, such as a l l - p l a s t i c thermos bottles and flat foam panels with vacuum insulation, the sulfonation step can be followed by reductive metallization. This results in a further dramatic reduction in permeation, especially when combined with a high barrier polymer overcoat to cover minor imperfections in the metallized surface. Chemical m o d i f i c a t i o n o f the s u r f a c e o f e n g i n e e r i n g p o l y m e r s i s an a t t r a c t i v e a p p r o a c h t o t h e p r o b l e m o f economically producing a b a r r i e r or a permselective structure with t a i l o r e d p r o p e r t i e s . The f o l l o w i n g d i s c u s s i o n w i l l f o c u s on a p p l i c a t i o n s o f t h i s t e c h n o l o g y Current address: Coalition Technologies, Ltd., 6648 River Road, Freeland, MI 48623 0097-6156/90/0423-0266$06.00/0 © 1990 American Chemical Society

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

14.

267

Improvement in Barrier Properties ofPolymers

WALLES

involving sulfonation(1-8). Related applications involving a s y m m e t r i c membranes f o r gas s e p a r a t i o n s have a l s o been d e m o n s t r a t e d , but w i l l not be c o n s i d e r e d i n d e p t h h e r e . T h i s l a t t e r membrane a p p l i c a t i o n i n v o l v e s s e l e c t i v e l y a l t e r i n g t h e p e r m e a b i l i t y o f one gas r e l a t i v e t o a n o t h e r without causing unacceptable r e d u c t i o n s i n the p e r m e a b i l i t y of the d e s i r e d penetrant. In t h e c a s e o f p o l y e t h e r s u l f o n e , i t has been shown t o be p o s s i b l e t o e s s e n t i a l l y d o u b l e t h e s e l e c t i v i t y o f an asymmetric membrane f o r t h e C 0 / C H and 2

0 /N 2

2

systems w h i l e


d e s i r e d C0

2

and

0

2

reducing o n l y by

the

permeability

of

about a f a c t o r o f two

4

the (9) .

The b a r r i e r work i n v o l v e s r e d u c i n g t h e p e r m e a b i l i t y o f v a r i o u s p o l y m e r s t o b o t h l i q u i d s and g a s e s . In t h e c a s e o f l i q u i d s , t h e o b j e c t i v e i s t o d e v e l o p medium l e v e l d i f f u s i o n b a r r i e r s t o v o l a t i l e o r g a n i c s s u c h as h y d r o c a r b o n f u e l s w h i c h have a t e n d e n c y t o s w e l l and p l a s t i c i z e many containers. F o r g a s e s , t h e o b j e c t i v e s a r e more demanding and r e q u i r e t h e development o f h i g h , o r e f f e c t i v e l y c o m p l e t e b a r r i e r f o r a p p l i c a t i o n s such as p r e v e n t i n g l o n g t e r m d i f f u s i o n o f a i r components i n t o a vacuum r e t a i n e d by plastics in insulating applications. T y p i c a l l y , chemically modified surface layers involve t h i c k n e s s e s r a n g i n g from l e s s t h a n 1 micrometer(μ) up t o 20μ, so t h e o v e r a l l mechanical p r o p e r t i e s o f t h e t r e a t e d o b j e c t s a r e h a r d l y a f f e c t e d by t h e p r o c e s s . Even i f one l i m i t s t h e d i s c u s s i o n t o m a t e r i a l s c o n t a i n i n g C-H bonds, p r a c t i c a l l y a l l e n g i n e e r i n g p l a s t i c s are covered except p u r e f l u o r o c a r b o n s and some s i l i c o n e s . Clearly, various g a s e s can r e a c t w i t h t h e c a r b o n - h y d r o g e n bonds on t h e s u r f a c e o f a p l a s t i c a r t i c l e and can r e d u c e t h e d i f f u s i o n c o e f f i c i e n t of penetrants i n the m a t e r i a l . The c h o i c e o f s u l f o n a t i o n as t h e p r e f e r r e d t r e a t m e n t , t h e r e f o r e , i s not b a s e d s o l e l y on t h e a b i l i t y t o m o d i f y t r a n s p o r t p r o p e r t i e s . Rationale

f o r the

Use

of Surface

Sulfonation

Our e x p l o r a t o r y e x p e r i m e n t s i n v o l v i n g t h e use o f f l u o r i n e t r e a t m e n t s r e s u l t e d i n c o n t a i n e r s w i t h a good b a r r i e r t o g a s o l i n e ; however, upon r e p e a t e d f l e x i n g , a l o s s o f b a r r i e r p r o p e r t i e s can r e s u l t . The b a r r i e r l a y e r s i n t h e s e c a s e s were up t o 0.1 μ t h i c k . A d d i t i o n a l s t u d i e s u s i n g 25μ f i l m s o f p o l y s t y r e n e , p o l y e t h y l e n e and p o l y p r o p y l e n e exposed t o f l u o r i n e f o r a l o n g e r time l e d t o t o t a l p u l v e r i z a t i o n of the f i l m s . The l o s s i n m e c h a n i c a l p r o p e r t i e s a p p e a r s t o be a s s o c i a t e d w i t h t h e l o c a l i z a t i o n o f e n e r g y a s s o c i a t e d w i t h t h e C-F bond f o r m a t i o n , which i n t u r n can b r e a k n e i g h b o r i n g C-C bonds o f t h e p o l y m e r backbone. Under c e r t a i n r i g o r o u s l y c o n t r o l l e d t r e a t m e n t p r o t o c o l s , t h e use o f f l u o r i n e has p r o v e n w o r k a b l e ( 1 0 ) , but i t was f e l t t h a t a l e s s a g g r e s s i v e agent a l l o w e d added p r o c e s s f l e x i b i l i t y f o r our work.


268

BARRIER POLYMERS AND STRUCTURES

S u r f a c e c h l o r i n a t i o n c a n p r o d u c e good b a r r i e r l a y e r s with l e s s tendency t o p r o v i d e f l e x u r e f a i l u r e s . U n f o r t u n a t e l y , c h l o r i n e r e a c t s t o o s l o w l y t o be p r a c t i c a l as a t r e a t m e n t a g e n t i n t h e absence o f p r o m o t i o n by UV light. I t i s c l e a r l y n o t c o n v e n i e n t t o use UV i n t h e i n t e r i o r o f c o n t a i n e r s , s o a l t e r n a t i v e a c t i v a t o r s were sought. Chemical a c t i v a t i o n of the c h l o r i n a t i o n r e a c t i o n was shown t o be p o s s i b l e u s i n g a m i x t u r e o f 10% SO3/90% C l

2


as s u c h o r f u r t h e r d i l u t e d w i t h a i r o r n i t r o g e n a t 25°C. The p r o c e s s l e d t o s i g n i f i c a n t l y u p t a k e s o f b o t h CI and SO3 (4) and p r o d u c e d good b a r r i e r s t o g a s o l i n e s , p a r t i c u l a r l y t o t h e e t h a n o l - and m e t h a n o l - c o n t a i n i n g t y p e s . Treatment o f t h e i n s i d e o f h i g h d e n s i t y p o l y e t h y l e n e (HDPE) a u t o m o t i v e gas t a n k s w i t h about 20% SO3 i n a i r f o l l o w e d by a i r p u r g i n g w i t h subsequent n e u t r a l i z a t i o n w i t h NH3 gas r e s u l t e d i n an e x c e l l e n t g a s o l i n e b a r r i e r (See F i g . 1).

C o n c e n t r a t i o n s o f about

75 and 200 micrograms

SO3 p e r

2

cm o f s u r f a c e r e d u c e s p e r m e a t i o n l o s s e s by 90 and 99%, r e s p e c t i v e l y i n ambient t e m p e r a t u r e p e r m e a t i o n t e s t s . As i n d i c a t e d i n F i g . 2 , t h e b a r r i e r l a y e r was f o u n d t o have -S03~NH groups t o a d e p t h o f 20-25 m i c r o m e t e r s . The +

4

t r e a t e d l a y e r has good r e s i s t a n c e t o f l e x u r e f a i l u r e s . When a 25 m i c r o m e t e r p o l y e t h y l e n e f i l m was s i m i l a r l y s u l f o n a t e d , i t was f o u n d t o have r o u g h l y 200% e l o n g a t i o n a t b r e a k and t w i c e t h e b r e a k i n g s t r e n g t h o f t h e u n t r e a t e d polyethylene. Of t h e f i r s t s e r i e s o f one t h o u s a n d s t a t i o n wagons e q u i p p e d w i t h t h e s e t a n k s , s e v e r a l were r e t r i e v e d from junked c a r s w i t h g a s o l i n e exposure times c o r r e s p o n d i n g t o more t h a n 90,000 m i l e s e a c h . In a l l o f t h e s e c a s e s , t h e s u l f u r s u r f a c e c o n c e n t r a t i o n , b a r r i e r p r o p e r t i e s and m e c h a n i c a l p r o p e r t i e s o f t h e t a n k w a l l s were f u l l y i n t a c t . Nature

that

of the B a r r i e r

Layer

Based on i n f r a r e d s p e c t r o s c o p i c a n a l y s i s , i t i s c l e a r f o l l o w i n g SO3 e x p o s u r e , s u b s t a n t i a l l y a l l of the

s u l f u r p r e s e n t i s i n t h e form o f : 1

-C-SO3H I

With t y p i c a l treatment p r o c e d u r e s , i t appears t h a t t h e s u l f o n a t e d p o l y m e r u n i t s a r e i n t e r s p e r s e d between 0-500 u n i t s o f u n s u l f o n a t e d p o l y m e r u n i t s as i l l u s t r a t e d by t h e f o l l o w i n g formula -CR-C (R ) (R ) - [C (H) (R) -C (R ) 1

SO3H

2

±

Polyethylene \ Polyacrylate

3

4

) Polycarbonate 5) Trycite Cellulose Cel ί ) Ξ_) Ace Acetate =j> Polypropylene

8>

Comparison with Other Films


273

NH

λ

+ 4

N a +

Li +

A\ Mylar Polyester =) Saran

_L J ziL 140 40 60 " 80 100 120 Surface Cone, of S 0 in Microgram per Cm Film

160

2

3

F i g u r e 3: D e m o n s t r a t i o n o f t h e d r a m a t i c r e d u c t i o n s i n oxygen permeability a t 25°C f o l l o w i n g s u r f a c e s u l f o n a t i o n t o d i f f e r e n t d e g r e e s . The e f f e c t s o f i n t r o d u c i n g d i f f e r e n t i o n s i n place of the N H i s also illustrated. The oxygen p e r m e a b i l i t i e s o f v a r i o u s r e s i n s a r e shown f o r c o m p a r i s o n . +

4


274



Reductive

Metallization

A n a t u r a l e x t e n s i o n o f t h e above i d e a s i n v o l v e s t h e c h e m i c a l r e d u c t i o n o f heavy m e t a l i o n s , p r e s e n t as counterions within the t r e a t e d surface region. In the case o f c o p p e r and s i l v e r , h i g h l y r e f l e c t i v e m e t a l l a y e r s c a n be o b t a i n e d w i t h a m e t a l l i c - t y p e t o t a l b a r r i e r i n some c a s e s . The e l e c t r i c a l s u r f a c e c o n d u c t i v i t y , which i s i o n i c b e f o r e the reduction, i s converted t o e l e c t r o n i c a f t e r the r e d u c t i o n t o free metal, thereby p e r m i t t i n g r a p i d electroplating i f desired. Moreover, f o r c e r t a i n a p p l i c a t i o n s , t h i s a p p r o a c h can be u s e d t o p r o d u c e an e x t r e m e l y h i g h b a r r i e r t o t h e passage o f gases. F o r example n o v e l t h e r m a l i n s u l a t i o n p a n e l s f o r r e f r i g e r a t o r s w i t h p l a s t i c - w a l l e d p a n e l s e n c l o s i n g a v a c u u m i z e d space w i t h v e r y l i t t l e gas b u t w i t h l o a d - b e a r i n g f i n e powders have been d e v e l o p e d (13-22). In a d d i t i o n t o a d d i n g s t r u c t u r a l i n t e g r i t y , c o r r e c t l y chosen powders added t o t h e e v a c u a t e d c a v i t y i n a vacuum c o n t a i n e r h e l p t o e l i m i n a t e gas from t h e s y s t e m o r g e n e r a t e a p r o d u c t o r p r o d u c t s which can be a d s o r b e d by a n o t h e r gas a d s o r b i n g m a t e r i a l such as a c t i v a t e d c a r b o n . F o r example, c a r b o n d i o x i d e i s r e a d i l y removed i n t h i s manner w i t h m i x t u r e s o f c a r b o n and l i t h i u m a l k o x i d e s such as l i t h i u m i s o p r o p o x i d e . The l i t h i u m i s o p r o p o x i d e r e a c t s w i t h c a r b o n d i o x i d e t o form l i t h i u m c a r b o n a t e and t o l i b e r a t e d i i s o p r o p y l e t h e r which i s s t r o n g l y a d s o r b e d by a c t i v a t e d c a r b o n ( 2 1 ) . A l t h o u g h c a r b o n d i o x i d e i s a l s o a d s o r b e d by t h e a c t i v a t e d c a r b o n , i t s l o w l y d e s o r b s , r e e n t e r s t h e gas phase a n d i s s u b s e q u e n t l y c o n v e r t e d t o d i i s o p r o p y l e t h e r where i t i s p e r m a n e n t l y removed from t h e gas p h a s e . S i m i l a r a p p r o a c h e s a r e p o s s i b l e w i t h o t h e r g a s e s , and i n some c a s e s , s i m p l e a c t i v a t e d c h a r c o a l i s s u f f i c i e n t . F o r demanding i n s u l a t i o n a p p l i c a t i o n s , vacuum w i t h i n t h e p l a s t i c c o n t a i n e r must be m a i n t a i n e d f o r 30 y e a r s o r more. To a c h i e v e such a s u p e r b a r r i e r , an u l t r a t h i n , v e r y r e g u l a r m e t a l l i c l a y e r c a n be c r e a t e d by c o m b i n i n g t h e p r e v i o u s l y d i s c u s s e d s u l f o n a t i o n treatments with reductive metallization. The m e t a l l a y e r i s e x t e n s i v e enough so t h a t a t l e a s t 95-99% o f t h e s u r f a c e i s c o v e r e d by m e t a l . An a d d i t i o n a l p r o b l e m i n u s i n g molded p l a s t i c s t o e n c l o s e vacuum and t o m a i n t a i n i t v i a an u l t r a t h i n m e t a l l i c b a r r i e r l a y e r a r i s e s from i r r e g u l a r m e t a l l i z a t i o n . This l a t t e r p r o b l e m , c a u s e d by r e s i d u a l mold s t r e s s e s , can be overcome by f i r s t s u l f o n a t i n g t h e s u r f a c e l i g h t l y t o p r o d u c e a water w e t t a b l e s u r f a c e , f o l l o w e d by t h e a p p l i c a t i o n o f a t h i n l a t e x c o a t i n g which d r i e s t o y i e l d a low s t r e s s s u r f a c e . T h i s s u r f a c e , i n t u r n can be s u l f o - m e t a l l i z e d as d i s c u s s e d below. F o r even h i g h e r i n t e g r i t y , t h e m e t a l l a y e r can be f u r t h e r c o a t e d w i t h a l a y e r o f a b a r r i e r c o p o l y m e r such as vinylidene chloride/vinyl chloride. The b a r r i e r polymer i s most c o n v e n i e n t l y a p p l i e d i n l a t e x form t o t h e e x p o s e d s u r f a c e o f t h e m e t a l l a y e r t o form a c o a t i n g o f a few micrometers t h i c k . S u i t a b l e b a r r i e r polymers i n c l u d e latexes that w i l l give a continuous f i l m at temperatures


14. WALLES

275


below t h e h e a t d i s t o r t i o n t e m p e r a t u r e o f t h e t h e o r g a n i c p o l y m e r u s e d t o make t h e p l a s t i c p a r t i t s e l f . A t y p i c a l example o f t h e p r o c e s s t o p r o d u c e a m e t a l l i z e d l a y e r i n v o l v e s t h e development o f a s u l f o n a t e d l a y e r o f micrometer t h i c k n e s s u s i n g the techniques d i s c u s s e d above. A degree o f s u r f a c e s u l f o n a t i o n o f o n l y 0.2 micrograms o f s u l f u r t r i o x i d e e q u i v a l e n t s p e r s q u a r e c e n t i m e t e r i s achieved by c o n t a c t i n g the s u r f a c e with dry a i r containing 2 percent s u l f u r t r i o x i d e a t 25°C f o r a p p r o x i m a t e l y one s e c o n d . A m e t a l l i z i n g b a t h b a s e d on one p a r t o f each o f the f o l l o w i n g i s c o n v e n i e n t l y used: 0.6% A g ( N H ) N 0 i n H 0 , 0.3% NaOH i n H 0 w i t h 0.15% g l u c o s e a n d 0.15% f r u c t o s e i n H 0 ( 2 1 ) . The s u l f o n a t e d s u r f a c e s are dipped i n t o the bath and m e t a l l i z a t i o n i s completed w i t h i n 1 minute. The t h i c k n e s s o f t h e m e t a l l a y e r s i n t h i s c a s e a r e a p p r o x i m a t e l y 0.03 m i c r o m e t e r s as d e t e r m i n e d by m i c r o s c o p y . In t h i s case, t h e l o c a t i o n o f e a c h m e t a l atom i s o r i g i n a l l y f i x e d b y t h e d i f f u s i o n o f SO3 3

2

3

2

2


2

i n t o the polymer, t h e r e b y e s t a b l i s h i n g the p o s i t i o n s p e c i e s a t t h e time o f r e d u c t i o n : Ο ι

of the

1 1

-C-S-0 N H

+ 4

Ag°

A c l o s e l y r e l a t e d s e c o n d method t o a c h i e v e an even d e n s e r m e t a l l i c l a y e r i n v o l v e s the i n t r o d u c t i o n o f t i n ions i n s t e a d o f s i l v e r f o l l o w e d by a s p r a y o f w a t e r - b a s e d s i l v e r - a m m o n i a complex, f r e s h l y mixed w i t h r e d u c e r . The t i n c a t a l y z e s the d e p o s i t i o n o f s i l v e r , r e s u l t i n g i n the formation o f c o l l o i d a l m e t a l l i c s i l v e r . Upon d r y i n g , a very regular, shiny m e t a l l i c s i l v e r layer with a thickness r a n g i n g from 10 t o 600 atoms i s p r o d u c e d a s i n d i c a t e d f o r m a l l y below: Ο -C-S-0 N H

+ 4

Sn°

Ag°

1 0

_

6 0 0

B a s e d on e x p e r i e n c e , under t h e above c o n d i t i o n s , p r o d u c t i o n o f a t l e a s t 80-120 s i l v e r atoms p e r s u l f o n a t e d c e n t e r i s adequate t o p r o v i d e a t o t a l m e t a l l i c - t y p e b a r r i e r t o t h e p a s s a g e o f a i r . These e x t r e m e l y t h i n s i l v e r l a y e r s , when p a r t o f a v a c u u m - t r e a t e d t h e r m a l i n s u l a t i o n p a n e l , c o n d u c t v e r y l i t t l e h e a t around t h e r i m s o f t h e p a n e l a s i s needed t o a c h i e v e t h e d e s i r e d h i g h t h e r m a l i n s u l a t i o n . F o r example, t h e t h e r m a l c o n d u c t i v i t i e s o f an a p p r o p r i a t e l y formed p a n e l i s t y p i c a l l y as low a s 0.007 w a t t s m /m C a s compared t o v a l u e s f o r p o l y s t y r e n e a n d p o l y u r e t h a n e foams o f 0.03-0.04 w a t t s m /m^°C and 0.016-0.025 w a t t s m /m C, r e s p e c t i v e l y (3). To i l l u s t r a t e t h e v a l u e o f t h e t r e a t m e n t , a vacuum c o n t a i n e r w i t h a s i l v e r l a y e r a p p r o x i m a t e l y 0.01 m i l i s compared w i t h v a r i o u s c a s e s i n T a b l e I . The 90/8/2 v i n y l 2o

2o


276


c h l o r i d e / a c r y l o n i t r i l e / s u l f o e t h y l methacrylate b a r r i e r terpolymer c o a t i n g i s a p p l i e d t o the completed m e t a l l i z e d container. The l a t e x had a p a r t i c l e s i z e o f about 0.22 m i c r o m e t e r and was a p p l i e d by d i p p i n g i n a 50% s o l i d s latex. The e x c e s s l a t e x i s a l l o w e d t o run o f f t h e s u r f a c e and t h e w a l l i s d r i e d a t 60°C f o r 15 m i n u t e s . The c o n t a i n e r i s a 1 q u a r t vacuum b o t t l e h a v i n g a s u r f a c e f a c i n g t h e e v a c u a t e d e n c l o s e d space o f 1500 cm w i t h an e v a c u a t e d volume o f 500 crn^, and a s t a n d a r d styrene/ a c r y l o n i t r i l e boundary w a l l t h i c k n e s s , e x c l u d i n g t h e t h i c k n e s s o f t h e m e t a l and b a r r i e r p l a s t i c o f 80 m i l s . The space e n c l o s e d by t h e boundary w a l l i s e v a c u a t e d t o a p r e s s u r e o f 0.01 mm Hg, and 80g o f a c t i v a t e d c h a r c o a l o f 0.2 m i c r o n s i z e i s added t o t h e e n c l o s e d space under vacuum. P r i o r t o a d d i t i o n t o t h e e n c l o s e d space, t h e c h a r c o a l i s a c t i v a t e d f o r 48 h o u r s a t 10"" mm Hg. The p e r m e a t i o n r a t e s d e t e r m i n e d u s i n g a mass s p e c t r o m e t e r were u s e d t o e s t i m a t e t h e p r o j e c t e d c o n t a i n e r l i f e b a s e d on t h e f a c t t h a t t h e a c t i v a t e d c h a r c o a l which f i l l s t h e e v a c u a t e d space can a d s o r b a t o t a l o f about 24-80 c c ( S T P ) o f a i r . The p r o j e c t e d l i f e , t h e r e f o r e , was e s t i m a t e d by d i v i d i n g t h e gas a d s o r b i n g c a p a c i t y by t h e a i r p e r m e a t i o n r a t e . 2


7

Table

Sample

No.

I : Comparison o f m e t a l l i z e d and containers (14) Coating

A i r P e r m e a t i o n Rate (cc(STP) a i r / d a y )

non

metallized

Projected Container L i f e

1

Metal & Barrier Plastic

0.056

1.2

2

Metal

3.2

7.5-25 days

3

Barrier Plastic

4

None

alone

1.1

-4

22.5

years

-75

days

alone 9

3-9

days

F u r t h e r c h a r a c t e r i z a t i o n of the s y n e r g i s t i c e f f e c t s of o v e r c o a t i n g m e t a l l a y e r s w i t h t h e b a r r i e r p o l y m e r was done u s i n g simple f l a t p o l y s t y r e n e f i l m s of 5 m i l t h i c k n e s s e s t h a t had been s u r f a c e s u l f o n a t e d t o p r o v i d e a low d e g r e e o f s u l f o n a t i o n o f 1.5 micrograms o f s u l f u r t r i o x i d e p e r cm . Two s t r i p s o f t h e s u r f a c e s u l f o n a t e d f i l m were c o a t e d w i t h d i f f e r e n t t h i c k n e s s e s o f t h e same b a r r i e r p o l y m e r as t h a t u s e d above. An a d d i t i o n a l s u l f o n a t e d s t r i p was not c o a t e d , but was m e t a l l i z e d as d e s c r i b e d above, and a f i n a l s t r i p was b o t h m e t a l l i z e d and c o a t e d w i t h a l a y e r o f 0.22 m i l s o f b a r r i e r polymer. The r e s u l t s o f oxygen t r a n s m i s s i o n measured by mass s p e c t r o m e t e r a t 25°C a r e r e p o r t e d i n 2


14.

WALLES

277


T a b l e I I and c l e a r l y show t h e d r a m a t i c improvement i n p e r f o r m a n c e when t h e b a r r i e r p o l y m e r and m e t a l l i z a t i o n a r e u s e d t o g e t h e r (14). H i g h e r d e g r e e s o f s u l f o n a t i o n as compared t o 1.5 micrograms SO3/CIÏ1 u s e d h e r e , e.g., 70 micrograms S 0 / c m d i s c u s s e d i n c o n n e c t i o n w i t h F i g . 3, c l e a r l y would p r o d u c e much h i g h e r b a r r i e r s t h a n t h a t shown f o r t h e u n c o a t e d l i g h t l y s u l f o n a t e d sample 4. N e v e r t h e l e s s , even t h e b e s t o f t h e s e samples would be o v e r an o r d e r o f magnitude p o o r e r t h a n t h e h i g h b a r r i e r a c h i e v e d i n sample 1. 2

2

3


Table

Sample

No.

I I : I l l u s t r a t i o n of the s y n e r g i s t i c e f f e c t s of m e t a l l i z a t i o n and a t h i n b a r r i e r p o l y m e r o v e r c o a t (14)

Coating

Coating

μς/οπι

2

Thickness or

(mil)

(0.01) (0.22)

Oxygen Transmission [cc(STP)/100 i n day atm]

1

Metal & Barrier Plastic

220 1200

2

Barrier Plastic

710

(0.13)

0.43

3

Barrier Plastic

1420

(0.26)

0.20

4

Surface Sulfonated (1.5 μς/σπι )

-

Untreated Control

-

2

0.013

25.0

2

5

25.2

Waste T r e a t m e n t C o n s i d e r a t i o n s Additional p r a c t i c a l c o n s i d e r a t i o n s t h a t are a t t r a c t i v e about t h e s u l f o n a t i o n p r o c e s s i s i t s s a f e t y and ease o f t r e a t m e n t o f waste components. Excess s u l f u r t r i o x i d e i s e a s i l y removed w i t h a gas s c r u b b e r t o y i e l d a s i m p l e t o h a n d l e s u l f u r i c a c i d stream, and w i t h t h e c o n v e n i e n t ammonia n e u t r a l i z a t i o n p r o c e s s d e s c r i b e d above, t h e p r i n c i p a l waste s t r e a m i s c o m p r i s e d o f water w i t h a s m a l l amount o f ammonium s u l f a t e . Methods o f a v o i d i n g waste by r e c y c l i n g o f SO3 i t s e l f have a l s o been d e s c r i b e d (7,8). Moreover, w i t h r e c e n t d e v e l o p m e n t s f o r i n - s i t u g e n e r a t i o n o f SO3 and NH3, t h e amount o f waste g e n e r a t e d can be r e d u c e d g r e a t l y (1) .


278



Conclusion Of s e v e r a l p o t e n t i a l l y a p p l i c a b l e a p p r o a c h e s t o r e d u c i n g t h e p e r m e a b i l i t y o f a broad spectrum o f i n e x p e n s i v e e n g i n e e r i n g r e s i n s used i n packaging, p r o c e s s e s b a s e d on s u r f a c e s u l f o n a t i o n a r e u n p a r a l l e l e d i n t h e d i v e r s i t y o f m o d i f i c a t i o n s t h a t can be a c h i e v e d . The approach i s r e l a t i v e l y simple t o perform d u r i n g molding o r i n p o s t m o l d i n g o p e r a t i o n s and l e a v e s t h e i n t r i n s i c mechanical p r o p e r t i e s of the substrate i n t a c t . The s u r f a c e t r e a t e d l a y e r s have good f l e x i b i l i t y even a t r e l a t i v e l y h i g h t r e a t m e n t l e v e l s , s i n c e c h a i n backbone s c i s s i o n and crosslinking i s rare. The s i m p l e s u l f o n a t e d b a r r i e r l a y e r i s v e r y e f f e c t i v e a g a i n s t n o n p o l a r components such as f u e l s and even c h l o r i n a t e d hydrocarbons. Under d r y c o n d i t i o n s , t h e b a r r i e r layer i s also highly e f f e c t i v e f o r suppressing the p e r m e a t i o n o f f i x e d gases such as oxygen o r n i t r o g e n . F o r h i g h e r b a r r i e r r e q u i r e m e n t s , t h e s u l f o n a t i o n t r e a t m e n t can be e f f e c t i v e l y combined w i t h r e d u c t i v e m e t a l l i z a t i o n t e c h n i q u e s t o produce v e r y h i g h b a r r i e r s . When combined w i t h b a r r i e r polymer o v e r c o a t s and gas a d s o r b i n g powdered f i l l e r s , i t i s p o s s i b l e t o produce super b a r r i e r s capable o f b e i n g u s e d i n vacuum p a n e l s and b o t t l e s f o r t h e r m a l insulation. For household r e f r i g e r a t o r s , o u t s i d e d i m e n s i o n s a r e f i x e d because o f s t a n d a r d i z e d k i t c h e n d i m e n s i o n s i n homes, a i r c r a f t and b o a t s . R e p l a c i n g p r e s e n t l y u s e d foam i n s u l a t i o n by v a c u m i z e d p l a s t i c p a n e l s s h o u l d p e r m i t t h i n n e r i n s u l a t i o n and t h e r e f o r e , more room inside the r e f r i g e r a t o r . More e n e r g y e f f i c i e n t r e f r i g e r a t o r s b a s e d on t h e s e h i g h l y i n s u l a t i n g p a n e l s a r e a l s o obvious p o s s i b i l i t i e s .

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Walles, W. E. U. S. Patent No. 4,775,587, 1988. Ihata, J., J . Polym. Sci., Part A, 1988, 26, 167. Walles, W. E. U. S. Patent No. 3,740,258, 1973. Walles, W. E. U. S. Patent No. 4,220,739, 1980. Walles, W. E. U. S. Patent No. 3,613,957, 1971. Walles, W. E., In-Mold Sulfonations System, U. S. Patent applied for. Walles, W. E., Process for the generation of sulfur trioxide reagent and sulfonation of the surface of polymeric resins,U. S. Patent applied for. Walles, W. E., Apparatus for the generation of sulfur trioxide reagent and sulfonation of the surface of polymeric resins,U. S. Patent applied for. Chiao, C. C. U. S. Patent No. 4,717,395, 1988. Gentilcore, J . F . , Trialo, M.A. and Waytek, A. J., Plast. Engr., 1978, 34, 40. Walles, W. E. U. S. Patent No. 3,770,706, 1973. Walles, W. E. U. S. Patent No. 3,625,751, 1971.


14. WALLES


13. W a l l e s , W. Ε . U. S. P a t e n t No. 14. W a l l e s , W. E . U. S. P a t e n t No. 15. W a l l e s , W. E. U. S. P a t e n t No. 16. W a l l e s , W. E . U. S. P a t e n t No. 17. W a l l e s , W. E . U. S. P a t e n t No. 18. W a l l e s , W. E . U. S. P a t e n t No. 19. W a l l e s , W. E . U.S. P a t e n t No. 20. W a l l e s , W. E . U. S. P a t e n t No. 21. Cheng, C, and W a l l e s , W. E . U. 4,745,015, 1988. 22. W a l l e s , W. E . U. S. P a t e n t No.

3,959,561,

1975.

January 25, 1990


RECEIVED

3,824,762, 1974. 3,828,960, 1974. 3,856,172, 1974. 3,921,844, 1975. 3,993,811, 1976. 4,000,246, 1976. 3,996,725, 1976. 4,457,977, 1984. S. P a t e n t No.


279

Barrier Polymers and Structures - American Chemical Society

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