Asbestos as a Reinforcement and Filler in Plastics - Advances in

3 Asbestos as a Reinforcement and Filler in Plastics JOHN W. AXELSON

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Johns-Manville Research Center, P . O . Box 5108, Denver, Colo. 80217

Four varieties of asbestos are used in the plastics industry: chrysotile, crocidolite, amosite, and anthophyllite. Some are used as raw fiber, felts, cloth yarns, and paper. Asbestos wets out in resin systems but is difficult to disperse. Because of its high chemical reactivity, under certain conditions it tends to cause some high temperature instability with cer tain resins—e.g., PVC and polypropylene. Generally, as bestos will improveflexuralmodulus of plastics 100% or more,flexuralstrength up to 50%, and heat distortion tem perature by 30°F or more. Thermal coefficient of expansion is also reduced. Impact strength can be reduced as much as 50% by adding asbestos. However, this apparently can be overcome by using lubricants or bond breakers on the asbestos to minimize the resin-asbestos bond; flexural properties and heat distortion temperature are not affected.

A sbestos has b e e n r e c o g n i z e d as a n i n d i v i d u a l m a t e r i a l f r o m t h e t i m e of M a r c o P o l o — i . e . , f o r m o r e t h a n 700 years.

H o w e v e r , its w i d e -

s p r e a d use d i d n o t o c c u r u n t i l t h e t w e n t i e t h c e n t u r y . T o d a y ' s e s t i m a t e d w o r l d w i d e asbestos u s e is almost five m i l l i o n tons.

Canada

produces

almost 4 0 % of this a m o u n t a n d R u s s i a almost one-half. W h a t is asbestos? T h e n a m e is a g e n e r i c t e r m g i v e n to a g r o u p o f fibrous

minerals.

T h e largest p o r t i o n contains o n l y o n e m i n e r a l w h i c h

is c a l l e d c h r y s o t i l e f r o m t h e s e r p e n t i n e g r o u p a n d is t h e w h i t e asbestos comprising about 9 5 % of the w o r l d production.

T h e second portion of

c o m m e r c i a l asbestos is i n t h e a m p h i b o l e g r o u p a n d has three varieties of i m p o r t a n c e . T h e first is c r o c i d o l i t e o r b l u e asbestos w h i c h is u s e d as a r e i n f o r c i n g fiber i n some plastics because of its a c i d resistance. I t is a v a i l a b l e as fiber, p a p e r , y a r n , felt, a n d c l o t h . i n these forms.

A m o s i t e is t h e s e c o n d

C h r y s o t i l e is also a v a i l a b l e

a m p h i b o l e b u t is n o t u s e d i n

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

3.

AXELSON

Table I.

Chemical Formulas of Asbestos

Chrysotile Crocidolite Amosite Anthophyllite Tremolite Actinolite


17

Asbestos in Plastics

Mg [(OH) Si 0 ]2 Na MgFe5[(OH)Si Oii]2 MgFe [(OH)Si Oii] (Mg, F e ) [ ( O H ) S i O i i ] 2 Ca Mg [(OH)Si Oii] Ca (Mg, Fe) [(OH)Si On] e

4

2

5

2

4

e

4

2

7

2

2

Figure 1.

Figure 2.

4

5

4

5

2

4

2

Plain view of chrysotile

Cross-sectional view of chrysotile

plastics as f a r as is k n o w n .

The third amphibole—anthophyllite—avail-

able o n l y as a short fiber, is u s e d extensively i n filled p o l y p r o p y l e n e . C h e m i c a l f o r m u l a s f o r t h e t w o f a m i l i e s of asbestos are g i v e n i n T a b l e I. F i g u r e 1 is a p l a i n v i e w of c h r y s o t i l e asbestos, a n d F i g u r e 2 is a cross-sectional v i e w . B o t h s h o w t h e h o l l o w , t u b u l a r n a t u r e of c h r y s o t i l e .

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

18

FILLERS AND REINFORCEMENTS

FOR PLASTICS

Asbestos is a n a t u r a l l y o c c u r r i n g m i n e r a l l a r g e l y m i n e d b y o p e n p i t b u t w i t h some b y u n d e r g r o u n d t e c h n i q u e s .

T h e r o c k , c o n t a i n i n g veins

of fiber, is b l a s t e d a n d c r u s h e d to a b o u t a 1-inch m a x i m u m size. m a t e r i a l t h e n goes t h r o u g h v e r t i c a l h a m m e r m i l l s c a l l e d

The

fiberizers

release t h e fiber. G y r a t o r y screens separate the fiber f r o m the rock. u n d e r s i z e d r o c k goes to t a i l i n g s ; the o v e r s i z e d r o c k goes to

to The

fiberizers

w h e r e the a c t i o n is r e p e a t e d ; t h e fiber is a i r a s p i r a t e d off the e n d of the screens to c y c l o n e collectors.

T h e fiber m a y b e processed

f u r t h e r to

r e m o v e u n d e s i r a b l e fractions or to c h a n g e its c h a r a c t e r , b u t e v e n t u a l l y


i t is g r a d e d a n d b a g g e d for s h i p m e n t . Table II.

Grading of Asbestos

Grade

Length or Distribution

No. 1 Crude No. 2 Crude

1/2 inch

Grade

4

7.0 2.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Table III.

Mesh 7.0 8.0 7.0 2.0 0.5 0.0 0.0 0.0 0.0

Analysis 10

Pan

Mesh

0.5 2.0 3.0 4.0 5.0 6.0 9.0 11.0 16.0

1.5 4.0 6.0 10.0 10.5 10.0 7.0 5.0 0.0

Approximate Comparative Lengths and Costs of Chrysotile Approximate Comparative Length inch y

2 3 4 5 6 7

Size

3 / 4 i n c h or longer 3/8 to 3/4 inch Quebec Screen

3K 3T 4D 4T 5D 5R 6D 7D 7R

by Screen

5/8 1/2 3/16 1/8 1/16 1/32

Approximate Price,

Delivered i/lb

45 27 13 10 7 4

Asbestos g r a d i n g is g e n e r a l l y d o n e b y a d r y screen analysis. T h e most p o p u l a r is the Q u e b e c screen test w h i c h designates the m a x i m u m ounces o n the t o p screen a n d the m i n i m u m ounces i n t h e p a n for a 1-lb sample.

T h e test p r o c e d u r e is v e r y specific, a n d t y p i c a l s a m p l e grade

designations are g i v e n i n T a b l e I I . T h e shorter the l e n g t h of the

fiber,

the h i g h e r t h e first d i g i t i n t h e classification; the l o w e r i n the a l p h a b e t


3.

Asbestos in

AXELSON

Table IV.

Color


Properties of Asbestos

Chrysotile

Property

19

Plastics

A mosite

Crocidolite blue

brown

469,000605,000 27.1 Χ 10

148,000203,000 23.6 Χ 10

w h i t e to

gray Tensile strength, 281,000psi 436,000 M o d u l u s of e l a s t i c i t y , 23.2 Χ 10 psi Hardness, mohs 2.5-4 Flexibility good Specific heat, 0.266 Btu/lb/°F Specific g r a v i t y 2.4-2.6 pH 10.3 R e f r a c t i v e index 1.50-1.55 F i b r i l diameter, A 160-300 Surface area, B E T , 1.7-60 m /gram Coeff. of c u b i c a l 5 X 10exp, °F C h a r g e i n water positive Isoelectric p o i n t 11.3-11.8 R e s i s t a n c e to acids poor R e s i s t a n c e to bases good

6

6

A

nthophyllite gray to brown 350,000

6

22.5 Χ

10

4 fair 0.201

5.5-6.0 poor 0.193

5.5-6.0 poor 0.210

3.2-3.3 9.1 1.70 600-900 9-10.5

3.1-3.25 9.1 1.64 600-900 8-9

2.9-3.2 9.4 1.61 600-900 6-7

negative

negative

negative

good good

good fair

good good

6

2

5

Table V .

Mechanical Properties of Asbestos-Reinforced

Material P h e n o l i c c r o c i d o l i t e felt P o l y e s t e r crocidolite felt M e l a m i n e formaldehyde chrysotile paper Phenolic chrysotile molding compound

Resins

Tensile Strength, psi

Flexural Strength, psi

Tensile Modulus, psi (x m

30,000 35,000 9,000

58,000 45,000 18,000

3.3 3.0 1.7

13,000

30,000

4.0

i n a grade series, the shorter the

fiber.

A d d i t i o n a l suffixes b y e a c h p r o

d u c e r i n d i c a t e the degree of openness of the

fiber.

T a b l e I I I lists a p

p r o x i m a t e average lengths for the v a r i o u s grades of asbestos fiber a n d also a n a p p r o x i m a t e d e l i v e r e d p r i c e . O n e of the attributes of asbestos fiber is its r e l a t i v e l y l o w p r i c e vs. its p e r f o r m a n c e . fiber.

N a t u r a l l y , the p r i c e is reflected b y the l e n g t h of t h e

L a t e r , w e s h o w that the shorter, l o w e r p r i c e d fibers are g e n e r a l l y

those that are u s e d i n plastics w i t h g o o d

effectiveness.

Asbestos exhibits u n i q u e properties ( T a b l e I V ) .

O n e p r o p e r t y not

l i s t e d i n T a b l e I V is its a b i l i t y to b e w e t out b y a l l r e s i n a n d latex systems. O c c a s i o n a l l y i t is difficult to disperse asbestos p r o p e r l y because the i n d i -


20

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

vidual

fibrils

are v e r y s m a l l a n d t e n d to a g g l o m e r a t e , b u t there is n o

e v i d e n c e t h a t asbestos is n o t easily w e t t e d out b y a l l systems. O n e of t h e u n i q u e p r o p e r t i e s of c h r y s o t i l e is the p o s i t i v e c h a r g e i t d e v e l o p s i n the presence of w a t e r ; this m a y h a v e some b e a r i n g o n its excellent w e t t a bility. Asbestos fiber c a n b e c o n s i d e r e d as b o t h a r e i n f o r c i n g fiber a n d a reinforcing

filler.

I n the first case, s p e c i a l l o n g grades of asbestos or

s p e c i a l forms s u c h as p a p e r , c l o t h , or felt are u s e d to o b t a i n h i g h p e r formance products.

S o m e of t h e properties w h i c h c a n b e o b t a i n e d are


s h o w n i n T a b l e V . A s a r e i n f o r c i n g filler, asbestos i m p a r t s m a n y p r o p e r ties w h i c h are not o b t a i n e d w i t h g r a n u l a r fillers. V a r i o u s advantages a n d d i s a d v a n t a g e s of asbestos as a r e i n f o r c i n g fiber or

filler

are s h o w n i n

Tables V I and V I I . Table V I . Advantages L o w cost E a s y flash r e m o v a l F l o w control in mold M i n i n u m fiber d e g r a d a t i o n G o o d flexural s t r e n g t h L o w water absorption H e a t resistance G o o d e l e c t r i c a l properties C h e m i c a l resistance Table VII. Advantages H i g h modulus Tensile improvement F l o w control i n mold G o o d surface finish Heat stability Dimensional stability L o w creep C h e m i c a l resistance H i g h e r hardness A r c resistance L o w water absorption L o w t h e r m a l coefficient

as a Reinforcing Fiber Disadvantages F a i r impact strength D a r k color P o s s i b l e m i x i n g difficulties

Asbestos as a Reinforcing Filler Disadvantages Increase i n resin v i s c o s i t y F a i r e l e c t r i c a l resistance S o m e abrasiveness Possible polymer degradation H i g h density

O n e c o n t r o l l a b l e aspect of asbestos that s h o u l d b e f u l l y r e c o g n i z e d is its effect o n the heat s t a b i l i t y of c e r t a i n p o l y m e r s . B e c a u s e of its h i g h surface area a n d c h e m i c a l r e a c t i v i t y , c h r y s o t i l e p a r t i c u l a r l y tends to d e crease the heat s t a b i l i t y of c e r t a i n p o l y m e r s s u c h as p o l y ( v i n y l c h l o r i d e ) and polypropylene.

H o w e v e r , w i t h proper stabilizers a n d antioxidants.


3.

AXELSON

Asbestos in

21

Plastics

b o t h p o l y m e r s c a n b e s t a b i l i z e d f o r p r o c e s s i n g temperatures a n d l o n g t e r m use at e l e v a t e d temperatures. T h e next tables a n d figures s h o w w h a t k i n d of p h y s i c a l p r o p e r t i e s c a n b e o b t a i n e d w i t h v a r i o u s asbestos

fibers.

Standard techniques were

u s e d to p r e p a r e a l l specimens, a n d testing w a s d o n e i n a c c o r d a n c e A S T M procedures.

F i g u r e s 3, 4, a n d 5 d e p i c t the i m p a c t a n d

strengths w h i c h c a n b e o b t a i n e d i n a p o l y e s t e r m i x w i t h asbestos

with flexural fibers

of v a r i o u s lengths ( 1 / 8 to 1/2 i n c h ) vs. a c o m m e r c i a l fiber w i t h a n o m i n a l


length (3/16 inch).

T h e asbestos

40001 10

for these tests w e r e p r e p a r e d

20 F K R

Figure 3.

fibers

SO

LOADING-%

Flexural strength for

chrysotile-polyester

f r o m c r u d e fiber. T h e s e w e r e c a r e f u l l y c u t b y h a n d to t h e d e s i r e d l e n g t h a n d t h e n o p e n e d g e n t l y to m i n i m i z e fiber s h o r t e n i n g b y p a s s i n g t h r o u g h a small impact mill.

T h e fibers w e r e i n c o r p o r a t e d i n t o t h e l i q u i d p o l y -

ester i n a s m a l l s i g m a b l a d e t y p e m i x e r . T h e final m i x w a s c o m p r e s s i o n m o l d e d at 300° F for 5 m i n at 500 p s i , a n d test specimens w e r e c u t f r o m the m o l d e d piece.

A s c a n be seen, fiber l e n g t h does not seem to h a v e

a n y significant effect o n the p h y s i c a l p r o p e r t i e s o b t a i n e d .


22

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

1201

lOOl -I

ao


/

/

/

/

1/4 N.0LA88

20

5

0

FBER LOADING -%

Figure 4. Notched impact strength for chrysotilepolyester

IN. At 8.

30

Figure 5. Unnotched impact strength for chrysotile-polyester


3.

23


AXELSON

T a b l e V I I I lists t h e g e n e r a l treatments w h i c h w e r e g i v e n to asbestos fiber before i n c o r p o r a t i o n i n a polyester resin. T h e treatments w e r e g e n e r a l l y d o n e i n a solvent s l u r r y w i t h subsequent d r y i n g a n d o p e n i n g of t h e asbestos.

S a m p l e p r e p a r a t i o n a n d testing w e r e as p r e v i o u s l y d e

s c r i b e d . P h y s i c a l p r o p e r t i e s w e r e not i m p r o v e d w i t h a n y of these treat ments.

T h i s a d d s to t h e e v i d e n c e for g o o d fiber w e t t i n g a n d t h e l a c k

of n e e d for fiber treatment. T a b l e s I X , Χ , X I , a n d X I I a n d F i g u r e s 6, 7, a n d 8 d e p i c t some p r o p


erties o b t a i n e d w h e n asbestos fiber is i n c o r p o r a t e d i n f o u r t y p i c a l resins. Table VIII. 1. 2. 3. 4. 5.

Fiber Treatments

C r o s s l i n k asbestos to resin F l e x i b i l i z e t h e fiber to resin b o n d C o a t asbestos t o i m p r o v e c o m p a t a b i l i t y E n c a p s u l a t e asbestos t o give i n t e g r a l b u n d l e s L e t free w a t e r react on asbestos surface Table I X .

Fiber

%

None 7M02

Added — 20 30 40 20

Glass, 1/4 inch

Asbestos in Polyethylene

Flexurol Strength, psi

Flexural Modulus, psi Χ 10

4170 4560 5840 5440 4800

1.54 2.82 4.21 6.44 3.50

Table X .

Asbestos

Added

—

4 0 % l o n g fiber (Plastibest #20) 4 0 % short fiber (7D04) 2 0 % 1/4-inch glass

5

Tensile Strength, psi Χ 10

5

3260 2440 3380 3900 3220

Impact Strength (Notched Izod) ftlbs/inch

Heat Distortion^

0.9 0.4 0.6 0.9 1.6

op

120 131 157 192 122

Asbestos in ABS


Impact Strength, (Notched Izod), ft- Distortion. op Ibs/inch



10,650

0.54

5855

1.42

190

8,765

1.11

4715

0.52

202

8,290

1.39

6340

0.58

208

10,350

0.58

5595

0.70

207

6


24

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

Table X I .

Asbestos in Phenolics Flexural Modulus, psi Χ 10


Material

Impact Strength (Notched Izod), ft-lbs/inch

6

A . T w o Stage P h e n o l i c P o w d e r p l u s Asbestos None 4 0 % 7 R F 0 2 fiber 6 0 % 7 R F 0 2 fiber o


0.78 1.44 2.03

0.28 0.20 0.39

13,700

1.03

0.32

9,800

1.31

0.30

8,900 13,500 12,900

B . Filled Commercial M o l d i n g Compound G e n e r a l purpose w o o d flour H e a t resistant J - M 7 T 1 5 asbestos

Table XII.

Asbestos

Added

Asbestos in Polystyrene

Heat Dostortion, °F



5195

2.91

2585

1.42

179

5180

6.24

3570

1.09

201

7410

5.97

2500

0.56

194

5895

4.86

2680

0.65

194

None 4 0 % l o n g fiber (plastibest #20) 4 0 % short fiber (7D04) 2 0 % 1/4-inch glass

5


Impact Strength (Notched Izod), ftlbs/inch

T h e p o l y e t h y l e n e samples for T a b l e I X w e r e p r e p a r e d b y p r e b l e n d i n g the r e s i n a n d fiber i n a t u m b l e r a n d t h e n fluxing o n a r o l l m i l l at 2 5 0 ° F for 10 m i n . Pieces w e r e c u t 4 X 4 inces f r o m the sheet off the m i l l a n d c o m p r e s s i o n m o l d e d to samples 4 % inches X 4 X 1 / 8 - i n c h . H o t p r e s s i n g w a s d o n e at 3 5 0 ° F for 5 m i n w i t h a 1-ton l o a d ; t h e n the m o l d w a s t r a n s f e r r e d to a w a t e r - c o o l e d press w h e r e a 20-ton l o a d w a s a p p l i e d o v e r 60 sec a n d h e l d for several m i n u t e s . S p a c e r bars w e r e u s e d to c o n t r o l t h i c k ness. C u t t i n g a n d testing of s a m p l e s w e r e a c c o r d i n g to A S T M p r o c e d u r e s . T h e p r e p a r a t i o n o f A B S samples for t h e d a t a i n T a b l e X started w i t h f u s i n g of the r e s i n o n a r o l l m i l l at 325° F a n d s l o w a d d i t i o n of the Sheets 8 X

fiber.

8 inches w e r e c u t a n d p l a c e d i n a m o l d to g i v e a s a m p l e

9 X 9 X 1 / 4

inch.

T h e y w e r e pressed at 4 0 0 ° F w i t h 100 tons w i t h a


3.

AXELSON

Asbestos in

Plastics

25

w a r m - u p t i m e of 5 m i n , 10 m i n for p r e s s i n g , a n d 15 m i n i n t h e c o o l i n g press. P h e n o l i c specimens i n T a b l e X I w e r e p r e p a r e d b y d r y b l e n d i n g a two-stage r e s i n a n d the fiber b e f o r e p l a s t i c a t i n g o n a r o l l m i l l at 2 9 0 ° F for IV2 m i n . T h e c o o l e d sheet w a s passed t h r o u g h a h a m m e r m i l l , a n d the resultant p o w d e r w a s c o m p r e s s i o n m o l d e d for 30 m i n at 290° F a n d 3000 p s i to g i v e specimens 9 X 9 X 1 / 8 i n c h . P o l y s t y r e n e w a s h a n d l e d


i n t h e same w a y as A B S except t h e r o l l m i l l t e m p e r a t u r e w a s o n l y 275 ° F .

100 20

40

20

60

40

% Fiber

% Fiber

Flexural Modulus

Htat Deflection (264 psi)

Figure 6.

Asbestos in

polyethylene

T h e increases i n m o d u l u s , flexural strength, a n d heat deflection t e m p e r a t u r e are t h e m o s t notable.

I m p r o v e m e n t i n these properties is the

p r i m a r y reason f o r u s i n g asbestos.

C o n v e r s e l y , the m a j o r deficiency is

the loss i n i m p a c t strength. It is h o p e d t h a t this c a n be o v e r c o m e b y t h e t e c h n i q u e d e s c r i b e d b y D u p o n t b y r e d u c i n g the b o n d b e t w e e n t h e

fiber

a n d the m a t r i x ( 1 ). S o m e recent w o r k not yet r e a d y for p u b l i c a t i o n shows t h a t this t e c h n i q u e does w o r k for asbestos i n r i g i d P V C . T h e

asbestos

is p r e t r e a t e d w i t h a l u b r i c a n t a n d p r e b l e n d e d w i t h P V C b e f o r e e x t r u s i o n . F i n a l properties of the e x t r u d e d a r t i c l e , i n c l u d i n g i m p a c t strength, h a v e e q u a l e d those of a n u n f i l l e d p a r t , a n d the m o d u l u s has s h o w n c o n s i d e r able improvement.

T h i s w o r k looks v e r y i n t e r e s t i n g a n d s h o u l d

a p p l i c a b l e to other systems.


be

26

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

R e c e n t w o r k w i t h p r o p e r l y s t a b i l i z e d p o l y p r o p y l e n e has s h o w n t h e effectiveness

o f c h r y s o t i l e vs. v a r i o u s other types of

fillers.

T h e work

r e p o r t e d i n T a b l e X I I I w i t h p o l y p r o p y l e n e u s e d t h e m i x i n g c h a m b e r of a This was roughly


B r a b e n d e r P l a s t i c o r d e r t o b l e n d the fillers a n d r e s i n .

General Purpose

Heat Resistant

Strength Lots Figure 7.

Asbestos in phenolics; two-weeks water saturation at 75°F



3.

AXELSON

Figure 8.

Asbestos in phenolics; two-weeks oven aging at 375°F

Table XIII.

Physical Properties of Filled Polypropylene

Flexural, Filler Unfilled Talc Wollastonite Anthoplyllite Chrysotile α

Strength

Impact Heat Strength Deflection (Notched), Temp, °F ft-lbs/inch

psi Modulus

5200 7200 5700 6900 9000

1.9 5.9 3.7 5.1 6.1

Χ Χ X Χ Χ

10 10 10 10 10

5 5 s 5 5

136 204 159 183 239

Heat Stability, hrs at 150°C 2000+ 2000+ 2000+ 1000 1500"

0.5 0.5 0.5 0.5 0.5

Contained special antioxidant.

Table X I V .

Filler CaC0 Chrysotile 3

a

27


Radiant Panel Flammability Test for H i g h Density Polyethylene-40% Filler Heat Evolution Factor, Q

Flame Spread Factor, F

10.8* 14.4

19.6 4.3

S

Flame Spread Index, I = F Q 8

213 62

Low because of drippage through screen support.


S

28

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

compacted into a disc about 1/4-inch thick a n d then compression m o l d e d u s i n g t h e h o t - c o l d press t e c h n i q u e d e s c r i b e d f o r p o l y e t h y l e n e .

However,

the h o t press t e m p e r a t u r e w a s 4 0 0 ° F . O n e significant f e a t u r e is t h e fire resistance w h i c h is i m p a r t e d to a n asbestos-filled r e s i n as s h o w n i n Table X I V .

Literature Cited


1. Speri, W. M., Jenkins, O. F., "Effect of Fiber-Matrix Adhesion on the Prop erties of Short Fiber Reinforced ABS," Ann. Tech. Conf., 28th, Society of Plastics Industry, Washington, D. C., 1973. RECEIVED October 11, 1973.


Asbestos as a Reinforcement and Filler in Plastics - Advances in

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