The Role of Fillers and Reinforcements in Plastics Chemistry

1 The Role of Fillers and Reinforcements in Plastics Chemistry RAYMOND

B. S E Y M O U R

Downloaded by UNIV OF CHICAGO on March 10, 2013 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0134.ch001

University of Houston, Houston, Tex. 77004

As with natural composites such as wood, leaves, feathers, and bones, the resin-like component in modern synthetic composites transfers the stress to the reinforcing component. Thus a strong interfacial bond is essential, and crack propa gation must be deterred in high strength composites. The discontinuous phase may consist of silicas, silicates, calcium carbonate, carbon black, and comminuted polymers or more functional reinforcements such as fibrous glass, graphite, boron and single crystals. While the reinforcements have been used primarily with thermosetting resins in the past, they are now being used to reinforce thermoplastics, and these new composites have added a new dimension to the plastics industry.

T i J " o s t m o d e r n a n d t r a d i t i o n a l o r g a n i c coatings a n d plastics c o n t a i n a d d i t i v e s , a n d h e n c e are composites

i n a b r o a d sense.

Additives

i n c l u d e gases i n c e l l u l a r p l a s t i c s , p i g m e n t s i n coatings, p l a s t i c i z e r s i n flexibilized

poly ( v i n y l c h l o r i d e ) , antioxidants i n weather-resistant plas-

tics, l u b r i c a n t s , a n d gloss-control agents as w e l l as fillers a n d r e i n f o r c e ments.

T h i s d i s c u s s i o n is l i m i t e d to composites

c o n t a i n i n g fillers a n d

reinforcements o n l y . A l t h o u g h s u c h a d i s c u s s i o n c o u l d i n c l u d e m a t e r i a l s s u c h as w o o d , leaves, feathers, a n d bones, i t is c o n f i n e d to composites c o n s i s t i n g of a s y n t h e t i c resinous o r c o n t i n u o u s phase a n d a n a t u r a l o c c u r r i n g o r s y n t h e t i c d i s c o n t i n u o u s o r filler phase.

T h e s t r e n g t h o f these

composites

d e p e n d s o n t h e i n t e r f a c i a l b o n d b e t w e e n these c o m p o n e n t s , t h e a b i l i t y of t h e c o m p o s i t e to deter c r a c k p r o p a g a t i o n , t h e s t r e n g t h o f t h e d i s c o n t i n u o u s phase, a n d , t o a lesser extent, t h e s t r e n g t h o f t h e c o n t i n u o u s resinous phase. 1 In Fillers and Reinforcements for Plastics; Deanin, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

2

FILLERS AND R E I N F O R C E M E N T S FOR PLASTICS

W h e n there is l i t t l e i n t e r f a c i a l a c t i o n , as is the case w i t h s p h e r e - r e s i n composites, the m o d u l u s of the c o m p o s i t e

(M)

glass

is r e l a t e d

to the m o d u l u s of the r e s i n ( M ), a n d the f r a c t i o n a l v o l u m e o c c u p i e d b y c

the

filler

(c)

as s h o w n b y the f o l l o w i n g E i n s t e i n - G u t h - G o l d

(EGG)

equation: M

+ 2.5c +

= M (l 0

14.1c ) 2

S i n c e there is some i n t e r f a c i a l b o n d i n g b e t w e e n the

filler

surface

a n d t h e r e s i n a n d the p a r t i c l e s t e n d to cluster, the E G G e q u a t i o n m u s t Downloaded by UNIV OF CHICAGO on March 10, 2013 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0134.ch001

be m o d i f i e d for c a r b o n b l a c k - r e s i n composites as f o l l o w s : M T h e shape f a c t o r (/)

= M (l 0

+ 0.67/c +

1.62/V)

is e q u a l to the r a t i o of the l e n g t h to the d i a m e t e r

of the filler p a r t i c l e s . T h e r a t i o of the diameter—i.e., t h i c k n e s s — i s c a l l e d t h e aspect r a t i o for l a m e l l a r

fillers.

W h e n c is greater t h a n 0.1, i t is essential to i n c l u d e a c r o w d i n g factor, β,

as suggested

by

Mooney.

The Mooney

e q u a t i o n for s i m p l e i n e r t

spheres i s :

T h e use of silicas, s u c h as f u m e d s i l i c a a n d q u a r t z a n d silicates, s u c h as c l a y a n d t a l c w h i c h are w i d e l y u s e d as

fillers,

is d i s c u s s e d i n

other chapters i n this v o l u m e . T h e s e fillers m a y be s p h e r o i d a l , l a m e l l a r , or a c i c u l a r . S u r f a c e t r e a t m e n t w h i c h increases the s t r e n g t h of the i n t e r f a c i a l b o n d is also d i s c u s s e d i n other chapters as are r e l e v a n t a p p l i c a t i o n s of composites o n c o r r o s i o n e n g i n e e r i n g a n d h o u s i n g . T h e r u b b e r i n d u s t r y a n d the plastics composite i n d u s t r y w e r e b u i l t primarily on empirical knowledge.

H o w e v e r , the f u t u r e g r o w t h of these

c o m p o s i t e i n d u s t r i e s w i l l d e p e n d l a r g e l y o n the i n t e l l i g e n t use of p e r f o r m a n c e d a t a a n d m o d e r n concepts of t h e i n t e r f a c i a l b o n d the c o n t i n u o u s a n d d i s c o n t i n u o u s phases of composites.

between

T h e latter is

sometimes c a l l e d m i c r o m e c h a n i c s . T h e h i s t o r y of t h e c o m p o s i t e i n d u s t r y i n c l u d e s n u m e r o u s successes as w e l l as some f a i l u r e s . F a i l u r e s for composites,

s u c h as r e i n f o r c e d

plastic pipe have usually resulted from an interfacial b o n d failure. T h i s t y p e of f a i l u r e is a g g r a v a t e d w h e n transitions o c c u r as a result of changes i n t e m p e r a t u r e d u r i n g service. T h u s , f a i l u r e s m a y o c c u r w h e n a m o r p h o u s p l a s t i c composites are h e a t e d a b o v e t h e i r glass t r a n s i t i o n t e m p e r a t u r e s , w h e n c r y s t a l l i n e p l a s t i c composites are h e a t e d a b o v e t h e i r m e l t i n g p o i n t s ,

In Fillers and Reinforcements for Plastics; Deanin, R., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

1.

3

Plastics Chemistry

SEYMOUR

a n d w h e n t h e r m o s e t t i n g r e s i n composites are h e a t e d a b o v e t h e i r u s e f u l temperatures. A s p r o o f of t h e i r n u m e r o u s successful a p p l i c a t i o n s , over 1.2 b i l l i o n pounds

of

fibrous

glass r e i n f o r c e d plastics w e r e

u s e d i n the

United

States i n 1972 ( 1 ). B e c a u s e of t h e i r o u t s t a n d i n g p e r f o r m a n c e i n m a r i n e , t r a n s p o r t a t i o n , c o n s t r u c t i o n , a n d corrosion-resistant a p p l i c a t i o n s , i t is exp e c t e d that the c o n s u m p t i o n of composites w i l l d o u b l e w i t h i n the next five years. A n n u a l past a n d p r e d i c t e d c o n s u m p t i o n d a t a for r e i n f o r c e d plastics are l i s t e d i n T a b l e I.


Table I.

A n n u a l Consumption in Millions of Pounds of Reinforced Plastics in the United States

Application

1967

1972

1978

Marine Transportation Construction Consumer Electrical C o r r o s i o n resistant Aircraft Appliances Miscellaneous

127 80 73 57 45 40 24 18 90

321 252 185 99 79 110 28 61 93

550 700 450 115 85 390 40 180 180

Total

544

1,227

2,800

B e c a u s e of t h e i r h i g h s t r e n g t h - t o - w e i g h t r a t i o , d u r a b i l i t y , a n d freed o m of d e s i g n , the w o r l d w i d e g r o w t h of these composites

should

be

c o m p a r a b l e w i t h the g r o w t h d a t a s h o w n for the U n i t e d States i n T a b l e I. C e r t a i n l y , the use of c o m p o s i t e d o u b l e b y 1979 (2).

materials i n W e s t e r n E u r o p e should

T h e d a t a o n t h e c o n s u m p t i o n of nonfibrous

fillers

are not as r e a d i l y d e l i n e a t e d as those o n fibrous reinforcements. T h e use of

filled

plastics has b e e n r e v i e w e d a n n u a l l y for m a n y years (3, 4, 5 ) .

W o o d flour, w h i c h is m a d e b y a t t r i t i o n g r i n d i n g of w o o d , is s u p e r i o r as a filler to the less fibrous g r o u n d shell flour. W o o d flour was u s e d b y B a e k e l a n d at the b e g i n n i n g of the 2 0 t h c e n t u r y a n d is s t i l l u s e d to r e i n force p h e n o l i c resins.

Composites

w i t h h i g h e r i m p a c t resistance

are

o b t a i n e d b y r e p l a c i n g the w o o d flour b y c e l l u l o s i c , asbestos, glass, a n d n y l o n fibers. T h e art w h i c h w a s d e v e l o p e d for p h e n o l i c r e s i n composites has b e e n e x t e n d e d to the r e i n f o r c e m e n t of polyester a n d e p o x y t h e r m o setting resins. F i b r o u s glass r e i n f o r c e d polyester composites n o w account for o v e r 80%

of the v o l u m e of p l a s t i c composites.

T h i s phase of the i n d u s t r y

s t a r t e d w i t h composites m a d e b y t h e h a n d l a y i n g u p of r e s i n i m p r e g n a t e d glass m a t . H o w e v e r , m u c h of the recent g r o w t h has b e e n associated w i t h b u l k m o l d i n g c o m p o u n d s ( B M C ) a n d sheet m o l d i n g c o m p o u n d s ( S M C ).


4

FILLERS AND R E I N F O R C E M E N T S FOR PLASTICS

I n j e c t i o n m o l d e d r e i n f o r c e d polyester r e s i n composites

h a v e also

con

t r i b u t e d to the g r o w t h of t h e r e i n f o r c e d segment of the plastics i n d u s t r y (θ). D e s p i t e l i m i t e d p r o d u c t i o n , the r o l e of r e i n f o r c e m e n t s i n h i g h p e r f o r m a n c e composites, (7).

s u c h as r e i n f o r c e d p o l y i m i d e s , is also i m p r e s s i v e

T h e s u p e r i o r i t y of the latter as s t r u c t u r a l m a t e r i a l s has justified t h e

use of m o r e s o p h i s t i c a t e d r e i n f o r c e m e n t s , s u c h as s a p p h i r e single crystals and graphite and boron

filaments.

T h e h i g h cost of s a p p h i r e r e i n f o r c e

ments has b e e n r e d u c e d b y s p i n n i n g these p r o d u c t s f r o m m o l t e n a l p h a alumina. Downloaded by UNIV OF CHICAGO on March 10, 2013 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0134.ch001

R e i n f o r c e m e n t was c o n s i d e r e d to b e l i m i t e d to t h e r m o s e t t i n g c o m posites p r i o r to 1950. T h i s art has n o w b e e n e x t e n d e d to t h e r m o p l a s t i c s , a n d one of the e a r l y a p p l i c a t i o n s w a s the p r o d u c t i o n of

fibrous

glass-

r e i n f o r c e d p o l y s t y r e n e m i n e s w e e p e r s i n 1955. H o w e v e r , c r y s t a l l i n e t h e r moplastics like nylon, rather than amorphous thermoplastics like poly styrene, are p r e f e r r e d .

A process for m a k i n g

n y l o n m o l d i n g p o w d e r s w a s p a t e n t e d i n 1958

fibrous

glass-reinforced

(8).

Table II. A n n u a l Consumption in Millions of Pounds of Reinforced Thermoplastics in 1971 and 1972 1971

1972

Polypropylene Styrene polymers Nylon Polyethylene Acetal Miscellaneous

Type of Plastic

22 19 12 6 3 5

28 20 16 7 4 7

Total

67

82

Reinforced

thermoplastics

(RTP)

are e n g i n e e r i n g plastics w h i c h

perform satisfactorily under conditions where unfilled thermoplastics fail. A s s h o w n i n T a b l e I I , the a n n u a l p r o d u c t i o n of R T P i n the U n i t e d States, w a s less t h a n one m i l l i o n p o u n d s i n 1964, g r e w to m o r e t h a n 80 m i l l i o n p o u n d s or almost 40,000 m e t r i c tons i n 1972 ( 9 ) .

T h e current annual

c o n s u m p t i o n of R T P i n W e s t e r n E u r o p e is 20,000 m e t r i c tons. accounts for m o r e t h a n h a l f of this v o l u m e .

Nylon

C o n s u m p t i o n of R T P i n

E u r o p e is e x p e c t e d to t r i p l e w i t h i n the next five years

(10).

P o t a s s i u m titanate m i c r o f i b e r s are b e i n g u s e d to p r o d u c e

composites

of n y l o n , acetal, p o l y p r o p y l e n e , a n d A B S . B e c a u s e t h e y a r e s m a l l , these single c r y s t a l m i n e r a l reinforcements are m o r e r a n d o m l y o r i e n t e d t h a n the l a r g e r

fibrous

glass p a r t i c l e s .

T h u s , m o l d i n g s of these

composites

are essentially i s o t r o p i c w h e r e a s fibrous glass—nylon composites are aniso tropic.

This sophisticated

filler

has also b e e n

composites that c a n b e e l e c t r o p l a t e d

u s e d to p r o d u c e

(11).


ABS

1.

SEYMOUR

Plastics

5

Chemistry

A s s h o w n i n F i g u r e 1, n y l o n composites

are n o w b e i n g u s e d suc-

cessfully as p u m p a n d compressor parts. T h e s e parts operate at h i g h t e m p e r a t u r e s a n d pressures a n d o u t p e r f o r m p r e v i o u s l y u s e d m e t a l parts. T h e m o l d e d parts s h o w n c o n t a i n fibrous glass w h i c h increases the r i g i d i t y , tensile s t r e n g t h , c r e e p resistance, a n d t e m p e r a t u r e resistance a n d reduces the t h e r m a l coefficient of e x p a n s i o n a n d m o i s t u r e a b s o r p t i o n of n y l o n 6,6. T h i s c o m p o s i t e also contains a p o l y t e t r a f l u o r o e t h y l e n e ( P T F E ) filler

w h i c h l u b r i c a t e s the m o v i n g parts. T h u s , the p e r f o r m a n c e of these

composites

demonstrates the r o l e of b o t h

fillers

a n d reinforcements i n

technology.


plastics

Figure 1.

Molded fibrous glass parts

M o s t of the 24 b i l l i o n p o u n d s of plastics p r o d u c e d i n t h e U n i t e d States i n 1972 w a s u s e d for g e n e r a l p u r p o s e a p p l i c a t i o n s . W h i l e the m o r e difficult p r o b l e m s w e r e s o l v e d b y s o p h i s t i c a t e d p l a s t i c composites,

the

m o r e e c o n o m i c a l fibrous glass r e i n f o r c e d polyesters c o n t i n u e d to a c c o u n t


6

FILLERS A N D R E I N F O R C E M E N T S FOR PLASTICS

f o r the b u l k o f the c o n s u m p t i o n o f r e i n f o r c e d plastics. O n e o f t h e m a j o r factors i n this g r o w t h w a s S M C . T h e rate o f f u t u r e g r o w t h o f R T P w i l l b e e q u a l l y d r a m a t i c . P o t a s s i u m titanate m i c r o c r y s t a l s a n d other e c o n o m i c a l w h i s k e r - l i k e fillers w i l l c o n t r i b u t e t o this g r o w t h .

L e a d e r s i n a l l segments o f the plastics i n d u s t r y

are confident that p l a s t i c composites w i l l c o n t i n u e t o solve p r o b l e m s t h a t c a n n o t b e s o l v e d w i t h t r a d i t i o n a l materials o f c o n s t r u c t i o n .


Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Chem. Week (1973) 112 (8), 27. Wildman, D., Plast. Aust. (1972) 23 (7), 15. Seymour, R. B., Mod. Plast. (1973) 50 (10A) 210, 216. Schoengood, Α. Α., SPE J. (1972) 28 (6), 22. Seymour, R. B., Ann. Rev. Ind. Eng. Chem., 1970 (1972) 305. Austin, C., Plast. Aust. (1972) 23 (3), 13. Witzel, J. M., Jablonski, R. J., Kruh, D., Chem. Tech. (1972) 2, 440. Bradt, R., U. S. Patent 2,877,501 (1959). Gross, S., Mod. Plast. (1973) 50 (1), 59. Wellman, J. F., Plast. Aust. (1972) 23 (6), 13. Weston, Ν. E., SPE J. (1972) 28, 37.

RECEIVED October 11, 1973.


The Role of Fillers and Reinforcements in Plastics Chemistry

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