Biodegradable Fillers in Thermoplastics - Advances in Chemistry

16 Biodegradable Fillers in Thermoplastics GERALD J. L. GRIFFIN

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Brunel University, Department of Polymer Science and Technology, Uxbridge, Middlesex, E n g l a n d

Increased degradability in landfill and composting of the common packaging thermoplastics has been achieved by incorporating a biodegradable filler into the plastics com pounds using standard hot-melt compounding techniques. A search of possible fitters disclosed that only raw starch satisfied the requirements of adequate thermal stability, minimum interference with melt-flow properties, and mini mum disturbance of product quality. Successful extrusion -blowing of layflat film in LDPE containing up to at least 30 wt % of starch is reported, and starches—principally maize, rice, and tapioca—have been successfully included in other products such asfibrillatedPP film, TPS injection moldings, extrusions, and thermoformings. The characteri zation of starches by scanning electron microscopy and narrow angle light scattering is described as part of this investigation.

' T ^ h e preservation of our environment has excited m u c h p u b l i c a n d A

technical discussion i n recent

years.

Special attention has been

f o c u s e d , p e r h a p s s o m e w h a t u n f a i r l y , o n t h e p a r t i c u l a r p r o b l e m s associated w i t h t h e i n c r e a s i n g p r o p o r t i o n o f plastics p a c k a g i n g m a t e r i a l s i n c o m m u n i t y d o m e s t i c refuse. Wallhàuser has p u b l i s h e d three d e t a i l e d articles (1, 2, 3 ) , w h i c h d e s c r i b e t h e s i t u a t i o n i n t h e F e d e r a l G e r m a n R e p u b l i c b u t nevertheless are o f g e n e r a l interest e s p e c i a l l y i n c o n n e c t i o n w i t h c o m posting a n d landfill procedures.

P o l y o l e f i n film has r e c e i v e d s p e c i a l c r i t i -

c i s m b e c a u s e o f its l o n g e v i t y u n d e r s o i l b u r i a l c o n d i t i o n s .

Because the

o n l y l i k e l y d e g r a d a t i o n processes a c t i n g o n b u r i e d polyolefins a r e s i m p l e o x i d a t i o n a n d m i c r o b i o l o g i c a l attack, t h e v a l u a b l e w o r k o f Scott (4) o n the c o n t r o l l e d p h o t o o x i d a t i o n Wallhàuser reports t h a t i n

of polymers

five-year

cannot provide

s o i l b u r i a l tests L D P E

a solution. h a d been

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

160

FILLERS

c o l o n i z e d b y Desulfovibrio

AND

REINFORCEMENTS FOR

PLASTICS

b a c t e r i a , a n d m a t e r i a l f r o m 2.5-meters

depth

h a d b e c o m e e m b r i t t l e d . M o r e r e c e n t l y N y k v i s t ( 5 ) has e s t a b l i s h e d t h a t L D P E is s l o w l y b i o d e g r a d e d i n compost; h e d e m o n s t r a t e d this b y e x p e r i ments u s i n g c a r b o n - 1 4 - l a b e l e d

polymer and detecting radioactive

C0

2

i n the air a s p i r a t e d f r o m the s a m p l e vessel. L o n g t e r m o x i d a t i o n studies of L D P E , w h i c h are of great interest to c a b l e a n d p i p e m a n u f a c t u r e r s , h a v e b e e n w e l l d o c u m e n t e d , a n d p o w e r f a c t o r m e a s u r e m e n t is the p r e f e r r e d m e t h o d for m o n i t o r i n g the o x i d a t i o n . T h e e a r l y w o r k is r e v i e w e d b y H a y w o o d ( 6 ) a n d suggests t h a t the o x i d a t i o n rates a r e n e g l i g i b l e at Downloaded by UNIV OF PITTSBURGH on September 21, 2013 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0134.ch016

r o o m t e m p e r a t u r e , b u t 1-mm t h i c k sheet w o u l d e m b r i t t l e i n a b o u t y e a r at 4 0 ° C .

one

H o w e v e r , temperatures a b o v e 4 0 ° C are c o m m o n i n c o m -

p o s t i n g . A l s o , o x y g e n diffusion rates i n t h e p o l y m e r g i v e extra significance to film thickness a n d t e m p e r a t u r e . E v i d e n t l y one c i r c u m s t a n c e w h i c h w o u l d encourage b o t h m o d e s of attack w o u l d be a n increase i n the specific surface a r e a of the m a t e r i a l ; Wallhàuser refers to the d e s i r a b i l i t y of s h r e d d i n g the w a s t e b e f o r e b u r i a l . A n a l t e r n a t i v e a p p r o a c h is to i n t r o d u c e a filler i n t o the m a t e r i a l w h i c h itself is s p e e d i l y d e g r a d e d , thus l e a v i n g a porous film r e a d i l y e n t e r e d b y m i c r o o r g a n i s m s a n d r a p i d l y s a t u r a t e d w i t h oxygen.

T h e selection of a

s u i t a b l e filler is t h e subject of this w o r k . Criteria

for Biodegradable

Filler Selection

T h e markets c u r r e n t l y satisfied b y plastics p a c k a g i n g films expect t h e i n d u s t r y to s u p p l y t h e m w i t h a p r o d u c t t h a t is strong, s m o o t h , odorless,

Figure picture

1. Scanning electron microscope of rice starch grains. Average grain size is about 5 μm.

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

16.

GRIFFIN

Biodegradable

161

Fillers

b a s i c a l l y colorless, n o n - t o x i c , w a t e r resistant, a n d cheap. A n y b i o d e g r a d a b l e filler m u s t n o t u n d u l y c o m p r o m i s e these qualities a n d m u s t b e a b l e to w i t h s t a n d p r o c e s s i n g temperatures for short p e r i o d s . f a l l w i t h i n the r a n g e 1 5 0 ° - 3 0 0 ° C .

These normally

T h e p r i m a r y r e q u i r e m e n t of

biode-

g r a d a b i l i t y is a c h i e v e d b y t h e filler a c t i n g as a p o t e n t i a l m a j o r n u t r i e n t f o r some m i c r o o r g a n i s m s o r b e i n g d e c o m p o s e d b y m i c r o o r g a n i s m n u t r i tion.

T h i s means, i n e v i t a b l y , t h a t t h e

filler

w i l l be organic i n nature.

L o w cost r e q u i r e m e n t s suggest t h a t a waste p r o d u c t f r o m another i n d u s t r y s h o u l d be c o n s i d e r e d , b u t a n i n t e r e s t i n g s u r v e y of i n d u s t r i a l wastes Downloaded by UNIV OF PITTSBURGH on September 21, 2013 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0134.ch016

b y G u t t ( 7 ) r e m i n d s us t h a t the o v e r w h e l m i n g b u l k of i n d u s t r i a l waste is m i n e r a l i n o r i g i n . C e r t a i n w e l l k n o w n l o w cost o r g a n i c wastes s u c h as l i g n i n a n d leather g r i n d e r y refuse are i m m e d i a t e l y e l i m i n a t e d b e c a u s e of color or o d o r , a n d p r o t e i n - b a s e d m a t e r i a l s are too t h e r m a l l y u n s t a b l e to be considered.

C e l l u l o s i c m a t e r i a l s are t r a d i t i o n a l i n g r e d i e n t s of t h e r m o

setting m o l d i n g c o m p o s i t i o n s , a n d W o r l d W a r I I experience w i t h m i l i t a r y e q u i p m e n t i n the tropics e s t a b l i s h e d the a c c e s s i b i l i t y of these fillers to b i o l o g i c a l attack. T h e p h y s i c a l n a t u r e of w o o d flour a n d c e l l u l o s e p u l p m a k e t h e m u n w e l c o m e h i g h - v o l u m e a d d i t i v e s i n t h e r m o p l a s t i c s because

Figure picture

2. Scanning electron microscope of potato starch grains. Average grain size is about 50 μπι.

the refined nature of the e x t r u s i o n - b l o w i n g a n d e x t r u s i o n - c o a t i n g t e c h nologies m a k e t h e m v e r y sensitive to changes i n t h e i r r h e o l o g i c a l p r o p erties. M i n i m u m particle/particle interaction i n

flowing

suspensions,

and

h e n c e m i n i m u m v i s c o s i t y increase, is a c h i e v e d b y systems i n w h i c h t h e s u s p e n d e d p a r t i c l e s are s m o o t h spheres or, e v e n better, s m o o t h e l l i p s o i d s w h i c h c a n orient to a m i n i m u m e n e r g y c o n f i g u r a t i o n i n l a m i n a r


flow.

162

FILLERS

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

Potato starch

25

20

No.X


15

10

20

Figure 3.

30

40

50

eo microns

Potato starch mean diameter

25

histogram

Jack bean starch

20-

15-

Figure

4. Jack bean starch diameter histogram

mean

T h i s t h e o r y has b e e n l o n g e s t a b l i s h e d f o r N e w t o n i a n fluids a n d is r e v i e w e d a n d extended i n the second D u t c h report o n viscosity a n d plast i c i t y , e s p e c i a l l y b y B u r g e r s ( 8 ) . A f u r t h e r r h e o l o g i c a l c o n s i d e r a t i o n is t h e q u e s t i o n of p a r t i c l e size d i s t r i b u t i o n . E v e s o n ( 9 ) f o u n d r e d u c t i o n s of u p to 1 6 % i n t h e r e l a t i v e v i s c o s i t y of 2 2 . 5 % m i c r o s p h e r e

suspensions

b y c h a n g i n g o n l y t h e size d i s t r i b u t i o n a w a y f r o m t h e h o m o d i s p e r s e . T h e s e considerations n a r r o w the field of s e a r c h to p a r t i c l e s of r e g u l a r geometries, a n d o n l y spores, seeds, d r i e d s i m p l e organisms, a n d starches remain for consideration.

Starches a r e t h e most a t t r a c t i v e m e m b e r s of

this g r o u p a n d w e r e selected f o r f u r t h e r s t u d y

(10).


16.

GRIFFIN

Characteristics

Biodegradable of

163

Fillers

Starches

L i t t l e needs to b e r e c o r d e d h e r e o n g e n e r a l starch t e c h n o l o g y other t h a n a reference to t h e r e m a r k a b l e atlas' of R e i c h e r t (11) c o m p r e h e n s i v e text of W h i s t l e r a n d P a s c h a l l (12).

a n d the r e c e n t

T h e c r i t e r i a set out

earlier are m e t to a r e m a r k a b l e degree b y a s m a l l g r o u p of c o m m e r c i a l l y a v a i l a b l e starches. T h e p a r t i c l e s c a n b e n e a r spheres, as i n the p o l y h e d r a l r i c e s t a r c h grains s h o w n i n F i g u r e 1, or e l o n g a t e d n e a r e l l i p s o i d s as w i t h the p o t a t o s t a r c h grains s h o w n i n F i g u r e 2. T h e s e g e o m e t r i c a l v a r i a t i o n s


are d e t e r m i n e d b y the m o d e of o c c u r r e n c e of t h e s t a r c h grains w i t h i n t h e p a r e n t p l a n t structures, c o m p o u n d s t a r c h grains g i v i n g rise to t h e f a c e t e d particles.

T h e r a n g e of p a r t i c l e sizes is f r o m 3 to 100 μιη, a n d t h e i r

Figure 5. Narrow angle light scatter ing pattern directly recorded on pho tographic plate following method of Stein and Rhodes. Sample was dis persion of wheat starch in Canada balsam solution in xylene held as film between microscope slide and cover

Figure 6. Same as Figure 5, but sample was dispersion of maize starch

Figure 7. Same as Figure 5, but sample was dispersion of rice starch


164

FILLERS

AND

REINFORCEMENTS FOR

PLASTICS

m e a s u r e m e n t was c o n s i d e r e d i m p o r t a n t i n this w o r k . S t e i n a n d R h o d e s s m e t h o d of s p h e r u l i t e size m e a s u r e m e n t s t a r c h suspensions, a n d S a m u e l s (14) particles i n light scattering work.

(3)

is d i r e c t l y a p p l i c a b l e to

has u s e d r i c e s t a r c h as c a l i b r a n t

S o m e c a u t i o n is i n d i c a t e d b e c a u s e of

t h e o c c u r r e n c e of s k e w e d a n d d o u b l e - p e a k e d p o p u l a t i o n s . S a m p l e h i s t o grams f r o m d i r e c t m i c r o s c o p y are s h o w n i n F i g u r e s 3 a n d 4. T h e q u a l i t y of the H

scatter c l o v e r l e a f varies g r e a t l y b e t w e e n starches, a n d a series

v

of examples p r o g r e s s i n g i n m e a n p a r t i c l e d i a m e t e r are s h o w n i n F i g u r e s 5, 6, a n d 7. T h e r e is also o c c a s i o n a l u n c e r t a i n t y a b o u t t h e s t a r c h g r a i n Downloaded by UNIV OF PITTSBURGH on September 21, 2013 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0134.ch016

d i m e n s i o n s q u o t e d i n the l i t e r a t u r e because the longest c h o r d m e a s u r e Table I. Starch

Mean Diameters of the Common Starch G r a i n s

0

Microscopy

Light Scattenng

Literature

Rice Maize Arrowroot Wheat

5 11 21 26

5.6 14.2 25.8 36.4

Jack bean Potato

24.5 25.5

30.8 55.2

3 to 8 A v . 15 — 2 t o 10 a n d 20 t o 35 — 15 t o 100

α

A l l dimensions in micrometers.

m e n t o n s t r e w n samples c a n b e q u o t e d w i t h o u t q u a l i f i c a t i o n . T a b l e I c o m p a r e s m y measurements w i t h c e r t a i n p u b l i s h e d values. T h e m i c r o s c o p y figures are of the f o r m D = p h o t o g r a p h s of settled suspensions. results are d e r i v e d f r o m H

v

(I -f- b)/2

and were determined on

T h e n a r r o w angle light scattering

m o d e H e - N e laser l i g h t s c a t t e r i n g e x p e r i

ments u s i n g Stein's e q u a t i o n D = 2 λ / χ sin (Θ/2) T h e l i t e r a t u r e figures are q u o t e d f r o m K n i g h t

(15).

Compounding A c k n o w l e d g e d difficulties i n r e l a t i n g l a b o r a t o r y r h e o m e t r y to p o l y m e r p r o c e s s i n g t e c h n o l o g y e n c o u r a g e d m e to a d o p t a " t i t r a t i o n " t e c h n i q u e f o r assessing the c o m p a t i b i l i t y of s t a r c h w i t h L D P E .

A set w e i g h t of

p o l y m e r was fluxed o n a l a b o r a t o r y t w o - r o l l m i l l , a n d a starch w a s a d d e d p r o g r e s s i v e l y u n t i l the h i d e of c o m p o u n d b r o k e u p or b e c a m e u n m a n ageable.

F o r the b l o w n film experiments the p o l y m e r u s e d w a s I m p e r i a l

C h e m i c a l Industries g r a d e Q 1 3 8 8 of d e n s i t y 0.920 at 2 3 ° C a n d m e l t flow

i n d e x 2 f o l l o w i n g m e t h o d 1 0 5 C of B r i t i s h S t a n d a r d S p e c i f i c a t i o n

2782. R i c e , w h e a t , potato, m a i z e , a n d t a p i o c a starches w e r e a l l b l e n d e d easily i n t o the fluxed p o l y m e r p r o v i d e d o n l y t h a t t h e y w e r e d r y a n d n o t


16.

Biodegradable

GRIFFIN

i n h a r d agglomerates.

165

Fillers

M i l l i n g times e x c e e d i n g 1 h r at r o l l temperatures

of 1 5 0 ° C c a u s e d n o v i s i b l e increase i n d i s c o l o r a t i o n , a n d light microscopy

subsequent

of films m a d e f r o m these m a t e r i a l s s h o w e d

discrete

i n t a c t s t a r c h p a r t i c l e s i n t h e p o l y m e r m a t r i x . C o n t r o l l i n g size d i s t r i b u t i o n b y u s i n g b l e n d s of s m a l l p a r t i c l e a n d l a r g e p a r t i c l e starches w e i g h t l o a d i n g s e x c e e d i n g 100 p h r to b e a c h i e v e d .

enabled

These concentrated

stocks w e r e g r a n u l a t e d f o r use as masterbatches b y c u t t i n g the stock as


strip f r o m the m i l l a n d f e e d i n g , after a i r c o o l i n g , to a r o t a r y c u t t e r .

ol

0

1

Figure 8. increasing Conversion

I 20

I I I I AO 60 Concn of S t a r c h - p h r

1

1 80

L

100

Melt flow index for two grades of LDPE with starch content. Maize starch only was used.

Processing

I n i t i a l w o r k w a s r e s t r i c t e d to s a m p l e sheet p r e p a r a t i o n b y p r e s s i o n m o l d i n g , h e a t s t a b i l i t y testing b y the e x t r u s i o n of a 12 X

com1-mm

r i b b o n , a n d e x t r u s i o n - b l o w n film trials u s i n g a l i n e b a s e d o n a S a m a f o r e x t r u d e r of 2 0 : 1 l:d r a t i o w i t h a 4 5 - m m d i a m e t e r s c r e w m a k i n g 3 0 0 - m m w i d e layflat at 25 m i c r o m e t e r n o m i n a l gage. T h e heat s t a b i l i t y p r o c e d u r e i n v o l v e d c o n t i n u o u s e x t r u s i o n at the lowest m a c h i n e s p e e d of a n L D P E r i b b o n c o n t a i n i n g 10 p h r s t a r c h w h i l e p r o g r e s s i v e l y r a i s i n g t h e h e a d a n d d i e temperatures. T a k i n g m a i z e s t a r c h as t y p i c a l , some v a p o r e v o l u t i o n o c c u r r e d at 2 3 0 ° C w h i c h w a s p r e s u m a b l y c a u s e d b y steam generation, a n d i t c a u s e d a r o u g h e n i n g of the surface of t h e extrudate. T h e t e m p e r a t u r e l i m i t of t h e e q u i p m e n t w a s 300 ° C , a n d at this l e v e l a p a l e c r e a m color d e v e l o p e d

i n the products.

The

onset of d i s c o l o r a t i o n w a s at a h i g h e r t e m p e r a t u r e t h a n e x p e c t e d , a n d i t w o u l d seem that t h e u n u s u a l e n v i r o n m e n t of the i s o l a t e d s t a r c h grains m a y be a significant r e t a r d i n g factor.


166

FILLERS

AND

REINFORCEMENTS FOR

PLASTICS

F i l m e x t r u s i o n - b l o w i n g w a s e v a l u a t e d b y setting t h e S a m a f o r

film

e x t r u s i o n l i n e to operate n o r m a l l y w i t h u n m o d i f i e d L D P E a n d t h e n p r o gressively i n c r e a s i n g the content of 100 p h r s t a r c h m a s t e r b a t c h i n the feed blend.

P r o v i d e d o n l y that the m a s t e r b a t c h w a s d r y , the s t a r c h /


L D P E c o m p o u n d e x t r u d e d as r e a d i l y as t h e u n m o d i f i e d m a t e r i a l w i t h

Figure 9. Rice starch grains, 5 μπι mean diameter, seen by polarized light microscopy in polypropylene film after extrusion at 230°C n o i n d i c a t i o n of i n c r e a s e d p o w e r c o n s u m p t i o n o n the n o r m a l m a c h i n e instruments.

A b o v e 30 p h r o c c a s i o n a l b u b b l e f a i l u r e s o c c u r r e d , b u t i t

w a s possible to b l o w t h e 100-phr m a s t e r b a t c h d i r e c t l y f o r short p e r i o d s . E a r l y difficulties w i t h screen p a c k b l o c k a g e w e r e later a v o i d e d b y c a r e f u l a t t e n t i o n to the c o n t r o l of m a s t e r b a t c h c o m p o u n d i n g flow

technique.

Melt

i n d e x measurements o n a series of L D P E / m a i z e c o m p o u n d s

were

m a d e a n d c o n f i r m e d t h e m o d e s t interference w i t h flow p r o p e r t i e s sug gested b y the e x t r u s i o n t r i a l s ; the results are p r e s e n t e d i n F i g u r e 8.

The

L D P E film p r o d u c e d was s i m i l a r i n f e e l a n d a p p e a r a n c e to u n m o d i f i e d film

w h e n the starch content w a s l o w , a p a r t f r o m a n increase i n surface

roughness w h i c h e l i m i n a t e d the b l o c k i n g t e n d e n c y of t h e film a n d d e creased its t r a n s p a r e n c y .

A t s t a r c h concentrations

a b o v e 15 p h r

the

p r o d u c t b e g a n to d e v e l o p a p l e a s i n g , p a p e r y f e e l w h i c h w a s v e r y p r o n o u n c e d at 30 p h r . I n v i e w of the success of these trials the w o r k w a s e x t e n d e d

to

establish t h e c o m p a t i b i l i t y of starches w i t h other t h e r m o p l a s t i c s b y s m a l l scale m i l l c o m p o u n d i n g .

So f a r , this has b e e n v e r i f i e d f o r a l l t h e c o m

m o n packaging thermoplastics.

W i t h polypropylene

it was

easier

to

e x t r u d e a b l e n d of P P granules a n d L D P E / s t a r c h m a s t e r b a t c h granules, a t e c h n i q u e a d o p t e d to a v o i d e x p o s i n g s t a r c h to h i g h temperatures w h i l e u n p r o t e c t e d b y a p o l y m e r m e l t envelope.

E v e n after e x t r u s i o n i n P P


16.

GRIFFIN

Biodegradable

167

Fillers

at 2 3 0 ° C the s t a r c h grains w e r e u n d a m a g e d as i n d i c a t e d b y t h e i r a p p e a r ance u n d e r p o l a r i z e d l i g h t m i c r o s c o p y

(Figure 9).

Extruded P P ribbon

w i t h 1 5 - p h r rice s t a r c h content c o u l d b e c o l d - d r a w n at u p to 12:1 r a t i o for

fibrillation. T h e p o l y s t y r e n e c o m p o u n d i n g trials w e r e s c a l e d u p first to a S h a w

3-kilo i n t e r n a l m i x e r , a n d l a t e r to

a Buss P R 1 0 0 continuous

mixer

e q u i p p e d w i t h a f a c e cutter f o r p e l l e t p r o d u c t i o n . T h e p r o d u c t w a s u s e d for m a k i n g e x t r u d e d sheet f r o m b l e n d s

w i t h toughened

polystyrene,

using a vented barrel Samafor extruder w i t h a 45-mm diameter

screw


of 2 5 : 1 l:d r a t i o a n d c o u p l e d to a 3 0 0 - m m slit d i e . T h e sheet p e r f o r m e d w e l l i n t h e r m o f o r m i n g trials of

deep disposable

drinking

cups.

The

same p o l y s t y r e n e master b a t c h w a s u s e d i n b l e n d s for i n j e c t i o n m o l d i n g trials a n d , once a g a i n p r o v i d e d o n l y t h a t the m a s t e r b a t c h w a s d r y , n o difficulties w e r e e x p e r i e n c e d w i t h m o l d i n g the c u s t o m a r y test pieces.

Figure 10. Scanning electron microscope picture of 30 phr maize starch-filled LDPE sheet, pressed sample, untreated Biological

Figure 11. Scanning electron mi croscope picture of same sample as in Figure 10 after 24 hr enzyme extraction at 35°C

Testing

T h e t i m e p r o b l e m associated w i t h s o i l b u r i a l tests w a s c i r c u m v e n t e d to a degree b y a d o p t i n g a d i r e c t e n z y m e attack p r o c e d u r e .

T h e presence

of a m y l a s e sources i n most soils is a s s u r e d b y the w i d e d i s t r i b u t i o n of organisms s u c h as B . subtilis.

F o r c o n v e n i e n c e a n α-amylase concentrate,

S i g m a C h e m i c a l C o . A - 6 7 5 5 , f r o m m a l t w a s u s e d i n the f o r m of a 0 . 1 % s o l u t i o n i n w a t e r w i t h a p p r o p r i a t e salts a n d buffers a n d h e l d at 35 ° C i n a n i n c u b a t o r . P o l y e t h y l e n e / s t a r c h sheet samples w e r e s u s p e n d e d i n this e n z y m e s o l u t i o n for 1 to 10 days w h e n , t y p i c a l l y , the surfaces

would

b e c o m e s l i m y p r o b a b l y because of a l a y e r of l i m i t dextrans w h i c h w e r e


168

FILLERS

AND

REINFORCEMENTS FOR

PLASTICS

r i n s e d off b e f o r e t h e samples w e r e d r i e d at r o o m t e m p e r a t u r e , v a c u u m m e t a l l i z e d w i t h A u / P d , a n d e x a m i n e d b y s c a n n i n g electron m i c r o s c o p y . F i g u r e s 10 a n d 11 s h o w a pressed L D P E sheet c o n t a i n i n g 30 p h r m a i z e starch before a n d after e n z y m e treatment. C o n t r o l samples i n c u b a t e d i n w a t e r over t h e same p e r i o d s h o w e d n o a p p a r e n t change. T h e s m a l l s u r face d i s t u r b a n c e s c r e a t e d b y the u n d e r l y i n g s t a r c h g r a i n s i n t h e u n t r e a t e d sheet h a v e d e v e l o p e d , after e n z y m e exposure, i n t o d e e p p i t s ; these p r o v e d to b e r a t h e r difficult objects for s c a n n i n g e l e c t r o n m i c r o s c o p y b e c a u s e of t h e f a i l u r e of the m e t a l l i z a t i o n to p e n e t r a t e i n t o the u n d e r c u t s , g i v i n g Downloaded by UNIV OF PITTSBURGH on September 21, 2013 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0134.ch016

rise to the f a m i l i a r electrostatic " f l a r e . "

Figure 12. Microtome cross section through 50-/xm thick LDPE blown film originally containing 30 phr starch but extracted for 10 days with enzyme solution at 35°C. Phase contrast transmitted light photography. F u r t h e r experiments w e r e c o n d u c t e d i n o r d e r to s h o w the e x t r a c t i o n effect i n d e p t h .

F o r example, extrusion-blown L D P E

film

containing

30 p h r m a i z e s t a r c h was e x t r a c t e d as a b o v e for 10 days a n d t h e n e m b e d d e d i n w a t e r - s o l u b l e w a x for m i c r o t o m y . F i g u r e 12 shows the a p p e a r ance of s u c h a s a m p l e i n cross section as seen b y p h a s e contrast m i c r o s c o p y , a n d i t is e v i d e n t that t h e m a t e r i a l has b e e n c o n v e r t e d i n t o a sponge. I n a n o t h e r m a t e r i a l , t h i n sheets of p o l y s t y r e n e c o n t a i n i n g 2 5 %

tapioca

s t a r c h w e r e e n z y m e - e x t r a c t e d a n d the change w a s r e v e a l e d b y s t a i n i n g the s t a r c h grains w i t h i o d i n e s o l u t i o n . 125-/xm t h i c k p o l y s t y r e n e extraction.

F i g u r e s 13 a n d 14 s h o w this

t r e a t e d i d e n t i c a l l y except

for

T h i s w o r k has b e e n p a r a l l e l e d b y s o i l b u r i a l

the

enzyme

experiments

w h i c h i n d i c a t e that s i m i l a r events take p l a c e . F o r e x a m p l e , b y f o l l o w i n g w e i g h t loss i t has b e e n e s t a b l i s h e d t h a t 8 0 % of t h e s t a r c h i n a n L D P E 50-/xm t h i c k film c o n t a i n i n g 15 p h r m a i z e s t a r c h has b e e n e x t r a c t e d i n m o i s t g a r d e n s o i l i n a b o u t 8 weeks at 25 ° C

(16).


Biodegradable

GRIFFIN


16.

169

Fillers

Figure 13. Toughened polystyrene sheet containing 25 phr tapioca starch photographed by transmitted light microscopy after staining starch with iodine

Figure 14. Piece from same sample sheet used for Figure 13 but stained and photographed after 10 days enzyme extraction at 35°C. Holes left by absent starch grains can just be seen. Conclusions A b i o l o g i c a l l y i n n o c u o u s filler has b e e n selected w h i c h appears to cause m i n i m u m d i s t u r b a n c e to t h e c o m m o n p a c k a g i n g t h e r m o p l a s t i c s as f a r as t h e i r p r o c e s s i n g a n d p r o p e r t i e s are c o n c e r n e d at l o a d i n g s of u p to 10 p h r ; a b o v e this l e v e l i t p r o d u c e s c o m p o s i t i o n s w h i c h a r e a t t r a c t i v e i n their o w n right.

I n L D P E films these m o r e h e a v i l y

have a papery quality.

T h i s filler, or r a t h e r g r o u p of

filled

compositions

fillers—the

plant

starches, resists d r y heat i n the n o r m a l plastics p r o c e s s i n g operations. T h e y are i n e r t to w a t e r at r o o m t e m p e r a t u r e b u t are r a p i d l y d i g e s t e d b y


170

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

the u b i q u i t o u s amylases; t h e p o r o s i t y thus g e n e r a t e d offers t h e m o s t f a v o r a b l e circumstances f o r b i o l o g i c a l a n d o x i d a t i v e attack. T h e m e c h a nism b y w h i c h the large enzyme molecules are able to penetrate t h e p o l y m e r films b e t w e e n t h e s t a r c h p a r t i c l e s is n o t e v i d e n t b u t is b e i n g i n v e s t i g a t e d . T r i a l s are also b e i n g e x t e n d e d t o l o n g t e r m s o i l a n d c o m p o s t b u r i a l s a n d t o other p o l y m e r s a n d p r o c e s s i n g m e t h o d s . Acknowledgments


T h e a u t h o r t h a n k s C o l o r o l l L t d . f o r t h e i r s u p p o r t o f this w o r k , a n d final

y e a r students a t B r u n e i U n i v e r s i t y , e s p e c i a l l y M r . P e t e r J e n k i n s ,

f o r p a t i e n t m a n i p u l a t i o n o f m i c r o s c o p e a n d laser.

Literature Cited 1. Wallhäuser, Κ. H., Verpackungs Rundschau (1972) 3, 266. 2. Wallhäuser, Κ. Η., Mull Abfall (1972) 1, 10. 3. Wallhäuser, Κ. Η., Preprints, Degradability of polymers and plastics, Plas tics Institute, London, 27 Nov. 1973. 4. Scott, G., Plastics Rubbers Textiles (1970) 1, 361. 5. Nykvist, N., Preprints, Degradability of polymers and plastics, Plastics Institute, London, 27 Nov. 1973. 6. Haywood, C. K., in "Polythene," Renfrew and Morgan, Eds., p. 135, Iliffe, London, 1960. 7. Gutt, W., Chem. Ind. (1972) 439. 8. Burgers, J. M., 2nd, Report on Viscosity and Plasticity. Verhandelingen der Konok. Nederl Akad. Eerste Sektie Deel XVL No. 4 North Holland Pub. Co. Amsterdam 1938. 9. Eveson, G. F., in "Rheology of Disperse Systems," pp. 61-83, Pergamon Press, London, 1959. 10. British Patent Application 23469/72, Assigned to Coloroll Ltd. 11. Reichert, E. T., Carnegie Inst. Washington Pub. No. 173 (1913). 12. Whistler, R. L., Paschall, E. F., "Starch Chemistry and Technology," Aca demic Press, New York, 1965. 13. Stein, R. S., Rhodes, M. B., J. Appl. Phys. (1960) 31, 1873. 14. Samuels, R. J., J. Poly. Sci. (1971) A2, 9, 2165. 15. Knight, J. W., 'The Starch Industry," Pergamon Press, London, 1969. 16. Dowding, P., private communication, Trinity College, Dublin, 1974. RECEIVED October 11, 1973.


Biodegradable Fillers in Thermoplastics - Advances in Chemistry

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