The Effects of Hostile Environments on Coatings ... - ACS Publications

12 Hostile Effects of Oxygenated Solvent Interaction with Type II Rigid Poly(vinyl Chloride) RICHARD F. MILLER

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Rice University, Department of Mechanical Engineering and Materials Science, Houston, TX 77251 PAUL Ε. RIDER University of Northern Iowa, Department of Chemistry, Cedar Falls, IA 50614

A hostile effect can be predicted for the interaction of various oxygenated solvents with Type II rigid poly(vinyl chloride) if the difference in the solubility parameters (δ -δ ) of the solvent-polymer system is less than ± 3.2H and if the hydrogen bonding potential, HBP, of the solvent-polymer system is less than or equal to zero. 1

2

Much of our present knowledge of s o l u t i o n s i s based on the principles developed by Hildebrand and Scott i n 1924 ( 1 ) . F o r t u n a t e l y , most organic solvents are nonpolar and t h e r e f o r e t h e i r i n t e r m o l e c u l a r forces are weak London or d i s p e r s i o n f o r c e s . Hildebrand used the term " r e g u l a r s o l u t i o n s " to d e s c r i b e s o l u t i o n s of nonelectrolytes and t h e i r nonpolar solvents. Additional t h e o r i e s on the s o l u b i l i t y of polymers were developed by F l o r y Ç2) and Huggins ( 3 ) . Probably the most important p u b l i c a t i o n s l e a d i n g t o the p r a c t i c a l use of s o l u b i l i t y t h e o r i e s by polymer s c i e n t i s t s were those published by B u r r e l l i n 1955 ( 4 ) and 1966 (_5). M o d i f i c a t i o n s i n the Hildebrand s o l u b i l i t y parameter concept f o r r e g u l a r s o l u t i o n s t o account f o r l a r g e r i n t e r m o l e c u l a r f o r c e s were made by Liebermann ( 6 ) , Crowley ( 7 ) , Hansen and Beerbower (8) and Nelson et a l . ( 9 ) . To evaluate the p o t e n t i a l h o s t i l e e f f e c t s of oxygenated solvents on Type I I r i g i d p o l y ( v i n y l c h l o r i d e ) , one must consider that PVC has very l i m i t e d s o l u b i l i t y . The most e f f e c t i v e solvents are those which appear to be capable of some form o f i n t e r a c t i o n with the polymer. Small (10) suggested that PVC i s a weak proton donor and e f f e c t i v e solvents are proton acceptors. Thus i t was proposed that the polymer would be s o l u b l e i n tetrahydrofuran; ketones, e.g. cyclohexanone, methyl i s o b u t y l ketone and n i t r o compounds such as nitrobenzene. Hansen (11) evaluated the solvency e f f e c t s of twenty-six solvents on p o l y ( v i n y l c h l o r i d e ) , a summary of h i s data with respect t o oxygenated solvents i s presented i n part i n Table I .

0097-6156/83/0229-0193S06.00/0 © 1983 American Chemical Society

Garner and Stahl; The Effects of Hostile Environments on Coatings and Plastics ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

194

EFFECTS OF HOSTILE ENVIRONMENTS

Table I . S o l u b i l i t y Data f o r P o l y ( v i n y l c h l o r i d e ) with Various Oxygenated Solvents (11-13, 21)


PVC

Methanol Ethanol 1-Propanol 1-Butanol 1-Pentanol Cyclohexanol

14.5 10.0 10.5 13.6 11.6 10.6

1.80 1.70 1.60 1.60 1.60 1.60

1.68 1.74 1.80 1.83 1.81 1.86

0.35 0.32 0.28 0.29 0.28 0.30

I I I I I I

Acetone Methyl E t h y l Ketone Methyl I s o b u t y l Ketone Cyclohexanone Isophorone

9.9 9.3 8.58

0.50 0.34 0.31

1.74 1.70 1.65

-0.45 -0.52 -0.49

M M M

9.9 9.9

0.43 1.05

1.80 1.85

-0.54 -0.11

S M

E t h y l Acetate Propyl Acetate η-Butyl Acetate Isoamyl Acetate

9.0 8.8 8.65 7.8

0.75 (0.80) 0.85 0.89

1.60 1.60 1.60 1.47

-0.22 (-0.20) -0.18 -0.01

I M M M

D i e t h y l Ether Dioxane Tetrahydrofuran M e t h y l - t - B u t y l Ether

7.4 10.0 9.5 7.07

1.20 1.20 0.73 0.965

1.96 1.85 1.70 1.96

0.00 0.00 -0.28 -0.20

I M S M

Dimethylformamide Dimethyl S u l f o x i d e

12.1 12.0

1.11 0.77

2.10 2.32

-0.09 -1.07

M M

S-completely soluble

soluble;

M-some v i s i b l e i n t e r a c t i o n ;

( )-values given are estimated

I-totally in

averages


12.

MILLER AND RIDER

Oxygenated Solvents and Poly (vinyl Chloride)

195

Since Hansen's work was completed, Rider (12, 13) has developed both a two-parameter and a four-parameter model i n order to estimate the e f f e c t s of the hydrogen bonding p o t e n t i a l , HBP, according to the equation shown:


HBP

= (b

x

- b ) 2

(C

x

-

C ) 2

wherein, the donor i s assigned a parameter, b, that r e f l e c t s i t s donating tendency and the acceptor i s assigned a parameter, C, that r e f l e c t s i t a c c e p t i n g tendency. The b parameter has u n i t s of Kcal/mole and the C parameter i s dimensionless. For the v i n y l c h l o r i d e r e s i n , the monomeric u n i t i s e t h y l chloride, t h e r e f o r e , the value for b i s estimated to be approximately 1.2 Kcal/mole (12) while the value f o r C of 1.10 was taken from the observed frequency s h i f t of methanol bonded chloroform as measured by Crowley et a l . (7) and from the b value and slope f o r the l i n e a r enthalpy - frequency shift r e l a t i o n s h i p reported by Rider (12, 13). Therefore, according to the Rider data (12, 13) i f the HBP i s p o s i t i v e , t h i s represents unfavorable hydrogen bonding and suggests that s o l u t i o n s would not be formed. A negative HBP value would r e f l e c t favorable hydrogen bonding, thereby suggesting s o l u t i o n formation. In p r a c t i c e , Seymour (14) s t a t e s that as a f i r s t approximation, and i n the absence of strong i n t e r a c t i o n s such as hydrogen bonding, s o l u b i l i t y or c o m p a t a b i l i t y on the molecular l e v e l can be expected i f 61-62 i s l e s s than ± 1.8 H. The question now a r i s e s whether h o s t i l e e f f e c t s i n c l u d e the a c t i o n wherein the p h y s i c a l and/or chemical i n t e g r i t y of a polymer i s a f f e c t e d without the r e s u l t a n t formation of a solution. In t h i s p a r t i c u l a r study, the formation of " r e g u l a r s o l u t i o n s " w i l l not be considered. Instead the p o s s i b l e h o s t i l e e f f e c t s of oxygenated s o l v e n t s w i l l be discussed wherein the solvents i n v e s t i g a t e d were expected to e x h i b i t no or as yet unreported i n t e r a c t i o n s with p o l y ( v i n y l c h l o r i d e ) . S e m i - r i g i d or Type I I r i g i d p o l y ( v i n y l c h l o r i d e ) specimens described by Seymour (15) were i n i t i a l l y i n v e s t i g a t e d to determine i f such polymers could be used i n s e r v i c e where the PVC could come i n t o contact with e i t h e r t - b u t y l a l c o h o l (TBA) or methyl t - b u t y l ether (MTBE). T h i s work now has been expanded to i n c l u d e a v a r i e t y of oxygenated s o l v e n t s (Table I) i n c l u d i n g those studied by Hansen (11). EXPERIMENTAL To evaluate the hostile effects of v a r i o u s oxygenated solvents on PVC, s t a t i c immersion t e s t s were conducted wherein t e s t specimens having an approximate surface area of 19.4 cm^ and an edge thickness of approximately 0.381 cm were exposed to from 20 to 200 ml of s o l v e n t . The t e s t s were run at 25°C i n g l a s s t e s t chambers having g l a s s racks on which the coupons



196

were suspended. Exposure times ranged from 6 to 72 hours, the coupons were then removed, d r i e d and reweighed i n the i n i t i a l studies i n v o l v i n g t - b u t y l a l c o h o l and methyl t - b u t y l ether (Table II).


Table I I . Weight Changes of PVC A l c o h o l and Methyl t - B u t y l Ether

Solvent

Time

Blank t-Butyl

Alcohol

Methyl t - B u t y l Ether

Specimens

wt. change

(hrs.) 6 72 6 72 6 72

Exposed

to

t-Butyl

wt. change

7o

(mg)

0.08 0.12 -0.05 -0.06 -0.81 -1.62

0.9 1.4 - 0.5 - 0.7 - 9.5 -19.0

In the v a r i o u s other solvents employed the specimens were visually inspected and submitted f o r p h y s i c a l t e s t i n g i n an e f f o r t to d i s c e r n changes i n t e n s i l e or p u l l i n g strength according to a m o d i f i c a t i o n of the procedure reported by S c h n e l l (16). These r e s u l t s are shown i n Table I I I . Table I I I . T e n s i l e and Ultimate Exposed to a H o s t i l e Enviroment

Strengths

Ultimate Strength (kg)

Solvent

Blank t-Butyl Alcohol Methyl t - B u t y l Ether 2-Propanol Propyl Acetate Acetone Dioxane Mmethylformamide Methyl E t h y l Ketone

of

PVC

Specimens

T e n s i l e Strength 1Q kg/m

55.4 56.3/56.75 43.1/41.31 55.8 43.58 25.4 44.49 disintegrated disintegrated

6

2

4.29 4.43 3.45/3.23 4.37 2.97 1.47 2.57

Attenuated total reflectance infrared spectroscopy was employed to determine the possible chemical m o d i f i c a t i o n of the PVC specimen exposed to t - b u t y l a l c o h o l and methyl t - b u t y l ether. I n f r a r e d spectroscopy has been used to study solvent absorption (17), o x i d a t i o n (18) and other degradation r e a c t i o n s of polymers (19). In the studies of the h o s t i l e e f f e c t s of methyl t - b u t y l ether and acetone, the solvent was concentrated and examined using conventional i n f r a r e d techniques.


12.

MILLER A N D RIDER

Oxygenated Solvents and Polyvinyl Chloride)

197

Finally, t h e PVC s p e c i m e n e x p o s e d t o m e t h y l t - b u t y l ether (MTBE) was e x a m i n e d by s c a n n i n g e l e c t r o n m i c r o s c o p y i n an e f f o r t to e v a l u a t e changes i n the s u r f a c e c h a r a c t e r i s t i c s o f the p o l y m e r .


Results

and D i s c u s s i o n

When r e v i e w i n g t h e s p e c t r u m o b t a i n e d on t h e PVC t e s t s p e c i m e n (Figure 1), t h e outstanding absorptions attributable to the a d d i t i o n o f CI appear at 8μ (1250 c m " * ) , CH2 d e f o r m a t i o n , and at 15 μ (665 cm"* ) , carbon-halogen s t r e t c h . These absorptions g r a d u a l l y weaken as the chain length increase, however, when Cl is not terminal, the stretch absorptions, which appear p r a c t i c a l l y without exception at 13.8 μ and 15.5 μ (725 and 645 cm"*) f o r c h l o r i n e , s h i f t b e y o n d 16 μ (625 c m " * ) . It is d i f f i c u l t to a s s i g n s p e c i f i c c h a r a c t e r i s t i c a b s o r p t i o n s i n t h i s p a r t i c u l a r s p e c t r u m when several halogen atoms are introduced into any one m o l e c u l e b e c a u s e o f t h e b r o a d r a n g e i n w h i c h t h e C - C l s t r e t c h bands a p p e a r . The I . R . s p e c t r u m i s f u r t h e r c o m p l i c a t e d by t h e p r e s e n c e o f p l a s t i c i z e r s and f i l l e r s . When c o n s i d e r i n g t h e s p e c t r u m o b t a i n e d a f t e r t h e PVC s p e c i m e n was e x p o s e d t o MTBE ( F i g u r e 2 ) , a r a t h e r s i g n i f i c a n t absorption a p p e a r s a t 610 c m " * w h i c h i s n o t c h a r a c t e r i s t i c o f a C - C l s t r e t c h band. It appears that this rather strong absorption results f r o m t h e p r e s e n c e o f T i O 2 on t h e s u r f a c e o f t h e t e s t specimen. Initially i t was b e l i e v e d that t h e MTBE was a b l e to dissolve t h e PVC u n i f o r m l y t h e r e b y l e a v i n g a c o a t i n g o f T i O on t h e s u r f a c e of the specimen, however, the reaction of a polymer w i t h a c o r r o s i v e i s dependent upon d i f f u s i o n o f the a t t a c k i n g r e a c t a n t . If the polymer i s at a temperature above its Tg t h e r e is a c o n s t a n t s e g m e n t a l m o t i o n t h a t f a v o r s d i f f u s i o n (20). T o b e t t e r understand the possible cause of the apparent h o s t i l e effect, t h e MTBE s o l u t i o n was c o n c e n t r a t e d u n d e r vacuum and a n a l y z e d . Infrared analysis of the concentrated MTBE solution revealed the presence of d i o c t y l phthalate, a p l a s t i c i z e r , and a l e s s e r amount o f a c a r b o x y l a t e . T h e r e f o r e , i t i s r e a s o n a b l e t o assume t h a t t h e MTBE i s c o m p a t i b l e w i t h t h e PVC and t h u s a b l e t o d i f f u s e i n t o and o u t o f t h e p o l y m e r c a r r y i n g w i t h i t the plasticizer, d i o c t y l p h t h a l a t e , and T1O2. However, because T i O 2 i s insoluble in t h e MTBE i t was d e p o s i t e d on t h e specimen's surface while t h e v a r i o u s o r g a n i c s were s o l u b i l i z e d . A s s u m i n g MTBE was a b l e t o d i f f u s e i n t o and o u t o f t h e P V C , carrying with it the v a r i o u s o r g a n i c a d d i t i v e s and depositing TiO on t h e s u r f a c e o f t h e s p e c i m e n , t h e n one w o u l d e x p e c t to see some s u r f a c e a d u l t e r a t i o n when c o m p a r e d t o a s p e c i m e n w h i c h was n o t e x p o s e d t o s u c h a h o s t i l e e n v i r o n m e n t . As expected, a rather dramatic difference was s e e n when comparing the surface of the specimen exposed t o MTBE t o one w h i c h had n o t ( F i g u r e 3,4). A significant "smoothing" of the surface of the specimen exposed t o MTBE t e n d s t o s u p p o r t the




DIGILAB FTS-IMX

3200

2400

1600

800

Wavenumbers Figure 1. IR spectrum of PVC test specimen.


400



12. MILLER AND RIDER

ο

1 (τ a,

I I

ι 5;


199



Figure 3. Scanning electron micrograph of PVC test specimen (*2000).

Figure 4. Scanning electron micrograph of PVC exposed to MTBE (*2000).


12.

MILLER AND RIDER



hypothesis that t h e MTBE a i d e d i n the u n i f o r m l a y e r o f T i O 2 on t h e s u r f a c e o f of d i f f u s i o n .

201

deposition of a rather t h e s p e c i m e n as a r e s u l t

The a c e t o n e employed i n a n o t h e r s t a t i c immersion t e s t was concentrated as in the case of the MTBE and a n a l y z e d . The infrared spectrum of the acetone concentrate indicated the p r e s e n c e o f a c a r b o x y l i c a c i d and p o s s i b l y a s h o r t c h a i n a l c o h o l species. Comparison of the i n f r a r e d spectrum obtained to those of known p o l y m e r b i n d i n g a g e n t s i n d i c a t e d that the carboxylic acid is s i m i l a r to those i n the Shell Versatic acid series, c l o s e l y r e s e m b l i n g V e r s a t i c 911 (22). Subsequent NMR a n a l y s i s of the acetone concentrate showed the presence of a multi-hydroxy 1 containing compound s u c h as p e n t a e r y t h r i t o l and a t l e a s t two t y p e s o f e t h e r m o e i t i e s , O - m e t h y l and -OCR3. A l t h o u g h t h e s t r u c t u r e o f t h e a c e t o n e s o l u b l e o r g a n i c s has not been c o m p l e t e l y elucidated, it is interesting to note the differences between the MTBE solubles and the acetone solubles, both of which exhibit hostile effects toward PVC. I t a p p e a r s t h a t MTBE, 6 = 7 . 0 7 , extracts less polar substituents w h e r e a s a c e t o n e , δ = 9 . 9 , e x t r a c t s t h e more p o l a r b i n d i n g a g e n t s . The a b s e n c e o f an a r o m a t i c a b s o r p t i o n i n b o t h t h e i n f r a r e d and t h e NMR s p e c t r u m o f t h e a c e t o n e s o l u b l e f r a c t i o n t e n d s t o s u p p o r t this conclusion. The d a t a p r e s e n t e d i n T a b l e I I I show t h e e f f e c t o f hostile solvents on the tensile strength of PVC. A l t h o u g h numerous other oxygenated solvents were employed a substantial number of the t e s t specimens e s s e n t i a l l y disintegrated while attempting t o remove them f r o m t h e t e s t chamber. However, w i t h the data presented, one c a n e a s i l y see that a hostile effect adversely a f f e c t s b o t h t h e c h e m i c a l and p h y s i c a l i n t e g r i t y o f t h e p o l y m e r . The definition of a hostile effect, proposed e a r l i e r , as an adverse i n t e r a c t i o n b e t w e e n p o l y m e r and s o l v e n t wherein the chemical and/or physical integrity of the polymer i s affected without the resultant formation of a "regular solution" has b e e n c l e a r l y shown. T h e n e e d now a r i s e s f o r an i m p r o v e d method by which h o s t i l e effects c a n be p r e d i c t e d . Therefore, i f one employs the generalized rule cited by Seymour (14) that c o m p a t a b i l i t y o r s o l u b i l i t y on t h e m o l e c u l a r l e v e l c a n be e x p e c t e d if 6χ-02 i s l e s s t h a n ± 1 . 8 H and t h a t t h e s w e l l i n g o f p o l y m e r s o c c u r s when 6^ - 6 is equal to ± 3.2H (20), t h e n one w o u l d expect some interaction b e t w e e n PVC and a l l of the solvents l i s t e d on T a b l e I , w i t h t h e p o s s i b l e e x c e p t i o n o f m e t h a n o l and 1-butanol. 2

If t h e d a t a p r e s e n t e d by R i d e r ( 1 2 , 13) i s c o n s i d e r e d then one w o u l d e x p e c t a s o l v e n t / p o l y m e r i n t e r a c t i o n with a l l of the p r e v i o u s l y mentioned s o l v e n t s w i t h the e x c e p t i o n of the alcohols and p o s s i b l y d i o x a n e . H o w e v e r , i f one c o n s i d e r s t h e generalized rule of Seymour (14, 20) and t h e hydrogen bonding potential data presented by R i d e r ( 12, 13) a suitable method by w h i c h a hostile effect c a n be p r e d i c t e d i s a c h i e v e d . Simply stated, a h o s t i l e e f f e c t c a n be p r e d i c t e d i f :



202

(1)

the (&\ - δ £ ) of the solvent-polymer system i s l e s s than ± 3.2H and


(2)

the hydrogen bonding p o t e n t i a l of the solvent-polymer system i s l e s s than or equal to zero

A p p l i c a t i o n of t h i s theory to the systems investigated i s c o n s i s t e n t w i t h the data obtained and the r e s u l t s are shown i n Table IV. Table IV.

H o s t i l e E f f e c t Data f o r P o l y ( v i n y l c h l o r i d e )

Solvent

δ

Methanol Ethanol 1-Propanol t-Butanol

5.35 0.85 1.35 3.25

1* 2 δ

HBP

Hostile

0.35 0.32 0.28 (0.25)

no no no no

Acetone Methyl E t h y l Ketone Methyl I s o b u t y l Ketone Cyclohexanone

0.15 -0.57 0.75

-0.52 -0.49 -0.54

yes yes Soluble

E t h y l Acetate η - P r o p y l Acetate η - B u t y l Acetate

-0.15 -0.35 -0.50

-0.22 (-0.20) -0.18

yes yes yes

Dioxane Tetrahydrofuran M e t h y l - t - B u t y l Ether

0.85 0.35 -2.08

0.00 -0.28 (-0.20)

yes Soluble yes

Dimethylformamide

2.95

-0.09

yes

Dimethyl

2.85

-1.07

yes

Sulfoxide

( ) i n d i c a t e s values

that are estimated based on a v a i l a b l e data


12. MILLER AND RIDER

Oxygenated Solvents and

Poly(vinyl

Chloride)

203

Literature Cited

1.


2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

Hildebrand, J.H. and Scott, R.L., "The Solubility of Nonelectrolytes", 3rd ed., Reinhold Corporation, New York, 1950. Flory, P.J., J. Chem. Phys., 1941, 9, 660. Huggins, M.L., J. Chem. Phys., 1941, 9, 440. Burrell, Η., Official Digest, Fed. Soc. Paint Technol., 1955, 27, 726. Burrell, Η., Official Digest, Fed. Soc. Paint Technol., 1966, 38, 34. Liebermann, E.P., Official Digest, Fed. Soc. Paint Technol., 1962, 34, 444. Crowley, J.D., Teague, G.S. and Lowe, J.W., J. Paint Technol., 1966, 38, 269. Hansen,C.M.and Beerbower, Α., "Encyclopedia of Chemical Technology", John Wiley and Sons, New York, 2nd ed., 1971, p. 889. Nelson, R.C., Hemwall, R.M. and Edwards, G.D., J. Paint Technol., 1970, 42, 636. Small, P.Α., J. Appl. Chem., 1953, 3, 71. Hansen, C.M., J. Paint Technol., 1967, 39, 104. Rider, P.E., J. Appl. Polymer Sci., 1980, 25, 2975. Rider, P.E., "Hydrogen Bonding Potential, HBP: A Model for Predicting Resin Solubilities in Organic Solvents", submitted for publication, 1982. Seymour, R.B. and Carraher, C.E., "Polymer Chemistry", Marcel Dekker, Inc., New York, 1981, pp. 61-68. Seymour, R.B., "Modern Plastics Technology", Reston Publishing Company, Inc., Reston, Va., 1975, pp. 192-193. Schnell, Η., Inst. Eng. Chem., 1959, 51, 157. Foster, R.S. and Vokening, V.B., Corrosion, 1959, 15(10), 85. Seymour, R.B., Tsang, H.S., and Warren, D., Poly. Eng. Sci., 1967, 7, 55. Jellinck, H.H.G., Flausmann, G.F., and Kryman, F.J., J. Appl. Polymer Sci., 1969, 13, 107. Seymour, R.B., Plastics vs. Corrosives, John Wiley and Sons, New York, 1982, p. 46. Seymour, R.B., "CRC Handbook of Chemistry and Physics", CRC Press, Inc., Cleveland, 61st ed., 1980, pp. 687-690. Afremov, L.C., Isakson, K.E., Netzel, D.A., Tessari, D.J. and Vandeberg, J.T., eds., "Infrared Spectroscopy: Its Use in the Coatings Industry", Federation of Societies for Paint Techology, Philadelphia, 1969, pp. 137-155.

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February 22, 1983


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