Polymer reflectance changed by gamma irradiation

Radiat. Phys. Chem. Vol. 34, No. 5, pp. 797-799, 1989 Int. J. Radiat. AppL Instrum., Part C

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POLYMER REFLECTANCE C H A N G E D BY G A M M A IRRADIATION A. A. HAMZA 1, M. A. KABEEL l and A. M. EL-SAID 2 IPhysics Department, Faculty of Science, Mansoura University, Mansoura and 2Misr Spinning and Weaving Co., E1-Mehala El-Kobra, Egypt (Received in revised f o r m 16 December 1988)

Abstract--The change in the colour of polymer fibre is suggested to develop a simple method for 3'-ray dosimetry. The spectral reflectance values of the unirradiated and 3,-irradiated nylon-6 and Dralon fibres were measured spectrophotometrically. Irradiation was carried out over a period of 24--1948h and the dose rate was maintained at 14.7_0.2rads -t. The tristimulus values, dominant wavelength and excitation purity of these samples were calculated. The change in these colorimetric parameters by the applied dose was evaluated. The colour difference between the unirradiated samples and those irradiated with different doses of 3,-irradiation was calculated. This study gives a clear picture about the changes in colour of fibre by 3,-irradiation.

INTRODUCTION

Extensive work has been done on the effects of ),-radiation on polymers and polymeric fibres. The radiation processing of textiles have been reviewed by Gilbert and Stannett (1967). Stannett et al. (1977) studied some fundamental considerations related to the radiation modification of fibres and fabrics. The influence of 7-radiation on the physical and chemical properties of polymers has been reported by Charlesby (1960) and Chapiro (1962). The physical and chemical changes that may occur in polymers after exposure to high-energy radiation have been evaluated by many techniques. Henley (1954) used poly(vinylchloride)-dye systems as a monitoring device for radiation and Lawandy (1982) has shown that the colour changes in a polymer can be used to determine radiation damage in this polymer. Keller (1982) presented a survey of a series of studies on the influence of crystallinity on the radiation-induced effects, cross-linking in particular, in polyethylene and paraffins. Hamza et al. (1986) used multiple-beam Fizeau fringes in transmission and in reflection for the studies of the optical properties of v-irradiated Dralon fibres. Empirical formulae were suggested to represent the variation of refractive indices and the birefringence with the dose in an attempt to find a suitable sensor for the determination of an unknown dose of radiation. Hamza and Mabrouk (1988) studied the optical anisotropy in ?-irradiated polymeric fibres under vacuum. They measured the refractive indices and birefringence of these fibres interferometrically. Recently Hamza et al. (1989) studied interferometrically the change of optical orientation function and molecular structure of nylon-6 fibres due to )'-irradiation under vacuum. The increasing use of )'-irradiation in industry

and medicine makes it necessary to develop simple methods for )'-ray dosimetry. COLOUR CHANGES IN IRRADIATED POLYMERS

Most polymers acquire a colour under irradiation as do most organic chemicals, but the range of doses in which discolouration becomes noticeable varies widely depending on the chemical structure of the polymer (Chapiro, 1962). The chemical changes in irradiated polymers include crosslinking, chain scission and recombination of broken chains (Parkison, 1969). Colour changes in irradiated polymers are very strongly dependent upon the type of irradiation used and upon the temperature at which radiation is carried out. The colour is sometimes different for irradiation carried out in vacuum and in air (Chapiro, 1956). The presence of trace amounts of additives (plasticizer, stabilizer, etc.) may further alter the discolouration. When various plastic containing dyes or pigments are subjected to radiation, these colours will change. The colour changes are caused by very small radiation doses which were used for dosimetry purposes. The changes in colour on or after irradiation arise from two causes (Charlesby, 1960): (i) the change due to the polymer itself, revealed by increase in absorption in the ultraviolet and violet end of the spectrum, and (ii) the appearance of new bonds in the visible region between 600 and 800 nm which have only been observed for plasticized polymer. In this work, a study of the colour changes in irradiated fibre is presented in order to introduce a basis for constructing a simple sensor for the measurement of different doses. These fibres are nylon-6 fibres from an Egyptian manufacturer and Dralon

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fibres which are Bayer textile fibres belonging to the group of polyacrylonitrile fibres.

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IRRADIATION PROCEDURE

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Irradiation was carded out using 10,000 Ci 6°Co. Dosimetry was achieved using the standard Fricke procedure. In this study; irradiations were carried out in the presence of air using sealed containers for a period of 24-1948 h. The dose rate was maintained at 14.7 ___0.2 rad s -]. The exposure doses applied to the two polymer fibres are 0, 1.27, 10.12, 22.46, 27.49 and 103.10 Mrad.

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EXPERIMENTAL RESULTS AND DISCUSSION Fig. 2. S p e c t r a l reflectance c u r v e s o f D r a l o n fibres.

The spectral reflectance curves for the substrates nylon-6, Dralon and all irradiated fibre samples were carded out using the (ACS 600) colour control system of applied Colour System, U.S.A., which is located in Misr Spinning and Weaving Company, E1-Mehala EI-Kobra, Egypt. The reflectance values were measured in the visible range of spectrum from 400 to 700 rim. The spectral reflectance curves of substrate and irradiated nylon-6 samples are shown in Fig. 1 and those of Dralon are given in Fig. 2.

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The X, Y, Z tristimulus values of the substrates and the irradiated fibres of the two samples are given in Table 1. The dominant wavelength 2d and purity Pe of each colour of irradiated samples were determined by the graphical method and are also given in Table 1. The purity Pe of each coiour gives an indication of the strength of that colour. An important aspect of colour appearance is the assessment of colour differences. The measurement of colour difference has a direct bearing on the establishment of perceptually uniform colour scales and is of considerable importance to industry when colour tolerance must be specified and controlled. The colour-difference AE(L*a*b*) equation is used in this study. It is represented as follows (Judd and Wyszecki, 1975):

AE(L*a*b*) = [(Aa*)2 + (Ab*) 2 + (AL*)2] 1i2 with

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Fig. 1. S p e c t r a l r e f l e c t a n c e c u r v e s o f n y l o n - 6 fibres. Table 1. Tristimulus values, dominant wavelength 2d and purity of the irradiated .' nylon-6 and Dralon fibres Tristimulus values Dose (Mrad)

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Purity

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0 1.27 10.12 22.46 27.49 103.10

82.46 80.07 81.26 76.09 75.21 74.72

87.26 84.85 86.48 81.01 79.57 79.11

90.19 85.40 80.51 62.04 58.59 55.48

568.59 566.96 568.37 570.24 571.06 572.12

0.0237 0.0399 0.0873 0.2034 0.2268 0.2542

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0 1.27 10.12 22.46 27.49 103.10

78.27 72.62 60.66 49.87 49.72 40.36

83.20 77.13 61.97 49.46 49.04 38.49

81.95 68.97 40.41 26.68 25.68 17.70

569.02 570.00 574.67 576.33 576.63 578.55

0.0555 0.1191 0.3030 0.4031 0.4185 0.4825

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Polymer reflectance changes by ~,-irradiation

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changes in the irradiated materials. The studied colourimetric parameters of the y-irradiated fibres, such as the tristimulus values, dominant wavelength and the purity, and their variations with the applied dose could be used as a basis for constructing a simple method for ~,-ray dosimetry.

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REFERENCES I

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Dose ( x l O 6 r e d s )

Fig. 3. RelationshipbetweencolourdifferenceAE(L*a*b*) and dose.

In these equations, the tristimulus values X0, Y0, Z0 define the colour of the nominally white object-colour stimulus. The colour differences were calculated between the substrate as a reference sample and other irradiated samples. Figure 3 represents the relationship between the colour difference values AE(L*a*b*) and dose. It is known that free radicals are produced as a result of treating polymers, oligomers and monomers with high energy radiation. Almost all the ionic species which are produced are destroyed by the immediate recombination of the ejected electrons with the parent positive molecule ions (cf. Stannett et al., 1977). This treatment is accompanied by colour

Chapiro A. (1956) Jr. Chim. Phys. 53, 895. Chapiro A. (1962) Radiation Chemistry of Polymeric Systems, p: 385. Interscience, New York. Charlesby A. (1960) Atomic Radiation and Polymers. Pergamon Press, Oxford. Gilbert R. D. and Stannett V. (1967) 1sot. Radiat. Technol. 4, 403. Hamza A. A. and Mabrouk M. A. (1988) Radiat. Phys. Chem. 32, 543. Hamza A. A., Ghander A. M., Oraby A. H., Mabrouk M. A. and Guthrie J. T. (1986) J. Phys. D: AppL Phys. 19, 2443. Hamza A. A., Ghander A. M. and Mabrouk M. A. (1989) Radiat. Phys. Chem. 33, 231. Henley E. J. (1954) Nucleonics 12, 62. Judd D. B. and Wyszecki G. (1975) Color in Business, Science and Industry, Wiley, New York. Keller A. (1982) In Developments in Crystalline Polymers, Vol. 1 (Edited by Bassett D. C.), p. 37. Applied Science, London. Lawandy S. N. (1982) Elastomerics 33. Parkison W. W. (1969) Encyclopedia of Polymer Science and Technology, Vol. 11. p. 783, Interscience, New York. Stannett V., Walsh W. K., Bittencourt E., Liepins R. and

Surles J. R. (1977) J. Appl. Polym. Sci., Appl. Polym. Symp. 31, 201.