Correlation between Macromolecular Parameters and the Average Breaking Strength of

Agave Fibers

A. PATEL,* J. R. PRASAD, afid S. K. NAYAK, Department of Physics, Berhampur University, Berhampur-760007, Orissa, India

Synopsis

The small-angle X-ray scattering method was applied to evaluate macromolecular param- eters of Agave fibers (Agave sisalana, A. cantala, A. hybrid, A. elongata, and A. ameniensis). The macromolecular parameters such as specific inner surface, percentage of void, length of coherence, range of inhomogeneity, and transversal lengths were evaluated. The correlation of macromolecular parameters with the average breaking strength of Agave fibers did not lead to a linear relation, however, the specific macromolecular organization in A. sisalana manifested higher breaking strength.

INTRODUCTION

It has been observed by several investigators that at the cradle of small- angle X-ray scattering fibers and very fine powders show a diffuse scattering phenomenon in the vicinity of the primary beam. These effects are due to inhomogeneity in the range of colloidal dimensions. Two theories on small- angle X-ray scattering have been developed, one by Guinierl and the other by Kratky? which are applicable to dilute systems and densely packed systems, respectively. In Guinier theory the interparticle interference is neglected, whereas in the theory suggested by Kratky the interparticle interference is predominant. With a special view to cellulose fibers there is the theory of small-angle scattering for blocks of parallel lamellae within each block, which are strongly interfering. Therefore the tail-end portion of the scattering curve is utilized to make a pore analysis of the scattering particles of the sample and the parameters such as the specific inner surface, the length of coherence, the ranges of inhomogeneity, the transversal lengths, and the percentage of void present in the sample are evaluated.

X-ray small-angle scattering is a process to explore the size, shape, and orientation of particles of colloidal dimensions as well as, in the two-phase systems, the volume share of the two phases and is a non-destroying test that gives an average of properties of a fiber bundle. We were tempted to apply this method of investigation on Agave fibers. Agave fibers are the world’s most important leaf fibers, comprising more than half the total commercial production of all leaf textile fibers. Most of the “soft” currency countries have a possibility of earning “hard” currency through exports of

* Present address: Department of Chemistry and Chemical Engineering, Stevens Institute of Technology, Castle Point Station, Hoboken, N.J., 07030, U S A .

Journal of Polymer Science: Polymer Chemistry Edition, Vol. 22, 34073415 (1984) @ 1984 John Wiley & Sons, Inc. CCC 0360-6376/84/113407-09$04.00

3408 PATEL, PRASAD, AND NAYAK

this material. The final goal here is to correlate between the fine structural characteristics and the textile properties. The textile property such as the average breaking strength of Agave fibers has been determined with the help of an Instron Tensil Tester and Stelometer.

EXPERIMENTAL

Sample

Agave fibers were obtained from the Sisal Research Station, Indian Coun- cil of Agriculture Research, Bamara, Orissa, India, in their purest form. The physical parameters of the samples are: color, yellowish white; length, 8.8 cm; density, 1.4 g / ~ c ; ~ a refractive index, 1.5.3b Agave fibers contain about 78% cel lulo~e.~ Components such as lignin and fat were removed by the process described by Roy.5 In many natural fibers like Agave fibers the long axis of the microcrystallite forms a constant angle with the fiber axis so that the sample can be taken as a two-phase densely packed, highly oriented system. In such a case no slit correction to the scattering curve is necessary and one can proceed with the estimation of parameters from the smeared- out scattering curves.

Small-Angle Measurements A Radon House X-ray apparatus with a Machlett A-2 X-ray diffraction

tube having a copper target was coupled with a highly sensitive stabilizer (+2% of fluctuation at unity power factor, from Adair, Dutt and Co., India). The X-ray unit was operated at 30 kV and 20 mA throughout the experi- ment. It delivered an intense X-ray beam to the crystal monochr~mator.~J The strictly monochromatized CuK, radiation of wavelength 1.54 A was allowed to pass through the rectangular slit of width 100 pm of the Kratky apparatus designed with special precautions to eliminate parasitic scatter- ing.8 The rectangular beam was intersected by the samples, which were filled in Mark capillary tubes. To avoid scattering due to air the chamber between the sample and the recording film was evacuated, the pressure difference being thus limited to the order of 1-2 torr. The total scattering curve, i.e., the smeared-out intensity, f versus X, was constructed, where X is given by

X = 2apO

and where a is the film-sample distance (23 cm), p is the transformation factor of the microphotometer (= 1001, and 8 is half of the scattering angle. Another curve between f i X ) . X 3 and X 3 was plotted to determine the run constant K, and background scattering constant K2. The value of K2 was subtracted from all the intensity data and the final scattering curve was p10tted.~

To calculate the primary beam intensity Po, the film was exposed for 15 s in the Kratky camera to the primary beam with continuous shifting of

MACROMOLECULAR PARAMETERS OF AGAVE FIBERS 3409

the film by a film shifting device.1° This was monitored microphotometri- cally, and the intensity was calculated by plotting the fversus X curve. The area was determined by planimetry. The value of Po was then calculated applying the relation

(Area under the curve of primary beam x highest time qf exposure of the sample)

(Time of exposure of the primary beam x microphotometer transformation factor)

Po =

THEORY AND DISCUSSION

Evaluation of Macromolecular Parameters of Agave elonga ta The invariant of the scattering curve introduced by Porodll is given by

Qexp = $" 7.X.dX 0

for smeared-out intensity (Fig. 3) while Q, is given by

2 Q,, = (?4rr)(e2/mc2)2 A3N2DPoa p w1w2

after Kratky" and Porod et a1;12 where w1 and w2 are the volume fraction of the void or air and matter, respectively, e is the electronic charge, m is the mass of electron, c is the velocity of light, A is the wavelength of X ray = 1.54 A, N is Avogadro's number = 6.025 x loz3, D is the effective sample thickness, Po is the intensity of the primary beam, a is the film sample distance = 23 cm, and p is the electron density of the scattering particle. The intensity, which decreases proportional to X - 3 , is based on the fact

a14t 9 Dewaxed Agave Elongata

O " * t \ 00 - E =I 0 ? ( x ) . d X

Area -60.5 cm2

0 o.mm 0 X- cm

Fig. 1. The scattering curve giving the value of E.

3410 PATEL, PRASAD, AND NAYAK

C t - 5

4 5

Agave Elongata - 7 - K 2 - 0 00151

r\ .d 0 r - n - v - v v

r\ -

6-#o-- I I I I 11 I I I

that there is homogeneous electron density distribution in each phase. The I (X) .X3 versus X 3 (Fig. 2) plot yields the background scattering constant k2 as the slope of the curve as suggested by Kratky.13

Percentage of Void The effective sample thickness D is given by

Here the compact density 6, is taken to be the density of cellulose, having a value equal to 1.60 g/cc as suggested by Ratho and Sahu,14 and the ap- parent density 6, is 1.4 ~ / c c ; ~ 9 is the inner diameter of the capillary tube = 0.1832 cm. The value of D thus calculated was 0.1603 cm.

The electron density of the substance is given by Kratky and Mih'olic15 as

where ZO/ZA is summation of atomic number/summation of atomic weights. The primary beam intensity Po was calculated as 23.5296.

I-

0.04

0 2 4

Fig. 3.

X I-

2 x (cm)

Fig. 3. The invariant curve.

6 8 x (cm)

The invariant curve.

MACROMOLECULAR PARAMETERS OF AGAVE FIBERS 3411

TABLE I

Transversal length Range of Coherence Specific inner inhomogeneity length surface (O/V) 4 1 2 1, = ll 1,

Sample (10-6 A-1) (A, ('4) (A, (A) Agave sisalana 4.06 107.31 9.85 x lo5 107.31 342.21 Agave cantala 1.81 375.07 22.05 x 105 375.07 502.72 Agave aneniensis 10.70 148.90 37.37 x 105 148.90 512.13 Agave elongata 4.29 88.33 9.31 x 105 88.33 345.23 Agave hybrid 8.50 150.00 4.70 x 105 150.00 204.00

On equating Qexp with Q,, we get

0.9875 x cm2 = (7.9 x 10-26/2~) A3NZDPoa p2 wIw2

Substitution of respective values in the above equation yielded that wlw2 = 9.48 x Since w2 N 1, the volume fraction of w 1 in the sample comes to 9.48 x i.e., 0.009%.

Specific Inner Surface

The specific inner surface, which is defined as phase boundary area per unit volume of (he dispersed phase, is given

C E L L U L O S E F I B E R S

Ameniensis

3 5.0 ;r5 log

Fig. 4. Specific inner surface ( O N ) in AO-'.

3412 PATEL, PRASAD, AND NAYAK

O/V = (87r/Aa) wlwz (Kl/Qexp)

Substitution of respective values yielded

O/V = 4.29 x A-l

Transversal Lengths

If we shoot arrows through the system in all directions and measure the average intersectional lengths of the arrows with the two phases and call them transversal lengths 1, and 1, we get

for this substance.

Range of Inhomogeneity

The range of inhomogeneity I , is given by

CELLULOSE FIBERS

1 1 0 0 K o 2 0 0 2 5 0 M o ~ ~

Fig. 5. Transversal length (iJ in A.

MACROMOLECULAR PARAMETERS OF AGAVE FIBERS 3413

I CELLULOSE F I B E R S

lM I Sisal L Elongato

Hybrid

Amoniomis 500

0 5 10 15 20 25 30 35 40

Fig. 6. Transversal length (iJ in 105 A.

since w2 N 1, 1, = I,; thus the range of inhomogeneity corresponds to the reduced mass in mechanics.

Length of Coherence

The coherence length 1, is given by

s i & X ) d X

or

where ,!? = ,,"&XI d X is the integrated scattered energy (Fig. 11, which is equal to 0.3025 x cm2.

On substituting the respective values we get

1, = 345.23 A

The macromolecular parameters of Agave sisalana, A. cantala, A. amen- iensis, and A. hybrid were also calculated using the above-mentioned pro-

3414 PATEL, PRASAD, AND NAYAK

CELLULOSE FIBERS I

1500 I Sisal b

500 I 100 150 200 250 300 350 400 450 5 9

Fig. 7. Length of coherence (1,) in A.

procedure under identical experimental conditions and are tabulated in Table I.

Average Breaking Strength

The average breaking strength of Agave fibers was evaluated using the Instron Tensile Tester and Stelometer at the Cotton Technological Research Laboratory, Matunga, Bombay, India, using the method suggested by Sun- daram et a1.16 The average breaking strengths of Agave sisalana, A. cantala, A. ameniensis, A. elongata, and A.hybrid were found to be equal to 1504.15 g/denier, 764.71 g/denier, 576.45 g/denier, 1330.79 g/denier, and 899.59 g/ denier, respectively.

To illustrate the dependence of physical properties on macromolecular parameters a number of graphs were plotted and these are shown in Figures 4 to 7.

CONCLUSION The curve between O/Vand average breaking strength (Fig. 4) indicates

that the breaking strength has a maximum value for a particular value of O/Vand it diminishes with higher or lower values of O/K O/V, jl , and 1, are interdependent. Higher values of O/V give lower values of t , and 1, and vice versa. Figures 5 and 6 are in conformity with the above conclusion. In Figure 7 the correlation of length of coherence with the average breaking strength is shown. It is found that the breaking strength has a maximum value for a particular value of length of coherence. These correlations of

MACROMOLECULAR PARAMETERS OF AGAVE FIBERS 3415

macromolecular parameters with the breaking strength of Agave fibers led to the conclusion that the macromolecular organization in Agave sisalana manifests higher breaking strength. This method may be useful to textile technicians as a statement of quality of fiber structure and their stand- ardization.

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3. J. M. Mathews, Textile Fibers, 6th ed., (a) p. 19; (b) p. 1099, John Wiley & Sons, New

4. G. W. Lock, Sisal, Longmans, London, 1969, p. 281, (1969). 5. S. C. Roy, Text. Res. J., 30, 451 (1960). 6. T. Johansson and A. Guinier, 2. Phys., 82, 587 (1933). 7. A. Guinier, C. R. Acad. Sci. (Paris), 223, 31 (1946). 8.0. Kratky, Boc. Conf: Symcuse Uniu. 1965, H. Brumberger, Ed., Gordon & Breach, New

9. T. Ratho, A. Patel, and 0. P. Singhal, J. Polym. Sci. Polym. Chem. Ed., 12, 2595-2602

(1963).

York, 1954.

York/London/Paris, p. 63, (1967).

(1974). 10. 0. Kratky, 2. Anal. Chem, 201, 161 (1964). 11. 0. Kratky, Naturwiss., 26, 94 (1938). 12. L. Kahovec, G. Porod, and H. Ruck, Kolloid Z., 133, 16 (1953). 13. 0. Kratky, Nuturforsch., 18, 180 (1963). 14. T. Ratho and N. C. Sahu, Kolloid 2. 2. Polym., 236, 43 (1970). 15. 0. Kratky and G. Miholic, J. Polym. Sci. A-2, 449 (1963). 16. V. Sundaram, Handbook of Methods of Tests, CTRL, Indian Council of Agricultural

Research, New Delhi, 2nd ed., p. 60, (1979).

Received July 7,1983 Accepted February 10,1984