Size Exclusion Chromatography of Polyethylenes - ACS Publications

6 Size Exclusion Chromatography of Polyethylenes Reliability of Data

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L.

A.

UTRACKI

and

M.

M.

DUMOULIN

N a t i o n a l Research C o u n c i l C a n a d a , Industrial Materials Research Institute, 75 Boulevard de Mortagne, M o n t r é a l , Q u é b e c , C a n a d a , J 4 B 6 Y 4

A reliable procedure for determination of molecular parameters: number, weight and z-averages of the molecular weight (M , i = n, w and z respectively) for polyethylenes, PE, by means of Size Exclusion Chromatography, SEC, has been developed. The Waters Sci. Ltd. GPC/LC Model 150C was used at 135°C with trichlorobenzene, TCB, as a solvent. The standard samples as well as commercial stabilized and not stabilized PE-resins were evaluated. The effects of: sampling, method of solution preparation, addition of antioxidant(s), thermal and shear degradation were studied. The adopted procedure allows reproducible determination of M and M , with a random error of ± 4% and M , with ± 9%, within 2 to 72 hrs from the i n i t i a l moment of preparation of solutions. i

n

w

z

While s e p a r a t i o n o f ions according t o s i z e had already been observed by Ungerer i n 1925 t h e f i r s t a p p l i c a t i o n o f t h e p r i n c i p l e t o polymers occurred 19 years l a t e r (I). Between 1960 and 1962, Vaughan and Moore (2) independently developed methods f o r p r e p a r a t i o n o f c r o s s l i n k e d polystyrene g e l beads. The l a t t e r author i s a l s o c r e d i t e d w i t h design of the a n a l y t i c a l SEC as we know i t today. Modern equipment O , 4) operates a t higher pressure, which combined w i t h the higher temperature r e q u i r e d f o r a n a l y s i s o f most p o l y o l e f i n s , results i n a drastic shortening o f column l i f e time. Tempered a l k a l i b o r o s i l i c a t e g l a s s e s , leached w i t h a c i d s t o produce uniform pore s i z e , may e v e n t u a l l y provide a s o l u t i o n (5-14). Unfortunately, they e x h i b i t two disadvantages : low e f f i c i e n c y and s o l u t e a d s o r p t i o n . P o l y e t h y l e n e s , PE, have been c h a r a c t e r i z e d by SEC s i n c e the m i d - s i x t i e s and frequent problems w i t h polystyrene g e l columns have been reported ( 6 ) . The low d e n s i t y PE, LDPE, because o f complexity o f the molecular weight and branching d i s t r i b u t i o n s , 0097-6156/84/0245

0097506.00/0

Published 1984, American Chemical Society

Provder; Size Exclusion Chromatography ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

98

SIZE EXCLUSION CHROMATOGRAPHY

enjoyed more a t t e n t i o n (3,15-23) than the h i s t o r i c a l l y newer, high d e n s i t y , HDPE (24, 25). the u l t r a high molecular weight, UHMWPE, have only r e c e n t l y (26, 27).

simpler, and The r e s u l t s on been published

In t h i s f i r s t r e p o r t on SEC of PE, we want to comment on r e p r o d u c i b i l i t y of the measurements. This has been discussed by Nakajima (24) and others (28). In both cases seven PE samples were d i s s o l v e d i n 1,2,4-trichlorobenzene, TCB, and t e s t e d at 130°C u s i n g 4 or 5 p o l y s t y r e n e - g e l columns. The standard deviations: σ = 6.43 and 3.4 to 5.6%, as w e l l as a = 7.43 and 3.4 to 4.4 were reported i n these p u b l i c a t i o n s , r e s p e c t i v e l y ( s u b s c r i p t η and w r e f e r s to number and weight averages). The maximum spread of values Δ = 17.4 and Δ = 25% was observed. The authors (28) reported significant time changes i n column s e p a r a t i o n p r o p e r t i e s . Standard d e v i a t i o n s i n low temperature SEC: σ = 4, σ = 5%, were reported (29, 30). η

w

η

ν

η

ν

Experimental

A Waters S c i . L t d , GPC/LC Model 150C w i t h Waters Model 130 Data Module was used. The instrument was operated at 135°C w i t h TCB as a solvent (HPLC grade from F i s h e r S c i . , f i l t e r e d through 0.5 Mm f i l t e r w i t h s i l i c a g e l ) . Four and f i v e μ-Styragel (Waters Sci. Inc.) columns w i t h pore s i z e s : (500), 1 0 , ΙΟ , 10 , 10^ A ( from pump to d e t e c t o r ) were c a l i b r a t e d using 21 narrow MWD polystyrene samples s u p p l i e d by Pressure Chemicals and Waters S c i . (peak molecular weight M = 826 to 1.987 χ 10 and p o l y d i s p e r s i t y r a t i o M^Mn = 1.02 to 1.21). The columns were c a l i b r a t e d (31) at 135°C u s i n g 0.06% of polymer (three standards per s o l u t i o n ) i n TCB. The c a l i b r a t i o n was checked once a week. 3

4

5

p

6

For c a l i b r a t i o n , the s o l u t i o n s were prepared overnight at ambiant temperature without a g i t a t i o n , f i l t r a t i o n or a d d i t i o n o f a n t i o x i d a n t s (a m i l d a g i t a t i o n and f i l t r a t i o n r e s u l t e d i n an increase of r e t e n t i o n time, RT, by 0.40 min, e q u i v a l e n t to a r e d u c t i o n of molecular weight by 26%). The c a l i b r a t i o n curve for the four columns Figure 1 was n o n - l i n e a r ; a d d i t i o n of the f i f t h , 500 À column, Figure 2 l i n e a r i z e d the dependence : log M

p

= 11. 655222 - 0.170919 RT,

30^RT^55

(1)

w i t h the standard e r r o r of estimate σ = 0.043816 and the c o r r e l a t i o n c o e f f i c i e n t r ^ = 0.99914. During the c a l i b r a t i o n , as w e l l as during the t e s t i n g , the same c o n d i t i o n s , l i s t e d i n Table I , were used. Neither spinning nor filtering o p e r a t i o n a l options were used.


UTRACK1 A N D D U M O U L I N

SEC of Polyethylenes

F i g u r e 1. C a l i b r a t i o n curve f o r f o u r μ-styragel columns tPS i n TCB at 135 °C).

1E+008r C = 0.02 wt°/o μ Styragel 500-3-4-5-6 FtowlumUrtwi. 1E+006

1E+004L-

1E+002 40 45 Retenttontiira(min}

F i g u r e 2. C a l i b r a t i o n curve f o r f i v e μ-styragel columns (PS i n TCB at 135 °C).


SIZE E X C L U S I O N

100

CHROMATOGRAPHY

TABLE I : SEC OPERATING CONDITIONS Columns :

3

Temperature : I n j . volume : Flow r a t e : Sen./scale : Solvent : Antioxidants :

Solutions :

3

4

5

4

5

6

6

I - μ-Styragel; 500, 1 0 , 1 0 , 1 0 , 1 0 A I I - μ-Styragel; 1 0 , 1 0 , 1 0 , 1 0 A 135°C 400 μL 1 mL/min 64/25 1, 2, 4-trichlorobenzene (TCB) I - Topanol ( 1 , 1 , 3 - t r i ( t e r - b u t y l hydroxy methyl phenyl)butane) and Nonox DLTDP (di l a u r y l t h i o d i p r o p i o n a t e ) ; 0.1 wt% i n s o l u t i o n I I - Santonox-R (4,4'-thio-bis-(6-terbutyl m-cresol); 0.02 wt% i n s o l v e n t . < 0.1 wt%; (90 min. at 165°C and 30 min. at 135°C)

The PE samples were d i s s o l v e d i n TCB at 165°C f o r 1.5 h r s , then t r a n s f e r r e d t o the SEC i n j e c t i o n chamber and a f t e r 30 min injected. I n the l a t e r stage of work, 0.1 wt% of two a n t i o x i d a n t s : Topanol and Nonox DLTDP were added t o the mobile phase only. The chromatograms (see Figure 3 ) were c o l l e c t e d and evaluated on Waters Data Module (see Table I I ).

TABLE I I : COMPUTATIONAL PARAMETERS

Low molecular weight l i m i t Area r e j e c t i o n Data c o l l e c t i o n : f i r s t s l i c e last s l i c e

1500 700 21 min. 43 min.

Commercial : high d e n s i t y , medium d e n s i t y , low d e n s i t y and linear low d e n s i t y PE's (HOPE, MDPE, LDPE and LLDPE r e s p e c t i v e l y ) were used. Their properties are l i s t e d i n Table I I I .


6.

UTRACKI A N D D U M O U L I N

TABLE I I I :

of Polyethylenes

101

THE CHARACTERISTICS OF THE COMMERCIAL PE RESINS

N°

RESIN

DENSITY p(Kg/L)

1 2

HDPE MDPE LDPE LLDPE

0.955 0.941 0.924 0.920

3 4

SEC

MELT INDEX ZERO SHEAR Ml(g/10min) VISCOSITY η (Pa.s)xlO ° 190°C

14

M /M

11

125 325 155 212

1.4 74.5 29.0 8.9

0.25 0.80 1.1

-3

11 32 8.5 6.3

Most o f the i n i t i a l work was done using the "as r e c e i v e d " HDPE r e s i n . The e f f e c t s o f i t s degradation during processing and t e s t i n g on the molecular weight parameters were also s t u d i e d ; i n the text the f o l l o w i n g code f o r these samples w i l l be used: V - as r e c e i v e d , G - mixed at 210°C f o r 15 min on a r o l l m i l l and granulated, M-in a d d i t i o n to G molded at 170°C i n 8 min, C and CC-in a d d i t i o n to M sheared f o r 0.5 and 1.5 hrs at 190°C and frequency ω = 0.1 ( r a d s / s ) .

Results F i r s t , a 50 ml s o l u t i o n was prepared o f the sample V without (V-0) and with (V-A) a n t i o x i d a n t s . The s o l u t i o n was poured i n t o 12 sampling b o t t l e s and i n j e c t e d immediately and then every 2 hrs f o r 72 h r s . The v a r i a t i o n o f M^ s with time f o r these samples i s shown i n F i g u r e s 4 and 5 , r e s p e c t i v e l y . f

The r e s u l t s were f i t t e d to the exponential r e l a t i o n : M. = M

1

(2)

. exp{-b.t}

Ο,Ι

r

1

where i = n, w and ζ f o r number, weight and z-average molecular weight, b£ i s the degradation k i n e t i c s constant and t i s the degradation time. The parameters o f eq. (2) along with the: r^-correlation coefficient squared, M^-average value o f the molecular weight, σ^-standard e r r o r o f the estimate and the A£-maximum spread, are l i s t e d in Table IV . The polydispersity r a t i o s : M /M o r M /M d i d not show any time dependence. For t h i s reason only t h e i r average values as w e l l as σ· and Δ.* are l i s t e d . w

n

z

n



CHROMATOGRAPHY

LLDPE

M M

FQ » LQ F * L-j = F2 • L-2 «

= 6.54x10* « 2.11 χ 105 Mz = 4.31 x 1 0 M / M = 6.58

1

n

w

s

z

n

Force integration: 20.00 No baseine off: 43.54 Frst sice time: 21.00 Last slice time: 43.04 Start of integration: 26.04 End of integration: 41.79

F i g u r e 3. Example o f chromâtogram w i t h t h e i n d i c a t e d l o c a t i o n o f t h e computational parameters.

HDPE

10*

(V-0)

M

2

= 8.8 x 1 0

4

10" M «43x10

4

M

4

w

10'

n

- 1.6 χ 10

M /M 2

5.8

n

- 5 5 ± 0.2

M /Mn z

5.4 5.0 0

8

16

24

32 40 Test time (hrs)

48

56

64

72

F i g u r e k. M o l e c u l a r weight averages v s . residence time a t 135 C; HDPE without a n t i o x i d a n t .


6. UTRACKI AND DUMOULIN


103

TABLE IV; STATISTICS OF SEC MEASUREMENTS OF HDPE WITHOUT ( I ) AND WITH ( I I ) ANTIOXIDANT

PARAMETER

M

0

£

b£

I without a n t i o x i d a n t s (V-0) 17,510 39.32 1. 2. Mw 46,845 101.27 3. M 95,321 181.44 z

4. 5.

Μ£

0.7484 0.6304 0.4429

16,055 43,098 88,312

5.99 6.15 6.70

28.0 31.1 39.4

2.68 5.50

1.49 3.45

5.4 17.8

35,483 125,076 421,945

3.89 3.48 9.48

16.3 18.7 47.5

3.53 11.91

4.25 9.99

14.6 41.6

,

Mw/Mn Mz/Mn

______

______

I I w i t h a n t i o x i d a n t s (V-A) 36,777 34.06 1. Mn 2. Mw 122,934 -56.37 3. M 391,302 -806.41 z

4. 5.

r

______

0.2480 0.0685 0.1659

Mw/Mn Mz/Mn

±σ£(%)

â£(%)

Next, seven randomly s e l e c t e d p e l l e t s o f ther e s i n V were d i s s o l v e d i n seven b o t t l e s and i n j e c t e d a f t e r 6 hrs a t 135°C. The s o l u t i o n s contained t h e two a n t i o x i d a n t s . The s t a t i s t i c s are shown i n Table V .

TABLE V: EFFECT OF PE SAMPLING ON SEC DATA

PARAMETER

M M

w

z

M /M M /M_ w

z

n

±σ(%)

Δ%

33,135 130,527 452,356

6.88 7.46 15.79

21 25 56

3.57 12.51

5.55 14.10

—

M£

—


SIZE E X C L U S I O N C H R O M A T O G R A P H Y

104

S i m i l a r l y , the processed samples (V through to CC) were each d i s s o l v e d and i n j e c t e d a f t e r 2 t o 17 h r s a t 135°C. The average values of molecular parameters are given i n Table VI . These solutions contained the two antioxidants. The standard d e v i a t i o n s v a r i e d from the minimum values of 1.72, 1.51 and 2.25 for M, M and M of sample C, r e s p e c t i v e l y t o the maximum values o f 5.99, 6.15 and 6.70 recorded f o r sample V. n

w

z

TABLE V I : EFFECT OF PROCESSING OF PE

HDPE CODE

V G M C CC

t i9o(min)

0 25.64 30.10 60.10 120.10

M

n

35,962 40,216 37,718 38,009 36,458

M

M

w

122,252 130,913 124,380 123,922 119,602

M /M z

2

397,110 393,728 383,230 357,619 337,851

n

10.99 9.81 10.18 9.41 9.28

To check on the general a p p l i c a b i l i t y of the method the remaining MDPE, LDPE and LLDPE were t e s t e d u s i n g the same experimental procedure. The r e s u l t s are shown i n "Figures 6 t o 8", r e s p e c t i v e l y . Discussion

As seen i n Table IV the and M f o r the s t a b i l i z e d s o l u t i o n s of the HDPE sample are l a r g e r than those f o r the u n s t a b i l i z e d ones by a f a c t o r of 2.2, 2.9 and 4.8 r e s p e c t i v e l y . As suming that t h i s v a r i a t i o n i s due t o thermal degradation during the d i s s o l u t i o n and t e s t i n g one can c a l c u l a t e the a c t i v a t i o n energy E = 62.5 ( k c a l / m o l e ) . This value compares w e l l w i t h E = 52.6 t o 66.1 determined (_32) at Τ = 375 t o 436 (°C) f o r HDPE of molecular weight o f 16 t o 23 thousand, respectively. The i n i t i a l r e s u l t s , and those c o l l e c t e d a f t e r prolonged storage i n the i n j e c t i o n chamber, were not c o n s i s t e n t with those collected w i t h i n the " s t a b l e p e r i o d " : 4^t^68 h r s . T h i s f a c t was f u r t h e r demonstrated i n another s e r i e s o f measurements where the samples were i n j e c t e d f o r 230 h r s . The i n i t i a l values of M£ w i d e l y s c a t t e r e d , whereas those f o r t>68 h r s s y s t e m a t i c a l l y increased w i t h time ( t h i s increase i s responsible f o r the negative values of b and b in Table IV ). Apparently, d i s s o l v i n g HDPE sample at 165°C f o r the p e r i o d o f 1.5 h r s i s not s u f f i c i e n t . Only a f t e r an a d d i t i o n a l 2.5 h r s i n the i n j e c t i o n chamber at 135°C i s the z

a

a

w


z


UTRACKI A N D DUMOULIN

HDPE

(VA)

. .······.-

Mi

M

-»

z

= 4.2 x 1 0

s

M w = 1.25x10

s

10= Mp = 3.6x10* t , ,

. ·

— - — _ - ^ _ — — — - > Λ ft . -

mma

15 14 M /M 2

n

M /M z

13 12 11 10

I *·*Τ

8

16

24 32 40 Test tine (hrs)

48

= 12 ± 1

n

56

64

72

Figure 5 . Molecular weight averages v s . residence time a t 1 3 5 °C; HDPE w i t h a n t i o x i d a n t s .

MDPE M M

-

.

w

= 3.25 x 1 0

ο

ο

ο

6

s

3.72x10*

... ·

M / M - 32 ± 5 ο * Π z

ο z

= 1.17Χ10

Mn-

*·

•

M /M

z

n

ο

ο

n

I 0

3

ο °

ι 6

[ 9 "fest time (hrs)

ο

ι 12

ο

I

15

1 18

Figure 6 . Molecular weight averages v s . residence time at 1 3 5 °C; MDPE w i t h a n t i o x i d a n t s .



LDPE

10

10*

10 10 M /M z

n

CHROMATOGRAPHY

M

w

-

1.55x10

s

M

w

» 4.26 x 1 0

s

M / M = 8.3 ± 0.9 z

n

8 6 6

12 15 "fest time (hrs)

18

Figure 7. Molecular weight averages v s . residence time at 135 °C; LDPE w i t h a n t i o x i d a n t s .

10

LLDPE

P «

Mi 10

4.35 x 1 0

s

Mw-2.12x10

s

z

P „ · 6.98 x 1 0

£

4

7 M /Pn z

M / M - 6.3 ± 0.4 z

0

3

6

9

12

15

n

18

21

24

lest time (hrs) F i g u r e 8. Molecular weight averages vs. residence time at 135 C; LLDPE w i t h a n t i o x i d a n t s .


6.

SEC

U T R A C ΚI A N D D U M O U L I N

of

107

Polyethylenes

d i s s o l u t i o n process completed and the s t a b l e , r e p r o d u c i b l e values of M^'s are obtained. On the other hand, prolonged h e a t i n g of the sample i n the presence of a n t i o x i d a n t s leads to gradual i n c r e a s e of M^'s f o r times t >, t ^ 32 h r s . The value of t was observed to vary from one r e s i n to another. I t i s worth n o t i n g that r f o r M£ i n V-A s e r i e s i s very low, i n d i c a t i n g a random v a r i a t i o n . The standard d e v i a t i o n s of these data (0^t^72) are σ = σ = 4% and σ = 9%, which compare q u i t e w e l l w i t h the p r e v i o u s l y quoted l i t e r a t u r e results. c

c

2

η

ν

ζ

I t has been reported (33) that MWD of HDPE can be d e s c r i b e d by the log-normal d i s t r i b u t i o n f u n c t i o n (34): p(x) = [ σ ( 2 π )

1/2

]"

1

2

exp {-t /2}

(3)

t = (χ-χ)/σ

where χ = l o g Μ, χ i s the mean value of χ and σ i s the standard d e v i a t i o n . D e f i n i n g the normal e q u i v a l e n t d e v i a t e as a p r o p o r t i o n of p(x) which exceeds the i n t e g r a l : p(s) - ( 2 π Γ

1 / 2

2

J ! e x p i - t / 2 > dt

(4)

œ

one can c o n v e n i e n t l y p l o t the p r o b a b i l i t y p r o b i t , where p r o b i t i s taken as (s+5).

function

as

ρ

vs.

U

The -A data f o l l o w Equation 3 q u i t e w e l l , w i t h χ = l o g M, M = 41,527 ± 878 and σ = 1.585 ± 0.005. On the o t h e r hand, the V-0 data cannot be represented by this f u n c t i o n . One can p o s t u l a t e that PE i n TCB undergoes a random s c i s s i o n s i m i l a r t o t h a t observed f o r polymer melts at much higher temperatures. In Figure 9 the i n t e g r a l d i s t r i b u t i o n curves of samples HDPE (V-0) and (V-A), both taken a f t e r 10 hrs of d i s s o l u t i o n , are shown i n the form of log-normal d i s t r i b u t i o n p l o t : M vs p r o b i t s . Two f a c t s are apparent: (1) the molecular weights of sample V-A (broken l i n e ) are s y s t e m a t i c a l l y h i g h e r than those of V-0 ( p o i n t s ) ; (2) when the V-A d i s t r i b u t i o n curve i s d i s p l a c e d v e r t i c a l l y t o c o i n c i d e w i t h that of V-0 i n the r e g i o n of low molecular weight, i t i s q u i t e apparent that the degradation p r e f e r e n t i a l l y a f f e c t e d the molecules w i t h M > 10->, w h i l e below t h i s value My-A » KMy_Q, w i t h Κ being a constant, Κ * 2.2. For M > 10* Κ i n c r e a s e s w i t h m o l e c u l a r weight approximately as: Κ =2.2 +2.1 l o g M. n

n

1

The above a n a l y s i s should not he construed as a u t h o r s o p i n i o n t h a t molecular weight d i s t r i b u t i o n , MWD, of P E s should f o l l o w log-normal p r o b a b i l i t y . The method o f a n a l y s i s i s general and does not r e q u i r e t h a t Equation 3 be obeyed; i f i t does, l o g M v s . p r o b i t i s a s t r a i g h t l i n e , which simply makes the f



10 [~

HDPE

6

10

CHROMATOGRAPHY

log—normal distr.

2

(V-0)

1

(V-A)

5 L

Κ

«•μ

\

\ ; ^

10

2

3

3.0

4.0

50 Probits

6.0

7.0

F i g u r e 9· Log-normal d i s t r i b u t i o n o f HDPE molecular weight a f t e r 1 . 5 h a t 1 6 5 °C and 1 0 h at 1 3 5 °C; 1 (upper l i n e ) - HDPE w i t h a n t i o x i d a n t ; c i r c l e s - HDPE without a n t i oxidant ; 2 (lower l i n e ) upper broken l i n e has been deplaced v e r t i c a l l y by a f a c t o r o f 2 . 2 t o c o i n c i d e w i t h the low molecular weight data o f u n s t a b i l i z e d sample.


UTRACKI AND DUMOULIN

6.

SEC of

109

Polyethylenes

work a l i t t l e e a s i e r . We found that the p l o t i s u s e f u l i n interpreting the data even i n the case o f multimodal distributions. The commercial r e s i n s are seldom a r e s u l t o f a s i n g l e p o l y m e r i z a t i o n ; i n order t o meet the s p e c i f i c a t i o n s they are blended. The r e s u l t s o f Table V show that the v a r i a b i l i t y o f M^'s i n t h i s s e r i e s i s l a r g e r than that i n Table IV ; i n the f i r s t case the r e s u l t s r e f e r t o average values f o r seven d i f f e r e n t p e l l e t s of HDPE-V d i s s o l v e d s e p a r a t e l y , i n the second to a v a r i a b i l i t y o f data of the same s o l u t i o n . The s t a t i s t i c a l a n a l y s i s of the f i r s t s e t o f data i n d i c a t e s that there i s about 9% p e l l e t - t o - p e l l e t v a r i a b i l i t y i n M . w

In Table VI the r e s u l t s o f SEC-testing of the processed samples are shown. The ^190 represents the e q u i v a l e n t degradation time at 190°C c a l c u l a t e d from the a c t u a l times and temperatures reported i n the t a b l e ; i n the c a l c u l a t i o n , a s impIe Arrhenian f u n c t i o n was assumed, w i t h the a c t i v a t i o n energy ΔΕ = 11.9 (kcal/mole) obtained d u r i n g the previous work (35). I n F i g u r e 10 the M^'s dependence on t\go i s shown. The r e s u l t s are most encouraging. I t can be seen that even prolonged h e a t i n g o f the r e s i n , under processing c o n d i t i o n s , does not lead t o a s i g n i f i c a n t a l t e r a t i o n of i t s M£ s. The onset o f degradation becomes apparent only f o r sample CC; here M i s 17.5% lower than that of sample sample V. Since standard d e v i a t i o n of the measurements i s ± 9.5% the drop i n M r e f l e c t s the true degradation. This i s more c l e a r l y v i s i b l e on Figure 10 , where the p o l y d i s p e r s i t y parameter, M /M , decreases s y s t e m a t i c a l l y from a value o f about 11 t o 9.3. The i n i t i a l l y more r a p i d decrease of t h i s parameter i s most l i k e l y due t o the easy access o f oxygen d u r i n g t h i s stage of the process - a f a c t o r neglected i n c a l c u l a t i n g t\gQ» 3

f

z

2

z

n

F i n a l l y , a few words on the general r e l i a b i l i t y o f t h e developed method o f the measurements. The method, as shown i n Figures 4 and 6 t o 8 works q u i t e w e l l f o r a l l PE's o f a normal, commercial range o f M^ s. We observed a need f o r longer d i s s o l u t i o n time o f HDPE than that o f LDPE o r LLDPE o f e q u i v a l e n t molecular weight. The adopted d i s s o l u t i o n time i s 1.5 h r s at 165°C and 2.5 h r s a t 135°C. With the weekly r e c a l i b r a t i o n procedure the long term r e p e a t a b i l i t y o f data during the two years p e r i o d was found t o be random, and w i t h i n the range o f the reported standard d e v i a t i o n s . Some i n i t i a l work on SEC of the UHMWPE has been conducted ; i t was found that the above c o n d i t i o n s were g r o s s l y inadequate. 1


SIZE E X C L U S I O N C H R O M A T O G R A P H Y

10

HDPE

DEGRADATION

190°C

-My, 10

9

8

I 0

,

25

50 75 t 190 (min)

. 100

i 125

F i g u r e 10. M o l e c u l a r weight parameters o f HDPE v s . the C; see t e x t . p r o c e s s i n g time at 190


6.

UTRACKI AND DUMOULIN


111

Acknowledgments The authors would l i k e t o thank Mr. J . Dufour f o r h i s c a r e f u l work i n c o l l e c t i n g the SEC data.

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26.

J. Claesson and S. Claesson, Arkiv. Kemi, 19A, 1 (1944). J.C. Moore, J. Polymer Sci., A2 835 (1964). E.E. Drott and R.A. Mendelson, J. Polymer Sci., Part A-2, 8, 1361, 1373 (1970). Polymer Laboratories "PLgel GPC columns" technical buletin 5/82. W. Haller, Nature, 206, 693 (1965). J.H. Ross and M.E. Casto, J. Polymer Sci., Part C, 21, 143 (1968). A. Titterton, Ind. Polym., May 1-2, 1973 pg. 83-88. A.R. Cooper, J. Polymer Sci., Polymer Phys. Ed., 12, 1969 (1974). L. Westerman, Chromatog. Sci., 13, 257 (1980). M. Kubin, J. Appl. Polymer Sci., 27, 2933, 2955 (1982). B.W. Hatt, Develop. Chromatogr., 1, 157 (1978). J.V. Dawkins and G. Yeadon, Develop. Polym. Charact., 1, 71 (1978). J.V. Dawkins, Pure Appl. Chem., 51, 1473 (1979). R.A. Ellis, Pigm. Res. Techn., Sept. 1979, pg. 10-21. Z. Grubisic, P. Rempp and H. Benoit, J. Polymer Sci., B5, 753 (1967). B.H. Zimm and W.H. Stockmayer, J. Chem. Phys., 17, 1301 (1949). J.A. Cote and M. Shida, J. Polymer Sci., Part A-2, 9, 421 (1971) J.A. Miltz and A. Ram, Polymer, 12, 685 (1971); A. Ram and J. Miltz, J. Polymer Sci., 15, 2639 (1971). G.R. Williams and A. Cervenka, Eur. Polymer J . , 8, 1009 (1972). S. Nakano and Y. Goto, J. Appl. Polymer Sci., 19 2655 (1975); ibid., 20, 3313 (1976). L. Wild, R. Ranganath and A. Barlow, J. Appl. Polymer Sci., 21, 3319, 3331 (1977). L. Lecacheux, J. Lesec and C. Quivoron, ACS Polymer Prepr., 23(2) 126 (1982). A. Hamielec, Pure Appl. Chem., 54, 293 (1982). N. Nakajima, J. Appl. Polymer Sci., 15, 3089 (1971); idid. 16, 2417 (1972). J.V. Dawkins and J.W. Maddok, Eur. Polymer J . , 7, 1537 (1971). A. Barlow and T. Ryle, Plastics Eng., August 1977, pg. 41-43.


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27. Polymer Laboratories, technical information 5/82. 28. G. Samay and L. Fuzes, J. Polymer Sci., Polymer Symp., 68, 185 (1980). 29. J.H. Duerksen and A. Hamielec, ACS Symp. on Analytical GPC, Chicago, Sept. 1967. 30. J.P. Busnel, Polymer, 23, 137 (1982). 31. A.E. Hamielec and A.C. Ouano, J. Liq.Chromatography, 1, 111 (1978). 32. H.H.G. Jellinek, J. Polymer Sci., 4, 13 (1949). 33. H. Wesslun, Makromol. Chem., 20, 111 (1956). 34. W.D. Lansing and E.O. Kraemer, J. Am. Chem. Soc., 57, 1369 (1935). 35. L.A. Utracki and J. Lara, Proceedings of the Int'l Workshop on Extensional Flows, Mülhouse - La Bresse, France, 24-28 January 1983. RECEIVED September 12, 1983


Size Exclusion Chromatography of Polyethylenes - ACS Publications

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