Study of the structural and thermal properties of plasma ... - Springer Link

Appl. Phys. A 92, 283–290 (2008)

Applied Physics A

DOI: 10.1007/s00339-008-4541-z

Materials Science & Processing

Study of the structural and thermal properties of plasma treated jute fibre

e. sinha1,u s.k. rout2 p.k. barhai2

1 2

Department of Physics, National Institute of Technology, Rourkela 769008, Orissa, India Department of Applied Physics, Birla Institute of Technology, Mesra, Ranchi, Jharkhand 835215, India

Received: 20 December 2007/Accepted: 14 April 2008 Published online: 27 May 2008 • © Springer-Verlag 2008 ABSTRACT Jute

fibres (Corchorus olitorius), were treated with argon cold plasma for 5, 10 and 15 min. Structural macromolecular parameters of untreated and plasma treated fibres were investigated using small angle X-ray scattering (SAXS), and the crystallinity parameters of the same fibres were determined by using X-ray diffraction (XRD). Differential scanning calorimetry (DSC) was used to study the thermal behavior of the untreated and treated fibres. Comparison and analysis of the results confirmed the changes in the macromolecular structure after plasma treatment. This is due to the swelling of cellulosic particles constituting the fibres, caused by the bombardment of high energetic ions onto the fibre surface. Differential scanning calorimetry data demonstrated the thermal instability of the fibre after cold plasma treatment, as the thermal degradation temperature of hemicelluloses and cellulose was found lowered than that of raw fibre after plasma treatment.

PACS 61.82.Pv;

1

61.82.Rx ; 52.77.-j; 61.10.Eq; 68.60.Dv

Introduction

In recent years, environmental concerns such as global warming, energy consumption and the desire to obtain products from renewable sources has skyrocketed the consumption of natural fibres for total or partial substitution of petroleum-based synthetic fibres which are neither biodegradable nor renewable [1]. Plant fibres such as jute, hemp, flax, coconut fibre etc. have some interesting characteristics. For example, cost effectiveness, renewable, available in huge quantities, and the low fossil-fuel energy requirements can offer good mechanical properties and low cost compared to synthetic fibres such as glass, carbon etc. [2]. These properties of natural fibres have attracted attention for their applications in engineering, building materials and structural parts for the automotive application where light weight is required. But all plant fibres are hydrophilic and their moisture contents can reach up to 3% – 13% [3], which limits their life span. The applications of natural fibres as reinforcements in composite materials require a strong adhesion between fibre and the synthetic matrix. But the hydrophilic nature of natural fibre causes weakening in the adhesion. Physical and chemu Fax: +91-0661-2462999, E-mail: [email protected]

ical treatments can be used to optimize this interface [4].The literature abounds with references to the surface modification of synthetic fibres by chemical, physical and physiochemical means [5–7]. In the past few years interest has increased in the use of cold-plasmas technique which is a very promising approach for surface modifications of human made as well as natural fibres [8, 9]. As a type of environmentally friendly physical surface modification technology, plasma treatment is a simple process with out any pollution. As is well known, plasma treatments has two sorts of effect on fibre surfaces; one is physically etching, using an inert gas such as argon etc. to modify the surface, the other is chemical graft, inducing some polar radicals, such as oxygen and nitrogen etc., to functionalize the surface of the fibres. A lot of literature has been published on the plasma treatment for improving surface properties [10, 11]. In this work jute fibres were treated with cold argon plasma for different periods of time. The macromolecular structure of the untreated and treated fibres were analyzed by small-angle X-ray scattering (SAXS) at room temperature whereas XRD were used to analyses changes in the degree of the crystallinity before and after plasma treatment. The influence of cold-plasma on the thermal behaviour of untreated and treated fibre was analyzed by DSC. 2

Experimental details and core mathematics

2.1

Materials

Jute fibres (Corchorus olitorius) were collected from the Central Research Institute of Jute and Allied fibre (CRIJAF), Kolkata. 2.2

Methods

2.2.1 Dewaxing. Collected fibres were dewaxed in the mixture of alcohol and benzene (1 : 2) as done by Roy [12]. As a result of this treatment, the specimen attains a “hohlraum” character (according to Porod [13] and Ratho et al. [14]), i.e., the substance occurs in layers like the pages of a book with free space in between. This is treated as a raw sample in this study. 2.2.2 Cold plasma treatment. The plasma chamber in which the jute fibers were treated is a small volume stainless steel chamber with length 30 cm and inner diameter 15 cm. The

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Applied Physics A – Materials Science & Processing

camera (Anton Park, Austria). The Cu K α lines were used as incident radiation from a PANalitica X-ray source (PW3830) at 40 kV (40 mA) operating voltage. The sample to detector distance “a” was 26.45 cm. The scattering intensities were collected in a two-dimensional, position sensitive image plate (Packard Bioscience). To have digitized data, the image plate was scanned in a cyclone storage phosphor scanner (Perkin Elmer) with the help of the supplied computer program “Optiquant”. The observed two-dimensional intensities were integrated over a line profile to convert into one-dimensional scattering data with the help of the supplied computer program “SAXS quant”. All the computational works were performed using a self-developed program written in MATLAB 6.5. The program comprises the computation of the relevant parameters by SAXS including one-and three-dimensional correlation functions. Theory. It has been shown by Vonk [15] that, for a general two-phase system having isotropic structure, the relation ∞ 16π

∞ s Ia (s) ds =

3

|gradη|2 dVr

4

0

(1)

0

holds good, where Ia (s) is the desmeared intensity in absolute units, η is the deviation of the electron density of the sample at any point from the mean value and s is the co-ordinate in the reciprocal or Fourier space given by the relation s = 2θ/λ, where 2θ , the scattering angle, is equal to x/a. Here x is the position coordinates of the scattered intensity from the centre of the primary beam. The above equation can be regarded as parallel to the well-known relation FIGURE 1 Experimental plasma chamber. In the figure, 1 – water-cooled tube (cathode); 2 – jute fibers; 3 – stainless steel chamber (anode); 4 – electrical leadthrough; 5 – view-port; 6 – gas inlet needle valve; 7 – isolation gate valve; 8 – vacuum pumping system

chamber wall serves as the anode and a centrally placed watercooled tube of length 25 cm and diameter 3 mm was used as the cathode. The advantage of using a cylindrical symmetry instead of a parallel plate configuration is that the jute fibers have been exposed to uniform plasma conditions all through. 20 W of quiescent dc power was applied to the assembly in an argon ambience at 10−1 mbar. The duration of exposure has been varied from 5 to 15 min for three different cases. The fibers were placed coaxially in the chamber between the anode and cathode and their location has been shown by a double dashed circle in Fig. 1. This particular configuration is scalable to suit industrial requirements. The jute fibre treated for 5 min plasma is treated as plasma 1, 10 min plasma treated fibre is treated as plasma 2 and 15 min plasma treated fibre is treated as plasma 3 hereafter. A side-view of the experimental plasma chamber is shown in Fig. 1 and its projection (top-view) has also been incorporated for the sake of clarity. 2.2.3 Small angle X-ray scattering (SAXS). X-ray measurement and computational analysis. Roomtemperature, smeared-out, small-angle X-ray scattering data for jute fibres were collected form a line collimated SAXSess

∞

∞ s Ia (s) ds =

η2 dVr ,

2

4π 0

∞

(2)

0

where 0 s Ia (s) ds is generally known as the invariant. If absolute intensities are not available, a very useful parameter R, given by the ratio of (1) and (2) can be obtained as ∞ ∞ ˜ ds 4π 2 0 s4 Ia (s) ds 6π 2 0 s3 I(s) |gradη|2 R= = = . ∞ ∞ 2 ˜ η2 0 s Ia (s) ds 0 s I (s) ds (3) 2

Here Ia (s) and I(s) are the desmeared and smeared-out intensities, respectively, in arbitrary units. The ratio R is a useful parameter for the characterization of the structure. In any ideal two-phase structure, the gradient at the phase boundary is infinite and consequently R also goes to infinity. However, if R is finite, the electron density changes from one phase to the other continuously over a region known as the transition layer of width or thickness E . The above equation has been transformed to variable x by Misra et al. [16] as 3 ˜ 2 x I(x) dx R = (3/2)(2π/λa) = (3/2)K 2 A3 /A1 . (4) ˜ x I(x) dx The value of R obtained from (4) determines the nature of the sample, as to whether it belongs to an ideal or non-ideal twophase system.

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In the case of a non-ideal two-phase system, the important parameter is the width of the transition layer E . The value of E can be obtained from C(r), the three-dimensional correlation function of a sample, normalized to unity at the origin, in real space. The equation connecting E and C(r) has been given by Vonk [15] as −4 dC(r) EV = . (5) R1 dr r=E V In order to obtain E , it is required to evaluate the value of C(r) at various values of r in real space. It has been shown by Mering and Tchoubar [17] that C(r) can be calculated from the expression ∞ s I˜(s)J0 (2πrs) ds C(r) = 0 ∞ , (6) s I˜(s) ds 0

where J0 is the Bessel function of the zero order and first kind. In the above expression, the three-dimensional correlation function C(r) is determined from the smeared-out intensity I(s), where the slit correction for infinite height given √ ∞ by the relation, I˜ = −∞ I( s2 + t 2 ) dt is incorporated and contained in the Bessel function J0 . Here ‘t ’ is the arbitrary variable representing the slit height and C(r) has been written in terms of x by Misra et al. [16] as ∞ 2πrx ˜ x I(x)J dx 0 λa C(r) = 0 ∞ . (7) ˜ dx x I(x) 0

For a layer structure, Kortleve and Vonk [18] have used the one-dimensional correlation function C1 (y). Mering and Tchoubar [17] have shown that ∞ sI(s)[J0 (Z) − Z J1(Z)] ds ∞ C1 (y) = 0 (8) 0 sI(s) ds Here Z = 2πsy and J1 is the Bessel function of the first order, first kind. When changed to the x variable, the above equation (Misra et al. [16]) reduces to ∞ ˜ x I(x)[J 0 (Z) − Z J1 (Z)] dx ∞ C1 (y) = 0 , (9) ˜ dx x I(x) 0

where Z = 2πsy/λa. It was shown by Vonk [15] that the position of the very first maximum in the one-dimensional correlation function gives the values of average periodicity transverse to the layers D. The value of D can be obtained by picking up the position of the first subsidiary maximum in C1 (y) vs. y curve. The equation: dC1 (y) −1(∆η)2 = (10) dy Dη2 y>E V derived by Vonk [15] can be used to calculate the value 2 of (∆η) , where (∆η) is the electron density difference beη2 tween the two phases. Here, the slope is taken at a point where y is greater than E V . It has been also proved by

285

Vonk [15] that the second differentials of C(r) and C1 (y) at the origin are given by the relation 2 2 d C1 (y) d C(r) =3 . (11) d y2 dr 2 y=0 r=0 For a layer structure, as shown by Vonk [11], the specific inner surface, S/V , defined as the phase boundary per unit volume of the dispersed phase, can be written as S/V = 2/D .

(12)

For a non- ideal, two-phase structure, the following relation holds good [15]: η2 ES = ϕ1 ϕ2 − , 2 (∆η) 6V

(13)

where ϕ1 and ϕ2 are the volume fractions of the matter and void region, respectively. For this, the phase boundary is shown at the middle of the transition layer. Assuming the sum of the volume fraction of both phases to be unity the values of ϕ1 and ϕ2 can be determined from the above relation. For the two-phase structure, an idea of the statistical distribution of crystalline (matter) and void regions can be formed by shooting arrows in all the possible directions. The average length of the arrow in the two phases are called the transversal lengths l¯1 and l¯2 . They are given by Mittelbach and Porod [19] as l¯1 = 4ϕ1 V/S

and l¯2 = 4ϕ2 V/S ,

(14)

with the range of inhomogeneity l¯r as 1 1 1 = + . l¯r l¯1 l¯2

(15)

The length of the coherence for a specimen, as given by Mittelbach and Porod is ∞ lc = 2 C(r) dr . (16) 0

The value of E can also be calculated by the Ruland method [20], from the plot of I(x)X vs. X −2 , known as a Ruland plot. The functional relationship of I(s) with s at the tail end of the SAXS pattern, for non-ideal, two-phase system, is given by πc 1 2 2 ˜ → ∞) = I(s − 2π E /3s . (17) 2 s3 Here c is the proportionality constant. For an ideal two-phase structure, E = 0 and hence the above equation reduces to Porod’s law. The above equation, when transformed to x , takes the form ˜ → ∞)x = πc/2(x −2 − π 3 c/3(λa))E 2 . I(x

(18)

The value of E can be calculated from the graph of I˜(s → ∞)x vs. x −2 , also known as a Ruland plot. Background correction. In no experimental set-up is it possible to record the SAXS pattern of the sample alone. A con-

286


tinuous background scattering is always mixed with the SAXS pattern of the experimental sample. It is, therefore, essential to apply the background correction to estimate the effect of continuous background scattering. Therefore special care must be taken to separate the SAXS intensity I(s) from the continuous background scattering Ibg (s) (Vonk [15]). 2.2.4 X-ray diffraction (XRD). Experimental techniques. The X-ray diffraction data were collected using a Philips Analytical X-ray Instrument, X’PertMPD (PW 3020 vertical goniometer and 3710 MPD control unit) employing Bragg–Brentano parafocusing optics. The XRD patterns were recorded with a step size of 0.01◦ on a 5–50◦ range with a scanning rate of 2◦ /min. Line focus Ni-filtered Cu K α radiation from an X-ray tube (operated at 40 kV and 30 mA) was collimated through a soller slit (SS) of 0.04 rad, a fixed divergence slit of 1◦ and a mask (5 mm) before it was diffracted from the sample. Experimental control and data acquisition were full automated through computer. Principle. The strains developed in the crystallites due to cold-plasma treatment manifest as a change in the lattice planes, causing line shifting. These changes in the lattice planes are measured by X-ray diffraction. Microstress causes diffraction line broadening, while macrostress causes line shifting. The relation between the broadening produced and the nonuniformity of the strain can be given by the formula b = ∆2θ = −2∆d tan θ/d , derived by differentiating the Bragg law. Here b is the extra broadening, over and above the instrumental breadth of the line due to a fractional variation in plane spacing ∆d/d to be calculated from the observed broadening. If di indicates the non-treated (unstressed) spacing and ds the spacing in the treated (strained) fibre, the microstrain in the particles in the direction normal to the diffracting plane is ∆d ds − du ε= = . (19) d du If ds > du , then ∆d/d is positive which indicates that the residual stress is tensile and if ds < du , then ∆d/d is negative indicating generation of residual compressive stress in the surface. This value of ∆d/d , however, includes both tensile and compressive strains. Assuming both are equal for microcrystallites, the value of ∆d/d must be divided by two to obtain the maximum tensile strain alone, or maximum compressive strain alone [21]. Again, the maximum microstress present in the sample can be defined as σstress =

ε E. 2

dex (CrI) of the fibres was calculated according to the Segal empirical method [22]. 2.2.5 Thermal analysis. DSC measurements were performed using a (TA Instrument, USA, Model No. Q 10) thermal analyzer. A heating rate of 10 K/min and a sample weight of 3 – 4 mg in an aluminum crucible with a pin hole were used in a nitrogen atmosphere (50 ml/min). 3

Result and discussion

3.1

Macromolecular structure of fibres

The experimental SAXS patterns for raw and plasma treated jute fibre at room temperature attain a minimum and stable value at x ≥ 0.4 cm. Hence the intensity at x = 0.4 cm is treated as background scattering intensity, subtracted from the observed intensity and plotted in the Fig. 2. The background-corrected SAXS intensities were used for subsequent calculation and plots. At the outset, five background corrected intensity values near the origin were fitted to ˜ → 0) = p exp(−qx 2 ) by least squares. a Gauss curve [23] I(s The values of the constants p and q were obtained as 191.4 and 419.9 for raw jute, whereas 68.57 and 549.92 for plasma 1, 26.47 and 866.97 for plasma 2 and 42.66 and 576.67 for plasma 3, respectively. Taking the values of p and q , the scattering curves for all the cases were extrapolated to x = 0. Each extrapolated point is indicated by the symbol “∆”, as shown in the Fig. 2. The method of the extrapolation has little effect on the relevant part of the correlation function; neither the position nor the height of the first maximum of the onedimensional correlation function is affected. The two integrals in (4) were calculated by the numerical integration using the Trapezoidal rule and the value of R was found to be positive for all the samples, as tabulated in Table 1. The small but positive value of R indicates that the electron density gradient at the phase boundary is finite, suggesting that the sample is a non-ideal, two-phase system [23]. After proper background correction, to have a clear idea on the samples, a double logarithmic plot was employed, and is shown in the Fig. 3. The slope of the each plot is given in the bracket of the legend for each sample suggesting the samples of non-ideal, two-phase system [24]. For the various values of r and y, the three- and onedimensional correlation function for the samples were computed, respectively and are shown in Figs. 4 and 6. We assume that the cellulose fibrils in jute fibre are arranged in

(20)

Putting in the value of the ε, we obtain σstress =

1 ∆d E, 2 d

(21)

where E is the elastic constant or generally known as the Young’s modulus of the material. The crystallite size of the samples was calculated using the well known Scherrer formula [21]. The crystallinity in-

FIGURE 2 Background-corrected, smeared-out scattering curve for different jute fibres

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Samples parameters (unit)

Raw jute

Plasma 1

Plasma 2

Plasma 3

R (10−4 Å−2 ) D (Å) S/V (×10−3 Å−1 ) E V (Å) E R (Å) ϕ1 (%) ϕ2 (%) l¯1 (Å) l¯2 (Å) σ

3.0542 850 2.3 47.5 45.5 0.806 0.194 1371.1 328 0.03

3.5667 980 2.04 46.2 44.2 0.847 0.153 1661.5 298.4 0.02

2.6660 1225 1.63 45.4 43.5 0.869 0.131 2129.0 318.5 0.01

3.9351 1025 1.95 44.9 42.3 0.845 0.155 1783.3 315.7 0.01

287

TABLE 1 The various physical parameters of the raw and plasma treated jute fibre derived from SAXS study

The curve showing the value of (−4/R) dC(r)/ dr vs. r values for different jute fibres; the values of E V for representative fibre are given in the parenthesis FIGURE 5

FIGURE 3

Double logarithmic plot for different jute samples

FIGURE 6 The curve showing the values of one-dimensional correlation function C1 (y) vs y values for raw jute, plasma 1, plasma 2 and plasma 3

FIGURE 4 The curve showing the three-dimensional correlation function C(r) vs. r values for raw jute, plasma 1, plasma 2 and plasma 3

layers, giving a lamellar structure [25]. That is why a onedimensional correlation function is applied and calculated for all the samples of the jute fibres. According to Vonk the width of the transition layer ( E V ) is obtained from the plot of −(4/R( dC(r)/ dr)) vs. r as plotted in Fig. 5. The value of the average periodicity transverse to the layer ( D) were obtained from the position of the first subsidiary maximum in one-dimensional correlation function (Fig. 6). The value of the specific inner surface ( S/V ), the volume fraction of matter and void (ϕ1 and ϕ2 ) and the transversal lengths in matter and void (l¯1 and l¯2 ) were estimated. All the main SAXS parameters are tabulated in Table 1. All the above parameters are consistent with those observed for other natural fibres like cotton [25] and sisal [26]. The width of the transition layer can also be calculated using Ruland’s method. The plot between X −2 vs. I(x)X is

popularly known as Ruland’s plot. The Ruland’s plots were plotted taking 40 background corrected intensity values as shown in Fig. 7. Straight lines were fitted taking 15 extreme points of the tail region of the corresponding scattering curve. The negative intercept of the regression line confirms the nonideal, two phase system [27]. The values of E R , the width of the transition layer, determined by the Ruland method [20], were computed for each sample on substituting the values of slope (m ) and y intercept (b) of the line in the relation, ER =

(−6b/m)1/2 2π/λa

and are tabulated √ in Table 1. The standard deviation of the intensities σ( I ) at the tail end of the SAXS pattern was calculated at the tail region of the SAXS curve of the samples and the values are well within permissible limits (0.5) (Table 1) [23]. Table 1 shows that the average periodicity transverse to the layer D was increased after the plasma treatment in comparison to the raw jute fibres. Similarly, the value of the volume fraction of the matter region ϕ1 and the value of the transversal length in matter phase l¯1 were found to increase after plasma treatment. This increase in D, ϕ1 and l¯1 suggest the swelling behavior of the cellulosic particle due to the plasma treatment. This may be due to the heat produced after the bombardment

288

Applied Physics A – Materials Science & Processing Ruland plot I(x)X vs. X −2 values for (a) raw jute, (b) plasma 1, (c) plasma 2 and (d) plasma 3 FIGURE 7

of high energetic ions on the fibre surfaces which causes an expansion of the matter region and a compression of the void region. However, it can be seen from Table 1 that the increasing trend of D, ϕ1 and l¯1 is upto that of the plasma 2 sample and then it declines for the plasma 3 sample. This suggests the rupturing of the cellulosic particle with the formation of a particle with new dimensions after plasma treatment for 15 min. The values of E , the width of the transition layer, as calculated by two different methods, i.e., the Vonk [23] method and the Ruland [20] plot method, referred to as E V and E R , respectively, are in the permissible range of deviation. 3.2

XRD analysis

Figure 8 shows the room temperature X-ray diffraction pattern of raw jute fibre samples before and after plasma treatment for 5, 10 and 15 min. The pattern shows the 002 peak is slightly shifting towards a lower angle indicating an increase in d -spacing. The microstress and percentage crystallinity are also calculated from the diffractogram and presented in Table 2. From the table, it is clear that the FWHM of the diffraction peak decreases after plasma treatment. The degree of crystallinity (CrI %), using the Segal empirical method, is found to increase after plasma treatment. The extent of crystallinity formation was also determined from the improvement in the intensity of the peaks [28]. From Table 2 we notice that the particle size increases after plasma treatment, may be due to the swelling of cellulosic particles constituents. This may be due to the bombardment of high energetic ions on the fibre surfaces. From Table 2 we can conclude that the plasma treatment causes

FIGURE 8 X-ray diffraction pattern of jute fibre samples before and after plasma treatment

tensile stress resulting in the increase of the d -spacing. It is also interesting to note from Table 2 that the FWHM of the plasma 3 samples is found to be higher, and the crystallite size lower, than that for plasma 2 samples. In X-ray crystallography it is known that peak broadening can arises in a number of ways including compositional inhomogeneity, the presence of defects in the crystal lattice, the presence of very fine particles, etc. In our case the observed higher broadening of the FWHM for plasma 3 than that of plasma 2 may be due to the presence of defects in the crystalline region of the fibre. The decreasing of the crystallite size after 15 min plasma treatment may be due to the rupture of cellulosic particle and this leads to the decrease in the degree of crystallinity as well. Increases in the crystallite size of cellulosic particles after plasma treatment

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Parameters

Study of the structural and thermal properties of plasma treated jute fibre Raw jute

Plasma 1

Plasma 2

Plasma 3

Peak position (2θ) 22.5 FWHM (2θ) 2.772 d (Å) 3.942 Crystallite size (nm) 29.25 ε 0 I002 (counts/s) 1664 Iam (counts/s) 569 CrI (%) 65.80 σstress (×10−4 N/tex) 0

22.4 2.692 3.966 30.01 0.006 1809 606 66.5 3

22.3 2.472 3.983 32.70 0.010 1960 612 68.7 6

22.1 2.493 4.020 32.34 0.020 1930 614 68.2 1.1

TABLE 2

The observed and calculated parameters from the X-ray diffrac-

tion pattern

FIGURE 9

DSC thermogram of raw and plasma treated jute fibres

for 5 and 10 min may have resulted in the improvement of the crystallinity of the fibre. 3.3

volume fraction of the matter phase ϕ1 and the value of the transverse length in matter phase l¯1 , were found to increase after plasma treatment which suggests the swelling behavior of the cellulosic particles caused by the heating effect of the plasma radicals which comes under energetic species. However, the increasing trends of these parameters tend to increase with plasma treatment times of up to 10 min and then declines for 15 min plasma treatment. This suggests rupturing of the cellulosic particles with the formation of particles with new dimensions after plasma treatment for 15 min. XRD analysis revealed that the crystallite size increases and crystallinity improves after 5 and 10 min plasma treatment due to swelling of the cellulosic particles. However, these properties of fibre were found to decline after 15 min plasma treatment due to rupture of the cellulosic particles. DSC results confirmed that the cold plasma treatment led to thermal instability, this being due either to the decrease in both phenolic and secondary alcoholic groups after plasma treatment, or to the oxidation of the lignin or hemicelluloses by the formation of new intermonomeric bond in them. ACKNOWLEDGEMENTS Author acknowledges Prof. J. Belare, IIT, Bombay, India, for providing the SAXS facility. Prof. N.V. Bhat, Emeritus professor physics, Bombay Textile Research Association, is acknowledged for useful discussion and suggestion on SAXS data analysis. Prof. T.N. Tiwari and Prof. S. Panigrahi, Department of Physics, NIT, Rourkela are acknowledged for thorough reading the manuscript and valuable suggestions. Mr. M.K. Sinha, Scientific Office and Mr. S. Mukherjee, SRF, Department of Applied Physics, BIT, Mesra are acknowledged for their help during the experimental set up design and plasma treatment on the jute fibre.

Thermal analysis

Figure 9 shows the thermal analysis of raw and plasma treated jute fibres. A broad endothermic peak observed in the temperature range of 60 – 140 ◦ C in both plasma treated, and raw jute, corresponds to the heat of vaporization of water absorbed in the fibres. It is reported [29] that in cellulose fibres, lignin degrades at a temperature of around 200 ◦ C while in other polysaccharides; such cellulose degrades at higher temperature. The plot shows that the degradation temperature of hemicelluloses lowers from 290.2 ◦ C for raw fiber to 270.5 ◦ C for plasma 3 samples. Cellulose degradation temperatures are also found to decrease from 365.3 ◦ C for raw to 351.3 ◦ C for plasma 3 fibres. The fibres degradation temperature becoming unstable may be due to the decrease in both phenolic and secondary alcoholic groups after plasma treatment [30]. These results can also be explained either by the oxidation of the lignin or hemicelluloses by the formation of new intermonomeric bonds in them. The oxidation of the lignin was already observed by Felby et al. [31]. 4

289

Conclusion

Jute fibres (C. olitorius) were treated with cold argon plasma for 5, 10 and 15 min. The theory and the technique of small-angle X-ray scattering were considered to be useful for investigating the macromolecular parameters of semi crystalline jute fibre. The results from SAXS revealed that the fibres were of non-ideal, two-phase structure. The value of periodicity transverse to the layer ( D),

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