New understanding on rapid irradiation oxidation of polyethylene

New understanding on rapid irradiation oxidation of polyethylene | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article New understanding on rapid irradiation oxidation of polyethylene Simei Liu, Manli Lu, Wenli Zhang, Weihua Liu, Mouhua Wang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9206304/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract To explore the ionizing radiation induced oxidation, three types of polyethylene (LDPE, UHMWPE and HDPE) were irradiated by gamma rays in Ar or air, and subsequently exposed to air. The evolution of carbonyl group and free radicals were studied by Fourier transform infrared microscopy measurement (FTIR) and electron paramagnetic resonance spectroscopy (EPR) techniques, respectively. It was found that all types of PE were rapidly oxidized during irradiation in air (i.e, direct irradiation oxidation) compared with storage in air after irradiation (i.e., post-irradiation oxidation). The oxidation product of carbonyl group on UHMWPE and HDPE for a 17-hour direct irradiation oxidation exceeded that for a 52-day post-irradiation oxidation. The carbonyl group on HDPE and UHMWPE increased gradually with time in the post-irradiation oxidation, while there was almost no such product formation on LDPE. EPR testing showed that the free radical decay on irradiated LDPE was much faster than that on HDPE and UHMWPE, indicating that the post irradiation oxidation was related to free radical oxidation. Additionally, ozone oxidation experiment and shielding irradiation oxidation experiment were designed and certified that the direct irradiation oxidation of PEs should be attributed to the highly active oxidative species induced in situ by gamma irradiation. Based on these findings, it was proposed that the rapid direct irradiation oxidation was a three-pathway oxidation reaction. This work would provide new insight to understand the direct irradiation oxidation of other polymers. ​ PE direct irradiation oxidation post-irradiation oxidation active oxidative species three-pathway oxidation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Highlights 1. Irradiation oxidation rate is much higher than post-irradiation oxidation. 2. Irradiation oxidation has stimulative effect on post-irradiation oxidation. 3. Ozone oxidation was evaluated to the contribution to irradiation oxidation. 4. A new irradiation oxidation pathway by in-situ active oxidative species was proposed. 1. Introduction Polyethylene (PE), a popular polymer material with excellent chemical stability, impact resistance, and electrical insulation, is widely used in packaging film, medical components, wires and cables, and many more [ 1 – 3 ]. Ionizing radiation has a wide range of usage and has become a common technique in modifying polymer materials [ 4 – 7 ]. When PE is exposed to ionizing radiation, it can undergo various chemical changes, including hydrogen evolution, free radical formation, double bond generation, crosslinking, and the production of oxidation products. The oxidation induced by ionizing radiation can significantly change the properties of PE products. In general, radiation-induced oxidation needs to be avoided, such as high crosslinked UHMWPE in artificial joints, nuclear wires and cables in nuclear reactor [ 8 ]. In other cases, radiation oxidation is desired to be enhanced, such as oxidative upcycling of post-consumer PE wastes [ 9 ]. The radiation-induced oxidation reaction of PE, related to the type of PE material, can occur during the irradiation process or after irradiation. Here, the former is called direct irradiation oxidation, while the latter is called post-irradiation oxidation. Due to the fact that post-irradiation oxidation can maintain for a long time and cause sustained changes in performance, it has been extensively and deeply studied [ 10 , 11 ]. It is widely accepted that the post-irradiation oxidation follows the free radical oxidation mechanism as shown in scheme 1 . The radicals stuck in the crystalline region, are known as trapped radicals. When the irradiated PE is exposed to oxygen, the trapped radicals migrate to the surface of crystalline lamellae and react with oxygen, subsequently, generate peroxy radicals (ROO˙). The hydrogen atom of imminent molecular chains is extracted by peroxy radicals, forming hydroperoxides (ROOH) and primary radicals. Then, the primary radicals are oxidized to further this cascade. Hydroperoxides are unstable and can degrade into a sequence of oxidation products with time, which are mainly ketones, esters and acids [ 12 – 14 ]. The formation of oxidation products is usually followed by the breaking of polymer backbones and the reduction of molecular weight, destroying structure and performance [ 15 – 17 ]. Therefore, the post-irradiation oxidation of PE is a long process, ranging from a few days to several years. In order to improve the long-term performance of radiation modified PE materials, adding free radical scavengers to the PE matrix can hinder the chain oxidation reaction, and then can effectively prevent post-irradiation oxidation. It is generally believed that direct irradiation oxidation also follows a free radical oxidation mechanism similar to post-irradiation oxidation [ 18 , 19 ]. More than half a century ago, Ohnishi revealed that the direct irradiation oxidation of PE was much faster than the post irradiation oxidation [ 20 ]. Recently, Lu found that vitamin E, a free radical scavenger used as antioxidant, could prevent post-irradiation oxidation of γ rays irradiated UHMWPE effectively, but could hardly prevent direct irradiation oxidation, in which an actively oxidative species during γ-rays irradiation was attributed the difference [ 21 ]. In addition, ozone (O 3 ) is inevitable to produce during the direct radiation process by air-radiolysis. Due to the highly reactivity of ozone, the contribution of ozone oxidation should be considered during the direct irradiation oxidation process [ 22 , 23 ]. Therefore, the direct irradiation oxidation process should be a complex process involving multiple types of oxidation, rather than just free-radical-initiated oxidation. In this work, the post-irradiation and direct irradiation oxidation of three types of PE were studied in detail. The possible pathways in direct irradiation oxidation was explored through ingenious experimental design. New viewpoints for direct irradiation oxidation of PE were proposed, which would provide a new insight for radiation-induced oxidative degradation of polymers. 2. Experimental 2.1 Materials Three types of PE samples were carried out in this work [ 24 ]: LDPE (1810D, crystallinity, i.e., \(\:{X}_{c}\) = 32.6%; melting point, i.e., \(\:{T}_{m}\) = 116.1 °C) and HDPE (5000S, \(\:{X}_{c}\) = 69.4%, \(\:{T}_{m}\) =137.0 °C) manufactured by Lanzhou Petrochemical Co., Ltd., China. UHMWPE ( \(\:{X}_{c}\) = 60.9%, \(\:{T}_{m}\) = 137.7 °C) was supplied from Jiujiang Zhongke Xinxing New Material Co., Ltd., China. All PE samples used in this work did not contain stabilizers. The lamellar thickness of LDPE, UHMWPE and HDPE was 9.3 nm, 36.8 nm and 33.6 nm, respectively, estimated according to Thomsone-Gibbs equation [ 24 , 25 ]. All available PE specimens were prepared in approximately 1.5 mm thickness, in the form of compression molding sheets. In preparation for measurements, all PE samples were prepared in approximately 200 µm thickness by sledge microtome (Model 1508A, Hedee). 2.2 Oxidation process 2.2.1 Direct irradiation oxidation and post-irradiation oxidation As for direct irradiation oxidation, the samples were irradiated at a dose rate of 5.8 kGy/h to an absorbed dose of 100 kGy in argon or air, by 60 Co gamma rays (resource activity 15.7×10 4 Ci, Shanghai Institute of Applied Physics, Chinese Academy of Sciences) at room temperature. Then, all irradiated samples were stored in air at room temperature and studied over time, considering it as post-irradiation oxidation process. The irradiated sample were characterized in air within 15 minutes after irradiation recorded as t = 0 d. 2.2.2 Shielding irradiation oxidation This experimental facility was used to explore the effect of ozone produced during irradiation on oxidation of PE in a sealed container. As shown in scheme 1 , two pieces of identical PE films were placed at opposite ends of a sealed container, one of which was exposed to irradiation, and the other was surrounded by lead bricks (5 cm thickness) to shield gamma rays. At the same time, a dosimeter was positioned in the shielded area created by lead bricks to calibrate the dose absorbed. The absorbed dose of dosimeter was about 0.4 kGy for the shielded sample, while it was 50 kGy for the unshielded one. 2.3 Ozone oxidation The ozonization of PE films was carried out by an ozone generator (MTS-CFG-3OA, China). The ozone–oxygen mixture supplied from ozone generator was administered to PE, receiving treatment for 4 hours. Ozone concentrations was about 40 mg/L used in this work. The oxygen gas flow rate was controlled at 0.6 L/min. 2.4 Characterization 2.4.1 Electron paramagnetic resonance spectroscopy (EPR) A JES-FA200 spectrometer working at X-band was performed on about 20 mg of irradiated samples to obtain EPR spectra in air. EPR spectra were recorded at 9.1 GHz microwave frequency, 1.0 mW microwave power, and 2.0 G modulation amplitude. The magnetic-field modulation frequency was maintained at 100 kHz and the scan time was 1 minute. The radical concentration was quantitated using the double integration comparison method, a standard (1.00×10 − 6 M TEMPOL in benzene) was used as absolute spin concentration [ 26 ]. 2.4.2 FTIR measurement The FTIR spectra measured in transmission mode were carried out by a spectrometer (VERTEX70 V, Bruker, Germany) to analyze and quantify the oxidation degree of PE, performing at a resolution of 2 cm − 1 with the spectral range of 400–4000 cm − 1 for 32 scans. The absorption peak at 2020 cm − 1 was considered impervious to small alterations in polymer structure and regarded as internal standard for spectral normalization [ 27 ]. In order to quantify the change in absorption band of functional group over time, the same integral range on baseline was adopted for the same absorption peak. 3. Results and discussion 3.1 Direct irradiation oxidation and post irradiation oxidation of three Pes Three types of PE (LDPE, HDPE, UHMWPE) were used in experiments. Each PE sample was divided into two groups: one group was irradiated in Ar and then stored in air; the other group was irradiated in air and then stored in air. The irradiation oxidation process and subsequent post-irradiation oxidation process were observed for both groups of samples. FTIR technique is an effective means to analyze the oxidation level of PEs. The changes in the FTIR spectra of all samples are illustrated in Fig. 2 . The absorption peak centered at 1718 cm − 1 is assigned to the vibrations of carbonyl group (C = O), which is thought to originate mainly from ketones [ 28 ]. The absorption peak centered at 2020 cm − 1 is assigned to the twisting of CH 2 [ 27 ]. Here, all the spectra were normalized by the absorption peak at 2020 cm − 1 . The intensity of carbonyl absorption is usually used to evaluate the oxidation degree of PE. The significant differences among the FTIR spectra for LDPE, UHMWPE and HDPE with time can be clearly seen from Fig. 2 (a)-(c). Compared with the original spectrum, there was no obvious change in the spectra of PEs after irradiation (t = 0 d). This indicated that almost no oxidation occurred during irradiation in the absence of oxygen. However, the carbonyl absorption peak at 1718 cm − 1 increased gradually with time when irradiated PE samples were exposed to air. The so-called post-irradiation oxidation occurred. As shown in Fig. 2 (a), a subtle increase in carbonyl absorption of LDPE was registered after exposure to air, and the carbonyl absorption quickly reached maximum within a few days. It can be clearly seen from Fig. 2 (b) (c) that the carbonyl absorption of HDPE and UHMWPE increased continuously with time in the range of 0 to 52 d, and the intensity was much higher than that of LDPE. In a word, the post-oxidation extent was low in LDPE, while it was much higher for HDPE and UHMWPE. The difference in post-oxidation rate should be resulted from the lower crystallinity degree of LDPE. As for the group irradiated in air as shown in Fig. 2 (d), (e), and (f), the intensity of carbonyl peak at 1718 cm − 1 increased sharply after irradiation for all three PEs. In this case, the oxidation is induced by ionizing radiation in the present of oxygen, then it is called direct irradiation oxidation. In the subsequent storage in air, the carbonyl peak increased gradually over time, indicating the post-irradiation oxidation also occurred. In terms of carbonyl peak intensity, the direct irradiation oxidation within 17 hours exceeded post-irradiation oxidation of 52 days. Interestingly, the air-irradiated LDPE showed an obvious post-irradiation oxidation differently from that irradiated in Ar. To analyze oxidation degree more intuitively, carbonyl absorbance values of all PEs were quantified as shown in Fig. 3 . It depicts the increasing values of carbonyl absorbance (ΔA post−irradiation ) during post-irradiation oxidation with period of 0 to 52 d for PE irradiated in Ar and air, and the carbonyl absorbance increment (ΔA irradiation oxidation ) of PE after direct irradiation oxidation. The ΔA irradiation oxidation was estimated by subtracting the carbonyl absorbance of the original sample from the carbonyl absorbance at 0 d. The ΔA post−irradiation was obtained by subtracting the carbonyl absorbance at 0 d from the carbonyl absorbance at 52 d in air. The build-up of carbonyl group for PEs during direct irradiation oxidation process appeared to be much more effective than that in post-irradiation oxidation. Among them, UHMWPE presented the highest oxidation degree (ΔA, 1.94) during direct irradiation oxidation was higher than that of post-irradiation oxidation for argon-irradiated UHMWPE stored for 52 d in air (ΔA, 1.34). Obviously, according to the ΔA value and oxidation time, it can be deduced that the rate of direct irradiation oxidation was much higher than that of post-irradiation oxidation. This result hinted that the oxidation behavior of the two processed was different. Further, the post-irradiation oxidation of UHMWPE and HDPE was almost independent of the irradiation atmosphere. As for UHMWPE, after a 52-day post irradiation oxidation, ΔA values for the samples irradiated in Ar and the in air increased by 1.34 and 1.36, respectively. As for HDPE, ΔA values were 1.60 and 1.09, respectively. However, for LDPE, the post-irradiation oxidation could only be observed on the sample irradiated in air. Apparently, direct irradiation oxidation had a certain stimulative effect on post-irradiation oxidation for LDPE. The weaker post-irradiation oxidation effect of LDPE was consistent with the previous reports [ 18 , 19 , 24 ]. The shift of oxidation degree to higher value was even more emphasized for LDPE irradiated in air than for that irradiated in Ar during post-irradiation oxidation. The significant difference ought to be attributed to the decomposition of hydroperoxides induced by irradiation during storage [ 29 ]. Furthermore, LDPE was a semi-crystalline polymer like other PEs, whereas the radicals decayed fast and post-oxidation effect was hardly observed. Significant differences between post-irradiation oxidation behavior of LDPE and other PEs (UHMWPE and HDPE) may be concerned with the difference in crystal structures. As is well-known, trapped radicals migrate to the lamellar surface, where they reacted with oxygen. Due to the thin thickness of lamellae of LDPE, some intermediate species formed on the surface might be difficult to stabilize, failing to subsequent oxidation reactions. The specific reasons need to be further studied, which is a significant issue for irradiation oxidation. 3.2 Decay of radicals in air The attenuation of free radical concentration must be considered in the study on the oxidation behaviors of irradiated PEs. The plot of free radical concentration as a function of time in air after irradiation is demonstrated in Fig. 4 . The initial radical concentrations for PEs were all in the order of 10 17 spins/g. The radical concentration of air-irradiated PEs was slightly lower than that of Ar-irradiated PEs. The initial radical concentration of LDPE irradiated in Ar was high, but it decayed rapidly. This was consistent with the phenomenon reported in the previous literature [ 19 ]. The radical concentration in LDPE swiftly decreased to 3% of the initial concentration within 4 days, while the radical decay rate of UHMWPE and HDPE was much slower due to their high crystallinity. This should be responsible for the higher post-irradiation oxidation extent for UHMWPE and HDPE. The free radicals in UHMWPE and HDPE exhibited similar decay behavior in post-irradiation oxidation, regardless of the irradiation environment. The oxidation kinetics after irradiation was thought to be related to the quantity of surviving radicals. Although a large number of initial radicals survived in LDPE, there was almost no post-irradiation oxidation when it was irradiated in Ar. However, the oxidation degree of LDPE reached a fairly high level through the direct irradiation oxidation process. This suggested that not only radical oxidation effect, but also other synergistic effects were attributed to the direct irradiation oxidation. The radiochemical reactions of ionizing radiation with air usually bring about radiolysis and the formation of ozone, even in closed glass containers [ 30 ]. Therefore, the additional study on the effect of ozone on PE was performed. 3.3 Ozone oxidation of PEs Ozone is one of the dominant air-radiolysis products. As a high active oxidant, ozone can oxidize polymer to introduce oxygen-containing groups, such as C = O, C–O–C and –COOH [ 30 ]. To explore the ozone (O 3 ) effect on irradiation oxidation of PEs, the oxidation behavior of PEs in a ozone atmosphere was investigated firstly. Figure 5 displays the absorption of carbonyl peak for LDPE, UHMWPE, and HDPE samples as a function of ozone oxidation time. It is seen that the significant growth in absorption of carbonyl for each PE sample with the extension of ozonation time. In addition, there was no free radical detected by EPR. Obviously, O 3 could cause strong oxidation for PE samples over a short time without the need for free radical initiation. Due to ozone generated simultaneously during the irradiation, the contribution of ozone in the direct irradiation oxidation process should be carefully studied. 3.4 Shielding irradiation experiment The special experimental apparatus was designed to verify the effect of ozone generated in the radiation field on PEs, as shown in Scheme 1 . The two groups of samples, i.e., irradiated and shielded samples, were loaded in the same container. So, two samples were believed to be under the same ozone environment during irradiation. The absorbed dose for the irradiated sample was 50 kGy and the shielded sample was only 0.4 kGy determined by dosimeter. Radiation-induced changes in carbonyl absorbance and EPR signal intensity after irradiation are presented in Fig. 6 . The direct oxidation occurred for the unshielded samples, and a large amount of free radicals were detected. On the contrary, the intensity of the carbonyl peak was hardly detected for the shielded PEs, and the EPR signal intensity of shielded PEs was rather low comparing to unshielded samples. It can be assumed that the influence of ozone oxidation on the shielded PE was rather slight. Although, ozone can brings strong oxidation to PEs, here, the concentration of O 3 produced by air radiolysis was too low to oxidize PE samples. Shah and Maxie have reported that ozone concentration by γ-ray radiosynthesis from air were very low, only 58.09 ppm at a dose of 10 kGy [ 31 ]. Therefore, ozone oxidation played a weak role in the radiation field due to the low concentration, and it could be excluded as the possibility of synergy to direct irradiation oxidation. 3.5 The mechanism of direct irradiation oxidation of PEs As can be concluded from above results, post-irradiation oxidation is usually thought as a slow reaction between free radicals and oxygen. It takes a certain amount of time for radicals to be transformed to oxidation products. However, direct irradiation oxidation was a rapid oxidation process compared with post-irradiation oxidation. Obviously, the rapid irradiation oxidation behavior cannot be explained by the slow radical oxidation alone, and there must be other oxidation pathways in irradiation oxidation process. And the behavior of ozone has been proved to make a minor contribution to direct irradiation oxidation. Meanwhile, it is seen that direct irradiation oxidation showed an acceleration impact on the oxidation degree of post-irradiation process for LDPE, and almost did not affect the post-irradiation oxidation of UHMWPE and HDPE. Hwang and Sagadevan also found that the decomposition of ozone under UV exposure produced active oxygen species which were highly oxidizing [ 32 ]. Therefore, active oxidative species are reasonably considered to be generated by gamma rays and contributed to the rapid irradiation oxidation. Based on the above results, a three-pathway mechanism for direct irradiation oxidation was proposed as shown in scheme 2 . Pathway 1 was a classical radical induced oxidation process whose reaction path was well accepted. It was a closed-loop reaction chain composed of a series of reactions. In this way, the interaction between radiation-induced radicals, containing alkyl and allyl radicals, and oxygen produced peroxide radicals. These peroxide radicals got hydrogenated from the surrounding PE chains, creating hydroperoxides. Decomposition of hydroperoxides at natural conditions could be appeared to form ketone effectively as well as fresh radicals, which in turn took part in the next oxidation process [ 33 ]. Pathway 2 was the oxidation process of active oxidative species. Basically, both the molecular chains of PE and oxygen could be activated by gamma rays, forming -*CH 2 - and active oxidative species (O 2 *). The in-situ activated oxygen excited by radiation triggered oxidation with polymer chains. Thus, pathway 2 was the consequence of the activation of oxygen, whose oxidation rate was much faster than that of pathway 1. This synergy of activated oxygen was a key factor and controlled the degree of direct irradiation oxidation. Activated oxygen was non-selective oxidation to three types of PEs. But it is not clear for its definite oxidation mechanism. No matter which pathway, numerous intermediate states must be passed before the oxidation products formed. It must be pointed out that dramatically enhanced oxidation degree of PEs only occurred in the direct irradiation oxidation process, likely due to the short-life active species. The reaction of pathway 2 ended as gamma rays exposure stopped, and the subsequent post-irradiation oxidation was only derived by radical oxidation. Pathway 3 was the ozone oxidation, which is a non-radical oxidation process. Although ozone can be generated indirectly through the radiolysis of air, its concentration under typical radiation conditions remains extreme trace amount. Accordingly, it was considered extremely minor contribution for direct irradiation oxidation of PEs. As a result, the direct irradiation oxidation was mainly the superposition effect of both in-situ oxidation of active oxygen species and radical oxidation, accompanying with trace amounts of ozone oxidation, in which the oxidation of active oxygen species played a major role. Since active oxygen species was not directly observed and it will be investigated in follow-up work. 4. Conclusion The effects of irradiation conditions and types of PE on oxidation behavior were investigated, with emphasis on the differences between direct irradiation oxidation and post-irradiation oxidation. The oxidation level for all PEs during direct irradiation oxidation was significantly higher than that of post-irradiation oxidation. HDPE and UHMWPE showed a significant post irradiation oxidation lasting a long time, while LDPE had weak one at the same conditions. The initial free radical concentration of all three irradiated PEs was not significantly different testing by EPR. The Radicals rapidly decayed and disappeared after three days on irradiated LDPE, while they still had about 20% of initial concentration after twenty days on HDPE and UHMWPE. These results indicated that the post irradiation oxidation of PEs was related to free radical oxidation, and the different post-irradiation oxidation of three types of PE might be attributed to their crystal structure. Ozone could rapidly oxidize PEs without producing large molecular free radicals. According to the shielding irradiation experiment, due to the low concentration of ozone by γ-rays radiolysis, the ozone oxidation was weak during direct irradiation oxidation of PEs. Finally, it was proposed that the rapid direct irradiation oxidation consisted of three reaction pathways: radical oxidation, active oxidative species oxidation and ozone oxidation induced by irradiation. Among them, the oxidation induced by active oxygen species may be the key factor for governing the oxidation level. Declarations Competing interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Author contributions Simei Liu: Conceptualization, Investigation, Writing - original draft, Methodology, Formal analysis; Manli Lu: Conceptualization, Writing - review & editing, Formal analysis, Methodology; Wenli Zhang: Data curation; Weihua Liu: Supervision, Investigation; Mouhua Wang: Writing - review & editing, Funding acquisition. Acknowledgements This work was funded by the Major Scientific and Technological Projects of National Natural Science Foundation of China (No.12375357), Shanghai Institute of Applied Physics, Chinese Academy of Sciences. References Moez AA, Aly S, Elshaer Y (2012) Effect of gamma radiation on low density polyethylene (LDPE) films: optical, dielectric and FTIR studies. 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Nucl Instrum Meth B 265(1):221–226 Kertesz ZI, Parsons GF (1963) Ozone Formation in Air Exposed to Cobalt-60 Gamma Radiation. Science 142(3597):1289–1290 Shah J, Maxie E (1966) Gamma-ray radiosynthesis of ozone from air. Int J Appl Radiat Isot 17(3):155–159 Hwang KC, Sagadevan A (2014) One-pot room-temperature conversion of cyclohexane to adipic acid by ozone and UV light. Science 346(6216):1495–1498 Ahn Y, Colin X, Roma G (2021) Atomic scale mechanisms controlling the oxidation of polyethylene: A first principles study. Polymers 13(13):2143 Scheme Scheme is available in the Supplementary Files section. Supplementary Files Scheme.docx Cite Share Download PDF Status: Under Review Version 1 posted Reviewers invited by journal 07 May, 2026 Reviewers agreed at journal 05 Apr, 2026 Editor invited by journal 28 Mar, 2026 Editor assigned by journal 27 Mar, 2026 First submitted to journal 26 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9206304","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":617885917,"identity":"3fdf53ec-4ca2-4037-8d32-ad3d53a5b37b","order_by":0,"name":"Simei Liu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Simei","middleName":"","lastName":"Liu","suffix":""},{"id":617885918,"identity":"cdda8cca-ccde-4666-b72d-719e0056f421","order_by":1,"name":"Manli Lu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Manli","middleName":"","lastName":"Lu","suffix":""},{"id":617885919,"identity":"b143549c-532c-43c3-9c90-17038798cc78","order_by":2,"name":"Wenli Zhang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Wenli","middleName":"","lastName":"Zhang","suffix":""},{"id":617885920,"identity":"53a49d13-e5e1-433a-bded-2943001e6eea","order_by":3,"name":"Weihua Liu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Weihua","middleName":"","lastName":"Liu","suffix":""},{"id":617885921,"identity":"1a290d3f-63df-4ceb-a17b-fd9f99e85e2b","order_by":4,"name":"Mouhua Wang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA7ElEQVRIiWNgGAWjYBCDBAYG5gMgkiQtbAkka+ExIE6pwfGzh1/dqDicZ3D8zOcPD3fY5TGwH37A8HMHHi1n8tKsc84cLjY4k7tNIvFMcjEDT5oBY+8Z3FrMDuSYGee2HU7ccCB3G0NiG3NiA0MOAzNjGx4t599AtZx/8/hDYlt9YgP/GwJabuQYPwZruZHDIJEIZDRIELDF/sYbM+acM+mJM288MwNqOV7MJvHM4GAvHi2S/TnGn3MqrBP7zic//vizrTqPnz/54YOfeLQAAZsEMi+BDUgcwKsBmFA+oGghoHoUjIJRMApGIAAAIFpZQgL6IrcAAAAASUVORK5CYII=","orcid":"https://orcid.org/0009-0008-5212-241X","institution":"Shanghai Institute of Applied Physics Chinese Academy of Sciences","correspondingAuthor":true,"prefix":"","firstName":"Mouhua","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2026-03-24 03:46:53","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9206304/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9206304/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106646591,"identity":"66ac5141-ada2-494c-9214-6527e9f0cc68","added_by":"auto","created_at":"2026-04-10 20:24:43","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":35087,"visible":true,"origin":"","legend":"\u003cp\u003eShielded radiation apparatus.\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9206304/v1/73ce24e5bdc5a11c1b62a48f.jpg"},{"id":106646593,"identity":"740cdff6-a497-4c89-b0a0-532807d61173","added_by":"auto","created_at":"2026-04-10 20:24:43","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":153044,"visible":true,"origin":"","legend":"\u003cp\u003eThe normalized infrared spectra of carbonyl for (a) LDPE, (b) UHMWPE, (c) HDPE after irradiation in Ar and (d) LDPE, (e) UHMWPE, (f) HDPE after irradiation in air varied with storage time in air. Storage time from a to f was: a. original, b. 0 d, c. 5 d, d. 10 d, e. 25 d, f. 52 d.\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9206304/v1/fd8a3e18dbb7147989e44904.jpg"},{"id":106646592,"identity":"ab13ed8f-e78e-4cc3-aec7-a90383b263aa","added_by":"auto","created_at":"2026-04-10 20:24:43","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":49128,"visible":true,"origin":"","legend":"\u003cp\u003eThe increment of carbonyl absorbance ΔA\u003csub\u003epost-irradiation \u003c/sub\u003e(A\u003csub\u003e1\u003c/sub\u003e - A\u003csub\u003e0\u003c/sub\u003e value; A\u003csub\u003e1\u003c/sub\u003e = carbonyl absorbance at 52 d; A\u003csub\u003e0\u003c/sub\u003e = carbonyl absorbance at 0 d) after post-irradiation storage time in air for 52 d for LDPE, UHMWPE and HDPE irradiated in argon and in air. The ΔA\u003csub\u003eirradiation oxidation\u003c/sub\u003e (A\u003csub\u003e0\u003c/sub\u003e - A\u003csub\u003e2\u003c/sub\u003e value; A\u003csub\u003e0\u003c/sub\u003e = carbonyl absorbance at 0 d; A\u003csub\u003e2\u003c/sub\u003e = original carbonyl absorbance) for PE samples after irradiation in air.\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9206304/v1/1a58eefc5fb1b25e7b26991d.jpg"},{"id":106646598,"identity":"5ee17b97-311a-4e29-bbd1-49f14c20d34b","added_by":"auto","created_at":"2026-04-10 20:24:44","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":43644,"visible":true,"origin":"","legend":"\u003cp\u003eRadical concentration evolution for PEs irradiated to 100 kGy in Ar or in air during storage in air.\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9206304/v1/9ad70c8e80794da5d489fe02.jpg"},{"id":106726822,"identity":"f4cb5353-43e1-4a71-a704-8da3aea7c1cf","added_by":"auto","created_at":"2026-04-12 18:37:21","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":37565,"visible":true,"origin":"","legend":"\u003cp\u003eThe normalized carbonyl absorbance of LDPE, UHMWPE and HDPE as a function of ozone oxidation time.\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9206304/v1/38f56ed5cef6a808a877f8b0.jpg"},{"id":106646594,"identity":"15cb5d9a-e941-4b1c-a7f7-33b3d831bd14","added_by":"auto","created_at":"2026-04-10 20:24:43","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":51326,"visible":true,"origin":"","legend":"\u003cp\u003e(a) carbonyl absorbance ΔA (A\u003csub\u003e1\u003c/sub\u003e – A\u003csub\u003e0\u003c/sub\u003e value; A\u003csub\u003e1\u003c/sub\u003e = carbonyl absorbance at 0 d; A\u003csub\u003e0\u003c/sub\u003e = original carbonyl absorbance); and (b) EPR signal intensity for unshielded and shielded PEs after irradiation to 50 kGy in air.\u003c/p\u003e","description":"","filename":"Picture6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9206304/v1/3c3c06cd9eb95aba1b816f3c.jpg"},{"id":106728202,"identity":"511be34f-62fd-4d84-9e93-e9194641b6e3","added_by":"auto","created_at":"2026-04-12 18:42:09","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":970217,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9206304/v1/b41e084a-8216-481f-abac-04c9e0935907.pdf"},{"id":106646597,"identity":"c2a65f2b-6fdd-42cc-8cd8-33823aa7c75b","added_by":"auto","created_at":"2026-04-10 20:24:44","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":128981,"visible":true,"origin":"","legend":"","description":"","filename":"Scheme.docx","url":"https://assets-eu.researchsquare.com/files/rs-9206304/v1/d7b28b024fe20f36a19d3592.docx"}],"financialInterests":"","formattedTitle":"New understanding on rapid irradiation oxidation of polyethylene","fulltext":[{"header":"Highlights","content":"\u003cp\u003e1. Irradiation oxidation rate is much higher than post-irradiation oxidation.\u003c/p\u003e\u003cp\u003e2. Irradiation oxidation has stimulative effect on post-irradiation oxidation.\u003c/p\u003e\u003cp\u003e3. Ozone oxidation was evaluated to the contribution to irradiation oxidation.\u003c/p\u003e\u003cp\u003e4. A new irradiation oxidation pathway by in-situ active oxidative species was proposed.\u003c/p\u003e"},{"header":"1. Introduction","content":"\u003cp\u003ePolyethylene (PE), a popular polymer material with excellent chemical stability, impact resistance, and electrical insulation, is widely used in packaging film, medical components, wires and cables, and many more [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Ionizing radiation has a wide range of usage and has become a common technique in modifying polymer materials [\u003cspan additionalcitationids=\"CR5 CR6\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. When PE is exposed to ionizing radiation, it can undergo various chemical changes, including hydrogen evolution, free radical formation, double bond generation, crosslinking, and the production of oxidation products. The oxidation induced by ionizing radiation can significantly change the properties of PE products. In general, radiation-induced oxidation needs to be avoided, such as high crosslinked UHMWPE in artificial joints, nuclear wires and cables in nuclear reactor [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. In other cases, radiation oxidation is desired to be enhanced, such as oxidative upcycling of post-consumer PE wastes [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The radiation-induced oxidation reaction of PE, related to the type of PE material, can occur during the irradiation process or after irradiation. Here, the former is called direct irradiation oxidation, while the latter is called post-irradiation oxidation. Due to the fact that post-irradiation oxidation can maintain for a long time and cause sustained changes in performance, it has been extensively and deeply studied [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIt is widely accepted that the post-irradiation oxidation follows the free radical oxidation mechanism as shown in scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The radicals stuck in the crystalline region, are known as trapped radicals. When the irradiated PE is exposed to oxygen, the trapped radicals migrate to the surface of crystalline lamellae and react with oxygen, subsequently, generate peroxy radicals (ROO˙). The hydrogen atom of imminent molecular chains is extracted by peroxy radicals, forming hydroperoxides (ROOH) and primary radicals. Then, the primary radicals are oxidized to further this cascade. Hydroperoxides are unstable and can degrade into a sequence of oxidation products with time, which are mainly ketones, esters and acids [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. The formation of oxidation products is usually followed by the breaking of polymer backbones and the reduction of molecular weight, destroying structure and performance [\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Therefore, the post-irradiation oxidation of PE is a long process, ranging from a few days to several years. In order to improve the long-term performance of radiation modified PE materials, adding free radical scavengers to the PE matrix can hinder the chain oxidation reaction, and then can effectively prevent post-irradiation oxidation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIt is generally believed that direct irradiation oxidation also follows a free radical oxidation mechanism similar to post-irradiation oxidation [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. More than half a century ago, Ohnishi revealed that the direct irradiation oxidation of PE was much faster than the post irradiation oxidation [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Recently, Lu found that vitamin E, a free radical scavenger used as antioxidant, could prevent post-irradiation oxidation of γ rays irradiated UHMWPE effectively, but could hardly prevent direct irradiation oxidation, in which an actively oxidative species during γ-rays irradiation was attributed the difference [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. In addition, ozone (O\u003csub\u003e3\u003c/sub\u003e) is inevitable to produce during the direct radiation process by air-radiolysis. Due to the highly reactivity of ozone, the contribution of ozone oxidation should be considered during the direct irradiation oxidation process [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Therefore, the direct irradiation oxidation process should be a complex process involving multiple types of oxidation, rather than just free-radical-initiated oxidation.\u003c/p\u003e \u003cp\u003eIn this work, the post-irradiation and direct irradiation oxidation of three types of PE were studied in detail. The possible pathways in direct irradiation oxidation was explored through ingenious experimental design. New viewpoints for direct irradiation oxidation of PE were proposed, which would provide a new insight for radiation-induced oxidative degradation of polymers.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eThree types of PE samples were carried out in this work [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]: LDPE (1810D, crystallinity, i.e., \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{X}_{c}\\)\u003c/span\u003e\u003c/span\u003e= 32.6%; melting point, i.e., \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{T}_{m}\\)\u003c/span\u003e\u003c/span\u003e = 116.1 \u0026deg;C) and HDPE (5000S, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{X}_{c}\\)\u003c/span\u003e\u003c/span\u003e= 69.4%, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{T}_{m}\\)\u003c/span\u003e\u003c/span\u003e=137.0 \u0026deg;C) manufactured by Lanzhou Petrochemical Co., Ltd., China. UHMWPE (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{X}_{c}\\)\u003c/span\u003e\u003c/span\u003e= 60.9%, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{T}_{m}\\)\u003c/span\u003e\u003c/span\u003e= 137.7 \u0026deg;C) was supplied from Jiujiang Zhongke Xinxing New Material Co., Ltd., China. All PE samples used in this work did not contain stabilizers. The lamellar thickness of LDPE, UHMWPE and HDPE was 9.3 nm, 36.8 nm and 33.6 nm, respectively, estimated according to Thomsone-Gibbs equation [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. All available PE specimens were prepared in approximately 1.5 mm thickness, in the form of compression molding sheets. In preparation for measurements, all PE samples were prepared in approximately 200 \u0026micro;m thickness by sledge microtome (Model 1508A, Hedee).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Oxidation process\u003c/h2\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1 Direct irradiation oxidation and post-irradiation oxidation\u003c/h2\u003e \u003cp\u003eAs for direct irradiation oxidation, the samples were irradiated at a dose rate of 5.8 kGy/h to an absorbed dose of 100 kGy in argon or air, by \u003csup\u003e60\u003c/sup\u003eCo gamma rays (resource activity 15.7\u0026times;10\u003csup\u003e4\u003c/sup\u003e Ci, Shanghai Institute of Applied Physics, Chinese Academy of Sciences) at room temperature. Then, all irradiated samples were stored in air at room temperature and studied over time, considering it as post-irradiation oxidation process. The irradiated sample were characterized in air within 15 minutes after irradiation recorded as t\u0026thinsp;=\u0026thinsp;0 d.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2 Shielding irradiation oxidation\u003c/h2\u003e \u003cp\u003eThis experimental facility was used to explore the effect of ozone produced during irradiation on oxidation of PE in a sealed container. As shown in scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, two pieces of identical PE films were placed at opposite ends of a sealed container, one of which was exposed to irradiation, and the other was surrounded by lead bricks (5 cm thickness) to shield gamma rays. At the same time, a dosimeter was positioned in the shielded area created by lead bricks to calibrate the dose absorbed. The absorbed dose of dosimeter was about 0.4 kGy for the shielded sample, while it was 50 kGy for the unshielded one.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Ozone oxidation\u003c/h2\u003e \u003cp\u003eThe ozonization of PE films was carried out by an ozone generator (MTS-CFG-3OA, China). The ozone\u0026ndash;oxygen mixture supplied from ozone generator was administered to PE, receiving treatment for 4 hours. Ozone concentrations was about 40 mg/L used in this work. The oxygen gas flow rate was controlled at 0.6 L/min.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Characterization\u003c/h2\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.4.1 Electron paramagnetic resonance spectroscopy (EPR)\u003c/h2\u003e \u003cp\u003eA JES-FA200 spectrometer working at X-band was performed on about 20 mg of irradiated samples to obtain EPR spectra in air. EPR spectra were recorded at 9.1 GHz microwave frequency, 1.0 mW microwave power, and 2.0 G modulation amplitude. The magnetic-field modulation frequency was maintained at 100 kHz and the scan time was 1 minute. The radical concentration was quantitated using the double integration comparison method, a standard (1.00\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e M TEMPOL in benzene) was used as absolute spin concentration [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.4.2 FTIR measurement\u003c/h2\u003e \u003cp\u003eThe FTIR spectra measured in transmission mode were carried out by a spectrometer (VERTEX70 V, Bruker, Germany) to analyze and quantify the oxidation degree of PE, performing at a resolution of 2 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with the spectral range of 400\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for 32 scans. The absorption peak at 2020 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was considered impervious to small alterations in polymer structure and regarded as internal standard for spectral normalization [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. In order to quantify the change in absorption band of functional group over time, the same integral range on baseline was adopted for the same absorption peak.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Direct irradiation oxidation and post irradiation oxidation of three Pes\u003c/h2\u003e \u003cp\u003eThree types of PE (LDPE, HDPE, UHMWPE) were used in experiments. Each PE sample was divided into two groups: one group was irradiated in Ar and then stored in air; the other group was irradiated in air and then stored in air. The irradiation oxidation process and subsequent post-irradiation oxidation process were observed for both groups of samples. FTIR technique is an effective means to analyze the oxidation level of PEs. The changes in the FTIR spectra of all samples are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The absorption peak centered at 1718 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is assigned to the vibrations of carbonyl group (C\u0026thinsp;=\u0026thinsp;O), which is thought to originate mainly from ketones [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. The absorption peak centered at 2020 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is assigned to the twisting of CH\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Here, all the spectra were normalized by the absorption peak at 2020 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The intensity of carbonyl absorption is usually used to evaluate the oxidation degree of PE.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe significant differences among the FTIR spectra for LDPE, UHMWPE and HDPE with time can be clearly seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (a)-(c). Compared with the original spectrum, there was no obvious change in the spectra of PEs after irradiation (t\u0026thinsp;=\u0026thinsp;0 d). This indicated that almost no oxidation occurred during irradiation in the absence of oxygen. However, the carbonyl absorption peak at 1718 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increased gradually with time when irradiated PE samples were exposed to air. The so-called post-irradiation oxidation occurred. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (a), a subtle increase in carbonyl absorption of LDPE was registered after exposure to air, and the carbonyl absorption quickly reached maximum within a few days. It can be clearly seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (b) (c) that the carbonyl absorption of HDPE and UHMWPE increased continuously with time in the range of 0 to 52 d, and the intensity was much higher than that of LDPE. In a word, the post-oxidation extent was low in LDPE, while it was much higher for HDPE and UHMWPE. The difference in post-oxidation rate should be resulted from the lower crystallinity degree of LDPE.\u003c/p\u003e \u003cp\u003eAs for the group irradiated in air as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (d), (e), and (f), the intensity of carbonyl peak at 1718 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e increased sharply after irradiation for all three PEs. In this case, the oxidation is induced by ionizing radiation in the present of oxygen, then it is called direct irradiation oxidation. In the subsequent storage in air, the carbonyl peak increased gradually over time, indicating the post-irradiation oxidation also occurred. In terms of carbonyl peak intensity, the direct irradiation oxidation within 17 hours exceeded post-irradiation oxidation of 52 days. Interestingly, the air-irradiated LDPE showed an obvious post-irradiation oxidation differently from that irradiated in Ar.\u003c/p\u003e \u003cp\u003eTo analyze oxidation degree more intuitively, carbonyl absorbance values of all PEs were quantified as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. It depicts the increasing values of carbonyl absorbance (ΔA\u003csub\u003epost\u0026minus;irradiation\u003c/sub\u003e) during post-irradiation oxidation with period of 0 to 52 d for PE irradiated in Ar and air, and the carbonyl absorbance increment (ΔA\u003csub\u003eirradiation oxidation\u003c/sub\u003e) of PE after direct irradiation oxidation. The ΔA\u003csub\u003eirradiation oxidation\u003c/sub\u003e was estimated by subtracting the carbonyl absorbance of the original sample from the carbonyl absorbance at 0 d. The ΔA\u003csub\u003epost\u0026minus;irradiation\u003c/sub\u003e was obtained by subtracting the carbonyl absorbance at 0 d from the carbonyl absorbance at 52 d in air.\u003c/p\u003e \u003cp\u003eThe build-up of carbonyl group for PEs during direct irradiation oxidation process appeared to be much more effective than that in post-irradiation oxidation. Among them, UHMWPE presented the highest oxidation degree (ΔA, 1.94) during direct irradiation oxidation was higher than that of post-irradiation oxidation for argon-irradiated UHMWPE stored for 52 d in air (ΔA, 1.34). Obviously, according to the ΔA value and oxidation time, it can be deduced that the rate of direct irradiation oxidation was much higher than that of post-irradiation oxidation. This result hinted that the oxidation behavior of the two processed was different.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFurther, the post-irradiation oxidation of UHMWPE and HDPE was almost independent of the irradiation atmosphere. As for UHMWPE, after a 52-day post irradiation oxidation, ΔA values for the samples irradiated in Ar and the in air increased by 1.34 and 1.36, respectively. As for HDPE, ΔA values were 1.60 and 1.09, respectively. However, for LDPE, the post-irradiation oxidation could only be observed on the sample irradiated in air. Apparently, direct irradiation oxidation had a certain stimulative effect on post-irradiation oxidation for LDPE. The weaker post-irradiation oxidation effect of LDPE was consistent with the previous reports [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe shift of oxidation degree to higher value was even more emphasized for LDPE irradiated in air than for that irradiated in Ar during post-irradiation oxidation. The significant difference ought to be attributed to the decomposition of hydroperoxides induced by irradiation during storage [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Furthermore, LDPE was a semi-crystalline polymer like other PEs, whereas the radicals decayed fast and post-oxidation effect was hardly observed. Significant differences between post-irradiation oxidation behavior of LDPE and other PEs (UHMWPE and HDPE) may be concerned with the difference in crystal structures. As is well-known, trapped radicals migrate to the lamellar surface, where they reacted with oxygen. Due to the thin thickness of lamellae of LDPE, some intermediate species formed on the surface might be difficult to stabilize, failing to subsequent oxidation reactions. The specific reasons need to be further studied, which is a significant issue for irradiation oxidation.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Decay of radicals in air\u003c/h2\u003e \u003cp\u003eThe attenuation of free radical concentration must be considered in the study on the oxidation behaviors of irradiated PEs. The plot of free radical concentration as a function of time in air after irradiation is demonstrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The initial radical concentrations for PEs were all in the order of 10\u003csup\u003e17\u003c/sup\u003e spins/g. The radical concentration of air-irradiated PEs was slightly lower than that of Ar-irradiated PEs. The initial radical concentration of LDPE irradiated in Ar was high, but it decayed rapidly. This was consistent with the phenomenon reported in the previous literature [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The radical concentration in LDPE swiftly decreased to 3% of the initial concentration within 4 days, while the radical decay rate of UHMWPE and HDPE was much slower due to their high crystallinity. This should be responsible for the higher post-irradiation oxidation extent for UHMWPE and HDPE. The free radicals in UHMWPE and HDPE exhibited similar decay behavior in post-irradiation oxidation, regardless of the irradiation environment.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe oxidation kinetics after irradiation was thought to be related to the quantity of surviving radicals. Although a large number of initial radicals survived in LDPE, there was almost no post-irradiation oxidation when it was irradiated in Ar. However, the oxidation degree of LDPE reached a fairly high level through the direct irradiation oxidation process. This suggested that not only radical oxidation effect, but also other synergistic effects were attributed to the direct irradiation oxidation. The radiochemical reactions of ionizing radiation with air usually bring about radiolysis and the formation of ozone, even in closed glass containers [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Therefore, the additional study on the effect of ozone on PE was performed.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Ozone oxidation of PEs\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOzone is one of the dominant air-radiolysis products. As a high active oxidant, ozone can oxidize polymer to introduce oxygen-containing groups, such as C\u0026thinsp;=\u0026thinsp;O, C\u0026ndash;O\u0026ndash;C and \u0026ndash;COOH [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. To explore the ozone (O\u003csub\u003e3\u003c/sub\u003e) effect on irradiation oxidation of PEs, the oxidation behavior of PEs in a ozone atmosphere was investigated firstly. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e displays the absorption of carbonyl peak for LDPE, UHMWPE, and HDPE samples as a function of ozone oxidation time. It is seen that the significant growth in absorption of carbonyl for each PE sample with the extension of ozonation time. In addition, there was no free radical detected by EPR. Obviously, O\u003csub\u003e3\u003c/sub\u003e could cause strong oxidation for PE samples over a short time without the need for free radical initiation. Due to ozone generated simultaneously during the irradiation, the contribution of ozone in the direct irradiation oxidation process should be carefully studied.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Shielding irradiation experiment\u003c/h2\u003e \u003cp\u003eThe special experimental apparatus was designed to verify the effect of ozone generated in the radiation field on PEs, as shown in Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The two groups of samples, i.e., irradiated and shielded samples, were loaded in the same container. So, two samples were believed to be under the same ozone environment during irradiation. The absorbed dose for the irradiated sample was 50 kGy and the shielded sample was only 0.4 kGy determined by dosimeter. Radiation-induced changes in carbonyl absorbance and EPR signal intensity after irradiation are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The direct oxidation occurred for the unshielded samples, and a large amount of free radicals were detected. On the contrary, the intensity of the carbonyl peak was hardly detected for the shielded PEs, and the EPR signal intensity of shielded PEs was rather low comparing to unshielded samples. It can be assumed that the influence of ozone oxidation on the shielded PE was rather slight. Although, ozone can brings strong oxidation to PEs, here, the concentration of O\u003csub\u003e3\u003c/sub\u003e produced by air radiolysis was too low to oxidize PE samples. Shah and Maxie have reported that ozone concentration by γ-ray radiosynthesis from air were very low, only 58.09 ppm at a dose of 10 kGy [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Therefore, ozone oxidation played a weak role in the radiation field due to the low concentration, and it could be excluded as the possibility of synergy to direct irradiation oxidation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.5 The mechanism of direct irradiation oxidation of PEs\u003c/h2\u003e \u003cp\u003eAs can be concluded from above results, post-irradiation oxidation is usually thought as a slow reaction between free radicals and oxygen. It takes a certain amount of time for radicals to be transformed to oxidation products. However, direct irradiation oxidation was a rapid oxidation process compared with post-irradiation oxidation. Obviously, the rapid irradiation oxidation behavior cannot be explained by the slow radical oxidation alone, and there must be other oxidation pathways in irradiation oxidation process. And the behavior of ozone has been proved to make a minor contribution to direct irradiation oxidation. Meanwhile, it is seen that direct irradiation oxidation showed an acceleration impact on the oxidation degree of post-irradiation process for LDPE, and almost did not affect the post-irradiation oxidation of UHMWPE and HDPE.\u003c/p\u003e \u003cp\u003eHwang and Sagadevan also found that the decomposition of ozone under UV exposure produced active oxygen species which were highly oxidizing [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Therefore, active oxidative species are reasonably considered to be generated by gamma rays and contributed to the rapid irradiation oxidation. Based on the above results, a three-pathway mechanism for direct irradiation oxidation was proposed as shown in scheme \u003cspan refid=\"Sch2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003ePathway 1 was a classical radical induced oxidation process whose reaction path was well accepted. It was a closed-loop reaction chain composed of a series of reactions. In this way, the interaction between radiation-induced radicals, containing alkyl and allyl radicals, and oxygen produced peroxide radicals. These peroxide radicals got hydrogenated from the surrounding PE chains, creating hydroperoxides. Decomposition of hydroperoxides at natural conditions could be appeared to form ketone effectively as well as fresh radicals, which in turn took part in the next oxidation process [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003cp\u003ePathway 2 was the oxidation process of active oxidative species. Basically, both the molecular chains of PE and oxygen could be activated by gamma rays, forming -*CH\u003csub\u003e2\u003c/sub\u003e- and active oxidative species (O\u003csub\u003e2\u003c/sub\u003e*). The in-situ activated oxygen excited by radiation triggered oxidation with polymer chains. Thus, pathway 2 was the consequence of the activation of oxygen, whose oxidation rate was much faster than that of pathway 1. This synergy of activated oxygen was a key factor and controlled the degree of direct irradiation oxidation. Activated oxygen was non-selective oxidation to three types of PEs. But it is not clear for its definite oxidation mechanism. No matter which pathway, numerous intermediate states must be passed before the oxidation products formed. It must be pointed out that dramatically enhanced oxidation degree of PEs only occurred in the direct irradiation oxidation process, likely due to the short-life active species. The reaction of pathway 2 ended as gamma rays exposure stopped, and the subsequent post-irradiation oxidation was only derived by radical oxidation.\u003c/p\u003e \u003cp\u003ePathway 3 was the ozone oxidation, which is a non-radical oxidation process. Although ozone can be generated indirectly through the radiolysis of air, its concentration under typical radiation conditions remains extreme trace amount. Accordingly, it was considered extremely minor contribution for direct irradiation oxidation of PEs.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs a result, the direct irradiation oxidation was mainly the superposition effect of both in-situ oxidation of active oxygen species and radical oxidation, accompanying with trace amounts of ozone oxidation, in which the oxidation of active oxygen species played a major role. Since active oxygen species was not directly observed and it will be investigated in follow-up work.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThe effects of irradiation conditions and types of PE on oxidation behavior were investigated, with emphasis on the differences between direct irradiation oxidation and post-irradiation oxidation. The oxidation level for all PEs during direct irradiation oxidation was significantly higher than that of post-irradiation oxidation. HDPE and UHMWPE showed a significant post irradiation oxidation lasting a long time, while LDPE had weak one at the same conditions. The initial free radical concentration of all three irradiated PEs was not significantly different testing by EPR. The Radicals rapidly decayed and disappeared after three days on irradiated LDPE, while they still had about 20% of initial concentration after twenty days on HDPE and UHMWPE. These results indicated that the post irradiation oxidation of PEs was related to free radical oxidation, and the different post-irradiation oxidation of three types of PE might be attributed to their crystal structure. Ozone could rapidly oxidize PEs without producing large molecular free radicals. According to the shielding irradiation experiment, due to the low concentration of ozone by γ-rays radiolysis, the ozone oxidation was weak during direct irradiation oxidation of PEs. Finally, it was proposed that the rapid direct irradiation oxidation consisted of three reaction pathways: radical oxidation, active oxidative species oxidation and ozone oxidation induced by irradiation. Among them, the oxidation induced by active oxygen species may be the key factor for governing the oxidation level.\u003c/p\u003e"},{"header":"Declarations","content":" \u003cp\u003e \u003cstrong\u003eCompeting interest:\u003c/strong\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e \u003cp\u003eSimei Liu: Conceptualization, Investigation, Writing - original draft, Methodology, Formal analysis; Manli Lu: Conceptualization, Writing - review \u0026amp; editing, Formal analysis, Methodology; Wenli Zhang: Data curation; Weihua Liu: Supervision, Investigation; Mouhua Wang: Writing - review \u0026amp; editing, Funding acquisition.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis work was funded by the Major Scientific and Technological Projects of National Natural Science Foundation of China (No.12375357), Shanghai Institute of Applied Physics, Chinese Academy of Sciences.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMoez AA, Aly S, Elshaer Y (2012) Effect of gamma radiation on low density polyethylene (LDPE) films: optical, dielectric and FTIR studies. 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Int J Appl Radiat Isot 17(3):155\u0026ndash;159\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHwang KC, Sagadevan A (2014) One-pot room-temperature conversion of cyclohexane to adipic acid by ozone and UV light. Science 346(6216):1495\u0026ndash;1498\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAhn Y, Colin X, Roma G (2021) Atomic scale mechanisms controlling the oxidation of polyethylene: A first principles study. Polymers 13(13):2143\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Scheme ","content":"\u003cp\u003eScheme is available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"PE, direct irradiation oxidation, post-irradiation oxidation, active oxidative species, three-pathway oxidation","lastPublishedDoi":"10.21203/rs.3.rs-9206304/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9206304/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cdiv class=\"SectionHeadings\"\u003e\u003cdiv class=\"SectionHeading\"\u003e\u003cdiv class=\"Paragraphs\"\u003e\u003cp\u003eTo explore the ionizing radiation induced oxidation, three types of polyethylene (LDPE, UHMWPE and HDPE) were irradiated by gamma rays in Ar or air, and subsequently exposed to air. The evolution of carbonyl group and free radicals were studied by Fourier transform infrared microscopy measurement (FTIR) and electron paramagnetic resonance spectroscopy (EPR) techniques, respectively. It was found that all types of PE were rapidly oxidized during irradiation in air (i.e, direct irradiation oxidation) compared with storage in air after irradiation (i.e., post-irradiation oxidation). The oxidation product of carbonyl group on UHMWPE and HDPE for a 17-hour direct irradiation oxidation exceeded that for a 52-day post-irradiation oxidation. The carbonyl group on HDPE and UHMWPE increased gradually with time in the post-irradiation oxidation, while there was almost no such product formation on LDPE. EPR testing showed that the free radical decay on irradiated LDPE was much faster than that on HDPE and UHMWPE, indicating that the post irradiation oxidation was related to free radical oxidation. Additionally, ozone oxidation experiment and shielding irradiation oxidation experiment were designed and certified that the direct irradiation oxidation of PEs should be attributed to the highly active oxidative species induced in situ by gamma irradiation. Based on these findings, it was proposed that the rapid direct irradiation oxidation was a three-pathway oxidation reaction. This work would provide new insight to understand the direct irradiation oxidation of other polymers.\u0026nbsp;​\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003c/div\u003e","manuscriptTitle":"New understanding on rapid irradiation oxidation of polyethylene","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-10 20:24:32","doi":"10.21203/rs.3.rs-9206304/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2026-05-07T10:12:12+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2026-04-05T21:33:02+00:00","index":0,"fulltext":""},{"type":"editorInvited","content":"Journal of Polymer Research","date":"2026-03-28T20:11:10+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-27T12:59:01+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymer Research","date":"2026-03-27T02:58:05+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"ef01450d-1e60-4105-adfd-7ec2e40d063e","owner":[],"postedDate":"April 10th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewersInvited","content":"","date":"2026-05-07T10:12:12+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-10T20:24:32+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-10 20:24:32","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9206304","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9206304","identity":"rs-9206304","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}