Metallization of Polymers - American Chemical Society

Chapter 19

Reactions of Metal Powders with Organic Polymers John Delmonte

Downloaded by COLUMBIA UNIV on March 9, 2013 | http://pubs.acs.org Publication Date: November 9, 1990 | doi: 10.1021/bk-1990-0440.ch019

Delsen Testing Laboratories, Glendale, CA 91201

Metal powders are comingled with l i q u i d epoxy polymers and with f i n e l y divided low density polyethylene (LDPE). The mixtures are exposed to temperatures exceeding the decomposition of the organic polymers, but below the melting point of the metal. Observations were made of the polymer-metal mixtures with the a i d of a d i f f e r e n t i a l scanning calorimeter (D.S.C.). Commercial grades of powdered i r o n , copper and aluminum were used. S i g n i f i c a n t d i f f e r e n c e s among the metals are reported in studies of the exotherm "spikes" which were generated. Data are reported on samples i n the presence of air, as well as in the presence of an i n e r t gas (Argon). Thermal decomposition of the subject epoxy was lowered most i n the presence of i r o n , and l e s s with copper, followed by aluminum. Metal powders influenced the D.S.C. curves of LPDE when conducted i n air,but had little e f f e c t i n the presence of Argon.

I n t e r a c t i o n between metals and polymers are u s u a l l y assessed from data on the performance of polymer adhesives and coatings upon metal surfaces. High temperature operations and environmental aging processes may produce i n s t a b i l i t y , observed i n d i s c o l o r a t i o n of the organic f i l m or by the loss of adhesive strength of the metal and the polymers. In many polymer-metal systems chemical bonds are formed that involve metal-oxygencarbon complexes. The oxygen source may be the atmosphere, oxide on the metal surface, or from the polymer (1). The degradation of polyethylene on copper i s i l l u s t r a t i v e of polymer oxidation i n v o l v i n g long-range 0097-6156/90/0440-0265$06.00/0 © 1990 American Chemical Society In Metallization of Polymers; Sacher, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.


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i n t e r f a c e e f f e c t s ( 2 ) . The f o r m a t i o n o f n o v e l o r g a n o m e t a l l i c compounds by t h e r e a c t i o n o f f i n e l y d i v i d e d m e t a l powders r e p r e s e n t s a p o w e r f u l t o o l f o r c h e m i c a l s y n t h e s i s ( 3 ) . S t u d i e s have been c o n d u c t e d on t h e b o n d i n g t o c o l d - r o l l e d s t e e l and e l e c t r o - g a l v a n i z e d s t e e l w i t h epoxy d i c y a n a m i d e a d h e s i v e s , u s i n g changes i n i n f r a r e d s p e c t r a to suggest i n t e r f a c i a l chemistry (4). The e f f e c t o f t h e d e g r a d a t i o n o f p o l y a c r y l a m i d e i n t h e p r e s e n c e o f i r o n o r oxygen has a l s o been r e p o r t e d ( 5 ) . T h i s paper w i l l d i s c l o s e a simple procedure f o r i d e n t i f y i n g p o t e n t i a l p r o b l e m a r e a s by s u b j e c t i n g c o m b i n a t i o n s o f two o r more d i v e r s e m a t e r i a l s t o h i g h t e m p e r a t u r e g r a d i e n t s . B o t h t h e r m o p l a s t i c and t h e r m o s e t t i n g polymers w i l l d i s p l a y h i g h c h e m i c a l r e a c t i v i t y as t h e y a r e exposed t o t e m p e r a t u r e s a p p r o a c h i n g t h e i r d e c o m p o s i t i o n . The s e n s i n g o f t h i s r e a c t i v i t y i s o b t a i n e d w i t h p r e c i s i o n on a d i f f e r e n t i a l scanning calorimeter. T h e r m o p l a s t i c polymers w i l l b e g i n to s o f t e n w i t h i n c r e a s i n g t e m p e r a t u r e and t h e r m a l l y decompose i n t o l o w e r m o l e c u l a r w e i g h t f r a c t i o n s . I t i s p r o b a b l e t h a t t h e more v o l a t i l e , l o w e r m.w. polymers w i l l demonstrate g r e a t e r tendency f o r chemical i n t e r a c t i o n w i t h the metal s u r f a c e s . An i n c r e a s i n g t e m p e r a t u r e g r a d i e n t may a l s o i n d u c e h o m o p o l y m e r i z a t i o n o f low m.w. polymers. I n t e r a c t i o n s w i l l a l s o be i n f l u e n c e d by a t m o s p h e r i c oxygen and hence i n t h e t e s t s w h i c h f o l l o w : c o m p a r i s o n s a r e made between a i r and i n e r t gas e x p o s u r e . In t h i s p a p e r t h e p r i n c i p a l i n f o r m a t i o n i s d e v e l o p e d on l i q u i d DER332 epoxy (Dow s B i s p h e n o l A o f d i g l y c i d y l e t h e r ) and (a f i n e l y d i v i d e d low d e n s i t y polyethylene). Several f i n e l y d i v i d e d metals; i r o n , c o p p e r and aluminum were b l e n d e d w i t h e q u a l volumes o f t h e above m e n t i o n e d p o l y m e r s . These were exposed d u r i n g h i g h temperature g r a d i e n t s i n the presence of atmospheric oxygen and a r g o n gas. I n g e n e r a l , t h e ASTM s c r e e n mesh s i z e f o r t h e A l , C u , and Fe powders u s e d were i n t h e 100 t o 200 mesh s i z e . P r e l i m i n a r y s t u d i e s i n d i c a t e d t h a t t h i s f i n e r mesh s i z e s y i e l d e d s l i g h t l y l o w e r d e c o m p o s i t i o n t e m p e r a t u r e s o f t h e polymer, though t h i s p a p e r f o c u s e s more upon t h e l a r g e d i f f e r e n c e o b s e r v e d between t h e t h r e e m e t a l powders s e l e c t e d . I t i s r e c o g n i z e d t h a t i n t e r a c t i o n s a r e c o n c e r n e d w i t h r e l a t i o n s h i p s between c o l o n i e s o f o r g a n i c m o l e c u l e s ( i f a powdered c o n s i s t e n c y ) o r low m o l e c u l a r w e i g h t l i q u i d / o r g a n i c p o l y m e r s , w i t h m o l e c u l a r c o l o n i e s of m e t a l l i c elements at t h e i r o u t e r m o s t i n t e r f a c e s . In t h e s e t e s t s t h e f o l l o w i n g m e t a l powders were u s e d : A. MD-2 01 - Aluminum Company o f A m e r i c a . B. Copper Powder - C-112 o f U.S. Bronze Co. C. I r o n Powder - MH-100 o f Hoeganaes Co. 1

PROCEDURE A modified d i f f e r e n t i a l

s c a n n i n g c a l o r i m e t e r was

used i n

In Metallization of Polymers; Sacher, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1990.


19. DELMONTE

Organic Polymers

267

t h e t e s t s t o f a c i l i t a t e t h e r a p i d removal o f v o l a t i l e s o r gaseous p r o d u c t s which might e v o l v e d u r i n g t h e c o u r s e o f t h e e x p e r i m e n t s . The b a s i c P e r k i n - E l m e r D.S.C. a p p a r a t u s and r e c o r d i n g system u s e d was Model - 2C. T h i s a p p a r a t u s i s s e n s i t i v e t o t h e t h e r m a l b e h a v i o r o f s m a l l samples when u s i n g aluminum pans o r cups (1/2 cm. d i a m e t e r ) . Sample s i z e s were g e n e r a l l y i n t h e range o f 10 t o 70 m i l l i g r a m s - d e p e n d i n g on t h e v o l u m e t r i c l o a d i n g o f t h e more dense m e t a l l i c component. The s m a l l sample s i z e promoted c o n f i d e n c e i n t h e exotherm o r endotherm d a t a , because o f t h e p r o x i m i t y o f t h e t h e r m o c o u p l e s e n s i n g d e v i c e on t h e cup. P r o c e d u r e s were s t a n d a r d i z e d as f a r as p o s s i b l e t o p e r m i t c o m p a r i s o n s between d i v e r s e m a t e r i a l c o m b i n a t i o n s . The m e t a l powders and p o l y m e r s u s e d i n t h e s e t e s t were commercial g r a d e s w i t h o u t f u r t h e r laboratory p u r i f i c a t i o n . RESULTS F i g u r e s 1 and 2 i l l u s t r a t e d t h e D.S.C. s c a n s f o r t h e b a s e epoxy r e s i n DER-332 a l o n e and i n c o m b i n a t i o n w i t h 50% volume c o n c e n t r a t i o n o f A l , Cu, and F e . The m e t a l f i l l e d specimens y i e l d e d s h a r p exotherm " s p i k e s " w h i c h were i n t e r p r e t e d as e v i d e n c e o f c h e m i c a l r e a c t i o n s . T h e r e i s a d e f i n i t e temperature a s s o c i a t e d w i t h the exothermic " s p i k e " o f each m e t a l . Sharp " s p i k e s " were n o t i n e v i d e n c e f o r t h e b a s i c n e a t r e s i n . The d e p t h o f t h e exotherm was g r e a t e s t f o r Fe, f o l l o w e d by Cu and A l . I n c r e a s i n g t h e volume p e r c e n t a g e o f Fe i n c r e a s e d t h e d e p t h o f t h e " s p i k e " , w h i l e d e c r e a s i n g t h e volume p e r c e n t a g e o f Fe t o l e s s t h a n 50%, d e c r e a s e d t h e d e p t h o f t h e s p i k e , w i t h o n l y minor d i f f e r e n c e s o f t h e t e m p e r a t u r e a t w h i c h t h e exo " s p i k e " o c c u r r e d . The r e f e r e n c e b a s e was e s t a b l i s h e d as a common denominator f o r a c h i e v i n g a u n i f o r m heat i n p u t t o t h e specimens t o m a i n t a i n 20"C. t e m p e r a t u r e g r a d i e n t p e r minute, t h e s h a r p n e s s o f t h e exotherm " s p i k e " was more e v i d e n t a t a 2 0 C . g r a d i e n t . As endo and exotherm r e a c t i o n s began t o t a k e p l a c e a f t e r d e c o m p o s i t i o n o f t h e polymer commenced above 300 ° C , t h e h e a t i n p u t s t o t h e specimens were overshadowed by c h e m i c a l r e a c t i o n s . However, t h e p r o f i l e s o f t h e D.S.C. c u r v e s were c o n s i s t e n t and i d e n t i f i e d w i t h a s p e c i f i c m e t a l - e p o x y c o m b i n a t i o n . R e s u l t s i n a i r and i n a r g o n a r e s i g n i f i c a n t l y d i f f e r e n t i n t h e i r D.S.C. p r o f i l e s as would be e x p e c t e d form t h e p o t e n t i a l o x i d i z i n g e f f e c t o f a i r . See T a b l e I . For comparison purposes F i g u r e 3 i l l u s t r a t e s the r e c o r d e d w e i g h t l o s s o f t h e DER 332 and t h e 50% Ep-Cu m i x t u r e a t a 20°C. p e r minute r i s e i n t e m p e r a t u r e . Most o f t h e epoxy r e s i n has decomposed and d i s a p p e a r e d above 3 6 0 C . W i t h o u t q u e s t i o n more m e a n i n g f u l d a t a has been g e n e r a t e d i n t h e above u s e o f t h e D.S.C. a p p a r a t u s . The D.S.C. c u r v e s s u g g e s t t h e p r e s e n c e o f i n t e r a c t i o n s above e

e




268

Figure 2. D.S.C. Scans of Epoxy and Combinations with A l , Cu, and Fe (In A i r ) .


19. DELMONTE

269

Organic Polymers

Table I .

P r i n c i p a l D.S.C

Exotherms

o f F i g u r e s 1 and 2

e

Approx. 4 0 9 C .

Base Epoxy

e

Approx .401 C. e

EP-Fe

332°C.

e

370 C.

Ep-Cu

369 C.

372 °C.

Ep-Al

379 C.

341 C. Downloaded by COLUMBIA UNIV on March 9, 2013 | http://pubs.acs.org Publication Date: November 9, 1990 | doi: 10.1021/bk-1990-0440.ch019

In Argon

Specimen

In A i r

80 U 60

I

I

1

160

1

260

e

e

1

1

360

1

'

'»

460

Temperature (°C) Figure 3. Weight Loss of Epoxy and Weight Loss of Epoxy and 50% Vol. of Cu.


270


the d e c o m p o s i t i o n t e m p e r a t u r e o f t h e epoxy polymer. F u r t h e r d a t a were o b t a i n e d on samples o f l o w d e n s i t y p o l y e t h y l e n e (LPDE) m i x t u r e s w i t h m e t a l p o w d e r s . L D P E i s g e n e r a l l y c o n s i d e r e d i n e r t t o many c h e m i c a l s . When h i g h t e m p e r a t u r e g r a d i e n t s o f 2 0 C. p e r m i n u t e were a p p l i e d t o m i x t u r e s o f LDPE a n d m e t a l p o w d e r s , i t was f o u n d t h a t c l o s e l y i d e n t i c a l D.S.C. c u r v e s w e r e o b t a i n e d i n a r g o n g a s . From t h e d a t a f o r LDPE, LDPE-Fe, LDPE-Cu, a n d LDPEA l , t h e 5 0 % Fe/LDPE was s e l e c t e d f o r i l l u s t r a t i o n i n F i g u r e 4. On t h e o t h e r h a n d , w h e n t e s t s w e r e p e r f o r m e d i n a i r , w i d e l y d i s s i m i l a r d a t a w e r e o b t a i n e d S e e F i g u r e 5. The p r e s e n c e o f o x y g e n p r o d u c e s u n t o w a r d e f f e c t s o n t h e d e c o m p o s i t i o n o f LDPE i n t h e p r e s e n c e o f A l , C u , a n d F e . I t was n o t e d t h a t t h e p r o f i l e s o f t h e s e c u r v e s w e r e r e p e a t a b l e . Many u n e x p l a i n e d r e a c t i o n s o c c u r r e d d u r i n g polymer decomposition i n t h e presence o f metal powders.


e

CONCLUSIONS 1. T h e d a t a p r o v i d e d b y M e t a l - p o l y m e r D.S.C. c u r v e s p r o v i d e new i n s i g h t o n h i g h t e m p e r a t u r e r e a c t i o n s . 2. T h e p r e c i s e t e m p e r a t u r e s f o r t h e e x o t h e r m i c " s p i k e s " o f t h e D.S.C. c u r v e s f o r e p o x y - m e t a l p o w d e r s i n b o t h a i r a n d o x y g e n s u g g e s t new r e a c t i o n s n o t p r e v i o u s l y reported. 20.00

U Ul C 10.00 -j < υ Σ

0.00 50.00

150.00

250.00

350.00

450.00

TEMPERATURE

Figure 4. D.S.C. Scan of LDPE and i n Combination with 50% Vol. of Cu. (In Argon).


DSC


19. DELMONTE

Organic Polymers

Literature Cited 1. Leidheiser, H. J r . and Deck, P. Science 2 Sept. 1988, 241, 1176. 2. Chan, M. and Allara, D.L. Polym. Eng. S c i . 1974, 4, 12. 3. Rieke, R. Science 8 Dec. 1989, 246, 1260. 4. Carter, R.O., Dickie, R.A., and Holubka, J.W. Journal Polymeric Materials, Science and Enara. 1988, 58, 55. 5. Francois, J. et al. ACS Polymer Preprints 1987, 28, 694. RECEIVED May 16,

1990


in

Metallization of Polymers - American Chemical Society

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