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
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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
Deanin and Schott; Fillers and Reinforcements for Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
(3)
44
FILLERS AND REINFORCEMENTS
FOR PLASTICS
TENSILE STRENGTH
3
0
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(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
Deanin and Schott; Fillers and Reinforcements for Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
(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
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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
Deanin and Schott; Fillers and Reinforcements for Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
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
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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
Deanin and Schott; Fillers and Reinforcements for Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
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
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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
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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-
Deanin and Schott; Fillers and Reinforcements for Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
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
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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 -
Deanin and Schott; Fillers and Reinforcements for Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
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
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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.
Deanin and Schott; Fillers and Reinforcements for Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
psi %
5.
51
Mica as Reinforcement
SHEPHERD E T A L .
S A N , and N y l o n 6/6 Compounds SAN
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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.
Deanin and Schott; Fillers and Reinforcements for Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1974.