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Open Engineering

formerly Central European Journal of Engineering

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Influence of Silica (SiO2) Loading on the Thermal and Swelling Properties of Hydrogenated-Nitrile-Butadiene-Rubber/Silica (HNBR/Silica) Composites

Muhammad Amin
  • Department of Electrical Engineering, Ghulam Ishaq Khan Institute of Engineering Sciences and Technology, Topi, Pakistan
  • Other articles by this author:
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/ Abraiz Khattak
  • Corresponding author
  • Department for Management of Science and Technology Development, Ton Duc Thang University, Ho Chi Minh City, Vietnam
  • Faculty of Electrical & Electronics Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam
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/ Muhammad Ali
Published Online: 2018-08-11 | DOI: https://doi.org/10.1515/eng-2018-0025

Abstract

Hydrogenated-Nitrile-Butadiene-Rubber (HNBR) is known for its good physical strength. It is a widely used rubber in electrical insulation and other high performance applications. Performance of HNBR is affected in high temperature and an aggressive fluid environment. Adding silica to HNBR may overcome this problem. In order to investigate the effect of fluids and temperature on HNBR/silica composites we prepared multiple composites of HNBR with 8.3, 16.7, 33.4, 50 and 66.7 phr of silica (SiO2) by two roll compounding method. Swelling index and thermo gravimetric analyses were performed. Calculations of swelling indexes were performed at different time periods with ethanol, toluene and water. For thermo gravimetric analysis (TGA), thermo grams of samples were obtained and % char yields at 550 °C were analyzed for all samples. Improvements with the addition of silica were recorded up to a great extent in both analyses. Swelling index decreased with the addition of silica as compared to neat HNBR and reached an optimum position with 50 phr silica loading in ethanol, 8.3 phr in water and 66.7 phr in toluene. Moreover, the HNBR composite with 66.7 phr of silica was found to be the highest thermally stable sample and lost less than 60% of weight at 550 °C in comparison to neat HNBR in which 80% of weight loss occurred at 550 °C.

Keywords: HNBR; Composites; Silica; Loading; Filler; Mechanical properties

1 Introduction

Hydrogenated-Nitrile-Butadiene-Rubber (HNBR) is a prominent and widely used elastomer [1]. It is obtained by hydrogenation of Nitrile Butadiene Rubber (NBR) [2, 3]. HNBR is known for sustainability of its physical strength and other properties in exposure to heat, oil and other chemicals [4]. This tough nature of HNBR is provided by its saturated structure and existence of many polar groups. Due to this exceptional nature, it finds usage in many industries e.g. automotive, aerospace and electrical and thermal insulations etc. [5, 6]. Although HNBR is advantageous over NBR in fuel and oil resistance and has also better oxidation and heat resistance than Ethylene-Propylene-Diene-Monomer (EPDM), it decays in high temperature environments and also swells when exposed to solvents [7,8]. Thus, the resistance of HNBR needs to be enhanced for applications in high temperature and aggressive solvent environments.

Enhancement in the properties of materials has been an area of research for a long time. Addition of fillers, to the neat materials is an efficient method to enhance their properties [9, 10, 11, 12]. Different types of fillers are used to enhance properties of polymers. In order to get optimum results from fillers, some parameters are of great concern during the preparation of composites e.g. mixing time, mixing temperature and modifier content etc. [12, 13]. Fillers are broadly categorized in two classes, extended fillers and reinforcing fillers [14, 15]. Extended fillers are generally used for the extension of formulation e.g. ATH, ZnO and ground quartz. Whereas, reinforcing fillers are used for improvement of properties e.g. physical, mechanical and thermal properties. Examples of reinforcing fillers are silica and carbon black etc. Thus, the addition of fillers may result in increased thermal and swelling resistance of overall HNBR composite. Several types of fillers were used previously to improve properties of HNBR [16] e.g. CNT [17, 18] ATH [19] and CB [20] etc. However, very limited work has been carried out on the investigation of thermal and swelling properties of HNBR composites [21, 22, 23] and almost no literature is available on these properties for HNBR/silica composites.

Silica is a reinforcing filler which has good resistivity and thermal stability thus it can bring superior enhancements in the properties of the HNBR. Interaction of silanol group of silica and hydrogen bond in polar HNBR is the reason of improvement in the properties in HNBR/SiO2 composites [24]. However, further studies are required to find the effect of loading of silica to achieve the utmost thermal properties and swelling behavior of HNBR [25].

Like other fillers, concentration of silica is also an important parameter for the stability of polymer [26, 27, 28]. Although HNBR has been studied for silica fillers, thermal and swelling properties of HNBR/SiO2 composites for different concentration of silica has not been reported yet. This is necessary to achieve high performance HNBR/SiO2 composites.

Keeping in view the importance of thermal stability and swelling behavior for HNBR/SiO2, we fabricated neat HNBR and its five HNBR/SiO2 composites with 8.3, 16.7, 33.4,50 and 66.7 phr of micro silica by two roll compounding as per recommendation of standard ASTM D-3182-07. Later on, all samples were tested for swelling behavior in ethanol, toluene and water. For investigation of thermal properties thermo gravimetric analysis (TGA) was used.

In this work, we have mainly focused on finding the effect of silica loading to achieve enhanced swelling and thermal properties of HNBR /SiO2 composites.

2 Materials

2.1 Ingredients

HNBR was procured from Lanxess Chemicals (Germany) and micro-silica (5 μm) was obtained from Wuhan Newreach Chemicals (China). Other constituents such as zinc oxide (ZnO), stearic acid (SA), mercaptobenzothiazole (MBT), sulfur (S), Tetramethyl Thiuram Tetrasulfide (TMTD) and dioctyl phthalate (DOP), Pyrolytic Boron Nitride (PBN) were industrial grade products.

2.2 Preparation of Composites

Neat HNBR and its composites were fabricated with different loadings of silica. Two roll compounding method according to ASTM D-3182-07 was used for the preparation of samples [29]. At the start HNBR was masticated and then sulphur, ZnO, stearic acid were added one after other in a sequence as given in Figure 1. The vulcanizates were made in a bolt press machine by curing them at 165 °C temperature and 10 MPa pressure for 40 minutes. All constituents were mixed in parts per hundreds ratio (phr) as given in Table 1.

Sequence of constituents’ addition in preparation HNBR Composites
Figure 1

Sequence of constituents’ addition in preparation HNBR Composites

Table 1

HNBR Composites formulation recipes

3 Measurements, Instruments and Conditions

3.1 Swelling Properties

All six samples in approximately 1 cm × 1 cm of area and 2 mm thickness were used for the measurement of swelling properties [30, 31, 32, 33, 34]. Three solvents (water, ethanol and toluene) were used in the experiment. The dry samples’ weight (Wd) was initially recorded by an electronic digital sample having accuracy of 0.001 mg. The samples were then dipped in solvent. After a specific amount of time the weight of the swelled samples (Ws) was recorded. The measurements were also taken for multiple durations to find the effect of dipping time on the swelling of HNBR. The percentage swelling ratios for neat HNBR and its silica based composites for each solvent were then determined by the following formula [30, 31, 32, 33, 34].

%S.R.=100x[(WsWd)/Wd]

4 Thermal Properties

For measurement of thermal properties Thermo Gravimetric Analysis (TGA) was performed using TGA Q50 (TA instruments, USA) following ASTM E1131 and ISO 11358 standards [35, 36]. To investigate weight loss by increasing temperature, the temperature was varied from room temperature up to 550 °C and thermo grams were obtained for the samples. For comparative analysis, temperatures for 10 % weight loss and 50 % weight loss of all samples were recorded. Moreover, the % char yield was also analyzed for samples at 550 °C.

5 Results and Discussions

5.1 Analysis of Swelling Behavior

Measurements for swelling index recorded for each solvent (ethanol, toluene and water) were different. The reason for the different swelling behavior is the exertion of different magnitudes of force from each solvent which depends upon the static fluid pressure of the solvent. Swelling properties of HNBR for ethanol, water and toluene are discussed below.

In ethanol, swelling ratio of HNBR varied with the variation in silica loading.

An increase in swelling ratio with the increase of immersing time in ethanol is clear from Figure 2(a). This increase of swelling ratio is up to a certain value and then decreases. The decrease in swelling ratio is due to the dissolving of rubber compound in the ethanol [37, 38]. From Figure 2(b) it is clear that the increase in silica loading results in decrease of swelling ratio. The decrease in swelling ratio of HNBR is due to the force involved between silica particles rubber network. In ethanol HNBR-4 which has 50 phr silica shows better swelling behavior as compared to the other samples up to 140 hrs.

Swelling behavior of HNBR in ethanol (a) swelling ratio vs. swelling time (b) swelling ratio vs. silica concentration
Figure 2

Swelling behavior of HNBR in ethanol (a) swelling ratio vs. swelling time (b) swelling ratio vs. silica concentration

Figure 3 shows trend of variation of swelling ratio in toluene vs. immersing time and silica concentration.

Swelling behavior of HNBR in toluene (a) swelling ratio vs. swelling time (b) Swelling ratio vs. silica concentration
Figure 3

Swelling behavior of HNBR in toluene (a) swelling ratio vs. swelling time (b) Swelling ratio vs. silica concentration

In toluene, decrease in swelling ratio was also recorded with the increase of silica loading. Thus, increase of silica resulted in overall compression of the HNBR/silica composite. It also emerged that the swelling ratio of HNBR in toluene was much higher in comparison to ethanol, which reflects higher affinity of HNBR to toluene than ethanol. However, in toluene HNBR-5 with 66.7 phr silica loading showed the best swelling behavior for all time durations, while for ethanol the swelling index reached an optimum point at 50 phr silica loading.

Unexpectedly, the swelling resistance of HNBR was higher in the case of water in comparison to ethanol and toluene.

From Figure 4(a) it is clear that the swelling ratio increases with the increase of immersing time in water. Moreover, it can also be observed that 8.3 phr loading of silica gives a minimum value of the swelling ratio for HNBR/SiO2 composite. After 8.3 phr loading the swelling ratio continuously increased. This is due to the fact that silica absorbs water, because of the presence of silanol group (Si-OH) in silica which forms a hydrogen bond with water and hence the higher the silica content the higher the swelling of HNBR/SiO2 composite [39, 40]. However, as shown in Figure 4(b) at 50 phr loading of silica the graph almost becomes a horizontal straight line which means that further loading of silica does not affect the swelling behavior of HNBR. In other words the HNBR reaches its maximum swelling limit.

Swelling behavior of HNBR in water (a) swelling ratio vs. swelling time (b) Swelling ratio vs. silica concentration
Figure 4

Swelling behavior of HNBR in water (a) swelling ratio vs. swelling time (b) Swelling ratio vs. silica concentration

5.2 Thermo Gravimetric Analysis (TGA)

In order to analyze thermal stability of each formulation its individual thermo gram was obtained which are given in Figure 5(a-e). The loss of weight was faster in the case of HNBR-0 while it was observed that the length of the slope of weight loss curve increased as function of silica loading. At the end of experiment at 550 °C the HNBR-0 lost almost 80% of its weight while HNBR-5 with 66.7 phr silica lost almost less than 60 % which is evident of improved of thermal stability through addition of silica.

From Figure 6 it is clear that sample HNBR-5 is more stable in comparison with other samples and hence gave highest value 383.84 °C for 10 % loss in weight. The same trend was followed when the temperature was increased and HNBR-5 was stable in comparison to other samples by having 50% loss in weight at the highest temperature of 459.23 °C. From Figure 6 it is also clear that by increasing the concentration of silica the thermal stability of rubber increases which is due to the internal strong Si-O bonding in SiO2 as well as firm interaction of silanol group of silica with polymer network.

Temperature at 10 % and 50% wt. loss with respect silica concentration
Figure 6

Temperature at 10 % and 50% wt. loss with respect silica concentration

Neat sample (HNBR-0) gave the smallest char yield which was approximately 10 % of initial weight of the sample, whereas HNBR-5 gave the highest char yield which is 42.12 % of the initial weight of the sample as shown in Figure 7. From Figure 7 it is also clear the char yield increased with the increase of silica loading.

Char Yield at 550 °C versus silica concentration
Figure 7

Char Yield at 550 °C versus silica concentration

6 Conclusions

Multiple HNBR/SiO2 composites were prepared with different loadings of silica and tested for swelling behavior and thermal properties. Silica improved the swelling and thermal properties of HNBR but deteriorated in water. Composite with 8.3 phr silica was found with the best swelling behavior in water and for ethanol and toluene the optimum loadings of silica were 50 phr and 66.7 phr respectively. From TGA it emerged that composite with 66.7 phr of silica was more thermally stable and showed loss of weight less than 60 % at 550 °C, which was less in comparison with other samples. Thermo grams obtained from TGA also showed that by increasing silica loading the weight loss in HNBR/SiO2 was decreased.

References

  • [1]

    Agnelli, S., G. Ramorino, S. Passera, J. Karger-Kocsis, and T. Riccò. “Fracture resistance of rubbers with MWCNT, organoclay, silica and carbon black fillers as assessed by the J-integral: effects of rubber type and filler concentration.” Express Polymer Letters 6, no. 7 (2012): 581-587. Google Scholar

  • [2]

    Perraud, Sophie, Marie-France Vallat, Marie-Odile David, and Jerzy Kuczynski. “Network characteristics of hydrogenated nitrile butadiene rubber networks obtained by radiation crosslinking by electron beam.” Polymer Degradation and Stability 95, no. 9 (2010): 1495-1501. Google Scholar

  • [3]

    Marshall, A. J., I. R. Jobe, T. Dee, and C. Taylor. “Determination of the degree of hydrogenation in hydrogenated nitrile-butadiene rubber (HNBR).” Rubber chemistry and technology 63, no. 2 (1990): 244-255. Google Scholar

  • [4]

    Madhuranthakam, Chandra Mouli R., Qinmin Pan, and Garry L. Rempel. “Continuous process for production of hydrogenated nitrile butadiene rubber using a Kenics® KMX static mixer reactor.” AIChE journal 55, no. 11 (2009): 2934-2944. Google Scholar

  • [5]

    Minglei, Zhang Chunmei Du Huatai Pang, and Zhou Yi. “Influence of Different Fillers on Performance of HNBR Ablative Materials [J].” Aerospace Materials & Technology 6 (2010): 015. Google Scholar

  • [6]

    Wang, Xunzhang, Liqun Zhang, Yang Han, Xiangke Shi, Weimin Wang, and Dongmei Yue. “New method for hydrogenating NBR latex.” Journal of Applied Polymer Science 127, no. 6 (2013): 4764-4768. Google Scholar

  • [7]

    Hashimoto, K., N. Watanabe, M. Oyama, and Y. Todani. “127th ACS Rubber Division Meeting.” Los Angeles, California (24 April 1985) (1985). Google Scholar

  • [8]

    Cai, Wei-ting, Li-qun Zhang, and Ming TIAN. “Study on the properties of HNBR composites reinforced by silicate nano-short fiber.” China Rubber Industry 54, no. 12 (2007): 709. Google Scholar

  • [9]

    Chen, Shuguo, Haiyang Yu, Wentan Ren, and Yong Zhang. “Thermal degradation behavior of hydrogenated nitrile-butadiene rubber (HNBR)/clay nanocomposite and HNBR/clay/carbon nanotubes nanocomposites.” Thermochimica Acta 491, no. 1 (2009): 103-108. Google Scholar

  • [10]

    Kalachandra, S. “Influence of fillers on the water absorption of composites.”Dental Materials 5, no. 4 (1989): 283-288. Google Scholar

  • [11]

    Gårdebjer, Sofie, Anna Bergstrand, Alexander Idström, Camilla Börstell, Stefan Naana, Lars Nordstierna, and Anette Larsson. “Solid-state NMR to quantify surface coverage and chain length of lactic acid modifed cellulose nanocrystals, used as fillers in biodegradable composites.” Composites Science and Technology 107 (2015): 1-9. Google Scholar

  • [12]

    Wypych, George. Handbook of fillers. Chem Tec Pub., 2010. Google Scholar

  • [13]

    Cai, Wei-ting, Li-qun Zhang, and Ming TIAN. “Study on the properties of HNBR composites reinforced by silicate nano-short fiber.” China Rubber Industry 54, no. 12 (2007): 709. Google Scholar

  • [14]

    Guth, Eugene. “Theory of filler reinforcement.” Journal of applied physics 16, no. 1 (1945): 20-25. Google Scholar

  • [15]

    Kashiwagi, Takashi, Fangming Du, Jack F. Douglas, Karen I. Winey, Richard H. Harris, and John R. Shields. “Nanoparticle networks reduce the flammability of polymer nanocomposites.” Nature materials 4, no. 12 (2005): 928-933. Google Scholar

  • [16]

    Guan, Yue, Ling-Xin Zhang, Li-Qun Zhang, and Yong-Lai Lu. “Study on ablative properties and mechanisms of hydrogenated nitrile butadiene rubber (HNBR) composites containing different fillers.” Polymer Degradation and Stability 96, no. 5 (2011): 808-817. Google Scholar

  • [17]

    Wu, Wenjing, Yinghao Zhai, Yong Zhang, and Wentan Ren. “Mechanical and microwave absorbing properties of< i> in situ</i> prepared hydrogenated acrylonitrile–butadiene rubber/rare earth acrylate composites.” Composites Part B: Engineering 56 (2014): 497-503. Google Scholar

  • [18]

    Yue, Dongmei, Yunfang Liu, Zengmin Shen, and Liqun Zhang. “Study on preparation and properties of carbon nanotubes/rubber composites.” Journal of materials science 41, no. 8 (2006): 2541-2544. Google Scholar

  • [19]

    Wang, He, Xinyan Shi, and Shugao Zhao. “Effects of Magnesium Hydroxide on the Flame Retardancy of Ethylene-Vinyl Acetate Copolymers/Nitrile Rubber Blends.” Journal of Macromolecular Science, Part B 53, no. 5 (2014): 769-780. Google Scholar

  • [20]

    Zhao, Xingbo, Qiuyu Zhang, Junwei Gu, Dezhong Yin, and Changjie Yin. “Effects of Carbon Black on the Properties of HNBR Reinforced by in-situ Prepared ZDMA.” Polymer-Plastics Technology and Engineering 50, no. 15 (2011): 1507-1510. Google Scholar

  • [21]

    Promchim, Jantaraporn, Sirichai Kanking, Piyaporn Niltui, Ekachai Wimolmala, and Narongrit Sombatsompop. “Swelling and mechanical properties of (acrylonitrile-butadiene rubber)/(hydrogenated acrylonitrile-butadiene rubber) blends with precipitated silica filled in gasohol fuels.” Journal of Vinyl and Additive Technology (2014). Google Scholar

  • [22]

    Facio, Adali Castañeda, Aide Saenz Galindo, Lorena Farias Cepeda, Lluvia López López, and Ramón Díaz de León-Gómez. “Thermal Degradation of Synthetic Rubber Nanocomposites.” In Thermal Degradation of Polymer Blends, Composites and Nanocomposites, pp. 157-191. Springer International Publishing, 2015. Google Scholar

  • [23]

    Nasreddine, Victor, and Matthias Soddemann. “HNBR compositions with very high filler levels having excellent processability and resistance to aggressive fluids.” U.S. Patent 9,023,936, issued May 5, 2015. Google Scholar

  • [24]

    Nillawong, Manuchet, Pongdhorn Sae-Oui, and Chakrit Sirisinha. “Influences of Coagent Hybrid Ratios and Silanes on Viscoelastic Properties of Silica-Filled HNBR.” Advanced Materials Research 747 (2013): 564-567. Google Scholar

  • [25]

    Tangudom, Paveena, Sirinthorn Thongsang, and Narongrit Sombatsompop. “Cure and mechanical properties and abrasive wear behavior of natural rubber, styrene–butadiene rubber and their blends reinforced with silica hybrid fillers.”Materials & Design 53 (2014): 856-864. Google Scholar

  • [26]

    Arrighi, V., I. J. McEwen, H. Qian, and MB Serrano Prieto. “The glass transition and interfacial layer in styrene-butadiene rubber containing silica nanofiller.”Polymer 44, no. 20 (2003): 6259-6266. Google Scholar

  • [27]

    Javni, I., W. Zhang, V. Karajkov, Z. S. Petrovic, and V. Divjakovic. “Effect of nano-and micro-silica fillers on polyurethane foam properties.” Journal of cellular plastics 38, no. 3 (2002): 229-239. Google Scholar

  • [28]

    Pustak, Anđela, Matjaž Denac, Mirela Leskovac, Iztok Švab, Vojko Musil, and Ivan Šmit. “Polypropylene/silica micro-and nanocomposites modified with poly (styrene-b-ethylene-cobutylene-b-styrene).” Journal of Applied Polymer Science132, no. 6 (2015). Google Scholar

  • [29]

    ASTM D3182-07 (2012), Standard Practice for Rubber—Materials, Equipment, and Procedures for Mixing Standard Compounds and Preparing Standard Vulcanized Sheets, ASTM International, West Conshohocken, PA, 2012 Google Scholar

  • [30]

    ASTM D3616-95 (2014), Standard Test Method for Rubber—Determination of Gel, Swelling Index, and Dilute Solution Viscosity, ASTM International, West Conshohocken, PA, 2014 Google Scholar

  • [31]

    Cadambi, Rahul M., and Elaheh Ghassemieh. “The ageing behaviour of hydrogenated nitrile butadiene rubber/nanoclay nanocomposites in various mediums.” Journal of Elastomers and Plastics (2012): 0095244311429736. Google Scholar

  • [32]

    Mathew, Lovely, K. U. Joseph, and Rani Joseph. “Swelling behaviour of isora/natural rubber composites in oils used in automobiles.” Bulletin of Materials Science 29, no. 1 (2006): 91-99. Google Scholar

  • [33]

    Salmah, H., B. N. Azra, M. D. Yusrina, and H. Ismail. “A comparative study of polypropylene/(chloroprene rubber) and (recycled polypropylene)/(chloroprene rubber) blends.” Journal of Vinyl and Additive Technology 21, no. 2 (2015): 122-127. Google Scholar

  • [34]

    Wei, Dongya, Ning He, Jing Zhao, and Zhaobo Wang. “Mechanical, Water-Swelling, and Morphological Properties of Water-Swellable Thermoplastic Vulcanizates Based on High Density Polyethylene/Chlorinated Polyethylene/Nitrile Butadiene Rubber/Cross-Linked Sodium Polyacrylate Blends.” Polymer-Plastics Technology and Engineering 54, no. 6 (2015): 616-624. Google Scholar

  • [35]

    ASTM E1131-08 (2014), Standard Test Method for Compositional Analysis by Thermogravimetry, ASTM International, West Conshohocken, PA, 2014 Google Scholar

  • [36]

    ISO 11358-1:2014, Plastics – Thermogravimetry (TG) of polymers Google Scholar

  • [37]

    Berahman, R., Raiati, M., Mazidi, M. M., & Paran, S. M. R. (2016). Preparation and characterization of vulcanized silicone rubber/halloysite nanotube nanocomposites: Effect of matrix hardness and HNT content. Materials & Design, 104, 333-345. Google Scholar

  • [38]

    Liu, G., Hoch, M., Liu, S., Kulbaba, K., & Qiu, G. (2015). Quantitative exploration of the swelling response for carbon black filled hydrogenated nitrile rubber with three-dimensional solubility parameters. Polymer Bulletin, 72(8), 1961-1974. Google Scholar

  • [39]

    Carr, P. W., Dolan, J. W., Dorsey, J. G., Snyder, L. R., & Kirkland, J. J. (2015). Contributions to reversed-phase column selectivity: III. Column hydrogen-bond basicity. Journal of Chromatography A, 1395, 57-64. Google Scholar

  • [40]

    Lee, D., Ahn, G., & Ryu, S. (2014). Two-dimensional water diffusion at a graphene–silica interface. Journal of the American Chemical Society, 136(18), 6634-6642. Google Scholar

About the article

Received: 2016-07-03

Accepted: 2018-05-21

Published Online: 2018-08-11


Citation Information: Open Engineering, Volume 8, Issue 1, Pages 205–212, ISSN (Online) 2391-5439, DOI: https://doi.org/10.1515/eng-2018-0025.

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© 2018 Muhammad Amin et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License. BY-NC-ND 4.0

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