Inverse Gas Chromatography - American Chemical Society

Chapter 17

Surface Characteristics of Glass Fibers

Downloaded by CORNELL UNIV on May 30, 2017 | http://pubs.acs.org Publication Date: April 24, 1989 | doi: 10.1021/bk-1989-0391.ch017

E. Osmont and Henry P. Schreiber Chemical Engineering Department, Ecole Polytechnique, Montréal, Québec H3C 3A7, Canada Inverse Gas Chromatography (IGC) was applied to E-glass fiber surfaces modified by various silane coupling agents. Using homologous series of alcohol (acid) and amine (base) vapor probes, the acid/base interaction characteristics of the fibers were measured from 30 to 90°C. Unmodified E-glass was found to be amphipatic, significantly bonding with both acid and base vapors. Strong surface acidity was produced by a chloro-silane agent (CPTMS), while surface treatments with hexyldimethoxysilane (HDMS) and an aminosilane (APS) generated increasing degrees of basicity. The temperature dependence of these surface properties was established. Adsorption from solution of polyvinyl chloride (PVC) and of PMMA, respectively known to be an acid and a base from IGC measurements, showed the existence of selective sorption effects. PVC was strongly sorbed on basic glasses, while PMMA sorbed more readily on the acidic, CPTMS-treated glass. These findings are an origin for more extensive studies of the role played by interfaces in composites reinforced by the various fibers.

S i n c e i t s i n t r o d u c t i o n some y e a r s a g o , i n v e r s e g a s c h r o m a t o g r a p h y (IGC) has been r e c o g n i z e d a s a c o n v e n i e n t r o u t e t o the d e t e r m i n a t i o n o f thermodynamic i n t e r a c t i o n parameters f o r polymeric or other non-volatile stationary phases i n contact with selected v a p o r p r o b e s (1,2). T h e p r i n c i p l e s o f IGC e x p e r i m e n t s have also been extended t o two-component stationary phases ( 3 ) , thereby making i t p o s s i b l e to s p e c i f y thermodynamic i n t e r a c t i o n parameters for t h e components o f polymer b l e n d s (4,5), a s w e l l a s f o r f i l l e d polymers and other muIti-component systems. Despite these a t t r a c t i v e f e a t u r e s , l i m i t a t i o n s must b y r e c o g n i z e d o n t h e g e n e r a l 0097-6156/89/0391-0230$06.00/0 c

1989 American Chemical Society

Lloyd et al.; Inverse Gas Chromatography ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


17.

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applicability of IGC to the measurement of interaction thermodynamics (6). This i s d u e i n p a r t , i n some c a s e s , t o t h e p r e f e r e n t i a l p a r t i t i o n i n g of the probe molecule t o one o f t h e components i n a mixed s t a t i o n a r y phase. Further, the c a l c u l a t i o n of thermodynamic f u n c t i o n s depends on t h e e x i s t e n c e o f equilibria between volatile and s t a t i o n a r y phases. Failure to a t t a i n e q u i l i b r i u m compromises the v a l i d i t y of thermodynamic computa tions, even when only a single stationary phase i s present. Equilibrium conditions are readily attained when only non-polar materials a r e i n v o l v e d , b u t t e n d t o b r e a k down when t h e m a t e r i a l s u s e d i n t h e IGC e x p e r i m e n t c a n i n t e r a c t b y n o n - d i s p e r s i v e forces. The a b o v e l i m i t a t i o n s a r e p a r t i c u l a r l y r e s t r i c t i n g t o t h e many applications of muIti-component systems i n which highIy poIar m a t e r i a l s a r e used and t h e r e f o r e prompted recent m o d i f i c a t i o n s of t h e IGC m e t h o d ( 7 . 8 ) . T h e s e m o d i f i c a t i o n s r e s u l t i n t h e g e n e r a t i o n of c o m p a r a t i v e , i n t e r n a l l y c o n s i s t e n t indexes of a c i d or base functionality f o r a wide range of p o l y m e r s and the c o n s t i t u e n t s for polymer systems. Although the f o r m a l i t y of thermodynamic f u n c t i o n s i s l o s t , t h e a c i d / b a s e i n t e r a c t i o n i n d e x e s p r o m i s e t o be u s e f u l i n r a t i o n a l i z i n g such important a s p e c t s of b e h a v i o r as the d i s p e r s i o n of p a r t i c u l a t e s i n polymeric f l u i d s , the development of m e c h a n i c a l p r o p e r t i e s i n c o m p o s i t e s , and the d i f f u s i o n of vapors through polymeric membranes ( 9 ) . The p r e s e n t p a p e r c o n s i d e r s t h e acid/base i n t e r a c t i o n p o t e n t i a l of glass fibers. Of p a r t i c u l a r interest i s t h e r a n g e o f t h e s e i n t e r a c t i o n p o t e n t i a l s t h a t c a n be d e s i g n e d t h r o u g h s u r f a c e m o d i f i c a t i o n o f f i b e r s by v a r i o u s silane coupling agents. The c o n s e q u e n c e s o f d i v e r s e a c i d / b a s e p o t e n t i a l s a r e i l l u s t r a t e d by t h e a d s o r p t i o n onto the f i b e r s of polymers known t o be a c i d i c or b a s i c . The work adds to the recent l i t e r a t u r e ( 1 0 , 1 1 ) o n t h e u s e o f IGC f o r t h e s u r f a c e characteriza t i o n o f gI a s s f i b e r s . Experimental Section. i. Mater i a Is. Four g l a s s f i b e r specimens were used. One was an unsized E-glass, the others were surface treated with silane c o u p l i n g agents as f o l l o w s : CPTMS (3-chloropropyItrimethoxy silane) was applied from isopropanol/water mixtures a t pH 4 (acidification by glacial acet i c a c i d ) . HDMS (HexyIdimethylethoxy silane) was applied from acetone solut ion. APS ( 4 - a m i n o b u t y I d i m e t h y l e t h o x y silane) was also applied from acetone solut ions. For ease of p a c k i n g c h r o m a t o g r a p h i c columns, the f i b e r s were s c r e e n e d , w i t h 3 2 5 t o 4 0 0 mesh p a r t i c l e s r e t a i n e d f o r t h e s t u d y . C o l u m n s 1.5 m l o n g w e r e c o n s t r u c t e d o f s t a i n l e s s s t e e l t u b i n g t h a t had been d e g r e a s e d , w a s h e d , and d r i e d . The columns were used f o r IGC work w i t h a P e r k i n - E l m e r S i g m a II c h r o m a t o g r a p h , f i t t e d w i t h dual flame i o n i z a t i o n d e t e c t o r s . The vapor probes were reagent grade n-octane, ethanol, n-propanol, n-butanol, propylamine, b u t y l a m i n e , and e t h y l e n e diamine. T h e o c t a n e was u s e d a s a probe capable of interacting with substrates through van der Waals f o r c e s o n l y . The a l c o h o l s r e p r e s e n t e d Lewis a c i d s and the amines represented Lewis bases (12.13).


INVERSE GAS CHROMATOGRAPHY

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In adsorption measurements, PMMA a n d PVC w e r e t h e a d s o r b i n g m o l e c u l e s , t h e former from s o l u t i o n s i n t o l u e n e , t h e l a t t e r from THF solutions. Earlier work h a d shown PVC t o b e a s t r o n g a c i d (Z.fi)» w h i l e F o w k e s ( 1 4 ) r e p o r t s PMMA t o b e a L e w i s b a s e . The p o l y m e r s w e r e c o m m e r c i a l s a m p l e s , t h e PMMA w i t h Mw = 1.13 x 1 0 a n d t h e PVC w i t h Mw a b o u t 6.5 x 1 0 . A d s o r p t i o n m e a s u r e m e n t s were u n i f o r m l y a t 3 0 ± 1°C. 5


4

i i Procedures I n IGC d e t e r m i n a t i o n s , c o l u m n s w e r e s w e p t w i t h d r y n i t r o g e n a t 140°C f o r a p p r o x i m a t e l y 1h p r i o r t o t h e i n t r o d u c t i o n of vapor probes. Vapors were injected a t extreme d i l u t i o n by m i c r o s y r i n g e s , and experimental temperatures ranged from 30 t o 90°C. Inlet p r e s s u r e s were i n t h e v i c i n i t y o f 2 0 p s i g . a n d He c a r r i e r g a s f l o w r a t e s w e r e c o n t r o l l e d a t 15 ± 1 m l / m i n . Octane probes generated symmetrical e l u t i o n peaks, leading t o standard o c a l c u l a t i o n s o f r e t e n t i o n times and s p e c i f i c r e t e n t i o n volumes, V (1.2). Polar probes generated skewed peaks, necessitating measurement c o n v e n t i o n s d e s c r i b e d i n d e t a i l i n R e f e r e n c e 7. A l l d a t a quoted here a r e averages o f 5 s e p a r a t e vapor i n j e c t i o n s . The o V d a t a bear t h e f o l l o w i n g e r r o r s : F o r n - o c t a n e , ± 2% o v e r t h e entire t e m p e r a t u r e r a n g e ; f o r p o l a r p r o b e s , ± 5 % a t T50. T h e i n c r e a s e d h i g h t e m p e r a t u r e u n c e r t a i n t y i s d u e t o o the d i m i n i s h e d v a l u e s o f V a t h i g h e r e x p e r i m e n t a l temperatures. For a d s o r p t i o n s t u d i e s , a polymer s o l u t i o n was p r e p a r e d a t an i n i t i a l s o l u t e c o n c e n t r a t i o n i n t h e span 0.5 t o 2.5 w t - % . A carefully weighed sample of glass f i b e r was i n t r o d u c e d i n t o a 100-ml o r 250-ml a l i q u o t a n d s h a k e n f o r 2 4 h a t t h e e x p e r i m e n t a l temperature. Following an a d d i t i o n a l 24 t o 48 h. p e r i o d f o r s e d i m e n t a t i o n , t h e s u p e r n a t a n t f l u i d was f i l t e r e d t h r o u g h a c o a r s e glass plug. An a l i q u o t o f t h e c l e a r l i q u i d was e v a p o r a t e d t o d r y n e s s u n d e r vacuum a t 60°C. P u m p i n g w a s c o n t i n u e d f o r several hours f o l l o w i n g the attainment o f invariant s o l i d s weight, using a S a r t o r i u s microbalance for the l a t t e r purpose. Polymer adsorbed, Cads., was c a l c u l a t e d from thed i f f e r e n c e i n i n i t i a l and f i n a l s o l u t i o n concentrations andexpressed as weight adsorbed/unit area of glass surface. F o r t h i s purpose, an apparent s u r f a c e a r e a of 0. 22 m2/gm w a s u s e d , b a s e d on m i c r o s c o p i c e v a l u a t i o n of fiber geometry. The c a l c u l a t i o n assumes that t h e f i b e r s were non-porous and t h a t s a m p l e s v i e w e d by m i c r o s c o p y were r e p r e s e n t a t i v e of the bulk. D a t a r e p r o d u c i b i l i t y w a s f r o m ± 7 t o ± 9% i n a l l c a s e s . g

g

g

R e s u l t s and Discussion 1. IGC R e s u I t s T a b l e I s u m m a r i z e s t h e c o m p o s i t i o n o f c o l u m n s u s e d in this work. The r e l a t i v e l y high solid loadings were necessitated b y t h e low r e t e n t i o n volumes r e s u l t i n g from low s p e c i f i c s u r f a c e a r e a s . S p e c i f i c r e t e n t i o n volumes and a c i d / b a s e interaction parameters are given i n Table I I ;a l l dataa r e r e f e r r e d t o a reference temperature o f 30°C. The i n t e r a c t i o n p a r a m e t e r , ft, w a s c a l c u l a t e d from the retention volumes f o r n-butanol andbutylamine, f o l l o w i n g theprecedents of References 7


17.

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OSMONT& SCHREIBER

o a n d 8. A c c o r d i n g l y , f o r a c i d i c s u b s t r a t e s , w h e r e t h e [ V ] exceeds that f o r the a c i d i c a l c o h o l , g

n = 1 - (V ) /(V ) g

b

g

a

< 0

g


a

b

a

s

e

(1)

o For b a s i c s t a t i o n a r y phases, where t h e [ V ] the b a s i c butylamine,

ft = ( V g ) / ( V g )

b

a

c

i

d

exceeds

that f o r

-1 > 0

(2)

On this basis, unsized E-glass i s a mild a c i d , i t s n value f a l l i n g o u t s i d e t h e band o f v a l u e s near 0, that i s generally associated with amphipatic solids or with materials able to i n t e r a c t through d i s p e r s i o n forces alone. The e f f e c t s of surface treatment are quite distinct with appreciable acidity being i n t r o d u c e d b y CPTMS c o a t i n g s ( c o l u m n 2 ) , a n d m o d e r a t e b a s i c i t y by APS (column 4). HMDS s i z i n g p r o d u c e s r e l a t i v e l y m i l d c h a n g e s i n s u r f a c e c o n d i t i o n , t h e n e t e f f e c t b e i n g a weak surface basicity. Table II r e p o r t s t h e ft v a l u e s f o r PVC a n d PMMA, a s d e t e r m i n e d earlier. The former i s a s t r o n g a c i d and t h e l a t t e r i s d i s t i n c t l y basic, i n agreement with t h e f i n d i n g s o f Fowkes and c o w o r k e r s (14). Table C o l u m n Number: S t a t i o n a r y Phase Surface Treatment Wt. o f s t a t i o n a r y phase (g)

I . Column D e s c r i p t i o n 1 E-glass N i l 5.27

f o r IGC E x p e r i m e n t s

2 E-glass CPTMS 4.43

3

4

E-glass HDMS 5.06

E-glass APS 5.82

CPTMS = 3 - c h l o r o p r o p y l t r i m e t h o x y s i l a n e HDMS = hexyIdimethoxysilane APS = aminopropyItrimethoxysilane o The l o w V i n T a b l e I I w a r r a n t comment. Pristine glass i s known t o h a v e highly reactive surfaces ( 1 5 ) , so that large r e t e n t i o n volumes might be e x p e c t e d . H o w e v e r , a s shown b y S h a f r i n and Z i s m a n ( 1 5 ) , surface activity i n aged glass surfaces i s greatly reduced through the presence, often through chemical a d s o r p t i o n , of l a y e r s able t o produce e i t h e r a c i d or base surface characteristics. The p r e c o n d i t i o n i n g i n o u r e x p e r i m e n t s was insufficient to free the surfaces of strongly bonded species; t h e r e f o r e , the data f o r t h eu n s i z e d s u r f a c e s cannot be a s c r i b e d t o the p r o p e r t i e s o f t r u l y bare g l a s s . Another c o n t r i b u t i o n to the g

0

low V v a l u e s a r i s e s f r o m t h e c o n v e n t i o n o f c o m p u t i n g c h r o m a t o g r a phic results on t h e b a s i s o f weight o f s t a t i o n a r y phase. When s o l i d s w i t h low s u r f a c e a r e a s are involved, this leads t o an g


234


Table

II.

C o m p a r i s o n o f R e t e n t i o n V o l u m e s a t 30°C ( R e t e n t i o n volumes i n m l . g " )


1

Column Number:

2

1

4

3

Probe: nC8

1.77

2.46

Butanol

6.08

5.25 >0..8 3.14 >1.. 1 2.58

Propanol

5.27

Ethanol

4.06

Butylamine

6.93

Propylamine

5.74

17.48 >1 .2 16.14

Ethylene d i am i ne

8.83

ft* *

-0.14

Calculated

7.44

4.07

>0.,5

>0..7

>2., 1

6.91

3.25

>0..6

>0..5

>0. 5

6.34

2.69

4.07

3.51

>1 , .3

>1,.2

>1,.3 2.26

2.69

17.51

3.59

2.26

-2.33

0.16

from V ° f o r b u t a n o l

For polymers used b o t h a t 30°C.

3.11

1.81

g

i n t h i s work;

and butyl ftp = VC

-1.33;

0.83 amine. ftp = MMA

0.91,


17.

235


OSMONT & SCHREIBER

a p p a r e n t r e d u c t i o n i n V , w h i c h i s somewhat m i s l e a d i n g . For example, r e c e n t work w i t h r u t i l e ( T i 0 ) s t a t i o n a r y phases ( 7 ) , has g i v e n octane r e t e n t i o n volumes i n the v i c i n i t y of 100 ml.g" . Specific s u r f a c e s i n t h e s e c a s e s w e r e a p p r o x i m a t e l y 8 m /g, w h i c h is about 30 times greater than i n the present work. By r e c a l c u l a t i n g t h e p r e s e n t d a t a on a b a s i s o f u n i t s u r f a c e a r e a , i t g

2

1

2

o , leads to V i n t h e r a n g e o f 50 t o 100 m l . g " , a n d n o t g r e a t l y out of line with other particulate stationary p h a s e s u s e d i n IGC exper iments. A f i n a l comment i n c o n n e c t i o n w i t h T a b l e I I p e r t a i n s to the 1

g

o o probe-to-probe v a r i a t i o n i n V . A general decrease i n V with decreasing probe c h a i n l e n g t h i s i n d i c a t e d by t h e o f f s e t numbers i n T a b l e I I . On a p e r c e n t b a s i s , the v a r i a t i o n i s small when acid/base interactions occur between p r o b e / s u b s t r a t e p a i r s , but b e c o m e s c o n s i d e r a b l y l a r g e r when a c i d / a c i d o r b a s e / b a s e p a i r s a r e in contact. A t c o n s t a n t T, the increasing volatility of s h o r t e r - c h a i n p r o b e s may b e e x p e c t e d t o p r o d u c e variations, such as those exemplified b y (-0H) p r o b e s i n c o l u m n 2, a n d b y (-NH ) p r o b e s i n c o l u m n 4. T h a t i s , c h a n g e s o f 20 t o 4 0 % p e r C H - g r o u p are observed, when only dispersion forces are active. The


g

2

2

o v a r i a t i o n s of V p e r amino group i n column 2 and p e r h y d r o x y l g r o u p i n c o l u m n 4, a m o u n t i n g t o l e s s than 10% per CH group, suggest that the s t r e n g t h of acid/base i n t e r a c t i o n s decreases w i t h increasing alkyl chain length. The increasing importance of weaker, dispersion force contributions to the o v e r a l l bonding e n e r g y may b e r e s p o n s i b l e f o r t h e o b s e r v a t i o n . Finally, though the retention volume f o r the diamine probe in contact with CPTMS-treated g l a s s i s a p p r e c i a b l e , i t i s i n l i n e w i t h values for other basic probes used i n t h i s work. T h e r e s u l t , i n d i c a t i v e of an a p p a r e n t h e a d - t o - t a i l o r i e n t a t i o n o f t h e p r o b e m o l e c u l e on t h e g l a s s s u r f a c e , d i s p l a y s another facet of the a p p l i c a t i o n s to which t h e IGC m e t h o d may b e p u t . The temperature dependence of interaction variables for components of r e i n f o r c e d polymer systems i s of g r e a t importance, g i v e n the range of temperatures over which such systems are processed and used. Since the thermodynamic basis of IGC parameters links these w i t h interaction enthalpies (1,2), interaction data o r i g i n a t i n g f r o m IGC w i l l f o l l o w t h e t r e n d s s e t by t h e f o r m a l t h e r m o d y n a m i c d a t a . I n t h i s r e g a r d , t h e IGC m e t h o d has a c o n s i d e r a b l e advantage over alternative methods f o r evaluating interactions among the components of non-volatile materials. Since IGC e x p e r i m e n t s a r e r e a d i l y c a r r i e d out over wide temperature ranges, they overcome difficulties inherent in the use of other parameters, such as the s o l u b i l i t y parameter, which i s g e n e r a l l y e s t i m a t e d at f i x e d temperatures, or over narrow ranges of the v a r i a b l e , l e a v i n g undetected p o s s i b l e changes i n the m i s c i b i l i t y of components. The t e m p e r a t u r e s c a n i n t h i s work was limited primarily by increasing experimental u n c e r t a i n t i e s as r e t e n t i o n times decreased w i t h r i s i n g temperature. Nevertheless, useful r e s u l t s w e r e o b t a i n e d t o a maximum o f 90°C. T h e s e r e s u l t s g

2


236


are

displayed

i n Figures

1,2, a n d 3 i n t e r m s o f A r r h e n i u s - t y p e

o p l o t s showing In V as a f u n c t i o n o f r e c i p r o c a l a b s o l u t e temperature. F i g u r e 1 g i v e s the temperature dependence for the octane probe, Figure 2 gives the a c i d i c b u t a n o l , and F i g u r e 3 g i v e s the r e s u l t s f o r the b u t y l a m i n e probe. The r e p r e s e n t a t i o n i n F i g u r e 1 l e a d s to linear and roughly parallel r e l a t i o n s h i p s in a l l cases. Thus, a l t h o u g h the a b s o l u t e retention capacities of the glass substrates vary with the applied surface sizing, the bonding energies w i t h n-octane are constant. I n o t h e r w o r d s , t h e number of interaction sites for o c t a n e may b e c o n s i d e r e d g r e a t e r o n APS- a n d CPTMS- t r e a t e d f i b e r s t h a n o n HMDS a n d u n t r e a t e d v e r s i o n s o f t h e f i b e r ; however, t h e f o r c e s i n v o l v e d a t t h e p r o b e / s u b s t r a t e c o n t a c t a r e t h e same. This i s not u n e x p e c t e d , g i v e n the n o n - p o l a r n a t u r e o f t h e p r o b e . The pattern of results in Figures 2 and3 i s q u i t e d i f f e r e n t . When acidic butanol i s the probe molecule, linear relations are generated with the s t r o n g l y a c i d i c CPTMS-sized g l a s s s u b s t r a t e , but i n c r e a s i n g n o n - l i n e a r i t y i s observed when going i n the direction of increased substrate basicity, that i s ,i n the s e q u e n c e HMDS, u n s i z e d , a n d A P S - t r e a t e d g l a s s . Conversely, when using the amine p r o b e , n o n - l i n e a r i t y i s p r o d u c e d w i t h the a c i d i c , CPTMS-sized g l a s s , and t o a lesser degree w i t h unsized g l a s s , but e s s e n t i a l l y l i n e a r p l o t s a r e o b t a i n e d w i t h the b a s i c s u r f a c e s . The s y s t e m a t i c d i f f e r e n c e s i n t e m p e r a t u r e d e p e n d e n c e d i s c u s s e d above are related to the presence o r absence of acid/base functionality at interfacial contacts. I n s p e c t i o n o f F i g u r e s 1, 2 and 3 shows t h a t the p r e d o m i n a n c e o f d i s p e r s i o n f o r c e s r e s u l t s i n w h a t seem t o b e r o u g h l y c o n s t a n t s l o p e s i n a l l c a s e s . Significant s l o p e r e d u c t i o n s are noted i n F i g u r e s 2 and 3 f o r those cases where a c i d / b a s e f o r c e s a r e e x p e c t e d t o be s i g n i f i c a n t f a c t o r s . In those i n s t a n c e s , ( f o r example b u t a n o l / A P S - t r e a t e d g l a s s i n F i g u r e 2 or butyI amine/CPTMS-treated g l a s s in F i g u r e 3) there are s h i f t s from l e s s e r t o g r e a t e r s l o p e s a s t e m p e r a t u r e s r i s e i n t o the 50 t o


g

o -70°C r a n g e . A t t h e same t i m e , a p r o n o u n c e d r e d u c t i o n i n t h e V values i s apparent. A tentative interpretation calls tor molecular crowding o f those probe vapors capable of interacting with t h e s u b s t r a t e s through n o n - d i s p e r s i v e f o r c e s . These f o r c e s weaken a t i n c r e a s i n g t e m p e r a t u r e s until the probe molecules, whether p o l a r o r not, adopt s u r f a c e o r i e n t a t i o n s s i m i l a r t o those taken on by octane. Thereupon, they interact with the surface m a i n l y through v a n der Waals f o r c e s . Partial justification of these speculations follow from a c t i v a t i o n e n e r g i e s computed from F i g u r e s 1 t o 3, a n d r e p o r t e d i n T a b l e I I I . In a d d i t i o n T a b l e I I I c o n t a i n s a c t i v a t i o n e n e r g i e s for the r e t e n t i o n o f the d i a m i n e probe, n o t i n c l u d e d i n t h e p r e c e d i n g figures. The data are c a l c u l a t e d only for linear p o r t i o n s of the Arrhenius representations. A roughly constant value n e a r 2.5 Kcal/mol i s obtained when d i s p e r s i o n f o r c e s a r e d o m i n a n t . This a p p l i e s not o n l y to the octane probe, but t o a c i d / a c i d and base/base p a i r s as w e l l . The s t r o n g e s t acid/base c o n t r i b u t i o n s a r e p r o d u c e d b y -OH/APS, d i a m i n e / C P T M S , a n d t o a lesser degree -NH /CPTMS i n t e r a c t i o n s . T h i s f o l l o w s the sequence o f i n t e r a c t i o n 2


Surf ace Characteristics of Glass Fibers


17. OSMONT & SCHREIBER


237



238






239

240


potentials F i g u r e 4.

Table

i n d i c a t e d by t h e r e s p e c t i v e n p a r a m e t e r s ,

I I I . A c t i v a t ion Energies for Probe/Substrate (E in Kcal.mol" ) +

S u b s t r a t e : Probe:


E-glass CPTMS-sized HDMS-sized APS-sized

n-Octane 2..4 2. 8 2..0 2..4

as

shown

in

Interactions

1

Butanol 2..7 2,.6 2,.3 0,.25

Butylamine 1. .2 0,.44 2,. 1 2 .7

Ethylene

Diamine

1., 1 0. 23 2..0 3.. 1

A final reflection o f t h e complex temperature dependence p h e n o m e n a i s s e e n i n F i g u r e 5, s h o w i n g t h e v a r i a t i o n o f fi i t s e l f . Interestingly, t h e pronounced acid and base characteristics p r o d u c e d b y CPTMS a n d A P S t r e a t m e n t s , respectively, increase as the temperature r i s e s a b o v e t h e r e f e r e n c e 30°C, r e a c h i n g a b r o a d p e a k a t a p p r o x i m a t e l y 60°C. A t h i g h e r t e m p e r a t u r e s , a c i d a n d b a s e strengths decrease. T h i s p e r m i t s a n e l a b o r a t i o n t o b e made o n t h e ideas advanced above. In the c a s e s s t u d i e d , a c i d / b a s e and d i s p e r sive force interactions coexist, the latter being more t h e r m o l a b i l e a t lower t e m p e r a t u r e s . As a r e s u l t , inherent s u r f a c e acidity or b a s i c i t y increases at f i r s t with r i s i n g temperatures, and decreases substantially once a specific temperature is exceeded. This temperature overcomes the energy b a r r i e r f o r t h e detachment of molecules retained by t h e o p e r a t i v e a c i d / b a s e forces. An a d d i t i o n a l observation arising f r o m F i g u r e 5, p e r t a i n s t o polymer p r o c e s s i n g . The d a t a i s such that a t p r o c e s s i n g temperatures, typically above approximately 150°C, a l l of the g l a s s s u r f a c e s a p p e a r t o b e a m p h i p a t i c , w i t h ft n e a r 0. F r o m t h e s e v a r i o u s arguments, i t i sreasonable t o conclude that: - Silane c o u p l i n g agents exert powerful effects on t h e interaction potential of glass fiber surfaces, enabling t h e user to design either acidic or basic functionality into these r e i n f o r c i n g s t r u c t u r e s f o r polymer composites. - The e x i s t e n c e of acid/base i n t e r a c t i o n s r e s u l t s i n d i s t i n c t orientations of a d s o r b i n g m o i e t i e s a t the s u b s t r a t e s u r f a c e and allows f o r greater concentrations of sorbed species than i sthe c a s e when o n l y d i s p e r s i o n f o r c e s a r e a c t i v e . - Strong non-dispersive interactions are temperature dependent and their importance i n the cases studied here d i m i n i s h e s g r e a t l y a b o v e a p p r o x i m a t e l y 70°C. - Different interactions may e x i s t between reinforcing m o i e t i e s and polymer m a t r i x e s a t p r o c e s s i n g , as opposed to use temperatures. General trends suggest that s u r f a c e m o d i f i c a t i o n s exert greater influence on u s e p r o p e r t i e s than on p r o c e s s i n g behav io r . ii. Sorption Results: Acid/base interactions a r e expected to p r o d u c e p r e f e r e n t i a l a s s o c i a t i o n s among t h e a f f e c t e d c o m p o n e n t s o f


17.

O S M O N T & SCHREIBER


E'(K


241

cal)

F I G U R E 4. D e p e n d e n c e of on a c i d / b a s e i n t e r a c t i o n s . Q ^

octane; diamine.

#

butanol)

retention Probes: A

volume

butyl amine;

activation

energies

and


242

INVERSE GAS

CHROMATOGRAPHY


2J0-I

-3.CH

F I G U R E 5. T e m p e r a t u r e for glass fibers: E-glassi Q APS-treat.

dependence

# CPTMS-treatj

o f

interaction

HDMS-treat j

parameter

and





243

a polymer system. Local compositional heterogeneity is a consequence of these a s s o c i a t i o n s , thereby lending support to contentions that, as a general rule, muIti-component polymer systems a r e considered as heterogeneous (8,16). Preferential adsorption, d r i v e n by a c i d / b a s e f o r c e s , was d e m o n s t r a t e d r e c e n t l y by Fowkes ( 1 7 ) , f o r p o l y m e r s i n t e r a c t i n g with filler particles. The b e h a v i o r o f t h e v a r i o u s l y s i z e d g l a s s f i b e r s a s a d s o r b e n t s f o r macromolecules s e l e c t e d for present purposes, i s summarized i n F i g u r e s 6 a n d 7. T h e f o r m e r s h o w s t h e s o r p t i o n o f a c i d i c P V C ; t h e l a t t e r s h o w s t h e a d s o r p t i o n o f b a s i c PMMA. Both s o r p t i o n sequences d i s p l a y theexpected s e l e c t i v i t y . The adsorption o f PVC i s f a v o r e d o n A P S - t r e a t e d g l a s s , w h i l e PMMA i s a d s o r b e d most v o l u m i n o u s l y on C P T M S - s i z e d g l a s s . The adsorption processes i n both cases a r e a f f e c t e d by t h e s o l v e n t s used. Both THF a n d t o l u e n e a r e c o n s i d e r e d t o b e b a s e s ( 1 7 ) ,e s p e c i a l l y the former. T h e r e f o r e , these s o l v e n t s tend t o compete f o r a d s o r p t i o n s i t e s , p a r t i c u l a r l y on a c i d i c s u r f a c e s . T h i s may i n h i b i t somewhat the adsorption o f PMMA; i t may a l s o f a v o r t h e s o r p t i o n o f PVC o n basic substrates. Further, with regard to the adsorption data, both polymers produce Langmuir- type isotherms when glass s u b s t r a t e s a r e amphipatic (E-glass and HMDS-treatment), or a r e of like acid/base functionality as the polymer. The plateaus c h a r a c t e r i s t i c o f L a n g m u i r i s o t h e r m s a r e n o t p r o d u c e d when strong acid/base i n t e r a c t i o n s a r e i m p l i e d ( t h a t i s , PVC o n A P S - t r e a t e d g l a s s a n d PMMA o n C P T M S - t r e a t e d glass). Qualitatively, this indicates the formation of polymeric monolayers i n t h e former cases and t h e development of m u l t i l a y e r s i n the l a t t e r , n o t a b l y i n regions o f t h e s u r f a c e marked by t h e p r e s e n c e o f s t r o n g a c i d o r base s i t e s . Further surface diagnostics are required to elaborate on t h e s e h y p o t h e s e s . Finally, t o support theq u a l i t a t i v e contention of acid/base d r i v i n g forces for the s e l e c t i v e sorption displayed above, the adsorption data were p l o t t e d a g a i n s t t h eftv a l u e o f t h e v a r i o u s glass substrates. The r e s u l t s o f t h i s procedure a r e shown i n Figure 8. T o a v o i d e x c e s s i v e c r o w d i n g , F i g u r e 8 i s r e s t r i c t e d t o a d s o r p t i o n d a t a from s o l u t i o n s w i t h i n i t i a l polymer c o n c e n t r a t i o n s at nominally 1.0 a n d 1.5 w t - % . T h e p a t t e r n of results i s representative of the e n t i r e adsorption sequence. The s t r o n g correlation between acid/base driving forces and a d s o r p t i o n behavior i sunmistakeable. W h i l e i s o t h e r m s w e r e c o n d u c t e d a t 30°C o n l y , t h e t r e n d s i n F i g u r e 8 s h o u l d p e r s i s t a n d become a c c e n t u a t e d t o a p p r o x i m a t e l y 60°C, j u d g i n g f r o m t h e t e m p e r a t u r e v a r i a t i o n o f 0 documented i n Figure 5. At higher temperatures, the tendency s h o u l d d i m i n i s h and under p r o c e s s i n g c o n d i t i o n s , no preferential s o r p t i o n e f f e c t s should remain. Some s e r i o u s consequences appear t o a r i s e from t h e p r e s e n t results. In m a t e r i a l c o m p o s i t e s i n v o l v i n g g l a s s fibers, proper ties strongly a f f e c t e d by i n t e r f a c i a l conditions should be p a r t i c u l a r l y s e n s i t i v e to the s e l e c t i o n of surface modifying agents. A d h e s i o n a t m a t r i x / f i b e r i n t e r f a c e s i s an o b v i o u s c a s e i n p o i n t , as a r e the mechanical p r o p e r t i e s of the system at high load; that i s , i n the region of non-linear response. T h e IGC method, and n o t a b l y i t s a b i l i t y t o o f f e r comparative indexes of acid/base activity, i s useful as a guide to p r e f e r r e d surface


INVERSE GAS

244


c

ads.

(mg

/

CHROMATOGRAPHY

m) 2

F I G U R E 6. A d s o r p t i o n i s o t h e r m s f o r P V C o n i O E-glassj DAPS-treat.

4> C P T h S - t r e a t j

? HOMS-treat?

and




Cads, (mg / m )


2

O

APS-treat.


245

246

INVERSE GAS

Cad

CHROMATOGRAPHY

(mg/m*)


•3.0

•2.0

-3.0

1

.

-20

.

I

-I©

0

FIGURE 8. P o l v m e r adsorption acid/base concept: . P V C f r o * I X ( 0 ) a n d 1.5X « ? ) PMMA f r o m I X < » ) a n d 1 . 5 X < ^ >

on glass

i

10

1 20 fibers,

—12 as f u n c t i o n

solution; solution.


of

17.

OSMONT & SCHREIBER

SurJace Characteristics of Glass Fibers


treatments for r e i n f o r c i n g f i b e r s . Thus, treatments leading to strongly b a s i c s u r f a c e s may be p r e f e r e n t i a l l y selected for m a t r i x e s , s u c h a s PVC, w h i c h r e g i s t e r a s L e w i s acids. However, b a s i c m a t r i x e s may b e n e f i t f r o m s u r f a c e t r e a t m e n t s r e n d e r i n g g l a s s fibers acidic. Strong acid/base c o u p l i n g , thereby designed into composite s t r u c t u r e s , should b e n e f i t property r e t e n t i o n during use of the a r t i c l e s . F i n a l l y , the s t r o n g temperature dependence of i n t e r a c t i o n s i s again noted: the aging or p r o p e r t y l o s s of polymer s y s t e m s may b e t h e r e s u l t , at least i n part, of temperature fluctuations, which necessitate composition adjustments at m o l e c u l a r or domain l e v e l s . AcknowIedament s In p a r t , t h i s w o r k was s u p p o r t e d b y g r a n t s from the Natural Sciences and E n g i n e e r i n g Research C o u n c i l , Canada. We a r e grateful to Owens-Corning F i b e r g l a s s , Granville, OH for i t s support and f o r the s u p p l y of screened, sized, glass fiber samples. U s e f u l d i s c u s s i o n s w i t h D r . S h e l d o n P. W e s s o n , Textile Research I n s t i t u t e , P r i n c e t o n , N.J. are p a r t i c u l a r l y noted.

Literature Cited 1. Braun, J.M.; Guillet, J.E. Adv. Polym. Sci. 1976, 21, 108. 2. Gray, D.G. Prog. Polym. Sci. 1977, 5, 1. 3. Deshpande, D.D.; Patterson, D.; Schreiber, H.P.; Su, C.S. Macromolecules 1974, 7, 530. 4. DiPaola-Baranyi, G.; Richer, J.; Prest, W.M. Jr., Can. J. Chem 1985, 63, 223. 5. DiPaola-Baranyi, G.; Degre, P. Macromolecules 1981, 14, 1456. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

Olabisi, O.; Robeson, L.M.; Shaw, M.T. Polymer-Polymer Miscibility: Academic Press: New York, 1979, chapter 3. Boluk, Y.M.; Schreiber, H.P. Polym. Comp. 1986, 7, 295. Schreiber, H.P. in Proc. XIII Internat. Conf. in Org. Coatings Sci.Tech., Athens, Greece, July 1987, p. 367. Carre, A.; Garnet, D.; Schultz, J.; Schreiber, H.P. J. Macromol. Sci., Chem. 1986, A-23, 1. Saint-Four, C.; Papirer, E. J. Colloid Interface Sci. 1983, 91, 69. Chabert, B.; Chauchard, J.; Lachenal, G.; Philibert, T.; Soulier, J.P. Comptes Rendus Acad. Sci. 1982, 295, 987. Drago, R.S.; Vogel, G.G.; Needham, T.E. J. Amer. Chem. Soc. 1971, 93, 6014. Cuckor, P.M.; Prausnitz, J.M. J. Phys. Chem. 1972, 76, 598. Fowkes, F.M.; Mostafa, M.A. IEC Prod. R&D. 1978, 17, 3. Shafrin, E.G.; Zisman, W.A. J. Amer. Ceram. Soc. 1967, 50, 487. Alexander, G.; Bradshaw, S.; Dodd, K.; Guthrie, J.T.; Mason, T. In Proc. XIII Internat. Conf. in Org. Coatings Sci. Tech. Athens, Greece, July, 1987, p. 133. Fowkes, F.M. J. Adhesion Sci. Tech. 1987, 1, 7.

RECEIVED October26,1988

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247

Inverse Gas Chromatography - American Chemical Society

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