Dynamic Melt Rheology of PolyethyleneâIonomer Blends - ACS

Chapter 8

Dynamic Melt Rheology of Polyethylene—Ionomer Blends

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Gary R. Fairley and Robert E. Prud'homme Centre de Recherche en Sciences et Ingénierie des Macromolécules, Chemistry Department, Laval University, Québec G1K 7P4, Canada

The addition of a copolymer has been shown to be a method of improving the mechanical properties of polyethylene/polyamide blends. One copolymer which has had particular success i s poly(ethylene-comethacrylic acid) (EMA) where the acid groups are partially neutralized by metal ions (EMA-salt). Dynamic melt rheology studies were carried out on PE/EMA and PE/EMA-salt in order to better understand the role of EMA-salt as a compatibilizer in the PE/EMA/PA system. The time-temperature super position principle was applicable in all cases for G' . Also, G' super master curves were constructed for blends of PE/EMA and PE/EMA-salt when the EMA and EMA-salt are derived from the same parent polymer. Superposition of G" was possible for a l l blends containing EMA in the free acid form, but not for those in the salt form, with the extent of deviation from superposability being a function of EMA-salt concentration. P o l y ( e t h y l e n e - c o - m e t h a c r y l i c a c i d ) (EMA), where t h e a c i d groups a r e p a r t i a l l y on f u l l y n e u t r a l i z e d (EMA-salt) by m e t a l i o n s , a r e i n t e r e s t i n g m a t e r i a l s because o f t h e i r unique p r o p e r t i e s as homopolymers (1-2) and t h e i r a b i l i t y t o c o m p a t i b i l i z e c e r t a i n i n c o m p a t i b l e b l e n d s (3-14). EMA-salts a r e l i g h t weight t r a n s p a r e n t m a t e r i a l s p o s s e s s i n g low t e m p e r a t u r e impact and f l e x toughness, good a b r a s i o n and solvent r e s i s t a n c e (1-2). EMA (5) and EMA-salts (15) have been used i n b i n a r y b l e n d s i n o r d e r t o i n c r e a s e t h e impact s t r e n g t h and t e n s i l e s t r e n g t h o f polyamides (PA). EMA and E M A - s a l t s have a l s o r e c e n t l y been used t o improve t h e toughness of poly(ethylene terephthalate) while m a i n t a i n i n g l o w p e r m e a b i l i t y t o hydrocarbons and o t h e r o r g a n i c solvents (16). 0097-6156/89/0395~0211$06.00A) ο 1989 American Chemical Society

Utracki and Weiss; Multiphase Polymers: Blends and Ionomers ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

212

MULTIPHASE POLYMERS: BLENDS AND IONOMERS

EMA and E M A - s a l t s can a l s o be used t o improve t h e m e c h a n i c a l p r o p e r t i e s o f i n c o m p a t i b l e b l e n d s (3-14) . The r o l e o f t h e EMA o r EMA-salt i n t h e s e systems i s not f u l l y u n d e r s t o o d . In a recent p u b l i c a t i o n , we have s t u d i e d t h e p o l y e t h y l e n e / E M A - s a l t / P A system by l o o k i n g a t t h e two b i n a r y systems from which i t i s made: PE/EMAs a l t and EMA-salt/PA (17) . C o n c e r n i n g t h e EMA-salt/PA system, i t has been s u g g e s t e d t h a t an a m i d a t i o n r e a c t i o n can o c c u r between t h e NH t e r m i n a l groups o f t h e PA and t h e COOH groups o f t h e EMA, i n a d d i t i o n t o p o s s i b l e hydrogen b o n d i n g (5) . However, v e r y l i t t l e work has been c a r r i e d out i n o r d e r t o d e t e c t i n t e r a c t i o n s i n t h e PE/EMA-salt system. I n our p r e v i o u s s t u d y ( 1 7 ) , PE/EMA-salt b l e n d s were shown t o be c o m p a t i b l e (not i n t h e thermodynamic sense) f o r a g i v e n m i x i n g t e c h n i q u e and p a r a m e t e r s . I t was a l s o p o i n t e d out t h a t t h e r e i s s e p a r a t e c r y s t a l l i z a t i o n o f PE and EMA-salt i n PE/EMA-salt b l e n d s , w i t h o u t any p e r t u r b a t i o n o f t h e c r y s t a l s t r u c t u r e o r degree o f c r y s t a l l i n i t y o f t h e o t h e r component. Since the i n t e r a c t i o n s leading t o the c o m p a t i b i l i z a t i o n of the mechanical p r o p e r t i e s i n PE/EMA-salt b l e n d s do not o c c u r i n t h e c r y s t a l l i n e phase, t h e y must be p r e s e n t i n t h e amorphous phase. Thus, i t i s t h e o b j e c t o f t h e p r e s e n t s t u d y t o i n v e s t i g a t e t h e dynamic m e l t p r o p e r t i e s o f PE/EMA and PE/EMA-salt b l e n d s i n o r d e r t o b e t t e r u n d e r s t a n d t h e morphology o f t h e s e systems, as w e l l as t o shed some l i g h t on t h e e x i s t e n c e o f i o n i c domains i n PE/EMA and PE/EMA-salt b l e n d s . 2

EXPERIMENTAL Materials The LDPE's were o b t a i n e d from Monsanto (LDPE-M8011) and Dow Chemical (LDPE-493c); the poly(ethylene-co-methacrylic a c i d ) ) ( N u c r e l - 1 2 1 4 ) and ionomers ( S u r l y n - 8 6 6 0 and S u r l y n - 9 9 5 0 ) were g r a c i o u s l y p r o v i d e d by t h e Dupont C h e m i c a l Company. Surlyn-9950 was refluxed in p-xylene at 130°C for a p p r o x i m a t e l y 1 h, a f t e r which t h e polymer g e l was p l a c e d i n a s o l u t i o n o f 2:1 (v/v) 2N H C l / t e t r a h y d r o f u r a n (THF). The m i x t u r e was r e f l u x e d f o r 24 h w i t h v i g o r o u s s t i r r i n g i n o r d e r t o c o n v e r t a l l t h e n e u t r a l i z e d a c i d groups t o t h e i r f r e e a c i d form. T h i s EMAZn-0 sample was t h e n r e f l u x e d i n a 1:2(v/v) s o l u t i o n o f s a t u r a t e d z i n c s u l f a t e / T H F w i t h v i g o r o u s s t i r r i n g f o r a p e r i o d o f 5 days t o o b t a i n an EMA-Zn s a l t c o n t a i n i n g more s a l t t h a n t h e o r i g i n a l EMAZn-20 sample. The p e r c e n t i o n i z a t i o n , which was v e r i f i e d by IR s p e c t r o s c o p y (18), was found t o be 40%. Some c h a r a c t e r i s t i c s o f t h e homopolymers and copolymers used i n t h i s s t u d y a r e shown i n T a b l e I : p e r c e n t a c i d c o n t e n t , p e r c e n t neutralization, number-average molecular weight (Μη), p o l y d i s p e r s i t y i n d e x (Mw/Mn) and t h e nomenclature used. A l l pure components and b l e n d s were p r e p a r e d by m i x i n g i n a M i n i Max molder, model CS-183 ( 1 9 ) . The m i x i n g o f a l l samples was c a r r i e d out a t 150°C f o r a p e r i o d o f 10 min. The samples were s u b s e q u e n t l y i n j e c t e d i n t o a c y l i n d r i c a l mold c a v i t y w i t h a d i a m e t e r o f 15.8 mm and a t h i c k n e s s o f 3.0 mm. A l l b l e n d s were p r e p a r e d w i t h t h e LDPE-493c sample, e x c e p t t h o s e w i t h EMA-Na and EMA which were p r e p a r e d w i t h t h e LDPEM8011 sample. r

r


r

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Rheology ofPolyethylene-1onomer Blends

Measurements Dynamic m e c h a n i c a l p r o p e r t i e s were measured on a Rheometrics System-4 rheometer w i t h p a r r a l l e l p l a t e geometry. The c y l i n d r i c a l samples were p l a c e d between t h e p a r r a l l e l p l a t e s and m e l t e d . The gap between t h e p l a t e s was s u b s e q u e n t l y reduced t o 1.2 mm and, a f t e r r e l a x a t i o n o f t h e sample, t h e a p p r o p r i a t e measurements c a r r i e d o u t . Dynamic m e c h a n i c a l p r o p e r t i e s o f a l l pure components a n d b l e n d s were measured a s a f u n c t i o n o f p e r c e n t s t r a i n and i n d i c a t e d a l i n e a r v i s c o e l a s t i c r e g i o n up t o a p p r o x i m a t e l y 30-35 p e r c e n t . T h e r e f o r e , a l l r h e o l o g i c a l e x p e r i m e n t s were conducted a t a s t r a i n r a t e o f 20 p e r c e n t . I n c a s e s where t h e r m a l d e g r a d a t i o n o c c u r r e d (as seen i n t i m e sweep), t h e h e a t i n g chamber was c o n t i n u o u s l y purged w i t h l i q u i d n i t r o g e n . Frequency sweeps, and i n some c a s e s f r e q u e n c y - t e m p e r a t u r e sweeps, were performed on a l l pure components and b l e n d s . RESULTS Homopolymers and Copolymers F i g u r e 1 shows t h e f r e q u e n c y dependence o f t h e a b s o l u t e v a l u e o f t h e complex v i s c o s i t y η * f o r EMA-Zn-0 and EMA-Zn-40 a s compared t o EMA-Zn-20. I t c a n be seen i n t h i s f i g u r e t h a t t h e z e r o s h e a r v i s c o s i t y T ] i s a s y m p t o t i c a l l y approached f o r a l l t h e EMA-salt and EMA samples. This result i s consistent with the observation o f E a r n e s t , Macknight e t a l . (18,20-21) who have shown t h a t t h e z e r o s h e a r v i s c o s i t y i s a s y m p t o t i c a l l y approached f o r EMA and i t s m e t h y l e s t e r ; however, i t i s n o t f o r i t s 70% n e u t r a l i z e d sodium s a l t , which i s n o t i n c o n s i s t e n t w i t h t h e f a c t t h a t t h e l a r g e s t s a l t c o n t e n t o f F i g . 1 i s 40%. F i g u r e 2 shows t h e master c u r v e o f G' and t h e pseudo-master c u r v e o f G f o r pure EMA-Zn-20, f o r a temperature range o f 120 t o 250°C, u s i n g a r e f e r e n c e temperature o f 150°C. As c a n be seen, t h e r e i s good s u p e r p o s i t i o n o f t h e G' d a t a onto a s i n g l e c u r v e . U s i n g t h e same s h i f t f a c t o r s a and r e f e r e n c e temperature a s used i n G', s u p e r p o s i t i o n o f G" was attempted. There i s a c l e a r breakdown o f t i m e - t e m p e r a t u r e s u p e r p o s i t i o n , p a r t i c u l a r l y a t h i g h frequencies. This thermorheological complexity i s c h a r a c t e r i s t i c o f E M A - s a l t s which e x h i b i t microphase s e p a r a t i o n o f i o n i c domains (18, 20-21). F o r t h e same r e f e r e n c e temperature a n d temperature range, t h e r m o r h e o l o g i c a l c o m p l e x i t y was a l s o d i s p l a y e d i n t h e EMA-Na a n d EMA-Zn-40 samples. I n c o n t r a s t , EMA shows good s u p e r p o s i t i o n o f b o t h G' and G o v e r a temperature range o f 120°C t o 250°C, u s i n g a r e f e r e n c e temperature o f 150°C a n d t h e same s h i f t f a c t o r s ( F i g u r e 3) . I d e n t i c a l r e s u l t s were o b t a i n e d f o r t h e s u p e r p o s a b i l i t y o f G' a n d G f o r EMA-Zn-0. Q

w

fc

n

M


213

214


T a b l e I : C h a r a c t e r i z a t i o n o f t h e Polymers Used

POLYMER

CODE

% ACID

EMA-Zn-0 EMA-Zn-20

ION

% ION

15 S u r l y n 9950

EMA-Zn-40

Mn(kg/mol) M /M w

n

16

2.9

15

Zn

20

16

2.9

15

Zn

40

16

2.9

Na

50

13

3.1

EMA-Na

S u r l y n 8660

9

EMA

N u c r e l 1214

12

18

3.9

LDPE

Dow 493c

0

139

6.0

LDPE

Monsanto 8011

0

4

11

,

,

-1

0

1

, 2

I 3

LOG ω (rad/s) F i g u r e 1. Complex v i s c o s i t y T|* v e r s u s a n g u l a r f r e q u e n c y ω f o r EMA-Zn-40, EMA-Zn-20 and EMA-Zn-0.


8.

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-3

-2

Rheology ofPolyetkylene-Ionomer Blends

0

-1

1

2

-2

LOG a cj (rad/s) t

F i g u r e 2. G' master c u r v e a n d G pure EMA-Zn-20.

-3

-

2

-

1

w

1

0

pseudo-master

curve f o r

2

LOG α ω (rad/s) {

F i g u r e 3.

G' and G" master c u r v e s f o r pure EMA.


215

216


Blends The f o l l o w i n g f i v e b i n a r y systems were s t u d i e d : PE/EMA, PE/EMA-Na, PE/EMA-Zn-40, PE/EMA-Zn-20 and PE/EMA-Zn-0. These systems were i n v e s t i g a t e d f o r c o m p o s i t i o n s o f 20, 40, 60 and 80 p e r c e n t by weight PE o v e r a t e m p e r a t u r e range o f 120 t o 250°C M a s t e r c u r v e s o f G' were c o n s t r u c t e d f o r a l l c o m p o s i t i o n s o f t h e f i v e d i f f e r e n t b i n a r y systems u s i n g a r e f e r e n c e temperature o f 150°C A t y p i c a l r e s u l t o f a G' master c u r v e i s g i v e n i n F i g u r e 4, which i s a 40/60 b l e n d o f PE/EMA-Zn-20. As seen, s a t i s f a c t o r y s u p e r p o s i t i o n i s a t t a i n e d f o r G' i n t h e s e b l e n d s . U s i n g t h e same s h i f t f a c t o r s as f o r G', s u p e r p o s i t i o n was a t t e m p t e d f o r G". As can be seen, t h e r e i s a d e f i n i t e breakdown o f t h e t i m e - t e m p e r a t u r e superposition p r i n c i p l e at high frequencies ( F i g . 4). I d e n t i c a l r e s u l t s were o b t a i n e d f o r PE/EMA-Zn-40 and PE/EMA-Na b l e n d s . For t h e s e PE/EMA-salt systems, as t h e amount o f ionomer p r e s e n t i n t h e b l e n d d e c r e a s e s , t h e f r e q u e n c y range o v e r which s u p e r p o s i t i o n o f G i s p o s s i b l e i n c r e a s e s . As seen i n a d i f f e r e n t p e r s p e c t i v e , t h e d e c r e a s e i n G as a f u n c t i o n o f temperature a t h i g h f r e q u e n c i e s i s r e d u c e d upon t h e a d d i t i o n o f PE t o PE/EMA-salt b i n a r y systems. M a s t e r c u r v e s can be c o n s t r u c t e d f o r b o t h G' and G" o v e r a t e m p e r a t u r e range o f 120 t o 250°C, u s i n g a r e f e r e n c e temperature o f 150°C, f o r b o t h PE/EMA-Zn-0 and PE/EMA b i n a r y systems. A typical r e s u l t i s g i v e n i n F i g u r e 5, which shows master c u r v e s o f G' and G" f o r a 60/40 PE/EMA-Zn-0 b l e n d . To summarize t h e s e r e s u l t s , we f i n d s u p e r p o s a b i l i t y o f b o t h G' and G" f o r PE/EMA systems (EMA i n t h e f r e e a c i d form) and s u p e r p o s a b i l i t y o f G' but not o f G f o r PE/EMA-salt systems. F u r t h e r m o r e , t h e degree o f n o n - s u p e r p o s i b i l i t y o f G i n PE/EMA-salt systems i n c r e a s e s w i t h an i n c r e a s e i n ionomer c o n t e n t . These r e s u l t s i n d i c a t e t h a t t h e n o n - s u p e r p o s i b i l i t y o f G i n PE/EMA-salt systems i s due s o l e l y t o t h e p r e s e n c e o f i o n i c domains which o c c u r as a r e s u l t o f t h e n e u t r a l i z a t i o n o f t h e f r e e a c i d groups by m e t a l i o n s i n t h e pure EMA copolymer. However, t h e f a c t t h a t s u p e r p o s i t i o n a p p l i e s t o G' and G" does not n e c e s s a r i l y i m p l y t h a t t h e systems behave as s i n g l e phase systems s i n c e i t has been shown (22-23) t h a t two-phase b l e n d s can a c t as t h e r m o - r h e o l o g i c a l l y s i m p l e m a t e r i a l s f o r polymer b l e n d s c o n s i s t i n g o f polymers o f h i g h p o l y d i s p e r s i t y , a l t h o u g h we b e l i e v e t h a t t h i s i s a r e l a t i v e l y rare case. F o r p o l y m e r s , i t has been s u g g e s t e d t h a t t h e C o l e - C o l e r e p r e s e n t a t i o n o f t h e i m a g i n a r y p a r t (T] ) o f t h e complex v i s c o s i t y v e r s u s i t s r e a l p a r t (Τ]') shows c e r t a i n i m p o r t a n t d i f f e r e n c e s f o r homogeneous systems as compared t o heterogeneous systems (22-27). A c c o r d i n g t o t h i s p r o p o s a l , f o r homogeneous systems, a unique c i r c u l a r a r c i s g i v e n which passes t h r o u g h t h e o r i g i n whereas f o r a heterogeneous system, a s e r i e s o f i n t e r p e n e t r a t i n g a r c s i s g i v e n . F i g u r e 6 shows C o l e - C o l e p l o t s f o r pure EMA-Zn-20 a t 150°C and 180°C. U n f o r t u n a t e l y due t o t h e h i g h p o l y - d i s p e r s i t y o f t h e pure polymers s t u d i e d , t h e c i r c u l a r a r c p a s s i n g t h r o u g h t h e o r i g i n i s t o o f a r from t h e r e a l a x i s , not p e r m i t t i n g t h e u n e q u i v o c a l d e t e r m i n a t i o n o f t h e e x i s t e n c e o r absence o f more t h a n one c i r c u l a r arc. T h i s i s a c h a r a c t e r i s t i c o f a l l pure components s t u d i e d h e r e i n as w e l l as t h e i r b i n a r y b l e n d s . n

M

n

n

n

N


8.

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Rheology ofPolyethyUne-Ionomer Blends

1 Y Ο SE

ο

...;·.·.'. 180 C %·%·'·· 210 C

ο iQ.

120 C " * * 150 * C

Ο

o-1 ο

ο H -1

-3

0

-2

1

-2

2

LOG a cj (rad/s) t

F i g u r e 4. G' master c u r v e and G" pseudo-master c u r v e f o r a 40/60 b l e n d o f PE/EMA-Zn-20.

1 h

SE

σ ι α.

ο

1

ο o-1 ο

-3

Ο

0ο ο

_l

• 1 0

L_

1

2

3

4

-2

LOG a cj (rad/s) t

F i g u r e 5. G' and G" master PE/EMA-Zn-0.

curves

f o r a 60/40 b l e n d o f


217

218


Han (28-34) has found t h a t t h e temperature independence o f G' when p l o t t e d a g a i n s t G" t o be a u n i v e r s a l f e a t u r e o f a l l homogeneous v i s c o - e l a s t i c f l u i d s . T h i s a u t h o r has a l s o p o s t u l a t e d t h e g e n e r a l r u l e t h a t , f o r a m i s c i b l e b l e n d / t h e G'-G" p l o t i s invariant to changes i n blend concentration, while f o r heterogeneous b l e n d s such i n v a r i a n c e i s n o t observed. However, R o l a n d (35) has shown an example o f a m i s c i b l e b l e n d e x h i b i t i n g a v a r i a t i o n i n t h e G'-G" p l o t as a f u n c t i o n o f c o m p o s i t i o n , which i s a t v a r i a n c e w i t h t h e above-mentioned p r o p o s a l . I n t h i s s t u d y , G'-G p l o t s o f t h e pure polymers show a temperature i n v a r i a n c e f o r t h o s e polymers n o t c o n t a i n i n g m e t a l ions. F o r example, F i g u r e 7 shows G'-G p l o t s f o r pure EMA-Zn-20 at three d i f f e r e n t temperatures. As c a n be seen and as i s t h e case f o r EMA-Na and EMA-Zn-40 samples, t h e r e i s a d e v i a t i o n i n t h e G'G p l o t a t h i g h f r e q u e n c i e s as t h e temperature i s i n c r e a s e d . B i n a r y b l e n d s o f PE/EMA-Zn-0 and PE/EMA show no temperature dependence o f t h e G'-G p l o t s as a f u n c t i o n o f temperature. In the case o f b l e n d s o f PE/EMA-Zn-20, PE/EMA-Zn-40 and PE/EMA-Na, t h e r e i s an u p r i s e i n t h e G'-G" p l o t a t h i g h f r e q u e n c i e s . A typical r e s u l t i s g i v e n i n F i g u r e 8, which i s f o r a 60/40 PE/EMA-Zn-20 blend a t three d i f f e r e n t temperatures. I n b l e n d s o f PE/EMA-salt, t h e amount o f d e v i a t i o n i n G'-G p l o t s as a f u n c t i o n o f temperature i s reduced as t h e c o n c e n t r a t i o n o f PE i n t h e b l e n d i s i n c r e a s e d . The d e v i a t i o n o f G'-G as a f u n c t i o n o f temperature, i n b l e n d s c o n t a i n i n g EMA-salt, c a n be s i m p l y r e l a t e d t o t h e n o n - s u p e r b i l i t y o f G f o r pure E M A - s a l t s . S i n c e p l o t s o f G'-G a r e temperature dependent i n some o f t h e systems s t u d i e d , t h e i r c o m p o s i t i o n dependence was i n v e s t i g a t e d a t a constant temperature. As seen i n F i g u r e 9 f o r t h e PE/EMA-Zn-20 system, t h e r e i s a s t r o n g c o m p o s i t i o n dependence o f G'-G p l o t s as i s t h e case f o r a l l t h e systems s t u d i e d . Furthermore, t h e composition dependence becomes more i m p o r t a n t as t h e second component i n t h e b l e n d becomes more d i f f e r e n t t h a n pure PE (increase i n percent acid content and i n c r e a s e i n p e r c e n t neutralization) . I t i s w e l l known (36-39) t h a t i n a two phase polymer system where t h e r e i s a sharp i n t e r f a c e and no i n t e r a c t i o n s between t h e phases t h a t i n t e r l a y e r s l i p p a g e f r e q u e n t l y o c c u r s . This i n t e r l a y e r slippage gives r i s e t o a reduction i n blend v i s c o s i t y o r a n e g a t i v e d e v i a t i o n from a d d i t i v i t y i f t h e v i s c o s i t y i s p l o t t e d as a f u n c t i o n o f c o m p o s i t i o n a t a g i v e n temperature and frequency. F i g u r e 10 shows t h e a b s o l u t e v a l u e o f t h e complex v i s c o s i t y f o r t h e PE/EMA-Zn-20 system a t 150°C f o r 0.1, 1, 10, 100 and 500 Hz as a f u n c t i o n o f c o m p o s i t i o n . These r e s u l t s i n d i c a t e t h a t t h e complex v i s c o s i t y v a r i e s l i n e a r l y as a f u n c t i o n o f c o m p o s i t i o n . T h i s i s a t y p i c a l r e s u l t f o r PE/EMA and PE/EMA-salt b l e n d s , as t h e PE/EMA-Zn-O, PE/EMA, PE/EMA-Zn-40 and PE/EMA-Na show t h e same linear relationship between t h e complex viscosity and t h e c o m p o s i t i o n a t 150°C. The s c a t t e r o f t h e d a t a becomes more i m p o r t a n t a t l o w e r f r e q u e n c i e s because t h e p r e c i s i o n o f t h e s e values i s lower. F i g u r e 11 shows t h e a b s o l u t e v a l u e o f t h e complex v i s c o s i t y as a f u n c t i o n o f c o m p o s i t i o n f o r t h e PE/EMA-Zn-20 system a t 210°C a t 1, 10, 100, and 500 Hz. I n t h i s c a s e , t h e system shows p o s i t i v e d e v i a t i o n s from t h e a d d i t i v i t y r u l e ( s t r a i g h t l i n e ) . n

n

n

n

n

n

n

n

n


8.

Rheology ofPolyethylene-Ionomer Blends


600

^

400 L

σ α.

150 C

Ρ* 200

''180 C 500

1000

1500

2000

1

η (Ρα.s) F i g u r e 6. A Cole-Cole representation of the imaginary part as a f u n c t i o n o f i t s r e a l p a r t (Τ]' ) o f t h e complex v i s c o s i t y f o r p u r e EMA-Zn-20 a t 150 and 1 8 0 ° C .

ο 150deg • 180deg * 210deg

-1

F i g u r e 7. 210°C.

G' v s . G

0 LOG G" (ΚΡα) n

1

f o r p u r e EMA-Zn-20 a t 150, 180


and

219

220


ο

ο 180 C

Ο

1

5

0

C

ο

Λ&

Ql

Ô ο q

0

-1 LOG G" (kPa)

F i g u r e 8. G' v s . G" f o r a 60/40 PE/EMA-Zn-20 150, 180 and 210°C.

• ΡΕ •80/20 ^60/40 '40/60 '20/80 •s9950

Q-

sample a t

^ » »ο •

fi* Ο Ο

-1 LOG G" (ΚΡα)

F i g u r e 9. G' v s . G" f o r p u r e ΡΕ, pure EMA-Zn-20, and 80/20, 60/40, 40/60, 20/80 PE/EMA-Zn-20 b l e n d s .


8.


FAIRLEY& PRUD'HOMME

1E5

1Hz »

w

1E4

-

δ

-m

1Ηζ____, 10Hz

Q. 100Hz 1000f 500Hz

100

1

1

1

40 60 PERCENT PE

20

1 80

100

Figure 10. Complex v i s c o s i t y (η*) versus composition f o r PE/EMA-Zn-20 at 150 °C and 0.1/ l 10/ 100 and 500 Hz. f

1E4

40 60 PERCENT PE

100

Figure 11. Complex v i s c o s i t y (η*) versus composition f o r PE/EMA-Zn-20 at 210°C and l 10, 100 and 500 Hz. f


221

222


I n g e n e r a l , f o r PE/EMA o r PE/EMA-salt systems, a p l o t o f complex v i s c o s i t y as a f u n c t i o n o f c o m p o s i t i o n follows the a d d i t i v i t y r u l e o r shows p o s i t i v e d e v i a t i o n s from a d d i t i v i t y , depending on t h e temperature and f r e q u e n c y . Super-Master Curves E a r n e s t and MacKnight (18) have found t h a t super-master c u r v e s , o r composite-master c u r v e s , can be c o n s t r u c t e d f o r G' o f EMA, EMA-salt and EMA-ester, a l l d e r i v e d from t h e same p a r e n t polymer. In this work, we have studied three systems c o n t a i n i n g t h e same p o l y e t h y l e n e , b l e n d e d w i t h t h r e e d i f f e r e n t components d e r i v e d f r o m t h e same p a r e n t polymer. These systems a r e PE/EMA-Zn-0, PE/EMAZn-20 and PE/EMA-Zn-40. Not o n l y f o r t h e pure copolymers was i t found t h a t super-master c u r v e s c o u l d be c o n s t r u c t e d f o r G', b u t a l s o f o r a l l b l e n d s c o n t a i n i n g an i d e n t i c a l PE c o n t e n t . F i g u r e 12 shows t h e s e super-master c u r v e s as a f u n c t i o n o f c o m p o s i t i o n o f t h e blends; as c a n be seen, t h e r e i s q u i t e a r e g u l a r v a r i a t i o n o f G' v e r s u s f r e q u e n c y as a f u n c t i o n o f c o m p o s i t i o n . The v a l u e o f G', a t a g i v e n low f r e q u e n c y , i n c r e a s e s as t h e PE c o n t e n t i s i n c r e a s e d and t h e amount o f i n c r e a s e d i m i n i s h e s w i t h t h e f r e q u e n c y u n t i l we have convergence o f a l l super-master c u r v e s a t h i g h f r e q u e n c i e s . I f we use EMA-Zn-0 or the corresponding PE/EMA-Zn-0 b l e n d as a r e f e r e n c e , we can d e f i n e a f r e q u e n c y s h i f t f a c t o r a ' as t h e f r e quency needed t o superpose pure EMA-Zn-20, o r pure EMA-Zn-40, o r t h e c o r r e s p o n d i n g b l e n d o f PE/EMA-Zn-20 o r PE/EMA-Zn-40, onto t h e corresponding reference curve. F i g u r e 13 shows t h e c o m p o s i t i o n dependence o f t h e a ' ' s f o r b o t h PE/EMA-Zn-40 and t h e PE/EMA-Zn20 system. As can be seen, t h e r e e x i s t s a l i n e a r r e l a t i o n s h i p between t h e f r e q u e n c y s h i f t f a c t o r a ' and t h e c o m p o s i t i o n o f t h e blend. These a ' ' s can be t r a n s l a t e d i n t o temperature s h i f t f a c t o r s ÀT's a c c o r d i n g t o t h e method o f Shohamy and E i s e n b e r g (40). These Δτ'β a r e g i v e n as a f u n c t i o n o f c o m p o s i t i o n i n F i g u r e 14. As can be seen, t h e r e e x i s t s a l i n e a r r e l a t i o n s h i p between t h e temperature s h i f t f a c t o r s and t h e c o m p o s i t i o n i n b o t h t h e PE/EMA-Zn-40 and PE/EMA-Zn-20 systems. T

T

T

T

DISCUSSION The n e u t r a l i z a t i o n o f t h e a c i d groups i n EMA i s known t o i n f l u e n c e t h e i r r h e o l o g i c a l and o t h e r p h y s i c a l p r o p e r t i e s (20). I t has been e s t a b l i s h e d (18) t h a t , f o r t h e p e r c e n t i o n c o n t e n t s o f t h e EMAs a l t s used i n t h i s s t u d y , i o n i c c l u s t e r s e x i s t g i v i n g r i s e t o i o n i c microdomains which remain i n t a c t w e l l above t h e c r y s t a l l i n e m e l t i n g temperature. These i o n i c microdomains have an average r a d i u s o f 810 nm and c o n t a i n a p p r o x i m a t e l y 70 i o n s surrounded by a s h e l l o f hydrocarbon chains (41). These i o n i c microdomains a c t as thermoreversible cross-links; an i n c r e a s e i n the percent n e u t r a l i z a t i o n r e s u l t s i n an i n c r e a s e i n t h e c o n c e n t r a t i o n o f t h e r m o r e v e r s i b l e c r o s s - l i n k s and a c o r r e s p o n d i n g i n c r e a s e i n t h e melt v i s c o s i t y . The s u p e r p o s a b i l i t y o f G' and t h e n o n - s u p e r p o s i b i l i t y o f G i n pure EMA-salts has been r e p o r t e d by E a r n e s t and MacKnight (18) f o r an EMA-salt above t h e s o - c a l l e d c r i t i c a l c l u s t e r c o n c e n t r a t i o n , n


8.



2

as w e l l as PE/EMA-Zn b l e n d s c o n t a i n i n g 20, 40, 60 and 80% PE

1.00 KEMA-Zn-40

0.75

Ο o

0.50

0.25

0.00 0

20

40 60 PERCENT LDPE

80

100

F i g u r e 13. L o g a£ a s a f u n c t i o n o f b l e n d c o m p o s i t i o n f o r PE/EMA-Zn-40, PE/EMA-Zn-20 and PE/EMA-Zn-0 systems.


223

224


50

Dynamic Melt Rheology of PolyethyleneâIonomer Blends - ACS

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