Barrier Polymers and Structures - American Chemical Society

Chapter 12

Permeability of Competitive Oxygen-Barrier Resins Orientability and Effect of Orientation 1

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Downloaded by FUDAN UNIV on February 8, 2017 | http://pubs.acs.org Publication Date: May 9, 1990 | doi: 10.1021/bk-1990-0423.ch012

R. Shastri , H. C.Roehrs ,C. N.Brown ,and S. E. Dollinger 1

Materials Science and Development Laboratory, Central Research, The Dow Chemical Company, 1702 Building, Midland, MI 48674 Films Research Laboratory, Dow Chemical U.SA., Granville, OH 43023

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In barrier packaging, i t is generally accepted that orientation of the barrier resin reduces its gas permeability. Most of the published data, however, corresponds to low barrier resins. No supporting data exists yet for either high or intermediate barrier resins. To fill that void, the orientability and the s e n s i t i v i t y of oxygen permeability to orientation for six competitive oxygen barrier resins were evaluated. The barrier resins evaluated in this investigation include: an experimental grade Vinylidene chloride/vinyl chloride (VDC) copolymer, aromatic nylon MXD-6, amorphous nylon SELAR PA 3426, polyacrylic-imide XHTA-50A and two EVOH resins - EVAL EP-E105 and SOARNOL D. With the exception of both the EVOH grades, the remaining four barrier resins were orientable in the s o l i d state. Generally, amorphous resins SELAR PA 3426 and p o l y a c r y l i c - i m i d e XHTA-50A were easier to orient than the semicrystalline resins, VDC copolymer and aromatic nylon MXD-6. In the case of both EVAL EP-E105 and SOARNOL D resins, a l l attempts to orient from the solid state were unsuccessful. The effect of orientation on permeability is dependent on the morphological nature of the b a r r i e r resin. Semicrystalline polymers, VDC copolymer, and aromatic nylon MXD-6 0097-6156/90/0423-0239$06.00/0 © 1990 American Chemical Society

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


240

BARRIER POLYMERS AND STRUCTURES

showed little i f any improvements in permeability at low orientation levels and in the absence of additional heat treatment. The VDC copolymer, in fact, showed higher permeability - 1.5 times the permeability of the unoriented film with b i a x i a l o r i e n t a t i o n . This is believed to be due to microvoid development as a result of solid state orientation of the VDC copolymer after c r y s t a l l i n i t y is f u l l y developed. The effect of o r i e n t a t i o n on amorphous barrier resins, SELAR PA 3426 and XHTA50A is to decrease permeability by 5-30% in both resins depending on the level of orientation. W i t h t h e g r o w i n g demand f o r c o e x t r u d e d p r o d u c t s , b a r r i e r plastics h a v e shown s i g n i f i c a n t g r o w t h i n t h e l a s t several years. H i s t o r i c a l l y , the high b a r r i e r resins market h a s been d o m i n a t e d by t h r e e l e a d i n g m a t e r i a l s — vinylidene chloride (VDC) c o p o l y m e r s , e t h y l e n e v i n y l alcohol (EVOH) c o p o l y m e r s , and n i t r i l e r e s i n s . Since 1985, however, t h e r e has been a l o t o f i n t e r e s t w o r l d w i d e i n t h e development o f moderate t o i n t e r m e d i a t e b a r r i e r r e s i n s , as a p p a r e n t f r o m t h e i n t r o d u c t i o n o f a number o f such resins, notably, aromatic nylon MXD-6 from M i t s u b i s h i Gas C h e m i c a l Company, amorphous n y l o n s SELAR PA b y Du P o n t a n d NovamidX21 b y M i t s u b i s h i Chemical I n d u s t r i e s , p o l y a c r y l i c - i m i d e c o p o l y m e r EXL (introduced e a r l i e r a s XHTA) by Rohm and Haas and c o p o l y e s t e r B010 by Mitsui/Owens-Illinois. Understanding the structure-property relationships i n b a r r i e r p o l y m e r s i s an a r e a o f p r i m a r y i n t e r e s t t o package d e s i g n e r s . In t h e c a s e o f most b a r r i e r r e s i n s , the e f f e c t o f e n v i r o n m e n t a l v a r i a b l e s such as temperature and r e l a t i v e h u m i d i t y on p e r m e a b i l i t y a r e g e n e r a l l y w e l l known w h i l e a w e a l t h o f knowledge i s b e i n g a c q u i r e d on t h e e f f e c t s o f g e o m e t r i c v a r i a b l e s s u c h as t h i c k n e s s , and p o l y m e r s t r u c t u r a l p a r a m e t e r s such as c h e m i c a l s t r u c t u r e , c r y s t a l l i n i t y and m o l e c u l a r p a c k i n g . An a d d i t i o n a l k e y p a r a m e t e r w h i c h i n f l u e n c e s t h e permeability o f a p o l y m e r b e s i d e s t h o s e c i t e d above i s the state of orientation. In t h e d e s i g n o f p a c k a g e s t r u c t u r e s , o r i e n t a t i o n i s o f p a r t i c u l a r v a l u e as most p a c k a g e f o r m i n g p r o c e s s e s i n h e r e n t l y i n d u c e some d e g r e e of o r i e n t a t i o n i n the f a b r i c a t e d s t r u c t u r e . Though improvements i n transport characteristics with o r i e n t a t i o n have been r e p o r t e d e a r l i e r i n l i t e r a t u r e (JLz. ϋ) , t h e y p e r t a i n p r i m a r i l y t o low b a r r i e r p o l y m e r s s u c h as p o l y e t h y l e n e (PE) and p o l y p r o p y l e n e (PP). The r e d u c e d permeability w i t h o r i e n t a t i o n has been a t t r i b u t e d t o enhanced c r y s t a l l i n i t y d e v e l o p e d from m o l e c u l a r a l i g n m e n t accompanying o r i e n t a t i o n . There i s l i t t l e reported


12. SHASTRI ET AL.

Permeability ofCompetitive Oxygen-Barrier Resins

e v i d e n c e , however, o f t h e e f f e c t o f o r i e n t a t i o n on the p e r m e a b i l i t i e s o f medium and h i g h b a r r i e r r e s i n s o t h e r t h a n some r e c e n t l y p u b l i s h e d d a t a on EVOH c o p o l y m e r s (iLz

121) · It i s , t h e r e f o r e , important to e v a l u a t e the e f f e c t s of o r i e n t a t i o n on the permeabilities of competitive medium t o h i g h oxygen b a r r i e r p o l y m e r s . This study was i n i t i a t e d to f i l l that void.


Experimental Materials . The competitive oxygen b a r r i e r resins investigated include: Dow C h e m i c a l Company's v i n y l i d e n e chloride/vinyl chloride (VDC) copolymer (experimental g r a d e XU 32009.02), M i t s u b i s h i Gas C h e m i c a l Company s a r o m a t i c n y l o n MXD-6, Du P o n t s amorphous n y l o n SELAR PA 3426, Rohm & Haas's p o l y a c r y l i c - i m i d e XHTA-50A and two EVOH r e s i n s — K u r a r a y ' s EVAL EP-E105 (44 mole% e t h y l e n e c o n t e n t ) and N i p p o n G o h s e i ' s SOARNOL D (29 mole% e t h y l e n e content). 1

1

Film Preparation. E x t r u s i o n c a s t f i l m s of each b a r r i e r r e s i n , a p p r o x i m a t e l y 7-10 m i l i n t h i c k n e s s , were p r o d u c e d by c o e x t r u s i o n as t h r e e - l a y e r s t r u c t u r e s , 30 t o 32 m i l s t h i c k , between e i t h e r HDPE o r PP s a c r i f i c i a l s k i n s . C o m p r e s s i o n m o l d e d c o n t r o l f i l m s o f VDC copolymer, 1-2 mil in thickness, were prepared by reheating extrusion c a s t f i l m s between t h e p l a t e n s of a molding press. Orientation. S o l i d s t a t e post o r i e n t a t i o n of i n d i v i d u a l f i l m s was a c c o m p l i s h e d w i t h a l a b o r a t o r y s c a l e T. M. Long Stretcher. Using a standard 4-inch square s t r e t c h i n g head, t h e f i l m samples were o r i e n t e d up t o 3.5X in either one or both directions. For biaxial orientation, simultaneous stretching mode was employed. The o r i e n t a t i o n temperature s e l e c t e d f o r each b a r r i e r r e s i n was the lowest p o s s i b l e t e m p e r a t u r e above i t s g l a s s transition temperature which would allow uniform stretching. F o r t h e amorphous p o l y m e r s , t h e o r i e n t a t i o n t e m p e r a t u r e s r a n g e d f r o m 5° t o 25°C above t h e i r glass transition temperatures, while optimal orientation temperatures f o r the s e m i c r y s t a l l i n e r e s i n s ranged from 25° t o 50°C b e l o w t h e c o r r e s p o n d i n g c r y s t a l l i n e m e l t i n g temperatures. The o r i e n t a t i o n c o n d i t i o n s a r e summarized i n T a b l e I. Oxygen B a r r i e r M e a s u r e m e n t s . Oxygen p e r m e a b i l i t i e s of u n o r i e n t e d c o n t r o l f i l m s and o r i e n t e d f i l m s were measured a t 23.5°C and 65% RH on an O x t r a n 1050 permeability tester.


241


242


Table

I.

Orientation

Orientation Temp. B a r r i e r Resins

of Barrier

Stretching Rate (in/sec)

120

4

EVAL EP-E105

140-150

1-4

SOARNOL D

140-150

0.2 - 1

105

4

140

2

VDC c o p o l y m e r

MXD-6

Resins

Observations non-uniform stretching very difficult; splitting very difficult; splitting orientable below T easily orientable; has t o be adequately dry easily orientable c c

SELAR PA 342 6 175 XHTA-50A


12. SHASTRI ET AL.


R e s u l t s and

243 Permeability of Competitive Oxygen-Barrier Resins

Discussion

Orientability. W i t h t h e e x c e p t i o n o f b o t h t h e EVOH g r a d e s , t h e r e m a i n i n g b a r r i e r r e s i n s were orientable. Generally, t h e amorphous r e s i n s SELAR PA 3426 a n d polyacrylic-imide XHTA-50A f a c i l i t a t e d more uniform s t r e t c h i n g when compared t o s e m i c r y s t a l l i n e r e s i n s , VDC c o p o l y m e r a n d a r o m a t i c n y l o n MXD-6. E f f o r t s t o o r i e n t VDC c o p o l y m e r f i l m s r e s u l t e d i n uneven s t r e t c h i n g . Adjusting orientation conditions y i e l d e d no a p p a r e n t improvements i n o r i e n t a b i l i t y . The non-uniform o r i e n t a t i o n of t h i s f i l m i s a t t r i b u t e d t o the development o f s u f f i c i e n t c r y s t a l l i n i t y i n t h e e x t r u s i o n cast f i l m p r i o r t o o r i e n t a t i o n . Orientation o f a r o m a t i c n y l o n MXD-6 was r e n d e r e d somewhat d i f f i c u l t by t h e o c c u r r e n c e o f r a p i d cold c r y s t a l l i z a t i o n above 100°C. The c o l d c r y s t a l l i z a t i o n phenomenon as s e e n i n f i g u r e 1 i s s i m i l a r t o t h e w e l l known c o l d c r y s t a l l i z a t i o n b e h a v i o r o b s e r v e d i n o t h e r c r y s t a l l i z a b l e p o l y a m i d e s a n d PET. To c o m p e n s a t e f o r t h i s , v e r y s h o r t h e a t - u p t i m e s h a d t o be e m p l o y e d f o r successful orientation. In t h e c a s e o f b o t h EVAL EP-E105 a n d SOARNOL D resins, attempts t o u n i a x i a l l y o r i e n t t o 2. 5X were unsuccessful, as t h e f i l m s split and cracked upon drawing. Reducing t h e s t r e t c h r a t e and i n c r e a s i n g t h e o r i e n t a t i o n t e m p e r a t u r e y i e l d e d no s i g n i f i c a n t e f f e c t . As s u c h , b i a x i a l o r i e n t a t i o n o f t h e s e two EVOH f i l m s was not a t t e m p t e d . The d i f f i c u l t y e x p e r i e n c e d i n o r i e n t a t i o n o f EVOH f i l m s i s not s u r p r i s i n g . I k a r i (£) i n d e e d r e p o r t s that d r a w i n g b e l o w t h e s o f t e n i n g p o i n t o f EVOH r e s i n s y i e l d s s l i g h t u n e v e n n e s s a n d c r a c k s a r e l i k e l y t o a p p e a r when t h e draw r a t i o i s i n c r e a s e d . He a t t r i b u t e s t h i s t o t h e c r y s t a l l i z a t i o n accompanying s t r e t c h o r i e n t a t i o n . This i s e s p e c i a l l y t r u e f o r low e t h y l e n e c o n t e n t EVOH g r a d e s . T h o u g h we were u n s u c c e s s f u l in orienting EVOH r e s i n s , m o n o a x i a l l y as w e l l a s b i a x i a l l y o r i e n t e d EVOH f i l m s a r e c o m m e r c i a l l y a v a i l a b l e (EVAL EF-XL m o n o a x i a l l y o r i e n t e d f i l m from K u r a r a y and EXCEED b i a x i a l l y o r i e n t e d film from Okura Industrial Company). Review o f l i t e r a t u r e i n d i c a t e s t h a t t o improve o r i e n t a t i o n i n EVOH resins requires one o r more o f t h e f o l l o w i n g : (1) rapidly quench the sheet from melt to retard crystallization prior to stretching; (2) p l a s t i c i z e t h e sheet (14-16) w i t h w a t e r o r g l y c o l s t o i m p r o v e c h a i n mobility during stretching; (3) b l e n d a s m a l l amount o f n y l o n 6,12 (2) o r t h e r m o p l a s t i c e l a s t o m e r (TPE) b l o c k c o p o l y m e r (XI) (as i n SOARNOL STS r e c e n t l y i n t r o d u c e d by N i p p o n G o h s e i ) ; o r (4) c h o o s e h i g h e r e t h y l e n e c o n t e n t grades. I n f a c t , K u r a r a y h a s two s p e c i a l l y d e s i g n e d h i g h e r ethylene content grades — EVAL EP-K (38 m o l e % e t h y l e n e c o n t e n t ) t o a l l o w deep draw f o r m i n g w i t h o u t




si

3

i


12. SHASTRIETAL.


f i b r i l l a t i o n o f t h e b a r r i e r l a y e r (&) i n s o l i d p r e s s u r e f o r m i n g a n d EVAL EP-G (48 mole% e t h y l e n e c o n t e n t ) f o r b i a x i a l l y oriented film structures. The r e d u c e d v i n y l a l c o h o l c o n t e n t , i n e f f e c t , l o w e r s t h e amount o f h y d r o x y l groups which usually a c t as a c r o s s l i n k between molecules, thereby a f f e c t i n g the o r i e n t a t i o n behavior d u r i n g d r a w i n g (JLS.) . S o l i d s t a t e o r i e n t a t i o n o f b o t h amorphous r e s i n s amorphous n y l o n SELAR PA 342 6 and XHTA 50A y i e l d s r i g i d , crystal clear films. In t h e o r i e n t a t i o n o f SELAR PA 3426 amorphous n y l o n , t h e f i l m s were d r i e d o v e r n i g h t a t 60°C t o reduce t h e absorbed moisture l e v e l i n t h e f i l m p r i o r to orientation. T h i s was n e c e s s a r y t o a v o i d f o a m i n g i n the film when heated above i t s glass transition temperature. Effect of Orientation. The measured oxygen p e r m e a b i l i t y data a r e summarized i n Tables I I and I I I . The permeability values f o r the unoriented films are c o n s i s t e n t with the expected values. S e m i c r y s t a l l i n e p o l y m e r s , VDC c o p o l y m e r a n d a r o m a t i c n y l o n MXD-6 ( T a b l e I I ) showed l i t t l e i f any r e d u c t i o n i n p e r m e a b i l i t y a t t h e s e moderate o r i e n t a t i o n l e v e l s . In f a c t , r e c e n t u n p u b l i s h e d work h a s shown t h a t a r o m a t i c n y l o n MXD-6 e x h i b i t s an i n i t i a l i n c r e a s e i n p e r m e a b i l i t y up t o 3X o r i e n t a t i o n f o l l o w e d by a s i g n i f i c a n t r e d u c t i o n in permeability at higher orientation l e v e l s . The VDC c o p o l y m e r a l s o showed h i g h e r p e r m e a b i l i t y w i t h m o d e r a t e b i a x i a l o r i e n t a t i o n — 1.5 t i m e s t h e p e r m e a b i l i t y o f t h e unoriented film. This i s believed t o be due t o o r i e n t a t i o n o f t h e polymer a f t e r c r y s t a l l i n i t y i s f u l l y developed. I f t h e o r i e n t a t i o n o f VDC c o p o l y m e r s i s i n d u c e d p r i o r t o f u l l development o f c r y s t a l l i n i t y i n t h e m a t e r i a l , one would n o t e x p e c t t o s e e an i n c r e a s e d oxygen permeability. In commercial p r a c t i c e , t h e r e f o r e , forming o f VDC c o p o l y m e r s t r u c t u r e s i s n o r m a l l y done on r a p i d l y quenched polymer to orient i t while still i n the amorphous s t a t e a t t e m p e r a t u r e s n e a r o r above t h e T o f VDC copolymer. Two p l a u s i b l e e x p l a n a t i o n s for the observed higher permeability o f o r i e n t e d VDC c o p o l y m e r s a p p e a r l i k e l y . They are, formation of microvoids during solid state orientation o r a change i n the nature or size of c r y s t a l l i t e s during o r i e n t a t i o n . DSC c h a r a c t e r i z a t i o n o f t h e same f i l m s showed a n o t i c e a b l e d i f f e r e n c e i n t h e i r crystallinities — 24% f o r t h e b i a x i a l l y o r i e n t e d film v s . 33% f o r t h e e x t r u s i o n c a s t f i l m . Also the melting transition a p p e a r s t o be somewhat b r o a d e n e d f o r t h e b i a x i a l l y o r i e n t e d f i l m ( F i g u r e 2) s u g g e s t i n g an i n c r e a s e in the d i s t r i b u t i o n of c r y s t a l l i t e size. However, wide a n g l e x - r a y d i f f r a c t i o n s t u d i e s r e v e a l no i n d i c a t i o n o f any s t r u c t u r a l d i f f e r e n c e s between t h e e x t r u s i o n c a s t and the b i a x i a l l y o r i e n t e d f i l m . T h i s seems t o s u p p o r t t h e m


245

246


T a b l e I I . E f f e c t o f O r i e n t a t i o n on Oxygen B a r r i e r C h a r a c t e r i s t i c s of Semicrystalline B a r r i e r Resins

0

p e r m e a b i l i t y 023.5°C & 65% RH ( c c - m i l / 1 0 0 i n 24 h r . atm) 2


2

A.

VDC Copolymer

( e x p e r i m e n t a l g r a d e XU

C o m p r e s s i o n molded f i l m Extrusion cast f i l m Biaxially oriented - 2 . 5 x 2 . 5 B.

32009.02) 0.20 ± 0.02 0.20 ± 0.01 0.30 ± 0 . 0 1

A r o m a t i c N y l o n MXD-6

Extrusion Biaxially

cast oriented

0.37 ± 0.09 Q.39

- 2 χ 2

T a b l e I I I . E f f e c t o f O r i e n t a t i o n on Oxygen B a r r i e r C h a r a c t e r i s t i c s o f Amorphous B a r r i e r R e s i n s

0

p e r m e a b i l i t y (323.5°C & 65% RH (Ho-mil/100 i n 24 h r . atm) 2

2

A.

Amorphous N y l o n SELAR PA 342 6

Extrusion cast U n i a x i a l l y o r i e n t e d - 2.5x B i a x i l l y oriented - 2 . 5 x 2 . 5 B.

1.40 ± 0.31 1.14 ± 0.07 1.01 ± 0 . 0 1

P o l y a c r y l i c - i m i d e XHTA-50A

Extrusion cast Uniaxially oriented Biaxially

oriented

- 2x 2.5x - 2 χ 2

3.12 ± 0.17 2.95 ± 0.04 2.84 2,76 ± Q . Q3


12. SHASTRIETAL.


O O

O


w

o o

CM (M m (MB

CM *3 o x 0*3

(MX *3

c

c

O-i

(M^

••Hi—«

o m

.t—«

00 3*3 LO 4)x XL IxJU

(MO 43 XO O X

i

I

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/

Μ

ω

(DU

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American Chemical Society Library 1155 15th St., N.W. Koros; Barrier Polymers Structures Washington, D.C. and 20038 ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

247

248


c o n t e n t i o n o f m i c r o v o i d s development from s o l i d state orientation o f t h e VDC c o p o l y m e r . Indeed, this h y p o t h e s i s i s c o r r o b o r a t e d by t h e o b s e r v a t i o n s o f n o n uniform stretching o f VDC c o p o l y m e r films. The characteristic necking behavior i s associated with y i e l d e d a n d u n y i e l d e d zones, which i s expected t o l e a d to formation o f microcrazes responsible f o r the observed higher permeability. The effect of orientation on amorphous barrier r e s i n s SELAR PA 3426 and XHTA-50A a r e shown i n T a b l e I I I . The measured oxygen p e r m e a b i l i t y o f 1.4 c c - m i l / 1 0 0 i n 24 h r . atm f o r u n o r i e n t e d e x t r u s i o n c a s t SELAR PA 3426 f i l m i s r e d u c e d b y 19% upon u n i a x i a l o r i e n t a t i o n , w h i l e t h e permeability o f b i a x i a l l y o r i e n t e d f i l m s a r e 28% l o w e r than that of extrusion cast film. Similarly, the d e c r e a s e i n oxygen p e r m e a b i l i t y w i t h 2X and 2.5X u n i a x i a l o r i e n t a t i o n i n XHTA-50A a r e 5% and 9% r e s p e c t i v e l y , f r o m the measured v a l u e o f 3.1 c c - m i l / 1 0 0 i n - 24 h r . atm f o r unoriented film. The c o r r e s p o n d i n g reduction in p e r m e a b i l i t y w i t h 2X χ 2X b i a x i a l o r i e n t a t i o n i s 12%. The e f f e c t o f o r i e n t a t i o n on oxygen p e r m e a b i l i t y o f the medium a n d h i g h b a r r i e r resins i s s e e n t o be d e p e n d e n t upon t h e m o r p h o l o g i c a l n a t u r e o f t h e b a r r i e r resin prior to orientation. A p l o t o f t h e oxygen t r a n s m i s s i o n r a t e s as a f u n c t i o n o f t h e o v e r a l l draw ratio ( f i g u r e 3) i l l u s t r a t e s t h i s c l e a r l y . While t h e semicrystalline p o l y m e r s , VDC c o p o l y m e r , a n d a r o m a t i c n y l o n MXD-6, show l i t t l e change i n t h e p e r m e a b i l i t y with m o d e r a t e amounts o f o r i e n t a t i o n i n the s o l i d state, o r i e n t a t i o n o f t h e amorphous p o l y m e r s SELAR PA 3426 a n d XHTA-50A c a u s e s r e d u c t i o n i n t h e p e r m e a b i l i t y by 5-30% i n both resins, depending upon the overall level of orientation. The permeability reductions seen i n amorphous b a r r i e r r e s i n s a g r e e v e r y w e l l w i t h t h e e x p e c t e d changes as p e r p r e d i c t i v e r e l a t i o n s h i p s c o r r e l a t i n g t h e p o l y m e r structural index, "Permachor" values t o i t s gas permeability (19-21). However, f o r t h e s e m i c r y s t a l l i n e p o l y m e r s , t h e changes o b s e r v e d i n t h e p e r m e a b i l i t i e s a r e significantly l o w e r t h a n t h e r e d u c t i o n s o f o v e r 30% p r e d i c t e d from e m p i r i c a l r e l a t i o n s . A c c o r d i n g t o Salame ( 19-21) , s u c h l a r g e r e d u c t i o n s a r e e x p e c t e d f r o m t h e increase i n tortuosity c a u s e d by t h e l i n i n g up o f crystallites. Y e t , e x p e r i m e n t a l l y , such g r e a t e r d e g r e e s of reduction i n permeability are t y p i c a l l y observed only a t o r i e n t a t i o n l e v e l s g r e a t e r t h a n 5X. P a u l o s and Thomas (ϋ) i n d e e d f o u n d r e d u c t i o n i n t h e oxygen p e r m e a b i l i t y i n HDPE o f l e s s t h a n 10% a t 2-2.5X o r i e n t a t i o n s . Swaroop and Gordon (22) a l s o r e p o r t relatively insignificant change i n oxygen p e r m e a b i l i t y o f PET a t draw r a t i o s l e s s than three. Our r e s u l t s f o r MXD-6 and VDC c o p o l y m e r a r e consistent with these f i n d i n g s .


2

2


12.

SHASTRIETAL.

Permeability ofCompétitive Oxygen-Barrier Resins

10


ΧΗΤΑ-50 Α °

ο

w

•

Φ

SELAR ΡΑ 3426

α

• 1

α

Η

(0

ο ο •

MXD-6 ο ο

•

•

Φ

Φ

VDC Copolymer

Overall

Draw Ratio

F i g u r e 3 . Oxygen t r a n s m i s s i o n r a t e s as a f u n c t i o n o f t h e o v e r a l l draw r a t i o , i l l u s t r a t i n g t h e dependence on t h e m o r p h o l o g i c a l n a t u r e o f t h e barrier resin prior to orientation.


249

250



Conclusion The r e s u l t s h e r e s u g g e s t t h a t amorphous p o l y m e r s a r e more r e a d i l y o r i e n t a b l e than s e m i c r y s t a l l i n e polymers. The d i f f i c u l t y i n orientability of semi-crystalline resins can be a t t r i b u t e d t o t h e f a c t t h a t c r y s t a l l i n i t y i s f u l l y d e v e l o p e d i n t h e f i l m s p r i o r t o t h e o r i e n t a t i o n s t e p . .In commercial practice, therefore, these polymers a r e r a p i d l y quenched t o p e r m i t o r i e n t a t i o n w h i l e s t i l l i n t h e amorphous s t a t e . The e f f e c t o f o r i e n t a t i o n on t h e oxygen p e r m e a b i l i t y i s dependent upon t h e m o r p h o l o g i c a l n a t u r e o f t h e b a r r i e r resin prior to orientation. For the semicrystalline p o l y m e r s , VDC copolymer, and a r o m a t i c n y l o n MXD-6, l i t t l e change was o b s e r v e d i n t h e p e r m e a b i l i t y w i t h o r i e n t a t i o n from t h e s o l i d - s t a t e . However, s o l i d - s t a t e o r i e n t a t i o n o f t h e amorphous p o l y m e r s SELAR PA 342 6 a n d XHTA-50A was shown t o d e c r e a s e p e r m e a b i l i t y by 5-30% i n b o t h r e s i n s , d e p e n d i n g upon t h e l e v e l o f o r i e n t a t i o n .

Literature Cited 1. De Candia, F . ; Vittoria, V . ; Peterlin, A. Journal Polym. Sci., Polym. Phys. 1985, 23, pp. 1217-1234. 2. Holden, P.S.; Orchard, G. A. J ; Ward, I. M. Journal Polym. Sci., Polym. Phys. 1985, 23, pp. 709-731. 3. Paulos, J . P.; Thomas, E. L. Journal Appl. Polym. Sci. 1980, 25, pp. 15-23. 4. De Candia, F . ; Vittoria, V.; Rizzo, G . ; Titomanlio, G. Journal Macromol. Sci., Phys. 1986, B25 (3), pp. 365-378. 5. Devries A. J . Polym. Eng. Sci., 1983, 23 (5), pp. 241-246. 6. Ikari, K. Proceedings of the International Coextrusion Conference COEX Europe '86, 1986, Cologne, pp. 21-56. 7. Okata, H . ; Okaya, T . ; Kawai, S. Proceedings of the International Coextrusion Conference COEX America'86, 1986, pp. 63-87. 8. Foster, R. H. Polym. News, 1986, 11, pp. 264-271. 9. Culter, J . D. Journal Plast. Film & Sheeting, 1985 1, pp. 215-225. 10. Mitsutani, Α.; Morimoto, O. Research and Development Report No. 30, Nippon Chemtec Consulting Inc., JAPAN, 1985. 11. Schroeder, G. O. FUTURE-PAK '84, Second International Ryder Conference on Packaging Innovations, 1984, pp. 333-355. 12. Ikari, K. Proceedings of the Second International Conference on Coextrusion Markets and Technology COEX '82, 1982, pp. 1-42.



12. SHASTRI ET AL. Permeability of Competitive Oxygen-Barrier Resins 251

13. EVAL Technical Bulletin, Kuraray Co. L t d . , No. KIC102. 14. Japan Kokai 50-144776, "Saponified Ethylene-Vinyl Acetate Copolymer Films," assigned to Toyobo, 1975. 15. Japan Kokai 50-144777, "Saponified Ethylene-Vinyl Acetate Copolymer Films," assigned to Toyobo, 1975. 16. Chiba, T . , et a l . US 3,419,654, 1968. 17. Moriyama, T . ; Asano, K.; Iwanami, T. Proceedings of the International Coextrusion Conference COEX Europe '86, 1986, pp. 69-103 18. Yoshida, H . ; , Tomizawa, K.; Kobayashi, Y. Journal Appl. Polym. Sci., 1979, 24, pp. 2277-2287. 19. Salame, M. Polym. Eng. S c i . , 1986, 26 (22), pp. 1543-1546. 20. Salame, M. Journal Plast. Film & Sheeting, 1986, 2, pp. 321-334. 21. Salame, M. FUTURE-PAK '84, Second International Ryder Conference on Packaging Innovations, 1984, pp. 119-136. 22. Swaroop Ν.; Gordon, G. A. Polym. Eng. Sci., 1980, 20 (1), pp. 78-81. RECEIVED November 14, 1989


Barrier Polymers and Structures - American Chemical Society

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