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15 SAIB in Coatings
Downloaded by UNIV OF ARIZONA on September 13, 2013 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0041.ch015
CHARLES H. CONEY Eastman Chemical Products Inc., Kingsport, Tenn. 37662
A systematic synthesis of sucrose e s t e r s began at the Research Laboratories of Tennessee Eastman,in 1956. Simultaneously, e v a l u a t i o n of these preparations as p o t e n t i a l commercial products w i t h s p e c i a l emphasis as components of surface coatings was conducted by the Technical Service and Development Laboratories of E a s t man Chemical Products. From t h i s cooperative e f f o r t , success came i n the form of a very unusual and unique compound, the mixed a c e t a t e - i s o b u t y r a t e e s t e r of sucrose - SAIB. The preparation of these e s t e r s i s f a i r l y s t r a i g h t forward (1^) . Sucrose and an excess of the anhydride are heated i n the presence of the corresponding sodium or potassium s a l t . The crude e s t e r then i s d i s s o l v e d i n hexane and washed w i t h d i l u t e aqueous sodium hydroxide to remove the r e s i d u a l a c i d , c a t a l y s t and c o l o r . The hexane i s then s t r i p p e d under reduced pressure. At the beginning of t h i s study, the octaacetate e s t e r was a commercial product, but the other sugar esters were not commercially a v a i l a b l e . Thus, the o c t a s u b s t i t u t e d e s t e r s of p r o p i o n i c , b u t y r i c , i s o b u t y r i c , v a l e r i c , 2-methyl b u t y r i c , and 2 - e t h y l hexanoic acids were prepared (Table I ) . I t was found t h a t , although the octapropionate e s t e r i s a g l a s s y s o l i d i n a super-cooled s t a t e , i t soon c r y s t a l l i z e s . Sucrose o c t a i s o b u t y r a t e i s a very viscous l i q u i d a f t e r melting but, w i t h i n a few hours, begins to c r y s t a l l i z e . The b u t y r a t e , the v a l e r a t e , the 2-methyl b u t y r a t e , and the 2 - e t h y l hexanoate octa e s t e r s , each e x i s t e d as l i q u i d s which d i d not c r y s t a l l i z e . I t i s i n t e r e s t i n g to note that the octaisobutyrate e s t e r on c r y s t a l l i z a t i o n forms a very symmetrical, s p h e r i c a l mass as i n d i v i d u a l c r y s t a l s r a d i a t e from the nucleus.
213 In Sucrochemistry; Hickson, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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Table I . Sucrose Ester Modified Cellulose Acetate Butyrate Films (50/50 Ratio)
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Type of Octa-Ester
Appearance
Acetate
Very brittle
Propionate
Hazy, brittle
Isobutyrate
Opaque, brittle
Butyrate
Soft, tacky
Valerate
Soft, tacky
2-Ethyl hexanoate
Very soft film
When t h e s u c r o s e e s t e r s w e r e e v a l u a t e d a s m o d i f i e r s f o rc e l l u l o s e acetate butyrate, the c r y s t a l - p r o d u c i n g compounds g a v e b r i t t l e a n d sometimes h a z y o r opaque f i l m s a s t h e y c o n t i n u e d t o c r y s t a l l i z e , even i n the presence o f t h e c e l l u l o s e polymer (Table I I ) . On the other hand, t h e l i q u i d e s t e r s performed as p l a s t i c i z e r s f o rc e l l u l o s e acetate butyrate, producing s o f t and t a c k y f i l m s a t 50% m o d i f i c a t i o n . Because o f t h i s softening a c t i o n , sucrose e s t e r s , forming l o w - v i s c o s i t y l i q u i d s , were e l i m i n a t e d from commercial c o n s i d e r a t i o n . I t a l s o was e s t i m a t e d t h a t t h e s e e s t e r s c o u l d n o t comp e t e c o s t w i s e w i t h t h e commonly u s e d , c o a t i n g s p l a s t i cizers. Table I I . Sucrose Esters Type of Octa-Ester
Physical Nature
Acetate
Crystalline
Propionate
Crystalline
Isobutyrate
Crystalline
n-Butyrate
Liquid
Valerate
Liquid
2-Methyl butyrate
Liquid
2-Ethyl hexanoate
Liquid
Melting Point, °C
45 64
To o v e r c o m e t h e d i l e m m a e i t h e r o f c r y s t a l l i n e o r l o w - v i s c o s i t y compounds, t h e m i x e d e s t e r s were p r o duced and i n v e s t i g a t e d . S e v e r a l o f those were found to produce v i s c o u s l i q u i d s which would n o t c r y s t a l l i z e . From e v a l u a t i o n s i n c o m b i n a t i o n w i t h v a r i o u s f i l m - f o r m i n g p o l y m e r s , s u c r o s e a c e t a t e i s o b u t y r a t e was s e l e c t e d as p r o d u c i n g p r o p e r t i e s most d e s i r a b l e a s a c o a t i n g s modifier (Figure 1 ) . O f c o u r s e , t h e r e a r e many p o s s i b l e combinations from t h e v a r i o u s r a t i o s o f a c e t y l t o i s o b u t y r y l groups. From a s t u d y o f t h i s f a c t o r , i t
In Sucrochemistry; Hickson, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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Figure 1
was d e t e r m i n e d t h a t b e t w e e n 2 a n d 3 a c e t y l , a n d 5 a n d 6 i s o b u t y r y l groups gave most d e s i r a b l e p r o p e r t i e s . In a d d i t i o n , t h e random v a r i a t i o n o f t h e a r r a n g e m e n t o f t h e two s u b s t i t u e n t g r o u p s i n c r e a s e s m o l e c u l a r i n h o m o g e n e i t y and r e d u c e s t h e t e n d e n c y t o c r y s t a l l i z e . This h i g h - v i s c o s i t y , r e s i n o u s , mixed a c e t a t e - i s o b u t y r a t e e s t e r was f o u n d t o m o d i f y c e l l u l o s i c - b a s e d c o a t i n g s i n a way t h a t c o u l d e x t e n d t h e f i l m - f o r m i n g polymer,giving higher solids without appreciably loweri n g c o a t i n g f i l m h a r d n e s s (20 . T h i s a s p e c t and severa l o t h e r d e s i r a b l e p r o p e r t i e s o f t h e e s t e r w i l l be c o v ered i n the remaining d i s c u s s i o n . A l t h o u g h t h i s e s t e r p e r f o r m s i n s e v e r a l ways l i k e
Figure 2
In Sucrochemistry; Hickson, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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Figure 3
a polymeric m a t e r i a l , i t i s a c t u a l l y a large, bulky m o l e c u l e o f a b o u t 834 m o l e c u l a r w e i g h t ( F i g u r e 2 ) . Of c o u r s e , i t i s e s s e n t i a l t h a t m o s t c o a t i n g s m o d i f i e r s have a degree o f r e s i s t a n c e t o w a t e r . As m e n t i o n e d e a r l i e r , the e s t e r i f i c a t i o n of a l l of the hydroxyl g r o u p s on s u c r o s e c h a n g e s i t s h y d r o p h i l i c - l i p o p h i l i c b a l a n c e (HLB) a n d s u r f a c e e n e r g y t o a h i g h d e g r e e . T h i s r a d i c a l change p r o b a b l y i s due, i n p a r t , t o t h e h i g h d e n s i t y o f r e a c t i o n s i t e s a v a i l a b l e on s u c r o s e and to the high degree of conversion t o the e s t e r . The h y d r o p h o b i c i t y o f S A I B c a n be i l l u s t r a t e d b y i t s high contact angle w i t h water. The i n i t i a l a n g l e o f c o n t a c t was f o u n d t o be 110-115°. The p r o d u c t i s a l s o very s t a b l e i n the presence of water. We f o u n d , i n t h e e a r l y w o r k , t h a t , a s one m i g h t e x p e c t , t h e d e g r e e o f h y d r o l y t i c s t a b i l i t y o f t h e m i x e d e s t e r i n c r e a s e s as the r a t i o of i s o b u t y r y l to a c e t y l i n c r e a s e s . When immersed i n b o i l i n g w a t e r f o r f o u r d a y s , i t h y d r o l y z e d t o t h e e x t e n t o f o n l y 0.3% b y w e i g h t . The h i g h v i s c o s i t y o f t h e a c e t a t e - i s o b y t y r a t e e s t e r ( F i g u r e 3) may be r e d u c e d d r a m a t i c a l l y b y a n i n c r e a s e i n temperature (Figure 4). A s an e x a m p l e , i t s v i s c o s i t y o f g r e a t e r t h a n 1 0 0 , 0 0 0 c p s a t 25°C c a n be r e d u c e d t o 1,000 c p s a t 68°C, o r t o 100 c p s a t 100°C. At e l e v a t e d temperatures, the e s t e r l o s e s i t s i n a c t i v e r o l e as m o d i f i e r - e x t e n d e r and f u n c t i o n s as p l a s t i c i z e r o r e v e n s o l v e n t f o r some p o l y m e r s . This b i f u n c t i o n a l p r o p e r t y makes i t a v a l u a b l e component o f h e a t - s e a l c o a t i n g s and h o t - m e l t adhesives.
In Sucrochemistry; Hickson, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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20
40
Figure 4.
60
80 100 Temperature, °C
120
140
160
Viscosity of SAIB as influenced by temperature
I n t o d a y ' s need t o reduce s o l v e n t e m i s s i o n s , h i g h s o l i d s c o a t i n g s have h i g h p r i o r i t y . Two p r o p e r t i e s o f the product s u i t i tp a r t i c u l a r l y w e l l as a m o d i f i e r f o r h i g h - s o l i d s coatings; these a r e : low s o l u t i o n v i s c o s i t i e s , and minimum e f f e c t upon c o a t i n g s h a r d n e s s . One can see t h e v i s c o s i t y o f an a c e t a t e - i s o b u t y r a t e s o l u t i o n i s g r e a t l y a f f e c t e d by s l i g h t changes i n concent r a t i o n at high l e v e l s of the product, but i s r e l a t i v e l y u n a f f e c t e d a t l o w o r medium l e v e l s ( F i g u r e 5 ) . A 1 0 0 - f o l d r e d u c t i o n o f v i s c o s i t y i s produced by t h e a d d i t i o n o f 10% s o l v e n t . Likewise, f a i r l y high levels o f t h e e s t e r may b e u s e d w i t h some p o l y m e r s w i t h o u t appreciably a f f e c t i n g f i l m hardness (Figure 6 ) . As an e x a m p l e , up t o 5 0 % S A I B may b e u s e d w i t h c e l l u l o s e a c e t a t e w i t h o u t c a u s i n g a g r e a t change i n f i l m h a r d ness. A l s o , 50% SAIB w i l l m o d i f y c e l l u l o s e n i t r a t e t o produce a s u r f a c e hardness g r e a t e r than t h a t o f t h e unmodified film. Therefore, because o f t h i s f i l m hardness e f f e c t and t h e low s o l u t i o n v i s c o s i t y e f f e c t , t h i s e s t e r f i n d s one o f i t s p r i n c i p a l a p p l i c a t i o n s a s an extender t o increase coatings s o l i d s . SAIB h a s b e e n u s e d f o r a number o f y e a r s i n c o a t i n g s and s a t u r a n t s f o r t h e t r a n s p a r e n t i z i n g o f paper (Figure 7 ) .
In Sucrochemistry; Hickson, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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1 I 100
I
I
I
90
80
70
I
I
I
I
60
50
40
30
SAIB, Wt. % Figure 5. Solution viscosity of SAIB in typical coatings solvents
Figure 6. Effect of SAIB on cellulose esterfilmhardness
In Sucrochemistry; Hickson, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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Figure 7
Three p r o p e r t i e s , w h i c h I have n o t y e t d i s c u s s e d , make t h i s e s t e r e s p e c i a l l y s u i t e d f o r t h a t p u r p o s e . F i r s t , and a s i d e from i t s good c l a r i t y and low c o l o r , t h e p r o d u c t has a r e f r a c t i v e index c l o s e t o t h a t o f c e l l u l o s e f i b e r (3) ( T a b l e I I I ) . Thus t h e i n d i v i d u a l f i b e r s o f a p a p e r t e n d t o "disappear" as t h ee s t e r surrounds and reduces the l i g h t r e f l e c t e d from t h e f i b e r ' s s u r f a c e . Table I I I . R e f r a c t i v e Index SAIB COTTON JUTE
-
n
2 0
° 1.454 1.555 1.536
S e c o n d l y , SAIB h a s l o w v o l a t i l i t y even a t e l e v a t e d t e m p e r a t u r e s ( F i g u r e 8) a n d t h u s p r o v i d e s a v e r y permanent degree o f t r a n s p a r e n c y to t h epaper. Compared w i t h d i o c t y l p h t h a l a t e and p o l y - a - m e t h y l s t y r e n e , s u c r o s e a c e t a t e - i s o b u t y r a t e h a s much l e s s w e i g h t l o s s a t t e m p e r a t u r e s a s h i g h a s 171°C. Thirdly, sucrose acetate-isobutyrate i s r e s i s t a n t t o d i s c o l o r a t i o n on exposure t o heat and u l t r a v i o l e t l i g h t , adding t o t h e q u a l i t y o f t h etransparentized paper. D e s p i t e i t s l i q u i d f o r m , when u s e d a t t h e correct l e v e l , theester gives a d r y f e e l to t h e paper.
In Sucrochemistry; Hickson, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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Hours Figure 8.
Volatility of poly-a-methylstyrene and dioctyl phthalate at 350°F
The h i g h v i s c o s i t y a n d w e t t i n g c h a r a c t e r i s t i c s o f t h e p r o d u c t make i t a n e f f i c i e n t d i s p e r s a n t f o r c o a t i n g s p i g m e n t s (£) • The d i s p e r s i o n , w h i c h may c o n t a i n v a r i o u s amounts o f s o l v e n t t o c o n t r o l v i s c o s i t y , forms a s t a b l e s u s p e n s i o n w h i c h i s c o m p a t i b l e w i t h many c o a t i n g s systems and w h i c h c a n be used t o t i n t t h e s e systems. The e s t e r c a n be u s e d a s t h e medium i n p r a c t i c a l l y a l l o f t h e pigment d i s p e r s i o n techniques. These i n c l u d e t h e t h r e e - r o l l m i l l , s a n d m i l l , b a l l m i l l , a t t r i t o r , and t h e p r o c e s s o f f l u s h i n g o f wet pigment c a k e (55) . I n t h e wet pigment cake f l u s h i n g method, sucrose a c e t a t e - i s o b u t y r a t e h a s b e e n f o u n d t o b e much m o r e e f f i c i e n t t h a n o t h e r media such as a l k y d s and o i l s o r d i n a r i l y u s e d f o r t h i s p u r p o s e {6)• Very l i k e l y , the p r o p e r t i e s o f v i s c o s i t y , h y d r o p h o b i c i t y and t h e pigment w e t t i n g c h a r a c t e r i s t i c s o f t h i s e s t e r , combine t o s e p a r a t e t h e p i g m e n t f r o m t h e w a t e r more r a p i d l y and to a h i g h e r e x t e n t . S u c r o s e a c e t a t e - i s o b u t y r a t e may b e e m u l s i f i e d r e a d i l y w i t h a s u r f a c t a n t m i x t u r e h a v i n g a n HLB v a l u e o f 1 4 , T a b l e I V . T h e e s t e r i s h e a t e d t o a b o u t 70°C a n d an i n v e r s i o n t e c h n i q u e i s u s e d t o p r o d u c e a n o i l - i n water-type emulsion having e x c e l l e n t s t a b i l i t y . As i n t e r e s t i n c r e a s e s i n w a t e r - b a s e d c o a t i n g s a s a means o f r e d u c i n g a i r p o l l u t i o n , i t i s s i g n i f i c a n t t h a t SAIB e m u l s i o n s may b e u s e d i n l a t e x - b a s e d c o a t i n g s (5).
In Sucrochemistry; Hickson, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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CONEY
Table IV.
SAIB E m u l s i o n Ingredients SAIB Surfactant Water
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Formation Weight % 40 5 55 100
The p r o d u c t h a s t h e d e s i r a b l e p r o p e r t y o f i m p a r t ing adhesion t o several p l a s t i c surfaces. I t can i n c r e a s e a d h e s i o n o f l a c q u e r s (£) t o m o l d e d o r e x t r u d e d c e l l u l o s e acetate, c e l l u l o s e acetate butyrate, nylon and a c r y l i c s , a n d t o c e l l o p h a n e a n d M y l a r f i l m . SAIB i s c o m p a t i b l e w i t h a wide v a r i e t y o f p o l y m e r s , r e s i n s , p l a s t i c i z e r s , o i l s , and waxes. Thus, t h e s u c r o s e e s t e r may b e u s e d i n many t y p e s o f c o a t i n g s f o r v a r i o u s a p p l i c a t i o n s both f o r indoor and e x t e r i o r e x p o s u r e , i n c l u d i n g wood c o a t i n g s , m e t a l c o a t i n g s , c l o t h and p a p e r c o a t i n g s , p l a s t i c l a c q u e r s , p r i n t i n g i n k s , and h e a t - s e a l i n g a d h e s i v e s . Many s u i t a b l e f o r m u l a t i o n s have been d e v e l o p e d f o r t h e s e a p p l i c a t i o n s ( 7 , 2 ) . As one c a n s e e , SAIB i s a v e r y v e r s a t i l e compound for use i n coatings. I t s v e r s a t i l i t y extends i n t o several other f i e l d s . I t i sused as an a d d i t i v e i n p l a s t i c s e x t r u s i o n t o o b t a i n improved m i l l i n g propert i e s a n d i n c r e a s e d s u r f a c e h a r d n e s s (£) . A special g r a d e o f t h i s e s t e r i s u s e d i n many c o u n t r i e s a s a s o f t d r i n k m o d i f i e r f o r f l a v o r i n g - o i l suspension and c l o u d i n g p u r p o s e s (9)• I t i s a l s o r e p o r t e d t o be used as a n i n g r e d i e n t i n e x p l o s i v e s , a d h e s i v e s , p o l i s h e s , cosmetics, photographic f i l m (10), and perfumes. A m a t e r i a l as unique as t h i s sugar e s t e r i s c e r t a i n t o f i n d u s e i n many y e t u n r e a l i z e d a p p l i c a t i o n s .
Abstract The physical nature of the acetic, propionic, butyric, isobutyric and valeric esters of sucrose ranges from crystalline solids to low-viscosity liquids. As coatings modifiers, the crystalline compounds have a tendency to form crystals within the film while the liquid compounds cause the film to soften as a plasticizer would do. In the search for a coatings modifier which would perform as an extender, mixed esters were investigated. It was discovered that the completely esterified mixed acetic and isobutyric ester of sucrose produced some unusual properties alone and also when combined with various film formers. A major aspect of sucrose acetate isobutyrate (SAIB) is its capability of extending polymers to
In Sucrochemistry; Hickson, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
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impart various properties without degrading the physical toughness and hardness of the coating, unlike many other modifiers. The low viscosity of SAIB in most solvents contributes to the attainment of high-solids coatings. These coatings are utilized in interior and exterior applications for wood, paper, plastic, and metal surfaces. This ester is finding use in a wide spectrum of applications other than coatings, including adhesives for laminating plastic film, printing inks, hot-melt coatings, heat reactivated adhesives, transparentized paper, pigment dispersions and soft drinks. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Touey, G.P., Davis, H.E., U.S. Patent 2,931,802, April, 1960. Gearhart, W.M., Ball, F.M., U.S. Patent No. 3,076, 718. February, 1963. Scott, J.R., Roff, W.J., "Handbook of Common Polymers," page 134, CRC Press, 1971. Coney, C.H., American Ink Maker, (1966). XLIV, (3). Coney, C.H., Draper, W.E., U.S. Patent 3,318,714, May, 1967. Coney, C.H., Draper, W.E., Defensive Publication 745,090, December, 1968. Coney, C.H., American Ink Maker, (1969), XLVII, (1). January. Gearhart, W.M., Wilson, E.W., SPE Journal, (1960), 16, (10). British Patent No. 1,118,019 (Aktieselskabet CoRo), June, 1968. Ferrania, Belgian Patent 609,231.
Biographic Notes Charles H. Coney, B.S., Industrial res. chem. Educated at Univ. of South Carolina. Joined Eastman Chemical Products, Inc. in 1948; technical service and development of chemicals for plastics, protective and decorative coatings. Coatings Chemical Laboratory, Tech. Service and Devel. Div. Eastman Chemical Products, Inc., Kingsport, Tennessee 37662 U.S.A.
In Sucrochemistry; Hickson, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.
