{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,30]],"date-time":"2026-09-30T22:09:13Z","timestamp":1790806153345,"version":"4.1.0"},"reference-count":44,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2025,4,3]],"date-time":"2025-04-03T00:00:00Z","timestamp":1743638400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"European Union\u2019s Horizon Europe research and innovation programme","award":["101059909"],"award-info":[{"award-number":["101059909"]}]},{"name":"Allowance for Top consortia for Knowledge and Innovation (TKIs) of the Ministry of Economic Affairs and Climate","award":["101059909"],"award-info":[{"award-number":["101059909"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>Polypropylene (PP), a widely used recyclable plastic in packaging and engineering applications, is prone to thermo-oxidative degradation during reprocessing and molding at high temperatures. Antioxidants (AOs) are essential for stabilizing PP in both its virgin and recycled states. The quantity of AO added is critical: insufficient amounts can lead to poor stabilization, while excessive amounts can cause safety concerns due to build-up. This study presents a modified approach to measure the Oxidation Induction Temperature (OIT) using Differential Scanning Calorimetry (DSC), particularly for recycled PP from waste that contains unpredictable contaminations. This modified approach ensures the safety of the calorimetry cell by limiting the oxidation reaction and preventing the release of volatile compounds during measurements. By performing DSC measurements in inert environments, we obtain the OIT, which can be correlated to residual intact AO levels. This approach to monitoring AO levels is demonstrated in both open- and closed-loop recycling of rigid PP. Although the presence of contamination is known to catalyze thermo-oxidative degradation in PP, our results indicate that recycled PP from open-loop collection still contains sufficient residual AO that allows it to withstand limited thermal reprocessing. However, this tendency of AO retention leads to significant build-up during closed-loop recycling when AOs are added to each cycle, where the PP grade remains fairly homogeneous and the dispersity (\u0110) does not significantly increase over multiple recycling loops.<\/jats:p>","DOI":"10.3390\/ma18071640","type":"journal-article","created":{"date-parts":[[2025,4,4]],"date-time":"2025-04-04T03:36:45Z","timestamp":1743737805000},"page":"1640","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["Monitoring Antioxidant Consumption and Build-Up in Polypropylene During Open-Loop and Closed-Loop Mechanical Recycling"],"prefix":"10.3390","volume":"18","author":[{"ORCID":"https:\/\/orcid.org\/0009-0006-6015-621X","authenticated-orcid":false,"given":"Niek","family":"Knoben","sequence":"first","affiliation":[{"name":"Brightlands Materials Center, Urmonderbaan 22, 6167 RD Geleen, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Max","family":"Vanhouttem","sequence":"additional","affiliation":[{"name":"Brightlands Materials Center, Urmonderbaan 22, 6167 RD Geleen, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Aike","family":"Wypkema","sequence":"additional","affiliation":[{"name":"Brightlands Materials Center, Urmonderbaan 22, 6167 RD Geleen, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1312-4603","authenticated-orcid":false,"given":"Nithya","family":"Subramanian","sequence":"additional","affiliation":[{"name":"Brightlands Materials Center, Urmonderbaan 22, 6167 RD Geleen, The Netherlands"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,4,3]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"105440","DOI":"10.1016\/j.resconrec.2021.105440","article-title":"United States plastics: Large flows, short lifetimes, and negligible recycling","volume":"167","author":"Di","year":"2021","journal-title":"Resour. Conserv. Recycl."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"e1700782","DOI":"10.1126\/sciadv.1700782","article-title":"Production, use, and fate of all plastics ever made","volume":"3","author":"Geyer","year":"2017","journal-title":"Sci. Adv."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"768","DOI":"10.1126\/science.1260352","article-title":"Plastic waste inputs from land into the ocean","volume":"347","author":"Jambeck","year":"2015","journal-title":"Science"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"116984","DOI":"10.1016\/j.trac.2023.116984","article-title":"Current trends of unsustainable plastic production and micro(nano)plastic pollution","volume":"160","author":"Walker","year":"2023","journal-title":"TrAC Trends Anal. Chem."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"129","DOI":"10.1099\/mic.0.000749","article-title":"Plastic waste as a global challenge: Are biodegradable plastics the answer to the plastic waste problem?","volume":"165","author":"Narancic","year":"2019","journal-title":"Microbiology"},{"key":"ref_6","first-page":"84","article-title":"A Review of Plastic Waste Management Strategies","volume":"2","author":"Siddiqui","year":"2013","journal-title":"Int. Res. J. Environ. Sci."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"e2000415","DOI":"10.1002\/marc.202000415","article-title":"Mechanical Recycling of Packaging Plastics: A Review","volume":"42","author":"Schyns","year":"2021","journal-title":"Macromol. Rapid Commun."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"129827","DOI":"10.1016\/j.jclepro.2021.129827","article-title":"Plastic pollution and packaging: Corporate commitments and actions from the food and beverage sector","volume":"331","author":"Phelan","year":"2022","journal-title":"J. Clean. Prod."},{"key":"ref_9","unstructured":"Plastics Europe (2023). Plastics\u2014The Fast Facts 2023, Plastics Europe."},{"key":"ref_10","unstructured":"Eurostat (2024, December 19). 41% of Plastic Packaging Waste Recycled in 2022. Available online: https:\/\/ec.europa.eu\/eurostat\/web\/products-eurostat-news\/w\/ddn-20241024-3."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"230","DOI":"10.1016\/j.wasman.2024.11.029","article-title":"Losses and emissions in polypropylene recycling from household packaging waste","volume":"191","author":"Kasper","year":"2025","journal-title":"Waste Manag."},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Nov\u00e1k, I., Popelka, A., \u0160pitalsk\u00fd, Z., Krupa, I., and Tavman, S. (2015). Polyolefin in Packaging and Food Industry. Polyolefin Compounds and Materials, Springer.","DOI":"10.1007\/978-3-319-25982-6_7"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"631","DOI":"10.1080\/03602559.2013.866247","article-title":"Recent Advances in Polyolefins\/Natural Polymer Blends Used for Packaging Application","volume":"53","author":"Sam","year":"2014","journal-title":"Polym.-Plast. Technol. Eng."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"2899","DOI":"10.1002\/pen.24182","article-title":"Mechanical reprocessing of polyolefin waste: A review","volume":"55","author":"Yin","year":"2015","journal-title":"Polym. Eng. Sci."},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Ambrogi, V., Carfagna, C., Cerruti, P., and Marturano, V. (2017). 4\u2014Additives in Polymers. Modification of Polymer Properties, William Andrew.","DOI":"10.1016\/B978-0-323-44353-1.00004-X"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"109","DOI":"10.1016\/0308-8146(82)90006-1","article-title":"Polyolefins for food packaging","volume":"8","author":"Shorten","year":"1982","journal-title":"Food Chem."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"110260","DOI":"10.1016\/j.polymdegradstab.2023.110260","article-title":"Long term thermo-oxidative degradation and stabilization of polypropylene (PP) and the implications for its recyclability","volume":"208","author":"Gijsman","year":"2023","journal-title":"Polym. Degrad. Stab."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"McKeen, L.W. (2014). Introduction to the Effect of Heat Aging on Plastics. The Effect of Long Term Thermal Exposure on Plastics and Elastomers, Elsevier.","DOI":"10.1016\/B978-0-323-22108-5.00002-3"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"1661","DOI":"10.1007\/s00289-011-0560-6","article-title":"Thermal degradation behavior of polypropylene in the melt state: Molecular weight distribution changes and chain scission mechanism","volume":"67","author":"Qian","year":"2011","journal-title":"Polym. Bull."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"110082","DOI":"10.1016\/j.polymdegradstab.2022.110082","article-title":"Restabilization\u201430 years of research for quality improvement of recycled plastics review","volume":"203","author":"Pfaendner","year":"2022","journal-title":"Polym. Degrad. Stab."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"152","DOI":"10.1002\/pen.760050312","article-title":"The deterioration of polypropylene by oxidative degradation","volume":"5","author":"Oswald","year":"1965","journal-title":"Polym. Eng. Sci."},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Coleman, E.A. (2011). 23\u2014Plastics Additives. Applied Plastics Engineering Handbook, William Andrew.","DOI":"10.1016\/B978-1-4377-3514-7.10023-6"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"441","DOI":"10.1016\/S0141-3910(02)00101-5","article-title":"Degradation and stabilization of polyolefins from municipal plastic waste during multiple extrusions under different reprocessing conditions","volume":"77","author":"Santos","year":"2002","journal-title":"Polym. Degrad. Stab."},{"key":"ref_24","doi-asserted-by":"crossref","unstructured":"Karlsson, S. (2004). Recycled Polyolefins. Material Properties and Means for Quality Determination. Long Term Properties of Polyolefins, Springer.","DOI":"10.1007\/b94173"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"498","DOI":"10.1016\/j.polymertesting.2004.11.012","article-title":"Interlaboratory test on polymers: Determination of antioxidants in polyolefins","volume":"24","author":"Ritter","year":"2005","journal-title":"Polym. Test."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"3225","DOI":"10.1021\/jf070102+","article-title":"Antioxidant Content of and Migration from Commercial Polyethylene, Polypropylene, and Polyvinyl Chloride Packages","volume":"55","year":"2007","journal-title":"J. Agric. Food Chem."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"3455","DOI":"10.1002\/jssc.201000491","article-title":"Determination of antioxidants in polyolefins using total dissolution methodology followed by RPLC","volume":"33","author":"Green","year":"2010","journal-title":"J. Sep. Sci."},{"key":"ref_28","unstructured":"(2018). Plastics\u2014Differential Scanning Calorimetry (DSC)\u2014Part 6: Determination of Oxidation Induction Time (Isothermal OIT) and Oxidation Induction Temperature (Dynamic OIT). Standard No. ISO 11357-6:2018."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"243","DOI":"10.1007\/s10973-008-9389-0","article-title":"Determination of oxidation parameters by DSC for polypropylene stabilized with hydroxytyrosol (3,4-dihydroxy-phenylethanol)","volume":"96","author":"Peltzer","year":"2009","journal-title":"J. Therm. Anal. Calorim."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"53","DOI":"10.1016\/j.resconrec.2015.05.014","article-title":"The recyclability benefit rate of closed-loop and open-loop systems: A case study on plastic recycling in Flanders","volume":"101","author":"Huysman","year":"2015","journal-title":"Resour. Conserv. Recycl."},{"key":"#cr-split#-ref_31.1","unstructured":"European Union (2022). Commission Regulation"},{"key":"#cr-split#-ref_31.2","unstructured":"(EU) 2022\/1616. Off. J. Eur. Union, 243, 3-46."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"965","DOI":"10.1021\/acssuschemeng.2c05497","article-title":"Technical, Economic, and Environmental Comparison of Closed-Loop Recycling Technologies for Common Plastics","volume":"11","author":"Uekert","year":"2023","journal-title":"ACS Sustain. Chem. Eng."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"107537","DOI":"10.1016\/j.resconrec.2024.107537","article-title":"Closed-loop recycling of polypropylene: A case study on mechanical recycling of separately collected yogurt cups in Austria","volume":"205","author":"Traxler","year":"2024","journal-title":"Resour. Conserv. Recycl."},{"key":"ref_34","unstructured":"Der Gr\u00fcne Punkt (2024, November 01). Produktspezifikation 05\/2012 Fraktions-Nr. 324. Available online: https:\/\/www.nedvang.nl\/wp-content\/uploads\/2019\/03\/PP-DKR-324.pdf."},{"key":"ref_35","unstructured":"(2019). Plastics\u2014Determination of Tensile Properties\u2014Part 1: General Principles. Standard No. ISO 527-1A:2019."},{"key":"ref_36","unstructured":"(2022). Plastics\u2014Determination of the Melt Mass-Flow Rate (MFR) and Melt Volume-Flow Rate (MVR) of Thermoplastics. Standard No. ISO 1133:2022. Part 1: Standard Method."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"108353","DOI":"10.1016\/j.polymertesting.2024.108353","article-title":"Accurate determination of polyethylene (PE) and polypropylene (PP) content in polyolefin blends using machine learning-assisted differential scanning calorimetry (DSC) analysis","volume":"131","author":"Bashirgondabi","year":"2024","journal-title":"Polym. Test."},{"key":"ref_38","unstructured":"Jansen, M., Velzen, U.T.V., and Pretz, T. (2015). Handbook for Sorting of Plastic Packaging Waste Concentrates, Wageningen UR Food & Biobased Research."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"13065","DOI":"10.1021\/acsapm.4c01927","article-title":"Assessment of Different Application Grades of Post-Consumer Recycled (PCR) Polyolefins from Material Recovery Facilities (MRFs) in the United States","volume":"6","author":"Cecon","year":"2024","journal-title":"ACS Appl. Polym. Mater."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"13363","DOI":"10.1007\/s10973-022-11505-2","article-title":"Recycling of metallocene isotactic polypropylene: Importance of antioxidants","volume":"147","author":"Cerrada","year":"2022","journal-title":"J. Therm. Anal. Calorim."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"83","DOI":"10.1016\/j.polymertesting.2005.08.011","article-title":"Oxidation induction time studies on the thermal degradation behaviour of polyoxymethylene","volume":"25","author":"Archodoulaki","year":"2006","journal-title":"Polym. Test."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"775","DOI":"10.1002\/1521-3935(20010301)202:6<775::AID-MACP775>3.0.CO;2-G","article-title":"Kinetics of the Thermal and Thermo-Oxidative Degradation of Polystyrene, Polyethylene and Poly(propylene)","volume":"202","author":"Peterson","year":"2001","journal-title":"Macromol. Cheistry Phys."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"907","DOI":"10.1016\/j.polymertesting.2013.04.008","article-title":"Real-time quantitative analysis of volatile products generated during solid-state polypropylene thermal oxidation","volume":"32","author":"Richaud","year":"2013","journal-title":"Polym. Test."}],"container-title":["Materials"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1996-1944\/18\/7\/1640\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,9]],"date-time":"2025-10-09T17:09:27Z","timestamp":1760029767000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1996-1944\/18\/7\/1640"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,4,3]]},"references-count":44,"journal-issue":{"issue":"7","published-online":{"date-parts":[[2025,4]]}},"alternative-id":["ma18071640"],"URL":"https:\/\/doi.org\/10.3390\/ma18071640","relation":{},"ISSN":["1996-1944"],"issn-type":[{"value":"1996-1944","type":"electronic"}],"subject":[],"published":{"date-parts":[[2025,4,3]]}}}