Mica as a Reinforcement for Plastics - Advances in Chemistry (ACS

5 Mica as a Reinforcement for Plastics

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P. D .

SHEPHERD,

F.

J.

GOLEMBA,

and F. W .

MAINE

Fiberglas Canada, Ltd., G u e l p h , Ontario, Canada

Theoretically, mica flakes (100-μ diameter) and other plate lets can reinforce plastics as efficiently asfibersfor unidirec tional composites; for planar isotropic composites platelets are more efficient thanfibers.Strength and modulus of mica composites are a function of flake aspect ratio and volume fraction. Strengths measured to date are lower than possible, owing to flaws in the flakes. Suitably prepared mica will reinforce ABS, SAN, and nylon 6/6 to yield useful injection moldable compounds with moduli higher than present RTP's, flexural strengths comparable with RTP's, and impact strengths less than RTP's. In ternary composites of mica/ glassfiber/thermoplasticresin, up to 60 wt % solids, maxi mum in modulus, flexural strength, and impact strength does not occur at a single composition. Therefore, in any applica tion, desired properties must be compromised.

T j l a k e o r p l a t e l e t m i n e r a l s a r e materials n o t g e n e r a l l y r e c o g n i z e d as r e i n f o r c i n g elements.

W e have f o u n d that m i c a , w h e n suitably pre

p a r e d , w i l l increase the strength a n d m o d u l u s o f some c o m m o n p o l y m e r s . T h i s p a p e r outlines the p r i n c i p l e s of platelet r e i n f o r c e m e n t a n d c o m p a r e s t h e t h e o r e t i c a l b e h a v i o r of platelets as r e i n f o r c e m e n t w i t h t h e b e h a v i o r of fibers a n d spheres.

E x p e r i m e n t a l results c o m p a r e p o l y m e r s r e i n f o r c e d

w i t h mica a n d mica/glass-fiber combinations

to glass-fiber

reinforced

compounds. Theoretical

Principles

P o l y m e r s r e i n f o r c e d w i t h platelets c a n b e treated i n a m a n n e r s i m i l a r to discontinuous-fiber r e i n f o r c e m e n t .

Consider a platelet composite i n

w h i c h t h e platelets a r e : ( 1 ) square w i t h side L, thickness t (2) p e r f e c t l y a l i g n e d 41 Deanin and Schott; Fillers and Reinforcements for Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

42

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

(3)

p e r f e c t l y b o n d e d to the m a t r i x

(4)

evenly spaced

(5)

l i n e a r l y elastic to f a i l u r e

S i n c e the platelets a n d m a t r i x h a v e different elastic m o d u l i , s t r a i n i n g i n tension of s u c h a c o m p o s i t e causes shear stress at t h e p l a t e l e t - m a t r i x interface. T h i s is analogous to the case of fibers i n a p l a s t i c m a t r i x . T h e s e shear stresses t r a n s m i t the a p p l i e d l o a d to t h e platelets, c a u s i n g tensile stress, σ , i n the platelets. S i n c e the shear stresses increase w i t h distance Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on March 8, 2018 | https://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0134.ch005

ρ

f r o m the center of t h e flake (as for fibers), the tensile stress i n the p l a t e l e t is not constant b u t is a m a x i m u m at the flake center a n d decreases w i t h distance f r o m t h e center.

T h u s , there w i l l be a c r i t i c a l l e n g t h of p l a t e l e t

w h i c h m u s t b e e x c e e d e d for the flakes to b e stressed to t h e i r f a i l u r e stress, σ * . T h i s c r i t i c a l l e n g t h d i v i d e d b y thickness is the c r i t i c a l aspect r a t i o . ρ

M a t r i c e s t h a t are elastic to f a i l u r e h a v e b e e n e x a m i n e d b y P a d a w e r and Beecher ( I ) herd

(2).

w h i l e d u c t i l e matrices h a v e b e e n c o n s i d e r e d b y S h e p

When

the m a t r i x is d e f o r m i n g

m o d u l u s ( E ) has b e e n s h o w n ( I ) c

E

(MRF) + E

= EV

c

P

P

e l a s t i c a l l y , the

composite

to b e : m

( l -

(1)

V) p

where: E

=

p l a t e l e t elastic m o d u l u s

=

25 X

=

platelet v o l u m e f r a c t i o n

=

m a t r i x elastic m o d u l u s

p

V

p

E

m

MRF =

10

6

p s i for m i c a

modulus reduction j

factor

tanh u u (G

m

"

-

«£

a = =

G

m

=

P

+ (1

V )'" p

-

V ) P

aspect r a t i o L/t

m a t r i x shear

modulus

T h e t h e o r e t i c a l m o d u l i for m i c a composites h a v e b e e n c a l c u l a t e d assuming G

m

= 200,000 p s i a n d are i l l u s t r a t e d i n F i g u r e 1. T h e t h e o r e t i c a l

m o d u l u s for a system of fibers a n d spheres w i t h t h e same m o d u l u s c a n also b e c a l c u l a t e d u s i n g K e l l y ' s ( 3 ) equations for fibers a n d N i e l s e n ' s equations for spheres.

T h e results of these c a l c u l a t i o n s are also

Deanin and Schott; Fillers and Reinforcements for Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

(4)

shown

5.

Mica

SHEPHERD E T A L .

as

43

Reinforcement

20 0.7

15 MODULUS (106 P S I )

1

0


5

ι

CL

.0

Figure

1.

ι

ι

30 50

Theoretical

i n F i g u r e 1 for comparison.

a v

w

100 300 ASPECT RATIO

modulus

s

1000

of mica-reinforced

plastics

It is a p p a r e n t t h a t platelets a n d fibers are

m o r e efficient stiffening agents t h a n spheres; f o r aspect ratios greater t h a n 50, plates a n d fibers are essentially e q u i v a l e n t . A s the c o m p o s i t e d e f o r m s , the shear stress i n the m a t r i x , n e a r the m a t r i x - p l a t e l e t i n t e r f a c e , a n d the tensile stress i n the p l a t e l e t increase. F o r m a t r i c e s t h a t are elastic to f a i l u r e , the c o m p o s i t e m a t r i x shear s t r e n g t h , a , is r e a c h e d or the flakes f a i l . m

fails w h e n t h e Padawer and

B e e c h e r h a v e c a l c u l a t e d the c o m p o s i t e stress f o r these t w o c o n d i t i o n s : C o m p o s i t e stress for flake f r a c t u r e ŒP C

=

σ * (SRF) V

a ' (1 -

+

p

ρ

= m

V) p

(2)

where: σ * ρ

=

SRF = = a ' m

a* m

p l a t e l e t tensile s t r e n g t h strength reduction factor 1 —

tanh u u

. (1

, — sech

ν u) '

v

=

stress i n the m a t r i x at c o m p o s i t e f a i l u r e

^

σ */3

=

m a t r i x tensile s t r e n g t h

Λ

C o m p o s i t e stress at m a t r i x f a i l u r e a c

where: M P F =

= T

m

(MPF) +

matrix performance

= a " (1 m

V) p

factor


(3)

44

FILLERS AND REINFORCEMENTS

FOR PLASTICS

TENSILE STRENGTH

3

0


(KSI)

' V

p

j

it)

3d bo ibo—3Ô0

= 0.2

e

1000

ASPECT RATIO

Figure

Theoretical

2.

tensile strength of mica-reinforced plastics

T h e c o m p o s i t e s t r e n g t h is t h e n the lesser of σ

ρ 0

or a

m c

brittle

. T h e strength

of S A N r e i n f o r c e d w i t h m i c a platelets, of s t r e n g t h 300,000 p s i , w a s c a l c u l a t e d f r o m this t h e o r y a n d is i l l u s t r a t e d i n F i g u r e 2 ( m i c a strengths u p to 450,000 p s i h a v e b e e n m e a s u r e d b y O r o w a n

(5).

A l s o s h o w n i n F i g u r e 2 is the e x p e c t e d s t r e n g t h of fiber- a n d s p h e r e r e i n f o r c e d S A N , c a l c u l a t e d u s i n g Piggott's ( β ) tions, r e s p e c t i v e l y .

A g a i n , spheres

a n d N i e l s e n s (4)

equa

are m u c h less efficient t h a n

or platelets, b u t fibers are n o w m o r e efficient r e i n f o r c e m e n t for fractions greater t h a n 0.2.

fibers

volume

H o w e v e r , since platelets r e i n f o r c e i n a p l a n a r

d i m e n s i o n r a t h e r t h a n o n l y l o n g i t u d i n a l l y , p l a t e l e t composites m o r e efficient i n p r o d u c i n g p l a n a r i s o t r o p i c composites

than

will

be

fibers.

F o r the S A N s y s t e m , the s t r e n g t h c a l c u l a t i o n s p r e d i c t that t h e c o m posite fails b y m a t r i x a n d not flake f a i l u r e u n d e r a l l c o n d i t i o n s .

However,

for s o m e p o l y m e r s t h e m a t r i x w i l l f a i l at l o w aspect ratios a n d the

flakes

w i l l f a i l at h i g h aspect r a t i o s ; the c o n t r o l l i n g factor is the m a t r i x shear strength. F o r m a t r i c e s that are d u c t i l e a n d flow at a constant shear stress, T , m

composite

strength again depends

greater t h a n ( a * A m )

ratio.

F o r aspect

ratios

1 ( t h e c r i t i c a l aspect r a t i o ) , t h e flake stress

—

p

o n aspect

reaches σ * ; for ratios less t h a n the c r i t i c a l aspect r a t i o , t h e flakes d o n o t ρ

f a i l b u t p u l l out of the m a t r i x . T h e p r e d i c t e d c o m p o s i t e

strength

(2)

u n d e r these c o n d i t i o n s i s : for a < a

c r i t

icai a

for O p t i c a l σ

0

=

c

= ψ

(α +

σ* (l ρ

1) V

p

+

a"

V

m

p

+

(1 -

p

a ' (1 m

(4)

V) 7 ) P


(5)

5.

Mica

SHEPHERD E T A L .

as

45

Reinforcement

F i g u r e 3 illustrates the p r e d i c t e d c o m p o s i t e strengths f o r m i c a i n a polycarbonate For

m a t r i x . T h e c r i t i c a l aspect r a t i o for this system is 49.

aspect ratios greater t h a n 49, t h e m i c a platelets w i l l f r a c t u r e ;

for

aspect ratios less t h a n 49, the flakes d o not f a i l b u t are p u l l e d out of t h e m a t r i x i n t a c t . T h e latter case is analogous to the m a t r i x f a i l u r e case w h e n the

m a t r i x is b r i t t l e .

I n any

r e a l c o m p o s i t e system,

strengths c a l c u l a t e d here are r e d u c e d


poor matrix-platelet adhesion, a n d platelet

:D

30 50

the

theoretical

b y voids, platelet misalignment,

Ï0Ô

flaws.

300

Ï000

ASPECT RATIO

Figure

3.

Theoretical tensile strength of ductile plastics

T h e s t r e n g t h of a n a l i g n e d d i s c o n t i n u o u s calculated using K e l l y a n d Tyson's psi strength i n a polycarbonate

(7)

fiber

fiber

equations.

composite can

be

F o r fibers of 300,000

m a t r i x , the c o m p o s i t e s t r e n g t h is also

s h o w n i n F i g u r e 3, the c r i t i c a l aspect r a t i o for a p p a r e n t that a n a l i g n e d

mica-reinforced

fibers

b e i n g 25.

c o m p o s i t e is s i g n i f i c a n t l y stronger

the e q u i v a l e n t p l a t e l e t c o m p o s i t e for aspect ratios less t h a n 200.

It is than How-

ever, t h e fiber c o m p o s i t e is s t r o n g o n l y i n one d i r e c t i o n ; the transverse tensile s t r e n g t h w o u l d b e a b o u t 8000 p s i . T h e p l a t e l e t c o m p o s i t e , o n t h e other h a n d , w i l l h a v e the same s t r e n g t h i n t h e transverse d i r e c t i o n as i n the l o n g i t u d i n a l direction.

F u r t h e r , i f the platelets are not

perfectly

a l i g n e d b u t r a n d o m l y a r r a n g e d i n a p l a n a r h a b i t , the c o m p o s i t e s t r e n g t h a n d m o d u l u s w i l l not be a f u n c t i o n of testing d i r e c t i o n , as by Economy Although

demonstrated

(9). it is p o s s i b l e

t h e o r e t i c a l l y to p r e d i c t

the

strength

m o d u l u s of the three types of composites b a s e d o n the p r e v i o u s

and

assump-

tions, o n l y the fiber- a n d s p h e r e - r e i n f o r c e d composites c a n be d o n e a c c u rately.

T h i s is b e c a u s e the

fibers

a n d spheres

can

be

characterized

a c c u r a t e l y w h i l e the p l a t e l e t m a t e r i a l s g e n e r a l l y u s e d c a n n o t ; for e x a m p l e , the s t a t i s t i c a l d i s t r i b u t i o n of glass-fiber strengths is k n o w n w h i l e that for m i c a flakes of 100-μ d i a m e t e r c a n n o t be d e t e r m i n e d . ratio measurement

on a

fiber

I n a d d i t i o n , aspect

is s t r a i g h t f o r w a r d w h i l e that for


mica

46

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


FLEXURAL

FLEXURAL STRENGTH (KSI)

MODULUS (10

6

PSI)

o

ioo—zucr ASPECT RATIO

Figure 4.

Experimental

effect of mica aspect ratio on strength and modulus (8)

flakes c a n n o t b e absolute since t h e flakes a r e n o t r e g u l a r i n p l a n a r d i m e n sions o r i n thickness.

Nevertheless, experimental w o r k has substantiated

the theoretical predictions

that strength a n d m o d u l u s

are a nonlinear

f u n c t i o n w i t h respect t o aspect r a t i o a n d that strength a n d m o d u l u s a r e a l i n e a r f u n c t i o n w i t h respect to v o l u m e f r a c t i o n ; F i g u r e 4 illustrates t h e d e p e n d e n c e o f s t r e n g t h a n d m o d u l u s o n aspect r a t i o ; F i g u r e 5 illustrates the linear dependence of strength a n d modulus o n volume fraction.

FLEXURAL STRENGTH (KSI)

V/0 MICA Figure

5.

Experimental

effect of mica volume fraction modulus

on strength and


5.

SHEPHERD E T A L .

Material

Mica as

47

Reinforcement

Properties

A l t h o u g h m e c h a n i c a l p r o p e r t i e s increase c o n t i n u o u s l y u p to 85 w t % m i c a , as s h o w n i n F i g u r e 5, i n j e c t i o n m o l d i n g is feasible o n l y f o r c o m positions less t h a n 6 0 w t % . T w o c o m p l e t e l y different types o f c o m pounds

will

therefore

be considered:

injection

moldable

a n d only


compression moldable.

Figure 6.

Flexural modulus response surface for 6/6 composites (10 psi)

mica/glass-fiber/nylon

6

F o r t h e i n j e c t i o n m o l d a b l e c o m p o u n d s , w e e x a m i n e d t h e effect o f m i c a content a n d of g l a s s / m i c a ratios o n m e c h a n i c a l properties f o r S A N , A B S , n y l o n 6 / 6 a n d t h e r m o p l a s t i c polyester matrices.

T h e complete

response surface f o r 0 - 6 0 w t % glass a n d m i c a has b e e n d e t e r m i n e d f o r the n y l o n 6 / 6 , A B S , a n d polyester systems. F i g u r e s 6, 7, a n d 8 illustrate the t y p e o f surface generated f o r t h e n y l o n 6 / 6 system f o r flexural m o d ulus,

flexural

strength, a n d n o t c h e d i z o d i m p a c t strength, r e s p e c t i v e l y ;

t h e A B S , S A N , a n d polyester systems y i e l d s i m i l a r surfaces. T h e s e i n d i c a t e that t h e m a x i m u m i n m o d u l u s ,

flexural

strength does n o t o c c u r at t h e same c o m p o s i t i o n .

figures

strength, a n d i m p a c t F i g u r e 6 shows t h e

m a x i m u m m o d u l u s to b e at 0 w t % glass, 60 w t % m i c a , a n d the m i n i m u m at 0 w t % glass, 0 w t % m i c a ; F i g u r e 7, t h e m a x i m u m flexural strength at 60 w t % glass, 0 w t % m i c a a n d t h e m i n i m u m at 0 w t % glass, 12 w t % m i c a (0.2 χ 6 0 ) ; F i g u r e 8, t h e m a x i m u m i m p a c t s t r e n g t h at 45 w t % glass (0.75 X 6 0 ) , 0 w t % m i c a a n d t h e m i n i m u m at 7 w t % glass, 0 w t % m i c a o r 0 w t % glass, 60 w t % m i c a . T h u s , n o single c o m p o s i t i o n gives

American Chemical Society Library 16th St.and N.Reinforcements W. Deanin 1155 and Schott; Fillers for Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1974. Washinnton. D. C. 20036

48

FILLERS AND REINFORCEMENTS


187

Figure 7.

FOR PLASTICS

60§ MICA

Flexural strength response surface for 6/6 composites (10 psi)

mica/glass-fiber/nylon

3

07

60^ GLASS

Figure 8.

Notched izod impact strength response surface for fiber /nylon 6/6 composites (ft-lb/inch)

mica/glass-


5.

Mica

SHEPHERD E T A L .

as

49

Reinforcement

a m a x i m u m i n a l l p r o p e r t i e s , a n d a c o m p o s i t i o n m u s t b e selected to y i e l d the d e s i r e d trade-off i n properties. T w o types of p r o d u c t s w o u l d b e of interest r e l a t i v e to existing glassfiber

R T P ' s : (1)

high modulus, and (2)

i m p r o v e d m o d u l u s w i t h little

loss of i m p a c t strength. F o r the present, w e w i l l c o m p a r e the properties


of six n e w c o m p o u n d s b a s e d o n this w o r k : (1)

n y l o n 6 / 6 , 20 w t % glass fiber, 30 w t % m i c a ( R F M 2030)

(2)

n y l o n 6 / 6 , 50 w t %

(3)

A B S , 20 w t % glass fiber, 30 w t % m i c a ( A F M 2030)

(4)

A B S , 50 w t %

(5)

S A N , 20 w t %

glass, 30 w t %

(6)

S A N , 50 w t %

m i c a ( B M 5000)

m i c a ( R M 5000)

m i c a ( A M 5000) m i c a ( B F M 2030)

E v e n at these h i g h r e i n f o r c e m e n t levels i n j e c t i o n m o l d i n g w a s f e a s i b l e . I n fact these composites m o l d e d as r e a d i l y as t h e i r 20 w t %

glass-

fiber counterparts w i t h c y c l e times e q u a l to or less t h a n t h e 20 w t %

glass

c o m p o u n d , as the d a t a i n T a b l e I illustrate. Table I.

M e c h a n i c a l properties

of

Cycle Times for Various Compounds

Compound

Part Size, oz

Cycle Time, sees.

20 w t % glass-fiber S A N B F M 2030 B M 5000

1.20 1.55 1.60

29 23 22

20 w t % g l a s s - f i b e r / n y l o n 6 / 6 R F M 2030 R M 5000

1.45 1.80 1.80

13 10 10

20 w t % g l a s s - f i b e r / A B S A F M 2030 A M 5000

1.17 1.46 1.50

20 21 20

the glass c o m p o u n d s w e r e c o m p a r e d therefore w i t h the 20 w t %

glass-

fiber composites c o m p o u n d e d a n d m o l d e d o n the same e q u i p m e n t .

Table

I I s u m m a r i z e s the properties of the composites

m e a s u r e d to date.

In

g e n e r a l , these n e w composites h a v e h i g h e r m o d u l i , e q u a l strengths a n d heat d i s t o r t i o n temperatures, a n d s o m e w h a t l o w e r i m p a c t strengths t h a n the c o m p a r a b l e

glass r e i n f o r c e d c o m p o u n d .

T h e o n e e x c e p t i o n is R F

2030 w h e r e a l l p r o p e r t i e s are e q u a l to or greater t h a n 20 w t %

glass-

reinforced nylon 6/6. F o r composites greater t h a n 60 w t % m i c a , o n l y c o m p r e s s i o n m o l d i n g p r o d u c e s g o o d composites.

W e have studied thermosetting a n d thermo-

p l a s t i c matrices r e i n f o r c e d w i t h 50 v o l %

mica.

M o d u l i m u c h higher

t h a n existing c o m p o u n d s w e r e o b t a i n e d ; the strengths w e r e at least c o m -


50

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

Table II.

Properties of A B S ,

ABS 20% Specific g r a v i t y Specific v o l u m e , i n / l b M o l d s h r i n k a g e ( 1 / 4 " section), in/in Tensile strength, psi T e n s i l e m o d u l u s , 10 p s i F l e x u r a l strength, psi F l e x u r a l m o d u l u s , 10 p s i Shear strength, psi Compressive strength, psi Izod impact strength notched, f t - l b / i n unnotched ft-lb/in H e a t distortion temperature at 66 p s i , °F a t 264 p s i , °F


3

GF

AFM

6

AM

5000

1.52 18.3

1.52 18.3

1.19 23.4

6

2030

.0006 10,700 0.81 14,770 0.81 6,220 11,700

.007 11,620 2.15 17,860 2.04 8,410 17,500

.0014 9,470 2.12 14,000 2.13 7,410 16,400

1.3 4.3

0.8 2.8

0.6 2.4

230 222

212 204

228 219

p a r a b l e w i t h a n d often greater t h a n e x i s t i n g c o m p o u n d s .

T h e properties

of m i c a - r e i n f o r c e d thermosets s t u d i e d to d a t e are c o m p a r e d w i t h e x i s t i n g c o m p o u n d s i n T a b l e III.

F o r the p h e n o l i c c o m p o u n d s ,

the m o l d i n g

c y c l e w a s 3 m i n or e q u a l to that f o r c o m m e r c i a l c o m p o u n d s . Table III.

Compression-Molded Thermoset Composites (50 vol % mica) Flexural Strength, Flexural 10 psi 10

Compound

3

Experimental mica/epoxy Experimental mica/polyester Experimental mica/phenolic Commercial mica/phenolic Commercial B . M . C . Table IV.

Polystyrene SAN N y l o n 6/6 Polyester Polypropylene Polyethylene

24.0 23.0 21.0 8-10 10-20

6.4 6.8 7.5 2.5-5.0 1.4-2.0

Compression-Molded Mica Thermoplastic Composites" Flexural

Matrix

Modulus, psi

6

Strength,

50 vol % mica 24.0 30.0 27.0 27.0 25.0 18.0

10 psi z

Flexural

Modulus,

glass

50 vol % mica

17.5 23.2 42.0 34.0 10.5 14.0

6.5 7.7 6.5 6.9 5.5 4.5

40 wt

%

10

e

40 wt

glass 1.50 1.85 1.60 1.60 0.95 1.10

° B y comparison with 40 wt % glass compounds.


psi %

5.

51

Mica as Reinforcement

SHEPHERD E T A L .

S A N , and N y l o n 6/6 Compounds SAN


20% GF

BFM

Nylon 6/6 2030 BM 5000

20% GF

RFM

2030 RM 5000

1.24 22.4 .0005

1.53 18.2 .0014

1.55 17.9 .0015

14,770 1.32 20,100 1.28 8,870

12,000 2.34 19,200 2.43 8,600

9,900 2.55 14,500 2.68 7,100

15,490 .77 23,370 .94 10,320

17,990 2.33 26,140 2.04 11,050

13,760 2.57 18,000 1.93 9,510

19,000 .9 3.4

20,270 0.8 2.3

15,560 0.5 2.3

18,900 0.9 7.7

20,200 1.4 7.6

16,000 0.9 4.2

211 207

237 230

229 227

1.24 22.4 .005

485 452

1.60 17.3 .0038

550 473

1.55 17.9 .0054

487 445

T h e p r o p e r t i e s o f m i c a - r e i n f o r c e d t h e r m o p l a s t i c s s t u d i e d t o date a r e c o m p a r e d w i t h 4 0 w t % glass c o m p o u n d s

( t h e highest a v a i l a b l e ) i n

T a b l e I V . S i n c e these c o m p o u n d s m u s t b e r e m o v e d f r o m t h e m o l d c o l d , m o l d i n g times are c o n s i d e r a b l y l o n g e r t h a n t h e thermoset c y c l e , g e n e r a l l y a b o u t 3 0 - 4 5 m i n u t e s . T h e n o t c h e d i m p a c t s t r e n g t h o f t h e thermoset a n d t h e r m o p l a s t i c composites are a l l same, f o r p r a c t i c a l purposes, h a v i n g a value about 1 f t - l b / i n c h . Conclusions F l a k e r e i n f o r c e m e n t o f plastics offers a u n i q u e s o l u t i o n t o t h e a n i sotropy of

fiber-reinforced

plastics. M i c a platelets w i l l r e i n f o r c e m a n y

p o l y m e r s , b o t h thermoset a n d t h e r m o p l a s t i c , t o give h i g h m o d u l u s c o m posites.

C o m b i n a t i o n s o f m i c a a n d glass-fiber w i t h t h e r m o p l a s t i c resins

g i v e composites o f i m p r o v e d i m p a c t s t r e n g t h c o m p a r e d w i t h m i c a - o n l y composites.

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

Padawer, G. E., Beecher, N., Polym. Eng. Sci. (1970) 10, 185. Shepherd, P. D., Ph.D. Thesis, University of Toronto, Canada, 1969. Kelly, Α., "Strong Solids," pp. 121-125, Clarendon Press, Oxford, 1968. Nielsen, L. E., J. Appl. Polym. Sci. (1966) 10, 97. Orowan, V. Ε., Z. Phys. (1933) 82, 235. Piggott, M. R., Acta Met. (1966) 14, 1429. Kelley, Α., Tyson, W. R., J. Mech. Phys. Solids (1969) 13, 329. Lusis, J., Woodhams, R. T., Xanthos, M., Polym. Eng. Sci. (1973) 13, 139. Economy, J., Wohrer, L. C., Matkovich, V. I., SAMPE J. (Dec./Jan. 1969).

RECEIVED October 11, 1973.


Mica as a Reinforcement for Plastics - Advances in Chemistry (ACS

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