Homogeneous radiation crosslinking of ultra-high molecular weight polyethylene in molten state

Homogeneous radiation crosslinking of ultra-high molecular weight polyethylene in molten state | 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 Homogeneous radiation crosslinking of ultra-high molecular weight polyethylene in molten state Jing Wang, Lei Han, Manli Lu, Weihua Liu, Wenli Zhang, Mouhua Wang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6791256/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Oct, 2025 Read the published version in Journal of Polymer Research → Version 1 posted 5 You are reading this latest preprint version Abstract Generally, the radiation crosslinking of polyethylene (PE) only occurs in the amorphous region, so there should be significant differences between the radiation crosslinking of polyethylene in a completely amorphous state in the molten state and in a semi crystalline state at room temperature. In order to investigate these differences, ultra-high molecular weight polyethylene (UHMWPE) was crosslinked irradiated by an electron beam (EB) both at room temperature and in the molten state. The crosslinked UHMWPE samples were then characterized using Fourier Transform Infrared Spectroscopy (FTIR), swell ratio test, Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD). The FTIR results demonstrated that the yields of trans-vinylene of molten crosslinked samples were significantly higher than that of the room temperature crosslinked samples. It was worth to note that the melting point of the room temperature crosslinked samples gradually increased from 135.7 o C for original sample to 144.8 o C for 300 kGy crosslinked sample. Conversely, the melting point of molten crosslinked samples significantly decreased from 135.7 o C for original sample to 116.2 o C of 300 kGy crosslinked sample. The crystal size of the molten crosslinked samples decreased with increase dose by SEM. The XRD analysis indicated that crystal types were not affected by irradiation conditions. Finaly, the rearrangement and recrystallization behavior of the two kinds of radiation crosslinked UHMWPE were proposed. In the molted state, the molecular chains of UHMWPE are entirely in an amorphous phase, then the crosslinking reaction occurs uniformly. UHMWPE EB Irradiation Crosslinking molten state morphology Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Ultra-high molecular weight polyethylene (UHMWPE) stands out among polymers due to its excellent heat resistance, chemical stability, biocompatibility, and self-lubricating properties. [ 1 – 4 ] Its properties, such as wear resistance, can be notably promoted by ionizing radiation crosslinking which enhanced the interaction between molecular chain by the crosslinked site. [ 5 , 6 ] Radiation crosslinking can effectively improve the performance of UHMWPE without introducing excess chemical reagent or other impurities. So, this unique feature makes it an ideal option for ensuring durability and reliability in biomedical applications. [ 7 – 10 ] As a result, radiation crosslinked UHMWPE has been applied in the manufacturing of artificial joints, wires and cables, and numerous other industries. [ 11 – 13 ] The wear resistance and mechanical properties of crosslinked UHMWPE are related to the crosslink density. As it is well known, UHMWPE contains crystalline and amorphous regions. When UHMWPE is irradiated at room temperature, crosslinking occurs only in the amorphous region, while no crosslinking occurs in the crystalline region. The radiation crosslinking process general uses Co-60 γ-rays or electron beam (EB) as ionizing irradiation source. [ 14 – 16 ] EB irradiation of UHMWPE near the melting point has been used to promote its crosslinking for surgical implant. [ 17 , 18 ] In previous study, we patented that radiation crosslinking in a molten state can be used to increase the crosslinking efficiency of UHMWPE. However, these researches lack systematically investigate the crosslinking of UHMWPE in the molten state in terms of absorbed dose, thermal properties, and crystal morphology. In this study, to clarify the differences between molten crosslinking and traditional crosslinking, UHMWPE was irradiated by EB both in molten state and at room temperature. The chemical reactions, crosslink density and crystal morphology changes of the crosslinked UHMWPE are investigated used Fourier transform infrared spectroscopy (FTIR), swell ratio test, differential scanning calorimetry (DSC), and X-ray diffraction (XRD) and scanning electron microscope (SEM). 2. Experimental 2.1 Materials and sample preparation UHMWPE sheets (1.5 cm × 5 cm × 0.15 cm, molecular weight 2.0×10⁶) were supplied by Beijing Antong Yitai Medical Technology Co., Ltd. These samples were sealed in vacuum bags for EB irradiation. Xylene, potassium permanganate and concentrated sulfuric acid were all purchased from Sinopharm Chemical Reagent Co., Ltd. 2.2 Irradiation Irradiation experiment was carried out in an oven equipped with a window by which EB could penetrate and irradiate to samples. For high temperature irradiation, the samples were heated to 150°C for about 10 min in the oven under a nitrogen, then cooled down to 135°C and irradiated with a 1.5 MeV EB. For room temperature irradiation, the samples were irradiated directly without heating. Each irradiation cycle delivered a dose of 5 kGy, and the target absorbed dose was achieved through multiple repeated irradiations. 2.3 Characterization 2.3.1 Fourier transform infrared spectrometer (FTIR) The FTIR spectra were carried out by a spectrometer (VERTEX70 V, Bruker, Germany), performing at a resolution of 4 cm − 1 with 32 scans. The absorption peak at 2020 cm − 1 was considered impervious to small alterations in polymer structure and regarded as internal standard for normalization. [ 19 , 20 ] 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. The trans-vinylene index (TVI) was calculated using the formula: $$\:TVI=\frac{{\text{A}}_{965{\:\text{c}\text{m}}^{-1}}}{{\text{A}}_{2020\:{\text{c}\text{m}}^{-1}}}$$ where the A 2020 cm−1 and A 965 cm−1 are peak areas at 2020 cm − 1 and 965 cm − 1 , respectively. 2.3.2 Swell ratio test The crosslink density of the samples was determined according to the method of swell ratio test specified in ASTM F 2214. The radiation crosslinked UHMWPE was cut into small square samples of approximately 1.0 g each, and their initial weights were accurately measured. These samples were then immersed in a xylene solution at 120°C for 6 hours to allow for swelling. After swelling, the weights of the samples were measured again. [ 21 , 22 ] The swell ratio (qs), crosslink density (Vd) were calculated using the following formulas: where m s and m o represent the weight of the swollen sample and original sample respectively. 2.3.3 Differential scanning calorimeter (DSC) analysis DSC was used to evaluate the crystallinity and melting point of samples conducted by Mettler Toledo DSC 3 calorimeter. The measured sample weight for the analyses was in the range of 4.0 mg to 6.0 mg. All the dynamic scans were recorded between 30 and 180 °C in N 2 at a heating rate of 10 °C/min. The crystallinity was calculated by comparing the fusion enthalpy with a 100% crystalline PE (293 J/g). 2.3.4 X-ray diffraction (XRD) XRD (Bruker D8 ADVANCE, Germany) was employed to analyze thin, smooth-surfaced samples with a thickness of 100–200 µm. The scan range covered from 5° to 60° at a scan rate of 10°/min. 2.3.5 Scanning electron microscope (SEM) The samples were first etched with a mixture of potassium permanganate and concentrated sulfuric acid at 100°C for 5 min and then at 60°C for 15 min, then washed with an acid solution at 0°C to remove any residual reactants. After that, the samples washed with hydrogen peroxide and acetone, respectively, to ensure a clean surface, then dried at room temperature. After sputter-coating the samples with gold to enhance conductivity, an Apreo model scanning electron microscope (Fei, USA) was used to analyze their surfaces. The secondary electron (SE) mode was utilized for observations, and the accelerating voltage was set at 20 kV. 3. Results and discussion 3.1 FTIR analysis Ionizing radiation induces several chemical reactions in UHMWPE, such as crosslinking and the formation of trans-vinylene groups. The extent of these chemical reactions is correlated with the absorbed dose. Here, FTIR technique was used to detect the generation of trans-vinylene groups of EB irradiated UHMWPE, as illustrated in Fig. 1 . The trans-vinylene group centers at 965 cm − 1 in FTIR spectrum, and all the spectra have been normalized using the peak centered at 2020 cm − 1 . Figure 1 a shows the FTIR spectra of trans-vinylene of the samples irradiated at room temperature, while Fig. 1 b displays the spectra of the samples irradiated in the molten state. In both irradiation conditions, the band of trans-vinylene gradually increase with the absorbed dose. The intensity of the samples irradiated in the molten state is significantly stronger than that irradiated at room temperature. By calculating the trans-vinylene index (TVI), the yield of trans-vinylene under both irradiation conditions can be observed more intuitively. As seen in in Fig. 1 c, a higher dose leads to an increase TVI. It is clearly seen that the TVI value for the samples irradiated in the molten state is approximately 2 to 3 times that of irradiated at room temperature. These results indicate that the chemical reactions occurring during the irradiation of UHMWPE in the molten state are more intense, and it may hint that more crosslinking occurs in molten state. 3.2 Swell ratio test Crosslinking network along the polyethylene chains can restrict the movement of the molecular chains segment, and make the polymer molecules unable to fully dissolve in the solvent. When swelling in xylene, the swell ratio of crosslinked UHMWPE decreases as crosslink density increase. UHMWPE samples were swollen in a xylene solvent at 120°C for 6 h, and the swell ratio of the samples was calculated by the weighing method, as shown in Fig. 2 a. The swell ratio (qs) of crosslinked UHMWPE decreases with an increase of dose. When the dose is less than 50 kGy, the swell ratio of the samples irradiated in molten state is remarkably lower than that of irradiated at room temperature. However, when the dose exceeds 100 kGy, the swell ratio decreases slightly with rising dose, i. e. the swell ratio gradually decreases to a limit. Further, the crosslink density of the samples was calculated based on the swell ratio as shown in Fig. 2 b, and similar results obtain as Fig. 2 a. These results indicate that at a lower dose irradiation the crosslinking of UHMWPE irradiated in the molten state is significantly higher than that irradiated at room temperature. However, at higher doses exceeding 100 kGy, there is no significant difference between the two irradiation conditions. In such cases, due to the saturation effect of the swelling, this method becomes less effective for accurate measurement the crosslinking. Compared with the results of TVI monotonically increasing with dose, it may mean that swelling test becomes less reliable for evaluating UHMWPE crosslinking at high dose irradiation. 3.3 Thermal analysis The crosslinking can induce the rearrangement of the molecular chain segments of UHMWPE, then lead to change crystal morphology. In this study, the differential scanning calorimetry (DSC) analysis was employed to measure the variations in the melting point of irradiated UHMWPE. Figure 3 a represents the DSC curves of the first heating. According to Fig. 3 a, the melting point of the samples irradiated at room temperature gradually increases with an increase of the dose. The melting peak increases from 135.7°C for original sample to 144.8°C for 300 kGy sample. In addition, a new peak appears in the low temperature region for the samples of 200 and 300 kGy. These results indicate the rearrangement induced by irradiation. To eliminate the effect of thermal history, DSC for second heating was analyzed, as shown in Fig. 3 b. In this case, the melting point at high temperature almost no change around 135°C. The low temperature melting peak becomes distinct, and its temperature consistent with that observed during the first heating. The melting point reflects the size of crystalline, i.e. the thickness of lamellae. Therefore, these results indicate that the presence of two sizes of crystalline in the samples irradiated at room temperature, and suggest that crosslinking networks are nonuniform in polymer matrix. Figure 3 c-d depicts the DSC curves of the samples irradiated in molten state. It can be observed that first heating and second heating curves are nearly identical. Only one melting peak appeared on the curves, and it decreases progressively with the increase of absorbed dose. The melting point of the 300 kGy sample drastically decreased from 135.7 ℃ to 116.2 ℃, which is close to the melting point of LDPE. These results indicate that a significant change in the crystalline structure of UHMWPE irradiated in the molten state. Moreover, the results also indicate that as the dose increases, the crosslinking reaction continuously occurs with a uniform manner in the molten state. Furthermore, comparing the DSC curves of the two irradiation conditions at the same dose (Fig. 4 ), it is obviously found that the low temperature peaks of the samples irradiated at room temperature is in the same position as that of irradiated in molten state. It hints that the size of the new lamellae for the samples irradiated at room temperature is same as that of irradiated in molten state. 3.4 Crystal characterization The XRD patterns of the irradiated UHMWPE under two irradiation conditions are shown in Fig. 5 . The diffraction peaks of [110] and [200] correspond to the orthogonal form species of the UHMWPE crystal. [ 23 , 24 ] Under both conditions, the XRD diffraction peaks do not change significantly. Even after high dose irradiation such as 300 kGy, the X-ray diffraction of the sample before and after irradiation remain unchanged. These results indicate that the crystal type of UHMWPE does not affect by irradiation. Figure 6 presents the SEM images of UHMWPE samples irradiated in molten state. It is clear seen that the crystal size of the samples decreased with increase dose. Although not displayed here, there are no change observed for the samples irradiated at room temperature. 3.5 Discussion Unlike chemical crosslinking, which use chemical agents to initiate crosslinking reactions, the rearrangement and crystallization behavior of PE chain segments induced by ionizing radiation are not affected by chemical reagents or other impurities. Here, it is considered that the crystal morphology rearrangement mainly affected by cross-linking sites. Based on all the above results, the rearrangement and recrystallization behavior of EB irradiation crosslinked UHMWPE is illustrated in Scheme 1 . At room temperature, the radiation crosslinking reaction occurs in the amorphous region, while there is no crosslinking is in the crystalline region. Irradiation induce a seirs of rearrangement, thickening the original crystal A and forming a new thinner lamellae B. When the crosslinked sample is remelting, all the crystals transform into an amorphous melt. However, the whole melt consists of two parts, one is from the original crystalline region, and the other is from the crosslinked amorphous region. Due to restricted by the crosslinking network, molecular chain cannot penetration each other, and the two parts remain independent. When the melt is cooled down, the two parts recrystallize individually into two types of crystal. The crystal A is almost independent on dose, because this part is from the original crystalline region with almost non-crosslinking during irradiation. However, the crystal B is the new one from the original amorphous region, and its size decrease with increasing dose. In contrast, while it is irradiated in the molten state, UHMWPE is all in amorphous state. Under this condition, EB irradiation will induce molecular chain crosslink to form a uniformly distributed crosslinking network. As in the amorphous region at room temperature, the crosslinking network hinders the crystallization and only form thinner lamellae. Moreover, as the degree of crosslinking increases, the crystal size decreases. Because these crosslinking sites are uniformly distributed, only one melting peak is detected by DSC analysis. Therefore, irradiation UHMWPE in the molten state can be considered as homogeneous crosslinking, while irradiation at room temperature is heterogeneous crosslinking. 4. Conclusion UHMWPE was crosslinked both at room temperature and in molten state. The chemical structure, crosslink density, and crystal morphology of the crosslinked UHMWPE under two crosslinking conditions were systematically characterized. The FTIR results indicated that the yield of trans-vinylene groups in irradiated UHMWPE increased with dose under both conditions, but with a higher trans-vinylene index (TVI) observed for samples irradiated in the molten state. It is worth emphasizing that for the UHMWPE irradiated at room temperature, its melting point increased with the rising dose. Specifically, it increased from 135.7°C for the original sample to 144.8°C for the sample irradiated at a dose of 300 kGy. In contrast, for the UHMWPE irradiated in the molten state, the melting point decreased significantly as the dose increased, dropping from 135.7°C for the original sample to 116.2°C for the 300 kGy sample. These results reflect the opposing crystalline morphology changes of irradiated UHMWPE under the two conditions. At room temperature, radiation crosslinking occurred only in the amorphous regions, not in the crystalline regions. The irradiation treatment induced rearrangement of molecular chain segments, thickening the original lamellas, and increasing its melting point. In contrast, in molten state, the molecular chains are entirely in an amorphous phase, enabling the crosslinking reaction to occur uniformly, which can thus be considered as “homogeneous”. In this situation, due to the crosslinking network restricting the free crystallization of the molecular chains, the crystal size decreased remarkably as the crosslinking density increased. In summary, radiation crosslinking of UHMWPE in the molten state not only improves the formation of double bond and crosslinking point, but also results in a more uniform crosslinked network structure. Declarations Competing Interest declaration. All the authors have no competing interests to declare that are relevant to the content of this article and have no financial or proprietary interests in any material discussed in this article. Data Availability Statement The data supporting this article have been included in the main text. Raw data are available upon request to the authors. Author contributions Conceptualization: [Mouhua Wang],[Jing Wang]; Methodology: [Mouhua Wang],[Wenli Zhang],[Weihua Liu]; Formal analysis and investigation: [Mouhua Wang],[Jing Wang]; Writing - original draft preparation: [Mouhua Wang],[Manli Lu],[Jing Wang]; Writing - review and editing: [Lei Han],[Jing Wang],[Manli Lu]; Funding acquisition: [Mouhua Wang]; Resources: [Mouhua Wang]. Acknowledgements This study was funded by the National Natural Science Foundation of China (NO.12375357) and the Major Science and Technology Program of Shanghai Institute of Applied Physics, Chinese Academy of Sciences. 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Schemes Scheme 1 is available in the Supplementary Files section Supplementary Files image10.png Scheme. 1 Mechanism of homogeneous cross-linked UHMWPE irradiated in molten state. Cite Share Download PDF Status: Published Journal Publication published 26 Oct, 2025 Read the published version in Journal of Polymer Research → Version 1 posted Reviewers agreed at journal 09 Jul, 2025 Reviewers invited by journal 09 Jul, 2025 Editor invited by journal 28 Jun, 2025 Editor assigned by journal 04 Jun, 2025 First submitted to journal 04 Jun, 2025 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. 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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-6791256","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":482775321,"identity":"b88a476e-1e1e-4192-bb21-52a999553655","order_by":0,"name":"Jing Wang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Jing","middleName":"","lastName":"Wang","suffix":""},{"id":482775322,"identity":"eb3a6e90-0ea8-4366-a000-d02958285757","order_by":1,"name":"Lei Han","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Lei","middleName":"","lastName":"Han","suffix":""},{"id":482775323,"identity":"0e108ded-fcb4-4c5d-89e6-782551d7dce6","order_by":2,"name":"Manli Lu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Manli","middleName":"","lastName":"Lu","suffix":""},{"id":482775324,"identity":"9e6449b3-84c5-44c7-99e6-4536c91ed1c4","order_by":3,"name":"Weihua Liu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Weihua","middleName":"","lastName":"Liu","suffix":""},{"id":482775325,"identity":"5eab03a1-96c3-4950-936b-5335a01f6a7a","order_by":4,"name":"Wenli Zhang","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Wenli","middleName":"","lastName":"Zhang","suffix":""},{"id":482775326,"identity":"23d867e5-69c2-4c91-9461-2c2a68dd2b31","order_by":5,"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":"University of Chinese Academy of Sciences","correspondingAuthor":true,"prefix":"","firstName":"Mouhua","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2025-05-31 13:39:57","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6791256/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6791256/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10965-025-04641-4","type":"published","date":"2025-10-26T16:16:21+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":86523455,"identity":"42c01163-98e9-417d-94d3-810c8bd7edb9","added_by":"auto","created_at":"2025-07-11 15:30:10","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":237140,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra changes with dose for trans-vinylene on UHMWPE: (a) irradiated at room temperature (r. t.), (b) irradiated in molten state, (c) dependence of TVI on dose.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-6791256/v1/333ae96bb28b21548e2661f1.png"},{"id":86523454,"identity":"d241355c-a337-4483-98a0-7d4e481cc30e","added_by":"auto","created_at":"2025-07-11 15:30:10","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":118125,"visible":true,"origin":"","legend":"\u003cp\u003eSwell ratio (qs) and crosslink density (Vd) of irradiated UHMWPE with dose.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-6791256/v1/2eb018ece18401b6e4b78106.png"},{"id":86524133,"identity":"29070aaa-9fc2-4f88-81e5-ca4431ccb101","added_by":"auto","created_at":"2025-07-11 15:38:10","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":332269,"visible":true,"origin":"","legend":"\u003cp\u003eDSC curves of irradiated UHMWPE under different dose. (a) first heating curves and (b) second heating curves for the sample irradiated at r. t. (c) first heating and (d) second heating curves for the sample irradiated in molten state.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-6791256/v1/87c4ff42a4e77636ea018615.png"},{"id":86524135,"identity":"086f43ba-203e-483f-8c35-06f67a3766f4","added_by":"auto","created_at":"2025-07-11 15:38:10","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":171544,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the melting peaks between the samples irradiated at r.t. (second heating of DSC curves) and samples irradiated in molten state (first heating of DSC curves).\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-6791256/v1/e157dc2a6cf6b314b58fbb40.png"},{"id":86525211,"identity":"a26fbee7-1ed1-47fd-acbb-5f45c677feb0","added_by":"auto","created_at":"2025-07-11 15:46:10","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":265170,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of irradiated UHMWPE. (a) irradiated at room temperature; (b) irradiated in molten state.\u003c/p\u003e","description":"","filename":"image8.png","url":"https://assets-eu.researchsquare.com/files/rs-6791256/v1/3449a810523b04f478669ee3.png"},{"id":86523457,"identity":"9b3b9022-1229-4533-978c-837a2ca394ba","added_by":"auto","created_at":"2025-07-11 15:30:10","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":334951,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of irradiated UHMWPE in molten state. (a) original sample, (b) 100 kGy irradiation, (c) 200 kGy irradiation, (d) 300 kGy irradiation.\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-6791256/v1/664116546b32b1a988290f2c.png"},{"id":94490696,"identity":"d3356a47-3632-4a92-90bc-b8eaeb38a3a7","added_by":"auto","created_at":"2025-10-27 17:13:45","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2035204,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6791256/v1/2cac2135-635b-4602-9e9b-74e1e97351ac.pdf"},{"id":86523458,"identity":"d8e2d356-9319-463b-96cc-5bc3172dbc13","added_by":"auto","created_at":"2025-07-11 15:30:10","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":325217,"visible":true,"origin":"","legend":"\u003cp\u003eScheme. 1 Mechanism of homogeneous cross-linked UHMWPE irradiated in molten state.\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-6791256/v1/7188f2be2692b29540637911.png"}],"financialInterests":"","formattedTitle":"Homogeneous radiation crosslinking of ultra-high molecular weight polyethylene in molten state","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eUltra-high molecular weight polyethylene (UHMWPE) stands out among polymers due to its excellent heat resistance, chemical stability, biocompatibility, and self-lubricating properties.\u003csup\u003e[\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e Its properties, such as wear resistance, can be notably promoted by ionizing radiation crosslinking which enhanced the interaction between molecular chain by the crosslinked site.\u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e Radiation crosslinking can effectively improve the performance of UHMWPE without introducing excess chemical reagent or other impurities. So, this unique feature makes it an ideal option for ensuring durability and reliability in biomedical applications.\u003csup\u003e[\u003cspan additionalcitationids=\"CR8 CR9\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e As a result, radiation crosslinked UHMWPE has been applied in the manufacturing of artificial joints, wires and cables, and numerous other industries. \u003csup\u003e[\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e\u003cp\u003eThe wear resistance and mechanical properties of crosslinked UHMWPE are related to the crosslink density. As it is well known, UHMWPE contains crystalline and amorphous regions. When UHMWPE is irradiated at room temperature, crosslinking occurs only in the amorphous region, while no crosslinking occurs in the crystalline region. The radiation crosslinking process general uses Co-60 γ-rays or electron beam (EB) as ionizing irradiation source.\u003csup\u003e[\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e EB irradiation of UHMWPE near the melting point has been used to promote its crosslinking for surgical implant.\u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e In previous study, we patented that radiation crosslinking in a molten state can be used to increase the crosslinking efficiency of UHMWPE. However, these researches lack systematically investigate the crosslinking of UHMWPE in the molten state in terms of absorbed dose, thermal properties, and crystal morphology.\u003c/p\u003e\u003cp\u003eIn this study, to clarify the differences between molten crosslinking and traditional crosslinking, UHMWPE was irradiated by EB both in molten state and at room temperature. The chemical reactions, crosslink density and crystal morphology changes of the crosslinked UHMWPE are investigated used Fourier transform infrared spectroscopy (FTIR), swell ratio test, differential scanning calorimetry (DSC), and X-ray diffraction (XRD) and scanning electron microscope (SEM).\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1 Materials and sample preparation\u003c/h2\u003e\n \u003cp\u003eUHMWPE sheets (1.5 cm \u0026times; 5 cm \u0026times; 0.15 cm, molecular weight 2.0\u0026times;10⁶) were supplied by Beijing Antong Yitai Medical Technology Co., Ltd. These samples were sealed in vacuum bags for EB irradiation. Xylene, potassium permanganate and concentrated sulfuric acid were all purchased from Sinopharm Chemical Reagent Co., Ltd.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2 Irradiation\u003c/h2\u003e\n \u003cp\u003eIrradiation experiment was carried out in an oven equipped with a window by which EB could penetrate and irradiate to samples. For high temperature irradiation, the samples were heated to 150\u0026deg;C for about 10 min in the oven under a nitrogen, then cooled down to 135\u0026deg;C and irradiated with a 1.5 MeV EB. For room temperature irradiation, the samples were irradiated directly without heating. Each irradiation cycle delivered a dose of 5 kGy, and the target absorbed dose was achieved through multiple repeated irradiations.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3 Characterization\u003c/h2\u003e\n \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.1 Fourier transform infrared spectrometer (FTIR)\u003c/h2\u003e\n \u003cp\u003eThe FTIR spectra were carried out by a spectrometer (VERTEX70 V, Bruker, Germany), performing at a resolution of 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with 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 normalization.\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\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. The trans-vinylene index (TVI) was calculated using the formula:\u003c/p\u003e\n \u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e$$\\:TVI=\\frac{{\\text{A}}_{965{\\:\\text{c}\\text{m}}^{-1}}}{{\\text{A}}_{2020\\:{\\text{c}\\text{m}}^{-1}}}$$\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003ewhere the A\u003csub\u003e2020 cm\u0026minus;1\u003c/sub\u003e and A\u003csub\u003e965 cm\u0026minus;1\u003c/sub\u003e are peak areas at 2020 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 965 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.2 Swell ratio test\u003c/h2\u003e\n \u003cp\u003eThe crosslink density of the samples was determined according to the method of swell ratio test specified in ASTM F 2214. The radiation crosslinked UHMWPE was cut into small square samples of approximately 1.0 g each, and their initial weights were accurately measured. These samples were then immersed in a xylene solution at 120\u0026deg;C for 6 hours to allow for swelling. After swelling, the weights of the samples were measured again.\u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e The swell ratio (qs), crosslink density (Vd) were calculated using the following formulas:\u003c/p\u003e\n \u003cp\u003e\u003cimg 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\" width=\"451\" height=\"103\"\u003e\u003c/p\u003e\n \u003cp\u003ewhere m\u003csub\u003es\u003c/sub\u003e and m\u003csub\u003eo\u003c/sub\u003e represent the weight of the swollen sample and original sample respectively.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.3 Differential scanning calorimeter (DSC) analysis\u003c/h2\u003e\n \u003cp\u003eDSC was used to evaluate the crystallinity and melting point of samples conducted by Mettler Toledo DSC 3 calorimeter. The measured sample weight for the analyses was in the range of 4.0 mg to 6.0 mg. All the dynamic scans were recorded between 30 and 180 \u0026deg;C in N\u003csub\u003e2\u003c/sub\u003e at a heating rate of 10 \u0026deg;C/min. The crystallinity was calculated by comparing the fusion enthalpy with a 100% crystalline PE (293 J/g).\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.4 X-ray diffraction (XRD)\u003c/h2\u003e\n \u003cp\u003eXRD (Bruker D8 ADVANCE, Germany) was employed to analyze thin, smooth-surfaced samples with a thickness of 100\u0026ndash;200 \u0026micro;m. The scan range covered from 5\u0026deg; to 60\u0026deg; at a scan rate of 10\u0026deg;/min.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n \u003ch2\u003e2.3.5 Scanning electron microscope (SEM)\u003c/h2\u003e\n \u003cp\u003eThe samples were first etched with a mixture of potassium permanganate and concentrated sulfuric acid at 100\u0026deg;C for 5 min and then at 60\u0026deg;C for 15 min, then washed with an acid solution at 0\u0026deg;C to remove any residual reactants. After that, the samples washed with hydrogen peroxide and acetone, respectively, to ensure a clean surface, then dried at room temperature. After sputter-coating the samples with gold to enhance conductivity, an Apreo model scanning electron microscope (Fei, USA) was used to analyze their surfaces. The secondary electron (SE) mode was utilized for observations, and the accelerating voltage was set at 20 kV.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.1 FTIR analysis\u003c/h2\u003e\u003cp\u003eIonizing radiation induces several chemical reactions in UHMWPE, such as crosslinking and the formation of trans-vinylene groups. The extent of these chemical reactions is correlated with the absorbed dose. Here, FTIR technique was used to detect the generation of trans-vinylene groups of EB irradiated UHMWPE, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The trans-vinylene group centers at 965 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in FTIR spectrum, and all the spectra have been normalized using the peak centered at 2020 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea shows the FTIR spectra of trans-vinylene of the samples irradiated at room temperature, while Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb displays the spectra of the samples irradiated in the molten state. In both irradiation conditions, the band of trans-vinylene gradually increase with the absorbed dose. The intensity of the samples irradiated in the molten state is significantly stronger than that irradiated at room temperature.\u003c/p\u003e\u003cp\u003eBy calculating the trans-vinylene index (TVI), the yield of trans-vinylene under both irradiation conditions can be observed more intuitively. As seen in in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec, a higher dose leads to an increase TVI. It is clearly seen that the TVI value for the samples irradiated in the molten state is approximately 2 to 3 times that of irradiated at room temperature. These results indicate that the chemical reactions occurring during the irradiation of UHMWPE in the molten state are more intense, and it may hint that more crosslinking occurs in molten state.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Swell ratio test\u003c/h2\u003e\u003cp\u003eCrosslinking network along the polyethylene chains can restrict the movement of the molecular chains segment, and make the polymer molecules unable to fully dissolve in the solvent. When swelling in xylene, the swell ratio of crosslinked UHMWPE decreases as crosslink density increase. UHMWPE samples were swollen in a xylene solvent at 120\u0026deg;C for 6 h, and the swell ratio of the samples was calculated by the weighing method, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea. The swell ratio (qs) of crosslinked UHMWPE decreases with an increase of dose. When the dose is less than 50 kGy, the swell ratio of the samples irradiated in molten state is remarkably lower than that of irradiated at room temperature. However, when the dose exceeds 100 kGy, the swell ratio decreases slightly with rising dose, i. e. the swell ratio gradually decreases to a limit. Further, the crosslink density of the samples was calculated based on the swell ratio as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, and similar results obtain as Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea.\u003c/p\u003e\u003cp\u003eThese results indicate that at a lower dose irradiation the crosslinking of UHMWPE irradiated in the molten state is significantly higher than that irradiated at room temperature. However, at higher doses exceeding 100 kGy, there is no significant difference between the two irradiation conditions. In such cases, due to the saturation effect of the swelling, this method becomes less effective for accurate measurement the crosslinking. Compared with the results of TVI monotonically increasing with dose, it may mean that swelling test becomes less reliable for evaluating UHMWPE crosslinking at high dose irradiation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Thermal analysis\u003c/h2\u003e\u003cp\u003eThe crosslinking can induce the rearrangement of the molecular chain segments of UHMWPE, then lead to change crystal morphology. In this study, the differential scanning calorimetry (DSC) analysis was employed to measure the variations in the melting point of irradiated UHMWPE. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea represents the DSC curves of the first heating. According to Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, the melting point of the samples irradiated at room temperature gradually increases with an increase of the dose. The melting peak increases from 135.7\u0026deg;C for original sample to 144.8\u0026deg;C for 300 kGy sample. In addition, a new peak appears in the low temperature region for the samples of 200 and 300 kGy. These results indicate the rearrangement induced by irradiation. To eliminate the effect of thermal history, DSC for second heating was analyzed, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb. In this case, the melting point at high temperature almost no change around 135\u0026deg;C. The low temperature melting peak becomes distinct, and its temperature consistent with that observed during the first heating. The melting point reflects the size of crystalline, i.e. the thickness of lamellae. Therefore, these results indicate that the presence of two sizes of crystalline in the samples irradiated at room temperature, and suggest that crosslinking networks are nonuniform in polymer matrix.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec-d depicts the DSC curves of the samples irradiated in molten state. It can be observed that first heating and second heating curves are nearly identical. Only one melting peak appeared on the curves, and it decreases progressively with the increase of absorbed dose. The melting point of the 300 kGy sample drastically decreased from 135.7 ℃ to 116.2 ℃, which is close to the melting point of LDPE. These results indicate that a significant change in the crystalline structure of UHMWPE irradiated in the molten state. Moreover, the results also indicate that as the dose increases, the crosslinking reaction continuously occurs with a uniform manner in the molten state.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFurthermore, comparing the DSC curves of the two irradiation conditions at the same dose (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), it is obviously found that the low temperature peaks of the samples irradiated at room temperature is in the same position as that of irradiated in molten state. It hints that the size of the new lamellae for the samples irradiated at room temperature is same as that of irradiated in molten state.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Crystal characterization\u003c/h2\u003e\u003cp\u003eThe XRD patterns of the irradiated UHMWPE under two irradiation conditions are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The diffraction peaks of [110] and [200] correspond to the orthogonal form species of the UHMWPE crystal.\u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e Under both conditions, the XRD diffraction peaks do not change significantly. Even after high dose irradiation such as 300 kGy, the X-ray diffraction of the sample before and after irradiation remain unchanged. These results indicate that the crystal type of UHMWPE does not affect by irradiation.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e presents the SEM images of UHMWPE samples irradiated in molten state. It is clear seen that the crystal size of the samples decreased with increase dose. Although not displayed here, there are no change observed for the samples irradiated at room temperature.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003e3.5 Discussion\u003c/h2\u003e\u003cp\u003eUnlike chemical crosslinking, which use chemical agents to initiate crosslinking reactions, the rearrangement and crystallization behavior of PE chain segments induced by ionizing radiation are not affected by chemical reagents or other impurities. Here, it is considered that the crystal morphology rearrangement mainly affected by cross-linking sites. Based on all the above results, the rearrangement and recrystallization behavior of EB irradiation crosslinked UHMWPE is illustrated in Scheme \u003cspan refid=\"Sch1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eAt room temperature, the radiation crosslinking reaction occurs in the amorphous region, while there is no crosslinking is in the crystalline region. Irradiation induce a seirs of rearrangement, thickening the original crystal A and forming a new thinner lamellae B. When the crosslinked sample is remelting, all the crystals transform into an amorphous melt. However, the whole melt consists of two parts, one is from the original crystalline region, and the other is from the crosslinked amorphous region. Due to restricted by the crosslinking network, molecular chain cannot penetration each other, and the two parts remain independent. When the melt is cooled down, the two parts recrystallize individually into two types of crystal. The crystal A is almost independent on dose, because this part is from the original crystalline region with almost non-crosslinking during irradiation. However, the crystal B is the new one from the original amorphous region, and its size decrease with increasing dose.\u003c/p\u003e\u003cp\u003eIn contrast, while it is irradiated in the molten state, UHMWPE is all in amorphous state. Under this condition, EB irradiation will induce molecular chain crosslink to form a uniformly distributed crosslinking network. As in the amorphous region at room temperature, the crosslinking network hinders the crystallization and only form thinner lamellae. Moreover, as the degree of crosslinking increases, the crystal size decreases. Because these crosslinking sites are uniformly distributed, only one melting peak is detected by DSC analysis. Therefore, irradiation UHMWPE in the molten state can be considered as homogeneous crosslinking, while irradiation at room temperature is heterogeneous crosslinking.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eUHMWPE was crosslinked both at room temperature and in molten state. The chemical structure, crosslink density, and crystal morphology of the crosslinked UHMWPE under two crosslinking conditions were systematically characterized. The FTIR results indicated that the yield of trans-vinylene groups in irradiated UHMWPE increased with dose under both conditions, but with a higher trans-vinylene index (TVI) observed for samples irradiated in the molten state. It is worth emphasizing that for the UHMWPE irradiated at room temperature, its melting point increased with the rising dose. Specifically, it increased from 135.7\u0026deg;C for the original sample to 144.8\u0026deg;C for the sample irradiated at a dose of 300 kGy. In contrast, for the UHMWPE irradiated in the molten state, the melting point decreased significantly as the dose increased, dropping from 135.7\u0026deg;C for the original sample to 116.2\u0026deg;C for the 300 kGy sample. These results reflect the opposing crystalline morphology changes of irradiated UHMWPE under the two conditions. At room temperature, radiation crosslinking occurred only in the amorphous regions, not in the crystalline regions. The irradiation treatment induced rearrangement of molecular chain segments, thickening the original lamellas, and increasing its melting point. In contrast, in molten state, the molecular chains are entirely in an amorphous phase, enabling the crosslinking reaction to occur uniformly, which can thus be considered as \u0026ldquo;homogeneous\u0026rdquo;. In this situation, due to the crosslinking network restricting the free crystallization of the molecular chains, the crystal size decreased remarkably as the crosslinking density increased.\u003c/p\u003e\u003cp\u003eIn summary, radiation crosslinking of UHMWPE in the molten state not only improves the formation of double bond and crosslinking point, but also results in a more uniform crosslinked network structure.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eCompeting Interest declaration.\u003c/h2\u003e\n\u003cp\u003eAll the authors have no competing interests to declare that are relevant to the content of this article and have no financial or proprietary interests in any material discussed in this article.\u003c/p\u003e\n\u003ch2\u003eData Availability Statement\u003c/h2\u003e\n\u003cp\u003eThe data supporting this article have been included in the main text. Raw data are available upon request to the authors.\u003c/p\u003e\n\u003ch2\u003eAuthor contributions\u003c/h2\u003e\u003cp\u003eConceptualization: [Mouhua Wang],[Jing Wang]; Methodology: [Mouhua Wang],[Wenli Zhang],[Weihua Liu]; Formal analysis and investigation: [Mouhua Wang],[Jing Wang]; Writing - original draft preparation: [Mouhua Wang],[Manli Lu],[Jing Wang]; Writing - review and editing: [Lei Han],[Jing Wang],[Manli Lu]; Funding acquisition: [Mouhua Wang]; Resources: [Mouhua Wang].\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e\u003cp\u003eThis study was funded by the National Natural Science Foundation of China (NO.12375357) and the Major Science and Technology Program of Shanghai Institute of Applied Physics, Chinese Academy of Sciences.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eB Pierangiola, B Anuj, B Alessandro and A. Saverio(2017) Materials 10, 791.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eH Lin, L-M Dong, C Wang, T-X Liang and J-M Tian(2014)Key Eng. Mater 602\u0026ndash;603, 656\u0026ndash;660.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJ K B. Patil(2020) Eur. Polym. J 125, 109529.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eK.C.S.H.S.S. Patel(2020) Prog Polym. Sci 109.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eL Costa and P Bracco(2016) UHMWPE Biomaterials Handbook 43, 467\u0026ndash;487.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eK K Wannomae, S D Christensen, A A Freiberg, S Bhattacharyya, W H Harris and O K Muratoglu(2006) Biomaterials 27, 1980\u0026ndash;1987.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eE Oral and O K. Muratoglu(2007) Nucl. Instrum. Meth. B 265,18\u0026ndash;22.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eS Ge, X Kang and Y Zhao(2011) Wear 271, 2354\u0026ndash;2363.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eL Puppulin, W Zhu, N Sugano and G Pezzotti(2015) J Biomater. Appl 29, 791\u0026ndash;800.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eX Kang, C Yao, C Yang and P Feng(2018) Tribol. Trans 61, 539\u0026ndash;546.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eT M Grupp, M Holderied, M A Mulliez, R Streller, M Jager, W Blomer and S Utzschneider(2014) Acta. Biomater 10, 3068\u0026ndash;3078.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eF Liu, Y He, Z Gao and D Jiao(2021) Wear 203985, 482\u0026ndash;483.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eA Li, F Li, K Mai and Z Zhang(2022.) Adv. Polym. Tech.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eE Suljovrujic(2013) Radiat Phys. Chem 89, 43\u0026ndash;50.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eC P Stephens, R S Benson, M E Martinez-Pardo, E D Barker, J B Walkerc and T P Stephens(2005) Nucl. Instrum. Meth. B 236, 540\u0026ndash;545.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eK Y Lee(2010) Polym. Korea 34.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eE Oral, A S Malhi and O K Muratoglu(2006) Biomaterials 27, 917\u0026ndash;925.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eD Ferroni, V Quaglini, J Appl(2010) Biomater. Biom 8, 82.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eS Liu, Q Li, J Wang, M-L Lu, W-L Zhang, K Wang, W-H Liu and M-H Wang(2022)Polym. Degrad. Stab 196, 109846.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eM-L Lu, J Wang, W-L Zhang, W-H Liu and M-H Wang(2024) Polym. Degrad. Stab 224, 110742.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eYY/T 0813\u0026ndash;2010 交联超高分子量聚乙烯分子网状结构参数的原位测定标准方法.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eASTM F2214-23 Standard Test Method for In Situ Determination of Network Parameters of Crosslinked Ultra High Molecular Weight Polyethylene (UHMWPE).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eS Tsubakihara and M Yasuniwa(1996) Polym. J 28, 563\u0026ndash;567.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZ-Q Liu, X-C Yin, H Zhang, S Gao, Q-L Kuang and Y-H Feng(2024) Polymer, 190, 126498.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Schemes","content":"\u003cp\u003eScheme 1 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":true,"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":"UHMWPE, EB Irradiation, Crosslinking, molten state, morphology","lastPublishedDoi":"10.21203/rs.3.rs-6791256/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6791256/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eGenerally, the radiation crosslinking of polyethylene (PE) only occurs in the amorphous region, so there should be significant differences between the radiation crosslinking of polyethylene in a completely amorphous state in the molten state and in a semi crystalline state at room temperature. In order to investigate these differences, ultra-high molecular weight polyethylene (UHMWPE) was crosslinked irradiated by an electron beam (EB) both at room temperature and in the molten state. The crosslinked UHMWPE samples were then characterized using Fourier Transform Infrared Spectroscopy (FTIR), swell ratio test, Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD). The FTIR results demonstrated that the yields of trans-vinylene of molten crosslinked samples were significantly higher than that of the room temperature crosslinked samples. It was worth to note that the melting point of the room temperature crosslinked samples gradually increased from 135.7 \u003csup\u003eo\u003c/sup\u003eC for original sample to 144.8 \u003csup\u003eo\u003c/sup\u003eC for 300 kGy crosslinked sample. Conversely, the melting point of molten crosslinked samples significantly decreased from 135.7 \u003csup\u003eo\u003c/sup\u003eC for original sample to 116.2 \u003csup\u003eo\u003c/sup\u003eC of 300 kGy crosslinked sample. The crystal size of the molten crosslinked samples decreased with increase dose by SEM. The XRD analysis indicated that crystal types were not affected by irradiation conditions. Finaly, the rearrangement and recrystallization behavior of the two kinds of radiation crosslinked UHMWPE were proposed. In the molted state, the molecular chains of UHMWPE are entirely in an amorphous phase, then the crosslinking reaction occurs uniformly.\u003c/p\u003e","manuscriptTitle":"Homogeneous radiation crosslinking of ultra-high molecular weight polyethylene in molten state","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-11 15:30:05","doi":"10.21203/rs.3.rs-6791256/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-07-09T07:27:38+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-09T07:17:12+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Journal of Polymer Research","date":"2025-06-28T18:59:12+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-05T03:47:34+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymer Research","date":"2025-06-04T23:19:36+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":"July 11th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-10-27T16:38:55+00:00","versionOfRecord":{"articleIdentity":"rs-6791256","link":"https://doi.org/10.1007/s10965-025-04641-4","journal":{"identity":"journal-of-polymer-research","isVorOnly":false,"title":"Journal of Polymer Research"},"publishedOn":"2025-10-26 16:16:21","publishedOnDateReadable":"October 26th, 2025"},"versionCreatedAt":"2025-07-11 15:30:05","video":"","vorDoi":"10.1007/s10965-025-04641-4","vorDoiUrl":"https://doi.org/10.1007/s10965-025-04641-4","workflowStages":[]},"version":"v1","identity":"rs-6791256","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6791256","identity":"rs-6791256","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}