{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,20]],"date-time":"2026-09-20T05:06:08Z","timestamp":1789880768153,"version":"4.0.1"},"reference-count":57,"publisher":"MDPI AG","issue":"18","license":[{"start":{"date-parts":[[2026,9,14]],"date-time":"2026-09-14T00:00:00Z","timestamp":1789344000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>Acrylonitrile\u2013butadiene rubber (NBR) is one of the most widely used elastomers in healthcare products owing to its excellent mechanical performance, chemical resistance, and durability. However, conventional sulfur vulcanization systems rely on accelerators such as tetramethylthiuram disulfide (TMTD), 2-mercaptobenzothiazole (MBT), and 1,3-diphenylguanidine (DPG), which are associated with allergenic reactions and potential toxicological concerns. The replacement of these substances with naturally derived compounds represents an attractive strategy for developing safer and more sustainable elastomeric materials. In this work, three naturally occurring amino acids, L-cystine, L-cysteine, and creatine, were investigated as alternative health-friendly sulfur vulcanization accelerators in NBR compounds filled with carbon black. Their influence on curing characteristics, crosslink density, morphology, mechanical performance, viscoelastic behavior, thermal stability, and thermo-oxidative aging resistance of NBR composites was systematically evaluated and compared with that of conventional accelerator systems. The amino acids effectively promoted sulfur crosslinking, although their activity depended strongly on molecular structure. Cystine and creatine exhibited the most promising performance, providing cure characteristics and mechanical properties comparable to those achieved with commercial accelerators while maintaining satisfactory thermal stability and aging resistance of carbon black-filled rubber composites. These findings demonstrate that naturally occurring amino acids constitute promising bio-derived and non-allergenic alternatives to conventional sulfur vulcanization accelerators and may contribute to the development of safer elastomeric materials with reduced reliance on potentially hazardous or allergenic substances.<\/jats:p>","DOI":"10.3390\/molecules31183250","type":"journal-article","created":{"date-parts":[[2026,9,14]],"date-time":"2026-09-14T13:05:26Z","timestamp":1789391126000},"page":"3250","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Amino Acids as Sustainable Alternatives to Allergenic Sulfur Vulcanization Accelerators for Carbon Black-Filled Nitrile Rubber"],"prefix":"10.3390","volume":"31","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0963-9973","authenticated-orcid":false,"given":"Anna","family":"Sowi\u0144ska-Baranowska","sequence":"first","affiliation":[{"name":"Department of Chemistry, Institute of Polymer and Dye Technology, Lodz University of Technology, Stefanowskiego Street 16, 90-537 Lodz, Poland"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7110-290X","authenticated-orcid":false,"given":"Magdalena","family":"Maciejewska","sequence":"additional","affiliation":[{"name":"Department of Chemistry, Institute of Polymer and Dye Technology, Lodz University of Technology, Stefanowskiego Street 16, 90-537 Lodz, Poland"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,14]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Dufour, T. (2023). From Basics to Frontiers: A Comprehensive Review of Plasma-Modified and Plasma-Synthesized Polymer Films. Polymers, 15.","DOI":"10.3390\/polym15173607"},{"key":"ref_2","unstructured":"Hasan, M.R., Khan, M.A., and Wuest, T. (2024). Towards Industry 5.0: A Systematic Literature Review on Sustainable and Green Composite Materials Supply Chains. arXiv."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Bureewong, N., Injorhor, P., Krasaekun, S., Munchan, P., Waengdongbang, O., Wittayakun, J., Ruksakulpiwat, C., and Ruksakulpiwat, Y. (2023). Preparation and Characterization of Acrylonitrile Butadiene Rubber Reinforced with Bio-Hydroxyapatite from Fish Scale. Polymers, 15.","DOI":"10.3390\/polym15030729"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"2402458","DOI":"10.1002\/adem.202402458","article-title":"Elastomers for Soft Electronics: A Review from the Material\u2019s Perspective","volume":"27","author":"Chakraborti","year":"2025","journal-title":"Adv. Eng. Mater."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"130","DOI":"10.1016\/j.fuel.2016.11.060","article-title":"Effect of Different Sulphur-Based Crosslink Networks on the Nitrile Rubber Resistance to Biodiesel","volume":"191","author":"Linhares","year":"2017","journal-title":"Fuel"},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Rodgers, B., Tallury, S.S., and Klingensmith, W. (2016). Rubber Compounding. Kirk-Othmer Encyclopedia of Chemical Technology, Wiley.","DOI":"10.1002\/0471238961.1821020211120914.a01.pub3"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"475","DOI":"10.1016\/S0079-6700(96)00015-9","article-title":"Vulcanization and Crosslinking in Elastomers","volume":"22","author":"Akiba","year":"1997","journal-title":"Prog. Polym. Sci."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"24","DOI":"10.1002\/app.11659","article-title":"Chemistry of the Vulcanization and Protection of Elastomers: A Review of the Achievements","volume":"87","author":"Coran","year":"2003","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"592","DOI":"10.5254\/1.3547762","article-title":"Sulfur Vulcanization of Natural Rubber for Benzothiazole Accelerated Formulations: From Reaction to a Rational Kinetic Model","volume":"76","author":"Ghosh","year":"2003","journal-title":"Rubber Chem. Technol."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"512","DOI":"10.5254\/1.3547834","article-title":"Activators in Accelerated Sulfur Vulcanization","volume":"77","author":"Heideman","year":"2004","journal-title":"Rubber Chem. Technol."},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Sowi\u0144ska, A., Maciejewska, M., Guo, L., and Delebecq, E. (2019). Thermal Analysis and SEM Microscopy Applied to Studying the Efficiency of Ionic Liquid Immobilization on Solid Supports. Materials, 12.","DOI":"10.3390\/ma12101579"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"3458772","DOI":"10.1155\/adv\/3458772","article-title":"Amino Acids Used as a Potential Alternative to Commercially Used Allergenic Sulfur Elastomer Vulcanization Accelerators","volume":"2026","author":"Maciejewska","year":"2026","journal-title":"Adv. Polym. Technol."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"176815","DOI":"10.1016\/j.scitotenv.2024.176815","article-title":"2-Mercaptobenzothiazole-Derived Vulcanization Accelerators in Urine Samples from Chinese Adults","volume":"955","author":"Wu","year":"2024","journal-title":"Sci. Total Environ."},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Johansen, J.D., Mahler, V., Lepoittevin, J.P., and Frosch, P.J. (2020). Allergic Reactions to Rubber Components. Contact Dermatitis, Springer. [6th ed.].","DOI":"10.1007\/978-3-319-72451-5"},{"key":"ref_15","first-page":"100886","article-title":"A Comprehensive Overview of Conventional and Bio-Based Fillers for Rubber Formulations Sustainability","volume":"27","author":"Dadkhah","year":"2024","journal-title":"Mater. Today Sustain."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"122160","DOI":"10.1016\/j.indcrop.2025.122160","article-title":"Natural and Green Components as an Alternative to Petroleum-Based and Synthetic Products in Rubber Industry: A Review","volume":"237","year":"2025","journal-title":"Ind. Crops Prod."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Van Elburg, F., Grunert, F., Aurisicchio, C., Di Consiglio, M., Talma, A., Bernal-Ortega, P., and Blume, A. (2025). Sustainable Rubber Solutions: A Study on Bio-Based Oil and Resin Blends. Polymers, 17.","DOI":"10.3390\/polym17152111"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"2304","DOI":"10.1007\/s10924-021-02342-9","article-title":"Physical Properties of Cured Self-Green Epoxidized Natural Rubber with Amino Acid","volume":"30","author":"Riyajan","year":"2022","journal-title":"J. Polym. Environ."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"3981","DOI":"10.1002\/app.23065","article-title":"Naturally Occurring Amino Acid: Novel Curatives for Chloroprene Rubber","volume":"100","author":"Das","year":"2006","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_20","first-page":"25","article-title":"Naturally Occurring Amino Acids: A Suitable Substitute of N-N\/-Di-Phenyl Guanidine (DPG) in Silica Tyre Formulation?","volume":"66","author":"Debnath","year":"2013","journal-title":"KGK Kautsch. Gummi Kunststoffe"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"489","DOI":"10.1007\/s42464-024-00265-3","article-title":"Effect of Cerium Cysteine on the Vulcanisation Property and Thermo-Oxidative Ageing of Natural Rubber","volume":"27","author":"Liu","year":"2024","journal-title":"J. Rubber Res."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"4887","DOI":"10.1021\/ma2007255","article-title":"Rubber-Filler Interactions and Network Structure in Relation to Stress-Strain Behavior of Vulcanized, Carbon Black Filled EPDM","volume":"44","author":"Litvinov","year":"2011","journal-title":"Macromolecules"},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Robertson, C.G., Hardman, N.J., and Valentin, L. (2021). Nature of Carbon Black Reinforcement of Rubber: Perspective on the Original Polymer Nanocomposite. Polymers, 13.","DOI":"10.3390\/polym13040538"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"119115","DOI":"10.1016\/j.jclepro.2019.119115","article-title":"The Past, Present and Future of Carbon Black as a Rubber Reinforcing Filler\u2013A Review","volume":"247","author":"Fan","year":"2020","journal-title":"J. Clean. Prod."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"47","DOI":"10.2324\/ejsm.2.47","article-title":"The Main Mechanism and Cross-Linking Structure for Accelerated Sulfur Vulcanization","volume":"2","author":"Choi","year":"2006","journal-title":"e-J. Soft Mater."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"1131","DOI":"10.1002\/(SICI)1097-4628(19960815)61:7<1131::AID-APP9>3.0.CO;2-N","article-title":"Sulfur Vulcanization of Polyisoprene Accelerated by Benzothiazole Derivatives. III. The Reaction of 2-Bisbenzothiazole-2,2\u2032-Disulfide with Sulfur and ZnO in Polyisoprene","volume":"61","author":"Gradwell","year":"1996","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"1405","DOI":"10.1002\/(SICI)1097-4628(20000531)76:9<1405::AID-APP5>3.0.CO;2-B","article-title":"Benzothiazole-Accelerated Sulfur Vulcanization. IV. Effect of ZnO and Bis(2-Mercaptobenzothiazole)Zinc(II) on 2-Bisbenzothiazole-2,2\u2032-Polysulfide Formation in 2-Bisbenzothiazole-2,2\u2032-Disulfide and 2-Bisbenzothiazole-2,2-Disulfide\/Sulfur","volume":"76","author":"Morgan","year":"2000","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"2033","DOI":"10.1021\/es0491376","article-title":"Characterization of Aromatic Compound Sorptive Interactions with Black Carbon (Charcoal) Assisted by Graphite as a Model","volume":"39","author":"Zhu","year":"2005","journal-title":"Environ. Sci. Technol."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"9194","DOI":"10.1039\/C8SM01953C","article-title":"Catalytic and Networking Effects of Carbon Black on the Kinetics and Conversion of Sulfur Vulcanization in Styrene Butadiene Rubber","volume":"14","author":"Hosseini","year":"2018","journal-title":"Soft Matter"},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Maciejewska, M., Sowi\u0144ska, A., and Grocholewicz, A. (2021). Zinc Complexes with 1,3-Diketones as Activators for Sulfur Vulcanization of Styrene-Butadiene Elastomer Filled with Carbon Black. Materials, 14.","DOI":"10.3390\/ma14143804"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"e55367","DOI":"10.1002\/app.55367","article-title":"Effect of Dispersants on the Hydroxyapatite-Filled Natural Rubber Biocomposites with Enhanced Functional Properties","volume":"141","author":"Maciejewska","year":"2024","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"106222","DOI":"10.1016\/j.polymertesting.2019.106222","article-title":"Use of Carbon Black as a Reinforcing Nano-Filler in Conductivity-Reversible Elastomer Composites","volume":"81","author":"Szadkowski","year":"2020","journal-title":"Polym. Test."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"729","DOI":"10.1080\/09276440.2018.1534474","article-title":"Effect of Different Carbon Fillers on the Properties of Nitrile Rubber Composites","volume":"26","author":"Szadkowski","year":"2019","journal-title":"Compos. Interfaces"},{"key":"ref_34","doi-asserted-by":"crossref","unstructured":"Mark, J., Ngai, K., Graessley, W., Mandelkern, L., Samulski, E., Koenig, J., and Wignall, G. (2004). The Glass Transition and the Glassy State. Physical Properties of Polymers, Cambridge University Press.","DOI":"10.1017\/CBO9781139165167"},{"key":"ref_35","doi-asserted-by":"crossref","unstructured":"Nugrahani, I., and Jessica, M.A. (2021). Amino Acids as the Potential Co-Former for Co-Crystal Development: A Review. Molecules, 26.","DOI":"10.3390\/molecules26113279"},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Mas\u0142owski, M., Aleksieiev, A., Miedzianowska, J., Efenberger-Szmechtyk, M., and Strzelec, K. (2022). Antioxidant and Anti\u2013Aging Activity of Freeze\u2013Dried Alcohol\u2013Water Extracts from Common Nettle (Urtica dioica L.) and Peppermint (Mentha piperita L.) in Elastomer Vulcanizates. Polymers, 14.","DOI":"10.3390\/polym14071460"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"107715","DOI":"10.1016\/j.polymertesting.2022.107715","article-title":"Evolution of Crosslinking Networks Structure and Thermo-Oxidative Aging Behavior of Unfilled NR\/BR Blends with TBIR as Extra Functional Compatibilizer","volume":"115","author":"Shao","year":"2022","journal-title":"Polym. Test."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"201","DOI":"10.1080\/09593330.2012.689366","article-title":"Adsorption Mechanism of Sodium Dodecyl Benzene Sulfonate on Carbon Blacks by Adsorption Isotherm and Zeta Potential Determinations","volume":"34","author":"Zhao","year":"2013","journal-title":"Environ. Technol."},{"key":"ref_39","first-page":"38","article-title":"Influencia de la Composici\u00f3n Qu\u00edmica Superficial del Carb\u00f3n Activado en la Adsorci\u00f3n de Benzotiazoles","volume":"18","author":"Zaror","year":"2010","journal-title":"Ingeniare"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"1957","DOI":"10.1002\/app.1964.070080504","article-title":"Structural Characterization of Vulcanizates. Part IV. Use of Triphenylphosphine and Sodium Di-n-butyl Phosphite to Determine the Structures of Sulfur Linkages in Natural Rubber, Cis-1,4-polyisoprene, and Ethylene\u2013Propylene Rubber Vulcanizate Networks","volume":"8","author":"Moore","year":"1964","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"263","DOI":"10.1016\/j.polymertesting.2018.07.002","article-title":"Experimental Determination of the Quantity and Distribution of Chemical Crosslinks in Unaged and Aged Natural Rubber, Part 1: Peroxide Vulcanization","volume":"70","author":"Howse","year":"2018","journal-title":"Polym. Test."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"4359","DOI":"10.1007\/s10973-019-08187-8","article-title":"Thermal Characterization of the Effect of Fillers and Ionic Liquids on the Vulcanization and Properties of Acrylonitrile-Butadiene Elastomer","volume":"138","author":"Maciejewska","year":"2019","journal-title":"J. Therm. Anal. Calorim."},{"key":"ref_43","doi-asserted-by":"crossref","unstructured":"Sowi\u0144ska, A., Maciejewska, M., Guo, L., and Delebecq, E. (2020). Effect of SILPs on the Vulcanization and Properties of Ethylene-Propylene-Diene Elastomer. Polymers, 12.","DOI":"10.3390\/polym12061220"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"499","DOI":"10.1177\/0095244311413442","article-title":"Composition Analysis of Carbon Black-Filled Polychloroprene Rubber Compound by Thermo-Oxidative Degradation of the Compound","volume":"43","author":"Chakraborty","year":"2011","journal-title":"J. Elastomers Plast."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"2669","DOI":"10.1007\/s10973-019-08198-5","article-title":"Thermal Analysis Applied to Studying the Influence of Ionic Liquids on the Vulcanization, Thermal Stability and Damping Properties of Ethylene-Propylene-Diene Rubber","volume":"138","author":"Maciejewska","year":"2019","journal-title":"J. Therm. Anal. Calorim."},{"key":"ref_46","unstructured":"(2018). Rubber\u2014Measurement of Vulcanization Characteristics Using Curemeters\u2014Part 3: Rotorless Rheometer (Standard No. ISO 6502-3:2018)."},{"key":"ref_47","unstructured":"(2016). Plastics\u2014Differential Scanning Calorimetry (DSC)\u2014Part 1: General Principles (Standard No. ISO 11357-1:2016)."},{"key":"ref_48","unstructured":"(2017). Rubber, Vulcanized or Thermoplastic\u2014Determination of Effect of Liquids (Standard No. ISO 1817:2015)."},{"key":"ref_49","doi-asserted-by":"crossref","first-page":"521","DOI":"10.1063\/1.1723792","article-title":"Statistical Mechanics of Cross-Linked Polymer Networks II. Swelling","volume":"11","author":"Flory","year":"1943","journal-title":"J. Chem. Phys."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"115622","DOI":"10.1016\/j.matdes.2026.115622","article-title":"Enhanced Anti-Plasticizer Migration in GO\/EPDM Insulation for Composite Solid Propellants: Experimental Study and Molecular Dynamics Simulation","volume":"263","author":"Lu","year":"2026","journal-title":"Mater. Des."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"e53758","DOI":"10.1002\/app.53758","article-title":"Influence of Accelerators and Curing System Composition on the Cure Characteristics, Crosslinks Structure and Properties of Acrylonitrile-Butadiene Elastomer","volume":"140","author":"Maciejewska","year":"2023","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_52","unstructured":"(2017). Rubber, Vulcanized or Thermoplastic\u2014Determination of Tensile Stress-Strain Properties (Standard No. ISO 37:2017)."},{"key":"ref_53","unstructured":"(2003). Plastics and Ebonite\u2014Determination of Indentation Hardness by Means of a Durometer (Shore Hardness) (Standard No. ISO 868:2003)."},{"key":"ref_54","doi-asserted-by":"crossref","first-page":"47763","DOI":"10.1002\/app.47763","article-title":"Preparation of Dispersible Nanosilica Surface-Capped by Hexamethyl Disilazane via an in Situ Surface-Modification Method and Investigation of Its Effects on the Mechanical Properties of Styrene\u2013Butadiene\/Butadiene Rubber","volume":"136","author":"Zhang","year":"2019","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_55","unstructured":"(2011). Rubber, Vulcanized or Thermoplastic\u2014Accelerated Ageing and Heat Resistance Tests (Standard No. ISO 188:2011)."},{"key":"ref_56","doi-asserted-by":"crossref","unstructured":"Miedzianowska-Mas\u0142owska, J., Mas\u0142owski, M., and Strzelec, K. (2025). Biomass, Phyto-Ash, and Biochar from Beech Wood as Functional Additives for Natural Rubber-Based Elastomer Composites. Materials, 18.","DOI":"10.3390\/ma18071659"},{"key":"ref_57","doi-asserted-by":"crossref","unstructured":"Sowi\u0144ska-Baranowska, A., Maciejewska, M., and Duda, P. (2022). The Potential Application of Starch and Walnut Shells as Biofillers for Natural Rubber (NR) Composites. Int. J. Mol. Sci., 23.","DOI":"10.3390\/ijms23147968"}],"container-title":["Molecules"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1420-3049\/31\/18\/3250\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,20]],"date-time":"2026-09-20T04:12:08Z","timestamp":1789877528000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1420-3049\/31\/18\/3250"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,14]]},"references-count":57,"journal-issue":{"issue":"18","published-online":{"date-parts":[[2026,9]]}},"alternative-id":["molecules31183250"],"URL":"https:\/\/doi.org\/10.3390\/molecules31183250","relation":{},"ISSN":["1420-3049"],"issn-type":[{"value":"1420-3049","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,9,14]]}}}