Fillers and Reinforcements for Plastics

X-ray radiographs of the com posites established fiber distribution in the molded speci mens; infrared analyses on the polymers showed possible change...
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4 Asbestos-Reinforced Rigid Poly(vinyl chloride) A. CRUGNOLA and A. M. LITMAN

1

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L o w e l l Technological Institute, L o w e l l , Mass. 01854

Two rigid poly(vinyl chloride) polymers (a low and a high molecular weight sample) were reinforced at several concen­ trations with four chrysotile asbestos fibers of varying length and openness. Mechanical, thermal, and other physical tests were done on the resultant composites: load/elongation curves, impact, hardness, heat deflection temperature, and flammability. Complete analyses of the before and after processed polymers' molecular weight and molecular weight distribution were also done. X-ray radiographs of the com­ posites established fiber distribution in the molded speci­ mens; infrared analyses on the polymers showed possible changes in chemical structure. A new mixing technique incorporated the asbestos in the plastic. Resultant composite properties generally depended on four factors. In decreasing importance they are: (1) matrix polymer molecular weight, (2)fiberconcentration, (3) fiber "openness," (4) fiber length. T i t t l e r e s e a r c h has b e e n d o n e o n t h e r e i n f o r c i n g effects of asbestos o n rigid poly (vinyl chloride)

( P V C ) plastics ( I ) . T h i s c o m b i n a t i o n is

i n t e r e s t i n g because o f t h e i n h e r e n t p r o p e r t i e s of P V C a n d t h e u n i q u e characteristics o f asbestos fibers. R i g i d ( u n p l a s t i c i z e d ) P V C is a l o w cost, t o u g h t h e r m o p l a s t i c n o t e d f o r excellent c h e m i c a l a n d flame resistance a n d extensive p r o c e s s i n g v e r s a t i l i t y — p r o p e r t i e s w h i c h l e a d to countless a p p l i c a t i o n s i n b o t h t h e b u i l d i n g a n d t h e c h e m i c a l areas.

T w o such

p o l y m e r s w e r e u s e d i n this w o r k : a l o w m o l e c u l a r w e i g h t p r o d u c t of M

w

=

49,900 a n d a h i g h m o l e c u l a r w e i g h t p r o d u c t o f M

w

=

116,380.

Asbestos is a b r o a d t e r m a p p l i e d to a n u m b e r of n a t u r a l s i l i c a t e d m i n e r a l s that a r e i n c o m b u s t i b l e a n d c a n b e s e p a r a t e d either m e c h a n i c a l l y o r c h e m i c a l l y i n t o fibers o f v a r y i n g lengths a n d thicknesses.

L o w cost,

Present address: Army Materials and Mechanics Research Center, Watertown, Mass. 02172.

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

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

excellent h e a t resistance, a n d e x c e p t i o n a l m e c h a n i c a l b e h a v i o r

account

f o r the g r o w i n g use of asbestos i n t h e r e i n f o r c e d plastics i n d u s t r y . T h e r e are t w o

d i s t i n c t m i n e r a l o g i c a l classifications of

asbestos:

those

from

serpentine r o c k f o r m a t i o n s a n d those f r o m a m p h i b o l e r o c k f o r m a t i o n s . Asbestos

Mineral

— I . Amphibole

Serpentine

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Chrysotile

— I Anthophyllite

Amosite

Crocidolite

Tremolite

Actinolite

O f the six varieties c a t a l o g e d o n l y f o u r h a v e c o m m e r c i a l use as r e i n f o r c e ­ m e n t s : c h r y s o t i l e , amosite, a n t h o p h y l i t e , a n d c r o c i d o l i t e .

T h e chrysotile

asbestos accounts for a b o u t 9 5 % of w o r l d p r o d u c t i o n a n d is the m o s t w i d e l y u s e d i n plastics. T h e advantages of this fiber as a r e i n f o r c e m e n t a r e : (1) h i g h e r strength a n d m o d u l u s vs. glass fibers, ( 2 ) a p o s i t i v e s u r ­ face charge w h i c h promotes

fiber/matrix

w i d e r a n g e of lengths a n d d i a m e t e r s , ( 4 )

bonding, (3) a soft,

availability i n a

flexible

results i n m i n i m u m w e a r o n p r o c e s s i n g e q u i p m e n t .

quality w h i c h

T h e four chrysotile

fibers u s e d i n this s t u d y are d e s c r i b e d i n T a b l e I. Table I. Fiber

Asbestos Fibers Used"

Size, inch

7RS7

1/32

Paperbestos N o . 5

3/64

Paperbestos N o . 1

1/4

P l a s t i b e s t N o . 20

1/8-3/16

α

Description s h o r t s t a n d a r d fiber used i n t h e r m o p l a s t i c systems shorter v e r s i o n of Paperbestos No. 1 c l e a n , w e l l opened fiber of good length clean, m e d i u m l e n g t h fiber n o t opened v e r y m u c h

Fibers supplied by Johns Manville Co. and classification/descriptions are theirs.

Experimental Specimen Fabrication. A m e a s u r e d a m o u n t of P V C w a s p l a c e d i n a H e n c h e l m i x e r a n d m i x e d at m a x i m u m s p e e d ( 3600 r p m ) u n t i l the b a t c h t e m p e r a t u r e r e a c h e d 2 0 0 ° F . A t this t e m p e r a t u r e the s t a b i l i z e r w a s a d d e d ( 2 p p h b y w e i g h t of A d v a n c e s ' T - 3 6 0 , a s u l f u r - c o n t a i n i n g o r g a n o t i n c o m ­ p o u n d ) , a n d m i x i n g c o n t i n u e d u n t i l the t e m p e r a t u r e r e a c h e d 2 5 0 ° F ; at this t i m e the m a t e r i a l w a s d i s c h a r g e d i n t o a r i b b o n b l e n d e r for c o o l i n g (approximately 5 m i n ) .

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

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4.

CRUGNOLA A N D L i T M A N

Asbestos-Reinforced

PVC

31

Figure 1. Impact fracture surfaces (notched Izod). Top: Paperbestos No. 5/PVC; bottom: Plastibest No. 20/PVC. T h e asbestos w a s d r i e d i n a n o n - c i r c u l a t i n g a i r o v e n at 250° F f o r 24 hrs t o r e m o v e m o i s t u r e that o t h e r w i s e m i g h t p r e v e n t the fiber b u n d l e s f r o m s e p a r a t i n g i n the p r e m i x i n g o p e r a t i o n . T h e b r e a k u p o f t h e asbestos c l u m p s a n d the d r y - b l e n d i n g w i t h the stabilized polymer were done i n a specially designed m i x i n g device consisting o f a glass jar, a b a l l m i l l , a n d a n i t r o g e n source. T h e m i x i n g jar was e q u i p p e d w i t h a p e r f o r a t e d shaft r u n n i n g d o w n i t s l e n g t h w h i c h p e r m i t t e d the n i t r o g e n i n t r o d u c e d u n d e r a n o m i n a l pressure t o b e u n i f o r m l y d i r e c t e d t h r o u g h o u t the jar. A T e f l o n b e a r i n g seated at the center of the jar c o v e r p e r m i t t e d the b o t t l e to t u r n o n t h e b a l l m i l l i n d e p e n d e n t of the shaft. T h e P V C / a s b e s t o s mixtures obtained b y dry-blending were m i l l e d o n a F a r r e l l t w o r o l l m i l l a t 360° ± 5 ° F . S m a l l q u a n t i t i e s ( a p p r o x i m a t e l y 200 grams at the t i m e ) w e r e fluxed o n the 1 5 - i n c h l o n g rolls to

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

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

ensure t h o r o u g h f u s i o n a n d m i x i n g i n a short t i m e . T h e m i x i n g / f l u x i n g times d e p e n d e d s o m e w h a t o n fiber t y p e a n d content a n d v a r i e d b e t w e e n IV2 a n d 2 m i n . D e s p i t e the short times u s e d , t h e r e w a s n o e v i d e n c e of i n c o m p l e t e f u s i o n e i t h e r d u r i n g f l u x i n g or o n v i e w i n g t h e i m p a c t f r a c t u r e surfaces. T h i s is n o t to say t h a t e v e r y fiber w a s w e t w i t h p o l y m e r w h i c h w e t t i n g i n s t e a d d e p e n d e d o n the d e g r e e of fiber openness. T h i s is v i v i d l y d e m o n s t r a t e d i n the p h o t o g r a p h s of F i g u r e 1. F i n a l l y t h e c o m p o s i t e panels w e r e c o m p r e s s i o n m o l d e d i n a W a b a s h press at 2000 p s i . S e v e r a l sheets f r o m the m i l l i n g o p e r a t i o n w e r e crossp l i e d , p l a c e d i n a n o p e n f r a m e m o l d a n d b r o u g h t to t e m p e r a t u r e ( 3 5 5 ° ± 5 ° F for the h i g h m o l e c u l a r w e i g h t m a t r i x a n d 330° ± 5 ° F for the l o w m o l e c u l a r w e i g h t m a t r i x ) b e f o r e a p p l y i n g pressure. T h e pressure w a s m a i n t a i n e d for 1 m i n hot, t h e n the f r a m e w a s t r a n s f e r r e d to a c o l d press a n d the m a t e r i a l c o o l e d u n d e r the same pressure ( 2000 p s i ). C o m p o s i t e s of e a c h of the f o u r asbestos fibers w e r e f a b r i c a t e d at 15, 30, a n d 4 5 % fiber content i n e a c h of the t w o p o l y ( v i n y l c h l o r i d e ) plastics. Specimen Testing. T h e composites w e r e m e c h a n i c a l l y tested for tensile m o d u l u s , b r e a k i n g e l o n g a t i o n , b r e a k i n g s t r e n g t h , i m p a c t , h a r d ­ ness, a n d heat deflection. A S T M flammability e v a l u a t i o n s w e r e also p e r ­ f o r m e d . T h e effectiveness of t h e s p e c i m e n p r e p a r a t i o n t e c h n i q u e w i t h r e g a r d to the d i s t r i b u t i o n of the fibers w i t h i n t h e c o m p o s i t e w a s estab­ l i s h e d b y x - r a y r a d i o g r a p h s of selected samples. T h e p o l y m e r / m a t r i x m a t e r i a l s w e r e s t u d i e d b y ( 1 ) g e l p e r m e a t i o n c h r o m a t o g r a p h y to f o l l o w changes i n m o l e c u l a r w e i g h t a n d m o l e c u l a r w e i g h t d i s t r i b u t i o n c a u s e d b y t h e p r o c e s s i n g of the fiber/plastic m i x t u r e s into t h e composites a n d ( 2 ) i n f r a r e d analysis i n a n a t t e m p t to p i c k u p p o s s i b l e changes i n the c h e m i c a l s t r u c t u r e of the p o l y m e r s . Table II. 7RS7 Molecular

Weight

% Asbestos

α

High

Low

— 5.58 6.75 8.25

4.24 5.27 7.82 8.03

High

Low

— 5.47 6.65 8.07

4.24 6.46 6.70 7.28

Fiber

0 15 30 45 6

Tensile Modulus No. δ

6

Strain rate 4 . 5 % / m i n ; variation in values used to obtain average value = =fc 4%. Χ 10+ psi. 6

Results and

Discussion

T h e results of the t e s t i n g d o n e o n the composites

and their com­

ponents are p r e s e n t e d i n T a b l e s I I , I I I , I V , V , a n d V I a n d i n F i g u r e s 2, 3, 4, a n d 5. T h e findings are s u m m a r i z e d b e l o w . Tensile Modulus.

I n t r o d u c t i o n of asbestos fiber r a i s e d the m o d u l i

of the P V C plastics. T h e increase g e n e r a l l y i n c r e a s e d w i t h fiber c o n t e n t a n d was as m u c h as 1 0 0 %

at 4 5 % r e i n f o r c e m e n t .

Usually the higher

m o l e c u l a r m a t r i x plastics e x h i b i t e d h i g h e r m o d u l i t h a n the c o r r e s p o n d i n g l o w m o l e c u l a r w e i g h t m a t e r i a l s a l t h o u g h this effect was n o t consistent.

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

4.

Asbestos-Reinforced

CRUGNOLA AND L I T M A N

33

PVC

N o clear effects of either fiber l e n g t h o r fiber openness w e r e a p p a r e n t i n the results. Tensile Strength. A n increase i n tensile s t r e n g t h w a s g e n e r a l l y n o t e d u p o n the i n i t i a l i n t r o d u c t i o n of asbestos

fibers

i n P V C plastics.

increase p e a k e d , a n d t h e n the s t r e n g t h decreased

This

at t h e h i g h e r

fiber

content levels to the p o i n t w h e r e the r e i n f o r c e d samples e x h i b i t e d b r e a k i n g stresses l o w e r t h a n those of the n o n r e i n f o r c e d m a t e r i a l s . U s u a l l y the h i g h e r m o l e c u l a r w e i g h t m a t r i x composites

showed

somewhat

higher

strengths t h a n d i d the c o r r e s p o n d i n g l o w m o l e c u l a r w e i g h t s p e c i m e n .

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T h e reason for the u n e x p e c t e d l o w e r i n g at h i g h e r fiber contents is not c l e a r unless the h i g h e r fiber concentrations b r o u g h t w i t h t h e m a h i g h e r c o n c e n t r a t i o n of i n t e r n a l stress c o n c e n t r a t i n g flaws i n the

compression

m o l d e d sheets. Breaking Strain. A l t h o u g h the n o n r e i n f o r c e d plastics at this strain rate ( 4 . 5 % fibers

p e r m i n u t e ) w e r e p r o n e to n e c k i n g a n d d r a w i n g , o n c e the

w e r e i n t r o d u c e d the b r e a k i n g strains f e l l to a b o u t 2 %

(for

15%

fiber ). F u r t h e r increases i n fiber content f u r t h e r decreased t h e e l o n g a t i o n to b r e a k to levels of the o r d e r of 1 % .

N o c l e a r effect of fiber l e n g t h or

fiber openness w a s seen. I n g e n e r a l , u p to 3 0 % fiber content, the h i g h e r m o l e c u l a r w e i g h t samples e x h i b i t e d s o m e w h a t h i g h e r b r e a k i n g strains. Impact Strength. T h e m o s t i m p o r t a n t f a c t o r i n f l u e n c i n g the i m p a c t strength was the extent to w h i c h the asbestos fibers w e r e o p e n e d . of P V C Asbestos Composites" No. 1

No.

The

20

High

Low

High

Low

— 6.65 6.86 5.57

4.24 5.94 5.54 6.52

— 5.80 6.37 7.53

4.24 5.15 6.20 7.66

c l o s e d fiber structures a l w a y s gave h i g h e r i m p a c t strengths.

Somewhat

h i g h e r strengths w e r e associated w i t h the h i g h e r m o l e c u l a r w e i g h t m a t r i x p l a s t i c , the greater

fiber

concentrations, a n d the l o n g e r

fiber

lengths.

P h o t o g r a p h s of the f r a c t u r e surfaces of a c l o s e d fiber a n d a n o p e n

fiber

r e i n f o r c e d P V C a p p e a r i n F i g u r e 1. T h e s e , w e b e l i e v e , r e v e a l the m e c h a n i s m b y w h i c h t h e n o n - o p e n e d fibers e n h a n c e the i m p a c t s t r e n g t h of the composite.

Considerable energy must be i n v o l v e d i n p u l l i n g apart the

asbestos fibers d u r i n g the i m p a c t — e n e r g y u s e d i n o v e r c o m i n g f r i c t i o n a l forces, i.e., forces r e q u i r e d to p u l l i n d i v i d u a l fibers a w a y a n d past others. O n e m i g h t v i s u a l i z e these forces i n a m o d e l w h e r e a fasces s t r u c t u r e is p u l l e d a p a r t b y g r a s p i n g some of the rods o n one e n d a n d s o m e o n t h e i r

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

34

FILLERS AND REINFORCEMENTS

Table III.

Tensile Breaking Stress

7RS7 Molecular

Weight

% Asbestos

High

a

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No. δ Low

High

Low

4,656 5,251 4,726 4,679

6,256 6,978 7,270 5,734

4,656 5,572 5,889 5,435

Fiber

0 15 30 45 6

6,256 5,756 6,347 5,787

6

Strain rate 4.5%/min; variation in values used to obtain average value = ± Psi.

Table IV.

Molecular

Weight,

% Asbestos 0 15 30 45 α

High

4%.

Tensile Breaking Strain

7RS7

6

FOR PLASTICS

No. δ Low

High

Low

187 2.6 1.8 0.8

67 1.7 1.2 0.9

Fiber 187» 1.2 1.4 0.9

67 2.0 1.2 0.9

Strain rate 4.5%/min. Percent strain.

Table V . Polymer SCC—686* Ο—H—O 1—H—30 7—H—30 b

e

d

Molecular Weight before and after Processing/Molding M

N

56,570 52,730 58,630 46,140

M

w

116,380 129,500 125,700 125,100

M /M W

N

1.98 2.46 2.14 2.71

° Polymer before processing (non-reinforced). Polymer extracted after processing/molding (non-reinforced).

b

Table V I . Polymer SCC—600 Ο—L—Ο 1—L—30 7—L—30 6

e

d

α

Molecular Weight before and after Processing/Molding M

N

23,500 20,320 21,880 22,640

M

w

49,900 48,200 50,340 48,190

M /M W

2.11 2.38 2.30 2.13

° Polymer before processing (non-reinforced). Polymer extracted after processing/molding (non-reinforced).

6

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

N

4.

Asbestos-Reinforced

CRUGNOLA A N D L i T M A N

of PVC/Asbestos Composites

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No. 20

High

Low

6,256 7,343 5,315 3,709

4,656 5,406 4,349 3,748

of P V C Asbestos Composites

High

Low

6,256 6,319 6,423 3,618

4,656 5,508 3,876 4,719

α

No. 1

187 2.4 1.6 0.8

35

0

No. 1

High

PVC

No. 20 Low 67 1.6 1.0 0.7

High

Low

187 2.2 2.1 0.7

67 1.7 1.2 0.9

with Chrysotile Asbestos Fibers for H i g h Molecular Weight P V C M

z

186,600 234,200 219,600 238,300

Mz/Mw 1.61 1.81 1.75 1.91

Mz+i 249,100 350,800 325,000 370,000

Mz+i/Mz 1.30 1.30 1.48 1.56

Polymer extracted after processing/molding reinforced with No. 1 asbestos fibers— 30% fiber content. Polymer extracted after processing/molding reinforced with 7RS7 asbestos fibers— 30% fiber content c

d

with Chrysotile Asbestos Fibers for L o w Molecular Weight P V C Mz 94,120 93,100 94,920 86,620

Mz/Mw 1.88 1.93 1.89 1.79

Mz+i 159,200 148,800 149,800 133,700

Mz+i/Mz 1.69 1.59 1.58 1.54

Polymer extracted after processing/molding reinforced with No. 1 asbestos fibers— 30% fiber content Polymer extracted after processing/molding reinforced with 7RS7 asbestos fibers— 30% fiber content c

d

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

Figure 2.

Variation of impact strength with fiber content (reinforced rigid

other e n d .

T h e extent of this m e c h a n i s m a p p a r e n t l y d e p e n d s

PVC)

o n the

asbestos fiber b u n d l e s not b e i n g t h o r o u g h l y w e t out b y t h e m a t r i x since the better w e t o p e n asbestos fibers are f r a c t u r e d at t h e f r a c t u r e surface of the p o l y m e r . Heat Deflection Temperature.

I n a l l cases the heat deflection t e m -

p e r a t u r e w a s r a i s e d b y the i n t r o d u c t i o n of the asbestos

(6°-12°C

for

the h i g h m o l e c u l a r w e i g h t p l a s t i c a n d 2 ° - 8 ° C for the l o w m o l e c u l a r w e i g h t m a t e r i a l ) . T h i s t e m p e r a t u r e i n c r e a s e d w i t h i n c r e a s i n g fiber c o n -

Figure 3.

Variation of HOT with fiber content (reinforced rigid PVC)

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

4.

Asbestos-Reinforced

CRUGNOLA A N D L i T M A N

37

PVC

c e n t r a t i o n a n d / o r d e c r e a s i n g fiber openness. T h e m o l e c u l a r w e i g h t o f the s t a r t i n g plastics p r o v e d most i m p o r t a n t i n e s t a b l i s h i n g t h e a m o u n t o f i m p r o v e m e n t i n H D T . W h e r e a s the n o n - r e i n f o r c e d m a t e r i a l s differed b y o n l y 1 ° C the r e i n f o r c e d m a t e r i a l s d i f f e r e d b y as m u c h as 9 ° C . Hardness. T h e asbestos composites consistently s h o w e d l o w e r values of hardness t h a n d i d the n o n - r e i n f o r c e d plastics. T h e l o w e r i n g w a s greater the greater t h e c o n c e n t r a t i o n o f fiber. T h e s o m e w h a t h i g h e r hardness of the s t a r t i n g h i g h e r m o l e c u l a r w e i g h t m a t e r i a l a p p e a r e d t o b e reflected

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i n the s o m e w h a t h i g h e r hardness o f t h e h i g h e r m o l e c u l a r w e i g h t c o m -

Figure 4.

Variation of hardness with fiber content (reinforced rigid PVC)

posites. T h e l o w e r i n g o f the hardness w i t h the a d d i t i o n o f asbestos

fibers

m i g h t be e x p l a i n e d o n the basis o f the l o w stiffness o f these fibers. D e s p i t e the f a c t that the fiber has a v e r y h i g h m o d u l u s (ca. 20 X 1 0 p s i vs. 6

10 X 1 0 p s i f o r g l a s s ) , c h r y s o t i l e is also a n asbestos o f finest d i a m e t e r 6

7 Χ 10" i n c h vs. 2.6 Χ 10" i n c h f o r glass. T h e hardness test p r o b a b l y 7

4

subjects the fibers t o b e n d i n g , a n d as s u c h the stiffness ( E I ) d e p e n d s o n the fiber d i a m e t e r as w e l l as the m o d u l u s .

Since t h e asbestos is l o w e r

i n d i a m e t e r b y three orders o f m a g n i t u d e w h i l e o n l y h i g h e r b y a factor of 2 i n m o d u l u s , o n e w o u l d expect to observe l o w e r values o f b e n d i n g stiffness a n d l o w e r hardness. T h e densities o f t w o o f the 3 0 % composites w e r e d e t e r m i n e d , a n d values o f 1.65 a n d 1.58 g r a m s / c m

3

w e r e o b s e r v e d f o r samples 2 0 - H - 3 0

a n d 7-H-30, respectively. These compare favorably w i t h a theoretically c a l c u l a t e d 1.66 g r a m s / c m

3

f o r this fiber content a n d suggest t h a t t h e

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

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38

FILLERS AND REINFORCEMENTS

Figure

5.

Radiographs

of non-reinforced PVC

and

FOR PLASTICS

reinforced

e n t r a p m e n t of a i r i n the c o m p o s i t e is not a significant factor i n the o b s e r v e d hardness l o w e r i n g . Flammability. A l l t h e composites w e r e classified as n o n - b u r n i n g acc o r d i n g to A S T M 635. Fiber Distribution. A s s h o w n b y F i g u r e 5 the a i r m i x i n g t e c h n i q u e w e u s e d r e s u l t e d i n a u n i f o r m d i s p e r s i o n of the fibers i n the plastics. T h i s

Figure 6. Infrared spectra of polymer before and after processing with asbestos. Solid line: stabilized low molecular weight polymer before processing; dashed line: stabilized low molecular weight polymer after processing with No. 1 asbestos.

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

4.

CRUGNOLA A N D L i T M A N

Asbestos-Reinforced

39

PVC

w a s d o n e w i t h o u t affecting the r e l a t i v e degree of fiber openness

and/or

d a m a g i n g the fiber l e n g t h . Effect of Processing on the Asbestos Fibers. T h e N o . 1 fiber c o m posites w e r e e x a m i n e d f o r fiber d e g r a d a t i o n , a n d fibers d i d not a p p e a r to b e s i g n i f i c a n t l y s h o r t e n e d b y processing.

The microscopic view r e -

v e a l e d that the asbestos b u n d l e s h a d b e e n sheared so as to give rise t o somewhat

t h i n n e r b u n d l e s o f a p p r o x i m a t e l y t h e same

l e n g t h as t h e

original. and Molecular Weight Distribution. M o d i f i c a -

Molecular Weight

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tions i n average m o l c u l a r w e i g h t a n d m o l e c u l a r w e i g h t d i s t r i b u t i o n w e r e a c o n s e q u e n c e o f the m i x i n g / p r o c e s s i n g / m o l d i n g c y c l e o f the

asbestos

r e i n f o r c e d P V C plastics. T h e s e modifications w e r e m o r e a p p a r e n t i n the h i g h m o l e c u l a r w e i g h t m a t r i x m a t e r i a l t h a n i n the l o w . I n g e n e r a l , t h e y w e r e n o t m a r k e d l y different w h e n t h e plastics w e r e subjected

to t h e

p r o c e s s i n g / m o l d i n g c y c l e w i t h o u t the i n c l u s i o n o f the asbestos. A s a r u l e , the n u m b e r average m o l e c u l a r w e i g h t i n c r e a s e d , a n d t h e h i g h e r m o l e c u l a r w e i g h t averages i n c r e a s e d . T h i s o f course r e s u l t e d i n a significant increase i n t h e p o l y d i s p e r s i t y o r the broadness o f the m o l e c u l a r w e i g h t d i s t r i b u t i o n . F i n a l l y , a l t h o u g h f u r t h e r c o n f i r m a t i o n is c a l l e d for, t h e results also suggest that t h e N o . 1 fiber ( d e s c r i b e d as c l e a n ) m i n i m i z e s the changes i n m o l e c u l a r w e i g h t a n d m o l e c u l a r w e i g h t d i s t r i b u t i o n u n d e r g o n e b y t i i e p o l y m e r s (see T a b l e s V a n d V I ) . Table VII.

Glass vs. Asbestos-Reinforced Rigid P V C Glass Reinforced 20%

Property Impact strength, f t - l b s / i n notch H e a t deflection t e m p e r a t u r e , °F Density, grams/cm Flammability Tensile strength, psi U l t i m a t e elongation, % R o c k w e l l hardness, M C o s t of fiber 3

1.0-1.6

Asbestos

Reinforced 80%o

15% 1.2

1.4

170-180 176 1.49-1.58 non-burning non-burning 10,000 7,500 1.5-4.0 2.0-1.5 M80-88 M71-93 4.5(é/lb 55-60^/lb



176 1.62 7,500

Changes i n Chemical Structure. T h e i n f r a r e d s p e c t r a ( F i g u r e 6 ) s h o w e d several changes i n the p o l y m e r / s t a b i l i z e r c o m b i n a t i o n as a c o n sequence o f p r o c e s s i n g . cm"

1

O n e o f these, the loss o f a n a b s o r p t i o n a t 1550

w a s t i e d to alterations i n the s t a b i l i z e r m o l e c u l e .

i n v o l v e d t h e a p p e a r a n c e o f a b a n d at 1030 c m " . 1

Another change

This would

suggest

reactions l e a d i n g t o the o x i d a t i o n o f the S i n the s u l f u r c o n t a i n i n g o r g a n o t i n s t a b i l i z e r . P l a u s i b l e reactions (2) a r e :

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

40

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

0 R S S n —> R S 0 H 3

Ο Sn S R + — C

Ι

ci

>SnCl +

—C

I

> — Ο ­

I

s

o=s=o

R

R

I

I

T h e p r o p e r t i e s o b t a i n e d i n this s t u d y w e r e c o m p a r e d w i t h those i n

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t h e l i t e r a t u r e for glass r e i n f o r c e d r i g i d P V C (3)

(see

Table V I I ) .

The

m e c h a n i c a l a n d t h e r m a l p r o p e r t i e s o b t a i n e d b y r e i n f o r c i n g w i t h the 4.50 asbestos are f u l l y c o m p a r a b l e w i t h those o b t a i n e d w i t h c h o p p e d

glass

fibers. Literature

Cited

1. Cameron, A. B., Heron, G . F., Wicker, G . L., "Asbestos Reinforced Thermo­ plastics," 28th Ann. Tech. Conf. Reinforced Plastics/Composites, Institute S.P.I. 1973 section 11-B, p. 1. 2. Deanin, R. D . , L o w e l l Technological Institute, private communication. 3. Owens-Corning Fiberglass C o r p . , C o m p o u n d Selector, Jan. 1970. R E C E I V E D October 11,

1973.

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