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Effect of electron beam irradiation on surgical rubber gloves
Nuclear Instruments and Methods in Physics Research B 140 (1998) 171±177
Eect of electron beam irradiation on surgical rubber gloves Chantara Thevy Ratnam *, Khairul Zaman Malaysian Institute for Nuclear Technology Research, MINT, Bangi, 43000 Kajang, Malaysia Received 9 October 1997; received in revised form 26 November 1997
Abstract This paper outlines the eects of electron beam irradiation on surgical rubber gloves. The tensile strength, elongation at break and modulus were evaluated as function of dose range 20±100 kGy minimum dose, dose uniformity ratio, 3.1, and both, accelerated and normal aging, were used to study the stability of the irradiated gloves after irradiation. The surgical gloves were found to be useful up to the highest dose tested. Ó 1998 Elsevier Science B.V. Keywords: Irradiation; Electron beam; Dose; Gloves; Tensile properties
1. Introduction The radiation sterilization of medical devices has been carried out by using gamma rays from Co-60 and electron beam (EB) generated from accelerator. Although current industrial practices favour the use of gamma irradiators, for medical product sterilization, the demand for electron beam sterilization is growing as a result of ever increasing price of Co-60 source and its unstable supply. Electron beam technology enables irradiation at a high dose rate, thus, achieving at the same time a high product throughput as well as less damage caused by oxidative degradation. Besides
* Corresponding author. Tel.: 6 03 825 0510; fax: 6 03 820 2968; e-mail: [email protected]
this, the absorbed dose rate can be easily controlled and varied, switched on and o quickly with no radiation energy loss during shutdown, and need no replenishment with time. William [1] has discussed in detail the applications of EB for the sterilization of medical devices. Currently, USA, Canada, Denmark, Sweden, Switzerland, Germany, Poland and Japan are among the countries utilizing EB technology for sterilization of medical products [2]. In view of these advantages with regard to sterilization, Kamaruddin et al. [3] have established various parameters in the irradiation of surgical rubber gloves using our 3.0 MeV electron accelerator. Their ®ndings include the determination of product loading pattern in order to ensure that the gloves receive a minimum dose of 25 kGy. In our present work, we report on the eects of electron beam radiation on the physical and aging properties of surgical rubber gloves.
0168-583X/98/$19.00 Ó 1998 Elsevier Science B.V. All rights reserved. PII S 0 1 6 8 - 5 8 3 X ( 9 8 ) 0 0 0 0 4 - 4
172
C. Thevy Ratnam, K. Zaman / Nucl. Instr. and Meth. in Phys. Res. B 140 (1998) 171±177
2. Experimental
2.3. Temperature increase
2.1. Material
Special temperature indicators Type D641 manufactured by Technol Seven, Japan, were placed at the top and in the middle (®fth pair) of each box in order to measure the rise in temperature of the gloves during irradiation. The temperature was read immediately after irradiation.
Commercial grade powder free surgical rubber gloves of size 7 were supplied by a local glove manufacturer. The gloves, made from sulphur-vulcanized natural rubber latex, contain additives such as sulphur and zinc oxide. However, the exact formulation is not known. 2.2. Irradiation Boxes, with external dimensions of 29 cm ´ 15 cm ´ 4 cm, were ®lled with eight pairs of gloves and irradiated by double sided irradiation technique using the 3.0 MeV electron accelerator. Cellulose tri-acetate (CTA) ®lm was used to monitor the absorbed dose during irradiation. The CTA ®lms employed were of the type FTR125, supplied by Fuji Film, Japan. The irradiation dose (minimum dose), beam current and the dose rate employed in this work are detailed in Table 1. The dose uniformity ratio (DUR) was calculated for gloves irradiated at a minimum dose of 25 kGy with the following equation: DUR Dose maximum=Dose minimum:
2.4. Tensile properties measurements The gloves were cut into 115 mm long dumbbell shape as per die C of ASTMD412 [4]. The dumbbell were conditioned at 25°C overnight prior to tensile test measurements. The tensile strength (Ts), elongation at break (Eb), and modulus at 500% elongation (M500) of the irradiated and non-irradiated gloves were determined in accordance with the ASTM D412-C [4]. This was done using the Toyoseiki Strograph-R1 universal testing machine at a crosshead speed of 500 mm/min. 2.5. Accelerated aging In order to elucidate the eects of aging on the irradiated gloves, dumbbells which were cut from the gloves following ASTM D412-C [4] were aged at 70 2°C for 166 2 h in accordance with
Table 1 Eect of various EB irradiation parameters on tensile properties of surgical rubber gloves Dose (kGy)
Dose rate (kGy/s)
Current (mA)
Product temperature, °C (middle)
Ts (MPa)
Eb (%)
M500 (MPa)
0 20 20 20 20 25 25 25 25 40 50 50 50 50 100 ASTMD3577
) 0.12 1.18 2.35 3.53 0.12 1.18 2.35 3.53 3.53 0.12 1.18 2.35 3.53 3.53
)
) 40 40 40 40 45 50 50 50 55 55 60 60 70 85
29.1 0.5 30.2 0.4 30.03 0.6 30.01 0.5 29.98 0.4 28.79 0.8 29.31 0.7 29.16 0.5 31.05 0.5 29.92 0.4 29.66 0.6 29.78 0.4 29.11 0.4 29.11 0.5 30.71 0.5 24 min.
950 20 950 20 950 20 900 20 950 20 950 20 950 20 950 20 950 20 950 20 900 20 1000 2 0 1000 2 5 950 20 950 20 750 min.
2.45 0.03 2.36 0.04 2.37 0.02 2.49 0.02 2.44 0.01 2.34 0.03 2.4 0.03 2.36 0.04 2.42 0.02 2.34 0.03 2.42 0.01 2.33 0.04 2.36 0.03 2.39 0.01 2.46 0.02 5.5 max.
1 10 20 30 1 10 20 30 30 1 10 20 30 30
C. Thevy Ratnam, K. Zaman / Nucl. Instr. and Meth. in Phys. Res. B 140 (1998) 171±177
173
ASTM D573 [5] prior to tensile property measurements. Tests were done on both irradiated and non-irradiated samples. Again the dumbbell test pieces were conditioned at 25°C overnight before they were subjected to tensile tests.
oxidation of polymers. Radiation induced oxidation of polymers is a multistage process which, in general, is described by the same reactions as for usual oxidation processes [12±15]: Initiation:
2.6. Storage studies
RH ! R H;
In order to con®rm degradation during storage, the tensile properties of the irradiated gloves were measured after 1, 2, 3, 4, 5 and 6 months storage at room temperature. In all tensile measurements at least seven specimens (cut from three gloves) were tested. The average and standard deviations were calculated. The representative gloves for tensile measurements were always taken at the dose minimum with reference to CTA ®lm readings.
1
Propagation of the chain: R O2 ! RO2 ;
2
RO2 RH ! ROOH R :
3
Branching of the chain: ROOH ! RO HO;
4
RO RH ! ROH R;
5
HO RH ! HOH R :
6
Termination reactions: 3. Results and discussion
R R ! R ÿ R;
7
3.1. Tensile properties of irradiated surgical rubber gloves
ROO ROO ! ROOR O2 ;
8
R ROO ! ROOR:
9
A lot of polymers used in the medical ®eld show various degrees of degradation after irradiation exposure. This can be seen either by visual or mechanical measurements. The sterilizing radiation eects on selected polymers is described in detail by Skiens [6]. Whereas the detailed understanding of the radiation induced eects on polymers in oxidizing environments can be found in a few articles [7±10]. The absolute values of Ts, Eb and M500 of the gloves irradiated at various dose rates and the respective minimum doses are given in Table 1. It is apparent from Table 1 that the tensile properties do not show appreciable change with increasing dose and increasing dose rate. This indicates that the tensile properties of the gloves were not aected by EB irradiation during the irradiation exposure, even at 100 kGy minimum absorbed dose. However, in contrast, Kohjiya et al. [11] reported that the Ts and Eb of sulphur vulcanized natural rubber vulcanizates decreased with 10 kGy irradiation in gamma rays. This dierence could be explained by the light of radiation induced
Here, R and R represents the polymer chain and polymer radical respectively. Apart from this, from chemiluminicence (CL) measurements, Kadir and co-workers [16] have con®rmed the existence of peroxy radicals in irradiated sulphur vulcanized surgical rubber gloves. These oxidative reactions depend on oxygen diusion and have been discussed in detail by several workers [17,18]. The dierences between our results and Kohjiya et al. [11] are expected since the gamma irradiation from Cobalt 60 is delivered over a period of minutes to hours which allows for more oxygen diusion, resulting in increased oxidative degradation. On the contrary, the EB machine delivers the same dose in a fraction of a second, thus, limiting the oxygen diusion which results in less degradation. This suggests that EB would be a better choice for sterilization of rubber gloves. It is important to note that at a minimum dose of 25 kGy, a DUR of 3.1 was obtained in this study. This DUR value also in perfect agreement
174
C. Thevy Ratnam, K. Zaman / Nucl. Instr. and Meth. in Phys. Res. B 140 (1998) 171±177
with the previous report by Kamaruddin et al. [3] Thus, at a minimum dose of 25 kGy the maximum dose will be 78 kGy. Evidently, this study also con®rms that, the Ts, Eb and M500 of the gloves almost remain unchanged with increasing irradiation dose at the similar irradiation condition as the DUR established. In fact, the results in Table 1 indicate that 100 kGy is acceptable with respect to the tensile properties of the gloves. Hence, it would be safe to recommend the irradiation of these gloves using the 3 MeV EB machine for the purpose of sterilization as long as the minimum dose exceeds 25 kGy. 25 kGy is generally accepted as the minimum dose required to sterilize medical devices. 3.2. Product temperature control Absorbed dose is analogous to temperature rise, which relates to the same concept of absorbed energy per unit mass. An absorbed dose of 10 kGy is equal to 2.4 calories per gram, which would increase the temperature of water by 2.4°C [19]. Most polymeric materials have heat capacities lower than water and exhibit correspondingly higher temperature rise [20]. Generally, the rates of chemical reactions increase with temperature due to the greater proportion of molecules which have energies in excess of the activation energy, and this may apply to the radiation induced reactions in polymers. Referring to Table 1, we observed that there is an increase in temperature on the glove (product) with increasing dose and dose rate. However, with the double sided irradiation technique which was employed in this studies, the increase in temperature in the top and the ®fth pair of the gloves were found to be the same. Again, the retention in tensile properties of the gloves after irradiation con®rms that the increase in temperature does not cause any signi®cant damage to the gloves. This observation could be explained by the fact that in solid polymers the radiation induced reactions at elevated temperatures are also governed by their glass transition temperatures, Tg . Substantial changes in molecular mobility occur across this transition and the rate of chemical reactions is greatly aected [21]. Since the Tg of natural rubber is about )69°C [22], far
above the temperatures observed in Table 1, considerable eect was not noted. Consequently, it can be concluded that the gloves did not deteriorate at the range of temperatures which were observed during irradiation. Clearly, it is not necessary to provide cooling of the gloves before, during or after the irradiation treatment cycle. 3.3. Accelerated aging properties of EB irradiated surgical rubber gloves It is well known that some polymers such as polyethylene and polypropylene degrade by residual peroxy radicals during storage after irradiation. In addition, peroxides formed during the course of the irradiation can undergo thermal decomposition, providing a chain branching step which yields free radicals that can then participate in the oxidation propagation step [23]. The chemistry of auto-oxidation for polymers has been described in detail in the book by Grassie and Scott [24] and will not be discussed here. Therefore, in order to predict the degradation of irradiated gloves during storage, the physical properties of EB irradiated gloves were measured after the gloves were subjected to a temperature of 70 2°C for 166 2 h. Table 2 shows the tensile properties of surgical rubber gloves after aging. Comparison of the Ts before and after accelerated aging, shows that there is no remarkable change observed at all doses. However, a slight decrease in Eb and M500 is observed after aging indicating that degradation occurred during the accelerated aging. A similar tendency is also shown by the non-irradiated samples suggesting that the general decrease in M500 and Eb may not be associated with the oxidation chemistry involving reaction species previously formed by irradiation such as long-lived radicals or peroxides [7,23]. In agreement with this it should also be noted that the decline in the above properties with accelerated aging is marginal with increasing dose. However, the decrease in Eb on accelerated aging is very low compared with the ASTMD3577 [25] speci®cations which are shown in Table 2. Accelerated thermal aging experiments are very useful approach for predicting post-irradiation degradation, while actual room temperature aging experiments are also
C. Thevy Ratnam, K. Zaman / Nucl. Instr. and Meth. in Phys. Res. B 140 (1998) 171±177
175
Table 2 Eect of EB irradiation on accelerated aging properties of surgical rubber gloves Dose (kGy)
0 20 25 40 50 100 ASTM D3577
Before aging
After accelerated aging
TS (MPa)
Eb (%)
M500 (MPa)
TS (MPa)
Eb (%)
M500 (MPa)
29.1 0.5 29.98 0.4 31.05 0.5 29.92 0.4 29.11 0.5 30.71 0.5 24 min.
950 950 950 950 950 950 750
2.45 0.03 2.44 0.01 2.42 0.03 2.34 0.03 2.39 0.01 2.46 0.02 5.5 max.
30.31 30.37 29.86 30.87 30.06 30.05 18 min.
900 900 900 900 900 900 560
2.32 2.37 2.33 2.30 2.31 2.34 )
20 20 20 20 20 20 min.
0.5 0.6 0.4 0.5 0.8 0.4
20 20 20 20 20 20 min.
0.02 0.02 0.01 0.03 0.03 0.03
Dose rate: 3.53 kGy/s. Aging condition: 70 2°C/166 2 h.
done to further con®rm the severity of post-irradiation damage. 3.4. Storage eect It is apparent from Fig. 1 that the Ts values exhibit a uniform fall with storage time. Importantly, Fig. 1 also proves that the irradiated samples present more pronounced drop in Ts with storage time compared to the non-irradiated one. It has been reported that the species most often responsible for this phenomenon are the trapped radicals or peroxides [7,23]. Dunn et al. [26] has described that the peroxy radicals formed during irradiation of PP can lead to the formation of peroxides as in Eqs. (2), (8) and (9). The peroxides remain in the polymer for a long period of time, and upon dissociation causing chain scissions as a consequence of
Fig. 1. Storage eect on tensile strength of irradiated gloves.
which there is progressive deterioration in strength. The downward trend in Ts of the irradiated gloves clearly reveals the radiation induced degradation on storage. This observed trend towards lower values of Ts for the irradiated gloves is considered small based on the absolute values of the six months storage being within the speci®cation of ASTM D3577. In addition, it is evident from Figs. 2 and 3 that the Eb and M500 show only slight decrease with storage time, suggesting that the post-irradiation degradation is rather small and unlike as reported for PP [26]. This observation could be attributed to the dierence between PP and natural rubber in the nature of kinetic changes in radical concentrations as a function of time both during and after
Fig. 2. Storage eect on elongation at break of irradiated gloves.
176
C. Thevy Ratnam, K. Zaman / Nucl. Instr. and Meth. in Phys. Res. B 140 (1998) 171±177
in accordance to protocols established by the Association for the Advancement of Medical Instrumentation [28]. Acknowledgements
Fig. 3. Storage eect on Modulus 500 of irradiated gloves.
irradiation [27]. Elastomers are generally characterized by a high chain mobility at room temperature. This suggests that in natural rubber, a rapid termination of primary radicals during irradiation lowers the overall radical population, and account for less oxidative degradation during storage. On the other hand, PP is a semicrystalline polymer and the mobility of the radicals is strongly reduced in the crystalline region, and the post-irradiation survival is long resulting in severe storage embrittlement. These imply that the EB irradiation has only a minor in¯uence on the overall tensile properties during storage of the irradiated gloves. 4. Conclusions From the data obtained, it can be demonstrated that the EB sterilization up to 100 kGy delivered dose, has no deleterious eects on the tensile properties of the surgical rubber gloves. The retention in tensile properties up to a minimum dose of 100 kGy implies that the gloves are not degraded by the maximum dose absorbed while the minimum absorbed dose is above 25 kGy in the case of an irradiation with DUR up to 4. Thus, EB would seem to be a better choice for the sterilization of rubber gloves, considering our product quali®cation which identi®ed that the glove can be sterilized at maximum tolerable dose without causing any adverse eect on the properties of the gloves. Further to this, subsequent experiments will be carried to ``®ne tune'' the actual dose limits
The authors would like to thank the JICA team for the technical cooperation and Mr. Kamaruddin Bahari for his initial involvement in this work. A special appreciation also goes to Ms. Khuzaimah and N. Mohid for their assistance during the preparation of this manuscript.
References [1] J.M. Williams, Radiat. Phys. Chem. 42 (4) (1980) 585. [2] J.G. Leemhorst, Internat. J. Electron Beam Gamma Radiat, Process. 7 (1) (1993) 4. [3] B. Kamaruddin, H. Tachibana, Z.M.D. Khairul, in: Proceedings of National Executive Management Seminar On Electron Beam Sterilization of Medical Products, Kuala Lumpur, 1994. [4] ASTM D412, Standard test methods for rubber properties in tension, Annual Book of ASTM Standards, vol. 9.01, 1987. [5] ASTM D573, Standard test methods for rubber ± deterioration in air oven, Annual Book of ASTM Standards, vol. 9.01, 1988. [6] W.E. Skiens, Radiat. Phys. Chem. 15 (1980) 47. [7] R.L. Clough, K.T. Gillen, J. Polym. Sci., Polym. Chem. 19 (1981) 2041. [8] K.T. Gillen, R.L. Clough, J. Polym. Sci., Polym. Chem. 23 (1985) 2683. [9] K.T. Gillen, R.L. Clough, Polym. Deg. Stab. 17 (1989) 31. [10] K.T. Gillen, R.L. Clough, Poly. Eng. Sci. 29 (1989) 29. [11] S. Kohjiya, Y. Matsumura, S. Yamashita, T. Matsuyama, H. Yamaoka, Jpn. Rubber Assoc. 1 (1983) 39. [12] W. Hawkins, F. Winslow, in: E.M. Fettes (Ed.), Chemical Reactions of Polymers, Wiley/Interscience, New York, 1964. [13] M. Kryszewski, B. Nadolski, M. Znjewicz, J. Polym. Sci., Polym. Symp. 57 (1976) 129. [14] M. Dole, The Radiation Chemistry of Macromolecules, vols. 1 and 2, Academic Press, New York, 1972, 1973. [15] N. Billingham, P. Prentice, T. Walker, J. Polym. Sci., Polym. Symp. 57 (1976) 287. [16] Z.A. Kadir, F. Yoshii, F. Hosoi, K. Makuuchi, I. Ishigaki, J. Appl. Polym. Sci. 40 (1990) 799. [17] A.L. Buchachenko, J. Polym. Sci., Polym. Symp. 57 (1976) 599. [18] Y. Hori, S. Shimada, H. Kashiwabara, Polymer 18 (1977) 151.
C. Thevy Ratnam, K. Zaman / Nucl. Instr. and Meth. in Phys. Res. B 140 (1998) 171±177 [19] P.Z. Zbigniew, in: A. Singh, J. Silverman (Eds.), Radiation Processing of Polymers, Hanser, Munich, 1992. [20] L.H. Dunlap, Polym. Sci. A 2 (4) (1966) 673. [21] J.H. O'Donnel, in: E. Reichmanis, J.H. O'Donnell (Eds.), The Eects of Radiation on High-Technology Polymers, ACS Symp. Series, vol. 381, ACS, Washington DC, 1989. [22] I.R. Gelling, Rubber Chem. Technol. 58 (1985) 86. [23] R.L. Clough, in: Encyclopedia of Polymer Science and Engineering, vol. 13, 2nd edition, Wiley, New York, 1988, p. 667. [24] N. Grassie, G. Scott, Polymer Degradation and Stabilization, Cambridge University Press, Cambridge, 1985.
177
[25] ASTM D3577, Standard speci®cation for surgical rubber glove, Annual Book of ASTM Standards, vol. 9.01, 1988. [26] T.S. Dunn, E.E. Williams, J.L. Williams, Radiat. Phys. Chem. 19 (1982) 287. [27] J.L. Williams, T.S. Dunn, V.T. Stannett, Radiat. Phys. Chem. 19 (1982) 291. [28] AAMI, Standard guidelines for electron beam radiation sterilization of medical devices, Association for the Advancement of Medical Instrumentation Report, ASI/ AAMI ST31-1990, 1990.
Eect of electron beam irradiation on surgical rubber gloves Chantara Thevy Ratnam *, Khairul Zaman Malaysian Institute for Nuclear Technology Research, MINT, Bangi, 43000 Kajang, Malaysia Received 9 October 1997; received in revised form 26 November 1997
Abstract This paper outlines the eects of electron beam irradiation on surgical rubber gloves. The tensile strength, elongation at break and modulus were evaluated as function of dose range 20±100 kGy minimum dose, dose uniformity ratio, 3.1, and both, accelerated and normal aging, were used to study the stability of the irradiated gloves after irradiation. The surgical gloves were found to be useful up to the highest dose tested. Ó 1998 Elsevier Science B.V. Keywords: Irradiation; Electron beam; Dose; Gloves; Tensile properties
1. Introduction The radiation sterilization of medical devices has been carried out by using gamma rays from Co-60 and electron beam (EB) generated from accelerator. Although current industrial practices favour the use of gamma irradiators, for medical product sterilization, the demand for electron beam sterilization is growing as a result of ever increasing price of Co-60 source and its unstable supply. Electron beam technology enables irradiation at a high dose rate, thus, achieving at the same time a high product throughput as well as less damage caused by oxidative degradation. Besides
* Corresponding author. Tel.: 6 03 825 0510; fax: 6 03 820 2968; e-mail: [email protected]
this, the absorbed dose rate can be easily controlled and varied, switched on and o quickly with no radiation energy loss during shutdown, and need no replenishment with time. William [1] has discussed in detail the applications of EB for the sterilization of medical devices. Currently, USA, Canada, Denmark, Sweden, Switzerland, Germany, Poland and Japan are among the countries utilizing EB technology for sterilization of medical products [2]. In view of these advantages with regard to sterilization, Kamaruddin et al. [3] have established various parameters in the irradiation of surgical rubber gloves using our 3.0 MeV electron accelerator. Their ®ndings include the determination of product loading pattern in order to ensure that the gloves receive a minimum dose of 25 kGy. In our present work, we report on the eects of electron beam radiation on the physical and aging properties of surgical rubber gloves.
0168-583X/98/$19.00 Ó 1998 Elsevier Science B.V. All rights reserved. PII S 0 1 6 8 - 5 8 3 X ( 9 8 ) 0 0 0 0 4 - 4
172
C. Thevy Ratnam, K. Zaman / Nucl. Instr. and Meth. in Phys. Res. B 140 (1998) 171±177
2. Experimental
2.3. Temperature increase
2.1. Material
Special temperature indicators Type D641 manufactured by Technol Seven, Japan, were placed at the top and in the middle (®fth pair) of each box in order to measure the rise in temperature of the gloves during irradiation. The temperature was read immediately after irradiation.
Commercial grade powder free surgical rubber gloves of size 7 were supplied by a local glove manufacturer. The gloves, made from sulphur-vulcanized natural rubber latex, contain additives such as sulphur and zinc oxide. However, the exact formulation is not known. 2.2. Irradiation Boxes, with external dimensions of 29 cm ´ 15 cm ´ 4 cm, were ®lled with eight pairs of gloves and irradiated by double sided irradiation technique using the 3.0 MeV electron accelerator. Cellulose tri-acetate (CTA) ®lm was used to monitor the absorbed dose during irradiation. The CTA ®lms employed were of the type FTR125, supplied by Fuji Film, Japan. The irradiation dose (minimum dose), beam current and the dose rate employed in this work are detailed in Table 1. The dose uniformity ratio (DUR) was calculated for gloves irradiated at a minimum dose of 25 kGy with the following equation: DUR Dose maximum=Dose minimum:
2.4. Tensile properties measurements The gloves were cut into 115 mm long dumbbell shape as per die C of ASTMD412 [4]. The dumbbell were conditioned at 25°C overnight prior to tensile test measurements. The tensile strength (Ts), elongation at break (Eb), and modulus at 500% elongation (M500) of the irradiated and non-irradiated gloves were determined in accordance with the ASTM D412-C [4]. This was done using the Toyoseiki Strograph-R1 universal testing machine at a crosshead speed of 500 mm/min. 2.5. Accelerated aging In order to elucidate the eects of aging on the irradiated gloves, dumbbells which were cut from the gloves following ASTM D412-C [4] were aged at 70 2°C for 166 2 h in accordance with
Table 1 Eect of various EB irradiation parameters on tensile properties of surgical rubber gloves Dose (kGy)
Dose rate (kGy/s)
Current (mA)
Product temperature, °C (middle)
Ts (MPa)
Eb (%)
M500 (MPa)
0 20 20 20 20 25 25 25 25 40 50 50 50 50 100 ASTMD3577
) 0.12 1.18 2.35 3.53 0.12 1.18 2.35 3.53 3.53 0.12 1.18 2.35 3.53 3.53
)
) 40 40 40 40 45 50 50 50 55 55 60 60 70 85
29.1 0.5 30.2 0.4 30.03 0.6 30.01 0.5 29.98 0.4 28.79 0.8 29.31 0.7 29.16 0.5 31.05 0.5 29.92 0.4 29.66 0.6 29.78 0.4 29.11 0.4 29.11 0.5 30.71 0.5 24 min.
950 20 950 20 950 20 900 20 950 20 950 20 950 20 950 20 950 20 950 20 900 20 1000 2 0 1000 2 5 950 20 950 20 750 min.
2.45 0.03 2.36 0.04 2.37 0.02 2.49 0.02 2.44 0.01 2.34 0.03 2.4 0.03 2.36 0.04 2.42 0.02 2.34 0.03 2.42 0.01 2.33 0.04 2.36 0.03 2.39 0.01 2.46 0.02 5.5 max.
1 10 20 30 1 10 20 30 30 1 10 20 30 30
C. Thevy Ratnam, K. Zaman / Nucl. Instr. and Meth. in Phys. Res. B 140 (1998) 171±177
173
ASTM D573 [5] prior to tensile property measurements. Tests were done on both irradiated and non-irradiated samples. Again the dumbbell test pieces were conditioned at 25°C overnight before they were subjected to tensile tests.
oxidation of polymers. Radiation induced oxidation of polymers is a multistage process which, in general, is described by the same reactions as for usual oxidation processes [12±15]: Initiation:
2.6. Storage studies
RH ! R H;
In order to con®rm degradation during storage, the tensile properties of the irradiated gloves were measured after 1, 2, 3, 4, 5 and 6 months storage at room temperature. In all tensile measurements at least seven specimens (cut from three gloves) were tested. The average and standard deviations were calculated. The representative gloves for tensile measurements were always taken at the dose minimum with reference to CTA ®lm readings.
1
Propagation of the chain: R O2 ! RO2 ;
2
RO2 RH ! ROOH R :
3
Branching of the chain: ROOH ! RO HO;
4
RO RH ! ROH R;
5
HO RH ! HOH R :
6
Termination reactions: 3. Results and discussion
R R ! R ÿ R;
7
3.1. Tensile properties of irradiated surgical rubber gloves
ROO ROO ! ROOR O2 ;
8
R ROO ! ROOR:
9
A lot of polymers used in the medical ®eld show various degrees of degradation after irradiation exposure. This can be seen either by visual or mechanical measurements. The sterilizing radiation eects on selected polymers is described in detail by Skiens [6]. Whereas the detailed understanding of the radiation induced eects on polymers in oxidizing environments can be found in a few articles [7±10]. The absolute values of Ts, Eb and M500 of the gloves irradiated at various dose rates and the respective minimum doses are given in Table 1. It is apparent from Table 1 that the tensile properties do not show appreciable change with increasing dose and increasing dose rate. This indicates that the tensile properties of the gloves were not aected by EB irradiation during the irradiation exposure, even at 100 kGy minimum absorbed dose. However, in contrast, Kohjiya et al. [11] reported that the Ts and Eb of sulphur vulcanized natural rubber vulcanizates decreased with 10 kGy irradiation in gamma rays. This dierence could be explained by the light of radiation induced
Here, R and R represents the polymer chain and polymer radical respectively. Apart from this, from chemiluminicence (CL) measurements, Kadir and co-workers [16] have con®rmed the existence of peroxy radicals in irradiated sulphur vulcanized surgical rubber gloves. These oxidative reactions depend on oxygen diusion and have been discussed in detail by several workers [17,18]. The dierences between our results and Kohjiya et al. [11] are expected since the gamma irradiation from Cobalt 60 is delivered over a period of minutes to hours which allows for more oxygen diusion, resulting in increased oxidative degradation. On the contrary, the EB machine delivers the same dose in a fraction of a second, thus, limiting the oxygen diusion which results in less degradation. This suggests that EB would be a better choice for sterilization of rubber gloves. It is important to note that at a minimum dose of 25 kGy, a DUR of 3.1 was obtained in this study. This DUR value also in perfect agreement
174
C. Thevy Ratnam, K. Zaman / Nucl. Instr. and Meth. in Phys. Res. B 140 (1998) 171±177
with the previous report by Kamaruddin et al. [3] Thus, at a minimum dose of 25 kGy the maximum dose will be 78 kGy. Evidently, this study also con®rms that, the Ts, Eb and M500 of the gloves almost remain unchanged with increasing irradiation dose at the similar irradiation condition as the DUR established. In fact, the results in Table 1 indicate that 100 kGy is acceptable with respect to the tensile properties of the gloves. Hence, it would be safe to recommend the irradiation of these gloves using the 3 MeV EB machine for the purpose of sterilization as long as the minimum dose exceeds 25 kGy. 25 kGy is generally accepted as the minimum dose required to sterilize medical devices. 3.2. Product temperature control Absorbed dose is analogous to temperature rise, which relates to the same concept of absorbed energy per unit mass. An absorbed dose of 10 kGy is equal to 2.4 calories per gram, which would increase the temperature of water by 2.4°C [19]. Most polymeric materials have heat capacities lower than water and exhibit correspondingly higher temperature rise [20]. Generally, the rates of chemical reactions increase with temperature due to the greater proportion of molecules which have energies in excess of the activation energy, and this may apply to the radiation induced reactions in polymers. Referring to Table 1, we observed that there is an increase in temperature on the glove (product) with increasing dose and dose rate. However, with the double sided irradiation technique which was employed in this studies, the increase in temperature in the top and the ®fth pair of the gloves were found to be the same. Again, the retention in tensile properties of the gloves after irradiation con®rms that the increase in temperature does not cause any signi®cant damage to the gloves. This observation could be explained by the fact that in solid polymers the radiation induced reactions at elevated temperatures are also governed by their glass transition temperatures, Tg . Substantial changes in molecular mobility occur across this transition and the rate of chemical reactions is greatly aected [21]. Since the Tg of natural rubber is about )69°C [22], far
above the temperatures observed in Table 1, considerable eect was not noted. Consequently, it can be concluded that the gloves did not deteriorate at the range of temperatures which were observed during irradiation. Clearly, it is not necessary to provide cooling of the gloves before, during or after the irradiation treatment cycle. 3.3. Accelerated aging properties of EB irradiated surgical rubber gloves It is well known that some polymers such as polyethylene and polypropylene degrade by residual peroxy radicals during storage after irradiation. In addition, peroxides formed during the course of the irradiation can undergo thermal decomposition, providing a chain branching step which yields free radicals that can then participate in the oxidation propagation step [23]. The chemistry of auto-oxidation for polymers has been described in detail in the book by Grassie and Scott [24] and will not be discussed here. Therefore, in order to predict the degradation of irradiated gloves during storage, the physical properties of EB irradiated gloves were measured after the gloves were subjected to a temperature of 70 2°C for 166 2 h. Table 2 shows the tensile properties of surgical rubber gloves after aging. Comparison of the Ts before and after accelerated aging, shows that there is no remarkable change observed at all doses. However, a slight decrease in Eb and M500 is observed after aging indicating that degradation occurred during the accelerated aging. A similar tendency is also shown by the non-irradiated samples suggesting that the general decrease in M500 and Eb may not be associated with the oxidation chemistry involving reaction species previously formed by irradiation such as long-lived radicals or peroxides [7,23]. In agreement with this it should also be noted that the decline in the above properties with accelerated aging is marginal with increasing dose. However, the decrease in Eb on accelerated aging is very low compared with the ASTMD3577 [25] speci®cations which are shown in Table 2. Accelerated thermal aging experiments are very useful approach for predicting post-irradiation degradation, while actual room temperature aging experiments are also
C. Thevy Ratnam, K. Zaman / Nucl. Instr. and Meth. in Phys. Res. B 140 (1998) 171±177
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Table 2 Eect of EB irradiation on accelerated aging properties of surgical rubber gloves Dose (kGy)
0 20 25 40 50 100 ASTM D3577
Before aging
After accelerated aging
TS (MPa)
Eb (%)
M500 (MPa)
TS (MPa)
Eb (%)
M500 (MPa)
29.1 0.5 29.98 0.4 31.05 0.5 29.92 0.4 29.11 0.5 30.71 0.5 24 min.
950 950 950 950 950 950 750
2.45 0.03 2.44 0.01 2.42 0.03 2.34 0.03 2.39 0.01 2.46 0.02 5.5 max.
30.31 30.37 29.86 30.87 30.06 30.05 18 min.
900 900 900 900 900 900 560
2.32 2.37 2.33 2.30 2.31 2.34 )
20 20 20 20 20 20 min.
0.5 0.6 0.4 0.5 0.8 0.4
20 20 20 20 20 20 min.
0.02 0.02 0.01 0.03 0.03 0.03
Dose rate: 3.53 kGy/s. Aging condition: 70 2°C/166 2 h.
done to further con®rm the severity of post-irradiation damage. 3.4. Storage eect It is apparent from Fig. 1 that the Ts values exhibit a uniform fall with storage time. Importantly, Fig. 1 also proves that the irradiated samples present more pronounced drop in Ts with storage time compared to the non-irradiated one. It has been reported that the species most often responsible for this phenomenon are the trapped radicals or peroxides [7,23]. Dunn et al. [26] has described that the peroxy radicals formed during irradiation of PP can lead to the formation of peroxides as in Eqs. (2), (8) and (9). The peroxides remain in the polymer for a long period of time, and upon dissociation causing chain scissions as a consequence of
Fig. 1. Storage eect on tensile strength of irradiated gloves.
which there is progressive deterioration in strength. The downward trend in Ts of the irradiated gloves clearly reveals the radiation induced degradation on storage. This observed trend towards lower values of Ts for the irradiated gloves is considered small based on the absolute values of the six months storage being within the speci®cation of ASTM D3577. In addition, it is evident from Figs. 2 and 3 that the Eb and M500 show only slight decrease with storage time, suggesting that the post-irradiation degradation is rather small and unlike as reported for PP [26]. This observation could be attributed to the dierence between PP and natural rubber in the nature of kinetic changes in radical concentrations as a function of time both during and after
Fig. 2. Storage eect on elongation at break of irradiated gloves.
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in accordance to protocols established by the Association for the Advancement of Medical Instrumentation [28]. Acknowledgements
Fig. 3. Storage eect on Modulus 500 of irradiated gloves.
irradiation [27]. Elastomers are generally characterized by a high chain mobility at room temperature. This suggests that in natural rubber, a rapid termination of primary radicals during irradiation lowers the overall radical population, and account for less oxidative degradation during storage. On the other hand, PP is a semicrystalline polymer and the mobility of the radicals is strongly reduced in the crystalline region, and the post-irradiation survival is long resulting in severe storage embrittlement. These imply that the EB irradiation has only a minor in¯uence on the overall tensile properties during storage of the irradiated gloves. 4. Conclusions From the data obtained, it can be demonstrated that the EB sterilization up to 100 kGy delivered dose, has no deleterious eects on the tensile properties of the surgical rubber gloves. The retention in tensile properties up to a minimum dose of 100 kGy implies that the gloves are not degraded by the maximum dose absorbed while the minimum absorbed dose is above 25 kGy in the case of an irradiation with DUR up to 4. Thus, EB would seem to be a better choice for the sterilization of rubber gloves, considering our product quali®cation which identi®ed that the glove can be sterilized at maximum tolerable dose without causing any adverse eect on the properties of the gloves. Further to this, subsequent experiments will be carried to ``®ne tune'' the actual dose limits
The authors would like to thank the JICA team for the technical cooperation and Mr. Kamaruddin Bahari for his initial involvement in this work. A special appreciation also goes to Ms. Khuzaimah and N. Mohid for their assistance during the preparation of this manuscript.
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