[acs symposium series] sucrochemistry volume 41 || saib in coatings

15

SAIB in Coatings

CHARLES H. CONEY Eastman Chemical Products Inc., Kingsport, Tenn. 37662

A systematic synthesis of sucrose esters began at the Research Laboratories of Tennessee Eastman,in 1956. Simultaneously, evaluat ion of these preparations as po ten t i a l commercial products wi th spec ia l emphasis as components of surface coatings was conducted by the Technical Service and Development Laboratories of Eastman Chemical Products. From t h i s cooperative e f fo r t , success came i n the form of a very unusual and unique compound, the mixed acetate-isobutyrate ester of sucrose - SAIB.

The preparation of these esters i s f a i r l y s t r a igh t forward (1̂ ) . 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 ester then i s d issolved i n hexane and washed with d i l u t e aqueous sodium hydroxide to remove the res idua l a c i d , ca t a lys t and c o l o r . The hexane i s then s t r ipped under reduced pressure.

At the beginning of t h i s study, the octaacetate ester was a commercial product, but the other sugar esters were not commercially a v a i l a b l e . Thus, the octasubst i tuted esters of p rop ion ic , b u t y r i c , i sobutyr -i c , v a l e r i c , 2-methyl b u t y r i c , and 2-ethyl hexanoic acids were prepared (Table I ) . I t was found that , although the octapropionate ester i s a glassy s o l i d i n a super-cooled s ta te , i t soon c r y s t a l l i z e s . Sucrose octaisobutyrate i s a very viscous l i q u i d after melt ing but, wi th in a few hours, begins to c r y s t a l l i z e . The butyrate, the va le ra te , the 2-methyl butyrate, and the 2-ethyl hexanoate octa es ters , each exis ted as l i q u i d s which d id not c r y s t a l l i z e . I t i s i n t e re s t ing to note that the octaisobutyrate ester on c r y s t a l l i z a t i o n forms a very symmetrical, spher ica l mass as i n d i v i d u a l c rys t a l s radiate from the nucleus.

213

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In Sucrochemistry; Hickson, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

214 SUCROCHEMISTRY

T a b l e I . Sucrose Ester Modified Cellulose Acetate Butyrate Films

(50/50 Ratio)

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 were e v a l u a t e d as m o d i f i e r s f o r c e l l u l o s e a c e t a t e b u t y r a t e , t h e c r y s t a l - p r o d u c i n g compounds gave b r i t t l e and sometimes h a z y o r opaque f i l m s as 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 t h e p r e s e n c e o f t h e c e l l u l o s e p o l y m e r ( T a b l e I I ) . On t h e o t h e r hand, t h e l i q u i d e s t e r s p e r f o r m e d as p l a s t i c i z e r s f o r c e l l u l o s e a c e t a t e b u t y r a t e , p r o d u c i n g 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 s o f t e n i n g a c t i o n , s u c r o s e e s t e r s , f o r m i n g 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 f r o m c o m m e r c i a l 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 c i z e r s .

T a b l e I I . Sucrose Esters

Type of Octa-Ester Physical Nature Melting Point, °C

Acetate

Propionate

Isobutyrate

n-Butyrate

Valerate

2-Methyl butyrate

2-Ethyl hexanoate

Crystalline

Crystalline

Crystalline

Liquid

Liquid

Liquid

Liquid

45 64

To overcome t h e dilemma 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 d uced and i n v e s t i g a t e d . S e v e r a l o f t h o s e were f o u n d t o p r o d u c e v i s c o u s l i q u i d s w h i c h w o u l d 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 as a c o a t i n g s m o d i f i e r ( F i g u r e 1 ) . Of c o u r s e , t h e r e a r e many p o s s i b l e c o m b i n a t i o n s f r o m 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 g r o u p s . From a s t u d y o f t h i s f a c t o r , i t

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15. C O N E Y SAIB in Coatings 215

Figure 1

was d e t e r m i n e d t h a t between 2 and 3 a c e t y l , and 5 and 6 i s o b u t y r y l g r o u p s gave most d e s i r a b l e p r o p e r t i e s . I n 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 inhomo-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 .

T h i s h i g h - v i s c o s i t y , r e s i n o u s , m i x e d 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 p o l y m e r , g i v i n g h i g h e r s o l i d s w i t h o u t a p p r e c i a b l y l o w e r i 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 s e v e r a 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 e r e d i n t h e r e m a i n i n g 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

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216 SUCROCHEMISTRY

Figure 3

a p o l y m e r i c m a t e r i a l , i t i s a c t u a l l y a l a r g e , b u l k y 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 most c o a t i n g s m o d i f i e r s have a d e g r e e 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 , t h e e s t e r i f i c a t i o n o f a l l o f t h e h y d r o x y l g r o u p s on s u c r o s e changes 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) and 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 t o t h e h i g h d e g r e e o f c o n v e r s i o n t o t h e e s t e r .

The h y d r o p h o b i c i t y o f SAIB ca n be i l l u s t r a t e d by i t s h i g h c o n t a c t a n g l e w i t h w a t e r . 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 v e r y s t a b l e i n t h e p r e s e n c e o f w a t e r . We f o u n d , i n t h e e a r l y work, t h a t , as 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 t h e r a t i o o f i s o b u t y r y l t o 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% by 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 by an i n c r e a s e i n t e m p e r a t u r e ( F i g u r e 4 ) . As an e xample, 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 100,000 c p s a t 25°C can be r e duced t o 1,000 c p s a t 68°C, o r t o 100 c p s a t 100°C. A t e l e v a t e d t e m p e r a t u r e s , t h e 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 even s o l v e n t f o r some p o l y m e r s . T h i s 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 a d h e s i v e s .

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20 40 60 80 100 120 140 160 Temperature, °C

Figure 4. Viscosity of SAIB as influenced by temperature

I n t o d a y ' s need t o r e d u c e 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 t h e p r o d u c t s u i t i t p 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 c o a t i n g s ; t h e s e a r e : l o w 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 c o n c e n t r a t i o n a t h i g h l e v e l s o f t h e p r o d u c t , b u t i s r e l a t i v e l y u n a f f e c t e d a t low 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 p r o d u c e d by t h e a d d i t i o n o f 10% s o l v e n t . L i k e w i s e , f a i r l y h i g h l e v e l s o f t h e e s t e r may be u s e d w i t h some p o l y m e r s w i t h o u t a p p r e c i a b l y a f f e c t i n g f i l m h a r d n e s s ( F i g u r e 6 ) . As an example, up t o 50% SAIB may be 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 n e s s . 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 p r o d u c e a s u r f a c e h a r d n e s s g r e a t e r t h a n t h a t o f t h e unm o d i f i e d f i l m . T h e r e f o r e , b e c a u s e o f t h i s f i l m h a r d n e s s e f f e c t and t h e l o w 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 as an e x t e n d e r t o i n c r e a s e c o a t i n g s s o l i d s .

SAIB has been 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 p a p e r ( F i g u r e 7 ) .

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1 I I I I I I I I

100 90 80 70 60 50 40 30 SAIB, Wt. %

Figure 5. Solution viscosity of SAIB in typical coatings solvents

Figure 6. Effect of SAIB on cellulose ester film hardness

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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 f r o m 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 i n d e x 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 " d i s a p p e a r " as t h e e s t e r s u r r o u n d s and r e d u c e s t h e l i g h t r e f l e c t e d f r o m t h e f i b e r ' s s u r f a c e .

T a b l e I I I . R e f r a c t i v e I n d e x n 2 0 °

SAIB - 1.454 COTTON - 1.555 JUTE - 1.536

S e c o n d l y , SAIB has l o w v o l a t i l i t y e ven 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) and t h u s p r o v i d e s a v e r y permanent d e g r e e o f t r a n s p a r e n c y t o t h e p a p e r . 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 has much l e s s w e i g h t l o s s a t tempe r a t u r e s as h i g h a s 171°C.

T h i r d l y , 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 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 e x p o s u r e t o h e a t and u l t r a v i o l e t l i g h t , a d d i n g t o t h e q u a l i t y o f t h e t r a n s p a r e n t i z e d p a p e r . D e s p i t e i t s l i q u i d f o r m , when us e d a t t h e c o r r e c t l e v e l , t h e e s t e r g i v e s a d r y f e e l t o t h e p a p e r .

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220 SUCROCHEMISTRY

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 and 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 an 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 u s e d t o t i n t t h e s e s y s t e m s . The e s t e r c a n be used as 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 t e c h n i q u e s . 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 pig m e n t cake (55) .

I n t h e wet p i g m e n t ca k e f l u s h i n g method, 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 has been f o u n d t o be much more e f f i c i e n t t h a n o t h e r m e d i a s u c h 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)• V e r y l i k e l y , t h e 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 pig m e n t 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 t o 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 be 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 an HLB v a l u e o f 14, T a b l e I V . The e s t e r i s h e a t e d t o about 70°C and 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 an o i l - i n -w a t e r - t y p e e m u l s i o n h a v i n g 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 as 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 be 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).

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15. CONEY SAIB in Coatings 221

T a b l e I V . SAIB E m u l s i o n F o r m a t i o n

I n g r e d i e n t s SAIB S u r f a c t a n t Water

W e i g h t % 40 5

55 100

The p r o d u c t has 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 i n g a d h e s i o n t o s e v e r a l p l a s t i c s u r f a c e s . I t c a n 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 molded o r e x t r u d e d c e l l u l o s e a c e t a t e , c e l l u l o s e a c e t a t e b u t y r a t e , n y l o n and a c r y l i c s , and t o c e l l o p h a n e and 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 w i d e 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 be us 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 b o t h f o r i n d o o r 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 f o r u se i n c o a t i n g s . I t s v e r s a t i l i t y e x t e n d s i n t o s e v e r a l o t h e r f i e l d s . I t i s used 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 i m p r o v e d m i l l i n g p r o p e r t i e s and 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 s p e c i a l 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 as 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 s u s p e n s i o n 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 an 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 , c o s m e t i c s , p h o t o g r a p h i c f i l m ( 1 0 ) , and p e r f u m e s .

A m a t e r i a l as u n i q u e as t h i s s u g a r e s t e r i s c e r t a i n t o f i n d use 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 isobuty-rate (SAIB) is its capability of extending polymers to

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222 SUCROCHEMISTRY

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, trans-parentized paper, pigment dispersions and soft drinks. Literature Cited 1. Touey, G.P., Davis, H.E., U.S. Patent 2,931,802,

Apri l , 1960. 2. Gearhart, W.M., Bal l , F.M., U.S. Patent No. 3,076,

718. February, 1963. 3. Scott, J.R., Roff, W.J., "Handbook of Common

Polymers," page 134, CRC Press, 1971. 4. Coney, C.H., American Ink Maker, (1966).

XLIV, (3). 5. Coney, C.H., Draper, W.E., U.S. Patent 3,318,714,

May, 1967. 6. Coney, C.H., Draper, W.E., Defensive Publication

745,090, December, 1968. 7. Coney, C.H., American Ink Maker, (1969), XLVII,

(1). January. 8. Gearhart, W.M., Wilson, E.W., SPE Journal, (1960),

16, (10). 9. British Patent No. 1,118,019 (Aktieselskabet Co-

Ro), June, 1968. 10. 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.

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[acs symposium series] sucrochemistry volume 41 || saib in coatings

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