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J. Rad. Res. Appl. Sci., Vol.4, No. 1 (A), pp. 45 - 57 (2010)

Use of Chlorophenol Red Dyed Poly(vinyl alcohol) and Poly(vinyl butyral) Copolymer Films for Dosimetric Applications S. Eid, W. B. Beshir and S. Ebraheem National Center for Radiation Research and Technology, AEA, P.O. Box 29 Nasr City, Cairo, Egypt E-mail Seif_Dose@yahoo.com Received: 8 / 12 /2010. Accepted: 12 / 1 /2011.

ABSTRACT

Poly(vinyl alcohol) PVA, and poly(vinyl butyral co-polyvinyl alcohol co-vinyl acetate) (PVB-co-PVA/PVAC), containing acid base indicator dye (chlorophenol red) CPR, and a Cl-containing substance (chloral hydrate) may be useful for radiation dosimetry. Chlorophenol red in PVA films changes its color from purple to yellow by irradiation due to the lowering of the pH caused by the generated HCL from the radiolysis of chloral hydrate. The useful dose range extends up to 3.5 kGy. On the other hand, dyed copolymer films are bleached when exposed to gamma radiation with the useful dose range up to 8 kGy. Different concentrations of chloral hydrate were added to control the response dose range of application. The radiation chemical yield G(value) was calculated in presence and absence of chloral hydrate, where it increases with increase chloral hydrate concentration for both CPR/PVA and CPR/PVB copolymer films. Humidity during irradiation was also studied. The pre- and post-irradiation stability of the films was found to be satisfactory. Key words: dosimetry, chlorophenol red, PVA, (PVB-co-PVA/PVAC).

INTRODUCTION

Several thin polymeric film dosimeters have been successively developed and used as dosimeters for routine use in radiation processing by electron beam and gamma ray(1-4). Many dyed polymeric films had been developed and investigated for the possibility of being used to measure absorbed dose in nuclear reactors and doses of X-rays, gamma-rays and electron beam (5-9). A-chlorine containing polymer is not necessary for the reaction to occur. A similar color change can be produced if a halogen containing substance

S. Eid. et al., J. Rad. Res. Appl. Sci., Vol. 4, No. 1 (A) (2011) 46

is present in the dye containing matrix (10). New radiation sensitive indicators

consisting of poly(vinyl alcohol) film containing pH indicator dye and a water soluble chlorine containing substance have been developed (11-12).

In the current work, thin film of PVA and PVB copolymer colored with chlorophenol red containing different concentrations of chloral hydrate to give dosimeter films. The effect of humidity during irradiation as well as pre and post irradiation stability is examined.

EXPERIMENTAL

Materials

Chlorophenol red indicator [product of Sigma & Aldrish], PVA [average Mo. wt 25.000 fully hydrolyzed 99-100% product of J.T baker chemical Co.USA] and poly(vinyl butyral co-polyvinyl alcohol co-vinyl acetate) [average Mo. Wt. 70,000-100,000 product of Aldrish chemical company USA]

Preparation of stock dye solution

The stock of the sodium salt of the indicator was prepared by dissolving 0.08 g of chlorophenol red indicator [product of Sigma & Aldrish] in 1.9 ml of aqueous solution [NaOH] = 0.1N, and then the volume was complete by 95% Ethanol in a 50 ml volumetric flask .

Preparation of chlorophenol red films

Films were prepared by dissolving either 6 g of PVA [average Mo. wt 25.000 fully hydrolyzed 99-100% product of J.T baker chemical Co.USA] in 120 ml double distilled water or poly(vinyl butyral co-polyvinyl alcohol co-vinyl acetate) [average Mo. Wt. 70,000-100,000 product of Aldrish chemical company USA] in n-butanol. Complete dissolution was attained by stirring 3 hours at 60oC followed by continuous stirring for 24 hours at room temperature then left to cool.

For PVA films, polymer solution was divided into four parts each one of 30 ml volume and 3 ml of chlorophenol red indicator was added then 0.2, 0.4 and 0.6 g chloral hydrate were added to 3 parts and the fourth one was left without chloral hydrate. For PVB copolymer films, polymer solution was divided into four parts each one of 30 ml and 6 ml of chlorophenol red indicator was added then 0.2, 0.4 and 0.6 g chloral hydrate were added to three parts and the fourth one was left without chloral hydrate. Each solution was poured onto

S. Eid. et al., J. Rad. Res. Appl. Sci., Vol. 4, No. 1 (A) (2011) 47

10x10 cm horizontal glass plate and dried at room temperature for about 48 h. After stripping the films were cut into 1x1 cm pieces and were stored in the dark at (RH) of 33%, the film thickness was measured using digitrix-mark II thickness gauge to be 0.085+0.005 mm. Eight polymer films were obtained, 6 of them contain 13.33, 26.66 and 39.99 phr (part per hundred parts of polymer) chloral hydrate, three PVA films and the other three PVB-co-PVA/PVAC. The three PVA films contain the same chlorophenol red concentrations of 0.32 phr. The other three PVB-co-PVA/PVAC, contain chlorophenol red concentration of 0.64 phr. The rest 2 films were left without chloral hydrate.

Instruments

The absorption spectra of the un-irradiated and irradiated films were measured in the wavelength range of 200-600 nm using a UVIKON 860 spectrophotometer. The film thickness was measured using a Digitrix-Mark II thickness gauge (precision ±1 µm, 1 σ). Irradiation was carried out with the 60Co Gamma chamber 4000A irradiation facility (manufactured at Bhabha Atomic Research Centre, India). The absorbed dose rate in water was measured to be 3.75 kGy/h using reference alanine dosimeters. The temperature during gamma-ray irradiations was maintained at 372oC and the electronic equilibrium conditions were during irradiation.

RESULTS AND DISCUSSION

Absorption Spectra

The absorption spectra of chlorophenol red CPR/PVA with 0.32 phr dye and PVB-co-PVA/PVAC with 0.64 phr dye were recorded before and after irradiation to different doses and are shown in Figs. (1) and (2) respectively. Fig. (1) shows the absorption spectra of CPR/PVA films ([CPR]= 0.32 phr) without chloral hydrate the absorbance at 588 nm decreases slowly as the absorbed dose increases however, an apparent bleaching occurs at doses up to 10 kGy. Fig. (2) represents the absorption spectra of PVB-co-PVA/PVAC ([CPR]= 0.64 phr) of CPR without chloral hydrate. It could be noticed that the bleaching reaction occurs at high dose of 90 kGy.

The absorption spectra of chlorophenol red CPR/PVA with 0.32 phr dye and 13.33 phr chloral hydrate and PVB-co-PVA/PVAC with 0.64 phr dye and 39.99 phr chloral films were recorded before and after irradiation to different doses and are shown in Figs. (3) and (4), respectively. The absorption spectra of the unirradiated film show in Fig. (3), a main absorption band in the visible

S. Eid. et al., J. Rad. Res. Appl. Sci., Vol. 4, No. 1 (A) (2011) 48

region at 588 nm which is characteristic to purple color. Due to irradiation, the amplitude of this peak at 588 nm decreases gradually while a little peak at 423 nm begins to develop and increase with increasing dose. This is due to the consequent lowering of the pH of the film caused by the HCL generated from the radiolysis of chloral hydrate. Fig. (4) shows PVB-co-PVA/PVAC with 0.64 phr dye and 39.99 phr chloral films have a main absorption band in the visible region characteristics to yellow color peaking at 423 nm, because of the pH effect of the media. The amplitude of this band decreases gradually with the increase of gamma-dose i.e. CPR bleached at dose up to 10 kGy.

Dose, kGy

WaveLength, nm

300 400 500 600 700

Absorbance

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1 02 13 24 35 46 67 88 10

Fig. (1): Absorption spectra of CPR/PVA films without chloral hydrate unirradiated and irradiated to different absorbed doses. [CPR] = 0.32 phr.

Dose, kGy

WaveLength, nm

300 400 500 600 700

Absorban

ce

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

1 02 103 164 90

Fig. (2): Absorption spectra of PVB-co-PVA/PVAC without chloral hydrate unirradiated and irradiated to different absorbed doses. [CPR] = 0.64 phr.

S. Eid. et al., J. Rad. Res. Appl. Sci., Vol. 4, No. 1 (A) (2011) 49

Dose, KGy

Wavelength, nm

300 400 500 600 700

Abso

rban

ce

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1 02 0.253 0.54 15 1.256 1.57 28 3.5

Fig. (3): Absorption spectra of CPR/PVA films containing chloral hydrate unirradiated and irradiated to different absorbed doses. [CPR] = 0.32 phr, [CH] = 13.33 phr.

Dose, kGy

WaveLengh, nm

300 400 500 600 700

Abs

orba

nce

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

1 02 13 24 35 6

Fig. (4): Absorption spectra of PVB-co-PVA/PVAC films containing chloral hydrate unirradiated and irradiated to different absorbed doses. [CPR] = 0.64 phr, [CH] = 39.99 phr.

Response curves

The response curves of CPR/PVA films with 0.32 phr chlorophenol red and different chloral hydrate concentrations are shown in Fig. (5). The response were established in terms of change in absorbance per thickness (A.mm-1) at

S. Eid. et al., J. Rad. Res. Appl. Sci., Vol. 4, No. 1 (A) (2011) 50

D o s e , k G y

0 1 2 3 4

A.

mm

-1

0

2

4

6

8

1 0

1 2

1 4

1 6

1 8

2 0

1 3 . 3 3 2 6 . 6 63 9 . 9 9

[ C H ] , p h r

588 nm against the absorbed dose (∆A=A0-Ai, where A0 and Ai are values of absorbance at 588 nm for the unirradiated and irradiated films respectively). Each point on the dose response curve represents the mean of optical density measurement of five dosimeter films irradiated to the same dose. It can be noticed that all curves show the same trend but differ in response value. The useful dose range extends up to 3.5 kGy.

Fig. (6) shows the response curves of PVB-co-PVA/PVAC with 0.64 phr of CPR and different chloral hydrate concentration, in terms of change in absorbance per thickness at 423 nm against the absorbed dose. The useful dose range extends up to 8 kGy.

Fig. (5): Response curves of CPR/PVA films containing 0.32 phr CPR and different chloral hydrate concentrations, max = 588 nm.

Dose, kGy

0 2 4 6 8 10

A.m

m-1

0

2

4

6

8

10

12

14

16

18

20

13.3326.6639.99

[CH], phr

Fig. (6): Response curves of PVB-co-PVA/PVAC films containing 0.64 phr CPR and different chloral hydrate concentrations, max = 423 nm.

S. Eid. et al., J. Rad. Res. Appl. Sci., Vol. 4, No. 1 (A) (2011) 51

Fig. (7) Represents the response curves of CPR/PVA and PVB-co-PVA/PVAC films without chloral hydrate. max = 588 nm for PVA and max = 423 nm for PVB. In which the dose range of CPR/PVA extends up to 10 kGy, while for PVB-co-PVA/PVAC up to 90 kGy.

Dose, kGy

0 2 4 6 8 10 12 14 16 18 20 90 95100

A.m

m-1

0

2

4

6

8

CPR/PVACPR/PVB Co polymer

Fig. (7): Response curves of CPR/PVA and PVB-co-PVA/PVAC films without chloral hydrate. max = 588 nm for PVA and max = 423 nm for PVB.

The radiation chemical yield (G-Value)

The radiation-chemical yield (G-value) is defined as the number of moles of dye degraded by the absorption of 1 J of energy (mol/J). The G-value is calculated from the general relation(13).

G (-dye) = ΔA/D.ε.ρ.b (mol/J)

Where , A is the change in absorbance at max, b is the optical path length (1cm), ε is the linear molar extinction coefficient at max (L.mol-1cm-1), ρ is the density of the dosimeter (g.cm-3), D is the absorbed dose (Gy).

The relation between Ao/b (cm-1) as a function of concentration of CPR (in mol/L) giving straight lines, its slope is the molar extinction coefficient, ; and for CPR/PVA it was calculated to be 1777.77L. mol-1.cm-1 and for PVB-co-PVA/PVAC was 12307.06 L. mol-1.cm-1. The density of PVA is 1.25 g/cm3 while for PVB-co-PVA/PVAC is 1.083 g/cm3. The G-value for CPR calculated for both PVA and PVB-co-PVA/PVAC films containing different concentrations of chloral hydrate and the results are tabulated in Table (1).

S. Eid. et al., J. Rad. Res. Appl. Sci., Vol. 4, No. 1 (A) (2011) 52

Table (1): The calculated G-values for both CPR/PVA and CPR/PVB copolymer at different chloral hydrate concentrations

Chloral hydrate, phr G-value, mol.J-1

CPR/PVA PVB-co-PVA/PVAC

0 0.0522 0.585x10-4

13.33 0.3865 0.0126

26.66 0.4273 0.0169

39.99 0.4811 0.0228

From this table, it can be seen that the G-value increases with the increase of chloral hydrate concentrations for both PVA and PVB-co-PVA/PVAC films.

Humidity during irradiation

The effect of relative humidity (RH) during irradiation on the response of CPR/PVA and PVB-co-PVA/PVAC films were investigated by irradiating the films 0.32phr CPR/PVA with 13.66 phr chloral hydrate and 0.64 PVB-co-PVA/PVAC with 39.99 phr chloral hydrate to a dose of 2.5 kGy at different relative humidity (0, 12, 23, 54, 76 and 92% RH). The different relative humidity was maintained by using different saturated salt solutions(14). The films were stored before irradiation for three days period under the same relative humidity conditions as when irradiated, so that equilibrium moisture content in dosimeter is established during irradiation.

Fig. (8) represents the variation in Ai/Ao at 588 nm for PVA and 423 nm for PVB-co-PVA/PVAC, as function of percentage relative humidity during irradiation, relative to that at 33% one. It can be seen that for PVB-co-PVA/PVAC films, the response of the films are almost flat in the range of RH from 0-95%, where the variation in response over the whole RH range never exceed 5%. While in CPR/PVA films, there is a gradual decrease in response with the increase of RH. This film can be used as a label only in the RH range from 10-50 RH%.

S. Eid. et al., J. Rad. Res. Appl. Sci., Vol. 4, No. 1 (A) (2011) 53

Relative Humidity, RH%

0 20 40 60 80 100 120

Relat

ive

Abso

rban

ce, A

i/Ao

0.96

0.98

1.00

1.02

1.04

CPR/PVA at 588 nmCPR/PVB Co- at 423 nm

Fig. (8): Variation of relative Ai/Ao of CPR/PVA and CPR/PVB-co-PVA/PVAC films as a function of relative humidity during irradiation. max = 588 nm for PVA and max = 423 nm for PVB.

Pre-irradiation stability

The color stability of CPR/PVA and CPR/PVB-co-PVA/PVAC films were tested before irradiation by storing the films at 35% RH at room temperature under laboratory fluorescent light. Fig. (9) represents the change in Ai/Ao of the tested films, were measured at 588 nm for PVA films and 423 nm for PVB co-polymer films at different intervals time during the storage period of 30 days. It can be seen that, both films exhibit excellent stability before irradiation, where the variation in absorbance during the 30-day storage period is less than + 2%.

Time, days

0 5 10 15 20 25 30 35

Relative Abs

orba

nce, A

i/Ao

0.96

0.98

1.00

1.02

1.04 PVA (=588 nm)PVB co polymer (=423 nm)

Fig. (9): Pre- irradiation stability of CPR/PVA ([CPR] = 0.32 phr) and CPR/ PVB-co-PVA/PVAC ([CPR] = 0.64 phr) films.

S. Eid. et al., J. Rad. Res. Appl. Sci., Vol. 4, No. 1 (A) (2011) 54

Post-irradiation stability

CPR/PVA films containing 0.32 phr of dye with 13.66 phr chloral hydrate, and CPR/ PVB-co-PVA/PVAC films containing 0.64 phr dye with 39.99 phr chloral hydrate, irradiated to a dose of 2.5 kGy, then stored at 35% RH at room temperature 25+3oC in the laboratory fluorescent light. The absorbance of these films were measured at 588 nm for PVA films and 423 nm for PVB-co-PVA/PVAC one, at different intervals of time during the storage period of 30 days. The change in absorbance as a function of storage times relative to that zero time immediately after irradiation, are shown in Fig. (10). From this figure, it can be seen that, CPR/ PVB-co-PVA/PVAC films show a good stability, while CPR/PVA films show a gradual decrease in absorbance, with around 4%, during the first 10 days then tends to be stable to the end of the storage period.

Time, days

0 5 10 15 20 25 30 35

Rel

ative

Abso

rban

ce, A

i/Ao

0.90

0.95

1.00

1.05

1.10

PVA (=588 nm)PVB co polymer (=423 nm)

Fig. (10): Post- irradiation stability of CPR/PVA ([CPR] = 0.32 phr) and CPR/PVB-co-PVA/PVAC ([CPR] = 0.64 phr) films.

CONCLUSION

By irradiating CPR/PVA films containing chloral hydrate, the color of these films changes from purple to yellow indicating the acid formation. These films can be used as dosimeters in the dose range 0.5-3.5 kGy reflecting the suitability for use in some food irradiation applications. CPR/ PVB-co-PVA/PVAC films are bleached when exposed to gamma rays. The useful dose range of these films extended up to 8 kGy. The dose range depends on chloral hydrate concentrations. Both films have negligible humidity effects in the range of 0-50% RH, as well as good pre- and post- irradiation stability.

S. Eid. et al., J. Rad. Res. Appl. Sci., Vol. 4, No. 1 (A) (2011) 55

REFERENCES

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6. Abdel-Fattah, A.A. and Miller, A., Temperature and time combined effects on radiochromic film dosimeters. Radiat. Phys. Chem., 47, 611 (1996).

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material. U.K., pat. Aplication G.B., 21, 249 A.

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