1. Introduction

Poly styrene-divinyl benzene type ion exchange materials having sulfonic acid and quaternary ammonium functional groups are widely used in various nuclear industries related applications where prolonged service in adverse environmental condition is required. In nuclear industrial applications organic resin materials are used for elimination of radioactive and other ionic impurities from water in moderator circuits [1]. In view of the extensive application of organic ion exchange materials in nuclear industries, their technological development started long back and are now made available at commercial scale to satisfy the needs of these industries. In spite of widespread applications of ion exchange materials, there are some problems related to their durability over a prolonged time period. The consistent performance of these materials depends upon the chemical nature of polymeric resin material, adverse environmental factors namely humidity, acid rain, temperature fluctuation and time of exposure to ultraviolet (UV) radiation, presence of traces of solvents, catalyst, metals and metal oxides from processing equipment and containers. In outdoor applications, these ion exchange materials very often deteriorate due to weathering process creating negative impact on their lifetime [2, 3]. The inability of polymeric resin materials to resist degradation conditions often becomes visible within a short span. In some situations, few hours of exposure to degradation conditions may result in extensive structural damage. The degradation process may lead to macromolecular chain bond breaking resulting in decrease in average molar mass or may lead to cross-linking thereby increasing the molar mass. Aging of polymeric materials will result alteration of polymer properties in long-term due to weathering conditions [4]. As a result, there is an increasing challenge in front of manufacturers to ensure about the life expectancy guarantee of their polymeric resin materials, particularly under the conditions which are difficult for inspection or failure catastrophic [5]. The wide spread utilization of polymeric resin materials has created the condition of emergence related to performance durability of these materials under stringent long-term exposure conditions. These problems related to durability of polymeric resin materials are associated with in-service environmental conditions and handling procedures during maintenance, repair and modifications. Since the repair or replacement of degraded polymeric resin materials is both labour and capital intensive, the durability of these materials is one of the critical issues from both safety and economic point of view.

The photo-degradation brought about by solar UV radiations is the most serious problem associated with an organic based resin. The solar waves consist of UV radiations in the wavelengths range of 290 to 400 nm, corresponding to the energies in the range of 415 to 300 kJ/mol. These energies associated with the solar UV radiations are similar to the bond energies of many organic molecules. When specific functional groups of an organic compound absorb UV radiation the chemical reactions are initiated liberating free radicals which further speedup the photo degradation process. Among the UV radiations, most harmful are the UV-B radiations which are in the wavelength range of 280 to 315 nm having high energy in the order of 426–380 KJ mol^-1, while UV-A radiations in the wavelength range of 315 to 400 nm are less harmful having comparatively less energy in the order of 389 and 300 KJ mol^-1 [6]. The deleterious effect of these radiations will depend on the chemical nature of the material, climatic conditions namely temperature, humidity, exposure time, presence of traces of solvents, catalyst, metals and metal oxides from processing equipment and containers [7]. Photo-degradation can take place via chain breaking or cross-linking in absence of oxygen and via photo-oxidative degradation in presence of oxygen. In most polymers, elevation in temperature condition and prolonged exposure to pollutants will raise the photo-oxidative sensitivity thereby triggering the photo-oxidative degradation process [8]. Exposure to UV radiations is usually observed superficially which is indicated in terms of embrittlement (surface cracking), discolouration and loss of transparency. Further exposure to UV radiations will bring about photolytic, photo-oxidative, and thermo-oxidative reactions in the resin materials resulting in the photo-degradation of polymeric resin materials which is usually superficially and slowly degrades the entire material by changing the chemical structure of the polymeric material [9]. Depending upon the nature of the polymeric resin material, the photo degradation may results in polymer chain scission, cross-linking leading to irreversible change in physico-chemical conditions and also changes at the molecular level [10]. Subsequent to UV exposure, the polymeric resin material follows different degradation routes via formation of free radicals and breaking of the polymer chains thereby losing its mechanical properties and molecular weight making the materials useless after some time [11].

The photo degradation of industrial grade ion exchange resins operating under severe environmental stress conditions is a serious problem with economic and environmental implications. Previous research focused mainly on the study of bulk mechanical properties, surface chemistry and surface morphology of the polymeric materials exposed to UV radiations for different exposure period [12, 13].  The study was also performed to understand the role of sensitizers in accelerating the efficiency of the photo-degradation and the mechanism of UV light induced photo-oxidation and photolysis processes in polymeric materials [14, 15]. A detail review was published on photo-degradation of polystyrene polymers which emphasise mainly on the degradation mechanism of polymers and role of stabilisers in photo-degradation [16]. However, in spite of extensive application of polymeric resin materials in nuclear as well as in the chemical industry, not much work is reported in the literature related to performance of photo-degraded polymeric resin materials [17]. Therefore, in the present investigation, a systematic study was performed on the ion uptake reaction kinetics and uptake behaviour of fresh and photo-degraded nuclear grade anion exchange resin Indion GS 300, using non-destructive radiotracer analytical technique.

2. Materials and Methods

2.1. Ion exchange resin

The anion exchange resin Indion GS-300 as supplied by the manufacturer (Ion exchange India Limited, Mumbai) was a nuclear grade resin in the OH^– form with quaternary ammonium functional group having polystyrene matrix. The particle size was in the range of 0.3 to 1.2 mm, operating pH range was 0-14, maximum operating temperature of 60^oC having the exchange capacity of 1.40 meq./mL. The moisture content of the resin was 51.9%.

2.2. Radio isotope used

The ⁸²Br radioactive tracer isotope used here was supplied by Board of Radiation and Isotope Technology (BRIT), Mumbai, India. The isotope used is an aqueous solution of ammonium bromide in dilute ammonium hydroxide having half life of 36 d, radioactivity of 5mCi and γ- energy of 0.55 MeV [18].

2.3. Conditioning of the ion exchange resin

The resin grains of 30-40 mesh size were used for the present investigation. The soluble impurities of the resin were removed by repeated soxhlet extraction using water. Moreover, distilled methanol was used occasionally to remove non-polymerized organic impurities. The resin in hydroxide form was converted into bromide form with 10% potassium bromide in a conditioning column. Then the resin was washed with distilled deionized water until the washings were bromide free. The resin in the bromide form was air dried over P₂O₅ and used for further study (hereafter referred as fresh resin).

2.4. Photo-degradation of ion exchange resin

The photo-degradation of the resin was carried in a UV chamber in an ambient atmosphere where the temperature was nominally 25^oC–29^oC, with a humidity of 30-50%. The resin was photo-degraded in a UV chamber by exposing them to radiation of wavelength 284 nm and 384 nm for 24 h. After 24 h the degraded resin was washed with distilled water and ethanol mixture to remove the degraded polymeric fractions. The resin was then air dried and used for further study (hereafter referred as λ₃₈₄ photo degraded resin and λ₂₈₄ photo degraded resin).

2.5. Study on bromide ion uptake and reaction kinetics

The fresh and degraded resins in bromide form weighing 1.000 g (m) were equilibrated with 200 mL (V) labeled bromide ion reaction medium (0.200M) of known initial activity (Ai) at a constant temperature of 30.0^oC. The temperature of the reaction medium was maintained constant using an in-surf water bath. The bromide ion-isotopic exchange reaction can be represented as:

R-Br + Br*^–_(aq.) R-Br* + Br ^– _(aq.)               (1)

Here R-Br represents ion exchange resin in bromide form; Br*^–_(aq.) represents aqueous bromide ion reaction medium labeled with ⁸²Br radiotracer isotope.

The activity in counts per minute (cpm) of 1.0 mL of the reaction medium was measured at an interval of every 2 minutes for 3 h. The solution was transferred back to the same bottle containing labeled reaction medium after measuring the activity. The final activity (A_f) of the equilibrated labeled bromide ion reaction medium was measured after 3h. The activity in counts per minute (cpm) was measured with γ -ray spectrometer equipped with NaI (Tl) scintillation detector. The activity measured at various time intervals was corrected for background counts. The procedure adopted for labeling the reaction medium was same as mentioned previously [19]. The percentage and amount of bromide ions exchanged on the resin in mmol were obtained from the A_i, A_f, values and the amount of exchangeable bromide ions in 200 mL of reaction medium. The study was extended further by equilibrating the fresh and degraded resins with 0.300M and 0.500M labeled bromide ion reaction medium at 30.0^oC. Similar set of experiments were repeated by equilibrating 1.000 g of fresh and degraded resins in bromide form with 0.200M labeled bromide ion reaction medium at higher temperatures up to 45.0^oC.

2.5. Fourier-transform infrared spectroscopy (FTIR) analysis

FTIR analysis of fresh and photo-degraded resins was performed using a Bruker Optik, ALPHA-T FTIR spectrometer having gold mirror interferometer with ZnSe beam splitter. The ATR probe consisted of a zinc selenide focusing element and a diamond internal reflectance element. The probe was brought into intimate contact with the sample surface using mechanical pressure. 32 scans were collected over the spectral range of 400 cm^-1 to 4000 cm^-1. The probe was purged with dry air and background spectra were collected before each sample spectrum was taken.

2.6. Scanning Electron Microscopy (SEM) analysis

The degradation studies of ion exchange resins was also studied by examining the surface morphology of fresh and photo degraded resin samples using JSM-6380LA Scanning Electron Microscope (Jeol Ltd., Japan). The powders were precisely fixed on an aluminum stub using double sided graphite tape and then were made electrically conductive by coating in a vaccum with a thin layer of carbon, for 30 seconds and at 30 W. The pictures were taken at an excitation voltage of 15 KV and a magnification of ×250 to ×500.

Table 1. Effect of temperature of reaction medium on isotopic ion uptake reaction kinetics and isotopic uptake using fresh/photo-degraded Indion GS 300 resins.

Amount of ion exchange resin in bromide form = 1.000 g; Concentration of labeled bromide ion reaction medium = 0.200M; Volume of labeled bromide ion reaction medium = 200 mL; Amount of exchangeable bromide ions in 200 mL labeled reaction medium = 40.00 mmol

Table 2. Concentration effect on isotopic ion uptake reaction kinetics and isotopic uptake using fresh/photo-degraded Indion GS 300 resins.

Amount of ion exchange resin = 1.000 g; Volume of labeled ionic reaction medium = 200 mL; Temperature of reaction medium = 30.0 ^oC

3. Results and Discussion

3.1 Effect of photo-degradation on isotopic ion uptake reaction kinetics

In the present investigation it was observed that the initial activity of solution decreases rapidly due to rapid ion uptake reaction, then due to slow ionic uptake the activity of the solution decreases slowly due and finally remains nearly constant. Previous investigations have shown that the above ionic uptake reactions are of first order, as a result the logarithm of activity when plotted against time gives a composite curve in which the activity initially decreases sharply and thereafter very slowly giving nearly straight line, evidently rapid and slow ion adsorption reactions were occurring simultaneously [19]. The activity exchanged due to rapid, slow uptake reactions as well as the specific reaction rate (k) of rapid ion uptake reactions were calculated in the same way as explained previously [20-22]. The amount of bromide ions exchanged (mmol) on the resin were obtained from the initial and final activity of solution and the amount of ions in 200mL of solution.

It was observed that, under identical experimental conditions, with rise in temperature from 30.0°C to 45.0°C, the k values (min^-1) for bromide ion uptake reactions were observed to decrease for fresh as well as for λ₃₈₄ and λ₂₈₄ photo- degraded resins (Table 1). Thus for 0.200M bromide ion concentration when the temperature was raised from 30.0 ^oC to 45.0 ^oC, the k values decrease from 0.238 to 0.226 min^-1 for fresh resin, from 0.198 to 0.181 min^-1 for λ₃₈₄ photo- degraded resin and from 0.156 to 0.142 min^-1 for λ₂₈₄ photo-degraded resin (Table 1).

It was observed that, under identical experimental conditions, with rise in concentration of bromide ions in the solution from 0.200M to 0.500M, the k values (min^-1) for ion uptake reactions were observed to increase for fresh as well as for λ₃₈₄ and λ₂₈₄ photo-degraded resins (Table 2). Thus at 30.0 ^oC when the bromide ion concentration was raised from 0.200M to 0.500M, the k values increase from 0.238 to 0.276 min^-1 for fresh resin, from 0.198 to 0.223 min^-1 for λ₃₈₄ photo-degraded resin and from 0.156 to 0.176 min^-1 for λ₂₈₄ photo-degraded resin (Table 2).

From the results, it appears that under identical experimental conditions, ion uptake reaction rate decreases sharply as the photo-degradation wavelength decreases from 384 nm to 284 nm. Thus for 0.200M bromide ion concentration at a constant temperature of 30.0 ^oC, the k value was 0.238 min^-1 for fresh resin, which decreases to 0.198 min^-1 for λ₃₈₄ photo-degraded resin, which further decreases to 0.156 min^-1 for λ₂₈₄ photo-degraded resin (Table 1). Comparing the ion uptake reaction rate (k) in min^-1 for reactions performed at different temperatures of reaction medium and concentration of labeled bromide ion solution, it was observed that the k values decrease with decrease in photo-degradation wavelength.

3.2 Effect of photo-degradation on percentage isotopic ion uptake

 It was observed that for 0.200M labeled bromide ion solution, as the temperature of the reaction medium increases from 30.0^oC to 45.0^oC, the percentage of isotopic ion uptake decreases by 14.5% from 54.8% to 40.3% for fresh resins; by 15.6% from 50.5% to 34.9% for λ₃₈₄ photo-degraded resin and maximum by 24.3% from 45.9% to 21.6% for λ₂₈₄ photo-degraded resin (Table 1). For same temperature of reaction medium, similar decrease in percentage of bromide ion uptake was observed as the photo-degradation wavelength decreases from 384 nm to 284 nm. Thus for 0.200M labeled bromide ion solution at a constant temperature of 30.0 ^oC, in case of fresh resin the percentage of ion uptake was 54.8%, while for λ₃₈₄ photo-degraded resin 50.5% isotopic ion uptake was observed, indicating 4.3% decrease. Similarly, for λ₂₈₄ photo-degraded resin, the percentage of isotopic ion uptake was 45.9% indicating 8.9% decrease with reference to fresh resin (Table 1). Thus, it was observed that the decrease in wavelength has higher photo-degradation effect on the resin which is reflected by higher decrease in bromide ion uptake by the resin.

It was observed that at 30.0⁰C, as the concentration of labelled bromide ion solution increases from 0.200M to 0.500M, the percentage of isotopic ion uptake increases by 13.9% from 54.8% to 68.7% for fresh resins; by 13.3% from 50.5% to 63.8% for λ₃₈₄ photo-degraded resin and by 10.8% from 45.9% to 56.7% for λ₂₈₄ photo-degraded resin (Table 2). Thus, as the photo-degradation wavelength decreases the degradation effect on the resin was more which is reflected by less increase in isotopic ion uptake by the resin.

3.3 Thermodynamics of isotopic ion uptake reactions using fresh and photo-degraded resins

The energy of activation (E_a) for the bromide ion uptake reactions taking place in Indion GS 300 were calculated by using Arrhenius equation [23].

                                             k = A x e^–Ea/RT                                                             (2)

The plot of log₍₁₀₎k against 1/T gives a straight line graph (Figure 1), from the slope of the plot, energy of activation E_a values for ion uptake reactions using fresh and photo-degraded resins were calculated by the equation [23].

                                          E_a= slope x -2.303x R                                                                (3)

The enthalpy of activation ΔH^‡ value for the bromide ion uptake reactions using fresh and photo-degraded resins were calculated by using the Eyring-Polanyi equation [23, 24].

                                         log₁₀k/T = -ΔH ^‡/2.303RT  + log₁₀k_B/h + ΔS^‡ /2.303R                          (4)                    

Where:

k = reaction rate constant

T = absolute temperature

ΔH^‡ = enthalpy of activation

R = gas constant (8.314J.K⁻¹.mol⁻¹)

k_B = Boltzmann constant (1.3806 ×10⁻²³J⋅K⁻¹)

h = Planck’s constant (6.6261×10⁻³⁴J⋅s)

ΔS^‡ = entropy of activation

The plot of log₁₀k/T versus 1/T gives a straight-line graph (Figure 2), from the slope of which enthalpy of activation ΔH^‡   values for the bromide ion uptake reactions using fresh and photo-degraded resins were calculated by the equation

                 Slope = ΔH^‡ /-2.303R                                                                 (5)

From the intercept of the above plot, the entropy of activation ΔS^‡ values for the bromide ion uptake reactions using fresh and photo-degraded resins were calculated by the equation

           Intercept = 2.303 x log₁₀ (k_B/h) + ΔS^‡/R                                         (6)

Knowing the values of enthalpy of activation ΔH^‡ and entropy of activation ΔS^‡, free energy of activation ΔG^‡ for bromide ion uptake reactions using fresh and photo-degraded resins was calculated by the equation

                   ΔG^‡ = ΔH^‡ -TΔS^‡                                                                   (7)

It was observed that during isotopic ion uptake reactions using the fresh resin, the values of energy of activation         (-2.77 kJ.mol^-1), enthalpy of activation (-5.35 kJ.mole^-1), free energy of activation  (64.66 kJ.mol^-1) and entropy of activation (-0.231 kJ.K^-1mol^-1); which increases to  -4.66 kJ.mol^-1,   -7.24 kJ.mol^-1,   63.86 kJ.mol^-1   and    -0.234 kJ.K^-1mol^-1 respectively for λ₃₈₄ photo-degraded resin;  which further increases to  -5.05 kJ.mol^-1,   -7.63 kJ.mol^-1, 63.65 kJ.mol^-1 and -0.236 kJ.K^-1mol^-1 respectively for λ₂₈₄ photo-degraded resin under similar experimental conditions (Table 1). The thermodynamic parameters calculated here suggest that decrease in wavelength of UV radiations has more degradation effect on the resin resulting in less thermodynamic feasibility of the isotopic ion uptake reactions.

Figure 1. Arrhenius plot to determine energy of activation (E_a) for bromide isotopic ion uptake reactions performed by using fresh and photo-degraded Indion GS 300 resins.

Amount of ion exchange resin in bromide form = 1.000 g; Temperature range = 30.0-45.0⁰C; Concentration of labeled exchangeable bromide ion solution = 0.200M; Volume of labeled bromide ion solution = 200 mL; Amount of exchangeable bromide ions in 200 mL labeled solution = 40.00 mmol.

 Figure 2. Eyring-Polanyi plot to determine the enthalpy of activation ΔH^‡ and entropy of activation ΔS^‡ for bromide isotopic ion uptake reactions performed by using fresh and photo-degraded Indion GS 300 resins.

Amount of ion exchange resin in bromide form = 1.000 g; Temperature range = 30.0-45.0⁰C; Concentration of labeled exchangeable bromide ion solution = 0.200M; Volume of labeled bromide ion solution = 200 mL; Amount of exchangeable bromide ions in 200 mL labeled solution = 40.00 mmol.

3.4 Statistical Correlations

The results of present investigation show a strong negative correlation between temperature of the medium and bromide ion uptake reaction rate (min^-1) for the reactions performed by using fresh, λ₂₈₄ photo degraded and λ₃₈₄ photo degraded resins, having r values of -0.9938, -0.9986 and -0.9886 respectively (Figure 3). There also exist strong negative correlation between percentage of bromide ion uptake and temperature of the medium for the reactions performed by using fresh, λ₂₈₄ photo degraded and λ₃₈₄ photo degraded resins, having r values of -0.9992, -1.0000 and -1.0000 respectively (Figure 4).

However, a strong positive correlation was observed between the concentration of labeled ionic medium and bromide ion uptake reaction rate (min^-1) for the reactions performed by using fresh, λ₂₈₄ photo degraded and λ₃₈₄ photo degraded resins, having r values of 0.9998, 0.9993 and 0.9995 respectively (Figure 5). Also, a strong positive correlation was observed between the concentration of labeled ionic medium and percentage of bromide ion uptake for the reactions performed by using fresh, λ₂₈₄ photo degraded and λ₃₈₄ photo degraded resins, having r values of 0.9998, 0.9999 and 0.9990 respectively (Figure 6).

Figure 3. Correlation between temperature of reaction medium and bromide isotopic ion uptake reaction rate of the reactions performed by using fresh and photo-degraded Indion GS 300 resins.

Amount of ion exchange resin in bromide form = 1.000 g; Concentration of labeled bromide ion reaction medium = 0.200M; Volume of labeled bromide ion reaction medium = 200 mL; Amount of exchangeable bromide ions in 200 mL labeled reaction medium = 40.00 mmol

Correlation coefficient (r) for fresh resin =-0.9938; Correlation coefficient (r) for λ₃₈₄ photo degraded resin =-0.9886; Correlation coefficient (r) for λ₂₈₄ photo degraded resin = -0.9986

Figure 4. Correlation between temperature of reaction medium and percentage of bromide isotopic ion uptake for the reactions performed by using fresh and photo-degraded Indion GS 300 resins.

Amount of ion exchange resin in bromide form = 1.000 g; Concentration of labeled bromide ion reaction medium = 0.200M; Volume of labeled bromide ion reaction medium = 200 mL; Amount of exchangeable bromide ions in 200 mL labeled reaction medium = 40.00 mmol

Correlation coefficient (r) for fresh resin =-0.9992; Correlation coefficient (r) for λ₃₈₄ photo degraded resin =-1.0000; Correlation coefficient (r) for λ₂₈₄ photo degraded resin = -1.0000

Figure 5. Correlation between concentration of labeled bromide ionic solution and bromide isotopic ion uptake reaction rate of the reactions performed by using fresh and photo-degraded Indion GS 300 resins.

Amount of ion exchange resin = 1.000 g; Volume of labeled ionic reaction medium = 200 mL; Temperature of reaction medium = 30.0 ^oC

Correlation coefficient (r) for fresh resin = 0.9998; Correlation coefficient (r) for λ₃₈₄ photo degraded resin = 0.9995; Correlation coefficient (r) for λ₂₈₄ photo degraded resin = 0.9993

Figure 6. Correlation between concentration of labeled bromide ionic solution and percentage of bromide isotopic ion uptake for the reactions performed by using fresh and photo-degraded Indion GS 300 resins.

Amount of ion exchange resin = 1.000 g; Volume of labeled ionic reaction medium = 200 mL; Temperature of reaction medium = 30.0 ^oC

Correlation coefficient (r) for fresh resin = 0.9998; Correlation coefficient (r) for λ₃₈₄ photo degraded resin = 0.9990; Correlation coefficient (r) for λ₂₈₄ photo degraded resin = 0.9999

3.5 Characterisation of fresh and photo-degraded resin

3.5.1 FTIR spectrum of fresh and photo-degraded Indion GS 300 resin

The IR spectrum of the fresh Indion GS 300 resin is shown in Figure 7. The assignments of various bands and peaks made in this study are in reasonable agreement with those reported in the literature for similar functional groups. In the FTIR spectrum of fresh resin, the sharp strong broad band was observed at 3366 cm^-1 corresponding to the vibration of O-H bond of the water or the quaternary ammonium group (R₄-N⁺). This may be due to the moisture content of the fresh resins. The sharp band between 1380-1349 cm^-1 was for -C-N stretching while a variable absorption bands between 1633-1614cm^-1 was due to the stretching vibrations of –C=C- of alkenes group. The weak band at 3031cm^-1 was the characteristic stretching band for aromatic ring. A moderate band at 2925cm^-1 was due to the C-H stretching band for –CH₂ group. A moderate and sharp band at 1416cm^-1 and 1470cm^-1 was due to the –C-H bending bands for -CH₂ group. The variable band at 1511cm^-1 was the –C=C- stretching for aromatic ring, the sharp band at 828cm^-1 and moderate band at 705cm^-1 was the characteristic bands of p-substituted and o-substituted aromatic rings. Comparison of IR spectrum of fresh resin (Figure 7) and photo-degraded resin (Figures 8 and 9) indicate disappearance of characteristic –C-N stretching band at 1349cm^-1, -C-H stretching band at 3031cm^-1 for aromatic ring and a single band at 1614cm^-1 for -C=C-stretching in alkenes.

Figure 7.  FTIR Spectrum of fresh Indion GS 300 resin.

Figure 8.  FTIR Spectrum of λ₂₈₄ photo-degraded Indion GS 300 resin.

Figure 9.  FTIR Spectrum of λ₃₈₄ photo-degraded Indion GS 300 resin.

3.5.2 SEM study of fresh and photo-degraded Indion GS 300 resin

The SEM image of fresh ion exchange resins Indion GS 300 was taken to examine its surface morphology. The figure 10(a) showed the surface morphology of fresh Indion GS 300 resins which indicate its plane spherical structure having smooth surface.

The SEM image of λ₃₈₄ and λ₂₈₄ photo-degraded Indion GS 300 resin showed large cracks on the plane spherical surface of the resin (Figures 10b and 10c). The SEM image of λ₃₈₄ photo-degraded resin show hair cracks on the surface (Figure 10b). Whereas, in case of λ₂₈₄ photo-degraded resin, the completely broken surface with large cracks were observed (Figure 10c), indicating higher photo-degradation effect as compared to that of the fresh and λ₃₈₄ photo-degraded resin (Figures 10a and 10b).

Conclusion

In recent years, the industrial application of polymeric resin materials has increased considerably but it is now well established that these materials undergo rapid photo-degradation when exposed to solar UV radiations. The photo-degradation of resin materials is one of the most serious problems associated with an organic based resin. Among the solar UV radiations, most harmful are the high energetic UV-B radiations (280 to 315 nm) in comparison to UV-A radiations (315 to 400 nm) which are of less energy. The polymeric resin material Indion GS 300 in the present study after exposure to UV radiation of wavelength 284 and 384nm was studied for the percentage isotopic ion uptake, reaction kinetics and reaction thermodynamics. The results of the present investigation indicate that isotopic ion uptake reaction rate (min^-1), percentage of isotopic ion uptake are greatly affected for the reactions performed by using λ₂₈₄ and λ₃₈₄ photo degraded Indion GS 300 resin as compared to that of fresh Indion GS 300 resin. The increase in thermodynamic parameters like energy of activation (kJ.mol^-1), enthalpy of activation (kJ.mol^-1), free energy of activation (kJ.mol^-1) and entropy of activation (kJ.K^-1mol^-1) calculated for the isotopic ion uptake reactions using the fresh, λ₃₈₄ and λ₂₈₄ photo degraded Indion GS 300 resin give an indication that decrease in wavelength of UV radiations has catastrophic effect on the resin resulting in less thermodynamic feasibility of the isotopic ion uptake reactions.

Acknowledgement

The author is thankful to Professor Dr. R.S. Lokhande (Retired) for his valuable help and support by providing the required facilities so as to carry out the experimental work in Radiochemistry Laboratory, Department of Chemistry, University of Mumbai, Vidyanagari, Mumbai -400 058.

References

1. C.Srinivas, G.Sugilal and P.K.Wattal, Management of Spent Organic Ion-Exchange Resins by Photochemical

    Oxidation. WM’03 Conference, Tucson, Arizona (USA), February 23-27, 2003.

2. G. Wypych, Handbook of material weathering, 4^th edn. Chemtec Publishing, Toronto, p 211 (2008).

3. H. Zweifel, In book: Stabilization of polymeric materials. Springer-Verlag Berlin Heidelberg (1998).

4. M. Strlic, and J. Kolar, Aging and stabilization of papers. Distributed by the National and university Library,

    Turjaska 1, 1000 Slovenia (2005).

5. J. Goldshtein and S. Margel, Synthesis and characterization of polystyrene/2(5-chloro-2H-benzotriazole-2-

    yl)-6-(1, 1-dimethylethyl)-4-methyl-phenol composite microspheres of narrow size distribution for UV irradiation

    protection. Colloid Polym Sci 289, 1863–1874 (2011).

6. J. Pospisil and S. Nespurek, Addcon World conference, Cologne, Germany, 17–18 Oct 2006.

7. W. Schnabel, Polymer degradation: principle and practical applications. Chapter 14. München : Hanser

    International ; New York  (1981).

8. A. S. Maxwell, W. R. Broughton, G. Dean and G. D. Sims. Review of accelerated ageing methods and lifetime

    prediction techniques for polymeric materials. NPL Report DEPC MPR 016, National Physical Laboratory,  

   Teddington, Middlesex, ISSN 1744-0270 (2005).

9. L.Valkoa, E. Klein, P. Kovarik, T. Bleha and P. Simon, Kinetic study of thermal dehydrochlorination of poly (vinyl

    chloride) in the presence of oxygen: III. Statistical thermodynamic interpretation of the oxygen catalytic activity.

    Eur. Polym. J. 37,1123–1133 (2001).

10. R.R. Mohamed, Photostabilization of polymers. S. Palsule (ed), In book: Encyclopedia of Polymers and

      Composites, Springer-Verlag Berlin Heidelberg (2015). DOI 10.1007/978-3-642-37179-0_74-1

11. F.A. Bottino, A.R. Cinquegrani, G. Pasquale, L.L. Di and A. Pollicino, Chemical modification, mechanical

      properties and surface photooxidation of films of polystyrene. Polym. Test 12, 405–411(2003).

12. B.G. Kumar, R.P. Singh and T. Nakamura, Degradation of carbon fiber-reinforced epoxy composites by

      ultraviolet radiation and condensation. Journal of Composite Materials, 36(24), 2713-2721 (2002).

13. A.W. Signor, M.R. VanLandingham and J.W. Chin, Effect of ultraviolet radiation exposure on vinyl ester resins:

      characterization of chemical, physical, mechanical damage. Polymer Degradation and Stability, 79(2), 359-368

      (2003).

14. L.F.A. Pinto, B.E. Goi, C.C. Schmitt and M.G. Neumann. Photodegradation of polystyrene films

      containing UV- visible sensitizers. Journal of Research Updates in   Polymer Science 2(1), 39–47 (2013).

15. P. Gijsman and M. Diepens, Photolysis and photooxidation in engineering plastics. In M. C. Celina, N. C.

      Billingham, and J. S. Wiggins (Eds.), Polymer degradation and performance (pp. 287-306). (ACS Symposium

      Series; Vol. 1004). Washington: American Chemical Society, (2009). DOI: 10.1021/bk-2009-1004.ch024

16. E. Yousif and R. Haddad, Photodegradation and photostabilization of polymers, especially polystyrene: review.

      SpringerPlus, 2, Article No. 398 (2013).

17. A.N. Patange, Thermodynamics of Ion Exchange Reaction in Predicting the Ionic Selectivity Behavior of UV

      Radiation Degraded Nuclear-grade and Non-nuclear Grade Resins. Oriental Journal of Chemistry, 34(4), 2051-

      2059 (2018).

18. D.D. Sood, Proceedings of International Conference on Applications of Radioisotopes and Radiation in

      Industrial Development, edited by D.D. Sood, A.V.R. Reddy, S.R.K. Iyer, S. Gangadharan and G. Singh, BARC,

      Mumbai, India, p.47, (1998).

19. P.U. Singare, Studies on kinetics and thermodynamics of ion adsorption reactions by applications of short-

      lived radioactive tracer  isotopes. Ionics, 22(8), 1433-1443 (2016).

20. R.S. Lokhande and P.U. Singare, Comparative Study on Ion-Isotopic Exchange Reaction Kinetics by

     Application of Tracer Technique.  Radiochim. Acta, 95(3), 173-176 (2007).

21. R.S. Lokhande, P.U. Singare and V.V. Patil, Application of Radioactive Tracer Technique to Study the

      Kinetics and Mechanism of Reversible Ion-Isotopic Exchange Reaction using Strongly Basic Anion

      Exchange Resin Indion -850.  Radiochemistry, 50(6), 638-641 (2008).

22. R.S. Lokhande and P.U. Singare, Comparative Study on Iodide and Bromide Ion-Isotopic Exchange Reactions

      by Application of Radioactive Tracer Technique, J.Porous Mater., 15(3), 253-258 (2008).

23. L.K. Onga, A. Kurniawana, A.C. Suwandi, C.X. Linb, X.S. Zhao and S. Ismadji, Transesterification of leather

       tanning waste to biodiesel at supercritical condition: Kinetics and thermodynamics studies. The Journal of

       Supercritical Fluids, 75, 11–20 (2013).

24. V. Stavila, J. Volponi, A.M. Katzenmeyer, M.C. Dixon and M.D. Allendorf, Kinetics and mechanism of metal–  

       organic framework thin film growth: systematic investigation of HKUST-1 deposition on QCM electrodes,

       Chem. Sci., 3(5), 1531-1540 (2012).