Polymeric Materials for Corrosion Control - American Chemical Society

of both components of three separate polyurethane foam formulations. .... Table I. Foam Long-Term Stability for Formulation II -. Chemical Analysis. 0...
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Polyurethane Foam Component Lifetimes Κ. B . Wischmann Sandia National Laboratories, Albuquerque, ΝM 87185

Access deterrent foams are generated by mixing two sep­ arately stored and pressurized components upon demand. Investigations have been conducted concerning the aging of both components of three separate polyurethane foam formulations. The polyol component of the first formu­ lation, a propylene oxide adduct of phosphoric acid, hydrolyzes rapidly to give phosphoric acid. Since phosphoric acid can corrode the container as well as adversely affect the final foam properties, a second formulation not containing acid adduct was investi­ gated. This second polyol was isothermally aged at room temperature, 60°C and 71°C and reactions followed by acid number determination. A reaction between the polyol and the blowing agent, Freon 11, was found to give high acid content. Attempts to add inhibitors to lengthen this initiation period failed. Finally, a third formulation was designed which placed the Freon 11 in the isocyanate component thereby precluding the incompatibility of the blowing agent with the polyol. Subsequent aging studies indicate a long term (6-8 years) storage foam system could be achieved. *This work was performed at Sandia National Laboratories supported by the U. S. Department of Energy under Contract Number DE-AC04-76DP00789. S t o r e d prepacked p o l y u r e t h a n e foam components, e.g., i s o c y a n a t e , p o l y o l s , a r e prone t o c h e m i c a l a g i n g , thereby j e o p a r d i z i n g t h e i r i n ­ tended f u n c t i o n . I n f a c t , many vendors o f these Freon blown m a t e r i ­ a l s w i l l n o t guarantee t h e i r product f o r more than 90 days. This i s f o r a v a r i e t y o f reasons such as m o i s t u r e a t t a c k on t h e i s o c y a n a t e , b l o w i n g agent s e p a r a t i o n and g e n e r a l m a t e r i a l i n s t a b i l i t y , e.g., t h e r m a l d e g r a d a t i o n , i n c o m p a t i b i l i t y . Because o f t h e expense t o change-out foam components, we would l i k e our systems t o l a s t as l o n g as p o s s i b l e . A l t h o u g h g e n e r a l l y c o n s i d e r e d c h e m i c a l l y i n e r t , Freon 11 ( t r i 0097-6156/ 86/ 0322-0341 $06.00/ 0 © 1986 American Chemical Society

Dickie and Floyd; Polymeric Materials for Corrosion Control ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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c h l o r o f l u o r o m e t h a n e , CCI3F), the b l o w i n g agent used i n these foams, i s u n s t a b l e under c e r t a i n c o n d i t i o n s - For example, t h i s p o p u l a r i n d u s t r i a l r e f r i g e r a n t and a e r o s o l , i n the presence o f m o i s t u r e , w i l l r e a c t w i t h s t e e l o r aluminum f o r m i n g f r e e h y d r o c h l o r i c a c i d (1_,2)« As a r e s u l t , e f f o r t s a r e made t o m a i n t a i n anhydrous c o n d i t i o n s o r provide a c i d scavengers. A l t h o u g h not w i d e l y known, Freon 11 w i l l r e a c t w i t h p r i m a r y and secondary a l c o h o l s i n c l u d i n g p o l y o l s t o l i b e r a t e a l d e h y d e s , ketones and h y d r o c h l o r i c a c i d C3>^)* A l l the above mentioned r e a c t i o n s can be a c c e l e r a t e d w i t h temperature. At h i g h e r temperatures t h e r m a l d e c o m p o s i t i o n o f Freon 11 may produce h y d r o c h l o r i c a c i d ( 5 ) . E f f o r t s have been made t o f i n d s u i t a b l e s t a b i l i z e r s f o r t h i s f l u o r o c a r b o n ; u n f o r t u n a t e l y these e f f o r t s have met w i t h l i m i t e d s u c c e s s ( 6 - 8 ) . One o f the b e t t e r s t a b i l i z e r s , a - m e t h y l s t y rene was r e p o r t e d t o be e f f e c t i v e but f o r o n l y 3 months ( 6 ) . Because o f l o n g term r e q u i r e m e n t s , we became concerned w i t h the r e l i a b i l i t y o f these foam systems. In t h i s work t h r e e d i f f e r e n t p o l y u r e t h a n e foam f o r m u l a t i o n s were i n v e s t i g a t e d . The f i r s t was a deployed foam system i n which a c o r r o s i o n s t u d y was performed. Due t o i n c o m p a t i b i l i t i e s , a second and a t h i r d system had t o be f o r m u l a t e d and a g i n g s t u d i e s performed t o i n s u r e a foam system t h a t p r o v i d e d adequate a g i n g c h a r a c t e r i s t i c s . To determine the l a t t e r two s y s t e m s l o n g e v i t y , we s t a r t e d an a c c e l e r a t e d a g i n g program t o s i m u l a t e the i n d i v i d u a l foam component l i f e t i m e s . S p e c i f i c a l l y , the amine e q u i v a l e n t i n the i s o c y a n a t e component and h y d r o x y l e q u i v a l e n t and a c i d number i n the p o l y o l component were f o l l o w e d a t v a r i o u s temperatures (ambient, 60°, 71°C). L i f e t i m e e s t i m a t e s were made by A r r h e n i u s modeling o f the d a t a . The f o l l o w i n g r e s u l t s and d i s c u s s i o n d e s c r i b e the e f f o r t s made t o e v a l u a t e t h e a g i n g c h a r a c t e r i s t i c s o f these foam systems. 1

Experimental The f o r m u l a t e d i s o c y a n a t e and p o l y o l components s u p p l i e d by a vendor ( C o p l a n a r Corp.) were aged i n one g a l l o n s t e e l v e s s e l s . The v e s s e l s were r a t e d a t 250 p s i and equipped w i t h J e n k i n s b a l l v a l v e s and p r e s s u r e r e l i e f diaphragms ( s e t f o r 170 p s i ) . The vapor p r e s s u r e o f F r e o n 11 a t the h i g h e s t a g i n g temperature (71°C) was 60 p s i g g i v i n g a 4/1 s a f e t y margin. The a c t u a l i s o t h e r m a l a g i n g was c a r r i e d out a t ambient, 60° and 71°C. A n a l y s i s o f the i s o c y a n a t e was a c c o m p l i s h e d by p e r f o r m i n g an amine e q u i v a l e n t d e t e r m i n a t i o n ( p e r ASTM D1638). The p o l y o l component was a n a l y z e d f o r h y d r o x o l e q u i v a l e n t by an a c e t y l a t i o n p r o c e dure developed a t Sandia N a t i o n a l L a b o r a t o r i e s . An 0.8 gram sample i s a c e t y l a t e d w i t h a 1/9 a c e t i c a n h y d r i d e - p y r i d i n e m i x t u r e f o r 2 hours a t r e f l u x temperature and then the f r e e a c e t i c a c i d i s back t i t r a t e d w i t h base and compared t o a b l a n k . From t h i s i n f o r m a t i o n a h y d r o x o l e q u i v a l e n t can be c a l c u l a t e d . The p o l y o l a c i d number was d e t e r m i n e d by ASTM D2849. Background - C o r r o s i o n Study o f F o r m u l a t i o n 1 A two component p o l y u r e t h a n e f o r m u l a t i o n was s t o r e d i n the f i e l d i n s e p a r a t e 208 l i t e r (55 g a l ) v e s s e l s o f 0.95 cm w a l l t h i c k n e s s and under a 0.35 t o 0.9 MN/m (50-100 p s i ) over p r e s s u r e . Upon demand the components a r e mixed and d i s c h a r g e d t o form a r i g i d foam; r e 2

Dickie and Floyd; Polymeric Materials for Corrosion Control ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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q u i r e m e n t s n e c e s s i t a t e a foam d e n s i t y of 0.016 t o 0.032 g/cc (1-2 l b / f t ^ ) and 1-3 minute t a c k time. The p o l y o l component c o n s i s t s o f a p o l y p r o p y l e n e o x i d e adduct o f p h o s p h o r i c a c i d . Upon a g i n g i n the p r e s e n c e o f m o i s t u r e , t h i s phosphate e s t e r can h y d r o l y z e to phosp h o r i c a c i d which c o u l d l e a d t o c o r r o s i o n o f the m e t a l c o n t a i n e r as w e l l as change the r e s u l t a n t foaming c h a r a c t e r i s t i c s . To d e t e r m i n e whether a p o t e n t i a l l y hazardous c o n d i t i o n p r e v a i l e d a c o r r o s i o n s t u d y was conducted* The p o l y o l component was known t o c o n t a i n 26.8% by weight of the phosphate e s t e r . From a known h y d r o x y l number, a m o l e c u l a r weight of a p p r o x i m a t e l y 382 was c a l c u l a t e d . Assuming complete h y d r o l y s i s , about 7% by w e i g h t o f p h o s p h o r i c a c i d would be formed. A c t u a l l y comp l e t e h y d r o l y s i s i s u n l i k e l y , however, a worst case s i t u a t i o n was d e s i r e d f o r t h i s a c c e l e r a t e d s t u d y . There are two commonly used methods to d e t e r m i n e c o r r o s i o n r a t e s : 1) a w e i g h t l o s s t e c h n i q u e and 2) T a f e l e x t r a p o l a t i o n ( e l e c t r o c h e m i c a l method). A w e i g h t l o s s exp e r i m e n t was performed i n : 1) 7% p h o s p h o r i c a c i d i n water ( d i s s o c i a t e d ) , a g a i n a w o r s t case s i t u a t i o n and 2) w i t h c o n c e n t r a t e d a c i d ( e s s e n t i a l l y u n d i s s o c i a t e d ) as i t might appear i n an o r g a n i c medium. The i n i t i a l r a t e o f 0.188 and 0.043 mm/year i n 7% and concentrated p h o s p h o r i c a c i d r e s p e c t i v e l y d e c r e a s e d w i t h time, most l i k e l y due to c o r r o s i o n p r o d u c t b u i l d u p and i n s o l u b i l i t y i n c o n c e n t r a t e d a c i d . A v a l u e o f a p p r o x i m a t e l y 0.102 mm/year appears to be a r e a s o n a b l e e s t i mate f o r l o n g term exposure i n the 7% a c i d and about 0.003 mm/year f o r the c o n c e n t r a t e d p h o s p h o r i c a c i d . From t h i s d a t a i t was c o n c l u d ed t h a t the t e s t e d s t e e l shows b e t t e r r e s i s t a n c e i n c o n c e n t r a t e d r a t h e r than 7% p h o s p h o r i c a c i d . The i n i t i a l c o r r o s i o n r a t e f o r m i l d s t e e l i n 7% a c i d (pH=l) was v e r i f i e d by the T a f e l e x t r a p o l a t i o n method. R e s u l t s i n d i c a t e an i n i t i a l r a t e o f 0.18 mm/year which was i n c l o s e agreement t o the v a l u e d e t e r m i n e d by the weight l o s s method. The above r e s u l t s must be tempered w i t h the f o l l o w i n g c o n s i d e r a t i o n s t h a t were o m i t t e d from t h i s s t u d y : 1) the v e s s e l was under a c o n s t a n t p r e s s u r e o f 0.35 t o 0.7 MN/m^ (50-100 p s i ) and may r e a c h 2.0 MN/m^ (300 p s i ) when the m a t e r i a l i s d i s p e n s e d , t h i s would a f f e c t the c o r r o s i o n r a t e ; 2) the t e s t i s v e r y s e n s i t i v e t o e n v i r o n m e n t a l changes, e.g., t e m p e r a t u r e , s o l u t i o n homogeneity; 3) the t e s t s were not conducted on a c t u a l c o n t a i n e r m a t e r i a l s , d a t a i n the l i t e r a t u r e show t h a t some s t e e l s c o r r o d e a t a much h i g h e r r a t e i n p h o s p h o r i c a c i d ; and 4) t h e r e may be s u r f a c e d e f e c t s i n the v e s s e l t h a t c o u l d l e a d t o a c c e l e r a t e d l o c a l a t t a c k and premature f a i l u r e . W i t h t h e s e q u a l i f i c a t i o n s , assuming complete h y d r o l y s i s (which i s u n l i k e l y ) and i n c o m p l e t e d i s a s s o c i a t i o n , e x c e s s i v e c o r r o s i o n would not be e x p e c t e d . However, t h e s e c h e m i c a l changes w i l l a f f e c t the foaming c h a r a c t e r i s t i c s , t h e r e b y y i e l d i n g a p r o d u c t t h a t does not meet d e s i g n s p e c i f i cations. S i n c e the phosphate e s t e r ' s o n l y purpose was f i r e r e t a r d a t i o n , a new nonphosphate system was recommended f o r f u t u r e a p p l i c a t i o n s . The f o l l o w i n g d i s c u s s i o n a d d r e s s e s the r e s u l t s o f an a c c e l e r a t e d a g i n g s t u d y on t h i s f o r m u l a t i o n . Discussion - Accelerated

A g i n g Study o f F o r m u l a t i o n

2

A second new d i s p e n s a b l e r i g i d p o l y u r e t h a n e foam f o r m u l a t i o n was a c q u i r e d t h a t d i d not c o n t a i n the phosphate a d d u c t s . C r i t i c a l d e s i g n r e q u i r e m e n t s were the same as i n the f i r s t f o r m u l a t i o n . The r e s p e c -

Dickie and Floyd; Polymeric Materials for Corrosion Control ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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t i v e i s o c y a n a t e and p o l y o l components were p l a c e d i n ovens f o r i s o ­ t h e r m a l a g i n g . We have p r e v i o u s l y found t h a t about a 10% change i n amine and h y d r o x y l e q u i v a l e n t s would a l t e r foaming, e.g., t a c k t i m e , s u f f i c i e n t l y t o d e v i a t e from d e s i g n r e q u i r e m e n t s . Thus, l i f e t i m e e s ­ t i m a t e s a r e based on a 10% change i n the above a n a l y t i c a l parameters. A f t e r 180 days a g i n g , the i s o c y a n a t e aged a t a slow c o n t r o l l e d r a t e (see F i g u r e 1) whereas the p o l y o l showed a d r a m a t i c change a t 7l°C and 180 days a g i n g (see Table I ) . B e f o r e d i s c u s s i n g the reasons f o r the p o l y o l s u n u s u a l b e h a v i o r a d e s c r i p t i o n o f the i s o c y a n a t e a g i n g w i l l f o l l o w . F i r s t , i t was b e l i e v e d t h a t component A would show the most pronounced e f f e c t s o f a g i n g , s i n c e i s o c y a n a t e s a r e p a r ­ t i c u l a r l y s u s c e p t i b l e t o m o i s t u r e a t t a c k . I n a 14 month s t u d y , r e a c ­ t i o n w i t h the water was assumed t o be the p r i m a r y a g i n g r e a c t i o n determining isocyanate l i f e t i m e . I f one uses the amine e q u i v a l e n t a s a damage parameter, an A r r h e n i u s p l o t can be c o n s t r u c t e d (see F i g u r e 2). From t h i s d a t a an a c t i v a t i o n energy (fiJL) o f ^9.3 k c a l / m o l e was c a l c u l a t e d . ThisΔΕ corresponds q u i t e n i c e l y w i t h l i t e r a t u r e values (9) f o r o t h e r s i m i l a r i s o c y a n a t e r e a c t i o n s w i t h water. Employing the A r r h e n i u s p l o t , l i f e t i m e e s t i m a t e s can be made w i t h v a r i o u s a g i n g temperatures. For example, i f the i s o c y a n a t e component A was aged c o n t i n u o u s l y a t 23°C, i t would take 6-8 y e a r s f o r a 10% change i n amine e q u i v a l e n t t o take p l a c e . I f aged a t 49°C (120°F), i t would t a k e o n l y 2 y e a r s f o r the same amount o f a g i n g (see F i g u r e 3 ) . Based on these p r o j e c t i o n s , a m a t e r i a l change-out would be recommended i n 6-7 y e a r s .

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Table I.

Foam Long-Term S t a b i l i t y f o r F o r m u l a t i o n I I Chemical A n a l y s i s

0 Component A ( I s o c y a n a t e ) Amine E q u i v a l e n t , Ambient Amine E q u i v a l e n t , 60°C Amine E q u i v a l e n t , 71°C Component Β ( P o l y o l ) H y d r o x y l E q u i v a l e n t , Ambient H y d r o x y l E q u i v a l e n t , 60°C H y d r o x y l E q u i v a l e n t , 71°C A c i d Number, Ambient A c i d Number, 60°C A c i d Number, 71°C

30 days

90 days

180 days

142

142 142 144

142 144 147

142 145 150

104

105 107 107

104 104 107

106 108 191

0.2

0.8 2.0 2^0

0.6 1.5 3.0

1.0 2.0 111.0

The p o l y o l component Β e x p e r i e n c e d c a t a s t r o p h i c change i n both h y d r o x o l e q u i v a l e n t and a c i d number a t 71°C and 180 days a g i n g . Be­ cause o f the l a r g e i n c r e a s e i n a c i d number, i t was i n i t i a l l y thought t h a t Freon 11 ( t r i c h l o r o f l u o r o m e t h a n e ) was g e n e r a t i n g f r e e h y d r o ­ c h l o r i c a c i d by r e a c t i o n w i t h o t h e r components. Free h y d r o c h l o r i c a c i d was v e r i f i e d by a d d i n g AgN03 t o an aged p o l y o l sample and o b ­ t a i n i n g a p r e c i p i t a t e o f A g C l . The l i t e r a t u r e c e r t a i n l y c o n f i r m s t h e i n s t a b i l i t y o f Freon 11 ( 1 ) , t h e r e f o r e a s u p e r i o r s t a b i l i z e r was

Dickie and Floyd; Polymeric Materials for Corrosion Control ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

Polyurethane Foam Component Lifetimes

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Dickie and Floyd; Polymeric Materials for Corrosion Control ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

POLYMERIC MATERIALS FOR CORROSION CONTROL

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sought. Communication w i t h the m a n u f a c t u r e r , r e v e a l e d t h a t the s t a ­ b i l i z e r used i n Freon 11 was a m a t e r i a l c a l l e d a l l o o c i m e n e ( 2 , 6 - d i m e t h y l 2 , 4 , 6 - o c t a t r i e n e ) . The m a n u f a c t u r e r suggested employ­ i n g 1% by weight α-methylstyrene as a s t a b i l i z e r . The p o l y o l a g i n g s t u d y was r e p e a t e d u s i n g the newly s t a b i l i z e d t r i c h l o r o f l u o r o m e t h a n e , termed Freon 11A. At e x a c t l y the same a g i n g s t a t i o n (180 d a y s ) , a g a i n l a r g e changes i n h y d r o x y l e q u i v a l e n t and a c i d number o c c u r r e d . CC1 F + CH CH 0H Downloaded by UNIV OF CALIFORNIA SAN DIEGO on September 25, 2016 | http://pubs.acs.org Publication Date: October 14, 1986 | doi: 10.1021/bk-1986-0322.ch030

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CHC1 F + CH3CHO + 2

HC1

Why the r e a c t i o n t a k e s p l a c e so d r a m a t i c a l l y a t about 180 days r a t h e r t h a n g r a d u a l l y i s not u n d e r s t o o d ; perhaps i t i s s i m p l y due t o an i n ­ d u c t i o n p e r i o d o r perhaps the s t a b i l i z e r i s expended a t t h a t time. T h i s r e a c t i o n i s not a w i d e l y known t e x t book r e a c t i o n , i n f a c t , i t was o n l y found i n the p a t e n t l i t e r a t u r e ( 4 ) . However, t h i s r e a c ­ t i o n e x p l a i n s the evidence o f f r e e h y d r o c h l o r i c a c i d . S i n c e a c a r b o n y l group, e.g., aldehyde, was generated by the above r e a c t i o n , t h i s group s h o u l d be o b s e r v a b l e i n the IR. Subsequent IR scans o f the aged p o l y o l r e v e a l e d f o r m a t i o n o f a c a r b o n y l a t about 5.8 microns. Unaged p o l y o l shows n e g l i g i b l e c a r b o n y l f o r m a t i o n . A c c o r d i n g t o the p a t e n t ( 4 ) , t h i s r e a c t i o n i s p e c u l i a r t o any c h l o r o f l u o r o a l k a n e c o n t a i n i n g t h r e e o r more c h l o r i n e s , i . e . , t r i c h l o r o t r i f l u o r o e t h a n e s , C2F3CI3; t e t r a c h l o r o d i f l u o r o e t h a n e s , C2F3CI4. D i c h l o r o f l u o r o a l k a n e s , i . e . , Freon 12, d i c h l o r o d i f l u o r o ­ methane, are a p p a r e n t l y f r e e from such r e a c t i o n s . The r e a c t i o n o f F r e o n 11 w i t h a p o l y o l appears i n e s c a p a b l e ; c o n s e q u e n t l y l o n g term s t o r a g e o f foam systems of t h i s c o m p o s i t i o n a r e not a d v i s a b l e . Formulation

3

At t h i s j u n c t u r e , i t was d e c i d e d t o make a r a d i c a l f o r m u l a t i o n change. F i r s t , because o f the i n c o m p a t i b i l i t y o f the Freon 11 w i t h the p o l y o l , the F r e o n 11 would be removed from the p o l y o l and p l a c e d i n the i s o c y a n a t e component. Second, s i n c e 1/1 component r a t i o s a r e n e c e s s a r y t o accommodate the m i x i n g machine, d i f f e r e n t i s o c y a n a t e and p o l y o l components were f o r m u l a t e d t o e s t a b l i s h a p p r o p r i a t e v i s c o s i ­ ties. The f i n a l f o r m u l a t i o n i s shown below. Isocyanate PAPI-580 F r e o n 11

Component A

P o l y o l Component Β

117 pbw 33 pbw

PEP-550 DC-197 DABCO F r e o n 12

117 1 5 25

pbw pbw pbw pbw

I n subsequent a g i n g s t u d i e s the p o l y o l component showed v i r t u a l l y no change i n a c i d number a t any of the a g i n g t e m p e r a t u r e s (ambi­ e n t , 60°, 71°C) over 13 months. The i s o c y a n a t e was shown t o age s i m i l a r l y t o the i s o c y a n a t e i n F o r m u l a t i o n 2. As a r e s u l t , the above f o r m u l a t i o n i s b e i n g employed i n the f i e l d . Summary And Two

Conclusions

d i f f e r e n t dispensable r i g i d polyurethane

found inadequate

foam f o r m u l a t i o n s were

o v e ^ ^ P ^ g f o f ^ f i ^ j g ^ e f i r s t system c o n Library

1155 16th St., N.W. Dickie and Floyd; Polymeric Materials for Corrosion Control Washington, D.C. 20036 ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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348

POLYMERIC MATERIALS FOR CORROSION C O N T R O L

t a i n e d p h o s p h o r i c a c i d a d d u c t s which can h y d r o l y z e i n the p r e s e n c e o f m o i s t u r e , t h e r e b y c h a n g i n g t h e i r foaming c h a r a c t e r i s t i c s . A refor­ m u l a t e d system e x c l u d i n g t h e phosphate e s t e r s a l s o e x h i b i t e d poor a g i n g , s i m p l y because the Freon 11 b l o w i n g agent r e a c t s w i t h the p o l y o l l i b e r a t i n g f r e e h y d r o c h l o r i c a c i d , an unacceptable s i t u a t i o n . The l a t t e r r e a c t i o n was not common knowledge, y e t , i t must be r e c o g ­ n i z e d i n v i e w o f t h e w i d e - s p r e a d p o p u l a r i t y o f t h i s r e f r i g e r a n t and b l o w i n g agent* F i n a l l y , a t h i r d f o r m u l a t i o n was d e v i s e d w h i c h e x c l u d e d t h e use o f F r e o n 11 i n t h e p o l y o l component. F r e o n 11 was p l a c e d i n t h e i s o ­ c y a n a t e component and b o t h i s o c y a n a t e and p o l y o l components were changed t o meet v i s c o s i t y c o n s i d e r a t i o n s * Subsequent a g i n g s t u d i e s showed the i s o c y a n a t e t o age s i m i l a r l y t o the p r e v i o u s l y aged ( F o r ­ m u l a t i o n 2) i s o c y a n a t e . The p o l y o l showed v i r t u a l l y no i n c r e a s e i n a c i d number a t any a g i n g temperature o v e r 13 months. Thus, a t ambient t e m p e r a t u r e we would e x p e c t a 6-8 y e a r system l i f e t i m e on the i s o c y a n a t e b e f o r e a 10% change i n a n a l y t i c a l p r o p e r t i e s would d i c t a t e a m a t e r i a l change-out. The p o l y o l appears t o have a g r e a t e r l i f e ­ t i m e , but would p r o b a b l y be r e p l a c e d a t the same t i m e . Acknowledgments The a u t h o r g r a t e f u l l y acknowledges S. L. Pohlman f o r c o n d u c t i n g t h e c o r r o s i o n s t u d y , S. L. E r i c k s o n f o r t h e a n a l y t i c a l d a t a , and C. A r n o l d f o r h e l p f u l d i s c u s s i o n s . Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9.

Church, J . M . ; Mayer, J . H. J . Chem. Eng. 1961, 6, 449. Parmelee, H. M . : Downing, R. C. Soap S a n i t . Chem. 1950, 26, 114. Parmelee, H. M . ; Downing, R. C. Pro. Chem. S p e c i a l t i e s Manu­ facturers Assoc. 1950, 45, 47. Bauer, A. W. U . S . Patent 3 183 192, 1965. Eiseman, B. J. Progr. R e f r i g . S c i . Technol. 1973, 2, 643. Degginer, E . R . ; Knapp, W. Α.; Zuem, Η. E . U.S. Patent 3 352 789. Blodgett, F . W. U.S. Patent 3 361 833. DuPont, Belgium Patent 621 364. Wright, P; Cumming, A. P. C. " S o l i d Polyurethane Elastomers"; McClearen and Sons, 1969.

R E C E I V E D January 22, 1986

Dickie and Floyd; Polymeric Materials for Corrosion Control ACS Symposium Series; American Chemical Society: Washington, DC, 1986.