- Email: [email protected]
Effect of electron beam radio sterilization on cyclic olefin copolymers used as pharmaceutical storage materials
Radiation Physics and Chemistry 84 (2013) 223–231
Contents lists available at SciVerse ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Effect of electron beam radio sterilization on cyclic olefin copolymers used as pharmaceutical storage materials Hala Barakat a,b,n, Caroline Aymes-Chodur a, Johanna Saunier a, Najet Yagoubi a a b
Laboratoire Mate´riaux et Sante´ EA 401, IFR 141, Faculte´ de Pharmacie, Universite´ Paris Sud-11, 5 rue J. B. Cle´ment, 92296 Chˆ atenay-Malabry, France Quality Control Departement, Faculty of Pharmacy, Tishreen University, Latakia, Syria
a r t i c l e i n f o
abstract
Article history: Received 1 January 2011 Accepted 1 January 2012 Available online 7 June 2012
The aim of this work was to study the effect of radio-sterilization on cyclo olefin copolymers (COC), that can be used as pharmaceutical storage materials, both on the surface and in the volume of the material, and to investigate the impact of the presence of a lubricant. A cyclo olefin copolymer (TOPASs 8007) was treated with an electron beam radio-sterilization at different doses ranging from 25 to 150 kGy. Polymer structure and bulk properties were evaluated by Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and Size Exclusion Chromatography (SEC). A good correlation between those analytical techniques was observed: oxidation products were formed and crosslinking of chains occured. Although these modifications were important, the effect on the thermal properties was weak. The analysis by Reversed Phase High Performance Liquid Chromatography (RP-HPLC) of extraction’s solutions of COC after irradiation showed both a remarkable decrease of the extractable amount of polyphenolic antioxidant (Irganox 1010s) initially present in the matrix, and a generation of an important number of degradation products that represent potential migrants for pharmaceutical formulations. Surface modifications were evidenced by both (FTIR/ATR) and contact angle measurements of COC films. An increase in surface polarity of COC after radio-sterilization was observed. & 2012 Elsevier Ltd. All rights reserved.
Keywords: COC Electron beam radio-sterilization Crosslinking Low molecular weight compounds Surface modification Ageing
1. Introduction Cyclic olefin copolymers (COC) belong to a new class of amorphous polymers having remarkable combination of properties such as high transparency, low moisture uptake, glass-like texture, very high heat resistance and good chemical resistance (Naga et al., 2006; Rische et al., 1998; Yang et al., 2002; Young et al., 2003). These unique properties make COC interesting for numerous industrial applications and notably in medical and pharmaceutical fields (Yamazaki, 2004; Zhang et al., 2008). Indeed, COC are more and more used as medical devices and pharmaceutical packaging especially for injectables formulations (Topass) which require a suitable and reliable sterilization process. Electron beam irradiation has been used to sterilize medical goods for well over 50 years (Abraham et al.; Ansari and Datta, 2003; Fintzou et al., 2007; Haji-Saeid et al.). Because of its convenience and lower cost, it provides an interesting and preferable alternative sterilization method towards high temperature n Corresponding author at: Universite´ Paris Sud-11, IFR 141, Faculte´ de Pharmacie, Laboratoire Mate´riaux et Sante´ EA 401, 5 rue J. B. Cle´ment, 92296 Chˆatenay-Malabry, France. Tel.: þ 33 1 46 83 57 74; Fax: þ33 1 46 83 59 63. E-mail address: [email protected] (H. Barakat).
0969-806X/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radphyschem.2012.05.006
steam autoclaving or dry heat that can damage materials, induce degradation and lead to losses of both shape and mechanical properties. However, the high-energy electrons released from the interaction of electron beam particles with materials are known to create reactive intermediates and free radicals which follow several reaction paths and results in crosslinking and/or scission of the polymer chains (Chapiro, 1988; Clough, 2001; Davenas et al., 2002). This can modify the mechanical properties as well as the surface properties of the polymer (Majumder and Bhowmick, 1999). In addition to that, chain scissions cause the production of low molecular weight compounds (LMWC) (Buchalla and Begley, 2006; Buchalla et al., 1999; El Mansouri et al., 1998), which are susceptible to migrate from the bulk of polymer onto its surface and then to the surrounding medium (Bourges et al., 1992a; Lau and Wong, 2000). Such kind of surface modification and/or migration of leachables may affect the compatibility of the couple: content/container, which is an important safety requirement in the field of pharmaceutical packaging (Jenke, 2007). Furthermore degradation process may continue during postirradiation shelf-life storage due to the trapped free radicals that are able to react even when the irradiation has been performed since a long time (Goldman et al., 1996). It should be noticed that the degree of the modifications induced by irradiation depends on
224
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
the structure of the polymer as well as on the conditions of treatment before, during and after irradiation (irradiation dose, irradiation atmosphere and the amount of antioxidants added to the polymer). The aim of this work was firstly to study the effect of electrobeam radio-sterilization on cyclic olefin copolymers both in the bulk and on the surface of the material, then to investigate the impact of the presence of a lubricant on surface modifications induced by irradiation, and finally to evaluate post-irradiation ageing behavior. We focused on the following:
granules. In the case of contact angle measurements and poststerilization ageing studies, films were used. FTIR Microscopy analyses were performed on granules and plates. 2.2. Sample irradiation Samples were irradiated by an electron beam produced by a high power generator (10 MeV) from a 10 kW power accelerator (Ionisos, Fr.). Samples were exposed to three different irradiation doses: 25, 75, and 150 kGy. They were packed under ambient condition in plastic (small bags) sachets.
Modification of polymer chains (oxidation, scission and cross
linking) that might change the mechanical properties of COC and generate potential leachables like oligomers. Degradation of the antioxidant that could create compounds of potential toxicity. A preliminary study of surface modifications after irradiation by contact angle measurements, comparison of lubricated and non-lubricated polymer. Effect of accelerated post-irradiation ageing on polymer oxidation.
A dose of 25 kGy, which is the dose of sterilization recommended by regulatory authorities (Commission of the European Communities, 1990), was chosen as the lowest dose in our study. Two other higher doses (75 and 150 kGy) were applied to emphasize the effect of irradiation.
2. Experimental 2.1. Polymer We used a cyclo olefin copolymer (COC) called TOPASs 8007 supplied by Ticona (Germany). The polymer is an ethylene and norbornene based copolymer, it has been used in the form of granules (|ؼ2 mm), films (thikness¼ 100 mm) or plates (Fig. 1(a)). We compare the 8007-D61 grade to the 8007- S04 grade (without lubricant), which was partly studied in an other publication (Saunier et al., 2008). For the 8007-D61 granules, the surface has been coated with 0.2% of a wax (lubricant) for better injection molding processing. FTIR, Differential Scanning Calorimetry (DSC) and Size Exclusion Chromatography (SEC) were performed on both granules and films. For the analysis of extractables by HPLC, previous extractions were done on
2.3. Sample storage Irradiated samples were stored in the fridge (5 1C) to reduce the post-sterilization ageing effects. Post-sterilization ageing was studied by storing some of the samples at 50 1C during several weeks. 2.4. Size Exclusion Chromatography SEC analysis was performed at 60 1C in toluene on a PL laboratory PL-GPC 220 system: three detectors were used: a refractometer (DRI) (Polymer Laboratories, UK), a 220 R high temperature differential viscosimeter (DV) (Viscotek, UK and a PD 2040 high temperature laser light scattering (LS) detector (Precision Detectors, Inc., USA). Temperature was set at 60 1C. The solvent flow was of 1 mL/min. The SEC system was controlled by the PL-GPC 220 Controls software (version 2.01). The data acquisition and analysis were set by Viscotek softwares (Omnisec—version 4.0). The polymer concentration was 5 mg/mL. 200 mL was injected onto two Polymer Laboratories (PL) columns: a 100 A˚ and a mixed D whose molecular weights linear range stood respectively up to 4000 g/mol and between 200 and 4 106 g/mol (data given by the supplier), their granulometry was of 5 mm, their length was of 300 mm and their internal diameter of 7.5 mm. 2.5. Soxhlet extraction Soxhlet extraction was used to calculate the insoluble ratio of polymer chains with toluene as a solvent. The soxhlet extraction duration was of 24 h. Samples and cellulose thimbles were weighed before and after extraction. The mass of polymer after extraction corresponds to the insoluble part of the polymer (crosslinked chains). 2.6. FTIR
Fig. 1. (a) Structure of TOPASs 8007 D-61 (b) Structure of Irganox 1010.
The spectrometer apparatus was a Perkin-Elmer Spectrum 2000. It was used in both Attenuated Total Reflection (ATR) mode with a diamond crystal (Golden Gate-Specac) and in transmission mode. To express band intensity we used the height of the band. The wavelength range was set from 4000 to 400 cm 1 with a resolution of 4 cm 1during 16 scans. FTIR microscopy analysis (AutoImage FT-IR Microscope provided by Perkin Elmer) was performed on both lubricated non-irradiated granules in order to see the lubricant distribution and non-lubricated irradiated plates to follow the oxidation band after irradiation. The conditions were the following: The wavelength range was set from 4000 to 700 cm 1 with a resolution of 8 cm 1 during 8 and 30 scans for granules and plaques respectively. Granules were cut in slides of 60 mm thick with a microtome (Leica RM 2255) and plates were cut to get lumps of 0.95 mm thick. An image map was taken for granules and was
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
Table 1 Surface tension and polar component of surface tension for the three liquids used for contact angle measurement (data from digidrop softwares library). Liquid
Diiodomethane ethylene glycol
Surface tension, sS (mN/m)
51.8 48
Polar component of the surface tension, sp (mN/m) 0 (0%) 19 (40%)
of a size 35 35 mm2, while a line profile was realized on plates with an interval of 20 mm and for 114 points. 2.7. Differential Scanning Calorimetry DSC analysis was performed on a TA instrument Q1000. The heating/cooling rate was of 10 C1/min under nitrogen blanketing (50 mL/min). The temperature ranged was set between 0 and 160 C1. Hermetical aluminum pans (20 mL) were used. For glasstransition study, only the second temperature raise after a first heating/cooling cycle was exploited.
225
3. Results and discussion 3.1. Effect of electron beam irradiation on the COC bulk 3.1.1. Effect of radiation on polymer degradation
3.1.1.1. FTIR/Transmission. No extensive modification of COC FTIR spectra was observed after irradiation; only a slight alteration was observed around 1700 cm 1. In this frequency range, bands characteristic of CQO functions (1712 cm 1) grew with the irradiation dose (Fig. 2). It proved that some of the free radicals in the polymer chains created during irradiation had reacted with the oxygen of air. ˇ ´ erov et al., These observations agree with the work of (Sec ˇ (2008); and Kacarevic´-Popovic´ Zorica et al., (2006) who reported that the gamma ray-irradiation of TOPASs samples in air generated free radicals along the chains; these radicals reacted with molecular oxygen and the peroxy intermediates produced hydroperoxy, hydroxyl and ketone functions. Nakade et al. (2010) also reported the formation of oxidation functions of ethylene– norbornene copolymers after photo-irradiation and elucidated the mechanism of formation of photo-degradation products.
2.8. Contact angle measurement Samples were analyzed during the few days following irradiation and after storage at 50 1C during several weeks. Contact angle measurements were carried out on films after a liquid drop deposition, using a contact angle meter (GBX, France) coupled to the Digidrop Analysis Windropþþ (v1.00.01.01) software. Two liquids were used: diiodomethane (CH2I2, Merck Schuchardt OHG), and ethylene glycol (HOCH2CH2OH, E. Merck Darmstadt). The surface tension (gs) of each solvent as well as its polar (gp) components are given in Table 1. Ten drops deposited on each film sample of COC was analyzed. 2.9. Additives extraction To identify and quantify the additives in the polymer, we used a dissolution/precipitation process. 3 g of COC granules were dissolved at reflux in 50 mL of toluene at around 70 1C under stirring. After complete dissolution, the polymer was precipitated by slowly adding 50 mL of methanol under stirring. For the 150 kGy irradiated samples, the polymer was only partly soluble. Polymer was then removed from the extraction solution by filtration on a paper filter and the precipitate was carefully rinsed with methanol. Solutions containing additives, oligomers, and degradation products were then evaporated by use of a rotavapor at 60 1C (under vacuum). For the SEC experiment, the dry residue containing extractables was dissolved in 1.5 mL of toluene (HPLC grade, VWR), while for analysis by HPLC it was dissolved in a mixture of 1 mL of THF (HPLC grade, VWR) and 1 mL of acetonitrile (HPLC grade; VWR). Then, the solution was filtered on a 0.45 mm Teflon filter.
3.1.1.2. SEC. SEC analysis was done on the soluble fraction of polymer, it should be noticed that the polymer was soluble for 25 kGy and 75 kGy doses but the 150 kGy irradiated sample was only partially soluble. In order to quantify the amount of insoluble polymer, three different Soxhlet extractions in toluene were done on 150 kGy irradiated sample. An insoluble ratio of 45% 74% (n ¼3) was calculated. This ratio corresponds to the ratio of chemically crosslinked chains in the polymer, and it was in agreement with chromatogram intensities (Fig. 3) which showed a decrease of the soluble fraction of polymer with irradiation. Chromatograms showed also an enlargement of the weight distribution of the polymer after irradiation that can be attributed to both scissions and crosslinking of the polymer chain. Indeed, the polydispersity index Ip increased from 1.2 to 2.4 for the 0 and 150 kGy respectively (Fig. 4(a)). From the evolution of molecular weights presented in Fig. 4(b)–(d), it could be noticed that Mn, Mz and Mw began to increase after a 25 kGy dose and the increase of these masses became more important as the dose increased especially at 150 kGy, so we can conclude that crosslinking was the predominant phenomenon and that scission was not significant. Indeed for the 75 and 150 kGy samples, a marked shoulder appeared at an elution
2.10. HPLC We developed an HPLC method using two mobile solvents (methanol and water) and an elution gradient. The apparatus used was constituted of an Ultimate 3000 Dionex assembly with a gradient pump, an automatic injector and a photodiode Array detector. The column was a LiChrocarts 250-4 RP-18e (5 mm) (Lichrosphere, Interchim). The injection volume was of 20 mL and the flow rate was of 1 mL/ min. Acquisition was done using the ChromeleonTM software (Dionex).
Fig. 2. Zoom on the 1650–1800 cm 1 range of FTIR-transmission spectra of the non-irradiated sample and the 25, 75 and 150 kGy irradiated TOPASs 8007 D-61 samples.
226
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
volume of about 9.8 mL, which was characteristic of a new distribution of higher molecular weight. These findings were similar to the results obtained by J. Saunier (Saunier et al., 2008) who showed a predominance of crosslinking of non-lubricated TOPASs 8007 after electron beam irradiation.
3.1.1.3. DSC. A calorimetric study was conducted to put into evidence modifications in the thermal properties. The glass transition temperature for TOPASs 8007 D-61 was around 81 1C that is to say a temperature similar to the non-lubricated sample (Saunier et al., 2008). For the granules, as observed previously with non-lubricated samples, the differences between irradiated and non-irradiated samples were slight: a decrease of glass
Fig. 3. SEC chromatogram of TOPASs 8007 D-61 solution for the different irradiated doses.
transition temperature was observed with the irradiation dose (Fig. 5). This weak decrease (1 1C for 150 kGy sample) could be explained in part by the increase in chain ends because of branching (Gibbs and DiMarzio, 1958; Fox and Flory, 1950).
3.1.2. Effect of radiation on the antioxidant degradation The phenolic antioxidant found in the polymer, after extraction by a dissolution/precipitation process and analysis of the extract by HPLC, was Irganox 1010s (Fig. 1(b)). The extracted amount was about 1550 ppm. As illustrated in Fig. 6, the extractable level of Irganox 1010s had remarkably decreased as the irradiation dose increased. Similar profile of extractable amount of antioxidant after irradiation was observed previously (Saunier et al., 2008) for the non-lubricated polymer. This decrease might be explained by the degradation of the antioxidant or/and by the formation of covalent bonds between the degraded molecules and the polymer chains. Similar kind of bonding had already been reported (Allen et al., 1991).
Fig. 5. Evolution of the glass transition temperature with irradiation dose for TOPASs 8007 D-61 (n¼3).
Fig. 4. Evolution of polydisperty Index Ip (a) and molecular weight Mn (b) Mz (c) and Mw (d) (n¼ 3).
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
227
– the smallest retention times correspond to the more polar and to the smallest molecules. – as the detector was a diode array one set at wavelengths between 150 and 500 nm, all degradation products containing chromophores absorbing in this range could be detected.
Fig. 6. Evolution of the extractable amount of Irganox 1010 in TOPASs 8007 D-61 with the irradiation dose (n¼ 5).
Fig. 7. (a) SEC chromatogram of the extract of TOPASs 8007 D-61 after dissolution/precipitation for the different irradiation doses. (b) Comparaison of polymer distributions (dissolved polymer and soluble fraction of polymer in the dissolution precipitation extract) for the non-irradiated samples.
3.1.3. Effect of radiation on the generation of low molecular weight compounds (LMWC) LMWC were put into evidence by dissolution/precipitation extraction of the polymer and analyzing the extract by both SEC and HPLC. Chromatograms of the extracts corresponding to irradiated and non-irradiated polymers were compared. For SEC analysis (Fig. 7 (a)), the chromatogram of the extract corresponding to the non-irradiated samples revealed the presence of two major weight distributions, the first one assigned to the soluble fraction of the polymer after dissolution/precipitation process, this fraction was of lower molecular mass than the polymer itself (Fig. 7(b)). The second distribution corresponded to Irganox 1010 s. These two distributions decreased as the irradiation dose increased and new distributions corresponding to both polymer chain scission and degradation and recombination products of Irganox 1010s appeared. The study of these LMW molecules, and especially the degradation products of the antioxidant is an important deal because they are more able to migrate from the polymer into the pharmaceutical formulation than larger molecules and may induce toxicity. So to study these potential migrants, we followed the evolution of extractable degradation products of Irganox 1010s by HPLC analysis because it is a more selective and specific method than SEC. In the RP-HPLC system used we should remind that
On the HPLC chromatogram of the extract corresponding to the non-irradiated sample (Fig. 8(a) and (b)), there was a major peak representing Irganox 1010s and many other little peaks corresponding to both synthesis residues of Irganox 1010s and some of its degradation products that might result from a postageing process promoted by the extraction process: during extraction, polymer was heated at 60–70 1C in organic solvent during about 45 min. After irradiation, some of these peaks decreased with irradiation dose, and many new chromatographic peaks appeared. Others increased and some of them increased up till 25 kGy and then decreased for the higher doses. For a 25 kGy dose, a few new peaks were detected at short retention times (tr) (tr o 11 min or zone A) so they were characteristic of small molecules. A large number of other peaks corresponding to larger degradation products were detected in zone B (tr 411 min) even at retention time greater than that of Irganox 1010s. A significant decrease of the latter degradation products (zone B) was observed after irradiation at 75 kGy, on the contrary the intensity of the peaks located at shorter retention times (zone A) increased. This might be due to a further degradation of the longer degradation molecules by cleavage to form smaller degradation products. Indeed, zone A degradation products had a maximum of absorbance at wavelength 250 nm characteristic of carbonyl group (Fig. 8(b)), while the maximum absorbance for degradation products of zone B was at 280 nm characteristic of phenolic group (Fig. 8(a)). For the 150 kGy dose, the intensity of a majority of degradation products decreased and so it let the intensity of some degradation products which are smaller than them increase, while certain peaks had almost disappeared. These results were identical of those obtained with non-lubricated polymers that were previously studied, in other words: there is no impact of the presence of a lubricant on the degradation products generated after irradiation. From this study we can conclude that the sterilization dose 25 kGy generated a great number of extractable degradation products of Irganox 1010 s that means an important number of potential migrants; these products might be further degraded by increasing the irradiation dose. It should be noticed that degradation products of irganox 1010 s had been already studied in the literature (Allen et al., 1994, 1991; Bourges et al., 1992b). Allen detected more than 50 different compounds in a 50 kGy electron beam irradiated polypropylene sample, but most of them were of very low concentration and thus they could not be identified by mass spectroscopy. Bourges was able to identify four main degradation products after irradiation: a phenol, a quinone, a quinone methide and a hydroxylbenzaldehyde. In our study, the identification of degradation products of Irganox 1010 s by HPLC coupled to mass spectroscopy and the diffusion of these potential migrants into the pharmaceutical formulation will be discussed in further paper. As a conclusion on the bulk results, we have evidenced a predominant crosslinking as well as the formation of oxidation and degradation products. In the case of a pharmaceutical formulation which is in contact with the surface of such material, it is also important to evaluate the surface modification induced by electron beam irradiation.
228
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
Fig. 8. HPLC chromatograms of TOPASs 8007 D-61 extractables for non-irradiated sample and 25, 75 and 150 kGy irradiated samples. The detection was performed by a diode array set at wavelengths (a) 280 nm and (b) 250 nm.
3.2. Effect of electron beam irradiation on the surface 3.2.1. FTIR In order to understand the effect of lubricant on the modification of the irradiated polymer surface, the distribution of lubricant in polymer surface and bulk was studied. The ATR spectra of non-irradiated polymer showed absorbance bands at 3300, 1637 and 1564 cm 1 for the lubricated polymer (Fig. 9); these absorbance bands were characteristic of the presence of lubricant containing amide functions. The intensity of these bands was very important for polymer granules and very low for films. Indeed in the films, the adsorbance bands corresponding to the lubricant were shifted as compared with granules and were broader and of lower intensity. The analysis by FTIR microscopy/transmission of a 60 mm section of lubricated granules showed that there was no lubricant inside. This can be explained by the fact that granules were only coated with the lubricant and that the films were obtained by melting these coated granules. As observed in transmission, the ATR spectra of TOPAS 8007 D-61 showed the appearance of an absorbance band at 1712 cm 1 characteristic of a new CQO function, whose intensity increased with irradiation dose. In order to know if the effect of irradiation was homogenous on the surface and in the bulk of the polymer, the band of oxidation observed after irradiation was followed by microscopy in transmission mode. For the 150 kGy irradiated samples, a gradient of oxidation from the surface towards the bulk was observed, it was about 300 mm depth (Fig. 10).
Fig. 9. FTIR/ATR spectra of the non-irradiated lubricated and non-lubricated TOPASs 8007 Samples (granules and films).
This gradient could be explained by the kinetic of oxygen diffusion from surface into volume and must be confirmed by Electron Spin Resonance (ESR) analysis.
3.2.2. Contact angle measurements Contact angle measurements on the COC surfaces were measured on films before and after treatment by accelerated
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
229
Fig. 10. Profile line of CQO band as compared with a 3405 cm 1 band of polymer from Microscopy FTIR/Transmission for 150 kGy irradiated plates. 3405 cm 1 band represents a harmonic band or a combinated band of COC which was the same before and after irradiation.
Fig. 11. Evolution of contact angle of TOPASs 8007 (with and without lubricant) with two solvents for different irradiated doses.
electrons. The contact angles for the virgin untreated COC surface were about 40 731 and 68 721 for diiodomethane and ethylene glycol respectively, this result evidenced the apolar nature of COC because the contact angle increased as the polarity of solvent increased. No significant difference was observed between both kinds of COC (with and without lubricant) before irradiation, this may be due to the slight quantity of lubricant on the films surface as shown by FTIR/ATR. From the results given in Fig. 11, it can be seen that irradiation increased the contact angle of diiodomethane (the non-polar solvent) with COC surface, and in the same time decreased the contact angles for the polar one (ethylene glycol). It should be noticed that modifications of contact angle after irradiation were more important for the non-lubricated COC as compared with the lubricated one especially for the high doses (75 and 150 kGy). Hence, the surface polarity of COC increased with
irradiation. In order to understand the above changes, these results were correlated with those obtained with FTIR and HPLC. Indeed, the increase of polarity after irradiation can be correlated to the presence of surface polar groups such as (CQO) groups evidenced by FTIR analysis for both kinds of COC. This increase of polarity also results from the low molecular weight polar compounds that were formed during irradiation and that were observed by HPLC. But both analytical techniques did not help to answer why the impact of the lubricant on surface state of polymer was observed only after irradiation. We suggested that irradiation increased the surface roughness of polymer, and that is why these modifications were more important for non-lubricated polymers because one of the advantages of lubricant is to protect polymer surface from abrasion and friction. More detailed study of surface topography by Atomic Force Microscopy (AFM) and chemistry modification by X-ray Photoelectron Spectroscopy (XPS) appear to be essential for the better understanding of the effect of lubricant on surface modification. It should be noticed that the increase in surface polarity was in agreement with other studies realized on COC surfaces modified by oxygen plasma treatment (Bhattacharyya and Klapperich, 2007; Nikolova et al., 2004; Roy et al., 2010), which is known to incorporate oxygen containing functional groups onto a polymer surface (Hwang et al., 2008). Several examples in the literature showed that similar oxidation mechanisms could be achieved by electron beam irradiation (Burkert et al., 2009). 3.3. Post-irradiation ageing Ageing of irradiated TOPASs 8007 D-61 with time was studied. To simulate a long time ageing, an accelerated ageing was carried out by storing the polymers at 50 1C for 1 and 6 months. After a 1 month storage, an increase in the intensity of the CQO band at 1712 cm 1 was observed for the samples irradiated at 75 kGy as compared with the irradiated samples stored 4 months in fridge. For the 25 kGy irradiated samples this increase was less clear. However no increase was observed for the 150 kGy irradiated samples. After a 6 months storage, the CQO band intensity increased by a factor of 1.8 for the 25 kGy irradiated polymers and by a factor of 1.2 for the 150 kGy irradiated polymers when compared with the irradiated samples
230
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
Acknowledgments The authors would like to thank Ticona (Germany) for providing COC used in this study, as well as the Faculty of Pharmacy of Tishreen-University (Latakia–Syria) for the research funding. Special thanks to Vincent MAZEL for his kind help in FTIR microscopy analysis.
References
Fig. 12. Comparaison of the 1712 cm 1 relative absorbance for the irradiated samples stored in the fridge and samples stored 1 and 6 months at 50 1C. Samples were analyzed in FTIR/Transmission. Relative absorbance was defined as the ratio at 1712 cm 1 to the CQO band absorbance for the unaged and non-irradiated sample.
stored 4 months in fridge (Fig. 12). This process was certainly due to the existence of trapped radicals in the polymer that reacted with oxygen. Even if the number of trapped radicals generated by irradiation increased with the irradiation dose, the increase of the intensity of the CQO band after 6 months storage at 50 1C as compared with samples stored in the fridge, was more important for the less irradiated polymers. This phenomenon might be explained by a favorable diffusion of oxygen after 6 months through the polymer irradiated at 25 kGy in comparison with higher doses due to the crosslinking occurred after irradiation at 75 and 150 kGy. Our findings were partially in agreement with the results of Saunier et al. (2008) which showed similar increase of oxidation group in the samples stored 6 months in the fridge when compared with freshly irradiated polymers, but contrary to our results this increase was a function of irradiation dose.
4. Conclusion Electron beam radio-sterilization led to significant COC chain modifications with predominant crosslinking, however these modifications did not affect the thermal properties of the polymer. On the contrary, the consequence of these modifications was the generation of low molecular weight compounds such as oligomers and degradation products of the antioxidant. Such compounds were even found at 25 kGy, which is the maximum dose recommended for the sterilization of medical devices and pharmaceutical packaging. Unfortunately, low molecular weight compounds are able to migrate from the polymer to the formulations in contact with it and might induce potential toxicity. Therefore, they must be identified and their toxicity must be studied. Such study to identify degradation products and to evaluate their migration into medias of different polarities under accelerated conditions is currently in progress. Moreover, modifications of the surface state were evidenced after irradiation. An increase of surface polarity was observed, more important for the non-lubricated polymers as compared with lubricated ones. A more detailed study on the impact of sterilization and additives on the surface state seems to be essential because that might result in the adsorption of active agents on the polymer surface and as a consequence it might alter the compatibility of the polymer with the pharmaceutical formulations destined to be stored in.
Abraham, A.C., Czayka, M.A., Fisch, M.R., Electron beam irradiations of polypropylene syringe barrels and the resulting physical and chemical property changes. Radiat. Phys. Chem. 79, 83–92. Allen, D.W., Clench, M.R., Crowson, A., Leathard, D.A., Saklatvala, R., 1994. Characterisation of electron beam generated transformation products of irganox 1010 by particle beam liquid chromatography–mass spectrometry with on-line diode array detection. J. Chromatogr. A 679, 285–297. Allen, D.W., Leathard, D.A., Smith, C., 1991. The effects of gamma irradiation on the fate of hindered phenol antioxidants in food contact polymers. Analytical and 14C-labelling studies. Int. J. Radiat. Appl. Instrum. C Radiat. Phys. Chem. 38, 461–465. Ansari, I.A., Datta, A.K., 2003. An overview of sterilization methods for packaging materials used in aseptic packaging systems. Food Bioprod. Process. 81, 57–65. ˇ ´ erov, B., Marinovic´ Cincovic´, M.T., Popovic´, S., Nedic´, Z., Kac´arevic´-popovic´, Z., Sec 2008. Characterization of gamma irradiated ethylene–norbornene copolymer using FTIR, UV–vis and DSC Techniques. Polym. Bull. 60, 313–322. Bhattacharyya, A., Klapperich, C.M., 2007. Mechanical and chemical analysis of plasma and ultraviolet-ozone-surface treatments for thermal bonding of polymeric microfluidic devices. J. R. Soc. Chem., 876–882. Bourges, F., Bureau, G., Dumonceau, J., Pascat, B., 1992a. Effects of electron beam irradiation on antioxidants in commercial polyolefins: determination and quantification of products formed. Packag. Technol. Sci. 5, 205–209. Bourges, F., Bureau, G., Pascat, B., 1992b. Effects of electron beam irradiation on commercial polypropylene: kinetic study of antioxidant degradation. Packag. Technol. Sci. 5, 197–204. Buchalla, R., Begley, T.H., 2006. Characterization of gamma-irradiated polyethylene terephthalate by liquid-chromatography–mass-spectrometry (LC–MS) with atmospheric-pressure chemical ionization (APCI). Radiat. Phys. Chem. 75, 129–137. ¨ Buchalla, R., Boess, C., Bogl, K.W., 1999. Characterization of volatile radiolysis products in radiation-sterilized plastics by thermal desorption–gas chromatography–mass spectrometry: screening of six medical polymers. Radiat. Phys. Chem. 56, 353–367. Burkert, S., Kuntzsch, M., Bellmann, C., Uhlmann, P., Stamm, M., 2009. Tuning of surface properties of thin polymer films by electron beam treatment. Appl. Surf. Sci. 255, 6256–6261. Chapiro, A., 1988. Chemical modifications in irradiated polymers. Nucl. Instrum. Meth. B 32, 111–114. Clough, R.L., 2001. High-energy radiation and polymers: a review of commercial processes and emerging applications. Nucl. Instrum. Methods B 185, 8–33. Commission of the European Communities, 1990. CPMP Working Party on Quality of Medicinal Products. Note for Guidance. Davenas, J., Stevenson, I., Celette, N., Cambon, S., Gardette, J.L., Rivaton, A., Vignoud, L., 2002. Stability of polymers under ionising radiation: the many faces of radiation interactions with polymers. Nucl. Instrum. Methods B 191, 653–661. Gibbs, J.H., DiMarzio, E.A., 1958. Nature of the glass transition and the glassy state. J. Chem. Phys. 28, 373. El Mansouri, H., Yagoubi, N., Ferrier, D., 1998. Extraction of polypropylene additives and their analysis by HPLC. Chromatographia 48, 491–496. Fintzou, A.T., Badeka, A.V., Kontominas, M.G., Stahl, M.R., Riganakos, K.A., 2007. Changes in physicochemical and mechanical properties of electron-beam irradiated polypropylene syringes as a function of irradiation dose. Radiat. Phys. Chem. 76, 841–851. Fox, T.G., Flory, P.J., 1950. Second order transition temperatures and related properties of polystyrene. I. Influence of molecular weight. J. Appl. Phys. 21, 581. Goldman, M., Gronsky, R., Ranganathan, R., Pruitt, L., 1996. The effects of gamma radiation sterilization and ageing on the structure and morphology of medical grade ultra high molecular weight polyethylene. Polymer 37, 2909–2913. Haji-Saeid, M., Sampa, M.H.O., Chmielewski, A.G., Radiation treatment for sterilization of packaging materials. Radiat. Phys. Chem. 76, 1535–1541. Hwang, S.-J., Tseng, M.-C., Shu, J.-R., Her Yu, H., 2008. Surface modification of cyclic olefin copolymer substrate by oxygen plasma treatment. Surf. Coat. Technol. 202, 3669–3674. Jenke, D., 2007. Evaluation of the chemical compatibility of plastic contact materials and pharmaceutical products; safety considerations related to extractables and leachables. J. Pharm. Sci. 96, 2566–2581. ˇ Kacˇarevic´-Popovic´ Zorica, M., S.B., Marinovic´-Cincovic´ Milena, T., Nedic´ Zoran, Jovanovic´ Slobodan, M., 2006. Modification of ethylene–norbornene copolymer by gamma irradiation hemijska industrija 60, 311. Lau, O.-W., Wong, S.-K., 2000. Contamination in food from packaging material. J. Chromatogr. A 882, 255–270.
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
Majumder, P.S., Bhowmick, A.K., 1999. Surface and bulk-properties of EPDM rubber modified by electron beam irradiation. Radiat. Phys. Chem. 53, 63–78. Naga, N., Tsuchiya, G., Toyota, A., 2006. Synthesis and properties of polyethylene and polypropylene containing hydroxylated cyclic units in the main chain. Polymer 47, 520–526. Nakade, K., Nagai, Y., Ohishi, F., 2010. Photodegradation of some ethylene– norbornene random copolymers. Polym. Degrad. Stabil. 95, 2654–2658. Nikolova, D., Dayss, E., Leps, G., Wutzler, A., 2004. Surface modification of cyclo olefinic copolymers for optimization of the adhesion to metals. Surf. Interface Anal. 36, 689–693. Rische, T., Waddon, A.J., Dickinson, L.C., MacKnight, W.J., 1998. Microstructure and morphology of cycloolefin copolymers. Macromolecules 31, 1871–1874. Roy, S., Yue, C.Y., Lam, Y.C., Wang, Z.Y., Hu, H., 2010. Surface analysis, hydrophilic enhancement, ageing behavior and flow in plasma modified cyclic olefin copolymer (COC)-based microfluidic devices. Sensorors Actuatators B Chem. 150, 537–549.
231
Saunier, J., Aymes Chodur, C., Leclerc, B., Larbes, L., Yagoubi, N., 2008. Using COC as pharmaceutical or cosmetic storage material. II. Effect of electron beam radiosterilization. J. Appl. Polym. Sci. 109, 1829–1839. Topass, TOPAS Advanced Polymer, /www.topas.comS. Yamazaki, M., 2004. Industrialization and application development of cyclo-olefin polymer. J. Mol. Catal. A: Chem. 213, 81–87. Yang, T.C.K., Lin, S.S.Y., Chuang, T.-H., 2002. Kinetic analysis of the thermal oxidation of metallocene cyclic olefin copolymer (mCOC)/TiO2 composites by FTIR microscopy and thermogravimetry (TG). Polym. Degrad. Stabil. 78, 525–532. Young, M.-J., Chang, W.-S., Ma, C.-C.M., 2003. Polymerization kinetics and modeling of a metallocene cyclic olefin copolymer system. Eur. Polym. J. 39, 165–171. Zhang, J., Das, C., Fan, Z., 2008. Dynamic coating for protein separation in cyclic olefin copolymer microfluidic devices. Microfluids Nanofluids 5, 327–335.
Contents lists available at SciVerse ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Effect of electron beam radio sterilization on cyclic olefin copolymers used as pharmaceutical storage materials Hala Barakat a,b,n, Caroline Aymes-Chodur a, Johanna Saunier a, Najet Yagoubi a a b
Laboratoire Mate´riaux et Sante´ EA 401, IFR 141, Faculte´ de Pharmacie, Universite´ Paris Sud-11, 5 rue J. B. Cle´ment, 92296 Chˆ atenay-Malabry, France Quality Control Departement, Faculty of Pharmacy, Tishreen University, Latakia, Syria
a r t i c l e i n f o
abstract
Article history: Received 1 January 2011 Accepted 1 January 2012 Available online 7 June 2012
The aim of this work was to study the effect of radio-sterilization on cyclo olefin copolymers (COC), that can be used as pharmaceutical storage materials, both on the surface and in the volume of the material, and to investigate the impact of the presence of a lubricant. A cyclo olefin copolymer (TOPASs 8007) was treated with an electron beam radio-sterilization at different doses ranging from 25 to 150 kGy. Polymer structure and bulk properties were evaluated by Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and Size Exclusion Chromatography (SEC). A good correlation between those analytical techniques was observed: oxidation products were formed and crosslinking of chains occured. Although these modifications were important, the effect on the thermal properties was weak. The analysis by Reversed Phase High Performance Liquid Chromatography (RP-HPLC) of extraction’s solutions of COC after irradiation showed both a remarkable decrease of the extractable amount of polyphenolic antioxidant (Irganox 1010s) initially present in the matrix, and a generation of an important number of degradation products that represent potential migrants for pharmaceutical formulations. Surface modifications were evidenced by both (FTIR/ATR) and contact angle measurements of COC films. An increase in surface polarity of COC after radio-sterilization was observed. & 2012 Elsevier Ltd. All rights reserved.
Keywords: COC Electron beam radio-sterilization Crosslinking Low molecular weight compounds Surface modification Ageing
1. Introduction Cyclic olefin copolymers (COC) belong to a new class of amorphous polymers having remarkable combination of properties such as high transparency, low moisture uptake, glass-like texture, very high heat resistance and good chemical resistance (Naga et al., 2006; Rische et al., 1998; Yang et al., 2002; Young et al., 2003). These unique properties make COC interesting for numerous industrial applications and notably in medical and pharmaceutical fields (Yamazaki, 2004; Zhang et al., 2008). Indeed, COC are more and more used as medical devices and pharmaceutical packaging especially for injectables formulations (Topass) which require a suitable and reliable sterilization process. Electron beam irradiation has been used to sterilize medical goods for well over 50 years (Abraham et al.; Ansari and Datta, 2003; Fintzou et al., 2007; Haji-Saeid et al.). Because of its convenience and lower cost, it provides an interesting and preferable alternative sterilization method towards high temperature n Corresponding author at: Universite´ Paris Sud-11, IFR 141, Faculte´ de Pharmacie, Laboratoire Mate´riaux et Sante´ EA 401, 5 rue J. B. Cle´ment, 92296 Chˆatenay-Malabry, France. Tel.: þ 33 1 46 83 57 74; Fax: þ33 1 46 83 59 63. E-mail address: [email protected] (H. Barakat).
0969-806X/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.radphyschem.2012.05.006
steam autoclaving or dry heat that can damage materials, induce degradation and lead to losses of both shape and mechanical properties. However, the high-energy electrons released from the interaction of electron beam particles with materials are known to create reactive intermediates and free radicals which follow several reaction paths and results in crosslinking and/or scission of the polymer chains (Chapiro, 1988; Clough, 2001; Davenas et al., 2002). This can modify the mechanical properties as well as the surface properties of the polymer (Majumder and Bhowmick, 1999). In addition to that, chain scissions cause the production of low molecular weight compounds (LMWC) (Buchalla and Begley, 2006; Buchalla et al., 1999; El Mansouri et al., 1998), which are susceptible to migrate from the bulk of polymer onto its surface and then to the surrounding medium (Bourges et al., 1992a; Lau and Wong, 2000). Such kind of surface modification and/or migration of leachables may affect the compatibility of the couple: content/container, which is an important safety requirement in the field of pharmaceutical packaging (Jenke, 2007). Furthermore degradation process may continue during postirradiation shelf-life storage due to the trapped free radicals that are able to react even when the irradiation has been performed since a long time (Goldman et al., 1996). It should be noticed that the degree of the modifications induced by irradiation depends on
224
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
the structure of the polymer as well as on the conditions of treatment before, during and after irradiation (irradiation dose, irradiation atmosphere and the amount of antioxidants added to the polymer). The aim of this work was firstly to study the effect of electrobeam radio-sterilization on cyclic olefin copolymers both in the bulk and on the surface of the material, then to investigate the impact of the presence of a lubricant on surface modifications induced by irradiation, and finally to evaluate post-irradiation ageing behavior. We focused on the following:
granules. In the case of contact angle measurements and poststerilization ageing studies, films were used. FTIR Microscopy analyses were performed on granules and plates. 2.2. Sample irradiation Samples were irradiated by an electron beam produced by a high power generator (10 MeV) from a 10 kW power accelerator (Ionisos, Fr.). Samples were exposed to three different irradiation doses: 25, 75, and 150 kGy. They were packed under ambient condition in plastic (small bags) sachets.
Modification of polymer chains (oxidation, scission and cross
linking) that might change the mechanical properties of COC and generate potential leachables like oligomers. Degradation of the antioxidant that could create compounds of potential toxicity. A preliminary study of surface modifications after irradiation by contact angle measurements, comparison of lubricated and non-lubricated polymer. Effect of accelerated post-irradiation ageing on polymer oxidation.
A dose of 25 kGy, which is the dose of sterilization recommended by regulatory authorities (Commission of the European Communities, 1990), was chosen as the lowest dose in our study. Two other higher doses (75 and 150 kGy) were applied to emphasize the effect of irradiation.
2. Experimental 2.1. Polymer We used a cyclo olefin copolymer (COC) called TOPASs 8007 supplied by Ticona (Germany). The polymer is an ethylene and norbornene based copolymer, it has been used in the form of granules (|ؼ2 mm), films (thikness¼ 100 mm) or plates (Fig. 1(a)). We compare the 8007-D61 grade to the 8007- S04 grade (without lubricant), which was partly studied in an other publication (Saunier et al., 2008). For the 8007-D61 granules, the surface has been coated with 0.2% of a wax (lubricant) for better injection molding processing. FTIR, Differential Scanning Calorimetry (DSC) and Size Exclusion Chromatography (SEC) were performed on both granules and films. For the analysis of extractables by HPLC, previous extractions were done on
2.3. Sample storage Irradiated samples were stored in the fridge (5 1C) to reduce the post-sterilization ageing effects. Post-sterilization ageing was studied by storing some of the samples at 50 1C during several weeks. 2.4. Size Exclusion Chromatography SEC analysis was performed at 60 1C in toluene on a PL laboratory PL-GPC 220 system: three detectors were used: a refractometer (DRI) (Polymer Laboratories, UK), a 220 R high temperature differential viscosimeter (DV) (Viscotek, UK and a PD 2040 high temperature laser light scattering (LS) detector (Precision Detectors, Inc., USA). Temperature was set at 60 1C. The solvent flow was of 1 mL/min. The SEC system was controlled by the PL-GPC 220 Controls software (version 2.01). The data acquisition and analysis were set by Viscotek softwares (Omnisec—version 4.0). The polymer concentration was 5 mg/mL. 200 mL was injected onto two Polymer Laboratories (PL) columns: a 100 A˚ and a mixed D whose molecular weights linear range stood respectively up to 4000 g/mol and between 200 and 4 106 g/mol (data given by the supplier), their granulometry was of 5 mm, their length was of 300 mm and their internal diameter of 7.5 mm. 2.5. Soxhlet extraction Soxhlet extraction was used to calculate the insoluble ratio of polymer chains with toluene as a solvent. The soxhlet extraction duration was of 24 h. Samples and cellulose thimbles were weighed before and after extraction. The mass of polymer after extraction corresponds to the insoluble part of the polymer (crosslinked chains). 2.6. FTIR
Fig. 1. (a) Structure of TOPASs 8007 D-61 (b) Structure of Irganox 1010.
The spectrometer apparatus was a Perkin-Elmer Spectrum 2000. It was used in both Attenuated Total Reflection (ATR) mode with a diamond crystal (Golden Gate-Specac) and in transmission mode. To express band intensity we used the height of the band. The wavelength range was set from 4000 to 400 cm 1 with a resolution of 4 cm 1during 16 scans. FTIR microscopy analysis (AutoImage FT-IR Microscope provided by Perkin Elmer) was performed on both lubricated non-irradiated granules in order to see the lubricant distribution and non-lubricated irradiated plates to follow the oxidation band after irradiation. The conditions were the following: The wavelength range was set from 4000 to 700 cm 1 with a resolution of 8 cm 1 during 8 and 30 scans for granules and plaques respectively. Granules were cut in slides of 60 mm thick with a microtome (Leica RM 2255) and plates were cut to get lumps of 0.95 mm thick. An image map was taken for granules and was
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
Table 1 Surface tension and polar component of surface tension for the three liquids used for contact angle measurement (data from digidrop softwares library). Liquid
Diiodomethane ethylene glycol
Surface tension, sS (mN/m)
51.8 48
Polar component of the surface tension, sp (mN/m) 0 (0%) 19 (40%)
of a size 35 35 mm2, while a line profile was realized on plates with an interval of 20 mm and for 114 points. 2.7. Differential Scanning Calorimetry DSC analysis was performed on a TA instrument Q1000. The heating/cooling rate was of 10 C1/min under nitrogen blanketing (50 mL/min). The temperature ranged was set between 0 and 160 C1. Hermetical aluminum pans (20 mL) were used. For glasstransition study, only the second temperature raise after a first heating/cooling cycle was exploited.
225
3. Results and discussion 3.1. Effect of electron beam irradiation on the COC bulk 3.1.1. Effect of radiation on polymer degradation
3.1.1.1. FTIR/Transmission. No extensive modification of COC FTIR spectra was observed after irradiation; only a slight alteration was observed around 1700 cm 1. In this frequency range, bands characteristic of CQO functions (1712 cm 1) grew with the irradiation dose (Fig. 2). It proved that some of the free radicals in the polymer chains created during irradiation had reacted with the oxygen of air. ˇ ´ erov et al., These observations agree with the work of (Sec ˇ (2008); and Kacarevic´-Popovic´ Zorica et al., (2006) who reported that the gamma ray-irradiation of TOPASs samples in air generated free radicals along the chains; these radicals reacted with molecular oxygen and the peroxy intermediates produced hydroperoxy, hydroxyl and ketone functions. Nakade et al. (2010) also reported the formation of oxidation functions of ethylene– norbornene copolymers after photo-irradiation and elucidated the mechanism of formation of photo-degradation products.
2.8. Contact angle measurement Samples were analyzed during the few days following irradiation and after storage at 50 1C during several weeks. Contact angle measurements were carried out on films after a liquid drop deposition, using a contact angle meter (GBX, France) coupled to the Digidrop Analysis Windropþþ (v1.00.01.01) software. Two liquids were used: diiodomethane (CH2I2, Merck Schuchardt OHG), and ethylene glycol (HOCH2CH2OH, E. Merck Darmstadt). The surface tension (gs) of each solvent as well as its polar (gp) components are given in Table 1. Ten drops deposited on each film sample of COC was analyzed. 2.9. Additives extraction To identify and quantify the additives in the polymer, we used a dissolution/precipitation process. 3 g of COC granules were dissolved at reflux in 50 mL of toluene at around 70 1C under stirring. After complete dissolution, the polymer was precipitated by slowly adding 50 mL of methanol under stirring. For the 150 kGy irradiated samples, the polymer was only partly soluble. Polymer was then removed from the extraction solution by filtration on a paper filter and the precipitate was carefully rinsed with methanol. Solutions containing additives, oligomers, and degradation products were then evaporated by use of a rotavapor at 60 1C (under vacuum). For the SEC experiment, the dry residue containing extractables was dissolved in 1.5 mL of toluene (HPLC grade, VWR), while for analysis by HPLC it was dissolved in a mixture of 1 mL of THF (HPLC grade, VWR) and 1 mL of acetonitrile (HPLC grade; VWR). Then, the solution was filtered on a 0.45 mm Teflon filter.
3.1.1.2. SEC. SEC analysis was done on the soluble fraction of polymer, it should be noticed that the polymer was soluble for 25 kGy and 75 kGy doses but the 150 kGy irradiated sample was only partially soluble. In order to quantify the amount of insoluble polymer, three different Soxhlet extractions in toluene were done on 150 kGy irradiated sample. An insoluble ratio of 45% 74% (n ¼3) was calculated. This ratio corresponds to the ratio of chemically crosslinked chains in the polymer, and it was in agreement with chromatogram intensities (Fig. 3) which showed a decrease of the soluble fraction of polymer with irradiation. Chromatograms showed also an enlargement of the weight distribution of the polymer after irradiation that can be attributed to both scissions and crosslinking of the polymer chain. Indeed, the polydispersity index Ip increased from 1.2 to 2.4 for the 0 and 150 kGy respectively (Fig. 4(a)). From the evolution of molecular weights presented in Fig. 4(b)–(d), it could be noticed that Mn, Mz and Mw began to increase after a 25 kGy dose and the increase of these masses became more important as the dose increased especially at 150 kGy, so we can conclude that crosslinking was the predominant phenomenon and that scission was not significant. Indeed for the 75 and 150 kGy samples, a marked shoulder appeared at an elution
2.10. HPLC We developed an HPLC method using two mobile solvents (methanol and water) and an elution gradient. The apparatus used was constituted of an Ultimate 3000 Dionex assembly with a gradient pump, an automatic injector and a photodiode Array detector. The column was a LiChrocarts 250-4 RP-18e (5 mm) (Lichrosphere, Interchim). The injection volume was of 20 mL and the flow rate was of 1 mL/ min. Acquisition was done using the ChromeleonTM software (Dionex).
Fig. 2. Zoom on the 1650–1800 cm 1 range of FTIR-transmission spectra of the non-irradiated sample and the 25, 75 and 150 kGy irradiated TOPASs 8007 D-61 samples.
226
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
volume of about 9.8 mL, which was characteristic of a new distribution of higher molecular weight. These findings were similar to the results obtained by J. Saunier (Saunier et al., 2008) who showed a predominance of crosslinking of non-lubricated TOPASs 8007 after electron beam irradiation.
3.1.1.3. DSC. A calorimetric study was conducted to put into evidence modifications in the thermal properties. The glass transition temperature for TOPASs 8007 D-61 was around 81 1C that is to say a temperature similar to the non-lubricated sample (Saunier et al., 2008). For the granules, as observed previously with non-lubricated samples, the differences between irradiated and non-irradiated samples were slight: a decrease of glass
Fig. 3. SEC chromatogram of TOPASs 8007 D-61 solution for the different irradiated doses.
transition temperature was observed with the irradiation dose (Fig. 5). This weak decrease (1 1C for 150 kGy sample) could be explained in part by the increase in chain ends because of branching (Gibbs and DiMarzio, 1958; Fox and Flory, 1950).
3.1.2. Effect of radiation on the antioxidant degradation The phenolic antioxidant found in the polymer, after extraction by a dissolution/precipitation process and analysis of the extract by HPLC, was Irganox 1010s (Fig. 1(b)). The extracted amount was about 1550 ppm. As illustrated in Fig. 6, the extractable level of Irganox 1010s had remarkably decreased as the irradiation dose increased. Similar profile of extractable amount of antioxidant after irradiation was observed previously (Saunier et al., 2008) for the non-lubricated polymer. This decrease might be explained by the degradation of the antioxidant or/and by the formation of covalent bonds between the degraded molecules and the polymer chains. Similar kind of bonding had already been reported (Allen et al., 1991).
Fig. 5. Evolution of the glass transition temperature with irradiation dose for TOPASs 8007 D-61 (n¼3).
Fig. 4. Evolution of polydisperty Index Ip (a) and molecular weight Mn (b) Mz (c) and Mw (d) (n¼ 3).
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
227
– the smallest retention times correspond to the more polar and to the smallest molecules. – as the detector was a diode array one set at wavelengths between 150 and 500 nm, all degradation products containing chromophores absorbing in this range could be detected.
Fig. 6. Evolution of the extractable amount of Irganox 1010 in TOPASs 8007 D-61 with the irradiation dose (n¼ 5).
Fig. 7. (a) SEC chromatogram of the extract of TOPASs 8007 D-61 after dissolution/precipitation for the different irradiation doses. (b) Comparaison of polymer distributions (dissolved polymer and soluble fraction of polymer in the dissolution precipitation extract) for the non-irradiated samples.
3.1.3. Effect of radiation on the generation of low molecular weight compounds (LMWC) LMWC were put into evidence by dissolution/precipitation extraction of the polymer and analyzing the extract by both SEC and HPLC. Chromatograms of the extracts corresponding to irradiated and non-irradiated polymers were compared. For SEC analysis (Fig. 7 (a)), the chromatogram of the extract corresponding to the non-irradiated samples revealed the presence of two major weight distributions, the first one assigned to the soluble fraction of the polymer after dissolution/precipitation process, this fraction was of lower molecular mass than the polymer itself (Fig. 7(b)). The second distribution corresponded to Irganox 1010 s. These two distributions decreased as the irradiation dose increased and new distributions corresponding to both polymer chain scission and degradation and recombination products of Irganox 1010s appeared. The study of these LMW molecules, and especially the degradation products of the antioxidant is an important deal because they are more able to migrate from the polymer into the pharmaceutical formulation than larger molecules and may induce toxicity. So to study these potential migrants, we followed the evolution of extractable degradation products of Irganox 1010s by HPLC analysis because it is a more selective and specific method than SEC. In the RP-HPLC system used we should remind that
On the HPLC chromatogram of the extract corresponding to the non-irradiated sample (Fig. 8(a) and (b)), there was a major peak representing Irganox 1010s and many other little peaks corresponding to both synthesis residues of Irganox 1010s and some of its degradation products that might result from a postageing process promoted by the extraction process: during extraction, polymer was heated at 60–70 1C in organic solvent during about 45 min. After irradiation, some of these peaks decreased with irradiation dose, and many new chromatographic peaks appeared. Others increased and some of them increased up till 25 kGy and then decreased for the higher doses. For a 25 kGy dose, a few new peaks were detected at short retention times (tr) (tr o 11 min or zone A) so they were characteristic of small molecules. A large number of other peaks corresponding to larger degradation products were detected in zone B (tr 411 min) even at retention time greater than that of Irganox 1010s. A significant decrease of the latter degradation products (zone B) was observed after irradiation at 75 kGy, on the contrary the intensity of the peaks located at shorter retention times (zone A) increased. This might be due to a further degradation of the longer degradation molecules by cleavage to form smaller degradation products. Indeed, zone A degradation products had a maximum of absorbance at wavelength 250 nm characteristic of carbonyl group (Fig. 8(b)), while the maximum absorbance for degradation products of zone B was at 280 nm characteristic of phenolic group (Fig. 8(a)). For the 150 kGy dose, the intensity of a majority of degradation products decreased and so it let the intensity of some degradation products which are smaller than them increase, while certain peaks had almost disappeared. These results were identical of those obtained with non-lubricated polymers that were previously studied, in other words: there is no impact of the presence of a lubricant on the degradation products generated after irradiation. From this study we can conclude that the sterilization dose 25 kGy generated a great number of extractable degradation products of Irganox 1010 s that means an important number of potential migrants; these products might be further degraded by increasing the irradiation dose. It should be noticed that degradation products of irganox 1010 s had been already studied in the literature (Allen et al., 1994, 1991; Bourges et al., 1992b). Allen detected more than 50 different compounds in a 50 kGy electron beam irradiated polypropylene sample, but most of them were of very low concentration and thus they could not be identified by mass spectroscopy. Bourges was able to identify four main degradation products after irradiation: a phenol, a quinone, a quinone methide and a hydroxylbenzaldehyde. In our study, the identification of degradation products of Irganox 1010 s by HPLC coupled to mass spectroscopy and the diffusion of these potential migrants into the pharmaceutical formulation will be discussed in further paper. As a conclusion on the bulk results, we have evidenced a predominant crosslinking as well as the formation of oxidation and degradation products. In the case of a pharmaceutical formulation which is in contact with the surface of such material, it is also important to evaluate the surface modification induced by electron beam irradiation.
228
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
Fig. 8. HPLC chromatograms of TOPASs 8007 D-61 extractables for non-irradiated sample and 25, 75 and 150 kGy irradiated samples. The detection was performed by a diode array set at wavelengths (a) 280 nm and (b) 250 nm.
3.2. Effect of electron beam irradiation on the surface 3.2.1. FTIR In order to understand the effect of lubricant on the modification of the irradiated polymer surface, the distribution of lubricant in polymer surface and bulk was studied. The ATR spectra of non-irradiated polymer showed absorbance bands at 3300, 1637 and 1564 cm 1 for the lubricated polymer (Fig. 9); these absorbance bands were characteristic of the presence of lubricant containing amide functions. The intensity of these bands was very important for polymer granules and very low for films. Indeed in the films, the adsorbance bands corresponding to the lubricant were shifted as compared with granules and were broader and of lower intensity. The analysis by FTIR microscopy/transmission of a 60 mm section of lubricated granules showed that there was no lubricant inside. This can be explained by the fact that granules were only coated with the lubricant and that the films were obtained by melting these coated granules. As observed in transmission, the ATR spectra of TOPAS 8007 D-61 showed the appearance of an absorbance band at 1712 cm 1 characteristic of a new CQO function, whose intensity increased with irradiation dose. In order to know if the effect of irradiation was homogenous on the surface and in the bulk of the polymer, the band of oxidation observed after irradiation was followed by microscopy in transmission mode. For the 150 kGy irradiated samples, a gradient of oxidation from the surface towards the bulk was observed, it was about 300 mm depth (Fig. 10).
Fig. 9. FTIR/ATR spectra of the non-irradiated lubricated and non-lubricated TOPASs 8007 Samples (granules and films).
This gradient could be explained by the kinetic of oxygen diffusion from surface into volume and must be confirmed by Electron Spin Resonance (ESR) analysis.
3.2.2. Contact angle measurements Contact angle measurements on the COC surfaces were measured on films before and after treatment by accelerated
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
229
Fig. 10. Profile line of CQO band as compared with a 3405 cm 1 band of polymer from Microscopy FTIR/Transmission for 150 kGy irradiated plates. 3405 cm 1 band represents a harmonic band or a combinated band of COC which was the same before and after irradiation.
Fig. 11. Evolution of contact angle of TOPASs 8007 (with and without lubricant) with two solvents for different irradiated doses.
electrons. The contact angles for the virgin untreated COC surface were about 40 731 and 68 721 for diiodomethane and ethylene glycol respectively, this result evidenced the apolar nature of COC because the contact angle increased as the polarity of solvent increased. No significant difference was observed between both kinds of COC (with and without lubricant) before irradiation, this may be due to the slight quantity of lubricant on the films surface as shown by FTIR/ATR. From the results given in Fig. 11, it can be seen that irradiation increased the contact angle of diiodomethane (the non-polar solvent) with COC surface, and in the same time decreased the contact angles for the polar one (ethylene glycol). It should be noticed that modifications of contact angle after irradiation were more important for the non-lubricated COC as compared with the lubricated one especially for the high doses (75 and 150 kGy). Hence, the surface polarity of COC increased with
irradiation. In order to understand the above changes, these results were correlated with those obtained with FTIR and HPLC. Indeed, the increase of polarity after irradiation can be correlated to the presence of surface polar groups such as (CQO) groups evidenced by FTIR analysis for both kinds of COC. This increase of polarity also results from the low molecular weight polar compounds that were formed during irradiation and that were observed by HPLC. But both analytical techniques did not help to answer why the impact of the lubricant on surface state of polymer was observed only after irradiation. We suggested that irradiation increased the surface roughness of polymer, and that is why these modifications were more important for non-lubricated polymers because one of the advantages of lubricant is to protect polymer surface from abrasion and friction. More detailed study of surface topography by Atomic Force Microscopy (AFM) and chemistry modification by X-ray Photoelectron Spectroscopy (XPS) appear to be essential for the better understanding of the effect of lubricant on surface modification. It should be noticed that the increase in surface polarity was in agreement with other studies realized on COC surfaces modified by oxygen plasma treatment (Bhattacharyya and Klapperich, 2007; Nikolova et al., 2004; Roy et al., 2010), which is known to incorporate oxygen containing functional groups onto a polymer surface (Hwang et al., 2008). Several examples in the literature showed that similar oxidation mechanisms could be achieved by electron beam irradiation (Burkert et al., 2009). 3.3. Post-irradiation ageing Ageing of irradiated TOPASs 8007 D-61 with time was studied. To simulate a long time ageing, an accelerated ageing was carried out by storing the polymers at 50 1C for 1 and 6 months. After a 1 month storage, an increase in the intensity of the CQO band at 1712 cm 1 was observed for the samples irradiated at 75 kGy as compared with the irradiated samples stored 4 months in fridge. For the 25 kGy irradiated samples this increase was less clear. However no increase was observed for the 150 kGy irradiated samples. After a 6 months storage, the CQO band intensity increased by a factor of 1.8 for the 25 kGy irradiated polymers and by a factor of 1.2 for the 150 kGy irradiated polymers when compared with the irradiated samples
230
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
Acknowledgments The authors would like to thank Ticona (Germany) for providing COC used in this study, as well as the Faculty of Pharmacy of Tishreen-University (Latakia–Syria) for the research funding. Special thanks to Vincent MAZEL for his kind help in FTIR microscopy analysis.
References
Fig. 12. Comparaison of the 1712 cm 1 relative absorbance for the irradiated samples stored in the fridge and samples stored 1 and 6 months at 50 1C. Samples were analyzed in FTIR/Transmission. Relative absorbance was defined as the ratio at 1712 cm 1 to the CQO band absorbance for the unaged and non-irradiated sample.
stored 4 months in fridge (Fig. 12). This process was certainly due to the existence of trapped radicals in the polymer that reacted with oxygen. Even if the number of trapped radicals generated by irradiation increased with the irradiation dose, the increase of the intensity of the CQO band after 6 months storage at 50 1C as compared with samples stored in the fridge, was more important for the less irradiated polymers. This phenomenon might be explained by a favorable diffusion of oxygen after 6 months through the polymer irradiated at 25 kGy in comparison with higher doses due to the crosslinking occurred after irradiation at 75 and 150 kGy. Our findings were partially in agreement with the results of Saunier et al. (2008) which showed similar increase of oxidation group in the samples stored 6 months in the fridge when compared with freshly irradiated polymers, but contrary to our results this increase was a function of irradiation dose.
4. Conclusion Electron beam radio-sterilization led to significant COC chain modifications with predominant crosslinking, however these modifications did not affect the thermal properties of the polymer. On the contrary, the consequence of these modifications was the generation of low molecular weight compounds such as oligomers and degradation products of the antioxidant. Such compounds were even found at 25 kGy, which is the maximum dose recommended for the sterilization of medical devices and pharmaceutical packaging. Unfortunately, low molecular weight compounds are able to migrate from the polymer to the formulations in contact with it and might induce potential toxicity. Therefore, they must be identified and their toxicity must be studied. Such study to identify degradation products and to evaluate their migration into medias of different polarities under accelerated conditions is currently in progress. Moreover, modifications of the surface state were evidenced after irradiation. An increase of surface polarity was observed, more important for the non-lubricated polymers as compared with lubricated ones. A more detailed study on the impact of sterilization and additives on the surface state seems to be essential because that might result in the adsorption of active agents on the polymer surface and as a consequence it might alter the compatibility of the polymer with the pharmaceutical formulations destined to be stored in.
Abraham, A.C., Czayka, M.A., Fisch, M.R., Electron beam irradiations of polypropylene syringe barrels and the resulting physical and chemical property changes. Radiat. Phys. Chem. 79, 83–92. Allen, D.W., Clench, M.R., Crowson, A., Leathard, D.A., Saklatvala, R., 1994. Characterisation of electron beam generated transformation products of irganox 1010 by particle beam liquid chromatography–mass spectrometry with on-line diode array detection. J. Chromatogr. A 679, 285–297. Allen, D.W., Leathard, D.A., Smith, C., 1991. The effects of gamma irradiation on the fate of hindered phenol antioxidants in food contact polymers. Analytical and 14C-labelling studies. Int. J. Radiat. Appl. Instrum. C Radiat. Phys. Chem. 38, 461–465. Ansari, I.A., Datta, A.K., 2003. An overview of sterilization methods for packaging materials used in aseptic packaging systems. Food Bioprod. Process. 81, 57–65. ˇ ´ erov, B., Marinovic´ Cincovic´, M.T., Popovic´, S., Nedic´, Z., Kac´arevic´-popovic´, Z., Sec 2008. Characterization of gamma irradiated ethylene–norbornene copolymer using FTIR, UV–vis and DSC Techniques. Polym. Bull. 60, 313–322. Bhattacharyya, A., Klapperich, C.M., 2007. Mechanical and chemical analysis of plasma and ultraviolet-ozone-surface treatments for thermal bonding of polymeric microfluidic devices. J. R. Soc. Chem., 876–882. Bourges, F., Bureau, G., Dumonceau, J., Pascat, B., 1992a. Effects of electron beam irradiation on antioxidants in commercial polyolefins: determination and quantification of products formed. Packag. Technol. Sci. 5, 205–209. Bourges, F., Bureau, G., Pascat, B., 1992b. Effects of electron beam irradiation on commercial polypropylene: kinetic study of antioxidant degradation. Packag. Technol. Sci. 5, 197–204. Buchalla, R., Begley, T.H., 2006. Characterization of gamma-irradiated polyethylene terephthalate by liquid-chromatography–mass-spectrometry (LC–MS) with atmospheric-pressure chemical ionization (APCI). Radiat. Phys. Chem. 75, 129–137. ¨ Buchalla, R., Boess, C., Bogl, K.W., 1999. Characterization of volatile radiolysis products in radiation-sterilized plastics by thermal desorption–gas chromatography–mass spectrometry: screening of six medical polymers. Radiat. Phys. Chem. 56, 353–367. Burkert, S., Kuntzsch, M., Bellmann, C., Uhlmann, P., Stamm, M., 2009. Tuning of surface properties of thin polymer films by electron beam treatment. Appl. Surf. Sci. 255, 6256–6261. Chapiro, A., 1988. Chemical modifications in irradiated polymers. Nucl. Instrum. Meth. B 32, 111–114. Clough, R.L., 2001. High-energy radiation and polymers: a review of commercial processes and emerging applications. Nucl. Instrum. Methods B 185, 8–33. Commission of the European Communities, 1990. CPMP Working Party on Quality of Medicinal Products. Note for Guidance. Davenas, J., Stevenson, I., Celette, N., Cambon, S., Gardette, J.L., Rivaton, A., Vignoud, L., 2002. Stability of polymers under ionising radiation: the many faces of radiation interactions with polymers. Nucl. Instrum. Methods B 191, 653–661. Gibbs, J.H., DiMarzio, E.A., 1958. Nature of the glass transition and the glassy state. J. Chem. Phys. 28, 373. El Mansouri, H., Yagoubi, N., Ferrier, D., 1998. Extraction of polypropylene additives and their analysis by HPLC. Chromatographia 48, 491–496. Fintzou, A.T., Badeka, A.V., Kontominas, M.G., Stahl, M.R., Riganakos, K.A., 2007. Changes in physicochemical and mechanical properties of electron-beam irradiated polypropylene syringes as a function of irradiation dose. Radiat. Phys. Chem. 76, 841–851. Fox, T.G., Flory, P.J., 1950. Second order transition temperatures and related properties of polystyrene. I. Influence of molecular weight. J. Appl. Phys. 21, 581. Goldman, M., Gronsky, R., Ranganathan, R., Pruitt, L., 1996. The effects of gamma radiation sterilization and ageing on the structure and morphology of medical grade ultra high molecular weight polyethylene. Polymer 37, 2909–2913. Haji-Saeid, M., Sampa, M.H.O., Chmielewski, A.G., Radiation treatment for sterilization of packaging materials. Radiat. Phys. Chem. 76, 1535–1541. Hwang, S.-J., Tseng, M.-C., Shu, J.-R., Her Yu, H., 2008. Surface modification of cyclic olefin copolymer substrate by oxygen plasma treatment. Surf. Coat. Technol. 202, 3669–3674. Jenke, D., 2007. Evaluation of the chemical compatibility of plastic contact materials and pharmaceutical products; safety considerations related to extractables and leachables. J. Pharm. Sci. 96, 2566–2581. ˇ Kacˇarevic´-Popovic´ Zorica, M., S.B., Marinovic´-Cincovic´ Milena, T., Nedic´ Zoran, Jovanovic´ Slobodan, M., 2006. Modification of ethylene–norbornene copolymer by gamma irradiation hemijska industrija 60, 311. Lau, O.-W., Wong, S.-K., 2000. Contamination in food from packaging material. J. Chromatogr. A 882, 255–270.
H. Barakat et al. / Radiation Physics and Chemistry 84 (2013) 223–231
Majumder, P.S., Bhowmick, A.K., 1999. Surface and bulk-properties of EPDM rubber modified by electron beam irradiation. Radiat. Phys. Chem. 53, 63–78. Naga, N., Tsuchiya, G., Toyota, A., 2006. Synthesis and properties of polyethylene and polypropylene containing hydroxylated cyclic units in the main chain. Polymer 47, 520–526. Nakade, K., Nagai, Y., Ohishi, F., 2010. Photodegradation of some ethylene– norbornene random copolymers. Polym. Degrad. Stabil. 95, 2654–2658. Nikolova, D., Dayss, E., Leps, G., Wutzler, A., 2004. Surface modification of cyclo olefinic copolymers for optimization of the adhesion to metals. Surf. Interface Anal. 36, 689–693. Rische, T., Waddon, A.J., Dickinson, L.C., MacKnight, W.J., 1998. Microstructure and morphology of cycloolefin copolymers. Macromolecules 31, 1871–1874. Roy, S., Yue, C.Y., Lam, Y.C., Wang, Z.Y., Hu, H., 2010. Surface analysis, hydrophilic enhancement, ageing behavior and flow in plasma modified cyclic olefin copolymer (COC)-based microfluidic devices. Sensorors Actuatators B Chem. 150, 537–549.
231
Saunier, J., Aymes Chodur, C., Leclerc, B., Larbes, L., Yagoubi, N., 2008. Using COC as pharmaceutical or cosmetic storage material. II. Effect of electron beam radiosterilization. J. Appl. Polym. Sci. 109, 1829–1839. Topass, TOPAS Advanced Polymer, /www.topas.comS. Yamazaki, M., 2004. Industrialization and application development of cyclo-olefin polymer. J. Mol. Catal. A: Chem. 213, 81–87. Yang, T.C.K., Lin, S.S.Y., Chuang, T.-H., 2002. Kinetic analysis of the thermal oxidation of metallocene cyclic olefin copolymer (mCOC)/TiO2 composites by FTIR microscopy and thermogravimetry (TG). Polym. Degrad. Stabil. 78, 525–532. Young, M.-J., Chang, W.-S., Ma, C.-C.M., 2003. Polymerization kinetics and modeling of a metallocene cyclic olefin copolymer system. Eur. Polym. J. 39, 165–171. Zhang, J., Das, C., Fan, Z., 2008. Dynamic coating for protein separation in cyclic olefin copolymer microfluidic devices. Microfluids Nanofluids 5, 327–335.