Fiber Drawing from Blends of Polypropylene and Liquid-Crystalline

Chapter 7

Fiber Drawing from Blends of Polypropylene and Liquid-Crystalline Polymers 1

2

1

2

1

Y. Qin , M. M. Miller , D. L. Brydon , J. M. G. Cowie , R. R. Mather , and R. H. Wardman Downloaded by STANFORD UNIV GREEN LIBR on October 9, 2012 | http://pubs.acs.org Publication Date: July 9, 1996 | doi: 10.1021/bk-1996-0632.ch007

1

1

Scottish College of Textiles, Netherdale, Galashiels TD1 3ΗF, Scotland Department of Chemistry, Heriot-Watt University, Edinburgh EH14 4AS, Scotland 2

This paper discusses the drawing of polypropylene (PP) fibres, blended with liquid crystalline polymer (LCP) at a w/w ratio of 100/10, with the aim of enhancing fibre mechanical performance. After melt extrusion, the blended fibres consist of LCP fibrils surrounded by a PP matrix. These fibrils are, however, split after conventional one-stage drawing, and the tensile properties of the polyblend fibres are poorer than those of the corresponding pure PP fibre. By contrast, two -stage drawing, under carefully optimised conditions, can bring about some enhancement of fibre mechanical performance. In view of the very different structural properties of PP and LCPs, the use of a compatibilising agent has been studied to promote adhesion between the PP and LCP phases in the drawn fibres. It is shown that, whilst a compatibilising agent may indeed promote adhesion across the interface between the two phases, it will also increase LCP fibril fragmentation during the drawing process, with consequent impairment of fibre mechanical performance. A strategy is outlined for overcoming fibril fragmentation during drawing, using compatibilising agents which are themselves liquid crystalline. The blending o f polymers i s a technique which i s being increasingly applied f o r improving the mechanical properties of synthetic t e x t i l e fibres (1,2), for superior p r o p e r t i e s may be achieved which a r e not o b t a i n a b l e from any o f the i n d i v i d u a l blend components. By careful control o f blend composition and phase morphology, f i b r e p r o p e r t i e s can be adjusted t o meet 0097-6156/96/0632-0098$15.00/0 © 1996 American Chemical Society In Liquid-Crystalline Polymer Systems; Isayev, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1996.

Downloaded by STANFORD UNIV GREEN LIBR on October 9, 2012 | http://pubs.acs.org Publication Date: July 9, 1996 | doi: 10.1021/bk-1996-0632.ch007

7. QINETAL.

Fiber DrawingfromPP-LCP Blends

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specific requirements. Since the development and marketing of new polymers i s becoming ever more expensive, the technique of polymer blending i s p r o v i d i n g an a l t e r n a t i v e c o s t - e f f e c t i v e approach f o r producing materials with improved properties (3), and indeed s e v e r a l polyblend f i b r e s have found commercial success. More recently, the b l e n d i n g of conventional t h e r m o p l a s t i c s with l i q u i d c r y s t a l l i n e polymers (LCPs) has a t t r a c t e d considerable s c i e n t i f i c and industrial interest. LCPs generally possess r i g i d rod-like molecular chains and can e x i s t i n o r i e n t e d polydomains (4). These polydomains can be r e a d i l y a l i g n e d i n the d i r e c t i o n of flow during f a b r i c a t i o n , such that under c o n v e n t i o n a l processing c o n d i t i o n s , the LCP can develop a high degree of chain o r i e n t a t i o n . Indeed, a number of w e l l e s t a b l i s h e d commercial high performance f i b r e types have been developed from aromatic l y o t r o p i c polyamide and thermotropic copolyester LCPs (5). These LCP f i b r e s possess t e n a c i t i e s greater than 1.8 Ν tex~' and i n i t i a l moduli g r e a t e r than 40 Ν tex~^ , compared with a f i b r e t e n a c i t y of 0.7 Ν t e x ~ and i n i t i a l modulus of 12 Ν tex~' f o r conventional high t e n a c i t y p o l y e s t e r (PET) f i b r e . With the advance of LCP technology, c o n s i d e r a b l e a t t e n t i o n has been d i r e c t e d towards the blending of LCPs with conventional polymers (6-9). Indeed, the presence of a LCP as a minor component i n a conventional s y n t h e t i c f i b r e o f f e r s s e v e r a l major b e n e f i t s . For example, the low melt or s o l u t i o n v i s c o s i t y of the LCP f a c i l i t a t e s fibre extrusion ( 7 ) , and the fibre mechanical performance, notably t e n a c i t y and i n i t i a l modulus, can be improved by v i r t u e of the superior mechanical p r o p e r t i e s of the LCP (8,9). However, i n c o m p a t i b i l i t y between the conventional polymer and the LCP w i l l r e s u l t i n poor i n t e r f a c i a l adhesion between the two phases, with the r e s u l t that the reinforcement o f f e r e d by the LCP may be s e v e r e l y diminished. I n t e r f a c i a l adhesion may be c o n s i d e r a b l y improved by the a d d i t i o n of a c o m p a t i b i l i s i n g agent (10,11), very o f t e n i n the form of a g r a f t or block copolymer which possesses segments capable of i n t e r a c t i o n with each blend component. The c o m p a t i b i l i s i n g agent acts e s s e n t i a l l y as a polymeric s u r f a c t a n t , located at the i n t e r f a c e between the two phases. A f i n e r , more homogeneous d i s p e r s i o n of the LCP w i l l a l s o r e s u l t . The improved interfacial adhesion and d i s p e r s i o n g e n e r a l l y give r i s e to i n c r e a s e d mechanical performance. For example, the e f f e c t i v e n e s s of a maleic anhydride grafted polypropylene compatibilising agent i n improving the mechanical p r o p e r t i e s of injection-moulded blends of PP and LCPs has been amply demonstrated by B a i r d and coworkers (12-14). In the production of most s y n t h e t i c f i b r e s , i t i s also essential to draw (stretch) the f i b r e s after e x t r u s i o n , i n order to increase polymer chain o r i e n t a t i o n and thus enhance f i b r e mechanical p r o p e r t i e s . T h i s paper h i g h l i g h t s our research (15-19) on the hot-drawing of 1

In Liquid-Crystalline Polymer Systems; Isayev, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1996.

100

LIQUID-CRYSTALLINE POLYMER SYSTEMS

melt-extruded f i b r e s c o n s i s t i n g of a PP matrix and LCP as a minor component (PP/LCP W/W r a t i o 100/10).


Experimental M a t e r i a l s . Three thermotropic LCPs have been used i n our studies. Vectra A900, an aromatic c o p o l y e s t e r o f 1,4hydroxybenzoic a c i d and 2,6-hydroxynaphthoic a c i d , and V e c t r a B950, a copolymer of 2,6-hydroxynaphthoic a c i d , 4aminophenol and t e r e p h t h a l i c a c i d , were s u p p l i e d from the Hoechst Celanese Corporation. Both LCPs possess a melt temperature of 280°C. Rodrun LC3000, s u p p l i e d by U n i t i k a , i s a copolymer o f polyethylene t e r e p h t h a l a t e (PET) and 1,4-hydroxybenzoic a c i d , and possesses a melt temperature of 220°C. Two grades of PP were used: i n i t i a l l y , Appryl, s u p p l i e d from ICI, with a melt flow index (MFI) o f 3, and i n l a t e r work, S t a t o i l 151, from S t a t o i l L i m i t e d , with a MFI o f 14. Polybond 1001 (PP-AA), a polypropylene f u n c t i o n a l i s e d with 6% w/w a c r y l i c a c i d , was s u p p l i e d by BP Chemicals Limited. The f u n c t i o n a l i s e d c o m p a t i b i l i s i n g agents, FC1 , FC2 and FC3, were synthesised from PP-AA. An example i s given i n Figure 1 . F u r t h e r d e t a i l s are p u b l i s h e d elsewhere (20). Melt E x t r u s i o n and Hot Drawing. Melt e x t r u s i o n was carried out using a 25 mm single screw extruder ( E x t r u s i o n Systems Limited, Bradford, UK) with a 2.5 cm^ metering pump. For much o f the work, a s p i n n e r e t p l a t e with a s i n g l e hole of diameter 0.5 mm was used. However, for the i n i t i a l s t u d i e s o f the e x t r u s i o n o f f i b r e s c o n t a i n i n g c o m p a t i b i l i s i n g agents, a s p i n n e r e t was used with three holes, each of diameter 0.5 mm. The temperature p r o f i l e s adopted f o r extruding the PP/LCP blends were i n f l u e n c e d by the MFI o f the PP and the type of LCP. In the e a r l i e r work, where PP o f MFI=3 was used, the temperature p r o f i l e s were: PP/A900 PP/B950 PP/LC3000

230/285/285/285/280/280°C 230/300/300/300/290/290°C 200/270/270/270/270/260°C

Each p r o f i l e represents the temperatures o f the three b a r r e l zones, the metering pump and two h e a t i n g zones i n the d i e head. Later, when PP of MFI=14 was used, the temperature p r o f i l e was 200/240/240/240/240/240°C. Hot drawing of the extruded ('as-spun') f i b r e s was c a r r i e d out on a s m a l l - s c a l e drawing u n i t c o n s i s t i n g of two p a i r s o f advancing r o l l e r s and a hot p l a t e . One- o r two-stage drawing procedures were used. More d e t a i l e d accounts o f the e x t r u s i o n and drawing c o n d i t i o n s are p u b l i s h e d elsewhere (17,18).


7. QINETAL.


101

Tensile Testing. T e n s i l e p r o p e r t i e s were measured on a Nene t e n s i l e t e s t e r at 20°C and 65% r e l a t i v e humidity. The as-spun f i b r e s were tested with a gauge length of 20 mm and an extension r a t e of 2 mm min~ . The drawn f i b r e s were t e s t e d with a gauge length of 20 mm and an extension r a t e of 20 mm min~^ . Tests were c a r r i e d out f i v e to ten times f o r each sample, with a standard deviation g e n e r a l l y l e s s than 5%.


1

Hot—stage MicroscopyMicroscopy of samples was c a r r i e d out using e i t h e r a L e i t z or Olympus BH2 polarising microscope. Samples were prepared by p l a c i n g a s m a l l length of f i b r e between two g l a s s s l i d e s and h e a t i n g to 180-185°C, whereupon the PP melted and the LCP morphology could be observed. Fibre Crystallinity. F i b r e c r y s t a l l i n i t y was estimated by d i f f e r e n t i a l thermal a n a l y s i s , using a M e t t l e r FP90 instrument. Samples were heated over the temperature range 40-200°C, at a heating r a t e of 20°C min~ . Details of the procedure have been described elsewhere (18). 1

F i b r e E x t r u s i o n and Drawing As-spun F i b r e s . The as-spun PP/LCP blended f i b r e s a l l c o n s i s t e d of two separate phases. V e c t r a A900 and B950 showed w e l l developed f i b r i l s of 2-5 urn diameter with apparently smooth surfaces. Rodrun LC3000 c o n s i s t e d of f i b r i l s of s i m i l a r c r o s s - s e c t i o n , but of a r i b b o n - l i k e appearance with f a r l e s s c l e a r l y defined s u r f a c e s (17). As the PET component of Rodrun LC3000 c o n t a i n s - C H 2 - C H 2 u n i t s , Rodrun LC3000 w i l l e x h i b i t some c o m p a t i b i l i s i n g a c t i o n i n the polyblend. The PP matrix possesses a s t r u c t u r e of high e x t e n s i b i l i t y , i n which the polymer chains have l i t t l e o r i e n t a t i o n . The improvement i n the i n i t i a l modulus of as-spun PP f i b r e s which i s provided by the LCPs i s i l l u s t r a t e d i n Table I. T h i s observation accords with those of B a i r d and coworkers (12,13), who noted improvements i n the moduli of injection-moulded samples of PP where LCP was incorporated. The t e n s i l e strengths are, however, s t i l l low, so that f i b r e drawing remains e s s e n t i a l , to develop an o r i e n t e d molecular s t r u c t u r e f o r the PP matrix. One-stage Drawing. Table I a l s o shows the e f f e c t of conventional one-stage drawing at 150°C to maximum draw ratio. I t i s c l e a r that the pure PP f i b r e s possess the highest draw r a t i o and the best t e n s i l e p r o p e r t i e s . The r e s u l t s suggest that the lower draw r a t i o s obtained with the polyblend f i b r e s are the r e s u l t of r e s i s t a n c e to f i b r e drawing by the LCP f i b r i l s . I t i s noteworthy that the draw r a t i o f o r blended f i b r e s c o n t a i n i n g Rodrun LC3000, possessing short a l i p h a t i c hydrocarbon segments, i s c l o s e s t to that of the pure PP fibres, and also


102


appreciably greater two blended f i b r e s .

than

the draw r a t i o s

f o r the o t h e r

T a b l e I . Drawing Conditions and F i b r e P r o p e r t i e s o f PP and PP/LCP Blended F i b r e s (PP/LCP w/w r a t i o 100/10) PP As-spun f i b r e s I n i t i a l modulus, Ν tex" Increase over PP, %


1

PP/A900

1.08

One-staoe drawn f i b r e s (drawn a t 150°C) Maximum draw r a t i o 12.3 Tenacity, Ν tex0.931 I n i t i a l modulus, Ν tex8.74 1

1

Two-stage drawn f i b r e s Draw r a t i o a t 120°C 6.0 Draw r a t i o at 165°C 2.5 O v e r a l l draw r a t i o 15.1 Tenacity, Ν t e x 0.986 I n i t i a l modulus, Ν tex" 13.5 - 1

1

1.18 9.2

PP/B950

PP/LC3000

1.80 66.6

1.21 12.0

10.5 0.812

9.7 0.610

11.9 0.866

7.84

6.53

7.41

5.7 2.6 14.7 0.974

5.9 2.5 14.6 0.808

6.2 2.4 15.0 1.04

14.0

12.8

10.5

SOURCE: Adapted from r e f . 17.

Hot-stage photomicrographs have r e v e a l e d t h a t on one-stage drawing the Vectra A900 and B950 f i b r i l s were split i n t o small fragments, but the fragments still appeared to maintain a smooth surface structure, i n d i c a t i n g low i n t e r f a c i a l adhesion with the PP matrix (17). In the PP/LC3000 blend, the LCP phase changed from a r i b b o n - l i k e s t r u c t u r e to a rough-surfaced s h e e t - l i k e s t r u c t u r e (17), suggesting greater i n t e r f a c i a l adhesion. Two-stage Drawing. In view of the reduced mechanical performance of the one-stage drawn polyblend f i b r e s , a two-stage drawing process was devised. Optimum drawing c o n d i t i o n s were c a r e f u l l y e s t a b l i s h e d f o r the PP/A900 blend. The maximum draw r a t i o and temperature f o r the first stage were established as 6 and 120°C, respectively. For the second stage, the optimum c o n d i t i o n s were a temperature of 165°C to maximum draw r a t i o o b t a i n a b l e (17). I t i s c l e a r from Table I that i n a l l cases the o v e r a l l draw r a t i o was considerably i n c r e a s e d by twostage drawing. For pure PP f i b r e s , there was a l a r g e i n c r e a s e i n i n i t i a l modulus and a small i n c r e a s e i n f i b r e t e n a c i t y i n comparison with one-stage drawing. For the



7.

QINETAL.

Fiber Drawing from PP-LCP Blends

polyblend fibres, however, t h e r e were significant i n c r e a s e s i n both f i b r e t e n a c i t y and i n i t i a l modulus. Indeed, the PP/A900 f i b r e blend showed a 4% i n c r e a s e i n i n i t i a l modulus and the PP/LC3000 f i b r e blend a 5.4% i n c r e a s e i n t e n a c i t y , r e s p e c t i v e l y , over pure PP f i b r e s . Using hot-stage microscopy, i t has been shown that the two-stage drawing process reduces the extent of s p l i t t i n g of the Vectra A900 and B950 f i b r i l s (15,16). In two-stage drawn PP/LC3000 f i b r e s , the LCP phase e x i s t s i n a s h e e t - l i k e s t r u c t u r e (as i n the one-stage drawn polyblend f i b r e s ) , but the sheets seem to form a network across the drawn f i b r e s (17). In F i g u r e 2, f i b r e t e n a c i t i e s and i n i t i a l moduli are p l o t t e d as a f u n c t i o n of the o v e r a l l draw r a t i o i n the one- and two-stage drawing processes. For both mechanical p r o p e r t i e s , there i s g e n e r a l l y an apparent l i n e a r dependence on draw r a t i o , although on t h i s b a s i s the t e n a c i t y values of the PP/B950 blended f i b r e s and the modulus values of the PP/LC3000 blended f i b r e s are lower than expected. The reduced t e n a c i t y i n the PP/B950 f i b r e s may r e s u l t from the presence of amide l i n k a g e s i n the LCP main chain. The reduced modulus i n the PP/LC3000 fibres may reflect the g r e a t e r f l e x i b i l i t y of the copolyester chain i n the LCP as a r e s u l t of i t s constituent -CH2-CH2- units. Use o f C o m p a t i b i l i s i n g Agents For the LCP to impart to the drawn PP f i b r e s the d e s i r e d improvement i n mechanical performance, good adhesion between the two phases i s required (21). The i n t e r f a c i a l t e n s i o n across the phase boundaries must be low. Baird and coworkers (12) have noted that poor adhesion between the PP and LCP phases i n d i c a t e s i n c o m p a t i b i l i t y between the polymers, g i v i n g r i s e to reduced t e n s i l e s t r e n g t h and only a modest increase i n i n i t i a l modulus. Indeed, the two phases have h i g h l y incompatible s t r u c t u r e s : the PP matrix possesses a flexible aliphatic hydrocarbon s t r u c t u r e , whereas the LCP f i b r i l s possess a more r i g i d , aromatic p o l a r s t r u c t u r e . As B a i r d and coworkers have done f o r injection-moulded PP/LCP polyblends (12-14), we have i n v e s t i g a t e d the use of c o m p a t i b i l i s i n g agents as adhesion promoters between the two phases, and this aspect of the work has concentrated on PP/LC3000 blended f i b r e s , using a PP/LCP/compatiblising agent weight r a t i o of 100/10/2.5. Much of our a t t e n t i o n has been c e n t r e d on a commercially available product, Polybond 1001 (Figure 1). From Polybond 1001, h e r e a f t e r r e f e r r e d to as PP-AA, a wide v a r i e t y of g r a f t copolymers has been synthesised (20), and Figure 1 provides an example, FC1. Since PP-AA i s reported to decompose at temperatures s i g n i f i c a n t l y higher than 230°C, a lower extrusion temperature, 240°C, was used than b e f o r e . Moreover, Rodrun LC3000 can be processed at 240°C owing to i t s melt temperature of 220°C. PP of MF I 14 was more


103


104

CH

a

+

Ac0

\O/

C02/x

C02

^ \O

Ac

COOH Polybond 1001

200ΐ/Ν

2

-CH3COOH


vacuum CH 3 _

cox .

>co.

0

2

^g>OAc

FC1

Figure 1. Synthesis of FC1 from PP-AA. (Adapted from reference 20.)

_j

10

1

ι

ι

ι

11

12

13

14

U

15

Draw Ratio

F i g u r e 2. V a r i a t i o n of f i b r e t e n a c i t y , o, and i n i t i a l modulus, © , with draw r a t i o . Points l a b e l l e d 1 r e f e r t o t e n a c i t y values f o r PP/B950. Points labelled 2 refer to i n i t i a l moduli f o r PP/LC3000.


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QINETAL.

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s u i t a b l e f o r spinning at 240°C than the PP of MFI 3 used p r e v i o u s l y at the higher melt e x t r u s i o n temperatures. E f f e c t of C o m p a t i b i l i s i n g Agent FC1. The e f f e c t of i n c o r p o r a t i n g the f u n c t i o n a l i s e d c o m p a t i b i l i s i n g agent, FC1 , on LCP morphology within the as-spun blended f i b r e s has been studied (18). The blended f i b r e c o n t a i n i n g FC1 possesses a more widely dispersed LCP f i b r i l s t r u c t u r e , i n d i c a t i v e of reduced i n t e r f a c i a l tension between the PP matrix and LCP phase. Polyblend f i b r e s c o m p a t i b i l i s e d with PP-AA contain a much more o r i e n t e d s t r u c t u r e , and the LCP f i b r i l s have a d i s t i n c t l y higher aspect r a t i o . Table II l i s t s some t e n s i l e data obtained f o r onestage and two-stage drawn f i b r e samples c o n t a i n i n g pure PP, PP/LC3000 and PP/LC3000/FC1, r e s p e c t i v e l y . The compatibilised fibre e x h i b i t s the highest tenacity amongst the one-stage drawn samples but the lowest t e n a c i t y amongst the two-stage drawn samples. It is noteworthy too that a f t e r the second drawing stage the t e n a c i t y of the c o m p a t i b i l i s e d f i b r e f a l l s , i n c o n t r a s t to the behaviour of a l l the other polyblend f i b r e s we have s t u d i e d . This f a l l i n t e n a c i t y i s a consequence of the increased adhesion between the LCP and PP phases promoted by the c o m p a t i b i l i s i n g agent, and increased adhesion would be expected to have a d e t r i m e n t a l e f f e c t on f i b r e s drawn by a two-stage process. Table I I . E f f e c t o f C o m p a t i b i l i s i n g Agent, FC1, on the T e n a c i t i e s of One-stage and Two—stage Drawn PP/LC3000 Blended F i b r e s (PP/LCP W / W r a t i o 100/10)

PP

PP/LC3000

PP/LC3000/FC1

One-staae drawn f i b r e s Draw r a t i o Tenacity, Ν tex-.1

11 . 6 0. 643

11 . 5 0. 584

11 . 7 0. 713

Two-staae drawn f ibes Draw r a t i o Tenacity, Ν tex"-1

18. 1 0. 776

15. 0 0. 672

14. 5 0. 662

SOURCE: Adapted from r e f . 18. Microscopic evidence supports this explanation (18). L i t t l e d i f f e r e n c e i n LCP s t r u c t u r e has been observed amongst the one-stage drawn samples, but the LCP f i b r i l s i n the two-stage drawn PP/LC3000/FC1 f i b r e s are considerably smaller than i n the corresponding PP/LC3000 fibres. The greater fragmentation of the LCP f i b r i l s i n the compatibilised f i b r e s can be seen as a d i r e c t consequence of the increased adhesion between the PP and LCP phases.



106


E f f e c t o f PP-AA as a C o m p a t i b i l i s i n g Agent. Table I I I h i g h l i g h t s the t e n s i l e p r o p e r t i e s o f two-stage drawn PP/LC3000 f i b r e s using PP-AA i t s e l f as a c o m p a t i b i l i s i n g agent. There appears t o be l i t t l e d i f f e r e n c e i n the t e n a c i t i e s o f the f i b r e samples compared. Moreover, we have found no s i g n i f i c a n t d i f f e r e n c e i n the LCP f i b r i l l a r s t r u c t u r e o f PP/LC3000/PP-AA i n comparison with the f i b r i l l a r s t r u c t u r e o f the other two samples (18). These observations suggest that the c o m p a t i b i l i s i n g a c t i o n o f PP-AA d i f f e r s markedly from that o f FC1. Work by Xanthos et a l . (22) on blends o f PP-AA with PET e s t a b l i s h e d that the presence o f the a c r y l i c a c i d groups caused a f o u r fold reduction i n interfacial tension compared with standard PP. T h i s r e d u c t i o n was a t t r i b u t e d t o enhanced specific physical i n t e r a c t i o n s between the polar components o f the blend. Porter and Wang have (23) d i s c u s s e d the e f f e c t o f t r a n s e s t e r i f i c a t i o n r e a c t i o n s and their effect on c o m p a t i b i l i t y i n polymer blends, i n c l u d i n g those c o n t a i n i n g LCPs. Such r e a c t i o n s could occur between the a c r y l i c a c i d moieties present i n PP-AA and the e s t e r linkages i n the LCP during melt p r o c e s s i n g . The c o m p a t i b i l i s a t i o n e f f e c t appears, t h e r e f o r e , t o a r i s e from a s p e c i f i c i n t e r a c t i o n between the p o l a r a c r y l i c a c i d groups and the LCP i t s e l f , which reduces the i n t e r f a c i a l tension i n the blend, as i n d i c a t e d by the pronounced d i f f e r e n c e i n LCP f i b r i l s t r u c t u r e i n the a s spun f i b r e sample. This s p e c i f i c i n t e r a c t i o n does not appear t o have such a detrimental effect on f i b r e p r o p e r t i e s during two-stage drawing: the i n c r e a s e i n i n t e r f a c i a l adhesion between the PP and LCP phases i s l e s s than the increase promoted by FC1.

Table

E f f e c t o f P P - A A on Two-stage Drawn P Blended F i b r e s ( P P / L C P w/w r a t i o 1 0 0 / 1 0 )

I I I .

Sample

PP PP/LC3000 PP/LC3000/PP-AA

P / L C 3 0 0 0

Fibre thickness (tex)

Draw ratio

Extension (%)

Tenacity (N t e x )

2.56 5.81 3.37

24.1 12.9 12.4

14.9 15.9 21 .2

0.856 0.838 0.873

- 1

SOURCE: A d a p t e d from r e f . 18. Fibre Crystallinities. I t i s evident from the data listed i n Table IV that PP-AA causes a pronounced i n c r e a s e i n the c r y s t a l l i n i t y o f the polyblend fibres. 20% and 10% increases are observed over a l l the other samples f o r the as-spun and two-stage drawn f i b r e s , r e s p e c t i v e l y (18). This r e s u l t can a l s o be explained i n terms o f blend i n t e r a c t i o n s a r i s i n g from the a c r y l i c a c i d groups present i n PP-AA. No equivalent increase i n


7. QINETAL.


107

c r y s t a l l i n i t y i s promoted by the c o m p a t i b i l i s i n g agent, FC1, an observation p r o v i d i n g f u r t h e r evidence f o r the d i f f e r e n t c o m p a t i b i l i s i n g e f f e c t s of PP-AA and FC1.

Table IV.

C r y s t a l l i n i t y Data f o r F i b r e Samples

Sample

Crystallinity, % As-spun Two-stage drawn


PP

61 .8 64.3 61 .8 70.7

40.1 42.6 43.4 61 .7

PP/LC3000 PP/LC3000/FC1 PP/LC3000/PP-AA

SOURCE: Adapted from r e f . 18.

L i q u i d C r y s t a l l i n e G r a f t C o m p a t i b i l i s i n g Agents. The above r e s u l t s demonstrate that a graft copolymer c o m p a t i b i l i s i n g agent f u n c t i o n a l i s e d on PP-AA can indeed e f f e c t a s i g n i f i c a n t increase i n adhesion between the LCP f i b r i l s and PP matrix i n polyblend f i b r e s . However, t h i s strong i n t e r f a c i a l adhesion a l s o promotes fragmentation of the f i b r i l s during the drawing process. A strategy i s , t h e r e f o r e , r e q u i r e d which would c o n s i d e r a b l y reduce adhesion during the a c t u a l drawing process but would promote good adhesion i n the f i n a l drawn f i b r e s . To t h i s end, we are incorporating compatibilising agents s y n t h e s i s e d from PP-AA, which themselves possess l i q u i d c r y s t a l l i n e p r o p e r t i e s (19). Two examples, FC2 and FC3, are shown i n Figure 3. FC2 possesses a nematic phase over a small temperature range w e l l below the temperatures used f o r the drawing process. FC3, on the other hand, e x h i b i t s nematic p r o p e r t i e s over a wide temperature range, which covers the f i b r e drawing (and e x t r u s i o n ) temperatures. Table V shows the p r o p e r t i e s of

T a b l e V. T e n s i l e P r o p e r t i e s o f Two-stage Drawn PP/LC3000 Monofilament F i b r e s (PP/LC3000 r a t i o w/w 100/10) Draw ratio PP PP/LC3000 PP/LC3000/FC2 PP/LC3000/FC3

10.4 10.5 9.8 12.1

Tenacity (N t e x " )

I n i t i a l modulus (N t e x - )

0.935 0.986 0.860 0.995

8.53 5.56 4.31 6.27

1

1

SOURCE : Adapted from r e f . 19. some f i b r e s drawn by a two-stage process a f t e r e x t r u s i o n through a monofilament spinneret. I t i s noteworthy that


108



Liquid Crystalline Transitions.

Κ 68 Ν 74 I

FC2

OMe

Κ 120 Ν 260 I

FC3 Figure 3. Liquid crystalline functionalised compatibilising agents. (Reproduced with permission from reference 19. Copyright 1996 Elsevier.)

there i s a small, but d e f i n i t e increase i n f i b r e t e n a c i t y i n the sample c o n t a i n i n g FC3 over standard PP/LC3000 f i b r e , and a s i g n i f i c a n t increase i n i n i t i a l modulus. By c o n t r a s t , the f i b r e t e n a c i t y and modulus o f the sample c o n t a i n i n g FC2 are lower than those of PP/LC3000. It i s suggested that, since FC3 i s i n a nematic s t a t e during the drawing process, i t l u b r i c a t e s the s t r e t c h i n g of the PP chains over the LCP f i b r i l s . In the drawn f i b r e , however, i t promotes adhesion between LCP and PP. FC2, however, i s not i n a nematic s t a t e during f i b r e drawing and, t h e r e f o r e , does not confer a l u b r i c a t i n g e f f e c t . There i s a consequent l o s s i n t e n a c i t y and initial modulus i n the drawn f i b r e s . Acknowledgements The authors are g r a t e f u l to the former U.K. Science and Engineering Research Council f o r f i n a n c i a l assistance (Grant Réf. Nos. GR/F58776 and GR/H28417), and to Bonar T e x t i l e s Limited for financial assistance, technical d i s c u s s i o n s and the p r o v i s i o n of polymer samples.


7. QINETAL.


109

Literature Cited 1. 2. 3.


4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.

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Fiber Drawing from Blends of Polypropylene and Liquid-Crystalline

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