Polymer Characterization - American Chemical Society

6 Dynamic Mechanical Spectroscopy Using the Autovibron DDV-III-C S. M . W E B L E R , J. A. M A N S O N , 1 and R. W. L A N G

Downloaded by CHINESE UNIV OF HONG KONG on June 28, 2016 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch006

Lehigh University, Materials Research Center, Bethlehem, PA 18015

The Autovibron DDV-III-C is a forced vibration unit capable of operating at several constant frequencies for the determination of the dynamic mechanical response of a system. The automation provides a programmed heating rate, continuous sample tensioning, and acqui sition and reduction of data. Results obtained at several frequencies are reported for plain poly(vinyl chloride) (PVC), PVC modified with a methacrylate—buta diene—styrene terpolymer (MBS), and a commercially available mineral-reinforced polyamide. While prob lems have been encountered with sample alignment, tension adjustment, and measurement at low tan δ val ues, it is concluded that this instrument has good poten tial for the convenient determination of dynamic spectra of polymers and their composites.

I N

D E T E R M I N I N G T H E D Y N A M I C M E C H A N I C A L R E S P O N S E of a s y s t e m , it is

o f t e n d e s i r a b l e to w o r k w i t h a f o r c e d - v i b r a t i o n i n s t r u m e n t at a c o n stant f r e q u e n c y . O n e o f t h e i n s t r u m e n t s m o s t c o m m o n l y u s e d for t h i s p u r p o s e has b e e n the d i r e c t - r e a d i n g v i s c o e l a s t o m e t e r o r i g i n a l l y d e v e l o p e d b y T a k a y a n a g i (1, 2)—the R h e o v i b r o n . A c o m m o n m o d e l h a s b e e n t h e m o d e l D D V - I I ( l o a d c a p a c i t y , 0.1 k g f ) a n d i n r e c e n t y e a r s a 5 - k g f c a p a c i t y m o d e l , t h e D D V - I I I - C , w a s i n t r o d u c e d (3, 4). W h i l e v a l u a b l e r e s e a r c h has b e e n b a s e d o n results o b t a i n e d u s i n g such units, several problems have been recognized. Limitations i n c l u d e d i f f i c u l t y i n w o r k i n g at Τ > T , a n d u n d e s i r a b l y l o w r a n g e s i n tan δ a n d frequency. I n a d d i t i o n , m a i n t e n a n c e of p r o p e r t e n s i o n o n the s p e c i m e n is o f t e n far f r o m e a s y . T h e r e f o r e , t h e o p e r a t o r m u s t g i v e c o n s t a n t a t t e n t i o n to t h e i n s t r u m e n t o v e r a p e r i o d o f 4 h o r m o r e . M o r e d e t a i l e d d i s c u s s i o n s are a v a i l a b l e i n t h e l i t e r a t u r e (5, 6). g

1

T o whom correspondence should be addressed.

0065-2393/83/0203-0109$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.


110

POLYMER CHARACTERIZATION

T o r e m e d y or a l l e v i a t e some o f these p r o b l e m s , the R h e o v i b r o n m o d e l D D V - I I - B w a s m o d i f i e d a n d i m p r o v e d (5) b y p r o v i d i n g closed-loop control, a n d b y i m p r o v i n g a n d s i m p l i f y i n g the t e c h n i q u e u s e d to d e t e r m i n e t h e l o s s t a n g e n t a n d t h e s t o r a g e m o d u l u s . G a i n s i n a c c u r a c y , s i m p l i c i t y o f o p e r a t i o n , a n d a d a p t a b i l i t y to d i g i t a l p r o c e s s i n g of the data w e r e r e p o r t e d . T h e R h e o v i b r o n i t s e l f has b e e n auto m a t e d b y t h e m a n u f a c t u r e r (3) a n d t h e R h e o v i b r o n D D V - I I w a s a l s o a u t o m a t e d (6) t o p r o v i d e a u t o m a t i c c o n t r o l o f t e n s i o n , i n c r e a s e d s e n s i t i v i t y , a n d c a l c u l a t i o n a n d p r i n t o u t o f Ε ', Ε", a n d t a n δ. T h e l a t t e r u n i t h a s b e e n c o m m e r c i a l i z e d ( I m a s s , I n c . ) (4) as t h e A u t o v i b r o n , m o d e l D D V - I I - C . Recently a generally similar adaptation was introduced based o n the h y d r a u l i c a l l y operated R h e o v i b r o n D D V - I I I - C . A u t o m a t i o n o f a t o r s i o n a l p e n d u l u m (7) a n d a d i f f e r e n t c o n s t a n t - f r e q u e n c y i n s t r u m e n t (8) h a v e a l s o b e e n d e s c r i b e d . A l t h o u g h a full critical analysis of the operation of the A u t o v i b r o n D D V - I I I - C h a s n o t y e t b e e n p o s s i b l e , i t i s a p p r o p r i a t e to d e s c r i b e o u r e x p e r i e n c e w i t h t h i s n e w i n s t r u m e n t , a n d to m a k e p r e l i m i n a r y r e c o m m e n d a t i o n s w i t h r e s p e c t to o p e r a t i o n a n d f u t u r e i m p r o v e m e n t . B e c a u s e the i n s t r u m e n t is t h e first of its t y p e , the o b s e r v a t i o n s r e p o r t e d s h o u l d b e h e l p f u l to o t h e r i n v e s t i g a t o r s . R e s u l t s o b t a i n e d i n o u r l a b o ratory u s i n g a n a u t o m a t e d D D V - I I u n i t are also d e s c r i b e d for c o m parison. Instrumentation A s m e n t i o n e d p r e v i o u s l y , the m o d e l D D V - I I I - C R h e o v i b r o n (Toyo B a l d w i n Co.) has b e e n c o m b i n e d w i t h an automation package (Imass, Inc.). T h e i n s t r u m e n t m a i n t a i n s the essential characteristics of the R h e o v i b r o n D D V - I I I - C , u t i l i z i n g the original sample b e n c h , hy draulic system, load cell, a n d basic electronics. F o u r fixed frequencies o f 3.5, 1 1 , 3 5 , a n d 110 H z are a v a i l a b l e . S a m p l e s i z e s u p to 7 c m x 1 c m x 5 m m c a n b e h a n d l e d , w i t h a c l a i m e d range for c o m p l e x Y o u n g ' s m o d u l u s b e t w e e n 1 M P a a n d 1 0 0 G P a (1 G P a = 1 G N / m = 1 0 d y n e s / c m ) . A l o w - t e m p e r a t u r e c h a m b e r a l l o w s m e a s u r e m e n t s to b e t a k e n f r o m about - 1 4 0 to 175 °C w i t h a p r o g r a m m e d rate of t e m p e r a t u r e i n c r e a s e o f ~ 1 ° C / m i n . A s e c o n d c h a m b e r is p r o v i d e d for t e m p e r a t u r e s u p to 3 0 0 ° C . T h e a u t o m a t i o n p a c k a g e i s r e s p o n s i b l e f o r s a m p l e t e n s i o n i n g , phase angle m e a s u r e m e n t s , temperature c o n t r o l , data ac q u i s i t i o n , a n d data r e d u c t i o n . T h e k e y c o m p o n e n t s o f t h i s p a c k a g e are a l o c k - i n analyzer ( P r i n c e t o n A p p l i e d R e s e a r c h m o d e l 5204), a pro grammable calculator (Hewlett Packard m o d e l 9825A), a multiprogrammer (Hewlett Packard m o d e l 6940B), and an optional plotter ( H e w l e t t P a c k a r d m o d e l 9872B). T h e automation package can also be interfaced readily w i t h a Rheovibron m o d e l D D V - I I . T h e essential 2

2


1 0

6.

WEBLER ET AL.

Dynamic

Mechanical

111

Spectroscopy


- 4

0

-9

1_ «t

Log Figure

1 (ο

ω

Modulus

s

CM

(Ρο)

1. Comparison of the correct sample size vs. modulus DDV-II (—) and DDV-III (—) Rheovibrons.

for

the

d i f f e r e n c e s i n t h e t w o u n i t s are t h e d r i v i n g u n i t a n d t h e l o a d c a p a c i t y . T h e h y d r a u l i c d r i v i n g s y s t e m o f the D D V - I I I is r e p l a c e d b y a n e l e c t r o m e c h a n i c a l d r i v e r i n the s m a l l e r u n i t . T h e D D V - I I is c a p a b l e o f h a n d l i n g s a m p l e s i z e s u p to 5 x 0 . 0 5 x 0.4 c m ( F i g u r e 1 s h o w s a c o m p a r i s o n of s a m p l e sizes for the t w o m o d e l s ) w i t h a m a x i m u m l o a d c a p a c i t y o f 0.1 k g f a n d m o d u l u s r a n g e o f 1 0 0 k P a - 1 0 0 G P a . A s c h e m a is g i v e n i n F i g u r e 2. T e m p e r a t u r e p r o g r a m m i n g is e f f e c t e d t h r o u g h the c a l c u l a t o r i n c o n j u n c t i o n w i t h a p l a t i n u m r e s i s t a n c e t h e r m o m e t e r . F r o m —140 to - 4 5 °C t h e t e m p e r a t u r e is a l l o w e d to i n c r e a s e w i t h o u t r e g u l a t i o n at a rate o f 1 ° C / m i n . A t - 4 5 ° C p o w e r is s u p p l i e d to t h e h e a t e r s , a n d t h e t e m p e r a t u r e is c o n t r o l l e d b y p r o g r a m m i n g t h e a p p l i c a t i o n o f p o w e r . T h e t e m p e r a t u r e r i s e c a n a l s o b e c o n t r o l l e d at rates o t h e r t h a n 1 ° C / m i n through changes i n the operating program. F o r temperatures above 225 °C, the high-temperature c h a m b e r m u s t be u s e d . Phase-angle measurements u s i n g the l o c k - i n analyzer were i n c o r p o r a t e d to s i m p l i f y a u t o m a t i o n o f t h e m e a s u r e m e n t s , i m p r o v e r e s olution of small angles, a n d increase the range of tan δ measurements (4). T h e c a l c u l a t o r a l t e r n a t e l y s w i t c h e s t h e l o a d (P) a n d d i s p l a c e m e n t (X) s i g n a l t h r o u g h t h e m u l t i p r o g r a m m e r to t h e l o c k - i n a n a l y z e r . A f t e r a p r o g r a m m e d d e l a y for s e t t i n g o f the s i g n a l , t h e i n - p h a s e a n d q u a d r a t u r e c o m p o n e n t s o f t h e r e s p e c t i v e s i g n a l s are m e a s u r e d w i t h r e s p e c t


112


to a r e f e r e n c e s i g n a l f r o m t h e A u t o v i b r o n ( F i g u r e 3). T h e

complex

Y o u n g ' s m o d u l u s , E * , i s c a l c u l a t e d u s i n g E q u a t i o n 1. E*

=

R

PQ)

L

(xj + X q T

ν

(Pf +

2

(1)


T h e subscripts J a n d Q designate the in-phase a n d quadrature c o m p o n e n t s o f t h e r e s p e c t i v e s i g n a l s , R is a r a n g i n g a n d s c a l i n g f a c t o r , L i s the sample l e n g t h , a n d V is the o r i g i n a l sample v o l u m e . T h e phase d i f f e r e n c e , δ i s c a l c u l a t e d u s i n g E q u a t i o n 2. δ = φ

1

- φ

Xq arctan—Xi

PQ

= arctan—- Pj

2

(2)

W i t h E * a n d δ f r o m E q u a t i o n s 1 a n d 2, r e s p e c t i v e l y , t h e s t o r a g e

mod

u l u s , E', a n d l o s s m o d u l u s , £ " , c a n b e c a l c u l a t e d . E'

= |E*|cos δ

(3) δ

Ε" = \ E*\sin

(4)

tan δ = Ε 7 Ε '

(5)

T h e a c q u i r e d data are d i s p l a y e d w h i l e t h e p r o g r a m is r u n n i n g a n d s t o r e d o n m a g n e t i c - t a p e c a r t r i d g e s for f u r t h e r r e d u c t i o n . R e s u l t s c a n be p r i n t e d or plotted d u r i n g the r u n w i t h appropriate p r o g r a m m i n g ; p r o g r a m s for d a t a r e d u c t i o n a n d p l o t t i n g f r o m t a p e a r e a v a i l a b l e .

LOAD

SAMPLE

DISPLACEMENT Ί

RHEOVIBRON INTERFACE

RHEOVIBRON

TEMPERATURE SENSOR

π — π LOCK-1Ν ANALYZER

[TENSION

AMP

CALCULATOR

HEATERS

I

MULTI PROGRAMMER STEPPING MOTOR

PLOTTER Figure

2. Block diagram

of

Autovibron.


6.

WEBLER ET A L .

Dynamic

Mechanical

Spectroscopy

113

Figure 3. In-phase and quadrature components of the load (P) and dis placement (X) signals. Subscripts I and Q refer to in-phase and out-ofphase (quadrature) components; φ and fa are phase angles. Downloaded by CHINESE UNIV OF HONG KONG on June 28, 2016 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch006

7

Experimental P r o b l e m s a n d T h e i r C o r r e c t i o n . D u r i n g start-up a n d subsequent trials u s i n g the D D V - I I I - C , several significant problems were encountered. M u c h of our work has b e e n c o n d u c t e d u s i n g an automated D D V - I I because of problems w i t h the D D V - I I I . P r e l i m i n a r y work w i t h the large load capacity u n i t has s h o w n problems i n sample t e n s i o n i n g , load control, measurement of small phase angles, and programming. T h e s e difficulties are discussed later. Sample tension is c o n t r o l l e d b y the calculator through the m u l t i p r o g r a m m e r a n d a s t e p p i n g - m o t o r that m o v e s the l o a d a r m . T h e o r i g i n a l stepping-motor assembly u s e d springs to control tension a n d resulted i n e n o u g h lateral m o t i o n to p r e c l u d e maintenance of alignment. S u c h alignment is of critical importance, otherwise serious errors i n m o d u l u s a n d d a m p i n g can result. A c o m b i n a t i o n of shims to a l i g n the center of the load-arm w i t h the center of the d r i v e r a n d a n e w s c r e w - d r i v e n stepping-motor assembly (rede s i g n e d b y Imass, Inc.) have m i n i m i z e d lateral motion. H o w e v e r , e v e n w i t h these modifications, great care must still be taken w i t h c l a m p i n g a n d a l i g n ment of the s p e c i m e n . A l s o , b o w i n g i n the sample can be i n t r o d u c e d b y n o n u n i f o r m t i g h t e n i n g of the grips. Some scatter may be due to an inherent design p r o b l e m ; the manufacturer is currently r e v i s i n g the signal r e a d i n g section. A s was the case w i t h the A u t o v i b r o n D D V - I I (6), sample m o u n t i n g a n d alignment are two major flaws of the instrument. R e p r o d u c i b l e methods for sample m o u n t i n g have b e e n reported for the D D V - I I (9), a n d s i m i l a r m o d ifications s h o u l d be i n c l u d e d i n further redesign of the D D V - I I I system. T h e o r i g i n a l software calculated the D C voltage of the load signal b y s a m p l i n g the sine wave, c a l c u l a t i n g the a m p l i t u d e , a n d d i v i d i n g b y two to obtain the D C bias. Because of problems i n measuring the load, the program was m o d i f i e d to measure the D C voltage bias directly, b y m o m e n t a r i l y s w i t c h i n g off the sine wave. L o a d corrections are t h e n made b y the stepping-motor to m a i n t a i n a preset l i m i t . T h i s n e w load-control program functions acceptably through a programmed temperature r u n except i n the region around the glass transition temperature (T ). I m m e d i a t e l y after the transition, the sample is often put into compression. So far, r e l i a b l e mea surements of r u b b e r y m o d u l i o n the order of 10 M P a have b e e n obtained only occasionally. W h i l e m o n i t o r i n g the load signal (P) w i t h an oscilloscope, a p r o b l e m was e v i d e n t i n the s w i t c h i n g of the signal. T h e value of the load was intermittently recorded as zero. Because tension is a function of load, w h e n zero loads are recorded the instrument reacts b y m a k i n g drastic changes i n sample l e n g t h , 9



114


r e s u l t i n g i n incorrect m o d u l u s a n d phase angle measurements. T h i s p r o b l e m appears to have b e e n corrected b y the replacement o f a relay-readback board i n the multiprogrammer. A n o t h e r p r o b l e m has b e e n the determination of o p t i m u m settings of the phase controls on the l o c k - i n analyzer. After some experimentation it was d e t e r m i n e d that the in-phase a n d quadrature readings s h o u l d be set a p p r o x i mately equal i n magnitude a n d w i t h the same sign (positive or negative) u s i n g the reference angle potentiometer and quadrant selector of the l o c k - i n analyzer. U s e of these settings appears to reduce the time r e q u i r e d for the signal to stabilize, a n d facilitates ranging of the signals. T h e r a n g i n g sub routine has also b e e n r e w r i t t e n b y Imass to alleviate a p r o b l e m w i t h signal saturation that occurred w h e n the in-phase a n d quadrature components of the signal became u n b a l a n c e d . Performance. F i g u r e s 4 a n d 5 compare data at 110 H z from t w o samples of the same m e t h a c r y l a t e - b u t a d i e n e - s t y r e n e ( M B S ) - m o d i f i e d P V C i n the as-received c o n d i t i o n ( P V C 132-3). T h e s e samples were a n a l y z e d b y u s i n g the D D V - I I I - C A u t o v i b r o n before manufacturer revisions. T a b l e I shows P V C sample designations, weight-average m o l e c u l a r weight, M and r u b b e r c o n tents. Previous literature contains d e t a i l e d characterization of the P V C (10). T h e samples were o f s i m i l a r cross-sectional area and l e n g t h (see T a b l e I). T h e tests were r u n u s i n g an o s c i l l a t i n g displacement, A L , of 2.5 x 1 0 " c m , corre s p o n d i n g to an o s c i l l a t i n g strain, Ae, of 0.05%. Great care was taken w i t h sample m o u n t i n g a n d alignment. O v e r the temperature range from - 1 1 5 to 100 °C, values of the storage m o d u l u s ( £ ' ) obtained i n the two tests agreed w i t h i n less than 5%. B e l o w —75 °C (corresponding to tan δ ^0.02) significant scatter was e v i d e n t i n the loss m o d u l u s (E") a n d tan δ, a n d the slopes differed considerably, so that the value of tan δ at - 1 0 0 °C is —40% less i n F i g u r e 5 than i n F i g u r e 4. (The shapes of the E" and tan δ curves i n F i g u r e 5 are i n fact atypical.) C o n s i d e r a b l e scatter has also b e e n seen at l o w values of tan δ w i t h the A u t o v i b r o n D D V - I I - C (11). H o w e v e r , the peak for the M B S phase is clear l y e v i d e n t at about - 6 0 °C. W h i l e data for S p e c i m e n A ( F i g u r e 4) c o u l d be taken u p to 140 °C, it was not possible to e x c e e d 100 °C w i t h S p e c i m e n Β W9

3

Figure 4. Dynamic mechanic spec tra (110 Hz) of MBS-modified PVC (Sample 132-3A) using a DDV-IIIC Autovibron.

TEMPERATURE

(C)


6.

WEBLER ET A L .

Dynamic

Mechanical

115

Spectroscopy

10

0 •Ρ

σ Q- β

0

LU

-ι

c3 σ

U)


0

m y

Tan D e l t e

C9

m

m

TEMPERATURE

Figure 5. Dynamic mechanical spec tra (110 Hz) of MBS-modified PVC (Sample 132-3B) using a DDV-IIIC Autovibron.

w h i c h , for u n k n o w n reasons, d e f o r m e d excessively. V a l u e s of T a n d c o m p l e x m o d u l u s (E*) are reported i n T a b l e I I . F i g u r e 6 shows data o b t a i n e d for a P V C 132-4 sample u s i n g the D D V I I I - C u n i t after replacement of the p u m p a n d m o d i f i c a t i o n of the electronics b y the manufacturer. S a m p l e characteristics are g i v e n i n T a b l e s I a n d I I . T h e test was r u n u s i n g an o s c i l l a t i n g d i s p l a c e m e n t , A L , of 2 x 1 0 " c m (i.e., at Ac « 0.05%). T a n δ a n d E" values show c o n s i d e r a b l y less scatter t h a n before the instrument was m o d i f i e d (compare data i n F i g u r e s 4, 5, a n d 6). I n fact, E' results can n o w be r e p r o d u c e d at 110 H z to w i t h i n ± 2 % w h e n u s i n g s i m i l a r sample sizes. N e v e r t h e l e s s , the p r o b l e m of excessive sample deformation at Τ > T still exists. F i g u r e 7 illustrates data obtained w i t h an automated R h e o v i b r o n D D V - I I for two different specimens of the same material. T h e t w o samples h a d almost i d e n t i c a l l e n g t h , w i d t h , a n d thickness (see T a b l e II). B o t h samples w e r e m a c h i n e d i n the same m a n n e r a n d r u n b y the same operator u n d e r the same operating conditions. T h e i n i t i a l o s c i l l a t i n g displacement, A L , was 7.9 Χ 1 0 c m (i.e., Ae 0.01%) i n both cases. V a l u e s of E * agree to w i t h i n 9% at - 1 0 0 ° C 9

3

g

- 4

T a b l e I. P V C Characterization PVC Sample

designation 131-1 131-4 132-1 132-3 132-4 135-1 135-4

a

Values of M

w

M

Matrix" x 10

5

w

0.67 0.67 0.95 0.95 0.95 2.08 2.08

are from reference (10).


phr MBS 0 14 0 10 14 0 14


e

d

c

b

a

III III III II II III III II III III III II

L = sample length LIW = length -f- width LIA = length area Q = quenched sample Annealed 7 d at 65 °C

132-3A 132-3B 132-4 135-4 135-4 135-1 135-1 135-1 135-4 135-4-Q" 135-4-7* 131-4-Q*

Sample

Rheovibron Model

110 110 110 110 110 110 110 110 110 110 110 35

Frequency (Hz) g

94 95 92 83 83 93 93 82 94 93 92 76

T (°C)

at 4.240 4.125 2.657 2.047 2.240 3.794 2.727 2.107 2.690 2.674 2.638 2.389 2.867 2.790 1.824 1.521 1.639 2.889 2.124 1.731 1.836 1.796 1.774 1.599

9

Pa)

2.501 2.464 1.632 1.350 1.434 2.625 1.912 1.506 1.644 1.526 1.555 1.335

at 40 °C

(E* x Ι Ο "

at 0 °C

Modulus

-100 °C

Complex (cm)

4.942 4.956 4.136 6.48 6.45 3.766 4.142 5.38 4.106 4.048 3.990 6.31

L°

12.7 13.0 10.3 30.6 29.7 9.0 9.1 22.2 10.4 9.8 10.1 30.5

LAV* (cm~*)

T a b l e II. C o m p a r i s o n of D y n a m i c D a t a o n a Standard and M o d i f i e d P V C U s i n g A u t o v i b r o n and R h e o v i b r o n M o d e l D D V - I I


59.5 62.1 47.4 650 660 38 38 494 46.7 44.3 47.6 677

c

2

L/A ( cm~ )

25

Η Ο

ο Η Μ SJ Ν >

η Χ >

M

*! g

Ο r

6.

WEBLER ET A L .

Dynamic

Mechanical

117

Spectroscopy

10

9

*

σ

σ α.

8

c

LU

-i

U)

°

0


Tan

-2 0

Delta

-3 in

in

in

in

TEMPERATURE

C O

Figure 6. Dynamic mechanical spec tra of MBS-modified PVC (Sample 132-4, M =0.95 x 10 ; 14 phr MBS) using DDV-III-C Autovibron after revisions (110 Hz). w

5

a n d differ b y less t h a n 6% at 40 °C. I n the T r e g i o n E\ E", a n d t a n δ are v i r t u a l l y i d e n t i c a l . T h e t w o samples do not h o w e v e r , have the same E" a n d tan δ i n the r e g i o n from - 1 0 0 to 50 °C. F o r e x a m p l e , tan δ readings of 0.033 a n d 0.056 w e r e taken at - 2 5 °C for the t w o samples. T h e s e differences are as yet u n e x p l a i n e d a n d suggest c a u t i o n s h o u l d be e m p l o y e d w h e n a n a l y z i n g data. F i g u r e s 8 a n d 9 show data for P V C 135-1 u s i n g the D D V - I I I u n i t (before a n d after revisions) a n d the automated D D V - I I . T a n δ values are comparable from - 1 5 0 to 50 °C. T h e T m e a s u r e d u s i n g the D D V - I I I - C is 10°C h i g h e r t h a n the T o b t a i n e d w i t h the D D V - I I . T h i s difference p r o b a b l y reflects an effect o f the larger sample size i n the D D V - I I I . M o s t l i k e l y the average sample t e m perature lags b e h i n d the furnace temperature; this temperature l a g results i n the apparent increase i n T . A c o m p a r i s o n o f complex m o d u l u s (E*) data at 0 g

g

g

g

Figure 7. Dynamic mechanical spec tra of two replicate MBS-modified PVC samples (Sample 135—4, M = 2 x J O ; 14 phr MBS) using an auto mated DDV-II Autovibron. w

5

TEMPERATURE

C O


118

POLYMER

CHARACTERIZATION

10

σ •Ρ

σ ο-

θ

ι—I

•(S

UJ

-ι

ω ο

ϋ) -2 Ρ


ltd" Figure 8. Comparison of dynamic mechanical spectra of PVC (Sample 135-1, M = 2 x 10 ) using model DDV-III-C (-)and manual DDV11 (***) Autovibron.

S

5

w

in

s

in

in

TEMPERATURE

σ

CO

°C reveals an apparent 3 5 % decrease after m o d i f i c a t i o n of the D D V - I I I , w h i l e E * o b t a i n e d at 0 °C u s i n g the D D V - I I is 18% l o w e r than the n e w D D V - I I I value. T h e s e u n e x p l a i n e d differences suggest c a u t i o n s h o u l d be e m p l o y e d w h e n c o m p a r i n g data obtained from different instruments a n d operators. E r r o r analysis for the m a n u a l D D V - I I was addressed (9), a n d the analysis s h o u l d be extended to the automated unit. E r r o r s of u p to 5 0 % have b e e n reported (9) and w e r e attributed to the i n s t r u m e n t c o m p l i a n c e , sample y i e l d i n g a n d s l i p p i n g i n the clamps, sample a l i g n m e n t , the instrument's i n e r t i a , variable sample sizes, a n d structural changes i n the sample d u r i n g testing. E a c h p r o b l e m needs to be addressed before a thorough u n d e r s t a n d i n g of the automated u n i t w i l l be p o s s i b l e , a n d true material properties can be m e a s u r e d w i t h f u l l confidence.

10

* 0 σ 0-

8

C

LU U)

0

U)

Figure 9. Comparison of dynamic mechanical spectra of PVC (Sample 135-1, M = 2 x 10 ) using auto mated DDV-II (O) and DDV-III-C Autovibrons after manufacturer s revisions (—) at 110 Hz. w

s

s m

in

m

TEMPERATURE

CO


6.

Dynamic

WEBLER ET AL.

Mechanical

119

Spectroscopy

10

σ •Ρ

Ό

a.

•2

Θ

LU

-1

CD 0

U)


ο

Figure 10. Dynamic mechanical spectra (110 Hz) of MBS-modified PVC (Sample 135-4, M = 2 x 10 ; 14 phr MBS) as received (1), after 7 d at 65 C (2), quenched from 110 °C (3). These spectra were ob tained by using the DDV-III-C Autivibron after revisions. w

in

in ι

in

TEMPERATURE

in

(C)

5

Studies of the effect of t h e r m a l history a n d frequency of P V C a n d M B S m o d i f i e d P V C are u n d e r way. P r e l i m i n a r y results obtained u s i n g the D D V I I I - C o n q u e n c h e d P V C ( q u e n c h e d from 110 °C i n ice) are s h o w n i n F i g u r e 10 w i t h respect to a n as-received sample. T h e results show an increase i n d a m p i n g b e t w e e n Τ a n d Τ i n the q u e n c h e d sample s i m i l a r to the results of Struik (12). F i g u r e 10 also displays data for a sample that was q u e n c h e d i n ice from 110 °C a n d t h e n a n n e a l e d at 65 °C for a p e r i o d of 7 d. T h e d a m p i n g b e t w e e n 0 and 50 °C clearly had b e e n affected b y the aging process i n a m a n n e r s i m i l a r to data presented b y Struik (12). T h e m a n u a l R h e o v i b r o n is not u s e d easily at frequencies

Polymer Characterization - American Chemical Society

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