Development Of Material Specifications And Qualifications Of . - Nasa
Special Report No. 3 DEVELOPMENT OF MATERIAL SPECIFICATIONS A N D QUALIFICATIONS OF POLYMERIC MATERIALS FOR THE JPL SPACECRAFT MATERIALS GUIDEBOOK 111. POLYFLUOROCARBON F I L M S Prepared for: JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY PASADENA, CALIFORNIA JPL CONTRACT NO. 950745 UNDER NASA CONTRACT NO. NAS7-100 JPL COGNIZANT ENGINEER: HUGH MAXWELL GPO PRICE CFSTI PRICE(S) Hard copy (HC) Mlcrofiche (MF)
I \ i ' ' .t J u l y 12, 196.5 I -R ---7) e . ' - t Special Report No. 3 I a I I (DEVELOPMENT i OF MATERIAL SPECIFICATIONS A N D QUALIFICATIONS OF POLY M E R l C MATERIALS F O R THE JPL SPACECRAFT MATERIALS GUIDEBOOK 111. POLYFLUOROCARBON FILMS i Prepared for: I I 1 JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY PASADENA, CALIFORNIA JPL CONTRACT NO. 950745 UNDER NASA CONTRACT NO. JPL COGNIZANT ENGINEER: HUGH MAXWELL By: JUDITH A. BLACK JORGE HELLER DEAN 6. PARKINSON S R I Project PRD-5046-1 Approved: L I O N E L A. DICKINSON, D I R E C T O R P O L Y M E R & P R O P U L S I O N S C I E N C E S DIVISION 52 Copy No. .
ILLUSTRATIONS . TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INTRODUCTION EXPERIMENTAL RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii iii 1 2 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 DISCUSSION CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . ii 14
ILLUSTRATIONS Fig. 1 Complete Vacuum Apparatus f o r Thermal Vacuum Treatment Fig. 2 D e t a i l e d Drawing of Sample C e l l Assembly Fig. 3 P e r c e n t Weight Loss of T e d l a r and T e f l o n FEP Films a t 15OoC and 5 x mm Hg . . . . . Fig. 4 . . . . . . . . . . . . . Weight Loss p e r u n i t S u r f a c e Area of T e d l a r and T e f l o n FEP Films a t 15OoC and 5 x lo-" mm Hg Fig. 5 . . UV-Visible Spectrum of T e d l a r 40/s b e f o r e and a f t e r Thermal Vacuum Treatment . . . . . . . 9 .10 .ll . . . . .ll . . . . . .12 TABLES Table I Table I1 T a b l e I11 I)u Pont T e d l a r and Teflon F D Films . . . . . . . . . . . O u t g a s s i n g C h a r a c t e r i s t i c s of T e d l a r and T e f l o n FgP Films a t 15OoC and mm Hg (Weight Loss Data i n P e r c e n t ) . . . . . . . . . . . . . . . O u t g a s s i n g C h a r a c t e r i s t i c s of T e d l a r and T e f l o n FID Films a t 15OoC and mm Hg (Weight Loss Data i n g cm-2) . . . . . . . . . . . . . . . . . . . . . . . . . 7 8 8
SUMMARY P r e l i m i n a r y o u t g a s s i n g s t u d i e s w e r e performed on s e l e c t e d p o l y f l u o r o carbon f i l m s . F i v e t y p e s of f i l m , f o u r of t h e Tedlar* p o l y v i n y l f l u o r i d e f i l m s , and one T e f l o n FEP*, w e r e heated t o 15OoC and 5 x f o r o v e r 200 h o u r s . mm Hg Weight losses f o r a l l materials t e s t e d w e r e very low, r a n g i n g from z e r o t o about 0.5%. D u p l i c a t e t e s t specimens of T e f l o n FEP, d i f f e r i n g o n l y i n s i z e , were a l s o t e s t e d i n o r d e r t o estimate t h e e f f e c t of sample s i z e on weight l o s s e s , b u t no c l e a r r e l a t i o n s h i p was found. No condensable o i l s w e r e evolved from t h e t e s t specimens. A l l T e d l a r samples underwent v e r y s l i g h t d a r k e n i n g d u r i n g thermal vacuum t r e a t m e n t , and a n u l t r a v i o l e t - v i s i b l e spectrum was run on one of t h e s p e c i m e n s ; t h e T e f l o n FEP samples were unchanged. I n view of t h e i r l o w weight l o s s e s and t h e absence of condensable v o l a t i l e s , a l l t h e s e materials seem s u i t a b l e f o r s p a c e c r a f t a p p l i c a t i o n s . *Trademark f o r E . I . dupont de Nemours p o l y f l u o r o c a r b o n f i l m s . 1
INTRODUCTION The over-all objective of this program is to provide assistance to the JPL staff members in the development of specifications and procedures for polymeric spacecraft materials. This includes definitions of properties, tests, and environments which are sensitive and meaningful, and collection of pertinent property, environmental, and materials data for use in specifications. Of special importance to this program are the outgassing characteristics of various polymeric materials under thermal vacuum conditions. At the request of JPL cognizant engineers the first two classes of materials examined were epoxide adhesives and RTV silicone rubbers, and data for these have been reported.l," The third class of materials selected by JPL cognizant engineers were polyfluorocarbons, specifically Tedlar and FEP Teflon films. Samples were cut from the films as received from the manufacturer, and their weight loss characteristics at 15OoC and mm Hg determined. This temperature (150OC) approximates the temperature currently recommended for the sterilization of spacecraft . 'Development of Material Specification and Qualifications of Polymeric Materials for the JPL Spacecraft Materials Guidebook, Special Report No. I. Epoxide Adhesives 21bid., Special Report No. 11. RTV Silicone Rubbers 2
EXPERIMENTAL Materials Samples of T e d l a r ( p o l y v i n y l f l u o r i d e ) and T e f l o n FEP (copolymers of t e t r a f l u o r o e t h y l e n e and hexafluoropropylene) E.1 du Pont de Nemours. film w e r e obtained f r o m Some p r o p e r t i e s of t h e v a r i o u s f i l m s a s w e l l as sample w e i g h t s and a r e a s a r e summarized i n Table I . The f i l m s w e r e t e s t e d as r e c e i v e d from t h e m a n u f a c t u r e r ; no p r e t r e a t m e n t o r c u r i n g w e r e required. Techniques P r e p a r a t i o n of T e s t Samples T e s t samples of T e d l a r and Teflon FkP f i l m s w e r e c u t t o t h e d e s i r e d s i z e from s h e e t s of f i l m s u p p l i e d by t h e m a n u f a c t u r e r . Samples of T e d l a r w e r e c u t i n t o r e c t a n g l e s 3 x 10 cm; t h i s sample s i z e c o u l d be accommodated by t h e r e s i n p o t s w i t h o u t f o l d i n g o r c u r l i n g t h e f i l m s . Because of t h e s c a t t e r of p o i n t s observed i n t h e t e s t i n g of t h e T e d l a r samples, t h e T e f l o n FEP samples were c u t somewhat l a r g e r ( 6 x 22 c m and 3 x 22 cm) i n a n a t t e m p t t o improve t h e accuracy of t h e weight l o s s d e t e r m i n a t i o n s . These samples w e r e r o l l e d b e f o r e p l a c i n g i n t h e r e s i n p o t s . A l l samples were d u s t e d l i g h t l y w i t h a dry t i s s u e b e f o r e t e s t i n g t o remove any d u s t o r f o r e i g n m a t t e r from t h e f i l m s u r f a c e . The vacuum s y s t e m ( F i g . 1) which u t i l i z e s a mechanical roughing pump ( c a p a c i t y , 1 4 0 l i t e r s p e r minute) and a mercury d i f f u s i o n pump, c a n a c h i e v e r o u t i n e p r e s s u r e s of 1-5 x 10" mm Hg. P r e s s u r e s were measured w i t h an i o n i z a t i o n gauge ( C o n s o l i d a t e d Vacuum C o r p . ) c a l i b r a t e d f o r p r e s s u r e s from 0.025 mm t o lo-' mm Hg. T e s t specimens were p l a c e d i n modified r e s i n k e t t l e s ( F i g . 2) which w e r e h e a t e d i n o i l b a t h s . These c o n s i s t e d of s t a i n l e s s s t e e l b e a k e r s f i l l e d w i t h Dow s i l i c o n e o i l N o . 550 and h e a t e d by r e s i n k e t t l e h e a t i n g m a n t l e s . The b a t h t e m p e r a t u r e s were c o n t r o l l e d by Thermistemp temperature c o n t r o l l e r s (Yellow S p r i n g s Instrument Co., Model 63RA). The power t o t h e h e a t i n g m a n t l e s w a s
s u p p l i e d by a v a r i a b l e s u t o t n c s f c r m e r o i l baths a t 2' 3f t h e &Sired T h i s ar-angenezt m a i n t a i n e d t h e tenperature. I n g e n e r a l t h e b a t h tempera- t u r e s w e r e h e l d about f i v e d e g r e e s h i g h e r t o n a i n t a i n t h e d e s i r e d sample temperature. The tempePaturz of the o i l b a t h s was nieasured d i r e c t l y by a mercury thermometer suspsnded i n t h e b a t h ; t h e t e m p e r a t u r e i n s i d e t h e r e s i n p o t w a s determined from a thermocouple w i r e i n s e r t e d i n t o t h e thermocouple t u b e which extended i n t o t h e r e s i n p o t . Temperature measurements w e r e made u s i p g a k e d s and Morthrup Model 8692 p o t e n t i o m e t e r r e a d i n g d i r e c t l y i n degrees centigrade approximately i 0 . 5 C . l (Measurements w e r e a c c u r a t e t o The resin p o t led d i r e c t l y t o a l i q u i d n i t r o g e n t r a p which could be i s o l a t e d f r m the rest of t h e s y s t e n and i t s contents transferred i n t J 8 sampls kuLb s i l i t a b l e for s x b s s q u e n t g . l . c . , i n f r a r e d , or m a s s s p e c t r m z t r i c analysis. The t e s t specimers were p e r i o d i c a l l y r e m m e d from t h e s y s t e m and weighed on a Mettler "H" b a l a n c e , a z c u r a t e t o k 0 . 0 3 mg. Although c o n t i n u o u s weighing under vacugm i s r e e o g c i z e d as a s u p e r i o r method, the p r e s e n t s y s t e n w i l l accommodate f o u r d i f f e r e n t samples a t one t i m e and p e r m i t s a r a p i d s c r e e n i n g of m a t e r i a l s a s r e q u e s t s d by J P L . Thermal Vacuum T e s t i n Pmcedure The samples aEre t e s t e d a t 150 C c rd a p p r o x i m a t e l y 5 x mn Hg f o r t o t a l exposures sf 50-290 h o u r s . A t a p p r o x i m t f i y 24-hour i n t e r v a l s , t h e y were removed for r e i g b i n g . The tempezature of t h e o i l b a t h and of t h e i n t e r i o r of t h e r e s i n p a t l a s e l l a s t h e p r e s u r eof t h e s y s t e m , w e r e recorded a t t h i s t i n e Saxples were r e m w e d f r o m t h e r e s i n p o t s w i t h f o r c e p s , allowed t o C O Q L . weigried t o t h e n e a r e s t 0.01 mg, and r e t u r n e d t o t h e s y s t e n , which w a s i n m e d i a t e l y r e - e v a c u a t e d and t h e test c o n t i n u e d . The f o l l o w i n g r a w d z t n were r s x r d e d f o r e a c h tsst: (I) i n i t i a l weight and dimensions of t5e t e s t s p e c i m e m ; (2) weight of t h e t e s t specimens t o t h e n e s r e s t 0 . 0 1 m g iLt 24-hour i n t e r v a l s ; ( 3 ) t e m p e r a t u r e of t h e s y s t e m ; (4) changes i n colcs o r o t h e r p h y s i c a l p r o p e r t i e s of t h e sample ; and (5) o b s e r x a t i o n s r e l h t i n g t o o u t g a s s e d materials condensable o i l s cln such as t h e i n s i d e af t h e head ef t h e r e s i n pet, above t h e 4
l e v e l of h e a t i n g . U l t r a v i o l e t s p e c t r a of t h e f i l m s were o b t a i n e d on a Cary Model 1 4 spectrophotometer. RESULTS A p l o t of m a t e r i a l loss versus t i m e i s g e n e r a l l y of t h e form: C 3 - m m 0 0 7 Time, t S t e a d y S t a t e is r e p r e s e n t e d by t h e l i n e a r p o r t i o n (E) of t h e c u r v e - I n i t i a l Weight Loss i s t h e zero-time of t h e weight loss c u r v e ( A ) . Time u n t i l Steady ---S t a t e is t h e -becomes l i n e a r ( 7 ) . i n t e r c e p t of t h e l i n e a r p o r t i o n time r e q u i r e d b e f o r e t h e weight l o s s --- S t e a d y S t a t e L o s s Rate i s given by t h e s l o p e of t h e l i n e a r p o r t i o n of t h e weight l o s s c u r v e (AW/AT). A l l t h e s e p a r a m e t e r s are e s t i m a t e d g r a p h i c a l l y . Data a r e r e p o r t e d i n two sets of u n i t s ; i n p e r c e n t of t o t a l sample w e i g h t , and i n a b s o l u t e weight l o s s p e r u n i t a r e a of exposed s u r f a c e ( g cm-2). F i g u r e s 3 and 4 show t h e o u t g a s s i n g c u r v e s of t h e p o l y f l u o r o c a r b o n m a t e r i a l s t e s t e d a t 15OoC and lo* mm Hg f o r 216 h o u r s . The s c a t t e r i n g of p o i n t s i s due p r i m a r i l y t o t h e small sample s i z e s and c o r r e s p o n d i n g l y s m a l l weight l o s s e s . I t i s b e l i e v e d t h a t a l a r g e p e r c e n t a g e of t h e t o t a l weight l o s s i s due t o desorptiori:of s u r f a c e m o i s t u r e and gases, and t h a t some of t h e s e r e a d s o r b onto t h e materials w h i l e weighing i n a i r . 5
Continuous weighing under vacuum would, of c o u r s e , b e a v a s t l y s u p e r i o r method f o r t h i s type of sample. The most s t r i k i n g f e a t u r e of the weight l o s s c u r v e s i s t h e d i f f e r e n c e between t h e f i l l e d ( p i g n e n t e d ) m a t e r i a l s , TD 30/A u n f i l l e d transparent f i l m s . and TD 3 0 / B , and t h e Not only do t h e f i l l e d materials e x h i b i t l a r g e r weight losses but i n c o n t r a s t t o t h e o t h e r s , they e x h i b i t a n u n e q u i v o c a l , p o s i t i v e weight loss r a t e . If t h e l a r g e s c a t t e r i s t a k e n i n t o a c c o u n t , t h e c u r v e s f o r TD 3 0 / A and TD 3O/B may be c o n s i d e r e d identical. These two m a t e r i a l s d i f f e r from e a c h o t h e r only i n s u r f a c e p r e p a r a t i o n , which a p p a r e n t l y exerts no e f f e c t on t h e o u t g a s s i n g properties. I t may be s e e n by a comparison of P i g s . 3 a n d 4 , t?mt t h e t h i c k e r f i l m s , FEP-a and b ( 5 m i l l , shcw ar! illcrease i n rzllative weight l o s s when r e p l o t t e d i n t e r v s of a b s o l u t e weight l o s s p e r u n i t a r e a . This would i n d i c a t e t h a t t h e o u t g a s s i n g is not e n t i r e l y a s u r f a c e phenomenon, b u t i n v o l v e s removal of m a t e r i a l from t h e i n t e r i o r f t h e polymer sample as w e l l . T h i s i s c o r r o b o r a t e d by t h e f a c t t h a t a f t e r t h e t r e a t e d t e s t specimens had been exposed t o a i r f o r over two weeks they r e g a i n e d but l i t t l e of t h e weight l o s t under thernral vacuum t r e a t m e n t The T e d l a r t e s t specimens a11 unaeArwent a c o l o r change d u r i n g t h e r m a l vacuum t r e a t m e n t , g o i r g from w h i t e or water w h i t e t o a l i g h t brown. F i g u r e 5 show5 t h e "JFI-visicie spzctrum f r o n 2500 t o 6500A of TD 40/5 b e f o r e and a f t e r therwal V C U U I Tt r e a t m e n t . The s p e c t r a l c h a r a c t e r i s t i c s of t h e U\I curve aenair, s i m i l a r except f o r a n o v e r - a l l i n c r e a s e i n absorbance o f t h e t r e a t e d fi1i.l. The much g r e a t e r i n c r e a s e i n t h e UV r e g i o n s u g g e s t s formation of c c q j u g a t e d systems (-CH CH-) n Because of t h e s c a t t e r i n g of d a t a , t h e method of l e a s t s q u a r e s w a s a p p l i e d on t h e a s s . p t i t n h a t a steady s t a t e w a s achieved i n less t h a n 24 h o u r s . T a b l e s 1 and III s u m a r i z e t h e s e least s q u a r e s p a r a m e t e r s , t h e i n i t i a l weight l o s s e s and weight loss r a t e s , the weight l o s s a f t e r 200 h o u r s , and t h e r o o t rrrean square d e v i a t i o n s f o r each c u r v e . Weight l o s s e s range from 0 - 0 , 5 % by w e i g h t ' weight l o s s r a t e s a r e t a k e n a s z e r o f o r a l l m a t e r i a l s e x c e p t t h e pignented T s d i a r s , 3 0 / A acd 30/B, which l o s e weight a t a r a t e of aFproximately 0.001% p e r h o u r . 6
k o 4 O r c n c c, a, a, c, k G 4 -d d u c , . c d c 2d E: cd k G 3 L . rn k 9 k c,c, I u) a, r( P cd 4 cd a, rJ) c, cd a, H rn a, a, P 4 P 4 .d -rl n rn Cd k xa a, 0 C C cd a, a, rn C c, P a, 'D -rl rd k rn 2 E: 0 P P cd a, a, c 0 a, 4 h a a, 4 n 0 t 3 0 k k a cd 0 s .4 w cd x a, G P c E R, r o o o w z m 3 5 0 0 0 N O 0 E r n a! 21s p: @a 2 m 0 m 0 cd x P I & a, w w d kErc r3 m a! 0 0 0 0 N 0 In 0 0 @a 0 0 mv) h C rn E 4 -d y-l a, a -d k 0 5 c, a, k 0 7 .4 I cd k c, a, c, 'H 0 rl w n ak E: 0 .4. w a, E 7 rl h E: -rl m k a, 5 d h .o . a d o a o 4 CdP
Table I1 OUTGASSING CHARACTERISTICS O F TEDLAR AND TEFLON FEP FILMS A T 150 C and mm Hg (Weight Loss Data i n P e r c e n t ) rms Loss, 70 TD 40/S 0.14 0 0.14 0.02 TD 3 0 / A 0.39 0.075 0.54 0.04 TD 30/B 0.35 0.08 0.50 0.03 TD 2 0 / A 0- .05 --- 0- .05 -- Sample Tedlar T e f l n FEP % W t . Loss W t . Loss Rate %/lo0 hrs Material Initial W t . after 200 h r s Dev ia t i on w a 0.084 o 0.075 0.013 b 0.003 0.02 0.05 0.008 Table I11 OUTGASSING CHARACTERISTICS OF TEDLAR AND TEFLON FEP FILMS AT 15OoC and mm Hg (Weight Loss Data i n g cm-2) 8
-ION GAUGE I , 8- ION GAUGE DETECTOR DIFFUSION PUMP w U G \n TRAP VOLATILES FROM SAMPLE 1 & - T E S T SPECIMEN 'ER H I I O I BATH L N PUMP G T A -5046-4 FIG.l COMPLETE VACUUM APPARATUS FOR THERMAL VACUUM TREATMENT 9
TO TEMPERATURE CONTROLLER 0 RING SEAL TO POTENTIOMETER THERMOMETER -OIL TEMPERATURE READING TEMPE INSIDE TUBE /HEATING BATH MANTLE SAMPLE TI-5046-5 F I G . 2 DETAILED DRAWING OF SAMPLE CELL ASSEMBLY 10
0.7 0.6 A TD 30/B c 0.5 L 0 I n 0.4 cn v) '3 y3 0.3 0.2 0.I 0 0 20 40 60 80 100 TIME- 120 140 160 180 200 220 240 hours TR-5046-26 FIG.3 0.26 0 0 - 0.22 '5 0.I 8 PERCENT WEIGHT LOSS OF TEDLAR AND TEFLON FEP FILMS AT 150 C AND 5 x mm Hg 1 - t 0 TD 1 I I 1 - 401s 0 TD 30/A A TD 30/0 A 0 c pl 1 0 0 20 40 60 00 100 120 TIME -hours 140 160 180 200 220 240 TB- 5 0 4 6 - 27 FIG. 4 WEIGHT LOSS PER UNIT SURFACE AREA OF TEDLAR' AND TEFLON FEP FILMS AT 150 C AND 5 x mm Hg 11
I . I .o 0.9 0.8 0.7 W V lAFTER 0.6 z a 0.5 0 In m Q 0.4 0.3 0.2 0.I 0 FIG.5 UV-VISIBLE SPECTRUM OF TEDLAR 40,'s VACUUM TREATMENT 12 BEFORE AND AFTER THERMAL
DISCUSSION A v a s t amount of l i t e r a t u r e e x i s t s on t h e b e h a v i o r of T e f l o n (polytetrafluorethylene) i n s i m u l a t e d s p a c e environments.* J o l l e y and Reedd: have reviewed o v e r one hundred r e f e r e n c e s on t h i s s u b j e c t a l o n e , and numerous s u r v e y r e p o r t s on t h e p r o p e r t i e s of TFE p l a s t i c s have been published. -- Madorsky, e t aL4 have examined t h e t h e r m a l d e g r a d a t i o n of t h i s m a t e r i a l , as w e l l as s e v e r a l o t h e r f l u o r i n a t e d polymers, i n considerable d e t a i l . I n g e n e r a l , however, less i n f o r m a t i o n i s a v a i l a b l e on t h e h y d r o f l u o r i n a t e d materials such as T e d l a r , Lpoly(viny1 f l u o r i d e ) ] . I n c o n s i d e r i n g t h e c h e m i s t r y of t h e s e materials i t i s obvious t h a t polymer d e g r a d a t i o n would not be expected t o b e a s i g n i f i c a n t f a c t o r , e s p e c i a l l y i n t h e case of T e f l o n FEP. This i s c o n s i s t e n t w i t h t h e o b s e r v a t i o n t h a t t h e weight loss of t h i s material a t 15OoC i s indeed v e r y low. I t i s i n t e r e s t i n g t o note t h a t -he weight l o s s f o r sample FEP-a, 0.08% a f t e r 100 h o u r s , is e x a c t l y t h a t observed by J o l l e y and Reed. T h i s agreement may however be f o r t u i t o u s , s i n c e J o l l e y and Reed do n o t s u p p l y t h e dimensions of t h e i r t e s t sample. S i n c e T e f l o n FEP c o n t a i n s no a d d i t i v e s , and s i n c e d e g r a d a t i o n w i l l n o t o c c u r t o any e x t e n t a t 1 5 O o C , i t i s r e a s o n a b l e t o assume t h a t t h e s a m l l weight loss observed i s due p r i m a r i l y t o d e s o r p t i o n of s u r f a c e contaminants such as w a t e r and carbon d i o x i d e . T h i s c o n c l u s i o n i s not e n t i r e l y c o n s i s t e n t w i t h d a t a o b t a i n e d f o r two d i f f e r e n t sample s i z e s of t h e s a m e polymer which when reduced t o p e r c e n t o r g/cm2 s h o u l d e x h i b i t *Teflon has been found t o be h e a t s t a b l e u p t o 45OoC u n d e r vacuum. FEP, which i s a l s o t o t a l l y f l u o r i n a t e d , and d i f f e r s o n l y by t h e p r e s e n c e of CF, s i d e c h a i n on t h e polymer backbone, would be e x p e c t e d t o b e s i m i l a r t o T e f l o n . The s u b s t i t u t i o n of one o r more hydrogen atoms f o r f l u o r i n e , however, a l t e r s t h e polymer c o n s i d e r a b l y . For example, p o l y v i n y l f l u o r i d e ' s weight l o s s of 24OoC is s i m i l a r t o t h a t of T e f l o n a t 380OC. 3C. E . J o l l e y and J . C . Reed, Space/Aeronautics, F e b r u a r y 1963, p . 105 L . Madorsky, V. E . Hart, S . S t r a u s , and V. A . S e d l a k , J . R e s . N a t ' l . Bur. S t d . , 5 1 , 327-333 (1953). *S. - 13
i d e n t i c a l weight l o s s e s . The r e l a t i v e l y l a r g e d i s c r e p a n c y of about 50% i s a t t h e p r e s e n t t i m e not c l e a r , b u t c o u l d be due t o e x p e r i m e n t a l error. (Tables 1 1 , 1 x 1 . ) The samples of T e d l a r [ p o l y ( v i n y l f l u o r i d e ) ] behaved s i m i l a r l y t o t h o s e of FEP. I t w a s found, however, t h a t t h e pigmented samples (30/A and 30/B) e x h i b i t e d much h i g h e r weight l o s s e s t h a n t h e t r a n s p a r e n t Tedlar films. These pigmented T e d l a r f i l m s a l s o e x h i b i t e d f i n i t e rates of weight l o s s ; t h i s may i n d i c a t e t h a t t h e pigment employed i s somewhat A l l t h e Tedlar films v o l a t i l e o r c o n t a i n s v o l a t i l e contaminants. t e s t e d e x h i b i t e d some d i s c o l o r a t i o n . T h i s d a r k e n i n g i n c o l o r has been o b s e r v e d i n c o n j u n c t i o n w i t h t h e d e g r a d a t i o n of p o l y ( v i n y 1 f l u o r i d e ) and i s b e l i e v e d t o be due t o t h e formation of c o n j u g a t e d u n s a t u r a t i o n i n t h e polymer a s a r e s u l t of t h e e l i m i n a t i o n of HF. o b s e r v e d i s , however, of l i t t l e consequence. chloride) The s l i g h t d i s c o l o r a t i o n A s i n t h e c a s e of p o l y ( v i n y 1 e x t r e m e l y l a r g e c o l o r changes may t a k e p l a c e i n t h e m a t e r i a l w i t h o u t any s t r u c t u r a l changes b e i n g o b s e r v a b l e i n t h e i n f r a r e d s p e c t r a ; i . e . , degraded material c o n s t i t u t e s less t h a n a b o u t 1%of t o t a l sample. C ONCLUSI ONS I t has been found that a l l t h e p o l y f l u o r o c a r b o n f i l m s t e s t e d i n t h i s s t u d y have very low weight l o s s e s - - a l l w e l l below 1%--and t h e r e f o r e appear q u i t e s u i t a b l e f o r spacecraft use. I n view of t h e c o m p a r a t i v e l y l a r g e weight l o s s e s of t h e pigmented T e d l a r f i l m s ( 0 . 5 %as compared w i t h a p p r o x i m a t e l y 0 . 1 % f o r t h e u n f i l l e d m a t e r i a l s ) i t would be of i n t e r e s t t o i n v e s t i g a t e t h e p o s s i b l e u s e of a new, less v o l a t i l e pigment. 5 x The s l i g h t d a r k e n i n g of the T e d l a r specimens a t 15OoC and mm Hg i s not c o n s i d e r e d an i n d i c a t i o n of s e r i o u s d e g r a d a t i o n . 14
A plot of material loss versus time is generally of the form: 3 C - m m 0 0 7 Time, t Steady State is represented by the linear portion (E) of the curve Initial Weight Loss is the zero-time intercept of the linear portion of the weight loss curve (A). - Time until Steady State is the time required before the weight loss
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