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polypropylene films
Nuclear Instruments and Methods in Physics Research B 268 (2010) 1474–1477
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Effect of electron beam irradiation sterilization on the biomedical poly (octene-co-ethylene)/polypropylene films Shifang Luan a, Hengchong Shi a,c, Zhanhai Yao a, Jianwei Wang b, Yongxian Song a, Jinghua Yin a,* a
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China Shandong Weigao Group Medical Polymer Co., Ltd., Weihai 264209, PR China c Graduate University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100039, PR China b
a r t i c l e
i n f o
Article history: Received 18 September 2009 Received in revised form 8 January 2010 Available online 20 January 2010 Keywords: Electron beam irradiation Biomedical Poly (octene-co-ethylene) (POE) Polypropylene (PP) Films
a b s t r a c t The effect of electron beam irradiation with the dose ranging from 15 to 40 kGy on poly (octene-co-ethylene) (POE)/polypropylene (PP) films was investigated. Wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), yellowness index testing and mechanical performance measurement were applied to characterize the films. It demonstrated that crystalline structure exhibited little change, and degree of crystallinity slightly change under the irradiation treatment. Irradiation brought about oxidation of the films, forming hydroxyl groups of the peroxides and carbonyl groups. Tensile properties become worse as irradiation dose increased. Electron beam irradiation with the dose of 15–40 kGy has little effect on crystalline performance and a little influence for the POE/PP films, indicating a good irradiation resistance. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction Polypropylene (PP) is one of the most important biomedical polymers and widely used as medical devices including syringe, blood and blood component bag, infusion bag and catheter [1,2]. The medical devices are popularly sterilized by c-ray or electron beam because they require no chemicals and leave no residues [3]. However, the medical devices made of PP are not suitable for the irradiation sterilization because of their stiffening, yellowing, decreasing of tensile strength and so on [4,5]. The irradiation can make polymer chain fracture, branch and crosslink, bringing about decrease of molecular weight, and change in molecular structure, crystalline as well as morphology [6]. Effect of irradiation on PP is always an important issue for numerous years [7–20]. It is reported that the sensitivity of PP to irradiation can be improved via introducing another polymer constituent [6,21–28]. Among these, thermoplastic elastomers, such as poly (styrene-b-butadiene-b-styrene) (SBS) [6,24], poly (styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) [25], poly (ethylene-co-vinyl acetate) (EVA) [26] and ethylene–propylene rubber (EPR) [27,28], can improve the irradiation resistance of PP to a certain extent. Poly (octene-co-ethylene) (POE) is also a polyolefin thermoplastic elastomer, which has good compatibility with PP and can improve the toughness of PP [29–31]. It is expected that both toughness and
* Corresponding author. Tel./fax: +86 431 85262109. E-mail address: [email protected] (J. Yin). 0168-583X/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2010.01.014
irradiation resistance of PP are improved by the introduction of POE. Besides, POE is a kind of biomedical material, and POE/PP blends can be used as an alternative to flexible poly (vinyl chloride) (PVC) in medical field [32]. Thus, it is worthwhile to explore how irradiation sterilization affects crystalline, mechanical performance of POE/PP blends due to its scientific interest and practical applications. In this article, the effect of electron beam irradiation on crystalline, mechanical properties, chemical structure of the film surface, and yellowness index of POE/PP films was investigated under room temperature in the air. 2. Experimental 2.1. Materials Poly (octene-co-ethylene) (POE), Engage 8200, was supplied by Dow Chemicals (MFR = 5.0 g/10 min (190 °C, 2.16 kg)). Polypropylene (PP), W 331 was purchased from Singapore Polyolefin Company (MFR = 7.05 g/10 min (230 °C, 2.16 kg)). 2.2. POE/PP blends preparation POE/PP blends with 15 wt.% POE were prepared by a HAAKE PolyLab twin-screw extruder. Temperature profile: 160, 170, 180, 190, 190, 185 and 180 °C; Rotor speed: 60 rpm, POE and PP were sufficiently mixed and dried before these processes.
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2.3. Film preparation The prepared POE/PP blends were adequately dried, and applied to manufacture the POE/PP films with the thickness of about 300 lm via a HAAKE PolyLab single-screw extruder with film die. Temperature profile: 165, 175, 190, 185 and 180 °C; Rotor speed: 10 rpm. 2.4. Electron beam irradiation The films were put in an electron accelerator chamber (RDI Dynamitron, USA), irradiating with the dose of 15, 25 and 40 kGy (dose rate 1.1 KGy/s) at room temperature in the air. 2.5. Characterization 2.5.1. Wide angle X-ray diffraction (WAXD) The wide angle X-ray diffractograms of the POE/PP films were examined via Rigaku Dmax 2500 diffractometer (CuKa–Ni filtered irradiation, k = 0.0154 nm). All the curves were recorded in the plane perpendicular to the film surface in the scan interval of 2h from 10° to 40° at a scan rate of 5°/min. 2.5.2. Differential scanning calorimetry (DSC) The thermal behaviors of the samples were investigated with a Perkin–Elmer Model DSC-7 differential scanning calorimeter equipment under a nitrogen atmosphere. The samples were heated from 20 to 210 °C, kept at 210 °C for 5 min to eliminate heat history, cooled to 30 °C, then heated to 210 °C with a rate of 10 °C/ min. 2.5.3. Fourier transform infrared spectroscopy (FTIR) FTIR spectra of the POE/PP films were tested via a BRUKER Vertex 70 FTIR spectrometer with the attenuated total reflection accessories, scanning from 4000 to 400 cm1 at a resolution of 2 cm1 for 32 scans. 2.5.4. Yellowness index According to standard ASTM D 1925, yellowness index was measured by spectrophotometric colorimeter (Kangguang SC80C, China) with the transmission mode. For each sample, five measurements were tested and used to calculate an average value of the yellowness index. 2.5.5. Tensile properties The universal testing machine, Instron 1121, was applied to inspect the tensile properties of the films. For each sample, eight measurements were tested and used to calculate an average value of the tensile properties. The tests were performed following standard GB/T 1040.3-2006 (identical to ISO 527-3: 1995). 2.5.6. Melt flow rate (MFR) The measurements of MFR were carried out as stated by standard ASTM D 1238. For all the samples, the measuring temperature, 200 °C and the piston load, 2.16 kg. 3. Results and discussion 3.1. WAXD analysis The WAXD technique can give information of crystalline architecture and crystallinity of semi-crystallization polymer. It was applied to examine the effect of electron beam irradiation on the crystalline performance of POE/PP films. The WAXD curves of the neat and irradiated POE/PP films are provided in Fig. 1. It shows
Fig. 1. X-ray diffractograms of the neat and irradiated POE/PP films.
that comparing with the neat POE/PP films, the WAXD curves of the irradiated POE/PP films illustrate little difference, the peaks nearby 14°, 16.8°, 18.4°, 25.6° and 28.5° are attributed to the reflections of monoclinic structure of a crystal, i.e., (1 1 0), (0 4 0), (1 3 0), (0 6 0) and (2 2 0), respectively. Some investigations summarized by Mukherjee et al. [33] and Bhateja et al. [34] present that low doses of irradiation either do not alter or reduce the crystallinity of polyolefins, which are similar to our data. 3.2. DSC analysis DSC can effectively investigate the effect of irradiation on the thermal properties of polymer. Here, DSC is used to inspect the crystalline properties of the neat and irradiated POE/PP films. The melting and crystallization curves as well as the melting temperature (Tm1), the onset temperature of melting (Ton1), the heat of fusion (4Hm1) in the first heating process, the melting temperature (Tm2), the onset temperature of melting (Ton2), the heat of fusion (4Hm2) in the second heating process, the crystallization temperature (Tc), onset temperature of crystallization (Ton), the heat of crystallization (4Hc) in the cooling process are illustrated in Fig. 2, Tables 1 and 2, respectively. As shown in Fig. 2(a) and Table 1, the irradiation can damage the crystallites more seriously with the irradiation dose increasing, bringing about the continuous reduction of degree of crystallinity. From Fig. 2(b) and Table 2, the irradiation has nearly no influence on Ton and Tc in the cooling process. The 4Hc’s of the irradiated films are larger than that of the neat samples. The rise in degree of crystallinity probably is attributed to the chain scission located in the amorphous region. These molecular segments can recrystallize producing new crystallites. On the other hand, degree of crystallinity decreases slightly with the irradiation dose increasing from 15 kGy, which may be due to decrease in the ability of crystallization caused by chain branching. Furthermore, chain branching reduces thickness and perfection of crystallites, making both Ton2 and Tm2 decrease as irradiation dose increases in the second heating process (Fig. 2(c) and Table 2). For the films irradiated at the dose of 15 kGy, the crystallites prefer to recrystallize to form the thicker and more perfect crystals in the second heating process, illustrating a 4Hm2 larger than the neat sample [35]. The chain branching gets serious as the irradiation dose rises, inhibiting the recrystallization. 3.3. FTIR spectroscopic analysis FTIR is an effective technique to investigate effect of irradiation on the chemical structure of polymers. When PP or PP blends are treated by electron beam irradiation or c-ray irradiation, the
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S. Luan et al. / Nuclear Instruments and Methods in Physics Research B 268 (2010) 1474–1477 Table 2 Crystallization behavior of the neat and irradiated POE/PP films in the cooling process. Irradiation dose (kGy)
Tc (°C)
Ton (°C)
4Hc (J g1)
0 15 25 40
106.7 106.3 106.1 105.6
110.6 110.3 110.0 109.6
63.4 64.7 64.2 64.1
films are displayed in Fig. 3. For the irradiated POE/PP films, a peak of 3500 cm1 corresponding to the OH groups of the peroxides formed and a peak nearby 1726 cm1 indicating the formation of carbonyl groups of aldehydes and ketones due to the irradiation. 3.4. Yellow index analysis The yellowing phenomenon is the result of creation of highly colored groups, originating from the formation of conjugated double bonds or the entrapment of free radicals after irradiation [6]. As illustrated in Fig. 4, yellow index increases slightly with the irradiation dose, indicating a little oxidation reaction occurs in the POE/PP films and irradiation dose exhibits little influence, which is in good accord with the FTIR analysis. 3.5. Tensile properties and MFR analysis
Fig. 2. Thermal transition curves of the neat and irradiated POE/PP films. (a) Melting endotherms in the first heating process; (b) crystallization exotherms in the cooling process; and (c) melting endotherms in the second heating process.
irradiation creates free radicals in the molecular chain, and interacts with oxygen molecules, producing 1720 cm1 peak of carbonyl groups, 3400 cm1 peak of hydroxyl groups in the FTIR curve [1,5,6]. The FTIR spectra of the neat and irradiated POE/PP
As prepared in the Section 2.3 film preparation process, the POE/PP films can better exhibit the performance of commercial medical films used in the medical devices. The orientation of POE/PP films occurs and tensile properties of the films in the longitudinal and transverse direction are different. Table 3 lists tensile properties of the neat and irradiated POE/PP films. It reveals that longitudinal tensile strength decrease gradually, transverse tensile strength shows nearly no change as the irradiation dose increase. Longitudinal elongation at break slightly decreases when the POE/PP film was irradiated with irradiation dose of 15 kGy. It gets much smaller as the irradiation dose increases to 25 kGy and shows nearly no further alteration with the irradiation dose up to 40 kGy. Transverse elongation at break greatly decreases as the POE/PP film was irradiated by irradiation dose of 15 kGy. Then it slowly decreases as the irradiation dose further increases. The results imply that chain scission under the lower irradiation dose is primary, and chain scission gets more serious as the irradiation dose increases. Chain branching takes place at the higher irradiation dose (no gel was obtained via xylene reflux, indicating little chain crosslinking in the films). Chain scission and branching is a couple of competitive process. The conclusion is further proved by MFR data, which present that MFR decreases, then increases as the irradiation dose increases (Table 4). Further, one-way analysis of variance (ANOVA) in the software of Origin 7.5 was used to make the statistical evaluation on the tensile test results. Statistical significance is set at p-values of 0.05. According to ANOVA, at the 95% confidence level, the p-values of 0.05 or less are considered as statistically significant difference, and the p-values greater than 0.05 were regarded as no significant difference from a statistical viewpoint [36]. It exhibits that in the
Table 1 Melting behavior of the neat and irradiated POE/PP films in the heating process. Irradiation dose (kGy)
Tm1 (°C)
Tm2 (°C)
Ton1 (°C)
Ton2 (°C)
4Hm1 (J g1)
4Hm2 (J g1)
0 15 25 40
148.4 148.7 146.8 146.3
146.1 146.0 144.6 145.0
136.4 135.2 135.0 135.1
138.5 136.9 136.7 137.0
66.6 62.0 56.3 55.8
68.5 69.0 63.0 57.7
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4. Conclusions Electron beam irradiation of poly (octene-co-ethylene) (POE)/ polypropylene (PP) films could affect crystalline performance, chemical structure of the film surface and mechanical properties. It has been disclosed that crystalline structure exhibited little change, and degree of crystallinity slightly change under the irradiation treatment. Irradiation made the films oxidized, producing hydroxyl groups of the peroxides and carbonyl groups. Tensile properties get worse as irradiation dose increased. Generally, electron beam irradiation with the dose of 15–40 kGy has little influence on the crystalline performance and a little effect for the POE/PP films, revealing a good irradiation resistance. Acknowledgements Fig. 3. FTIR spectra of the neat and irradiated POE/PP films.
The authors acknowledge the financial support of the National Natural Science Foundation of China (Project Nos. 50833005, 50920105302, 50803064, 50873084). References
Fig. 4. Yellow index of the neat and irradiated POE/PP films.
Table 3 Tensile properties of the neat and irradiated POE/PP films. Irradiation dose (kGy)
Tensile strength (MPa)
Elongation at break (%)
Longitudinal
Transverse
Longitudinal
Transverse
0 15 25 40
78.9 ± 5.4 73.7 ± 4.0 68.1 ± 2.0 66.1 ± 4.9
22.8 ± 0.4 22.9 ± 0.1 23.4 ± 0.3 23.5 ± 0.3
438.4 ± 19.1 421.2 ± 33.5 264.4 ± 45.3 261.8 ± 52.4
80.5 ± 15.6 32.9 ± 6.5 30.4 ± 3.9 19.0 ± 2.7
Table 4 MFR of the neat and irradiated POE/PP films. Irradiation dose (kGy)
MFR (g/10 min)
0 15 25 40
5.2 ± 0.1 17.1 ± 0.5 5.8 ± 0.3 6.9 ± 0.2
case of longitudinal tensile strength, neat PP is statistically different from the samples irradiated with 25 kGy (p = 0.031) and 40 kGy (p = 0.031), and between the samples irradiated with different dose present no statistically significant difference. As for longitudinal elongation at break, neat PP is statistically different from the samples irradiated with 25 kGy (p = 0.005) and 40 kGy (p = 0.008), and the samples irradiated with 15 kGy show statistically significant difference from the samples irradiated with 25 kGy (p = 0.003) and 40 kGy (p = 0.005).
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Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Effect of electron beam irradiation sterilization on the biomedical poly (octene-co-ethylene)/polypropylene films Shifang Luan a, Hengchong Shi a,c, Zhanhai Yao a, Jianwei Wang b, Yongxian Song a, Jinghua Yin a,* a
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China Shandong Weigao Group Medical Polymer Co., Ltd., Weihai 264209, PR China c Graduate University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100039, PR China b
a r t i c l e
i n f o
Article history: Received 18 September 2009 Received in revised form 8 January 2010 Available online 20 January 2010 Keywords: Electron beam irradiation Biomedical Poly (octene-co-ethylene) (POE) Polypropylene (PP) Films
a b s t r a c t The effect of electron beam irradiation with the dose ranging from 15 to 40 kGy on poly (octene-co-ethylene) (POE)/polypropylene (PP) films was investigated. Wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), yellowness index testing and mechanical performance measurement were applied to characterize the films. It demonstrated that crystalline structure exhibited little change, and degree of crystallinity slightly change under the irradiation treatment. Irradiation brought about oxidation of the films, forming hydroxyl groups of the peroxides and carbonyl groups. Tensile properties become worse as irradiation dose increased. Electron beam irradiation with the dose of 15–40 kGy has little effect on crystalline performance and a little influence for the POE/PP films, indicating a good irradiation resistance. Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction Polypropylene (PP) is one of the most important biomedical polymers and widely used as medical devices including syringe, blood and blood component bag, infusion bag and catheter [1,2]. The medical devices are popularly sterilized by c-ray or electron beam because they require no chemicals and leave no residues [3]. However, the medical devices made of PP are not suitable for the irradiation sterilization because of their stiffening, yellowing, decreasing of tensile strength and so on [4,5]. The irradiation can make polymer chain fracture, branch and crosslink, bringing about decrease of molecular weight, and change in molecular structure, crystalline as well as morphology [6]. Effect of irradiation on PP is always an important issue for numerous years [7–20]. It is reported that the sensitivity of PP to irradiation can be improved via introducing another polymer constituent [6,21–28]. Among these, thermoplastic elastomers, such as poly (styrene-b-butadiene-b-styrene) (SBS) [6,24], poly (styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) [25], poly (ethylene-co-vinyl acetate) (EVA) [26] and ethylene–propylene rubber (EPR) [27,28], can improve the irradiation resistance of PP to a certain extent. Poly (octene-co-ethylene) (POE) is also a polyolefin thermoplastic elastomer, which has good compatibility with PP and can improve the toughness of PP [29–31]. It is expected that both toughness and
* Corresponding author. Tel./fax: +86 431 85262109. E-mail address: [email protected] (J. Yin). 0168-583X/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2010.01.014
irradiation resistance of PP are improved by the introduction of POE. Besides, POE is a kind of biomedical material, and POE/PP blends can be used as an alternative to flexible poly (vinyl chloride) (PVC) in medical field [32]. Thus, it is worthwhile to explore how irradiation sterilization affects crystalline, mechanical performance of POE/PP blends due to its scientific interest and practical applications. In this article, the effect of electron beam irradiation on crystalline, mechanical properties, chemical structure of the film surface, and yellowness index of POE/PP films was investigated under room temperature in the air. 2. Experimental 2.1. Materials Poly (octene-co-ethylene) (POE), Engage 8200, was supplied by Dow Chemicals (MFR = 5.0 g/10 min (190 °C, 2.16 kg)). Polypropylene (PP), W 331 was purchased from Singapore Polyolefin Company (MFR = 7.05 g/10 min (230 °C, 2.16 kg)). 2.2. POE/PP blends preparation POE/PP blends with 15 wt.% POE were prepared by a HAAKE PolyLab twin-screw extruder. Temperature profile: 160, 170, 180, 190, 190, 185 and 180 °C; Rotor speed: 60 rpm, POE and PP were sufficiently mixed and dried before these processes.
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2.3. Film preparation The prepared POE/PP blends were adequately dried, and applied to manufacture the POE/PP films with the thickness of about 300 lm via a HAAKE PolyLab single-screw extruder with film die. Temperature profile: 165, 175, 190, 185 and 180 °C; Rotor speed: 10 rpm. 2.4. Electron beam irradiation The films were put in an electron accelerator chamber (RDI Dynamitron, USA), irradiating with the dose of 15, 25 and 40 kGy (dose rate 1.1 KGy/s) at room temperature in the air. 2.5. Characterization 2.5.1. Wide angle X-ray diffraction (WAXD) The wide angle X-ray diffractograms of the POE/PP films were examined via Rigaku Dmax 2500 diffractometer (CuKa–Ni filtered irradiation, k = 0.0154 nm). All the curves were recorded in the plane perpendicular to the film surface in the scan interval of 2h from 10° to 40° at a scan rate of 5°/min. 2.5.2. Differential scanning calorimetry (DSC) The thermal behaviors of the samples were investigated with a Perkin–Elmer Model DSC-7 differential scanning calorimeter equipment under a nitrogen atmosphere. The samples were heated from 20 to 210 °C, kept at 210 °C for 5 min to eliminate heat history, cooled to 30 °C, then heated to 210 °C with a rate of 10 °C/ min. 2.5.3. Fourier transform infrared spectroscopy (FTIR) FTIR spectra of the POE/PP films were tested via a BRUKER Vertex 70 FTIR spectrometer with the attenuated total reflection accessories, scanning from 4000 to 400 cm1 at a resolution of 2 cm1 for 32 scans. 2.5.4. Yellowness index According to standard ASTM D 1925, yellowness index was measured by spectrophotometric colorimeter (Kangguang SC80C, China) with the transmission mode. For each sample, five measurements were tested and used to calculate an average value of the yellowness index. 2.5.5. Tensile properties The universal testing machine, Instron 1121, was applied to inspect the tensile properties of the films. For each sample, eight measurements were tested and used to calculate an average value of the tensile properties. The tests were performed following standard GB/T 1040.3-2006 (identical to ISO 527-3: 1995). 2.5.6. Melt flow rate (MFR) The measurements of MFR were carried out as stated by standard ASTM D 1238. For all the samples, the measuring temperature, 200 °C and the piston load, 2.16 kg. 3. Results and discussion 3.1. WAXD analysis The WAXD technique can give information of crystalline architecture and crystallinity of semi-crystallization polymer. It was applied to examine the effect of electron beam irradiation on the crystalline performance of POE/PP films. The WAXD curves of the neat and irradiated POE/PP films are provided in Fig. 1. It shows
Fig. 1. X-ray diffractograms of the neat and irradiated POE/PP films.
that comparing with the neat POE/PP films, the WAXD curves of the irradiated POE/PP films illustrate little difference, the peaks nearby 14°, 16.8°, 18.4°, 25.6° and 28.5° are attributed to the reflections of monoclinic structure of a crystal, i.e., (1 1 0), (0 4 0), (1 3 0), (0 6 0) and (2 2 0), respectively. Some investigations summarized by Mukherjee et al. [33] and Bhateja et al. [34] present that low doses of irradiation either do not alter or reduce the crystallinity of polyolefins, which are similar to our data. 3.2. DSC analysis DSC can effectively investigate the effect of irradiation on the thermal properties of polymer. Here, DSC is used to inspect the crystalline properties of the neat and irradiated POE/PP films. The melting and crystallization curves as well as the melting temperature (Tm1), the onset temperature of melting (Ton1), the heat of fusion (4Hm1) in the first heating process, the melting temperature (Tm2), the onset temperature of melting (Ton2), the heat of fusion (4Hm2) in the second heating process, the crystallization temperature (Tc), onset temperature of crystallization (Ton), the heat of crystallization (4Hc) in the cooling process are illustrated in Fig. 2, Tables 1 and 2, respectively. As shown in Fig. 2(a) and Table 1, the irradiation can damage the crystallites more seriously with the irradiation dose increasing, bringing about the continuous reduction of degree of crystallinity. From Fig. 2(b) and Table 2, the irradiation has nearly no influence on Ton and Tc in the cooling process. The 4Hc’s of the irradiated films are larger than that of the neat samples. The rise in degree of crystallinity probably is attributed to the chain scission located in the amorphous region. These molecular segments can recrystallize producing new crystallites. On the other hand, degree of crystallinity decreases slightly with the irradiation dose increasing from 15 kGy, which may be due to decrease in the ability of crystallization caused by chain branching. Furthermore, chain branching reduces thickness and perfection of crystallites, making both Ton2 and Tm2 decrease as irradiation dose increases in the second heating process (Fig. 2(c) and Table 2). For the films irradiated at the dose of 15 kGy, the crystallites prefer to recrystallize to form the thicker and more perfect crystals in the second heating process, illustrating a 4Hm2 larger than the neat sample [35]. The chain branching gets serious as the irradiation dose rises, inhibiting the recrystallization. 3.3. FTIR spectroscopic analysis FTIR is an effective technique to investigate effect of irradiation on the chemical structure of polymers. When PP or PP blends are treated by electron beam irradiation or c-ray irradiation, the
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S. Luan et al. / Nuclear Instruments and Methods in Physics Research B 268 (2010) 1474–1477 Table 2 Crystallization behavior of the neat and irradiated POE/PP films in the cooling process. Irradiation dose (kGy)
Tc (°C)
Ton (°C)
4Hc (J g1)
0 15 25 40
106.7 106.3 106.1 105.6
110.6 110.3 110.0 109.6
63.4 64.7 64.2 64.1
films are displayed in Fig. 3. For the irradiated POE/PP films, a peak of 3500 cm1 corresponding to the OH groups of the peroxides formed and a peak nearby 1726 cm1 indicating the formation of carbonyl groups of aldehydes and ketones due to the irradiation. 3.4. Yellow index analysis The yellowing phenomenon is the result of creation of highly colored groups, originating from the formation of conjugated double bonds or the entrapment of free radicals after irradiation [6]. As illustrated in Fig. 4, yellow index increases slightly with the irradiation dose, indicating a little oxidation reaction occurs in the POE/PP films and irradiation dose exhibits little influence, which is in good accord with the FTIR analysis. 3.5. Tensile properties and MFR analysis
Fig. 2. Thermal transition curves of the neat and irradiated POE/PP films. (a) Melting endotherms in the first heating process; (b) crystallization exotherms in the cooling process; and (c) melting endotherms in the second heating process.
irradiation creates free radicals in the molecular chain, and interacts with oxygen molecules, producing 1720 cm1 peak of carbonyl groups, 3400 cm1 peak of hydroxyl groups in the FTIR curve [1,5,6]. The FTIR spectra of the neat and irradiated POE/PP
As prepared in the Section 2.3 film preparation process, the POE/PP films can better exhibit the performance of commercial medical films used in the medical devices. The orientation of POE/PP films occurs and tensile properties of the films in the longitudinal and transverse direction are different. Table 3 lists tensile properties of the neat and irradiated POE/PP films. It reveals that longitudinal tensile strength decrease gradually, transverse tensile strength shows nearly no change as the irradiation dose increase. Longitudinal elongation at break slightly decreases when the POE/PP film was irradiated with irradiation dose of 15 kGy. It gets much smaller as the irradiation dose increases to 25 kGy and shows nearly no further alteration with the irradiation dose up to 40 kGy. Transverse elongation at break greatly decreases as the POE/PP film was irradiated by irradiation dose of 15 kGy. Then it slowly decreases as the irradiation dose further increases. The results imply that chain scission under the lower irradiation dose is primary, and chain scission gets more serious as the irradiation dose increases. Chain branching takes place at the higher irradiation dose (no gel was obtained via xylene reflux, indicating little chain crosslinking in the films). Chain scission and branching is a couple of competitive process. The conclusion is further proved by MFR data, which present that MFR decreases, then increases as the irradiation dose increases (Table 4). Further, one-way analysis of variance (ANOVA) in the software of Origin 7.5 was used to make the statistical evaluation on the tensile test results. Statistical significance is set at p-values of 0.05. According to ANOVA, at the 95% confidence level, the p-values of 0.05 or less are considered as statistically significant difference, and the p-values greater than 0.05 were regarded as no significant difference from a statistical viewpoint [36]. It exhibits that in the
Table 1 Melting behavior of the neat and irradiated POE/PP films in the heating process. Irradiation dose (kGy)
Tm1 (°C)
Tm2 (°C)
Ton1 (°C)
Ton2 (°C)
4Hm1 (J g1)
4Hm2 (J g1)
0 15 25 40
148.4 148.7 146.8 146.3
146.1 146.0 144.6 145.0
136.4 135.2 135.0 135.1
138.5 136.9 136.7 137.0
66.6 62.0 56.3 55.8
68.5 69.0 63.0 57.7
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4. Conclusions Electron beam irradiation of poly (octene-co-ethylene) (POE)/ polypropylene (PP) films could affect crystalline performance, chemical structure of the film surface and mechanical properties. It has been disclosed that crystalline structure exhibited little change, and degree of crystallinity slightly change under the irradiation treatment. Irradiation made the films oxidized, producing hydroxyl groups of the peroxides and carbonyl groups. Tensile properties get worse as irradiation dose increased. Generally, electron beam irradiation with the dose of 15–40 kGy has little influence on the crystalline performance and a little effect for the POE/PP films, revealing a good irradiation resistance. Acknowledgements Fig. 3. FTIR spectra of the neat and irradiated POE/PP films.
The authors acknowledge the financial support of the National Natural Science Foundation of China (Project Nos. 50833005, 50920105302, 50803064, 50873084). References
Fig. 4. Yellow index of the neat and irradiated POE/PP films.
Table 3 Tensile properties of the neat and irradiated POE/PP films. Irradiation dose (kGy)
Tensile strength (MPa)
Elongation at break (%)
Longitudinal
Transverse
Longitudinal
Transverse
0 15 25 40
78.9 ± 5.4 73.7 ± 4.0 68.1 ± 2.0 66.1 ± 4.9
22.8 ± 0.4 22.9 ± 0.1 23.4 ± 0.3 23.5 ± 0.3
438.4 ± 19.1 421.2 ± 33.5 264.4 ± 45.3 261.8 ± 52.4
80.5 ± 15.6 32.9 ± 6.5 30.4 ± 3.9 19.0 ± 2.7
Table 4 MFR of the neat and irradiated POE/PP films. Irradiation dose (kGy)
MFR (g/10 min)
0 15 25 40
5.2 ± 0.1 17.1 ± 0.5 5.8 ± 0.3 6.9 ± 0.2
case of longitudinal tensile strength, neat PP is statistically different from the samples irradiated with 25 kGy (p = 0.031) and 40 kGy (p = 0.031), and between the samples irradiated with different dose present no statistically significant difference. As for longitudinal elongation at break, neat PP is statistically different from the samples irradiated with 25 kGy (p = 0.005) and 40 kGy (p = 0.008), and the samples irradiated with 15 kGy show statistically significant difference from the samples irradiated with 25 kGy (p = 0.003) and 40 kGy (p = 0.005).
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