Latex Emulsions with Concrete - ACS Symposium Series (ACS

7 Latex Emulsions with Concrete PHILIP MASLOW

Downloaded by COLUMBIA UNIV on April 16, 2013 | http://pubs.acs.org Publication Date: November 27, 1979 | doi: 10.1021/bk-1979-0113.ch007

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PART A - THEORY OF EMULSIONS Emulsions are intimate mixtures of two immiscible l i q u i d s , one of them being dispersed i n the other i n the form of fine d r o p l e t s . A mixture of two miscible l i q u i d s , e . g . , water and a l c o h o l , or oil and kerosene, w i l l not produce an emulsion, but a more intimate degree of d i s p e r s i o n : a s o l u t i o n . On the other hand, it i s not possible to form an emulsion with two immiscible l i q u i d s alone, since such a system would lack the important f a c t o r of stability. In shaking s t r a i g h t water with toluene, f o r instance, the two l i q u i d s will separate immediately when shaking i s discontinued. The conditions change completely when a d i l u t e soap s o l u t i o n , instead of s t r a i g h t water, i s used and it is shaken with an oil. In doing so, a milky l i q u i d develops, which remains i n t h i s state without separating for a considerable length of time. Then, a typical emulsion i s formed. Therefore, three components are necessary to produce emulsions: two immiscible l i q u i d s , and a substance which helps to promote the emulsion and to keep it stable, i.e., the emulsifying agent, o r e m u l s i f i e r . To the naked eye, emulsions appear as uniform, opaque l i q u i d s or pastes of white or s l i g h t l y yellowish c o l o r . The microscope reveals that emulsions are by no means uniform substances. They are non-uniform and consist of a multitude of small d r o p l e t s , usually of s p h e r i c a l shape, and varying diameters, f l o a t i n g in the surrounding liquid. Emulsions with p a r t i c l e s 0-8412-0523-X/79/47-113-079$05.50/0 © 1979 American Chemical Society

In Plastic Mortars, Sealants, and Caulking Compounds; Seymour, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.


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of l a r g e d i a m e t e r are c a l l e d c o a r s e e m u l s i o n s , and those w i t h s m a l l p a r t i c l e s are f i n e e m u l s i o n s . The p a r t i c l e s and the l i q u i d s i n which they f l o a t are c a l l e d t h e phases o f an e m u l s i o n . The p a r t i c l e s are r e f e r r e d t o as the d i s c o n t i n u o u s phase, and the medium which i s the d i s p e r s i o n l i q u i d i s c a l l e d the c o n t i n u ous phase. A l s o , s i n c e the d r o p l e t s o f t h e d i s c o n t i n u ous phase are e n c l o s e d from a l l s i d e s , i t i s a l s o c a l l e d the i n t e r n a l phase, and the c o n t i n u o u s phase i s a l s o c a l l e d t h e e x t e r n a l phase. In the m a j o r i t y o f a l l e m u l s i o n s , one o f the phases i s water, o r an aqueous s o l u t i o n c o n t a i n i n g s a l t s , soluble organic material, c o l l o i d s , e t c . This i s a l s o c a l l e d the w a t e r phase. The o t h e r phase, t h e p a r t i c l e s o r d r o p l e t s , i s c a l l e d t h e o i l phase, even i f i t does not c o n s i s t o f o i l . Many s u b s t a n c e s c o n s t i t u t e the o i l phase, a l l h a v i n g one i m p o r t a n t common p r o p e r t y ; namely, t h e i r i n s o l u b i l i t y i n w a t e r . These may i n c l u d e h y d r o c a r b o n s , r e s i n s , waxes, n i t r o c e l l u l o s e , allcyds, r u b b e r , v i n y l s and a c r y l i c s . They are r e f e r r e d t o as " o i l " s i n c e t h e y behave i n e m u l s i o n s v e r y much l i k e o i l . The s u b s t a n c e s u s e d i n e m u l s i o n s may be c l a s s i f i e d i n t o two g r o u p s : t h o s e which e n t e r the w a t e r phase, and t h o s e w h i c h go i n t o t h e o i l phase. The f i r s t group making up t h e aqueous p o r t i o n , must be wat e r s o l u b l e , o r show a c e r t a i n a f f i n i t y toward w a t e r . T h i s group has t h e g e n e r a l name o f h y d r o p h i l i c subs t a n c e s (from t h e Greek "hydor", water, and " p h i l o s " , loving). The o t h e r group o f s u b s t a n c e s which go i n t o the o i l phase have no a f f i n i t y f o r water, are w a t e r r e p e l l e n t , b u t show marked a t t r a c t i o n t o o i l o r o i l like material. They are known as h y d r o p h o b i c subs t a n c e s (from "phobos", f e a r i n g ) . T y p i c a l h y d r o p h i l i c s u b s t a n c e s are w a t e r - s o l u b l e compounds, many m e t a l s a l t s , and s u b s t a n c e s c o n t a i n i n g a r e l a t i v e l y l a r g e number o f oxy- o r h y d r o x y l g r o u p s . T y p i c a l h y d r o p h o b i c s u b s t a n c e s are o i l s , f a t s , waxes and a l l compounds c o n t a i n i n g m a i n l y c a r b o n w i t h few o r no p o l a r g r o u p s . T h i s d i f f e r e n c e i s i m p o r t a n t i n the s e l e c t i o n o f o t h e r m a t e r i a l s which w i l l be b l e n d e d w i t h the e m u l s i o n , s u c h as pigments, f i l l e r s , cement, sand, and a l l o t h e r i n g r e d i e n t s which may go i n t o t h e making o f a c o n c r e t e o r m o r t a r .



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W i t h any g i v e n p a i r o f i m m i s c i b l e l i q u i d s , two types o f emulsions are p o s s i b l e . One i s t h a t i n which w a t e r i s t h e e x t e r n a l , and o i l , t h e i n t e r n a l phase, known as o i l - i n - w a t e r e m u l s i o n , o r w a t e r o u t s i d e emuls i o n (o/w). The o t h e r t y p e , w i t h o i l as e x t e r n a l , and w a t e r as t h e i n t e r n a l phase, i s known as w a t e r - i n - o i l e m u l s i o n , o r o i l o u t s i d e e m u l s i o n (W/o). I f an emuls i o n c o n t a i n s 50% water o r o t h e r aqueous s o l u t i o n , and 50% o i l o r o i l - l i k e s u b s t a n c e , i t i s p o s s i b l e t o p r o duce an O/W o r a W/O e m u l s i o n , which w i l l show t h e same p e r c e n t c o m p o s i t i o n b u t , n e v e r t h e l e s s , be two e n t i r e l y d i f f e r e n t emulsions. T h i s a l l depends on the method o f e m u l s i f i c a t i o n , t h e e m u l s i f y i n g agent, the s o l u b l e m a t e r i a l s i n t h e w a t e r phase, and t h e f i n e n e s s of p a r t i c l e s . The c h a r a c t e r i s t i c p r o p e r t i e s o f an e m u l s i o n are d i c t a t e d by t h e e x t e r n a l phase. I f water i s the e x t e r n a l phase (O/W), t h e e m u l s i o n may be d i l u t e d w i t h w a t e r and not w i t h o i l o r o r g a n i c s o l v e n t s . Just the o p p o s i t e i s t h e case w i t h a W/o e m u l s i o n , where t h e o i l i s t h e e x t e r n a l phase, and i t c a n be t h i n n e d w i t h organic solvents. S h o u l d w a t e r be added t o t h i s type o f e m u l s i o n , t h e v i s c o s i t y w i l l i n c r e a s e . T h i s i s one way o f v i s u a l l y d i s t i n g u i s h i n g between the two t y p e s . The t h i n n i n g method, u s i n g water, w i l l i n d i c a t e an o i l in-water emulsion i f the v i s c o s i t y i s reduced. If visc o s i t y i s i n c r e a s e d , i t would i n d i c a t e a w a t e r - i n - o i l emulsion. There a r e many t y p e s o f e m u l s i f y i n g agents which are used i n p r e p a r i n g e m u l s i o n s . As i n d i c a t e d , t h e y f a c i l i t a t e the e m u l s i f i c a t i o n and impart s t a b i l i t y t o the p r e p a r e d e m u l s i o n . Chemically, they belong t o d i f f e r e n t c l a s s e s o f compounds among w h i c h a r e s a l t s , a c i d s , b a s e s , and e s t e r s . P h y s i c a l l y , t h e y a r e subs t a n c e s o f medium m o l e c u l a r weight (above 300), and the m o l e c u l e s a r e o f e l o n g a t e d shape and b e l o n g t o t h e mixed p o l a r : n o n - p o l a r t y p e . These e m u l s i f y i n g agents have a v e r y d e f i n i t e b e a r i n g on t h e type o f e m u l s i o n produced and t h e p a r t i c l e s i z e o f the d i s p e r s e d d r o p lets. The e m u l s i o n s w h i c h a r e g e n e r a l l y u t i l i z e d i n cementitious compositions are o f the o i l - i n - w a t e r t y p e , h a v i n g a t l e a s t 50% w a t e r i n the c o m p o s i t i o n , a l t h o u g h some have l e s s than 50% water, and a r e s t i l l


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o i l - i n - w a t e r e m u l s i o n , and are s t a b l e i n the presence o f the v a r i o u s s a l t s and o x i d e s c o m p r i s i n g the make-up o f cement. Not a l l e m u l s i o n s are c o m p a t i b l e w i t h cem ent and i t would be a mistake to s e l e c t an e m u l s i o n which i s p r i m a r i l y i n t e n d e d f o r p r o d u c t i o n o f p a i n t o r a d h e s i v e s t o a c t as an admixture f o r a cement i t i o u s mortar.


PART Β - BUTADYENE STYRBNE LATICES As a r e s u l t o f the s y n t h e t i c rubber program i n s t i t u t e d d u r i n g World War I I , because o f the l a c k o f n a t u r a l rubber, methods f o r p r o d u c i n g s y n t h e t i c rubber were d e v e l o p e d which were b a s e d on the e m u l s i f i c a t i o n of d i f f e r e n t types o f l a t i c e s . Butadyene was, o f c o u r s e , the b a s i s f o r the s y n t h e t i c r u b b e r i n d u s t r y as a r e s u l t o f t h e s e programs. S t y r e n e was a m a t e r i a l i n p l e n t i f u l s u p p l y and was low i n c o s t . P o l y s t y r e n e , which i s a polymerized styrene, i s a hard m a t e r i a l which r e q u i r e s p l a s t i c i z i n g . I t may be p l a s t i c i z e d by one o f t h r e e ways: I n t e r n a l l y , where the p l a s t i c i z e r i s p a r t o f the c o p o l y m e r i c m o l e c u l e ; p r e - p l a s t i c i z e d , where the p l a s t i c i z e r i s added d u r i n g the p o l y m e r i z a t i o n ; p o s t - p l a s t i c i z e d , where the p l a s t i c i z e r i s emul s i f i e d s e p a r a t e l y and added t o the l a t e x . Polystyrene may be p l a s t i c i z e d i n t e r n a l l y by c o p o l y m e r i z i n g w i t h a r e a c t i v e monomer, such as butadyene. In the v a r i o u s e m u l s i o n s a v a i l a b l e , s t y r e n e c o n t e n t may be as h i g h as 85% w i t h the butadyene about 15%. The use o f b u t a d y ene i n t r o d u c e s a s m a l l amount o f u n s a t u r a t i o n i n the polymer which i s s u b j e c t t o o x i d a t i o n on a g i n g , w i t h p o s s i b l e h a r d e n i n g and y e l l o w i n g . The butadyene s t y r e n e l a t i c e s which are compa t i b l e w i t h c e m e n t i t i o u s compounds are copolymers. Ty p i c a l p h y s i c a l p r o p e r t i e s are g i v e n i n T a b l e 1. F o r purposes o f s i m p l i c i t y , the butadyene s t y rene l a t i c e s w i l l be r e f e r r e d t o as SBR l a t i c e s . Those w h i c h are c o m p a t i b l e w i t h cement, show e x c e l l e n t s t a b i l i t y i n the presence of such m u l t i v a l e n t c a t i o n s as c a l c i u m and aluminum. They are u n a f f e c t e d by the a d d i t i o n o f r e l a t i v e l y l a r g e amounts o f e l e c t r o l y t e s , such as sodium c h l o r i d e , c a l c i u m c h l o r i d e and h y d r o c h l o r i c acid. The SBR l a t i c e s may c o a g u l a t e i f s u b j e c t e d f o r


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l o n g p e r i o d s o f time t o h i g h t e m p e r a t u r e s , f r e e z i n g temperatures o r s e v e r e m e c h a n i c a l a c t i o n . They a r e not s t a b l e t o most a i r - e n t r a i n i n g a g e n t s , and t h e y s h o u l d n o t be used i n c o m b i n a t i o n w i t h a i r - e n t r a i n i n g cements.


T a b l e 1.

P r o p e r t i e s o f Butadyene S t y r e n e L a t e x

Percent S o l i d s Specific Gravity Weight p e r g a l l o n (pounds) pH P a r t i c l e S i z e Range (angstroms) V i s c o s i t y a t 25°C ( c e n t i p o i s e )

48 1.01 8.4 1°1900-2100 10-12

S u r f a c e T e n s i o n a t 25°C (dynes/Square cm.) T e n s i l e Strength (psi) E l o n g a t i o n (percent)

30-32 745 650

5

Structures Publishing Company

Suggested f o r m u l a t i o n s have been g i v e n f o r l a tex f o r t i f i e d cement m o r t a r s , used f o r t o p p i n g s and p a t c h i n g compounds, The r a t i o s o f sand t o P o r t l a n d cement a r e g e n e r a l l y 3:1; t h e p e r c e n t a g e o f l a t e x s o l i d s t o cement may range from 5%-20%, and the water/cement r a t i o may range from 0.35-0.50. i f t h e water/cement r a t i o i s t o o h i g h , f l o t a t i o n o f l a t e x s o l i d s may o c c u r , c a u s i n g the l a t e x p a r t i c l e s t o be unevenly d i s t r i b u t e d t h r o u g h t h e mix. There i s a d e f i n i t e d i f f e r e n c e i n r e s u l t s between wet cure and a i r - d r y c u r e . G e n e r a l l y , wet c u r e s o f unmodif i e d mixes g i v e b e s t p r o p e r t i e s , and a i r - d r y c u r e s o f l a t e x - m o d i f i e d mixes g i v e b e s t p r o p e r t i e s . S e t t i n g time o f an SBR m o d i f i e d cement composit i o n i s d e l a y e d . However, i n a c t u a l use, such mortar t o p p i n g s may o f t e n be walked on i n 12 t o 18 h o u r s , and may take l i g h t r u b b e r t i r e t r a f f i c i n 48 h o u r s . These times w i l l v a r y , depending upon t h e temperature, h u m i d i t y and t h e p e r c e n t a g e o f l a t e x i n the mix. T a b l e 2 shows the s e t t i n g time f o r SBR l a t e x / c e m e n t compositions .


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T a b l e 2.

S E A L A N T S ,

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S e t t i n g Time f o r SBR Latex/Cement

Latex/Cement Ratio 0.10 0.20 No L a t e x

M O R T A R S ,

Wa te r/Ceme nt Ratio 0.45 0.45 0.45

I n i t i a l Set (Hours) 6 5.5 2

F i n a l Set (Hours) 9 10 5



Water i n the l a t e x i s always i n c l u d e d i n the w a t e r / cement r a t i o . When t h e water/cement r a t i o i s r a i s e d and the l a t e x / c e m e n t r a t i o remains c o n s t a n t , t h e i n i t i a l and f i n a l s e t times a r e f u r t h e r d e l a y e d . In compressive s t r e n g t h development, the l a t e x m o d i f i e d m o r t a r s always have h i g h e r compressive s t r e n g t h s than the unmodified mortars, i n dry c u r e . A d d i t i o n s o f l a t e x t o a r a t i o g r e a t e r than 0.20 reduces compressive s t r e n g t h and i s e x p e n s i v e . T e n s i l e s t r e n g t h f o r SBR l a t e x m o d i f i e d m o r t a r s may average about 570 p s i . The t e n s i l e s t r e n g t h f o r wet c u r e d u n m o d i f i e d m o r t a r s i s about 410 p s i . I n g e n e r a l , t e n s i l e s t r e n g t h i s h i g h e r f o r the SBR modif i e d m o r t a r than f o r t h e u n m o d i f i e d m o r t a r u n d e r any c o n d i t i o n s o f c u r e . The h i g h e s t t e n s i l e s t r e n g t h i s o b t a i n e d a t the 0.20 l a t e x / c e m e n t r a t i o . F l e x u r a l s t r e n g t h f o r an SBR l a t e x m o d i f i e d mort a r may average 1650 p s i . F l e x u r a l s t r e n g t h f o r wet c u r e d u n m o d i f i e d m o r t a r i s about 810 p s i . These a r e f i g u r e s f o r a 0.20 l a t e x c e m e n t / r a t i o . At a 0.10 r a t i o , the f l e x u r a l s t r e n g t h s are about e q u a l . Bond s t r e n g t h f o r an SBR l a t e x m o d i f i e d m o r t a r i s about 580 psi. Bond s t r e n g t h f o r an u n m o d i f i e d P o r t l a n d cement m o r t a r i s about 250 p s i . The bond s t r e n g t h o f t h e m o d i f i e d m o r t a r s i s always h i g h e r t h a n t h a t f o r the u n m o d i f i e d m o r t a r under any c u r i n g c o n d i t i o n s . A n t i - f o a m agents are almost always used i n SBR l a t e x m o d i f i e d cement c o m p o s i t i o n s because t h e y i n c r e a s e mix d e n s i t y by m i n i m i z i n g a i r - e n t r a i n m e n t , thereby upgrading p h y s i c a l p r o p e r t i e s . Anti-foam agents may be added t o the SBR l a t e x b y the manufact u r e r o f the l a t e x and a d d i t i o n a l amounts may be a d ded by the f o r m u l a t o r o f the f i n a l c e m e n t i t i o u s m o r t a r c o m p o s i t i o n . The amount o f a n t i - f o a m added may range from 0.1% a n t i - f o a m s o l i d s on l a t e x s o l i d s up t o 3.5%.



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Some a n t i - f o a m m a t e r i a l s are b a s e d on s i l i c o n e r e s i n s , o t h e r s are b a s e d on p e t r o l e u m o i l s , and a l l o f them are i n t e n d e d t o d e p r e s s t h e s u r f a c e t e n s i o n o f t h e l a t e x e m u l s i o n . The a n t i - f o a m agents d e l a y the e n t r a p ment o f a i r i n mixes which i s always a p o s s i b i l i t y when m i x i n g l i q u i d s and s o l i d s , such as a m o r t a r i n a ceme n t m i x e r . T h i s r e s u l t s i n a d e n s e r m o r t a r which h a s b e t t e r abrasion r e s i s t a n c e , b e t t e r r e s i s t a n c e t o water a b s o r p t i o n , and h i g h e r c o m p r e s s i v e , t e n s i l e and bond strengths. M i x i n g o f a l l l a t e x m o d i f i e d cement c o m p o s i t i o n s s h o u l d be h e l d t o a minimum, i n any c i r c u m s t a n c e . A n t i foam agents c a n l o s e t h e i r e f f i c i e n c y i f they are o v e r mixed. They t e n d t o become e m u l s i f i e d a f t e r c o n t i n u o u s s h e a r a c t i o n and they no l o n g e r g i v e adequate p e r f o r m ance. I t has a l r e a d y been i n d i c a t e d t h a t SBR l a t i c e s are s t a b l e and are u n a f f e c t e d by t h e a d d i t i o n o f l a r g e amounts o f c a l c i u m c h l o r i d e . T h i s i s an i n d i c a t i o n t h a t c a l c i u m c h l o r i d e may be used w i t h an SBR l a t e x m o d i f i e d m o r t a r i n t h e same way t h a t i t i s used w i t h an u n m o d i f i e d cement m o r t a r . In g e n e r a l , t h e a d d i t i o n o f 2% c a l c i u m c h l o r i d e , b a s e d on the P o r t l a n d cement, improves t h e e a r l y compressive s t r e n g t h development, from 24 h o u r s t o 7 days. The w a t e r v a p o r t r a n s m i s s i o n c h a r a c t e r i s t i c s o f an SBR l a t e x m o d i f i e d m o r t a r are t w i c e as good as t h o s e o f an u n m o d i f i e d m o r t a r . The w a t e r v a p o r t r a n s m i s s i o n r a t e , as measured i n g r a i n s / s q u a r e foot/hour/inches mercury i s as f o l l o w s : U n m o d i f i e d Cement M o r t a r

WVTR = 9.9

SBR Latex/Cement M o r t a r (0.20 r a t i o )

WVTR = 4.1

PART C - POLYVINYL ACETATE LATICES The v i n y l r a d i c a l i s d e s i g n a t e d c h e m i c a l l y as CH2= CH-7 t h e r e f o r e , t h e term " v i n y l r e s i n s " c o u l d be a p p l i e d t o s u b s t i t u t e d e t h y l e n e s and t h e i r many c o p o l y m e r s . Among t h e s e c a n be i n c l u d e d p o l y e t h y l e n e , polystyrene, p o l y v i n y l chloride, p o l y v i n y l acetate, a c r y l i c e s t e r s , m e t h a c r y l i c e s t e r s and even some o f



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t h e s y n t h e t i c r u b b e r s , such as i s o p r e n e . V i n y l r e s i n s are c h i e f l y copolymers r a t h e r than homopolymers. Homopolymers are polymers i n which the monomeric u n i t s are a l l identical. T y p i c a l examples are p o l y v i n y l c h l o r i d e , p o l y v i n y l a c e t a t e and p o l y s t y r e n e . Copolymers are polymers i n which the monomeric u n i t s are d i f f e r e n t . T y p i c a l examples are p o l y v i n y l c h l o r i d e - p o l y v i n y l acetate resins, p o l y v i n y l c h l o r i d e - a c r y l o n i t r i l e res i n s , and p o l y s t y r e n e - b u t a d i e n e r e s i n s . However, comm e r c i a l v i n y l r e s i n s u s u a l l y c o n t a i n a s m a l l percentage o f a m o d i f y i n g r e s i n , s u c h as an a c i d o r an a c i d anhyd r i d e , which i s d i s t r i b u t e d randomly i n the polymer c h a i n s . The amount o f t h e s e m o d i f y i n g m a t e r i a l s i s r e l a t i v e l y s m a l l so t h e y may be c o n s i d e r e d copolymers. The p a r t i c u l a r v a l u e o f the c o p o l y m e r i z a t i o n t e c h n i q u e i s t h a t the p r o p e r t i e s o f the copolymer r e s i n s may be v a r i e d o v e r a wide range by a d j u s t i n g the type and amount o f the v a r i o u s monomers used i n t h e i r f o r m u l a tion. V i n y l r e s i n s are p o l y m e r i z e d and c o p o l y m e r i z e d c o m m e r c i a l l y by f o u r d i f f e r e n t p r o c e s s e s : b u l k , s o l v e n t , s u s p e n s i o n and e m u l s i o n . The e m u l s i o n p o l y m e r i z a t i o n p r o c e s s i s w i d e l y used i n the manufacture o f vinyl resins. In t h i s p r o c e s s , the monomer i s e m u l s i f i e d i n water, u s i n g a s u i t a b l e e m u l s i f y i n g agent. Of c o u r s e , the monomer must be s u b s t a n t i a l l y i n s o l u b l e i n w a t e r i n o r d e r t o o b t a i n a good e m u l s i o n . After polym e r i z a t i o n i s e s s e n t i a l l y complete, the e m u l s i o n may be b r o k e n and the r e s i n c o a g u l a t e d , washed and d r i e d ; or s u i t a b l e protective c o l l o i d s , buffers, corrosion i n h i b i t o r s , f u n g i c i d e s , e t c . may be added t o produce a s t a b l e l a t e x o f the p o l y m e r i c r e s i n . Non-Reemulsifiable

P o l y v i n y l Acetate

Latex

In p r o d u c i n g a p o l y v i n y l a c e t a t e l a t e x f o r use w i t h cement, the e m u l s i o n p o l y m e r i z a t i o n p r o c e s s i s utilized. A s m a l l p e r c e n t a g e , about 1%, o f a subs t a n c e l i k e m a l e i c a c i d i s added i n the p o l y m e r i z a t i o n r e a c t i o n so t h a t a copolymer i s formed. M a l e i c a c i d , i t s e l f , has an e t h y l e n i c type o f u n s a t u r a t i o n , b u t i t does not form homopolymers. S i n c e the amount i n t r o duced i s so s m a l l , the r e s u l t a n t polymer i s a c o p o l y mer. The i n t r o d u c t i o n o f the h i g h l y p o l a r c a r b o x y l


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groups on m a l e i c a c i d improves t h e a d h e s i o n c h a r a c t e r i s t i c s o f the p o l y v i n y l acetate. J u s t as t h e p o l y s t y r e n e - b u t a d i e n e r e s i n s a r e g e n e r a l l y r e f e r r e d t o as SBR r e s i n s , the p o l y v i n y l acetate resins are g e n e r a l l y r e f e r r e d t o as PVA r e s i n s . T y p i c a l p h y s i c a l p r o p e r t i e s o f a p o l y v i n y l acet a t e copolymer e m u l s i o n s u i t a b l e f o r use w i t h cement are g i v e n i n T a b l e 3.


T a b l e 3.

Properties

o f P o l y v i n y l Acetate Latex

Percent s o l i d s pH Weight/gal. Emulsion (lbs.) Weight/gal. S o l i d s (lbs.) Average P a r t i c l e S i z e F r e e Monomer Content Odor Borax Compatible P a r t i c l e Charge

52 410-6.5 8.9 9.76 Less than 2 Microns L e s s t h a n 1% Slight No Negative Structures Publishing Company

T h i s PVA l a t e x l e a v e s a d r i e d f i l m which i s f l e x i b l e w i t h o u t t h e a d d i t i o n o f a p l a s t i c i z e r . The f i l m has e x c e l l e n t w a t e r r e s i s t a n c e , l i g h t s t a b i l i t y , good a g i n g c h a r a c t e r i s t i c s and good f i l m c o n s o l i d a t i o n . T h i s p a r t i c u l a r PVA l a t e x may be used as a f i l m formi n g b i n d e r i n a water-based emulsion p a i n t . Its part i c u l a r c h a r a c t e r i s t i c s o f c o m p a t i b i l i t y w i t h cement have l e d t o wide uses o f t h i s l a t e x as an a d h e s i v e and an admixture f o r c e m e n t i t i o u s m o r t a r s and c o n c r e t e . There a r e a v a r i e t y o f d i f f e r e n t a p p l i c a t i o n s f o r a l l l a t e x e m u l s i o n s as b o n d i n g agents and admixtures. Some t y p e s have a g r e a t e r degree o f w a t e r r e s i s t a n c e than o t h e r s ; and, o f c o u r s e , t h e r e i s a wide range o f c o s t f a c t o r s . F o r purposes o f p r e s e n t a t i o n , i t i s assumed t h a t a l l t y p e s a r e u t i l i z e d a t about 4550% s o l i d s c o n t e n t . Re-emulsifiable

P o l y v i n y l Acetate Latex

In t h e d e s c r i p t i o n s o f PVA l a t i c e s , a l l t h e p r o p e r t i e s d e s c r i b e d a r e b a s e d on the f a c t t h a t t h e s e l a t i c e s , as w e l l as t h e SBR l a t i c e s , and t h e a c r y l i c l a t i c e s , are e s s e n t i a l l y non-reemulsifiable. When



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l a t i c e s were f i r s t d e v e l o p e d and used i n f o r m u l a t i n g p a i n t s , one o f the c h a r a c t e r i s t i c s t h a t was o b j e c t i o n a b l e was the l o n g p e r i o d o f time which had t o e l a p s e b e f o r e p a i n t f i l m s , c a s t from the o r i g i n a l SBR l a t i c e s , had c o a l e s c e d o r d r i e d enough t o be "washable." Sometimes, t h i s p e r i o d l a s t e d f o r as l o n g as s i x weeks. As p r o g r e s s was made i n p r o d u c i n g these l a t i c e s , p r o d u c t s were soon a v a i l a b l e on the market which produced f i l m s which c o u l d be washed i n v e r y q u i c k o r d e r . Where l a t i c e s are used as b o n d i n g agents i n themselves, an o b v i o u s problem d e v e l o p s . This i n v o l v e s the r a p i d d r y i n g o f a f i l m c a s t from a l a t e x c r e a t i n g a s i t u a t i o n whereby a subsequent placement o f a cement m o r t a r o r c o n c r e t e would not bond t o a d r i e d f i l m o f l a t e x . As an example, s h o u l d a f l o o r a r e a be t r e a t e d w i t h a l a t e x b o n d i n g agent i n i t s e n t i r e t y bef o r e the a p p l i c a t i o n o f a new c e m e n t i t i o u s t o p p i n g , the l a t e x f i l m would have d r i e d i n the f i r s t p a r t o f the area b e f o r e the l a s t p a r t o f the area had been coated. S i n c e the l a t e x f i l m becomes c o m p a r a t i v e l y h a r d , smooth and g l o s s y , the a d h e s i o n o f the subsequent t o p p i n g would be l e s s t h a n adequate. O t h e r t h a n by the method o f p r e p a r i n g a n e a t cement s l u r r y , u t i l i z i n g the l a t e x as p a r t of the gaugi n g water, t o p r o v i d e a b o n d i n g medium, t h e r e was one method a v a i l a b l e by which a l a t e x c o u l d be m o d i f i e d t o be u s e f u l as a f i l m - f o r m i n g b o n d i n g agent. T h i s i n v o l v e d m o d i f y i n g a l a t e x so t h a t i t would be r e e m u l s i f i a b l e , i . e . , a b l e t o be s o f t e n e d and r e t a c k i f i e d upon c o n t a c t w i t h a w a t e r - c o n t a i n i n g medium. Such a l a t e x would permit a p p l i c a t i o n o f a f i l m t o a s u r f a c e l o n g b e f o r e the subsequent a p p l i c a t i o n o f a water-based o v e r l a y . T h i s f i l m , o f c o u r s e , would dry, and r e semble a d r i e d f i l m o f a n o n - r e e m u l s i f i a b l e l a t e x . However, the d i f f e r e n c e would be t h a t t h i s f i l m would be r e s o f t e n e d upon c o n t a c t w i t h water, whereas the f i l m c a s t from the n o n - r e e m u l s i f i a b l e l a t e x would be a f f e c t e d very s l i g h t l y , i f at a l l . A f i l m c a s t from a r e e m u l s i f i a b l e l a t e x would have a t h i c k n e s s o f about one m i l , o r one t h o u s a n d t h o f an i n c h . A f i l m o f t h i s t h i c k n e s s would almost, o f n e c e s s i t y , have t o be a p p l i e d t o a smooth s u r f a c e i n order to leave a v i s i b l e f i l m . A p p l i c a t i o n t o a rough and/or porous s u r f a c e would r e s u l t i n the a b s o r p t i o n



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o f most o f t h e f i l m , l e a v i n g v e r y l i t t l e i n the g l u e l i n e as an a d h e s i v e , o f course, a f i r s t coat a p p l i c a t i o n c o u l d be used as a p r i m e r , f o l l o w e d by one o r more s u c c e e d i n g c o a t s which would n o t be absorbed. T h i s , o f c o u r s e , i s l a b o r i o u s and c o s t l y . T h e r e f o r e , a reemuls i f i a b l e l a t e x b o n d i n g agent i s n o t recommended f o r r e p a i r and maintenance, u n l e s s t h e s u r f a c e t o which i t i s a p p l i e d i s smooth. The most w i d e l y used a p p l i c a t i o n o f a r e e m u l s i f i a b l e PVA l a t e x i s as a b o n d i n g agent f o r p l a s t e r . I t i s used t o bond f i n i s h o r base c o a t gypsum, a c c o u s t i c a l o r P o r t l a n d cement p l a s t e r t o i n t e r i o r s u r f a c e s o f c u r e d c o n c r e t e c a s t i n p l a c e , s t o n e , u n g l a z e d t i l e , met a l , plywood, rock l a t h , p a i n t e d s u r f a c e s and even glass. The l a t e x b o n d i n g agent d r i e s q u i c k l y t o form a t h i n , f l e x i b l e f i l m with outstanding adhesive prop e r t i e s , p r o v i d i n g a permanent bond f o r p l a s t e r . I t i s g e n e r a l l y u n a f f e c t e d by t h e a l k a l i n i t y o f gypsum, l i m e p u t t y , o r P o r t l a n d cement mixes. I t i s r e s i s t a n t t o a c i d s , v i b r a t i o n , f r e e z i n g and thawing. The t e n s i l e and s h e a r s t r e n g t h s f a r e x c e e d those o f the mat e r i a l s w h i c h a r e bonded t o g e t h e r . T h i s type o f bondi n g agent found wide use i n t h e a p p l i c a t i o n o f t h i n f i l m , white f i n i s h p l a s t e r to c e i l i n g s o f h i g h r i s e b u i l d i n g s , e l i m i n a t i n g t h e need f o r s c r a t c h c o a t s and brown c o a t s . The a d h e s i v e r e p l a c e d the i n t e r m e d i a t e c o a t s and p r o v i d e d a s t r o n g e r bond f o r the w h i t e f i n ish plaster. U n f o r t u n a t e l y , t h e use o f p l a s t e r i n new c o n s t r u c t i o n h a s dwindled t o t h e p o i n t where the p l a s t e r i n g t r a d e s have almost d i s a p p e a r e d . Dry w a l l board i s b e i n g used almost e x c l u s i v e l y f o r w a l l s u r f a c e s . C e i l i n g s a r e now b e i n g p a i n t e d , t i l e d , s p r a y e d w i t h a c c o u s t i c a l m a t e r i a l s , o r are c o n s t r u c t e d as hung c e i l ings. About t h e o n l y members o f a s t r u c t u r e which a r e s t i l l b e i n g f i n i s h e d i n w h i t e p l a s t e r a r e columns and beams. The s u r f a c e t o be c o a t e d w i t h a r e e m u l s i f i a b l e PVA b o n d i n g agent s h o u l d be t h o r o u g h l y c l e a n , f r e e o f g r e a s e , d i r t and e f f l o r e s c e n c e . I f t h e a r e a i s c o a t e d w i t h w a t e r - s e n s i t i v e m a t e r i a l s , such as whitewash, c a l c i m i n e , o r p o o r l y bonded cement p a i n t , t h e s e must be removed. The a d h e s i v e i s a p p l i e d a t t h e r a t e o f 300 t o 400 square f e e t p e r g a l l o n . I t i s generally col o r e d t o e n a b l e the a p p l i c a t o r t o see what has been



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s p r a y e d . The f i l m which i s a p p l i e d has a low sheen which can be used as an i n d i c a t i o n o f adequate f i l m thickness. T h i s f i l m w i l l d r y and may be p l a s t e r e d i n as l i t t l e time as one h o u r . I t w i l l also retain i t s a d h e s i v e c h a r a c t e r i s t i c s and a b i l i t y t o be r e - e m u l s i f i e d f o r a p e r i o d as l o n g as 60 days, i n many c a s e s . However, i t i s a d v i s a b l e t o a p p l y p l a s t e r w i t h i n the f i r s t week a f t e r a p p l i c a t i o n o f the b o n d i n g agent. W i t h each s u c c e e d i n g p e r i o d o f time a f t e r t h i s f i r s t week, the a d h e s i v e q u a l i t i e s are reduced. Even though t h e r e i s a r e a c t i o n between the l i m e i n the p l a s t e r and the l a t e x f i l m , c a u s i n g i t t o s e t , the f i l m s t i l l r e t a i n s a degree o f s e n s i t i v i t y t o water. Therefore, i t i s i n d i c a t e d that these bonding agents not be used i n e x t e r i o r a p p l i c a t i o n s where w a t e r might r e s o f t e n the f i l m and l o o s e n the p l a s t e r . The same p r e c a u t i o n s would a p p l y i n u s i n g these a d h e s i v e s i n areas which might be s u b j e c t t o w a t e r damage, such as c e i l i n g s i n bathrooms o r k i t c h e n s where l e a k s might o c c u r from above. Figure 1 presents a t y p i c a l formulation f o r a ree m u l s i f i a b l e PVA l a t e x b o n d i n g agent. T h i s f o r m u l a t i o n i s based on a medium t o low m o l e c u l a r weight p o l y v i n y l a c e t a t e homopolymer which i s p l a s t i c i z e d e x t e r n a l l y to contribute to i t s re-emulsification properties. There are companies which make a v a i l a b l e a complete l a tex v e h i c l e which can be used d i r e c t l y w i t h l i t t l e o r no m o d i f i c a t i o n , e x c e p t the a d d i t i o n o f c o l o r and, poss i b l y , reduction o f s o l i d s content f o r cost reasons. G e n e r a l l y , a c o a l e s c i n g agent, i n the form o f a s o l v e n t , i s added t o the f o r m u l a so t h a t t h e r e w i l l be minimum d i f f i c u l t i e s i n f o r m i n g a c o n t i n u o u s f i l m a t low t e m p e r a t u r e s . Materials

Pounds/100 G a l l o n s

PVA Latex-homopolymer (NVM=55%) Chlorinated biphenyl Dipropylene g l y c o l dibenzoate Ammonium a c e t a t e C o l o r i n water d i s p e r s i o n Water Toluene

780 13 8 7 3 65 60 936 Structures Publishing Company

Figure 1.

Reemulsified PVA latex bonding agent


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T h i s f o r m u l a t i o n has a t o t a l s o l i d s c o n t e n t o f 4 9 % and i s a p p l i c a b l e ( i n i t s v i s c o s i t y ) b y s p r a y . O f c o u r s e , i t can a l s o be a p p l i e d by b r u s h and r o l l e r . T a b l e 4 p r e s e n t s some t y p i c a l p r o p e r t i e s o f t h i s bonding agent as t e s t e d i n accordance w i t h M i l i t a r y S p e c i f i c a t i o n MIL-B-19235 (Docks) Bonding Compound, Concrete. T a b l e 4,


Tensile

P r o p e r t i e s o f PVA L a t e x Bonding Agent

Strength

Specimens P.S.I. Neat cement 600 Ottawa sand mortar, 1:3 420 P e r l i t e p l a s t e r , 1:3 100 Accoustical plaster 160 Base c o a t p l a s t e r , 1:3 270 Finish plaster 65 Shear S t r e n g t h Cement m o r t a r

Failures F a i l e d i n bond F a i l e d i n bond Failed in plaster Failed in plaster Failed in plaster

398 Structures Publishing Company

PART D - ACRYLIC LATICES The a c r y l i c e s t e r r e s i n s are polymers and c o p o l y mers o f the e s t e r s o f a c r y l i c and m e t h a c r y l i c a c i d s . These r e s i n o u s m a t e r i a l s range i n p h y s i c a l p r o p e r t i e s from s o f t e l a s t o m e r s h a v i n g more than 1000% e l o n g a t i o n t o h a r d p l a s t i c s w h i c h can be sawed and machined. These h a r d p l a s t i c s are commonly known under the t r a d e names P l e x i g l a s s and L u c i t e . They have e x c e l l e n t i n i t i a l c o l o r , a c t u a l l y water-white, t h e y are s t a b l e t o l i g h t , do not d i s c o l o r o r degrade on a g i n g o r o u t d o o r expos u r e . These r e s i n s are a v a i l a b l e f o r many purposes as s o l u t i o n s i n o r g a n i c s o l v e n t s and as o i l - i n - w a t e r emulsions . A wide range o f p h y s i c a l and c h e m i c a l p r o p e r t i e s may be o b t a i n e d by changing the s i d e c h a i n s on the monomer i n making homopolymers, and a l s o b y m i x i n g the v a r i o u s monomers b e f o r e p o l y m e r i z a t i o n t o form c o p o l y mers. There are many v a r i a t i o n s o f combinations poss i b l e as w e l l as many v a r i a t i o n s i n m o l e c u l a r w e i g h t . The a c r y l i c e s t e r s may be p o l y m e r i z e d b y one o f the f o u r methods d e s c r i b e d i n p r e v i o u s s e c t i o n s ; namely,



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C O M P O U N D S

bulk, s o l u t i o n , suspension, o r emulsion. The b u l k method i s g e n e r a l l y u s e d t o produce the h a r d p o l y m e t h y l m e t h a c r y l a t e , the s o l u t i o n method f o r the polymers which are u l t i m a t e l y d i s s o l v e d i n s o l v e n t s , and t h e e m u l s i o n method f o r those polymers w h i c h are u s e d as latices. I n the e m u l s i f i c a t i o n p r o c e s s , a w a t e r s o l u b l e p e r o x i d e , such as hydrogen p e r o x i d e o r ammonium p e r s u l f a t e , i s used as the c a t a l y s t . The e m u l s i f y i n g agent may be a n i o n i c , c a t i o n i c o r n o n - i o n i c . E a c h w i l l have a d i f f e r e n t e f f e c t on the type o f l a t e x p r o d u c e d . T y p i c a l p h y s i c a l p r o p e r t i e s o f an a c r y l i c l a t e x e m u l s i o n s u i t a b l e f o r use w i t h cement are g i v e n i n T a b l e 5. T a b l e 5.

Properties

Percent s o l i d s pH Specific gravity Pounds p e r g a l l o n ^

J

o f A c r y l i c Latex 45% 9.4-9.9 1.054 8.8 M

4

_


The u s e s made o f t h i s e m u l s i o n as an admixture i n c e m e n t i t i o u s compounds are s i m i l a r t o t h o s e made w i t h SBR and PVA l a t i c e s . Among t h e s e , o f c o u r s e , we c a n i n c l u d e p a t c h i n g and r e s u r f a c i n g work, f l o o r u n d e r l a y ments, t e r r a z z o t i l e f l o o r i n g , s p r a y c o a t and f i l l c o a t a p p l i c a t i o n s , cement p l a s t e r and s t u c c o , t i l e g r o u t s , c r a c k f i l l e r s and p r e c a s t p a n e l s u r f a c i n g . The a d d i t i o n r a t e s o f a c r y l i c l a t i c e s are comparable t o t h o s e f o r the SBR and PVA l a t i c e s , r a n g i n g from 0.10 t o 0.20 l a t e x s o l i d s : cement. There are i n d i c a t i o n s t h a t the a c r y l i c r e s i n s may be added a t a r a t i o as low as 0.05. The u s u a l i n d i c a t i o n s about the v a r i a t i o n s i n s t r e n g t h c h a r a c t e r i s t i c s which depend on a d d i t i o n r a t e s a p p l y t o the a c r y l i c r e s i n s as w e l l . The same i s a l s o t r u e f o r water/cement r a t i o s and method o f c u r ing. The g e n e r a l l y recommended a d d i t i o n r a t e s f a l l i n the range o f 0.10 t o 0.20. Above t h i s l e v e l , some p r o p e r t i e s a c t u a l l y b e g i n t o drop. Below t h i s l e v e l , many p r o p e r t i e s are s t i l l more t h a n a d e q u a t e l y h i g h e r than f o r u n m o d i f i e d m o r t a r s . Many commercial f o r m u l a t i o n s are based on an a d d i t i o n r a t e a t t h i s l e v e l f o r p r i c e reasons.



7.

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93

Among t h e v a r i o u s a p p l i c a t i o n s which have n o t been t r e a t e d i n g r e a t e r d e t a i l are the spray coat a p p l i c a t i o n s and t h e underlayment a p p l i c a t i o n s . The s p r a y c o a t a p p l i c a t i o n s a r e based on combinations o f cement and o t h e r f i l l e r s , t o g e t h e r w i t h a l a t e x b i n d e r . These a p p l i c a t i o n s may be a p p l i e d by b r u s h , r o l l e r and t r o w e l , as w e l l as by s p r a y . They a r e o f t e n promoted as a s u b s t i t u t e f o r "rubbing" concrete. F l o o r underlayments a r e u t i l i z e d t o produce a l e v e l and smooth s u r f a c e b e f o r e p l a c i n g v i n y l t i l e , a s p h a l t t i l e , rubber t i l e , o r o t h e r r e s i l i e n t f l o o r i n g materials. A c r y l i c l a t e x m o d i f i e d underlayments a r e i d e a l l y s u i t a b l e f o r l e v e l i n g f l o o r s p r i o r t o the i n s t a l l a t i o n o f these s u r f a c i n g m a t e r i a l s , s i n c e these underlayments p r o v i d e an e x c e l l e n t s u b s t r a t e f o r bond i n g purposes, as w e l l as o f f e r i n g good c h e m i c a l r e s i s tance t o t i l e a d h e s i v e s and s o l v e n t s w h i c h some o f them c o n t a i n . PART Ε - DRY ACRYLIC ADMIXTURES There have been a number o f methods u t i l i z e d f o r i m p r o v i n g the p h y s i c a l p r o p e r t i e s and w o r k i n g c h a r a c t e r i s t i c s o f cement m o r t a r s by means o f d r y powder ad d i t i o n s t o t h e cement:sand m i x t u r e s . One o f t h e s e d r y powder admixtures i s a s y n t h e t i c polymer d e r i v e d from cellulose. There a r e s e v e r a l v a r i a t i o n s o f t h i s p o l y mer, two o f which have been w i d e l y used f o r t h i s p u r pose, namely, m e t h y l c e l l u l o s e and h y d r o x y e t h y l c e l l u lose. Both o f t h e s e a r e a v a i l a b l e i n d i f f e r e n t v i s c o s i t y ranges, when d i s s o l v e d i n water, and b o t h a r e s o l u b l e i n w a t e r . When t h e y a r e b l e n d e d i n t o a c e m e n t i t i o u s mix a t a d d i t i o n r a t e s o f 3% t o 5% on the cement c o n t e n t , t h e r e s u l t a n t p r o d u c t a c h i e v e s improved cha r a c t e r i s t i c s when mixed w i t h w a t e r . The p l a s t i c mor t a r i s more r e a d i l y workable and r e t a i n s w a t e r more completely. R e t e n t i o n o f w a t e r i s important, e s p e c i a l l y i n m o r t a r s which are used t o bond porous b r i c k s or o t h e r b u i l d i n g m a t e r i a l s . I n a d d i t i o n , g r e a t e r b o n d i n g c h a r a c t e r i s t i c s a r e o b t a i n e d . The use o f t h e s e c e l l u l o s i c m a t e r i a l s i n v a r i o u s a p p l i c a t i o n s has been c o v e r e d by many p a t e n t s i n the U n i t e d S t a t e s and i n Europe. Among t h e uses f o r these admixtures a r e the compounding o f g r o u t i n g systems, cement base p a i n t s ,



94

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M O R T A R S ,

S E A L A N T S ,

A N DC A U L K I N G

C O M P O U N D S

s t u c c o s , p a t c h i n g and r e p a i r f o r m u l a t i o n s , c e l l u l a r c o n c r e t e b l o c k s , sound i n s u l a t i n g m a t e r i a l s , r e f r a c t o r i e s , and even d e n t a l p r e p a r a t i o n s . One o f the major d i s a d v a n t a g e s o f t h e s e admixtures i s t h a t t h e y are wat e r r e s o l u b l e and t h e y may l e a c h o u t o f a c u r e d cement mortar. O t h e r attempts have been made t o u t i l i z e d r y powder p o l y v i n y l a l c o h o l and p o l y v i n y l a c e t a t e as admixtures f o r the same p u r p o s e . The p o l y v i n y l a l c o h o l i s r e a d i l y s o l u b l e i n water, and i t r e q u i r e s s i g n i f i c a n t amounts i n a d d i t i o n t o a c h i e v e any d i s t i n c t advantages. S i g n i f i c a n t amounts o f any v i s c o s i t y range o f p o l y v i n y l a l c o h o l c o n t r i b u t e t o an u n d e s i r a b l e i n c r e a s e i n v i s c o s i t y i n the cement m o r t a r . P o l y v i n y l a c e t a t e i n powder form has been used f o r t h i s purpose w i t h c o n s e quent improvements i n w o r k i n g c h a r a c t e r i s t i c s and phys i c a l properties. However, d r y powder p o l y v i n y l a c e t a t e does not form a t r u e polymer e m u l s i o n when d i s s o l v e d i n water. I t , t h e r e f o r e , may a l s o be d i s s o l v e d out o f a cement m o r t a r . The a c r y l i c r e s i n s may be s o p o l y m e r i z e d t h a t a r e s u l t a n t p r o d u c t may be o b t a i n e d which can be d i s p e r s e d i n w a t e r t o form a t r u e polymer e m u l s i o n . Such a p r o d u c t i s now a v a i l a b l e as a cement m o r t a r m o d i f i e r . By dry b l e n d i n g t h i s r e s i n w i t h appropriate cementitious m a t e r i a l s , i t i s p o s s i b l e t o f o r m u l a t e a one-package a c r y l i c m o d i f i e d cement m o r t a r . A d d i t i o n o f w a t e r t o the dry b l e n d w i l l produce a m o r t a r w i t h s u p e r i o r adh e s i o n and p h y s i c a l s t r e n g t h p r o p e r t i e s . Materials

pounds

S i l i c a sand No. 80 Mesh d r y P o r t l a n d cement, w h i t e A c r y l i c powder, d r y Sodium c i t r a t e Sodium c a r b o n a t e Dry w e t t i n g agent Hydroxyethyl c e l l u l o s e Water

250 100 10 0.5 1.0 2.0 0.5 70 434.0 Structures Publishing Company

Figure 2.

Dry acrylic cement mortar

Water i s added a t t h e time o f use on the j o b s i t e .



7.

M A S L O W


95

In a d d i t i o n t o t h e use of d r y a c r y l i c powders i n cement m o r t a r s , o t h e r t y p i c a l uses f o r t h e s e m o d i f i e r s are i n cement t o p p i n g s , c e r a m i c t i l e a d h e s i v e s , c e r a mic t i l e g r o u t s , w h i t e masonry p a i n t s and cement b l o c k fillers. I t i s o b v i o u s t h a t t h e s e compounds are more c o n v e n i e n t t o use w i t h the s i m p l e a d d i t i o n o f water, t h a n those compounds r e q u i r i n g the a d d i t i o n o f a l a t e x emulsion. As improvements are made i n t h e s e d r y powd e r s , t h e r e w i l l be more emphasis on t h i s type o f compound. At the p r e s e n t t i m e , the d r y powder a c r y l i c s are more c o s t l y than the l a t e x e m u l s i o n s on a d r y s o lids basis. PART F - EPOXY LATICES There has always been a d e s i r e f o r w a t e r - s o l u b l e epoxy r e s i n systems. A l t h o u g h epoxy r e s i n s were i n t r o duced a good many y e a r s ago, a l l attempts a t w a t e r s y s tems have met w i t h g e n e r a l f a i l u r e . The i n v e s t i g a t i o n s i n t o epoxy systems as e m u l s i o n s f o r use w i t h c o n c r e t e have been r o u g h l y d i v i d e d i n t o t h r e e g e n e r a l c l a s s i f i cations. The f i r s t attempts were i n the e m u l s i f i c a t i o n o f the epoxy r e s i n s t h e m s e l v e s . The problems and f a i l u r e s i n t h i s approach may be g e n e r a l i z e d as f o l l o w s : (a) The p o l a r i t y o f the epoxy r e s i n makes the c h o i c e o f s u r f a c t a n t o r e m u l s i f y i n g agent v e r y l i m i t e d and d i f f i c u l t ; (b) Poor c o m p a t i b i l i t y o f the epoxy r e s i n w i t h protective c o l l o i d ; (c) A l l s u r f a c t a n t s , e m u l s i f y i n g agents and comp a t i b l e p r o t e c t i v e c o l l o i d s promote h y d r o l y s i s o f the epoxy groups i n w a t e r systems; (d) Poor e m u l s i o n s t a b i l i t y and p o o r f r e e z e - t h a w s t a b i l i t y at b e s t ; (e) Phase i n v e r s i o n w i t h a l l c u r i n g a g e n t s ; (f) H i g h l e v e l s o f r e s i n r e q u i r e d . The second approach t o w a t e r systems has been the development and i n v e s t i g a t i o n o f w a t e r - s o l u b l e epoxy systems. The f a i l u r e i n t h e s e attempts may be summari z e d as f o l l o w s : (a)

A l l known w a t e r - s o l u b l e epoxy r e s i n s are


ali-

96

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M O R T A R S ,

S E A L A N T S ,

A N D

C A U L K I N G

C O M P O U N D S


p h a t i c p o l y - e p o x i d e s w h i c h e x h i b i t l i t t l e o r none o f the s t r e n g t h p r o p e r t i e s n o r m a l l y e x p e c t e d o f the epoxy resins; (b) A l l w a t e r - s o l u b l e epoxy r e s i n s h y d r o l y z e i n water; (c) R e a c t i o n , i f at a l l , w i t h c u r i n g agents, i s slow and s t i l l e x h i b i t s the s h o r t c o m i n g s o f low s t r e n g t h characte r i s t i c s . The t h i r d approach has been the d i r e c t a d d i t i o n o f epoxy r e s i n and c u r i n g agent t o cement. T h i s can be a c c o m p l i s h e d , b u t g e n e r a l l y r e q u i r e s the a d d i t i o n o f 20% t o 50% o f the r e s i n : c u r i n g agent c o m b i n a t i o n t o o b t a i n the d e s i r e d p r o p e r t i e s . T h i s approach i s a compromise, r e s u l t i n g i n a system which i s e c o n o m i c a l l y impractical. Because o f the g e n e r a l l y bad t o poor r e s u l t s o f p a s t attempts, i t became apparent t h a t an e n t i r e l y new and d i f f e r e n t approach t o the w a t e r d i l u t a b l e epoxy system had t o be f o l l o w e d , whereby the r e s i n e m u l s i o n c o u l d be added t o cement i n s m a l l q u a n t i t i e s and s t i l l a f f e c t the d e s i r e d i n c r e a s e i n p r o p e r t i e s . The p r o p e r t i e s d e s i r e d would be as f o l l o w s : (a) E m u l s i o n s t a b i l i t y and w a t e r d i l u t a b i l i t y from the time o f m i x i n g the r e s i n and c u r i n g agent u n t i l gellation; (b) A s e t time e q u i v a l e n t , o r n e a r l y e q u i v a l e n t , t o a cement system i t s e l f ; (c) H i g h s t r e n g t h p r o p e r t i e s ; (d) Good f r e e z e - t h a w s t a b i l i t y ; (e) R e t e n t i o n o f s t r e n g t h on r e w e t t i n g ; (f) T r o w e l i n g and f i n i s h i n g p r o p e r t i e s e q u i v a l e n t , o r n e a r l y e q u i v a l e n t , t o an u n m o d i f i e d m o r t a r system; (g) As low a r e s i n c o n t e n t as p o s s i b l e f o r economic r e a s o n s . I t becomes o b v i o u s t h a t many o f t h e s e p r o p e r t i e s c o u l d be o b t a i n e d by u s i n g a s t r a i g h t epoxy r e s i n , t y p i c a l l y , one o f the l i q u i d t y p e s , as one o f the components which would be e m u l s i f i e d a t the time o f mixing w i t h the c u r i n g agent. The c u r i n g agent, t h e r e f o r e , would have t o be an e m u l s i f y i n g agent, w e t t i n g agent and s u r f a c t a n t , as w e l l as a c u r i n g agent. Such



7.

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97

an agent i s now a v a i l a b l e c o m m e r c i a l l y f o r p r o d u c i n g epoxy e m u l s i o n s . These c u r i n g agents a r e p o l y m e r i c compounds w h i c h are w a t e r s o l u b l e , f o r m i n g e x c e l l e n t e m u l s i o n s w i t h epoxy r e s i n s . P o t l i f e may be v a r i e d , depending upon the c h o i c e o f c u r i n g a g e n t . P o t l i f e may a l s o be e x t e n d e d by t h e a d d i t i o n o f h i g h e r amounts o f w a t e r . The b a s i c p r i n c i p l e i n v o l v e s t h e p r e p a r a t i o n o f an epoxy e m u l s i o n j u s t p r i o r t o u s e . Previously, i n pree m u l s i f y i n g t h e epoxy r e s i n s and the c u r i n g a g e n t s , and p a c k a g i n g them s e p a r a t e l y , t h e e m u l s i o n s would b r e a k and s e p a r a t e i n t o phases, i n t h e package, o r upon m i x i n g . T h i s l a t e s t approach o f p r e p a r i n g t h e e m u l s i o n on job s i t e e l i m i n a t e s t h e s e problems. Upon p r e p a r i n g the e m u l s i o n s i n the f i e l d , and b l e n d i n g , t h e b l e n d i s a l r e a d y i n t h e p r o c e s s o f p o l y m e r i z a t i o n , and t h e r e i s no time f o r phase s e p a r a t i o n , e s p e c i a l l y , s i n c e t h e b l e n d i s added t o a c e m e n t i t i o u s c o m p o s i t i o n i n t h e same way t h a t a p r e v i o u s l y d e s c r i b e d l a t e x i s added. The u s e r i s aware t h a t t h e base m a t e r i a l i s 100% s o l ids. The amount o f w a t e r which i s added d e t e r m i n e s the s o l i d s content o f the emulsion. The u s e r knows e x a c t l y what t h e r e s i n : c e m e n t r a t i o i s . In p r e p a r i n g the e m u l s i o n i n t h e f i e l d , e q u a l p a r t s of a l i q u i d epoxy r e s i n h a v i n g an e p o x i d e e q u i v a l e n t o f 175-210 a r e mixed w i t h e q u a l p a r t s o f t h e e m u l s i f y ing c u r i n g agent. The m i x t u r e i s b l e n d e d and a l l o w e d t o sweat i n f o r 15 minutes f o r p o l y m e r i z a t i o n t o b e g i n . Water i s then added s l o w l y , m i x i n g c o n t i n u o u s l y , t o form t h e e m u l s i o n . The amount o f w a t e r added d e t e r mines whether i t i s a w a t e r - i n - o i l t y p e , o r an o i l - i n w a t e r t y p e . T h i s h a s a d e f i n i t e b e a r i n g on t h e r a t e o f polyme r i z a t i o n . When t h e epoxy r e s i n s a r e e m u l s i f i e d by t h i s method, and t h e e m u l s i o n i s added t o a c e m e n t i t i o u s mix, t h e r e i s an immediate s u r f a c e a c t i n g e f f e c t which g r e a t l y reduces t h e w a t e r r e q u i r e m e n t s o f cement. T h i s w a t e r - r e d u c i n g c h a r a c t e r i s t i c , o f a p p r o x i m a t e l y 15%, i s d e v e l o p e d w i t h low a d d i t i o n r a t e s o f t h e epoxy emuls i o n . The a d d i t i o n r a t e may be as low as 0.1 p a r t s o f e m u l s i o n s o l i d s p e r 100 p a r t s cement. The a d d i t i o n o f 2 p a r t s o f e m u l s i o n s o l i d s t o 100 p a r t s cement p r o d u ces s l i g h t l y lower w a t e r r e q u i r e m e n t s , b u t not below


98

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M O R T A R S ,

S E A L A N T S ,

A N D

C A U L K I N G

C O M P O U N D S

LATEX AND EPOXY ADHESIVES COMPARATIVE


A. Acrylic

Appearance

bill's Content

Milky White

45.0%

Primary Utt Bonding fresh concrete to old concrete. Concrete admiiture. Thin layer toppings.

B. PolyvinylAcetate

Milky White

55.0%

ReEmulsifiable

C. ButadieneStyrene

Bonding fresh concrete to old concrete. Concrete admixture. Thin layer toppings.

Milky White

48.0%

Bonding fresh concrete to old concrete. Concrete ad mixture. Thin layer toppings.

D. PolyvinylAcetate ReEmulsifiable

Milky White

Application Methods

Applicatiens

Brush, broom Underlayments spray, roller Stucco as adhesive. Grouting-mortar Terrazzo Home Kits Trowel as topping. Crack Fillers

Speciffcatitis MIL-B-19235

Cleaning Surface Preparation A. Remove oil, grease. Wet surface.

Brush, broom Underlayments spray, roller Stucco as adhesive. Grouting-mortar Terrazzo Trowel as Home Kits Crack Fillers topping.

Remove oil, grease.

Brush, broom Underlayments spray, roller Stucco as adhesive. Grouting-mortar Terrazzo Trowel as Home Kits topping. Crack Fillers

Remove oil, grease.

Bonding of plaster.

B.

Finishing Procedures Steel trowel, wood float. No excessive trowelling.

Steel trowel, wood float. No excessive trowelling.

Chemical las istance if Mortar ASTM-C-2S7-51T Acids—Fair Alkalis—Very Good Salts—Very Good Solvents—fair-Good

Acids—Fair Alkalis—Very Good Salts—Very Good Solvents—Fair-Good

Steel trowel Acids—Fair wood float. Alkalis—Very Good Salts—Very Good No excessive Solvents—Fair-Good trowelling.

MIX-Cement: Sand = 1:3 Latex Solids on Cement = 10-20% Water Cement Ratio = 0:45

Not used as an admixture.

I. Epoiies Cavering lata I. Epoxy — Polysulfk* a. Unfilled Β b. Filled

1:1 by volume Part A and PartB

a. 3040 min. b. 3040

a. 100 sq. ft. per I. as mortar sq. «. '/Γ thick, contain ing sand.

S

b. 25-38 sq. ft. P«r gal. II. Epoxy — Polyamide a. Unfilled Binder b. Filled

1:1 by volume Part A and Part Β

Light straw to amber

95 100%

a. 1-3 hours b. 1-3 hours

a. 100 sq. ft. per gal. as mortar 25 sq. ft. >/," thick, contain ing sand. b. 100-150 sq. ft. par ial.

Part A — Light straw IN. Epoxy Coal Tar & Unfiled

1:1 by volume Part A

Part Β — Black

100%

3040 min.

a. 30-50 sq. ft. pariai.

d con crete and other ma a. MMM-B-350A terials to hardened b. MMM-G-650A concrete. Setting dow New Jersey Turnpike els. Type lb, lib. Section 4.9.3 b. Filling cracks in con Standard Specifications crete to bond both 1965 sides of crack into an integral member. Type AASHO Specification la and lia. Designation M-200431 c. Bonding plastic con II. crete to hardened con Virginia Dept. of crete. Type lb and lib. Highways d. Preparation of epoxy mortars by adding sand. Types la, lia, III. e. Bonding skid-resistant materials to hardened concrete. Types lb, lib, III. f. Membrane between asphalt and concrete. Type III.

AASHO Specification Designation ^200431 III. AASHO Specification Designation M-200431 New Jen Section • Standard Specifications 1965 Ν. Y. State Dept. of Public Works Item #6006


Excellent to acids, alkalis, solvents, salts with maximum properties. Also maximum resistance to hydro static water pressure.

7.

MASLOW

99


AND BONDING AGENTS CHART

(•empressm


Strength: 2" Cubas ASTM-ClOf-M 3200 psi4100 psi

3400 psi3600 psi

3300 psi4000 psi

Strength: 1" Thick Briauettas ASTM-CltO-59 580 psi615 psi

350 psi450 psi

450 psi580 psi

ASTkK 34M1T 950 psi1400 psi

1000 psi1250 psi

D. PolyvinylAcetate Emulsifiable

NOTE- These compositions do not contain latex, but are applied over the latex film previously applied as an adhesive.

StrtRfth ISTM-C-IM-S Neat cement — 250-300 psi

Strength ASTIW-

1.3 Ottowa sand mortar 350420 psi 1 3 Perlite plaster 150-200 psi Finish plaster 30% Gauging plaster 70% Lime plaster 120-150 psi 1:3 Cowbay sand mortar 200-290 psi

1250 psi1650 psi

ButadieneStyrene

Accoustical plaster 100-170 psi 1:3 Brown coat 100-150 psi Unmodified mortar. 3000 psi Wet cure

Unmodified mortar. 410 psi Wet cure

Unmodified mortar. 750 psi

Tensile Compressive Strength Strength Α$ΤΙΜΜ0β ASTM-O-MI a. Binder with sand 12,00015,000 psi a. 30003500 psi b. Unfilled 8,00010,000 psi a. Binder with sand 10,00013,000 psi.

b. 35004000 psi

Tensile EwngatNi ASTM-D-3*!

a. 2.5-15%

Compressive Double) Shear Strength MMM-S-650A

a. 900-1000 psi b. 700-1000 psi

a. 6-25%

a. 400-500 psi b 500-650 psi

b. Unfilled 6,000-8,000 psi

Binder with sand 40005000 psi Unfilled 30004000 psi

VIBRATION TESTS — No failure DETERGENTS & ACIDS - No failure, slight stain

PolyvinylAcetate Re-Emulsifiable

a. 35-40%

a. 300-400 psi

Whin Nat Ta Usa May be used as a plas ter bond within 4540 :nin. Not for extreme chemical exposure. Do not use with airentrainers. Not for i-jnditions of high hy drostatic pressure.

Indoor and outdoor exposures. On con crete, steel, wood. Guniting. Thin sec tion topping can be used with accelerators, re tarded, water re ducing agents.

May be used as a plas ter bond within 45-60 min. Not for extreme chemical exposure. Do not use with airentrainers. Not for conditions of high hy drostatic pressure.

Indoor and outdoor May be used as a plas exposures. On con ter bond within 45-60 crete, steel, wood. min. Do not use with Guniting. Thin sec accelerators Not for tion topping. extreme chemical. Not for constant water immersion. Do not use with airentrainers. Indoors—ceilings primarily.

b. Cost is highest. c. For maximum chemical and physical properties. II. a. Generally proprietary compounds. b. Use where longer life is required and cost is factor.

a. On surfaces treated with rubber or resin curing membranes. b. On dirty surfaces. c. On weak concrete. d. On bituminous surfaces. a. On surfaces treated with rubber or resin curing membranes. b. On dirty surfaces. c. On weak concrete.

d. a. III. a. For lower cost applications of non-skid b. membranes. b. On bituminous concrete.

Limited use as a con crete bonding agent. Do not use as an ad mixture. Do not use under wet or humid conditions. Do not use at temperatures below 50 °F.

Where Net Te Use

Where To Use 1. a. Generally, on government agency projects.

c. For maximum chemical and physical properties.

a. 400800 psi

Whin Ta Usa Indoor and outdoor exposures. On con crete, steel, wood. Guniting. Thin sec tion topping.

On bituminous surfaces. Do not use for bonding new wet con crete to old. Oo not use where black color will be undesirable.

c. For resistance to grease, oil, gasoline and traffic wear.




100

P L A S T I C

M O R T A R S ,

S E A L A N T S ,

A N D

C A U L K I N G

C O M P O U N D S

the s t o i c h e m e t r i c amounts o f w a t e r r e q u i r e d t o h y d r o l y z e the cement. T h i s low a d d i t i o n r a t e i s i n c o n t r a s t t o the recommended a d d i t i o n r a t e f o r o t h e r l a t e x emuls i o n s o f 10% t o 20%· The a d d i t i o n o f s m a l l amounts o f epoxy e m u l s i o n t o a c e m e n t i t i o u s m i x t u r e improves t r o w e l a b i l i t y o f the r e s u l t a n t p r o d u c t tremendously, i n c o n t r a s t t o a t y p i c a l l a t e x admixture m o r t a r where the h i g h a d d i t i o n r a t e c r e a t e s d i f f i c u l t y i n t r o w e l i n g , because the l a t e x s o l i d s are b r o u g h t t o the s u r f a c e , e x e r t i n g a d r a g on the t r o w e l . The i n i t i a l s e t time o f an epoxy admixtured m o r t a r i s c o n s i d e r a b l y r e d u c e d , and t i e f i n a l s e t time i s a l s o a c c e l e r a t e d . T h i s r a p i d s e t t i n g o f an epoxy e m u l s i o n admixtured cement m o r t a r may be a t t r i b u t e d t o the p o l y m e r i z a t i o n o f the epoxy r e s i n , as w e l l as t o the a c c e l e r a t i o n i n the r a t e o f h y d r a t i o n o f the cement. The p h y s i c a l p r o p e r t i e s o f t h e s e m o r t a r s show phenomenally h i g h f l e x u r a l and t e n s i l e s t r e n g t h s , w i t h l i t t l e o r no l o s s i n compressive s t r e n g t h . For a l l p r a c t i c a l p u r p o s e s , a l e v e l o f 2% as an a d d i t i o n r a t e , produces r e s u l t s which a r e o u t s t a n d i n g , w i t h o u t e x c e s sive cost. Cured m o r t a r specimens have been exposed t o c o n t i n u o u s water immersion w i t h no l o s s i n p r o p e r ties . A d d i t i o n a l p o s s i b i l i t i e s f o r u s i n g t h e s e epoxy emuls i o n s are a p p a r e n t . A water-based epoxy system c o u l d c e r t a i n l y be used as a c u r i n g compound f o r f r e s h l y p l a c e d c o n c r e t e . There would be no i n c o m p a t i b i l i t y because b o t h are i n a w a t e r phase. A n o t h e r p o s s i b i l i t y i s t o use the epoxy e m u l s i o n s systems as b o n d i n g agents f o r p l a c i n g f r e s h c o n c r e t e onto hardened concrète» Even though most epoxy b o n d i n g agents a r e 100% s o l i d s , t h e y do p r e s e n t a problem o f f a s t s e t t i n g , so t h a t f r e s h c o n c r e t e must be p l a c e d q u i c k l y w h i l e t h e b o n d i n g agent i s s t i l l t a c k y . In u s i n g an epoxy e m u l s i o n system, a f i l m c o u l d be a p p l i e d f a r i n advance o f p l a c i n g conc r e t e , the p r e s e n c e o f w a t e r would p r o l o n g the s e t t i n g time, and i f c o n c r e t e s h o u l d be p l a c e d t o o soon, t h e r e would be no problem o f e n t r a p p i n g s o l v e n t , such as might be p r e s e n t i n o t h e r b o n d i n g a g e n t s . A n o t h e r advantage o f t h e epoxy e m u l s i o n s i s t h a t they do not p r e s e n t f i r e o r h e a l t h h a z a r d s . W i t h s t r e s s b e i n g l a i d by governmental a g e n c i e s on problems o f a i r p o l l u t i o n , wat e r based epoxy systems p r o v i d e an a l t e r n a t i v e answer. R E C E I V E D

April 2,

1979.


Latex Emulsions with Concrete - ACS Symposium Series (ACS

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