The PL-Dynamic Mechanical Thermal Analyzer and Its Application to

PL-Dynamic Mechanical Thermal Analyzer. 97. Frequency and strain amplitude are selected by push button with eight logarithmically spaced-frequencies f...
0 downloads 0 Views 1MB Size
5 The PL-Dynamic Mechanical Thermal Analyzer and Its Application to the Study of Polymer Transitions

Downloaded by CORNELL UNIV on May 15, 2017 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch005

R. E. W E T T O N Loughborough University, Department of Chemistry, Loughborough, United Kingdom

T . G . C R O U C H E R and J. W. M . F U R S D O N Polymer Laboratories, Ltd., Church Stretton, Salop, United Kingdom

A new instrument measurements

for small strain dynamic

of polymers

ature can be programmed Special spaced

Head

is reported. from

arrangement).

drive frequencies

selected on the front

-150

to 300

Eight

from

panel.

0.33

Applications

to 90

Clamping

using

thermal scans and computer quencies polymers, and

copolymers,

and

both

°C

Hz

can

be

geometrics

for

deformation

are

single-frequency

multiplexing

are given. Examples

temper­

°C (500

logarithmically

bending beam, shear, and elongational described.

mechanical

Sample

of several fre­

of application composites

are

to

homo-

presented

discussed.

^MEASUREMENTS

of

polymeric

materials, w h i c h were previously laborious, can n o w be

OF DYNAMIC

MECHANICAL

PROPERTIES

performed

automatically w i t h microprocessor-controlled

instrumentation. T h e

P L - d y n a m i c m e c h a n i c a l t h e r m a l analyzer ( P L - D M T A ) uses the w e l l established phase a n d amplitude technique w i t h digital measurement o f p h a s e to g i v e t a n δ r e s o l u t i o n s o f 0 . 0 0 0 1 . M e a s u r e m e n t s c a n

be

p e r f o r m e d at f i x e d f r e q u e n c y o v e r a t h r e e a n d o n e - h a l f d e c a d e r a n g e . A d y n a m i c stiffness range of o v e r four d e c a d e s a l l o w s m e a s u r e m e n t o f all transitions w i t h one sample. T h i s , together w i t h precise tempera­ ture p r o g r a m m i n g , i n the range f r o m - 1 5 0 to 300 °C, o p e n s u p n e w p o s s i b i l i t i e s for r e s e a r c h , a n a l y t i c a l , a n d q u a l i t y c o n t r o l 0065-2393/83/0203-0095$06.00/0 © 1983 A m e r i c a n C h e m i c a l Society

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

measure-

Downloaded by CORNELL UNIV on May 15, 2017 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch005

96

POLYMER CHARACTERIZATION

Figure 1. The PL-dynamic mechanical thermal analyzer. Key: the mechanical measuring head, left; the dynamic analyzer unit, top right; and the temperature programmer, bottom right. m e r i t s . T h e i n s t r u m e n t , as w e l l as m e a s u r e m e n t s o n a r a n g e o f p o l y ­ m e r systems, is d e s c r i b e d . Instrumentation T h e P L - D M T A c o m p r i s e s t h r e e b e n c h t o p u n i t s as s h o w n i n F i g u r e 1. T h e m e c h a n i c a l h e a d c o n t a i n s t h e s a m p l e i n a t e m p e r a t u r e e n c l o s u r e . T h e m a i n d e f o r m a t i o n m o d e s are b e n d i n g b e a m (either d o u b l e or single cantilever) a n d shear. T h e s a m p l e c l a m p i n g details i n these t w o a r r a n g e m e n t s are s h o w n i n F i g u r e s 2 a a n d b . T h e s a m p l e d i s k s for s h e a r s a n d w i c h o p e r a t i o n are m o u n t e d n o r m a l l y o n t h e f r a m e e x t e r n a l to t h e i n s t r u m e n t , a n d t h e c o m p l e t e a s s e m b l y is t h e n l o c a t e d o n the i n s t r u m e n t s . T h i s m e t h o d o f m o u n t i n g is p a r t i c u l a r l y u s e f u l w h e n m e a s u r i n g d i f f i c u l t s a m p l e s , s u c h as a d h e s i v e s . R e s u l t s q u o t e d i n this chapter were taken i n the b e n d i n g b e a m m o d e (typical sample s i z e 10 x 5 x 2 m m ) u n l e s s o t h e r w i s e s t a t e d . A n a l t e r n a t i v e h e a d a s s e m b l y for t h e t e n s i l e d e f o r m a t i o n o f f i l m s a n d f i b e r s at c o n s t a n t t e n s i o n is c u r r e n t l y b e i n g m a d e a v a i l a b l e . T h e o s c i l l a t i n g stress e x p e r i e n c e d b y t h e s p e c i m e n i s p r o p o r ­ t i o n a l to t h e d r i v e c u r r e n t f r o m t h e o s c i l l a t o r . T h e s t r a i n p r o d u c e d i s c o n v e r t e d to a p r o p o r t i o n a l v o l t a g e b y a n o n l o a d i n g t r a n s d u c e r . T h e d y n a m i c a n a l y z e r u n i t c o m p a r e s t h e p h a s e a n d a m p l i t u d e o f stress a n d s t r a i n a n d c o m p u t e s a b s o l u t e v a l u e s o f l o g m o d u l u s a n d t a n δ. T h e i n s t r u m e n t is e a s i l y c a l i b r a t e d b y an a d d e d mass t e c h n i q u e that t h e n m a k e s the i n s t r u m e n t absolute w h e n the g e o m e t r y constant for the s a m p l e u n d e r m e a s u r e m e n t is d i a l e d i n o n the front p a n e l . C a l i b r a t i o n needs checking only periodically.

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

5.

WETTON ET AL.

PL-Dynamic

Mechanical

Thermal

Analyzer

97

Downloaded by CORNELL UNIV on May 15, 2017 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch005

F r e q u e n c y a n d strain a m p l i t u d e are s e l e c t e d b y p u s h b u t t o n w i t h e i g h t l o g a r i t h m i c a l l y s p a c e d - f r e q u e n c i e s f r o m 0 . 0 3 to 9 0 H z a n d t h r e e c o n t r o l l e d strain l e v e l s c o v e r i n g a X 1 6 range. T e m p e r a t u r e is s e n s e d b y a p l a t i n u m resistance thermometer l y i n g i m m e d i a t e l y b e h i n d the s a m p l e . A t e m p e r a t u r e p r o g r a m m e r c o n t r o l s t h e b a l a n c e d h e a t o v e n to p r o d u c e u n i f o r m h e a t i n g rates f r o m 1 7 1 0 m i n (or less) to 2 0 7 m i n ( n o m i n a l ) . T h e t e m p e r a t u r e m a y b e c o n t r o l l e d i s o t h e r m a l l y at a n y point, or series of points, w i t h external c o m p u t e r control. Accuracy depends on the optimization of a n u m b e r of parameters. T e m p e r a t u r e u n i f o r m i t y i n t h i c k s p e c i m e n s c a n o n l y b e a c h i e v e d at a h e a t i n g rate o f a f e w d e g r e e s p e r m i n u t e . I n t h i n s p e c i m e n s t e m p e r a ­ ture d e f i n i t i o n is easier, b u t errors from d i m e n s i o n a l m e a s u r e m e n t s m a y b e c o m e significant i n m o d u l u s d e t e r m i n a t i o n s . T a n δ is r e s o l v e d t o 0 . 0 0 0 1 for v a l u e s l e s s t h a n 1.0 a n d , b e c a u s e i t i s d e t e r m i n e d as kE"/kE', e r r o r s i n t h e g e o m e t r y t e r m (k) d o n o t p r o d u c e e r r o r s i n t h i s term. T h e h i g h resolution n o w achieved produces sufficiently fine steps i n o u t p u t vs. t e m p e r a t u r e s u c h that e s s e n t i a l l y s m o o t h c u r v e s are p r o d u c e d f r o m t r a c e s o n a n o r m a l t w o - p e n r e c o r d e r . E x t e r n a l c o m p u t e r control of the m a i n functions / , T, strain, a n d h e a t i n g rate i s a v a i l a b l e t h r o u g h t h e I E E E ( I n s t i t u t e o f E l e c t r i c a l E n ­ g i n e e r s S t a n d a r d 488) i n t e r f a c e , a n d i n t h i s m o d e , r e s u l t s are d i s p l a y e d b o t h i n r e a l t i m e a n d s t o r e d for future m a n i p u l a t i o n . A n e x a m p l e o f t h e p o w e r o f e x t e r n a l c o m p u t e r c o n t r o l is s h o w n i n F i g u r e 3 i n w h i c h t h r e e f r e q u e n c i e s a r e m u l t i p l e x e d d u r i n g a s i n g l e t h e r m a l s c a n at 2 ° C / m i n . T h e s a m p l e is a n e x t r e m e l y h i g h m o d u l u s c a r b o n - f i l l e d e p o x y . b

Figure 2. (a) Sample clamping arrangement with a dual cantilever. Drive clamp vibrates perpendicular to sample, which can be mounted on one side only to accommodate expansion or contraction in length. Clamp frames are interchangeable to give variable length; and (b) shear sandwich geometry for rubbers and gels. The black discs repre­ sent the two samples, and the central plate is oscillated by the drive clamp.

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

i

i

.

1

1

50 1

• " t — ; Γ

ν.\>··*··Λ".'7

Γ

m

-

30

1

3

.

·ΓΟΟ' I . , Temp (dQgO

'

.



0.'33



»

'".

150 —Ι

·

1

ί



1

"••«."·.;/"·...

\

FrQquQnciQs

1

i

200

0.33,3

Α

Ι

g

S 30 Hz

ι

9.0-

9.5-

10.0-

Log E' *) 10.5^

Figure 3. Control by an external computer allows collection of data at a number of frequencies during a single thermal scan. Data collected for a carbon filled epoxy through the main T region.

Û

-1

-.2

-3

_.4

Tan S

Downloaded by CORNELL UNIV on May 15, 2017 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch005

5.

WETTON ET A L .

PL-Dynamic

Mechanical

Thermal

Analyzer

99

O n e advantage of t h i s m e t h o d is that a n y t e m p e r a t u r e errors i n the s a m p l e are i d e n t i c a l for e a c h f r e q u e n c y .

Downloaded by CORNELL UNIV on May 15, 2017 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch005

Results

and

Discussion

D y n a m i c m e c h a n i c a l t h e r m a l analysis ( D M T A ) senses any change i n m o l e c u l a r m o b i l i t y i n t h e s a m p l e as t h e t e m p e r a t u r e is r a i s e d o r l o w e r e d . T h e t i m e s c a l e r e q u i r e d for t h e m o l e c u l a r m o t i o n to m a n i ­ f e s t i t s e l f is d e t e r m i n e d b y t h e f r e q u e n c y , / , o f t h e i m p r e s s e d s i n u ­ s o i d a l stress. A p r o g r e s s i v e c h a n g e i n s t o r a g e m o d u l u s a n d p e a k i n g i n tan δ (energy lost/energy stored per cycle) occurs w h e n the average m o l e c u l a r r e l a x a t i o n t i m e , r , i s V2 π/. D M T A i s n o t d e p e n d e n t o n t e m ­ p e r a t u r e s c a n n i n g rate i n t h e s a m e w a y t h a t D S C - t y p e m e a s u r e m e n t s a r e . T h i s c a n b e d e m o n s t r a t e d m o r e a c u t e l y i n t h e a b i l i t y to o b t a i n i s o t h e r m a l data b y s c a n n i n g t h r o u g h the m o t i o n a l t i m e scale b y c h a n g i n g the frequency. T h i s information yields t h e n the relaxation t i m e s p e c t r u m (I, 2). M o r e than one transition w i l l n o r m a l l y be encountered i n the temperature plane. Figure 4 shows an example using a prequenched p o l y ( e t h y l e n e t e r e p h t h a l a t e ) . T h e m a i n t r a n s i t i o n (a ) at 8 5 ° C , 1 H z i s d u e to t h e o n s e t o f m i c r o - B r o w n i a n m o t i o n o f t h e m a i n c h a i n s a b o u t T . a

g

-100

- 50

0

50

100

150

200

250

Temperature (°C) Figure 4. PL-DMTA (1 Hz) scan for a quenched poly(ethylene tere­ phthalate) sample heated 5 °C/min. The scan shows a and β relaxation, crystallization, and melting.

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

100

POLYMER CHARACTERIZATION

Downloaded by CORNELL UNIV on May 15, 2017 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch005

T h i s t r a n s i t i o n occurs i n the a m o r p h o u s phase, a n d has a large m a g ­ nitude because of the h i g h v o l u m e fraction of amorphous phase pres­ e n t i n t h e q u e n c h e d s a m p l e . T h e t a n δ m a g n i t u d e , 0.6, a n d h a l f - w i d t h ( i g n o r i n g r e c r y s t a l l i z a t i o n o n s e t ) at 13 ° C , c o m p a r e to q u e n c h e d p o l y s t y r e n e v a l u e s o f 1.32 a n d 13 ° C at t h e s a m e s c a n n i n g r a t e . T h e r e d u c t i o n i n loss peak m a g n i t u d e w i t h o u t peak b r o a d e n i n g shows some crystallinity i n the q u e n c h e d sample. Quantitative information o f t h i s t y p e h a s n o t b e e n a v a i l a b l e p r e v i o u s l y as a l l e x p e r i m e n t a l parameters must be controlled. A t l o w t e m p e r a t u r e s t h e b r o a d β r e l a x a t i o n p r o c e s s i s o b s e r v e d at —60 ° C / H z , a n d i s d u e t o l o c a l i z e d m o l e c u l a r m o t i o n ( l o c a l m o d e ) o f t h e m e t h y l e n e a n d c a r b o x y l g r o u p s . I t c o m p r i s e s at l e a s t t w o o v e r l a p ­ p i n g r e l a x a t i o n s (3) a n d is r e l a t i v e l y i n s e n s i t i v e to c r y s t a l l i n i t y . W h e n m a i n c h a i n relaxations are i n v o l v e d i n the β process, g o o d i m p a c t strength normally results. A s the temperature is r a i s e d above T , the m o l e c u l a r freedom a c q u i r e d a l l o w s r a p i d c r y s t a l l i z a t i o n at t h i s h i g h d e g r e e o f s u p e r c o o l ­ i n g . T h e m o d u l u s t h u s r i s e s as c r y s t a l l i z a t i o n p r o c e e d s i n t h e r a n g e 1 1 0 — 1 5 0 ° C . F i n a l l y , at h i g h t e m p e r a t u r e s c a t a s t r o p h i c m e l t i n g o c c u r s at 2 0 0 ° C , a n d c l a m p i n g i s l o s t . I n p r i n c i p l e , t a n δ s h o u l d go t h r o u g h a s t e p at t h e m e l t i n g p o i n t a n d i n c r e a s e w i t h o u t l i m i t as t h e t e m p e r a t u r e is r a i s e d f u r t h e r . g

T h e r m a l s c a n n i n g at r e a s o n a b l y h i g h rates (5 ° G / m i n ) y i e l d s i n ­ formation that w o u l d not be o b t a i n e d i n very s l o w s c a n n i n g or isothermal experiments. In isothermal experiments annealing pro­ c e s s e s m a y o c c u r a n d t h e s a m p l e w o u l d c r y s t a l l i z e at a s i g n i f i c a n t l y lower temperature. D a t a t h r o u g h the m e l t i n g r e g i o n are d i f f i c u l t to o b t a i n w i t h r e l a ­ t i v e l y l o w m o l e c u l a r w e i g h t p o l y m e r s that have h i g h m e l t i n g points, s u c h as p o l y e s t e r s a n d n y l o n s . W h e n s u c h m a t e r i a l s m e l t t h e p r o c e s s is c a t a s t r o p h i c b e c a u s e t h e e q u i l i b r i u m l i q u i d h a s a l o w v i s c o s i t y . T h u s , c l a m p i n g i n t e g r i t y i s l o s t as s o o n as t h e c r y s t a l l i n e i n t e r a c t i o n s a r e l o s t . I t i s , h o w e v e r , r e l a t i v e l y e a s y to o b t a i n d a t a t h r o u g h t h e m e l t i n g range of a h i g h m o l e c u l a r w e i g h t , l o w m e l t i n g p o l y m e r , such as p o l y e t h y l e n e o x i d e . D a t a i n F i g u r e s 5 a n d 6 a r e f o r p o l y e t h y l e n e oxide of a m o l e c u l a r w e i g h t of approximately one m i l l i o n (Polyox grade). A r e l a t i v e l y short, t h i c k s a m p l e w i t h aspect ratio (length/ t h i c k n e s s ) o f t h r e e w a s u s e d to o b t a i n r e a s o n a b l e s a m p l e s t i f f n e s s o n the h i g h temperature side of the m e l t i n g region. Some sacrifice of m o d u l u s a c c u r a c y d u e to u n k n o w n e n d c o r r e c t i o n s is m a d e , p a r t i c u ­ l a r l y w h e r e m o d u l u s l e v e l s are h i g h . F i g u r e 5 s h o w s results for a s a m p l e c o o l e d q u i c k l y f r o m t h e m e l t to r o o m t e m p e r a t u r e , w h e r e it w a s h e l d for 2 h b e f o r e s c a n n i n g at 4 ° C / m i n a n d 1 H z . T w o p e a k s are e x h i b i t e d i n tan δ i n sympathy w i t h the decreases i n m o d u l u s . T h e

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

Downloaded by CORNELL UNIV on May 15, 2017 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch005

5.

WETTON ET AL.

PL-Dynamic

Mechanical

Thermal

Analyzer

101

h i g h e r p e a k (a ) c o i n c i d e s w i t h t h e o b s e r v e d m e l t i n g p o i n t , b u t t h e l o w e r t e m p e r a t u r e p e a k (a ') d o e s n o t a g r e e w i t h a n y m a j o r t h e r m a l event seen by D S C - t y p e techniques. Different thermal treatment a l t e r s t h e p o s i t i o n a n d m a g n i t u d e o f t h e a ' i n F i g u r e 6. T h e s a m p l e w a s c r y s t a l l i z e d at 6 0 ° C f o r 5 h t o a l l o w c o m p l e t e p r i m a r y c r y s t a l l i z a t i o n , a n d t h e a ' p r o c e s s o c c u r s at a h i g h e r t e m p e r a t u r e . T h e a process a p p a r e n t l y d e p e n d s o n the p e r f e c t i o n , or size of l a m e l l a e , a n d there is a strong parallel w i t h similar relaxations i n different types of polyethy l e n e (4). c

c

c

c

r

c

A n inherent consequence of the d y n a m i c m e c h a n i c a l method's r e s p o n s e to m o t i o n a l t i m e s c a l e i s t h a t m e a s u r e m e n t at h i g h e r f r e q u e n c i e s w i l l c a u s e t h e l o s s p e a k to b e o b s e r v e d at h i g h e r t e m p e r a tures. I n a m o r p h o u s h o m o p o l y m e r s the loss peak shifts w i t h m i n o r shape changes i n the t e m p e r a t u r e p l a n e . T h e shift factor is g i v e n b y t h e s e m i e m p i r i c a l W i l l i a m s , L a n d e l , a n d F e r r y ( W L F ) e q u a t i o n (5), w h i c h a p p r o x i m a t e s t o a s i m p l e A r r h e n i u s r e l a t i o n at t e m p e r a t u r e s far

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

Downloaded by CORNELL UNIV on May 15, 2017 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch005

102

POLYMER CHARACTERIZATION

a b o v e T . H o w e v e r , m a n y c o m m e r c i a l p o l y m e r s are p a r t i a l l y c r y s t a l l i n e , a n d c o p o l y m e r s are i n c r e a s i n g l y c o m m o n . I n s u c h cases the loss c u r v e s w i l l u s u a l l y change shape r a d i c a l l y w i t h change of m e a s u r e m e n t freq u e n c y . F i g u r e 7 s h o w s t h i s for a n e t h y l e n e - v i n y l acetate c o p o l y m e r ( 2 4 % v i n y l acetate) w h e r e t h e s h a r p e n i n g o f t h e l o s s c u r v e w i t h i n c r e a s i n g t e m p e r a t u r e results f r o m t w o effects. F i r s t t h e r e is a s h a r p e n i n g of the r e l a x a t i o n t i m e s p e c t r u m that is i n h e r e n t l y b r o a d for r a n d o m c o p o l y m e r s , a n d s e c o n d t h e r e is a n i m p r o v e m e n t i n s e g m e n t c o m p a t i b i l i t y as t h e t e m p e r a t u r e i s r a i s e d , l e a d i n g t o a m o r e h o m o g e n e o u s m a t e r i a l o n t h e m o l e c u l a r s c a l e . T h e l o s s p e a k h a l f - w i d t h at 3 0 H z i s s t i l l 18 ° C , a n d i s m u c h b r o a d e r t h a n o b s e r v e d f o r h o m o p o l y m e r s i n the same t e m p e r a t u r e range. g

T h e P L - D M T A c a n b e u s e d as a n a n a l y t i c a l i n s t r u m e n t i n t h e s a m e s e n s e as I R i s u s e d to d e t e r m i n e u n k n o w n s . T h e t h e o r y i s l e s s far d e v e l o p e d , h o w e v e r , a n d t h e t e c h n i q u e i s i n s o m e c a s e s e m p i r i c a l .

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

5.

PL-Dynamic

WETTON ET AL.

Mechanical

Thermal

Analyzer

103

T h e loss p e a k l o c a t i o n for a r a n d o m c o p o l y m e r m o v e s n o r m a l l y b e ­ t w e e n t h e l o c a t i o n for the p a r e n t h o m o p o l y m e r s i n a s i m i l a r w a y to T itself. H o w e v e r , i n e t h y l e n e - v i n y l acetate c o p o l y m e r s c r y s t a l l i n i t y l e v e l changes of the p o l y e t h y l e n e sequences disturb the average a m o r p h o u s phase c o m p o s i t i o n , a n d , c o n s e q u e n t l y , the a loss p e a k p o s i t i o n c h a n g e s o n l y s l i g h t l y (see F i g u r e 8), b u t i t s m a g n i t u d e d e ­ creases i n s y m p a t h y w i t h the a m o r p h o u s phase content. T h e peak h a l f - w i d t h i n t h e t e m p e r a t u r e p l a n e (30 H z ) i n c r e a s e s w i t h e t h y l e n e c o n t e n t u n t i l i t is t o o b r o a d to m e a s u r e s e n s i b l y at 7 . 5 % v i n y l a c e t a t e composition. As more and more ethylene sequences crystallize, w i t h increasing ethylene content, the amorphous phase becomes relatively r i c h e r i n v i n y l a c e t a t e c o m p o s i t i o n , a n d t h i s fact c a u s e s t h e l a c k o f shift i n p e a k p o s i t i o n . C l e a r l y , after p r o p e r t h e r m a l h i s t o r y c o n t r o l , a D M T A scan c a n p r o v i d e a g o o d i n d i c a t i o n of the c o m p o s i t i o n , or a l ­ t e r n a t i v e l y , i f c o m p o s i t i o n is k n o w n , i n f o r m a t i o n is o b t a i n e d o n the nature of the amorphous phase a n d crystallite interaction/crosslinking. g

Downloaded by CORNELL UNIV on May 15, 2017 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch005

a

T h e e x t r e m e cases of h e t e r o g e n e i t y i n c o p o l y m e r s is p r o v i d e d b y b l o c k a n d graft c o p o l y m e r s p a r t i c u l a r l y as e x e m p l i f i e d b y t h e r m o ­ plastic elastomers. I n these materials p h y s i c a l phase separation of g l a s s y o r c r y s t a l l i n e d o m a i n s i s n e c e s s a r y to p r o v i d e c r o s s - l i n k i n g . G o o d clear cut phase separation, w i t h e a c h phase e x h i b i t i n g a loss

9.0 h

οι ε

-60

-40

-20

0

20

40

Temperature (° C) Figure 7. Effect of frequency of measurement on loss peak position and shape for ethylene—vinyl acetate copolymer. Heating rate was 5 °C/min.

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

104

POLYMER CHARACTERIZATION

Downloaded by CORNELL UNIV on May 15, 2017 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch005

c

Temperature °C Figure 8. PL-DMTA scan (30 Hz) of ethylene-vinyl acetate copolymers with varying acetate contents. Crystallinity perturbs the amorphous phase composition. Key: —, 25% vinyl acetate; ,15% vinyl acetate; and —, 7.5% vinyl acetate.

p e a k c l o s e to its h o m o p o l y m e r p o s i t i o n a n d n o t s i g n i f i c a n t l y b r o a d ­ e n e d , is the r e q u i r e m e n t . D M T A characterizes f u r t h e r the r u b b e r a n d g l a s s y state m o d u l u s l e v e l s . T h e s e f e a t u r e s a r e n o t a t t a i n a b l e b y any other single t e c h n i q u e . Phase studies of this type can be ex­ t e n d e d to p o l y u r e t h a n e s y s t e m s , w h i c h a r e e s s e n t i a l l y m u l t i - b l o c k copolymers with poor chemical and physical definition. Figure 9 s h o w s data for t w o t y p e s o f p o l y u r e t h a n e . S a m p l e A is a n o r m a l for­ m u l a t i o n b a s e d o n polyester, s o m e w h a t greater t h a n b i f u n c t i o n a l i n — O H g r o u p s w i t h b u t a n e d i o l / m e t h y l e n e d i p h e n y l i s o c y a n a t e as c h a i n extenders. P h a s e s e p a r a t i o n is c l e a r cut w i t h the p o l y e s t e r a l o s s p e a k at - 8 ° C a n d 1 H z , a n d s o m e s t r u c t u r a l d i s o r d e r i n g at 7 0 ° C . S t r u c t u r a l i n t e g r i t y o f t h e n e t w o r k p e r s i s t s u p to 1 8 0 ° C . I n c o n t r a s t , m i c r o p h a s e s e p a r a t i o n w i t h s o m e p h a s e m i x i n g is a c h i e v e d i n t e n t i o n ­ a l l y i n S a m p l e Β to p r o d u c e a n o p t i c a l l y c l e a r p r o d u c t . T h e e x t e n t o f a

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

WETTON ET AL.

PL-Dynamic

Mechanical

Thermal Analyzer

Downloaded by CORNELL UNIV on May 15, 2017 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch005

5.

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

105

106

POLYMER CHARACTERIZATION

p h a s e m i x i n g is a s s e s s e d b y t h e D M T A t r a c e . A g a i n , c r o s s - l i n k i n g i n t e g r i t y is p r e s e r v e d u p to 1 8 0 ° C . A l t e r n a t i v e c l a m p i n g g e o m e t r y a l l o w s m e a s u r e m e n t o f soft s a m ­ p l e s ( < 1 0 N / m ) i n s h e a r , b u t t h e m a i n i n t e r e s t i n t h e s e c a s e s i s for e n g i n e e r i n g d a t a o n r u b b e r s t h a t c a n b e g e n e r a t e d u p to a 1 0 % s t r a i n l e v e l . M e a s u r e m e n t s o f this t y p e are not r e l e v a n t to t h e m a i n t h e m e o f t r a n s i t i o n m e a s u r e m e n t s , b u t this m o d e o f d e f o r m a t i o n is u s e f u l for s t u d y i n g t r a n s i t i o n p h e n o m e n a i n a d h e s i v e s a n d for s t u d y i n g the e a r l y part of cure i n c r o s s - l i n k i n g resins. F i g u r e 10 s h o w s a n a l t e r n a t i v e g e o m e t r y t h a t a l l o w s t e n s i l e m o d ­ u l u s m e a s u r e m e n t o f t h i n p o l y m e r f i l m s , t y p i c a l l y b e l o w 0.05 m m i n thickness. T h e geometry constant i n this m o d e is s h o w n i n the figure a n d i s m e r e l y t h e n o r m a l t e n s i l e v a l u e m o d i f i e d b y c o s 0 (the a n g l e b e t w e e n d r i v e d i r e c t i o n a n d film). T h e t e n s i o n is m o n i t o r e d b y the d i s p l a c e m e n t p r o d u c e d i n t h e d r i v e s p r i n g a n d i s s e e n d i r e c t l y as a p r o p o r t i o n a l c h a n g e i n t h e t r a n s d u c e r off-set v o l t a g e . A f t e r t e n s i o n a d j u s t m e n t s h a v e b e e n m a d e , t h e s a m p l e is c l a m p e d b y t h e c e n t r a l c l a m p w i t h n a r r o w c l a m p e d g e s a n d the t r a n s d u c e r is a d j u s t e d m a n u ­ a l l y to its n o r m a l w o r k i n g r a n g e . G o o d d a t a c a n b e g e n e r a t e d o n f i l m s i n regions o f m i n o r changes i n t e n s i o n t h r o u g h r e l a x a t i o n effects, b u t i t is n o t p r a c t i c a l i f stress r e l a x a t i o n o c c u r s s t r o n g l y . T h e n e w t e n s i o n h e a d i s d e s i g n e d t o r e m e d y t h i s p r o b l e m . F i g u r e 11 s h o w s d a t a o n r u b b e r t o u g h e n e d p o l y p r o p y l e n e f i l m s m o u n t e d as s h o w n i n F i g u r e 10. T h e r e g i o n o f e t h y l e n e - p r o p y l e n e r u b b e r r e l a x a t i o n c a n b e s e e n clearly i n Samples A a n d B . T h e rubber segments have b e e n incorpo­ rated d i f f e r e n t l y , a n d this is r e f l e c t e d i n the shape of the loss process. T h e D M T A t e c h n i q u e is o n e o f t h e f e w w a y s o f s t u d y i n g f i n e d i f f e r 8

2

Downloaded by CORNELL UNIV on May 15, 2017 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch005

2

Drive

Drive spring

Film. sample

2bt (cos 0) 2

K - - J -

Figure 10. Arrangement for tensile dynamic modulus measurements in thin films. The angle θ is between film and drive directions, and b, t, and I are width, thickness, and length, respectively.

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

5.

WETTON ET A L .

PL-Dynamic

Mechanical

Thermal

Analyzer

107

.08

.01

Downloaded by CORNELL UNIV on May 15, 2017 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch005

-100

Quenched P.P. film -50 0 + 40 Temperature (°C)

Figure 11. Rubber-modified polypropylene films measured through the ethylene—propylene rubber loss region. Geometry used is shown in Figure 10.

e n c e s i n f i l m structure of t h i s t y p e . S a m p l e A has a w i d e r range of m o l e c u l a r heterogeneity associated w i t h the r u b b e r segments than Sample B. C o m p a r i s o n of m o d u l i o b t a i n e d from b e n d i n g of short f i l m sam­ ples w i t h those o b t a i n e d from tensile measurements provides a m e t h o d f o r l o o k i n g at s k i n e f f e c t s i n f i l m s . I n n e r a n d o u t e r l a y e r s are w e i g h t e d e q u a l l y i n the tensile case, b u t the outer layers contribute m o r e to t h e b e n d i n g m o d u l u s . H i g h accuracy m o d u l u s a n d d a m p i n g characteristics m e a s u r e d on the P L - D M T A have p r o v e d u s e f u l i n s t u d y i n g the a g i n g characteris­ t i c s o f p o l y m e r g l a s s e s . I n b o t h , c r o s s - l i n k e d e p o x y s y s t e m s (6) a n d u n c r o s s - l i n k e d p o l y s t y r e n e (7, 8) t h e b a s i c e f f e c t s s e e m t h e s a m e . C o m p a r e d to t h e c o r r e s p o n d i n g a n n e a l e d (aged) g l a s s a q u e n c h e d s a m p l e h a s a l o w e r g l a s s y state m o d u l u s , b u t s u r p r i s i n g l y a h i g h e r d a m p i n g peak, w h e n scanned i n the temperature plane. T h e m o d u l u s c h a n g e o v e r a p e r i o d o f 1 w e e k , a n n e a l e d at 2 0 ° C b e l o w T , i s i n e x c e s s o f 1 0 0 % a n d t h e d a m p i n g l e v e l i n t h e g l a s s , at 3 0 ° C b e l o w T , decreases b y a factor of five i n the case of a n n e a l e d p o l y s t y r e n e . T h e l o w t e m p e r a t u r e (β) l o s s p r o c e s s i n t h e e p o x y s y s t e m s s h o w s a s h a r ­ p e n i n g w i t h a n n e a l i n g , b u t no significant shift i n c e n t r a l p o s i t i o n . g

g

Conclusions T h e P L - D M T A is a b l e to g i v e accurate data o n the w i d e s t p o s s i ­ b l e r a n g e o f p o l y m e r i c m a t e r i a l s . T h e r m a l s c a n n i n g at c o n s t a n t f r e ­ q u e n c y t y p i c a l l y c a n b e a c h i e v e d i n 1 h , c o m p a r a b l e to D S C t e c h ­ n i q u e s . T h e t e c h n i q u e is c o m p l e m e n t a r y to D S C i n t h a t m o t i o n a l t r a n s i t i o n s are o b s e r v e d , a l t h o u g h t h e r m o d y n a m i c t r a n s i t i o n s a r e a l -

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

108

POLYMER CHARACTERIZATION

ways detected b y the structural changes they produce.

Secondary

transitions are not o b s e r v a b l e b y t h e D S C m e t h o d n o r c a n s m a l l r e i n forcing phases be studied. T h e P L - D M T A m e t h o d detects a l l these transitions a n d a l l o w s f o r m u l a t i o n o f définitive c o n c l u s i o n s sample morphology

a n d phase

concerning

composition.

External computer control allows the full capabilities of thei n s t r u m e n t to b e e x p l o i t e d a n d i t is s h o w n that several different

mea-

surement frequencies can be multiplexed during a single temperature scan. A s data are stored i n the c o m p u t e r a n y r e q u i r e d data m a n i p u l a -

Downloaded by CORNELL UNIV on May 15, 2017 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch005

tion can be achieved

subsequently.

Literature Cited 1. Ferry, J. D. In "Viscoelastic Properties of Polymers"; Wiley: New York, 1961; p. 63. 2. Schwarzl, F.; Stavermann, A. J. Appl. Sci. Res. 1953, A4, 127. 3. Illers, K. H.; Breuer, H. J. Colloid Sci. 1963, 18, 1. 4. Mills, P. J.; Hay, J. N.; Cox, C., First PL-DMTA Users Meeting, Univ. of Warwick, 1981. 5. Ferry, J. D. In "Viscoelastic Properties of Polymers"; Wiley: New York, 1961; p. 203. 6. Richardson, M. J., First PL-DMTA Users Meeting, Univ. of Warwick, 1981; p. 9. 7. Wetton, R. E.; Woo, Y. H. Polymer, in press. 8. Wetton, R. E . Chemical Soc., Analytical Proc. Sept/Oct 1981. RECEIVED for review October 30, 1981. ACCEPTED October 11, 1982.

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.