Measurement of degree of crystallinity of cellulosic ...

MEASUREMENT OF DEGREE OF CRYSTALLINITY OF CELLULOSIC AND POLYAMIDE FIBRES FROM DATA FROM SORPTION EXPERIMENTS UDC 677.494.675.463: 677.017.632

S. F. Grebennikov, A. T. Kynin, L. E. Klyuev, and Z. V. Antonova

The degree of crystallinity, Xc, of man-made fibres is an important characteristic [i], which determines their strength [2], and their hygroscopicity and technological properties. At the same time, the values of x c obtained for polymers depend on the methods of measurement, which are orten laborious [3-5]. X-ray measurements are the most correct, but eren they do not always give an unambiguous result, since different levels of structural , order are characteristic of fibres [i], eren in the amorphous regions [6, 7], which brings about complexity in interpreting the results of an X-ray experiment. In this connection, it is of interest to have a rapid method of determining x c which reflects the service properties of fibres and is simple in'experimental execution. It is well known that many properties of fibres are connected with their moisture content (strength, deformation characteristics, physical state, and so on), interaction of amorphous-crystalline materials with water taking place mainly in the amorphous parts of the polymer and only slightly involving its crystalline portion [i]. Consequently, by determining the water absorption of amorphous-crystalline polymers one can determine their crystallinity, if one assumes that it does not change during the sorption process. However, the use of a single point on the isotherm (BET points [8, 9], the sorption values at a relative humidity, h, of 0.65 or 0.95 [4, I0]) to dotermine x c can lead to irregular results. A more suitable characteristic, which takes into consideration the entire isotherm and temperature dependence of sorption, is the whole integral heat of sorption. The thermal theoretical-probability model (TPM) equation of [ii] is.often used to describe sorption equi~ibrium~in polymer-vapdr'systems at various temperatures a =

a« (T) exp[

-- ( --

RT Inh/E)n],

where a0(T) is the limiting value of sorption at the temperature T; h = P/Ps; E is the characteristic energy of sorption; and n is a distribution parameter which is usually applicable for amorphous-crystalline polymers present in the glassy state; it is equal to 0.7. It is not hard to determine the constants of this equation by treatment of experimental data. From Eq. (I), the following expression follows for the total integral heat of sorption (which is equal to the heat of wetting)

where r is the ga~xaa function; a is the thermal coefficient of sorption along the isoerg RT in h = const, which takes account of the temperature dependence of~ 0 by the equation a0 (T) = a~ expl= (T--T0) ], where a~ is the limiting sorption at some standard temperature T o . From Eq. (2), it is evident that Q and a 0 are directly proportional, the proportionality constant being a complex of the constants in the TBM equation, consequently depending only on the nature of the polymer. For a wide class of natural hydrophilic polymers, this dependence is slight [12]; the ratio Q/a o is approximately 335 J/g of water (6.03 kJ/mole), where Q is expressed in J/g of dry polymer and a0 is expressed in g of water/g of dry polymer. The value is not suitable for man-made fibres, and the Q/ao ratio should be calculated for each specific polymer. Using the relationship ao=aô (l-~-xc), where a ô is the moisture capacity of the amorphous polymer, it is easy to obtain from Eq. (2) an expression which connects up Q and Xc: Translated from Khimicheskie Volokna, No. 4, pp. 37-39, July-August, article submitted August 24, 1988.

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1989.

Original

© 1990 Plenum Publishing Corporation

TABLE i. Sorption Properties and Degree of Crystallinity of Cellulosic Materials according

to [9, 10] o o ..~~

$~

I==ùi1.-=ù

Material

I" "

« 4.ùi,.-i

i"3 .~ ~

Cotton Wood cellulose Undrawn viscose fibre

O,ll5 O, 155 0,256

130 131 106

44.9 0,7 61,0 0,65 81,4 0,4

0,70 0,60 0,46

Unplasticized cellophane

O,273

116

95,0 0,4

0,38

O,270 Starch O, llO Native viscosefibre High-modulus viscose fibre O, 142

O~

~4J

0 185 150 137 45, 1 0,707 163 69,5 0,532

High~:strengthviscose fibre from Chatillon Company 0,206 141 from VNIIVproekt 0,198 146

87,3 0,429 86,8 0,424

0,01 0,70 0,54

0,43 0,43

TABLE 2. Sorption Properties and Degree of Crystallinity of Polyamide Materials (poly-ecaproamide) ao i , g of polymer

X¢

E, J/g of Q, J/g of watet

polymer

78,99

8,04 15,8 II,4 17,1 5,37 5,77 6,89 7,29 11,7 13,3 7,69 8,78 17,o~ 8,32 9,90 8,65 13,3 13,9 12,8 9,48 9,13 7,44 8,49

from litera- calcuture data lated

«

O,0772 O, 156" O, 113"

O, 169" 0,053" 0,057" 0,068" 0,072* O,112 O, 120 0,081 0,074 0,224 0,098 O, 123 O,095 O, 135 O, 138 O, 158 0,096 O,090 O,084 O, 108

76,7**

76,7** 78,3 83,3 71,7 88,9 57,2 63,9 60,6 68,3 74,4 75,6 60,6 74,4 76, I 66,7 59,4

0,61 [14] 0,40) 0,65} [17] 0,38) 0,74"{

0,70 ,51 0,68 / [l j 0,56 0,47

)

I

0,50

O, 585*** { 0,57 I

0,32 0,32 0,56

o,75

0,51 0,51 0,34

[ I I

|

0,59 o,61 0,69

0,56

I [16] [

I

I I j

0,67 0,35 0,53 0,29 0,78 0,76 0,71 0,70 0,52 0,45 0,68 0,64 0,30 0,66 0,59 0,64 0,45 0,43 0,47 0,61 0,62 0,69 0,65

*From swelling in water. **Mean for polyamides. ***Mean for given range of values.

where O =

1 - x t =óQ

(3)

ÆaaF(I/n)(I-- ctT)

(4)

Thereupon the proportionality coefficient b at the temperature T depends only on the type of polymer. Most of the quantities which appear in Eq. (4) are known for the most widespread man-made fibres. Thus, the temperature coefficient of sorption, a, is -4.6 × 10 -3 and -3.5 × 10 -3 per deg K for cellulosic and polyamide fibres, respectively. The parameter n for these is close to 0.7; and F(i/n) equals approximately 0.89. For all polyamides, the value

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of E is practically identical, its mean value being 76.7 J/g of water (1.38 kJ/mole of water). However, the lack of reliable determinations of a ~ does not permit one to calculate the coefficient b a priori. Nevertheless, the coefficient b may be estimated by use of regression analysis of the experimental data available in the literature. Experimental water sorption isotherms which are given in a number of works for polyamide [8, 14-17] and cellulosic [9, i0] materials were treated with the objective of determining the constants E and a0, which are neceßsary to calculate Q from Eq. (2). Then, using the so-calculated values of Q and the corresponding experimental values of x c which are given in the same sources, by the least squares method we determined values of the proportionality coefficient b, which were 4.13 × 10 -2 and 6.58 x 10 -3 g/J for polyamide and cellulosic fibres, respectively. Results of this treatment and a comparison of the x c values available in the literature and those calculated from Eq. (3) are given in Tables 1 and 2. The mean-squared deviations between the calculated and experimental values of x c were 14.6 and 6.7%, respectively for polyamide and cellulosic materials. The higher value in the first case is apparently to be explained by errors in the original data (the data in [8] and [17] deviate systematically from the calculated dependence, apparently because of the use of mean values to calculate Q). Nevertheless, the mean-squared deviations given above " indicate the suitability of this proposed method for calculating the degree of crystallinity of cellulosic and polyamide materials. Thus, for rapid determination of the degree of crystallinity one should representthe experimental points of the isotherm in the coordinates In a vs (-in h) °.? In these coordinates, the graph of Eq. (i) at n = 0.7 is a straight line of the form in a = ina0-[(RT/E) x (-in h] °'7, which permits one readily to determine a 0 and E grapho-analytically or by the least-squares method, using a computer. The calculation of x c is carried out from Eq. (3), for which Q is preliminarily calculated from Eq. (2). The reliability of the value of x c is higher, the more experimental points of the sorption isotherm there are available. Practice shows that four to five points are sufficient for engineering calculations. In this case, calculation of a 0 and E by the least squares method presents no complications, even without use of a computer. For polyamides, the calculation can be somewhat simplified, since in t h e m a 0 practically coincides with the moisture capacity values obtained from swelling in watet. Thereupon, one may take the value 76.7 J/g of water as the mean value for the energy of sorption, E, as has been noted already. CONCLUSIONS A rapid method has been worked out for measuring the degree of crystallinity of fibrous materials, which is based on a linear dependence of this quantity on the integral heat of sorption. It has been suggested to carry out practical calculations within the framework of the theoretical probability model of sorption, which permits one to calculate the integral heat of sorption from a minimum amount of experimental material, or attended with calorimetric measurements. Sorption constants and integral heats of water sorption have been given for a large set of hydrocellulose and polyamide fibres. LITERATURE CITED i. 2. 3. 4. 5. 6. 7.

326

K . E . Perepelkin, Fibre Structure and Properties [in Russian], Khimiya, Moscow (1985). L . S . Gerasimova, L. A. Gordeeva, et al., Effect of Low-molecular Compounds on the Properties PCA Yarns [in Russian], NIITÉKhIM, Moscow (1982). M. Ya. Ioelovich, X-Ray Structural Analysis of Cellulose, Abstracts of Reports at the Conference "Methods of Cellulose Investigation," Riga (1988), pp. 12-16. L. V. Van Krevelen, Properties and Chemical Structure of Polymers [in Russian], Khimiya, Moscow (1976), p. 416 A . A . Askadskii and Yu. M. Matveev, Chemical Structure and Physical Properties of Polymers [in Russian], Khimiya, Moscow (1983), p. 248 M. Ya. Ioelovich, A. E. Kraitus, et al., Khim. Drev., No. i, 31-37 (1982). I . F . Kaimin', V. P. Karlivan, and M. Ya. Ioelovich, Izv. Akad. Nauk Latv. SSR, No. 8, 112-113 (1979).

8.

9. 10. 11. 12. 13. 14. 15. 16. 17.

N. P. Lits, L. N. Mizerovskii, et al., Vysokomol. Soed., Ser. B, 24, No. 9, 645-647

(1982). V. M. I r k l e i , T. P. S t a r u n s k a y a , e t a l . , Khim. Volokna, No. 4, 28-29 ( 1 9 8 3 ) . E. Z. F a i n b e r g and N. V. M i k h a i l o v , Khim. Volokna, No. 3, 40-47 ( 1 9 6 7 ) . S. Grebennikov, V. S e r p i n s k i i , e t a l . , Khim. Ind. ( B u l g a r i a ) , 5__5, No. 7, 305-308 ( 1 9 8 3 ) . A.V. Dumanskii and A. F. Nekryach, K o l l o i d n . Zh., 1__7, No. 3, 168-170 ( 1 9 5 5 ) . S. F. Grebennikov and A. T. Kynin, Zh. P r i k l . Khim. 5_55, No. 10, 2299-2303 ( 1 9 8 2 ) . V. N. Lebedeva and A. E. Chalykh, I z v . Vuzov, S e r . Khim. Khfm. T e k h n o l . , 23, No. 10, 1268-1269 ( 1 9 8 0 ) . R. P u f f t and J . ~ebenda, J. Polymer S c i . , C, No. 16, 79-93 ( 1 9 6 7 ) . J . Sebenda and R. P u f f r . C o l l . Czech. Chem. Commun., 2__9, 60-74 ( 1 9 6 4 ) . L. P. Razumovskii, V. S. Markin, and G. E. Zaikov, Vysokomol. S o e d . , S e r . A, 3__7, No. 4, 675-688 ( 1 9 8 5 ) .

EFFECT OF ELECTROMAGNETIC TREATMENT OF VISCOSE ON STABILITY OF THE SPINNING PROCESS AND QUALITY OF TECHNICAL YARN UDC 677.463:021.23: 621.013

K. A. Malyshevskaya, O. P. Laletina, N. A. Mazur, and I. V. Afanas'ev

The stability of the spinning process and the quality of the final fibres and yarns are determined to a considerable degree by the gel-particle content of the viscose. By studies carried out in the Department of Man-made Fibres, Siberian Technological Institute, it has been shown that a reduction in gel-particle content of viscose and an improvement in itsfilterability can be achieved by the action of an electromagnetic field on the viscose. In the present article we examine the effect of electromagnetic treatment of viscose on spinning stability and on the quality of viscose technical yarns. An electromagnetic coil which created an alternating electromagnetic field was installed in the worm of the spinning section of a PN-300-13 machine (Fig. i). An electromagnetic field of 30 kA/m was created at a voltage of 32 V and a current of 4.3 A. The viscose was in the zone of electromagnetic field action for 3.6 sec. Our studies were carried out in the spinning and finishing works of the Krasnoyarsk "Khimvolokno" PO technical yarn manufacturing plant, at four spinning positions: on two of these experimenteal worms with coils were installed; the other.two positions were controls. The problem consisted in determining the stability of the spinning process from the duration of operation of the experimental spinning positions as compared with the controls, without replacement of spinnerets. The mean operation time of the experimental operating positions

8 ~~2V

/

9

I0 /

Fig. i. Scheme of assembly for electromagnetic treatment of viscose.on a PN-300-13 machine: i) filter cartridge; 2) precipitation bath; 3) electromagnetic coil; 4) worm; 5) spinneret; 6) tube; 7) iower spinning r011; 8) upper spinning roll; 9) plasticizing bath; i0) funnel. Translated from Khimicheskie Volokna, No. 4, pp. 39-40, July-August, 1989. ticle submitted July 26, 1988.

0015-0541/89/2104-0327512.50

© 1990 Plenum Publishing Corporation

Original ar-

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