Sangappa et al., J Fashion Technol Textile Eng 2015, 3:2 http://dx.doi.org/10.4172/2329-9568.1000119 Journal of Fashion Technology & Textile Engineering Research Article A SCITECHNOL JOURNAL Influence of Electron Irradiation on Tassr Non-mulberry Silk Fibers Y Sangappa1*, S Asha1, B Lakshmeesha Rao1, Mahadeva Gowda1 and R Somashekar2 1Department of Studies in Physics, Mangalore University, Mangalagangotri, Mangalore 574 199, India 2Department of Studies in Physics, University of Mysore, Manasagangotri, Mysore 570 006, India *Corresponding author: Y Sangappa , Department of Studies in Physics, Mangalore University, Mangalagangotri, Mangalore 574 199, India, Tel: +91 9845205065; E-mail: [email protected] Rec date: September 2, 2014 Acc date: February 17, 2015 Pub date: February 21, 2015 the field of characterization of silk (non-mulberry) to understand the properties in terms of its structural features and find ways of improving the quality of silk fibers by treatment. In recent days, there is a spurt of activities involving the exposure of silk fibers to high energetic beams, such a study was carried out by us on silk C108 and NB4D2, belonging to bivoltine race of the Bombyx mori family indicated significant changes in the microcrystalline parameters [9,10]. Takeshita et al have studied the physical, chemical and thermal properties electron beam irradiated Bombyx mori silk fibers [11]. Effects of gamma radiation on biodegradation of Bombyx mori silk fibers have been studied by Kojthung group [12]. All these studies were related mulberry silk. So far only few studies have reported the properties of wild silk fibers and no reports on irradiation effects on wild silk. Here we have irradiated silk fiber samples with 8 MeV electron beams of various doses and studied the structural changes, chemical and thermal properties of virgin and electron irradiated tassar nonmulberry silk fibers. Abstract In this work the effect of electron irradiation on the structural, chemical and thermal properties of tassar non-mulberry silk fibers was investigated. Tassar silk fiber (Antheraea mylitta) samples were irradiated in air at room temperature using 8 MeV electron beam in the range 0 to 100 kGy. Various properties of the irradiated fibers were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The wide angle X-ray scattering (WAXS) study shows the crystallite size (L) increases with increasing radiation dosage. It was found that the thermal stability of the fibers improved after electron irradiation. Keywords: Fiber; Electron irradiation; XRD; Chemical properties; Thermal properties Introduction Silk is semicrystalline biopolymer which is produced by Lepidoptera such as silk worm and species like spider, scorpions and mites which belong to Araneae and pseudoscorpionida respectively under class Archnida which belongs to Artropoda phylum [1,2]. Silkworm silk are classified as Mulberry (Bombyxmori) and NonMulberry (Tassar, Muga and Eri). In radiation chemistry, polymers were classified into two types: scission polymers and cross-linking polymers, and most biopolymers were placed into the scission polymers [3]. Recent developments in this field proved, that a variety of biopolymers could be cross-linked by irradiation of high energy radiation and tassar natural polymer tends to radiation cross-linking. Among the natural fibers, silk has a profound place in industrial applications. Silk has excellent intrinsic properties utilizable in biotechnological and biomedical fields as well as the importance of silkworm in the manufacture of textiles [4]. Sargunamani have studied the Ozone treatment on the properties of tassar silk fibers [5]. Yutaka Kawahara has studied micro voids in wild silk fibers using stannic acid treatment [6]. Divakar have studied the microstructure and micro rheological parameters of various wild silk fibers [7]. Gulrajani have studied structural variants of mulberry and tassar silk filaments [8]. In this context, there is a continued interest in Experimental Sample preparation Tassar silk is belongs to Antheraea mylitta family. Tassar silk cocoons were collected from the germplasm stock of the Department of Sericulture, University of Mysore, India. The fiber samples were obtained using the method mentioned in earlier work [9,10]. Electron irradiation Irradiation work was carried out at Microtron Center; Mangalore University, India, using 8 MeV Microtron accelerator. The electron beam feature is mentioned elsewhere [10]. X-Ray diffraction measurements Wide – angle X-ray diffraction patterns of the samples were recorded on a Rigaku Miniflex- II, X-ray diffraction instrument using CuKα radiation of wavelength λ=1.5406 Å at 40 kV and 100 mA with a scan rate of 1° /min. The diffraction angle ranged from 5° to 60 °. FT-IR spectroscopic analysis Fourier transform infrared (FT-IR) spectra of the unirradiated and EB irradiated tassar non-mulberry silk fiber samples was recorded in transmission mode using Thermo Nicolet, Avatar 370, FTIR spectrophotometer having a resolution 4 cm-1 in the wave number range 500-4000 cm-1. Differential scanning calorimetry (DSC) Thermal analysis of the tassar silk, with and without electron irradiation of natural polymer fibers were carried out using Mettler Toledo DSC 822 apparatus. The thermograms were obtained from the heating cycle run in a temperature range of 30-450°C at a constant heating rate of 10°C / min. under nitrogen atmosphere. All articles published in Journal of Fashion Technology & Textile Engineering are the property of SciTechnol, and is protected by copyright laws. Copyright © 2014, SciTechnol, All Rights Reserved. Sangappa Y, Asha S, Rao BL, Gowda M, Somashekar R (2015) Influence of Electron Irradiation on Tassr Non-mulberry Silk Fibers. J Fashion Technol Textile Eng 3:2. Citation: doi:http://dx.doi.org/10.4172/2329-9568.1000119 Results and Discussion X-ray diffraction study X-ray diffraction curves of pure and electron irradiated fiber samples are given in Figure 1. The average crystallite size of the crystallites was calculated from the Scherrer equation [13] with the method based on the width of the diffraction patterns obtained in the X-ray reflected crystalline region. The lattice strain and its variation for various values of the radiation doses (kGy) in polymer samples are very small and insignificant. Sample 2-theta (deg.) β (deg.) Crystallite size (nm) Lattice strain 0 kGy 20.86 1.76 4.8 0.04 25 kGy 19.91 1.30 6.48 0.03 50 kGy 20.24 1.18 7.15 0.02 100 kGy 20.68 1.45 5.48 0.03 Table 1: Structural parameters of non-mulberry pure and electron irradiated silk fibers for (020) reflection Fourier transforms infrared spectroscopy FT-IR measurements were carried out to investigate the nature of the chemical modifications caused by electron irradiation on the natural polymer tassar non-mulberry silk fiber. FT-IR spectra of tassar non-mulberry silk fiber pure and 8 MeV electron irradiated are shown in Figure 2 and corresponding band assignments are tabulated in Table 2. Figure 1: XRD scans of pure and 8 MeV electron irradiated fiber samples. In this study, the crystallite size (L in nm) was determined with the diffraction pattern obtained from the lattice planes at a 2θ of ~20; kλ L = β cosθ (1) where k is Scherrer constant, λ is X-ray wavelength, β is the full width at half maximum of the measured reflection and θ is peak value. The determined structural parameters such as crystallite size (L), lattice strain are given in Table 1. From the Table 1, it is very clear that the crystallite size (L) increases as radiation dose increases. Irradiation of polymers mainly causes two important changes. (1) Degradation of the polymer, wherein main chain scission takes place, leading to low molecular weight polymer. (2) Cross-linking which is chemical bonding between polymeric chains to form network polymers. Both of these effects cause changes in physical properties. Degradation of polymer leads to loss in mechanical strength, whereas cross linking improves the physical properties. Quite often these effects may occur simultaneously. The final result depends on the nature of the material, on the amount radiation, dosage rate and energy of the radiation. From the Table 1 it is evident that the crystallite size increases as radiation dose increases. It is known that the strength of the fibers irrespective of natural or man-made increases with increase in crystallite size [14]. This indicates that the electron irradiated fiber has higher tenacity than virgin fibers. Volume 3 • Issue 2 • 1000119 Figure 2: FTIR spectra of pure and electron irradiated fibers. The shift in frequency is correlated with force constant and bond length. The force constant values can be calculated from the expression [16] 1 ν = 2Πc k μ (2) where ν is the wave number, c the velocity of light, k the force constant and μ is the reduced mass. From the Table 3, it is interesting to note that the force constant decreases for C=O stretching band with increasing irradiation dosage. This decrease in force constant is due to interaction of high energy radiation with polymer matrix. From the Table 2, the observed IR band assignment for unirradiated tassar non-mulberry silk fiber is similar to earlier researcher [15]. From the infrared spectra it can be noticed that increasing irradiation dosage causes some observable changes in the spectrum of silk fiber in the wavenumber range 4000 – 600 cm-1. It induces some new • Page 2 of 4 • Citation: Sangappa Y, Asha S, Rao BL, Gowda M, Somashekar R (2015) Influence of Electron Irradiation on Tassr Non-mulberry Silk Fibers. J Fashion Technol Textile Eng 3:2. doi:http://dx.doi.org/10.4172/2329-9568.1000119 absorption bands and slight changes in the intensities of some absorption bands. Wavenumber (cm-1) Peak assignments 0 kGy 25 kGy 50 kGy 100 kGy N-H deformation 3440 3445 3444 3438 C=O stretching (amide I) 1632 1640 1633 1634 N-H bending 1540 1535 1527 - N-H in plane bending (amide II) 1231 1230 1231 1232 O-H bending 1162 1160 1157 1164 N-H rocking 960 962 960 960 N-C=O in plane bending (amide IV) 697 695 695 694 electron irradiated samples the decomposition temperature was slightly increased and the values are given in Table 4. The shifting of decomposition temperature (td) from 345-349 for irradiated fibers indicates that improvement of thermal stability of electron irradiated fibers. All the measurements were taken in an inert atmosphere of nitrogen and a temperature ranging from 30-400°C. The heating rate was 10°C/min. The unirradiated fiber showed enthalpy 124.56 J/g and it slightly goes on increasing as irradiation increases. In case of 25 kGy irradiated sample enthalpy is 145.32 J/g and in 100 kGy irradiated sample it was 147.14J/g. Increase in decomposition temperature and enthalpy suggests the requirement of higher amount of energy for breaking the bands compared to virgin samples. Table 2: IR peak assignments for unirradiated and electron irradiated samples The absorption band observed at 1632 cm-1 (amide I), 1540 cm-1 (amide II), 1231 cm-1 (amide III) and 697 cm-1 (amide IV) observed for the unirradiated sample. The significant alterations after 8 MeV electron beam irradiation one can see in the positions of amide I, II and III. The position of amide I that is C=O stretching peak at 1632 cm-1 has shifted to 1648 cm-1, amide II (N-H bending) are shifted to 1525 cm-1 and amide III shifting are very small namely 1-3 cm-1. Apart from these various shifts in the peak positions for the irradiated samples (Table 2), new peak start appearing around 3440 cm-1. The observed shifts in the wavenumber along with change in the peak intensify in the FTIR spectra indicate the occurrence of chemical modifications within the silk fiber due to electron irradiation which starts from the dose of 25 kGy. These results are understood by invoking the conformational changes introduced within the polymer due to electron irradiation. Sample C=O band variations N-H band variations Wavenumber (cm-1) Force Constant (N/cm) Wavenumber (cm-1) Force Constant (N/cm) 0 kGy 1632 10.77 3440 6.56 25 kGy 1640 10.88 3445 6.58 50 kGy 1632 10.78 3445 6.58 100 kGy 1637 10.81 3438 6.55 Table 3: FTIR modes of C=O and N-H band variations in Pure and Electron irradiated Tassar fibers Differential scanning calorimetric analysis Figure 3 shows the DSC thermograms of the pure and 8MeV electron irradiated silk fibers. The endothermic peak nearly at 70°C which is corresponding to the water evaporation appeared in all the cases except in 100 kGy irradiated sample [17]. The other strong endothermic transition is observed at 346 oC for pure is attributed to decomposition (td) of the fiber. In the case of Volume 3 • Issue 2 • 1000119 Figure 3: DSC thermograms of (a) pure, (b) 25kGy, (c) 50kGy and (d) 100 kGy electron irradiated fibers. Sample td (°C) Enthalpy (J/g) 0kGy 345.53 124.56 25kGy 347.76 145.32 50kGy 348.00 145.98 100kGy 348.33 140.14 Table 4: Thermal properties of pure and electron irradiate Tassar silk fibers Conclusions The main intension of this study was to investigate the influences of the electron irradiation on the structural, chemical and thermal properties of tassar non-mulberry silkfibers. From the wide angle Xray scattering (WAXS) study of electron irradiated silk fiber (Nonmulberry) samples; we have observed that even though there is not much change in the position of the X-ray reflections, an increasing trend in the value of microstructural parameters occurs. The significant change in microstructural parameters in polymer is due to • Page 3 of 4 • Citation: Sangappa Y, Asha S, Rao BL, Gowda M, Somashekar R (2015) Influence of Electron Irradiation on Tassr Non-mulberry Silk Fibers. J Fashion Technol Textile Eng 3:2. doi:http://dx.doi.org/10.4172/2329-9568.1000119 the effect of electron irradiation. FT-IR study reveals the structural changes occur due to electron irradiation. From the DSC study td the decomposition temperature slightly increases with irradiation. This reveals that a variety of biopolymer (tassar) could be cross-linked by the application of high energy electron beam irradiation (ionizing radiation). References 1. Kaplan D, Adams WW, Farmer B, Viney C (1994) Silk polymers material science and biotechnology. ACS Symposium Series 544. 2. Marsh RE, Corey RB, Pauling L (1955) An investigation of silk fibroin structure. Biochem Biophys Acta 16: 1-34. 3. 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