Effect of Gamma Irradiation on the Structural and Color Properties of CR 6-2 Polycarbonate 1

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1 Effect of Gamma Irradiation on the Structural and Color Properties of CR 6-2 Polycarbonate 1 M.M. Abutalib Physics Department, College of Science (Girls Branch), King Abdulaziz University, Jeddah, Saudi Arabia Received: 27/9/2014 Accepted: 2/11/2014 ABSTRACT Samples from sheets of CR 6-2 polymeric material have been exposed to gamma rays in the dose range KGy. The modifications induced in CR 6-2 samples due to gamma irradiation have been studied through different characterization techniques such as X-ray diffraction XRD, intrinsic viscosity, refractive index and color difference studies. The results indicated that the crosslinking is the dominant mechanism in the dose range KGy. This crosslinking destroyed the degree of order in the CR 6-2 samples associated with an increase in intrinsic viscosity values. This indicates an increase in the average molecular mass. Additionally, the non irradiated CR 6-2 sample showed significant color sensitivity towards gamma irradiation. The sensitivity in color change towards gamma irradiation appeared in the change in the blue color component of the non irradiated CR 6-2 film to yellow after exposure to gamma up to 400 KGy. This is accompanied by a net increase in the darkness of the samples. Key words: gamma; CR 6-2 polycarbonate; XRD, viscosity, refractive index, color changes. INTRODUCTION Ionizing radiation is a unique and powerful means for modifying the physical properties of polymers. Gamma irradiation of polymeric materials leads mainly to crosslinking and main chain scissions. Both processes coexist and either of them may predominate depending not only upon the chemical structure of the polymer, but also upon the conditions of irradiation (1). The crosslinking and main chain scission that take place during irradiation may lead to sharp changes in the physical properties of the polymer. On the other hand, CR 6-2 polycarbonate is an amorphous engineering thermoplastic notable for its high impact resistance. It has reasonably good temperature resistance, good dimensional stability. Polycarbonate particle track etched membranes are used as templates and in nano-tubes and nano-wires manufacturing (2). In addition, the application of radiation in polymer technology is of great importance with a view to achieve some desired improvements in polymer properties (3). It is already an established fact that interaction of radiation with polymers leads to chain scission, chain aggregation, formation of double bonds and molecular emission. As a consequence of this, the physico-chemical properties like optical, structural and chemical properties of the polymer are modified (4-11). The study of these changes may enhance their applications in different fields, e.g. for the evolution of high radiation doses (12). Radiation-induced modifications in polycarbonate have been studied extensively (13-17). The effect of radiation on polycarbonate is primarily chain scission. However, at increased doses, active sites or branching points created by scission may lead to crosslinks The present study deals with the investigation of the effect of gamma irradiation on the structural and optical properties of CR 6-2 polymer not only to obtain information concerning the interaction of gamma with CR 6-2, but also to study the feasibility of enhancing its properties, improving its performance in different fields. Corresponding author mabutalib@kau.edu.sa

2 EXPERIMENTAL PROCEDURE Samples: CR 6-2 is a polycarbonate-based film with a gloss first surface and a micromatte second surface. It has advantages over standard polycarbonate films in terms of dynamic strength, chemical resistance, dimensional stability, and cold formability. It has a chemical composition of C 16H 14O 3. It is manufactured by Farbenfabriken Bayer A.G., Leverkusen (Germany), with an average thickness of 300 µm and density 1.23 g/cm 3. Irradiation Facilities: A 60 Co source (manufactured by Atomic Energy of Canada, Ltd.) providing a dose rate of 2.4 Gy/min was used in the present study. The measurements were carried out 24 h after irradiation. Analysis of Irradiated Samples: X-ray diffraction measurements were carried out using a Philips powder diffractometer type PW 1373 goniometer. The diffractometer was equipped with a graphite monochromator crystal. The wavelength of the X-rays was A and the diffraction patterns were recorded in the 2 range (4-60 ) with scanning speed of 2 degrees per minute. Viscosity measurements were carried out in Oswald viscometer of the type pinkevitch Size 0 No. 2106, manufactured by Poulten, self, and LEE, LTD, England. This viscometer was calibrated in accordance with the standard method of test for kinematic viscosity specified in ASTM D 445-IP 71. Refractive index measurements were carried out using an Abbe refractometer (Type Reichert; mark II, Model-10480, New York). The accuracy of measuring the values of refractive indices, surface temperature of the prism and the wavelength of the light used were ± , o C and 5893 o A, respectively. Several values were measured for the same sample and the average values were considered. The transmission measurements were carried out using a Shimadzu UV Vis Nir scanning spectrophotometer, type 3101 PC. This unit measures in the wavelength range from 200 to 3000 nm. The Commission International de E Claire (CIE units x, y and z) methodology was used in this work for the description of colored samples (16). X-ray Diffraction: RESULTS AND DISCUSSION X-ray diffraction measurements were carried out on the non-irradiated and irradiated samples. The X-ray diffraction patterns of the samples are characterized by halos extending in the 2 range with maximum diffraction intensity observed at 2θ = 20 (Figure 1). The profile of the halos shows that the CR 6-2 polymer is a partly crystalline polymer with a dominant amorphous phase.

3 Fig. (1): X-ray diffraction patterns of the non irradiated and some irradiated CR 6-2 samples. The spectra of all samples were fitted with a Lorentz function. Thereby the integral intensities I (area) of the main diffraction peak were extracted and are represented in Figure 2. The figure shows that the integral intensity increases up to a maximum value around the 150 KGy irradiated sample, then decreases with increasing the gamma dose up to 400 KGy. The dose range, in which the integral intensity increases, indicates an increase in the crystallinity (ordering character) of CR 6-2 samples which can be attributed to degradation induced by gamma irradiation. This degradation increases the chain mobility and permits some molecules to re-crystallize, since the crystalline state is thermodynamic stable state (15). On the other hand, the decrease in integral intensity in the dose range KGy denotes a decrease in the amount of crystalline phase in the samples, indicating that the crystalline structure has been destroyed due to crosslinking. Fig. (2): Variation of the integral intensity of the CR 6-2 polymer with the gamma dose. 33

4 Since the halo's width at the half of maximal intensity W is inversely proportional to the crystallite size according to the Scherrer equation: L = (0.89 ) / ( W cos ) Where is the wavelength of the X-rays, values of W were calculated. Figure 3 shows the variation of W with the gamma dose. The figure reveals that W, and hence the crystallite size (thickness of the lamella) exhibited an opposite trend to that of the integral intensity. It shows a decrease in the dose ranges kgy indicating an increase in the crystallite size (width of the lamella). In the dose range kgy, it increases indicating a decrease in crystallite size. Fig. (3): Variation of the full width at half maximal intensity ( W) of the CR 6-2 polymer with the gamma dose. Intrinsic Viscosity: Solutions of different concentrations (0.2, 0.4, 0.6 and 0.8 %) were prepared from non-irradiated and irradiated CR 6-2 sheets using pure chloroform as a solvent. These dilute solutions were chosen to avoid any attractive secondary interactions between the polymer and solvent molecules which can be reflected in an increase of the viscosity in ways that accurate measurements can not be made. The time of flow (t) was measured, at room temperature (30 C); five times for each individual solution and the average values were considered. Figure 4 shows the dependence of intrinsic viscosity of CR 6-2 on the gamma dose. The intrinsic viscosity shows a decrease up to a minimum value around the 150 KGy irradiated sample, followed by an increase on increasing the gamma dose up to 400 KGy. The dose range in which the intrinsic viscosity decreases can be explained by the formation of shorter molecules as a result of degradation which causes both a random breaking of bonds and the formation of stable molecules with a lower molecular weight. While the increase in intrinsic viscosity in the dose ranges KGy, indicates an increase in the molecular mass of the polymer due to crosslinking.

5 Fig. (4): Variation of intrinsic viscosity of CR 6-2 polymer with the gamma dose. Refractive Index: Figure 5 illustrates the variation of the refractive index with gamma dose. The refractive index decreases in magnitude up to a minimum value at around the 150 KGy followed by an increase on increasing the dose up to 400 KGy. This behavior can be explained in terms of degradation and crosslinking induced by gamma irradiation. Such behavior facilitates the formation of free radicals that are chemically active. This allows the formation of covalent bonds between different chains (crosslinking), and, in turn, minimizes the anisotropic character of the CR 6-2 polymer samples, leading to the increase in refractive index. These results are in an agreement with those obtained by Shams-Eldin et al. (18), Where, they illustrated that the incident radiation activate the main polymer chain implying a main chain scission which result in a decrease of the refractive index. The same effect was also investigated by Ranby and Rebek (19). Fig. (5): Variation of the refractive index of CR 6-2 polymer with the gamma dose.

6 Color Properties: The transmission spectra of the irradiated and non irradiated CR 6-2 samples, in the wavelength range nm, have been investigated as show in Figure 6. Fig. (6): The transmission spectra for the non-irradiated and gamma irradiated CR 6-2 samples, measured in the wavelength range nm. Using these transmission data, the color intercepts (L * and b * ) were calculated and its variation with the gamma dose is shown in Figure 7. The accuracy in measuring L * is and for a * and b *. It can be seen that the color parameters b * and L * were significantly changed after exposure to gamma dose. The blue (-b * ) color component of the non-irradiated film changed into yellow (+b * ) after exposure to gamma irradiation up to 400 KGy. This is accompanied by a net increase in the darkness of the samples (-L * ). At the same time, the red (+a * ) color of the non irradiated sample was not affected by the gamma dose. Fig. (7): The variation of color intercepts L * and b * of CR 6-2 polymer with the gamma dose.

7 The color intensity E (color difference between the non irradiated sample and those irradiated with different gamma doses) was calculated and is plotted in Figure 8 as a function of gamma dose. The figure shows that E increased with increasing the dose, and accompanied by a significant increase in the yellow color components (+b * ). This indicates that the CR 6-2 polymer has a response to color change by gamma irradiation. These changes in color can be attributed to the trapping of the excited free radicals formed by ionization. Fig. (8): The variation of the color intensity E with the gamma dose. CONCLUSION The X-ray diffraction measurements indicated that the irradiation of CR 6-2 polymer with gamma in the dose range KGy increases the amorphous regions giving polymer resilience. The gamma irradiation in the dose range KGy led to a more compact structure of CR 6-2 polymer, which resulted in an increase in the average molecular mass and refractive index. The non irradiated CR 6-2 samples are nearly colorless; however, they showed significant color sensitivity towards gamma irradiation that appeared clearly in the change in the blue color component of the non irradiated CR 6-2 film to yellow after exposure to gammas up to 400 KGy. This is accompanied by a net increase in the darkness of the samples. REFERENCES (1) N. Singh, A. Qureshi, F. Singh and D. Avasthi, Materials Science and Engineering A, 457, 195 (2007). (2) C. Jerome, S. Demoustier-Chnpagne, R. Legras and R. Jerome, Chem. Eur. J., 6, 3089 (2000). (3) D. Sinha and K. Dwivedi, Radiat. Measu., 36, 713 (2003) (4) L. Calcagno, G. Compagnini and G. Foti, Nucl. Instr. Meth. B, 65, 413 (1992). (5) J. Pivin, Nucl. Instr. Meth. B, 84, 484, (1994) (6) S. Nouh, A. Abdel Naby, H. EL and Hussieny, Applied Radiat. Isotopes, 65, 1173 (2007). (7) A. Tidjani and Y. Watanabe, Journal of Polymer Science A, 33, 1455 (1995) (8) D. Sinha, G. Sarker, S. Ghosh, A. Kulshreshthta, K. Dwivedi and D. Fink, Radiat. Measu., 29, 599 (1997).

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