Application of a Modified Accelerating Rate Calorimeter to

Chapter 33

Application of a Modified Accelerating Rate Calorimeter to Decomposition Kinetic Studies Alexander N. Kalos

Downloaded by UNIV OF PITTSBURGH on February 18, 2016 | http://pubs.acs.org Publication Date: August 29, 1989 | doi: 10.1021/bk-1989-0404.ch033

Analytical and Engineering Sciences, The Dow Chemical Company, Freeport, T X 77541

Accelerating rate calorimeters (ARC) are customarily used to determine the overall reactivity of compounds. One limitation of these instruments is that pressure data at pre-exotherm temperatures are not recorded. However, such information may be important for the analysis of reactive systems in which pressure events are observed prior to the exotherm. An ARC has been modified so that pressure data can be acquired and stored for kinetic analysis by interfacing with a personal computer. Results are presented using this technique for the study of the decomposition chemistry of 4,4'-diisocyanatodiphenylmethane (MDI).

The Dow Chemical Company has m a i n t a i n e d a c o n t i n u i n g i n t e r e s t i n t h e s a f e h a n d l i n g o f c h e m i c a l s , p a r t i c u l a r l y those whose r e a c t i v i t y makes them u s e f u l monomers f o r commercial polymers. The t h e r m a l r e a c t i o n s o f 4 , 4 ' - d i i s o c y a n a t o d i p h e n y l m e t h a n e have been i n v e s t i g a t e d as p a r t o f t h i s program. T r a d i t i o n a l l y , the h a z a r d s o f p o t e n t i a l l y r e a c t i v e c h e m i c a l s a r e a s s e s s e d through the a p p l i c a t i o n o f a v a r i e t y o f t e c h n i q u e s such as D i f f e r e n t i a l Scanning C a l o r i m e t r y (DSC) ( 1 ) , Vent S i z i n g Package (VSP) (2) and A c c e l a r a t i n g Rate C a l o r i m e t r y (ARC) ( 3 ) . Among t h e s e , ARC i s p a r t i c u l a r l y u s e f u l s i n c e i t o f f e r s a good e s t i m a t e o f t h e o v e r a l l r e a c t i v i t y p r o f i l e o f r e a c t i v e s p e c i e s . ARCs were d e v e l o p e d t o a i d i n p r e d i c t i n g and t h e r e b y a v o i d i n g t h e r m a l l y - i n i t i a t e d runaway r e a c t i o n s i n p r o c e s s and s t o r a g e s i t u a t i o n s . Some o f t h e i n f o r m a t i o n t h a t i s p r o v i d e d from an ARC r u n i n c l u d e s t h e temperature a t which an exotherm i s f i r s t d e t e c t e d ( i . e . , the o n s e t o f an exotherm), the peak exotherm temperature, the h e a t r a t e d u r i n g the exotherm as w e l l as the t o t a l t h e r m a l and p r e s s u r e changes. One l i m i t a t i o n o f many ARC i n s t r u m e n t s , however, i s t h a t the temperature and p r e s s u r e d a t a a t temperatures below t h a t o f the o n s e t o f a n exotherm are n o t s t o r e d f o r subsequent a n a l y s i s . T h i s does n o t p r e s e n t a problem i n systems i n which h e a t may be the o n l y cause o f a runaway r e a c t i o n . However, such i n f o r m a t i o n may be v e r y i m p o r t a n t 0097-6156/89/0404-0428$06.00/0 ο 1989 American Chemical Society

In Computer Applications in Applied Polymer Science II; Provder, Theodore; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


33. KALOS

429

Modified Accelerating Rate Calorimeter

f o r t h e a n a l y s i s o f r e a c t i v e systems i n w h i c h s i g n i f i c a n t p r e s s u r e r i s e s o c c u r p r i o r t o t h e exotherm. Such events may go u n d e t e c t e d i f the ARC i s o p e r a t e d under " s t a n d a r d h a z a r d e v a l u a t i o n " c o n d i t i o n s . The d e c o m p o s i t i o n o f i s o c y a n a t e s t o c a r b o d i i m i d e s and c a r b o n d i o x i d e a t r e l a t i v e l y low temperatures i s w e l l known ( 3 . 4 ) . P r e s s u r e a c c u m u l a t i o n s would be e x p e c t e d i f these r e a c t i o n s o c c u r e d i n c l o s e d v e s s e l s . Q u a n t i t a t i v e pressure data f o r the thermal d e c o m p o s i t i o n o f MDI have n o t been r e p o r t e d . T h i s i n f o r m a t i o n i s i m p o r t a n t f o r t h e d e s i g n o f p r e s s u r e v e s s e l s w i t h adequate v e n t r e l i e f systems, s i n c e upon s t o r a g e , MDI may be exposed t o temperatures w e l l over 100 °F under e s s e n t i a l l y a d i a b a t i c c o n d i t i o n s . I n t h i s r e p o r t a m o d i f i e d ARC a p p a r a t u s i s d e s c r i b e d which c a n be used t o m o n i t o r t h e p r e s s u r e and temperature changes o f r e a c t i v e c h e m i c a l systems a t any temperature throughout t h e experiment. The p r i m a r y o b j e c t i v e o f t h i s work has been t o conduct experiments aimed a t t h e u n d e r s t a n d i n g o f t h e t h e r m a l d e c o m p o s i t i o n c h e m i s t r y o f MDI. The l o n g term scope o f t h i s work i s t o e v a l u a t e the h a z a r d s o f h a n d l i n g and s t o r i n g MDI and p r o v i d e d a t a w h i c h c a n be used f o r t h e d e s i g n o f s t o r a g e v e s s e l s o f a p p r o p r i a t e s i z e . Chemistry The s t r u c t u r e s o f MDI and o t h e r k e y r e l a t e d compounds a r e shown below. 2 0=C=N-R-N=C=0-

-> 0=C=N-R-NH>N-R-N=C=0

Ar. 3 0=C=N-R-N=C=0

-»

.C.

I

+ C0

0

(1)

Ar

I

(2)

I where R = -C.H.-CHL-C.H. 6 4 2 6 4

and A r -

Ar 0=C=N-R-

The f o r m a t i o n o f c a r b o d i i m i d e from 2 m o l e c u l e s o f MDI i s shown i n E q u a t i o n 1. C a r b o d i i m i d e f o r m a t i o n i s accompanied b y t h e e v o l u t i o n o f c a r b o n d i o x i d e , and t h i s r e a c t i o n i s b e l i e v e d t o be t h e p r i m a r y source o f p r e s s u r e upon t h e t h e r m a l d e c o m p o s i t i o n o f MDI. The f o r m a t i o n o f a c y c l i c s p e c i e s ( i s o c y a n u r a t e from 3 m o l e c u l e s o f MDI) i s shown i n E q u a t i o n 2. T h i s c y c l o t r i m e r i z a t i o n r e a c t i o n i s h i g h l y e x o t h e r m i c (-96 KJ/mol i n diglyme ( 6 ) ) and i s b e l i e v e d t o be the major source o f heat d u r i n g t h e e x o t h e r m i c r e a c t i o n o f MDI. Experimental S t a n d a r d ARC Experiments. The ARC apparatus i s manufactured by Columbia S c i e n t i f i c I n d u s t r i e s . The t h e r m a l d e c o m p o s i t i o n o f MDI was f i r s t s t u d i e d u s i n g t h e ARC under s t a n d a r d h a z a r d e v a l u a t i o n c o n d i t i o n s . Under these c o n d i t i o n s , t h e sample ( e n c l o s e d i n a



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COMPUTER APPLICATIONS IN APPLIED POLYMER SCIENCE II

p r e s s u r e - s e a l e d s t a i n l e s s s t e e l c o n t a i n e r ) i s h e a t e d a t 5-degree i n c r e m e n t s . A f t e r t h e h e a t i n g s t e p , t h e temperature i s m a i n t a i n e d f o r a 10-minute p e r i o d t o e q u i l i b r a t e t h e system. Then t h e i n s t r u m e n t m o n i t o r s any temperature changes due t o t h e sample i n t h e reaction vessel. I f a temperature r i s e i s n o t d e t e c t e d ( i . e . , t h e h e a t r i s e r a t e i s l e s s than 0.02 °C/min f o r a t l e a s t 5 m i n ) , t h e temperature o f t h e v e s s e l i s stepped-up t o t h e n e x t 5-degree increment and t h e p r o c e s s i s r e p e a t e d . On t h e o t h e r hand, i f a temperature r i s e i s observed, then t h e ARC a t t e m p t s t o m a i n t a i n t h e temperature o f t h e s u r r o u n d i n g s t o match t h a t caused b y t h e sample i n t h e c o n t a i n e r , so t h a t i t m a i n t a i n s i t e s s e n t i a l l y under a d i a b a t i c c o n d i t i o n s . I t i s o n l y d u r i n g t h i s time ( i . e . , d u r i n g t h e t r a c k i n g o f t h e exotherm) t h a t t h e p r e s s u r e and temperature d a t a a r e s t o r e d . These d a t a c a n be a c c e s s e d l a t e r f o r g r a p h i c a l p r e s e n t a t i o n on a s t r i p - c h a r t r e c o r d e r . However, a l l d a t a p r i o r t o ( o r a f t e r ) an exotherm a r e n o t s t o r e d d u r i n g a s t a n d r a d ARC r u n . Even though temperature and p r e s s u r e a r e c o n t i n u o u s l y b e i n g m o n i t o r e d t h r o u g h o u t the r u n , t h i s i n f o r m a t i o n i s n o t s t o r e d o r r e c o r d e d f o r f u r t h e r a n a l y s i s u n l e s s t h e onset o f an exotherm has been d e t e c t e d . T h i s i s one o f t h e l i m i t a t i o n s o f r u n n i n g t h e ARC i n t h i s manner, s i n c e s i g n i f i c a n t p r e s s u r e events p o s s i b l y o c c u r r i n g p r i o r t o t h e exotherm may n o t be d e t e c t e d . M o d i f i e d ARC Experiments. P r e s s u r e and temperature d a t a a t p r e exotherm temperatures may be c o l l e c t e d by r u n n i n g t h e ARC under m o d i f i e d c o n d i t i o n s . A s c h e m a t i c diagram o f t h e e x p e r i m e n t a l setup o f a m o d i f i e d ARC apparatus i s shown i n F i g u r e 1. The ARC i s c o n t r o l l e d by i t s own h a r d w i r e d c o n t r o l module. The temperature i s m o n i t o r e d by a s e t o f seven thermocouples c o n n e c t e d i n s e r i e s which measure t h e d i f f e r e n c e between t h e temperature o f the sample and t h a t o f i t s s u r r o u n d i n g s . The temperature i s m a i n t a i n e d by h e a t e r s which r e c e i v e t h e i r i n p u t s from t h e c o n t r o l module. A p r e s s u r e t r a n s d u c e r i s a t t a c h e d t o t h e sample c o n t a i n e r , g i v i n g b o t h an a n a l o g readout on a p r e s s u r e gauge and a d i g i t a l r e a d o u t on t h e c o n t r o l module p a n e l . I t s h o u l d be n o t e d t h a t pressure i s monitored but i t i s not p a r t o f the c o n t r o l loop. I n t h e m o d i f i e d ARC apparatus t h e temperature and p r e s s u r e d a t a are r o u t e d t o a p e r s o n a l PC-AT microcomputer f o r s t o r a g e and f u r t h e r a n a l y s i s . The ARC i s i n t e r f a c e d w i t h t h e microcomputer t h r o u g h an a n a l o g - t o - d i g i t a l d a t a a c q u i s i t i o n b o a r d (Data T r a n s l a t i o n 2805). These d i g i t a l temperature and p r e s s u r e r e a d i n g s a r e t h e n f e d i n t o the microcomputer which i s equipped w i t h a 30-MByte h a r d d i s k and L a b t e c h Notebook s o f t w a r e . T h i s s o f t w a r e performs t h e n e c e s s a r y c o n v e r s i o n s from v o l t a g e s i g n a l measurements t o s c i e n t i f i c u n i t s and a l s o p r o v i d e s a gate f o r t h e a n a l y s i s o f t h e d a t a w i t h o t h e r s o f t w a r e packages. Temperature r e a d i n g s were o b t a i n e d by i n s t a l l i n g an e x t e r n a l thermocouple on t h e w a l l o f t h e r e a c t i o n v e s s e l . S p l i c i n g i n t o t h e e x i s t i n g s e r i e s o f thermocouples was n o t a t t e m p t e d i n o r d e r t o a v o i d p o s s i b l e i n t e r f e r e n c e w i t h t h e normal c o n t r o l f u n c t i o n s o f t h e ARC. P r e s s u r e r e a d i n g s were o b t a i n e d by t a p p i n g d i r e c t l y i n t o t h e p r e s s u r e t r a n s d u c e r o f t h e ARC. I n t h i s c a s e , an a m p l i f i e r had t o be i n t e r p o s e d between t h e ARC and t h e d a t a a c q u i s i t i o n board i n order t o boost the s i g n a l . F i n a l l y , the thermocouple and t h e a m p l i f i e d p r e s s u r e t r a n s d u c e r w i r e s were



33. KALOS


431

a t t a c h e d t o a DT707 screw t e r m i n a l p a n e l w h i c h r e s i d e s on t h e bench t o p , o u t s i d e o f t h e computer. T h i s t e r m i n a l p a n e l i s c o n n e c t e d v i a a b u n d l e c o r d t o t h e DT2805 b o a r d which i s i n s t a l l e d i n s i d e t h e computer. I n a d d i t i o n t o t h e e x t r a hardware r e q u i r e d f o r t h e s e e x p e r i m e n t a l r u n s , t h e ARC was o p e r a t e d d i f f e r e n t l y t h a n under standard hazard evaluation conditions. Instead of heating, s e a r c h i n g and w a i t i n g , the samples were h e a t e d t o a s p e c i f i e d temperature and were then m a i n t a i n e d i s o t h e r m a l l y a t t h a t temperature f o r extended p e r i o d s o f t i m e . P r e s s u r e and temperature d a t a were t h e n m o n i t o r e d and s t o r e d i n t h e microcomputer a t a r a t e o f 1 Hz. I t s h o u l d be n o t e d t h a t the a p p a r a t u s r e v e r t s back t o normal o p e r a t i o n ( i . e . , t r a c k i n g an exotherm), i f a h e a t r i s e r a t e g r e a t e r t h a n 0.02 °C/min i s d e t e c t e d . Decomposition Product A n a l y s i s . Samples o f t h e d e c o m p o s i t i o n gases were removed from t h e sample spheres a t t h e end o f some s t a n d a r d ARC experiments and were a n a l y z e d by gas chromatography f o r CO^, H^, , 0 , CO, NO and CH.. Care was t a k e n t o m i n i m i z e a i r c o n t a m i n a t i o n 4χ 4 o f t h e GC samples, by c h i l l i n g the ARC spheres i n a l i q u i d n i t r o g e n b a t h p r i o r t o removal i n o r d e r t o e q u a l i z e t h e p r e s s u r e . However, some a i r c o n t a m i n a t i o n was u n a v o i d a b l e . An HP-5710 gas chromatograph w i t h a t h e r m a l c o n d u c t i v i t y d e c t e c t o r was used. A Porapac-N column was used t o d e t e c t CO^, w h i l e a m o l e c u l a r s i e v e column was used t o d e t e c t t h e o t h e r gases ( C r e s w i c k , Μ., The Dow Chemical Company, p e r s o n a l communication, 1988). o

R e s u l t s and D i s c u s s i o n S t a n d a r d A c c e l a r a t i n g Rate C a l o r i m e t r y . T y p i c a l r e s u l t s o f a s t a n d a r d ARC r u n a r e shown i n T a b l e I . The most noteworthy o b s e r v a t i o n from these experiments i s t h a t t h e e x o t h e r m i c r e a c t i o n o f MDI i s n o t d e t e c t e d a t temperatures below 246.4 °C.

T a b l e I . R e s u l t s o f S t a n d a r d Hazard E v a l u a t i o n ARC Run on MDI Exotherm Onset Temperature ( T i ) Pressure a t T i Maximum P r e s s u r e ( a t 267.2 °C) Maximum Heat Rate ( a t 260.4 °C) A d i a b a t i c Temperature R i s e T o t a l Heat o f R e a c t i o n Sample w e i g h t

246,.4 138..1 580,.0 0,.16 68,.8 19 3,.10

°C psia psia °C/min °C cal/g

I s o t h e r m a l D e c o m p o s i t i o n S t u d i e s . An exotherm was n o t d e t e c t e d i n any o f t h e i s o t h e r m a l experiments t h a t were conducted a t v a r i o u s i s o t h e r m s r a n g i n g from 100° t o 225 °C. T h i s was t r u e even a f t e r extended p e r i o d s o f time and a t a temperature o n l y 21 °C below t h e o n s e t o f the e x o t h e r m i c r e a c t i o n as d e t e r m i n e d by t h e s t a n d a r d ARC experiments (see T a b l e I ) . However, s i g n i f i c a n t p r e s s u r e a c c u m u l a t i o n s were d e t e c t e d a t i s o t h e r m s as low as 140 °C. I n f a c t ,


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COMPUTER APPLICATIONS IN APPLIED POLYMER SCIENCE II


a s l i g h t p r e s s u r e r i s e i s observed even a t 100 °C a f t e r s e v e r a l days, b u t t h i s r i s e i s t o o l o w t o q u a n t i t a t e a c c u r a t e l y . The p r e s s u r e p r o f i l e s o b t a i n e d from i s o t h e r m a l runs a t f i v e d i f f e r e n t temperatures u s i n g t h i s method a r e shown i n F i g u r e 2. I t can be observed t h a t i n g e n e r a l , t h e p r e s s u r e r i s e i s f a i r l y l i n e a r f o r most o f t h e d u r a t i o n o f t h e experiments so t h a t a z e r o - o r d e r a p p r o x i m a t i o n may be used t o f i t t h e d a t a . T h i s l i n e a r i t y was found t o h o l d even a f t e r 5 days f o r t h e 175 °C i s o t h e r m , r e a c h i n g a p r e s s u r e l e v e l o f a p p r o x i m a t e l y 300 p s i a ( t h i s was t h e l o n g e s t d u r a t i o n o f a l l t h e e x p e r i m e n t s ) . I n t h e case o f t h e 225 °C isotherm, the pressure accumulation f i n a l l y l e v e l s o f f a t a p p r o x i m a t e l y 1100 p s i a a f t e r one day. K i n e t i c A n a l y s i s . Gas chromatographic a n a l y s i s o f t h e headspace gases c o n f i r m s t h a t t h e predominant r e a c t i o n p r o d u c t i s C 0 . The n e g l i g i b l e presence o f and 0^ a r e p r o b a b l y due, a t l e a s t i n p a r t , t o a i r c o n t a m i n a t i o n d u r i n g sample p r e p a r a t i o n f o r t h e GC a n a l y s i s . The r e s u l t s o f t h e GC a n a l y s i s a r e shown i n T a b l e I I . 9

Table I I .

Summary o f GC A n a l y s i s o f t h e Decomposition Gases

Gas C02 N2 02 CO H2 NOx CH4

Percent Composition 95.02 4.14 0.41 0.43

S i n c e t h e p r e s s u r e b u i l d up i s p r i m a r i l y due t o t h e e v o l u t i o n o f CO^ as MDI i s b e i n g decomposed t o c a r b o d i i m i d e , t h e thermodynamic r e l a t i o n s h i p PV - nRT may be a p p l i e d t o c o n v e r t t h e p r e s s u r e p r o f i l e s t o p l o t s o f moles o f CO^ g e n e r a t e d v s . time. T h i s i s shown f o r t h e 225 °C i s o t h e r m i n F i g u r e 3. The t h e o r e t i c a l curve o b t a i n e d through t h e a p p l i c a t i o n o f z e r o - o r d e r k i n e t i c s i s a l s o shown i n t h i s p l o t and t h e d a t a seem t o be w e l l accommodated by t h i s r a t e l a w throughout t h e m a j o r i t y o f t h e r u n . The s l o p e o f t h e t h e o r e t i c a l c u r v e y i e l d s t h e z e r o - o r d e r r a t e c o n s t a n t . The z e r o - o r d e r r a t e c o n s t a n t s o b t a i n e d from f i v e i s o t h e r m a l experiments a r e shown i n T a b l e I I I . These r a t e c o n s t a n t s were used f o r t h e c o n s t r u c t i o n o f an A r r h e n i o u s p l o t ( F i g u r e 4) y i e l d i n g t h e a c t i v a t i o n energy f o r t h e r e a c t i o n , Ea - 139.3 k J / m o l . The a c t i v a t i o n energy f o r t h e c o r r e s p o n d i n g r e a c t i o n o f methyl i s o c y a n a t e has been r e p o r t e d as 132.2 kJ/mol ( 7 ) .


33.

KALOS

Pressure Transducer

ARC CONTROL MODULE

ARC

AMP


433


Thermocouple

DATA ACQUISITION BOARD

TERMINAL SCREW PANEL

MICROCOMPUTER

J

Figure 1. Modified accelerating rate calorimetry apparatus.

1.2

0

9

13

27

36

45

54

63

Time ( h r s ) Figure 2. Pressure profile of isothermal decomposition of 4,4'-methylene diphenyl diisocyanate.


434

COMPUTER APPLICATIONS IN APPLIED POLYMER SCIENCE Π

7 -r 65-


ο ^ ο

4

"

3ω 'o *

210 -f 0

28.8

57.6

72.0

100.8

129.6

3

Time Χ 10" (Sec) F i g u r e 3. Carbon D i o x i d e E v o l u t i o n from I s o t h e r m a l D e c o m p o s i t i o n o f MDI a t 225 °C.

2.0

2.1

2.2 (1/T) X 10

F i g u r e 4.

2.3 3

2.4

(1/°K)

A r r h e n i u s P l o t f o r Carbon D i o x i d e E v o l u t i o n .


33. KALOS


435

Table I I I . Summary o f Z e r o - o r d e r Rate C o n s t a n t s f o r t h e I s o t h e r m a l Decomposition o f MDI i n terms o f C0 E v o l u t i o n o

Temperature (°C)

Z e r o - o r d e r Rate

Constant

(mol/s) χ 1 0


140 160 175 200 225

1 0

0.09 0.92 4.77 24.8 96.2

A f u l l development o f t h e r a t e l a w f o r t h e b i m o l e c u l a r r e a c t i o n o f MDI t o y i e l d c a r b o d i i m i d e and C 0 i n d i c a t e s t h a t t h e r e a c t i o n s h o u l d t r u l y be 2nd-order i n MDI. T h i s would be o b s e r v e d e x p e r i m e n t a l l y under c o n d i t i o n s i n w h i c h MDI i s a t l i m i t i n g c o n c e n t r a t i o n s . T h i s i s n o t t h e case f o r these experimements; MDI i s p r e s e n t i n c o n s i d e r a b l e excess ( u s u a l l y 5.5-6 g o f MDI (4.7-5.1 ml) a r e used i n an 8.8 ml v e s s e l ) . So a t l e a s t a t t h e e a r l y s t a g e s o f r e a c t i o n , t h e carbon d i o x i d e e v o l u t i o n would be e x p e c t e d t o d i s p l a y pseudo-zero o r d e r k i n e t i c s . As t h e amount o f MDI i s d e p l e t e d , then 2nd-order k i n e t i c s s h o u l d be observed. I n f a c t , the a s y m p t o t i c p o r t i o n o f t h e 225 °C i s o t h e r m c a n be f i t t e d t o a 2ndo r d e r r a t e law. T h i s k i n e t i c a n a l y s i s i s c o n s i s t e n t w i t h a more d e t a i l e d mechanism f o r t h e d e c o m p o s i t i o n , i n w h i c h 2 m o l e c u l e s o f MDI form a c y c l i c i n t e r m e d i a t e through a thermally allowed [ 2 + 2 ] c y c l o a d d i t i o n , w h i c h i s formed a t s t e a d y s t a t e c o n c e n t r a t i o n s and may then decompose t o c a r b o d i i m i d e and carbon d i o x i d e . Isocyanates and o t h e r r e l a t e d compounds have been r e p o r t e d t o p a r t i c i p a t e i n [2 + 2] and [4 + 2] c y c l o a d d i t i o n r e a c t i o n s (8.9) . 9

Ar-NZTC—0 Jf Ar-N—Crro

Ar-Ny-C/ K*| /C-M) Ar-N^

>

>

Ar-N=C=N-Ar

+

CO

(3)

where A r = OCN-C.H.-CH -C^H,0

Conclusion These r e s u l t s i n d i c a t e t h a t s i g n i f i c a n t p r e s s u r e a c c u m u l a t i o n s may be observed under a d i a b a t i c c o n d i t i o n s i n c l o s e d v e s s e l s even a t temperatures much lower than t h e exotherm d u r i n g t h e t h e r m a l d e c o m p o s i t i o n o f MDI. The p r e s s u r e changes have been q u a n t i f i e d and r e g a r d l e s s o f w h i c h mechanism i s o p e r a t i v e t h e p r e s s u r e r a t e s c a n be w e l l approximated by z e r o - o r d e r k i n e t i c s . T h i s i n f o r m a t i o n a l o n g w i t h knowledge o f t h e e x t e n t o f foaming as a f u n c t i o n o f temperature s h o u l d be o f a i d i n t h e d e s i g n o f a p p r o p r i a t e v e s s e l s f o r t h e v e n t i n g o r d r a i n i n g o f t h i s m a t e r i a l i n t h e event o f a r e a c t i o n .


436

COMPUTER APPLICATIONS IN APPLIED POLYMER SCIENCE Π

The experimental conditions, even though under a controlled laboratory environment, are not too d i f f e r e n t from what may be observed i n a closed drum of this material exposed to ambient temperatures for prolonged periods of time. This paper emphasizes that using only the onset of an exotherm as an indication of the point of no return for a reactive chemical system may be i n s u f f i c i e n t , as pressure may accumulate even at temperatures much lower than the anticipated exotherm.


Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9.

Duswalt, A. A. Thermochim. Acta 1974, 8, 57. Leung, J. C . ; Fauske, H. K. Thermochim. Acta 1986, 104, 13. Townsed D. I . ; Tou, J. C. Thermochim. Acta 1980, 37, 1. Monagle, J. J.; Campbell, T. W. et a l J. AM. Chem. Soc. 1962, 84, 4822. Appleman, J . O.; DeCarlo, V. J. J. Org. Chem. 1967, 32, 1505. Bonetskaya, A. K. et a l Vysokomol. Soedin. Ser. A 1985, 27, 1269. Blake, P. G . ; Ijadi-Maghsoodi, S. Int. J. Chem. Kinet. 1982, 14, 945. Boedeker, J.; Koeckritz, A. Z. Chem. 1982, 22, 140. Nair V . ; Kim, K. H. J. Org. Chem. 1974, 39, 3763.

R E C E I V E D March 20, 1989


Application of a Modified Accelerating Rate Calorimeter to

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