Methods of investigation method of studying diamagnetic anisotropy of polypropylene fibres

])iamagnetic anisotropy of polypropylene fibres

1801

It was shown therefore that to increase the permeability of capillary membrane walls, the content of swelling agent has to be increased in the initial solution, the rate of solvent evaporation reduced at the pre-forming stage and the temperatttre of phase decomposition of the polymer solution, increased. Translated by E. SEVERE REFERENCES I. Res. Develop. Progr. Report No. 549. US Dept. of the Interior. Office of Saline Water p. 178, Wash., 1970 2. Ya. R. REIBA.RKH, L. P. PEREPECHKIN, G. A. BUDNITSKH a n d B. L. BIBER, Vysokomol. soyed. B19: 3, 207, 1977 (mot translated in Polymer Sei. U.S.S.R.) 3. B. KUNST and S. SOURIRAJAN, J. App1. Polymer Sci. 14: 8, 1970, 1983 4. L. P. PEREPECHKIN, Dis. n a soiskaniye ueh. st. dokt. tekhn, nauk, Mytishchi V N I I V proyekt., 1978 5. C. M. HANSEN, Industr. Engng. Chem. Product. Res. and Development 8: 1, p. 2, 1969 6. G. B. TANNY, J. Appl. Polymer Sci. 18: 7, 2149, 1974 7. D. V. VAN KREVELEN, Svoistva i khimicheskoye stroyeniye polimerov (Properties a n d Chemical Structure of Polymers). p. 416, Khimiya, Moscow, 1976 8. S. P. PAPKOV, Fiziko-khimicheskiye osnovy pererabotki polimerov (Physico-Chemieal Bases of Processing Polymer Solutions). p. 363, Khimiya, Moscow, 1971

Pol}'mer Science U.S.S.R. Vol. 25, lh-o.7, pp. 1801-1804, 1983 Prin~d in Poland

0032-3950/83 $10.00+.00 © 1984PergamonPress Ltd.

METHODS OF INVESTIGATION METHOD OF STUDYING DIAMAGNETIC ANISOTROPY OF POLYPROPYLENE FIBRES S. I. FEDOTOV, Yr. V. ZELE~EV, I. P. FEDOTOV and Yr. A. VOLKOV A. ~ . Kosygin Textile Institute, Moscow

(Received 2 February 1982) A comparison is made of results of birefringence and data of diamagnetic ~nisotropy of P P fibres and it was shown that birefringenee and refractive indices, calculated from diamagnetic anisotropy (determined by the Ya. G. Dorfman method) show a more satisfactory agreement with experimental results t h a n these characteristics calculated from polarizability values of - - C - - C - - bonds. * Vysokomol. soyed. A25: No. 7, 1555-1557, 1983.

1802

S.I.

)'EDOTOV e$ al.

IT Is known that the use of diamagnetic anisotropy enables the problem of evaluating macromolecular orientation in polymers to be solved. None of the physical properties related to crystallinity and dense packing of polymer chains changes as obviously as magnetic anisotropy [1]. 1~evertheless, X-ray and optical methods have remained up to recent times the chief methods of studying the morphology of polymer fibres. One of the causes of this is the fact t h a t methods of analysing meas'urements of magnetic anisotropy have beau insufficiently dealt with. A comparison is made in this study of birefringence (BR) and of magnetic auisotropy of crystals and P P fibres and it was shown that values of BR and refraction indices calculated from magnetic anisotropy show more satisfactory agreement with experimental results t h a n values calculated from polarizability values of - - C - - C - bonds. Diamagnetic anisotropy was measured in highly homogeneous magnetic field (magnetic field induction B ~ 5000 Hz) created b y the electromagnet of a I~MR spectrometer using the K r i s h n a n "click" method [2], according to the angle of twisting of a calibrated quartz arm N 10 #m in diameter. Samples were prepared of polymer fibres in the form of a beam 5 m m long and ~ 10 mg in weight and glued with shellac to a glass thread 10 m m long and 0.3 n u n in diameter, which was glued to a quartz support linked with the torsion head, according to methods previously described [3]. As a result of investigating the effect of polarizability of C--C and C - - H bonds on optical properties of hydrocarbon polymers of a n u m b e r of paraffiIts, the m a i n polarizability values of the :PP molecular chain were calculated. Various authors have obtained different polarizability values for a recurrent Lmit of the polymer. Thus, Denbigh [4] found t h a t the polarizability of a P P unit along a -- C ~ C-- C -chain is aj!-----186.36× 10 -"-5 em s, while in a direction perpendicular to the - - C - - C - - C - chain ~ 1 6 8 - 7 3 × 10 -25 cm3; B u n n and D a u b e n y [5] questioned polarizability values of the - - C - - C - - C - - bond derived b y Denbigh in view of the increased cross polarizability values and obtained the following results: nil ~ 163.12 × 10 -25 cm a and ~ 159.17 × 10-2~cma. Therefore, the anisotropy of polarizability of the - - C - - C - - C - - chaill according to Denbigh is A~=~ii--az~-17.62 × I0~ -~ cm3; according to B u n n a n d Daubeny Aa=~ H - a ~ = 3 . 9 5 × × 10 -~5 c m 3. I n their study Keedy, Powers and Stein [6] replaced data obtained b y Denbigh, B m m and D a u b e n y by m a i n polarizability values of the elementary cell of the P P crystal, according to its structural model given by l~atta [7] and calculated refractive indices and BR. According to results obtained by Denbigh, refractive indices n and BR ( A n ~ n l , - - n L ) are n ~ 1 " 5 7 and An~0-067 and according to results obtained b y B u n n and Daubeny ~ 1.51 and An=0.015 for P P with 100°/o crystallinity. Comparison with experimental results obtained on films [6, 8, 9] indicates that the B]~ value shows more satisfactory agreement with Denbigh's results, and the refractive index values with results obtained by B u n n and Daubeny. According to Padden and Keith the refraction index of a P P flhn with 70~o crystallinity n ~ 1.510. Wilchinsky observed for elongated P P films (40-70~o crystalliuity) BI~ within the range of 0.02-0.03 for the elementary cell. I f we adopt this value only for the chain of orientaion in the crystalline range, BI~ values for elementary cells, calculated from polarizability values of the - - C - - C - - C - - bo~d b y Denbigh and b y B u n n for P P with 50~o Crystallinity, are 0-033 and 0.007, respectively. I t is interesting to compare these results of polarizability of - - C - - C - - C - - chains with values of magnetic anisotropy. According to the Kirkwood formula [10] ~ g ~ - - 3 . 1 1 × 1 0 e x / ~ , relating polarizability a with diamagnetic susceptibility ha; we have AZ~ = -- 3.11 × 1 0 ' x / K ( x / ~ -- x / ~ ) , where K is the n u m b e r of chain electrons of the recurrent P P u n i t containit,g nine carbon atoms and eighteen hydrogen atoms.

D i a m a g n e t i c a n i s o t r o p y o f p o l y p r o p y l e n e fibres

1803

C a l c u l a t i o n w a s c a r r i e d o u t [6] u s i n g all b o n d s o f t h e r e c u r r e n t uni~. C a l c u l a t i o n o f aw~rage p o l a r i z a b i l i t y ~av u s i n g c h a i n p o l a r i z a b i l i t y d a t a o f I ) e n b i g h a n d o f B m m g i v e s a ~ v : ( 2 ~ : .4-~11)/3=174"6× l 0 -25 c m '~ a n d ~a~=160"49 × 10 -~s c m a. r e s p e c t i v e l y , O n t h e b a s i s o f t h e s e r a t i o s we o b t a i n a c c o r d i n g t o D e n b i g h Z g = - l l 0 . 3 × 10-6; z l Z a = - 5.8 × 10-6; a c c o r d i n g to B u n n , Z a = -- 105.7 × 10-6; ztZa= -- 1.2 × 10 -6. ~Vc use t h e m e t h o d of m a g a a c t o - c h e m i c a l a n a l y s i s t o d e t e r m i n e a v e r a g e d i a m a g n e t i c s u s c e p t i b i l i t y a n d t h e a n i s o t r o p y o f r e c u r r e n t u n i t i n a P P crystal. C o n s i d e r i n g t h a t final c a r b o n a t o m s c o r r e s p o n d a t t h e s a m e t i m e t o t w o a d j a c e n t e l e m e n t a r y cells, we e x c l u d e o n e CH2 g r o u p . I t is k n o ~ t t h a t a v e r a g e m o l e c u l a r s u s c e p t i b i l i t y v a l u e s p e r c a r b o n a n d h y d r o g e n a t o m i n paraffin a r e - - 8 × l 0 -6 a n d - - 2 × 10 -6, r e s p e c t i v e l y [11]. T h e n , d i a m a g n e t i c s u s c e p t i b i l i t y o f t h e c h a i n i n a n e l e m e n t a r y cell :~a------ (8.8 × 2.16} × 1 0 - 6 : - - 9 6 × 10 -6. D i a m a g n e t i c a n i s o t r o p y is d u e t o t h e p r e s e n c e of m a g n e t o - a n i s o t r o p i c m e t h y l e n e CH~- and methine CH-groups. Using the magneto-chemical analytical method developed by Dorflnan [ll] magnetic anisotropy of atoms may be calculated from the formula ,dZ= 1 "23" X/Z),d~-~- 1.Sz~,,

(1)

w h e r e AZ is m o l e c u l a r a n i s o t r o p y , z ~ - - a w ~ r a g e m o l e c u l a r v a l u e o f L a n g e v i n d i a m a g n e t i s m p e r a t o m ; Zp is t h e a v e r a g e m o l e c u l a r v a l u e of V a n - F l e k o v l ~ a r a m a g n e t i s m r e l a t e d t o o n e a.t~m. T h e CH2 m e t h y l e n e g r o u p h a s a p a r a m a g n e t i s m X~=0"6 × 10-% w h i l e t h e C t t m e t h i n e ~zroup Z r : 0 . 8 × 10. C o n s i d e r i n g t h a t Z~ is p r o p o r t i o n a l t o t h e p o l a r i z a b i l i t y o f a t o m s , we o b t a i n Z ~ c : 0 . 3 1 × 10 -6 i n m e t h y l e n e a n d Z p c : 0 . 6 × 10 -6 i n a m e t h i n e group. F r o m r a t i o (1) we find t h e a n i s o t r o p y of t h e c a r b o n a t o m A z c = - - 2 . 4 × l 0 -e i n m e t h y l e n e a n d JXc - - 3 . 5 × l 0 -6 i n m e t h i n e g r o u p . T h e r e f o r e , t h e a v e r a g e mag~xetic a n i s o t r o p y of c a r b o n a t o m s Axe---- -- 10 -6 × (2.4 × 2 + 3.5 × 3 ) / 5 : - - 3 - 1 × 10-*. ~'h~rthermore, d i a m a g n e t i c a n i s o t r o p y int r ( ~ i n c e d b y h y d r o g e n a t o m s s h o u l d b e c o n s i d e r e d . I n t h e g r o u p o f C H 2 z ~ = 0 - 1 3 × l 0 -* ~;at z~ZH=~0'8× 10-~; i n t h e C H g r o u p Z ~ = - - 0 . 2 0 × 1 0 -~ a n d AZH=:--I.O×IO -6, As a re,'ult, for t h e c h a i n of cell AZn= -- 10-~ × (0-8 × 4 + 1 . 0 × 3 ) / 7 = - - 0 . 9 × 10 -~. T h e r e f o r e , for t h e m a g n e t i c a a i s o t r o p y o f t h e c h a i n o f t h e cell we a d o p t t h e v a l u e -JX~--- - - 4 . 0 ~( 10 -6. Bas¢~t o n t h e m a g n e t i c c h a r a c t e r i s t i c s o b t a i n e d we c a l c u l a t e t h e p o l a r i z a b i l i t y v a l u e s , r e f r a c t i v e i n d i c e s a n d Bl%. T h e a v e r a g e p o l a r i z a b i l i t y o f t h e c h a i n ~ Z ~ / 9 " 2 K = 1 5 6 . 5 × :,: l 0 - ~ c m 3 ( w h e n Z ~ = - - 9 6 × 10-6). l~or a n e l e m e n t a r y cell c o n t a i n i n g four c h a i n s we h a v e ~.~=626 >~ l 0 -~5 c m a. E l e m e n t a r y cell v o l u m e V ¢ ~ 8 9 4 . 0 × 10 - ~ c m *. H e n c e t h e a v e r a g e n ~-

l ~ ) l a r i z a b i l i t y for u n i t v o l u m e asp=ac/Vc=O'070. U s i n g t h e L o r e n t z - L o r e n z f o r m u l a - 4~

-=-

3

1

nZ+2

C~sp, we c a l c u l a t e t l m r ~ f r a c t i v e i n d e x n ~ 1 . 4 9 7 .

A s a c o n s e q u e n c e o f a x i a l s y m m e t ~ T of t h e c h a i n m o d e l t h e a v e r a g e v a l u e of suscept i b i l i t y Z a = - - 9 6 × 10 -6 is l i n k e d w i t h s u s c e p t i b i l i t y a l o n g t h e -- C -- C . - C - - c h a i n ZH a n d t r a n s v e r ~ e s u s c e p t i b i l i t y Z± b y t h e r a t i o (2Z~q-Zli)/3 =Z~

ZI=X~--ztXa/3

Zh ~X±-F ~Z~ Tiierefore, Z ± = - - 9 4 . 7 × 10 -6 a n d ZII = - - 9 8 . 7 × 10 -6, ~.----152.3 × 10 -26 c m 3 a n d ~11= 165.4 × > 1 0 -26 c m ~.

F o r a n e l e m e n t a r y cell c o n t a i n i n g four c h a i n s we h a v e ~ t = 652 × 10 -25 era3; ~

609 ×

1804

S . I . FEDOTOV e~ ~,

X 10-'" e m 8. Calculation using the formula

gives the B R value for P P crystal with 100~o crystallinity zln=0.05. Refractive indices and B R values obtained show satisfactory agreement with experim e n t a l results for P P films [6]. We measured experimentally B R of P P fibres according to the degree of elongation 2. Fibres were elongated at 150 °. The following agreement was obtained between • and An:

4, % 250 An)< 10 ~ 25.1

350 28-2

400 29.7

500 30.1

These results indicate that BR is within the range of calculated v a l u e s - - 5 0 × 10 -~. Measurement of diamagnetic anisotropy of fibres with 2 = 700~o gives the value of 3 Z -- 1.53 × 10-5 which is much greater t h a n the m a x i m u m anisotropy following from resuhs of polarizability obtaiaed b y Btmn and Daubeny. On converting to 100% erystallinity mag~te~ie anisotropy is equal to A%= --2.7 × 10 -6.

Translated by E. SE)~ERE REFERENCES 1. P. SELWOOD, Magnetokhimiya, 2-yo pererab, i dop. izd., p. 457, Izd. inostr, lit., Moscow, 1958 2. K. S. KRISHNAN and S. PANERIES, P h i l . Trans. Roy. See. A234: 739, 265, 1935 3. K. S. KKISHNAN a n d A. MOOKHERJI, Phys. Rev. 50: 1, 860, 1936 4. K. G. DENBIGH, Trans. F a r a d a y Soc. 36: 233, 936, 1940 5. C. W. BUNN a n d DAUBENY, Trans. F a r a d a y See. 50: 383, 1173, 1954 6. D. A. KEEDY, J. POWERS and R. S. STEIN, J. Appl. Phys. 31: 11, 1911, 1960 7. G. NATTA, CORRADINI and M. CESARI, Rend. acad. nazl. ]ineci 8: 21, 365, 1956 8. F. J. PADDEN and H. D. KEITH, J. Appl. Phys: 30: 10, 1479, 1959 9. Z. W. WILCHINSKY, Meeting of the North Jersey section, Amer. Chem. See., New Jersey, 1959 10. J. G. KIRKWOOD, Phys. zeit. 33: 1, 57, 1932 11. Ya. G. DORFMAN, Diamagnetizm i khimieheskaya svyaz' (Diamagnetism and Chemical Bond). p. 231, Fizm~tgiz, 1961