Morphology of Polymers: Some Industrial Aspects - American

19 Morphology of Polymers: Some Industrial Aspects J. B R A N D R U P , Κ. H. B U R G , and H . C H E R D R O N

Downloaded by CHINESE UNIV OF HONG KONG on March 21, 2016 | http://pubs.acs.org Publication Date: December 10, 1981 | doi: 10.1021/bk-1981-0175.ch019

H O E C H S T A G , Kinststoff-Forschung, 6230 Frankfurt/Main 80, West Germany

One of the most important differences between low molecular weight compounds and macromolecules is to be seen in the many possibilities of influencing the morphology of polymers, and by this, in the possibilities of changing their physical properties in a controlled manner. Pronounced effects of the morphology exist on the mechanical and optical properties and in some cases also on the rheology of the polymer melt. The broad term morphology includes not only the shape and arrangement of amor phous and crystalline polymers or polymer segments, but also the crystallite structure of macromolecules. Some of the most important ways of influencing the polymer morphology are: • Biaxial or multiaxial orientation • Formation of multiphase polymer systems by mixing of two or more different polymers • Influencing the crystallization process. From the industrial point of view the change of polymer properties by influencing the morphology is of great importance for several reasons: • i n s t e a d o f changing the chemical s t r u c t u r e or composition of a polymer s i m i l a r or b e t t e r r e s u l t s may be achieved by mixing two or more polymers which i s i n many cases the more economical way (e.g. high impact copolymers versus high impact polymer b l e n d s ) . • In s e v e r a l cases the formation o f a s p e c i a l morphology imparts mechanical p r o p e r t i e s to "simple" macromolecules which h i t h e r t o have only be obtained with " e x o t i c " p o l y mers (e.g. high s t r e n g t h polyethylene f i b e r s ) . • Last not l e a s t , i n some cases changing the morphology of a polymer i s the only way to achieve c e r t a i n p r o p e r t i e s (e.g. polymer f i b r i d s ) .

©

0097-6156/81/0175-0289$5.00/0 1981 American Chemical Society

Stahl; Polymer Science Overview ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

290


1.

P O L Y M E R

Amorphous

SCIENCE

O V E R V I E W

Polymer-Blends

The mixing of two or s e v e r a l polymers g e n e r a l l y y i e l d s a two- or multiphase system although some homogeneous blends are known. This behavior i s due to the low entropy of mixing two polymers. Thus even small p o s i t i v e changes i n enthalpy of mixing y i e l d a p o s i t i v e f r e e energy of mixing which then causes incompatibility. The d i s t r i b u t i o n i n space of the two phases depends on the mode of f a b r i c a t i o n , on p h y s i c a l and chemical f a c t o r s and c e r t a i n l y on the c o n c e n t r a t i o n range considered. The f i e l d of polymer blends has been e x t e n s i v e l y i n v e s t i g a ted both from a t h e o r e t i c a l and a p r a c t i c a l p o i n t of view during the l a s t decade and s e v e r a l reviews are published (1, 2, 3, 4 ) . T h e o r e t i c a l l y there e x i s t four p o s s i b i l i t i e s to combine hard and s o f t polymers with each other. They are l i s t e d i n Table 1 together with some examples which have already found commercial interest. In t h i s r e p o r t we w i l l only consider type 3, i . e . mixtures of a r i g i d amorphous thermoplast with s m a l l amounts of an e l a s tomer which i s the u n d e r l y i n g p r i n c i p l e f o r a l l rubber toughened p l a s t i c s to improve impact behavior. In s o l i d polymers, the energy of impact i s d i s s i p a t e d by the formation of crazes or shear bands i n the m a t r i x . Both mechanisms are enhanced by the a d d i t i o n of a second e l a s t o m e r i c phase to the r i g i d polymer, but not a l t e r e d i n p r i n c i p l e . Chemical s t r u c t u r e , c o n c e n t r a t i o n , s i z e and d i s t r i b u t i o n of the rubber phase as w e l l as adhesion to the matrix determine processing and f i n a l p r o p e r t i e s , s p e c i f i c a l l y the impact s t r e n g t h . In the case o f a powder blend, l i k e PVC/rubber-systems, the c h a r a c t e r i s t i c powder data have a l s o to be taken i n t o account. The type of rubber chosen depends on the d e s i r e d mechanical p r o p e r t i e s and on the end use. I f , f o r example, e x c e l l e n t outdoor w e a t h e r a b i l i t y i s r e q u i r e d , the use i f s a t u r a t e d rubbers as elastomer phase i s p o s s i b l e . The p r e f e r r e d morphology of these rubber m o d i f i e d amorphous thermoplastics i s the d i s t r i b u t i o n of d i s t i n c t rubber p a r t i c l e s u n f i l l e d or f i l l e d i n an i s o t r o p i c matrix of the b a s i c polymer. T h i s was shown to be the case f o r rubber modified p o l y s t y r e n e and f o r ABS-type polymers. 5

Since these systems have been e x t e n s i v e l y d e s c r i b e d i n the l i t e r a t u r e we want to concentrate on another i n d u s t r i a l l y important amorphous polymer mixture, namely the PVC/rubberblends. Unexpectedly, PVC/rubber blends show under c e r t a i n circumstances q u i t e a d i f f e r e n t morphology. T h i s was shown experiment a l l y f o r c h l o r i n a t e d polyethylene and e t h y l e n e - v i n y l a c e t a t e copolymers as rubber phase.



B R A N D R U P

E T AL.

Figure L

Morphology

of

Polymers

Morphology of rubber modified high impact polystyrene.



Soft matrix + s o f t d i s p e r s e d phase

Soft matrix + hard d i s p e r s e d phase

Hard matrix + s o f t d i s p e r s e d phase

Hard matrix + hard d i s p e r s e d phase

Type 2:

Type 3:

Type 4:

Combinations

Polymer Mixtures (Polymer

Type 1:

Possible

TABLE I :

Blends)

of P r a c t i c l e

Elastomers

PVC

• PVC/ABS-Blends

• PC /ABS-Blends

• PPO/PS-Blends

• High impact

ABS

Interest

• High impact p o l y s t y r e n e and

High impact t h e r m o p l a s t i c s

Polymer f i l l e d

Elastomer-Blends

Combinations


3

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Morphology of Polymers: Some Industrial Aspects - American

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