{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,16]],"date-time":"2026-09-16T21:07:20Z","timestamp":1789592840251,"version":"build-2803163510"},"reference-count":45,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2026,1,24]],"date-time":"2026-01-24T00:00:00Z","timestamp":1769212800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>Recently, increasing attention has been paid to the application of sulfonic acids as alternative materials for the pickling process. The aim of the present study was to investigate the action of pickling with p-toluenesulfonic acid monohydrate on derma\u2019s collagen and the influence of this action on subsequent processes and properties of chromed and crust leather. The application of p-toluenesulfonic acid monohydrate in the pickling process led to a similar effect on collagen compared with conventional process. The solutions after experimental pickling contained lower amounts of total dissolved solids, total suspended solids, and chlorides. The chrome tanning process is improved after the pickling with p-toluenesulfonic acid monohydrate: the exhaustion of chromium compounds reaches 98%, while after conventional pickling, it is only 68.7%; accordingly, lower amounts of basic chromium sulfate can be used for chrome tanning to achieve the same chromium content in the wet blue leather. The crust leather produced after experimental pickling has properties close to the conventional one.<\/jats:p>","DOI":"10.3390\/ma19030471","type":"journal-article","created":{"date-parts":[[2026,1,26]],"date-time":"2026-01-26T12:41:16Z","timestamp":1769431276000},"page":"471","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Salt-Free Pickling with Sulfonic Acid as an Approach to Cleaner Leather Processing"],"prefix":"10.3390","volume":"19","author":[{"given":"Renata","family":"Bi\u0161kauskait\u0117-Ulinsk\u0117","sequence":"first","affiliation":[{"name":"Faculty of Chemical Technology, Kaunas University of Technology, Radvilenu pl. 19, 50254 Kaunas, Lithuania"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4974-7626","authenticated-orcid":false,"given":"Virgilijus","family":"Valeika","sequence":"additional","affiliation":[{"name":"Faculty of Chemical Technology, Kaunas University of Technology, Radvilenu pl. 19, 50254 Kaunas, Lithuania"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,1,24]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"126017","DOI":"10.1016\/j.jclepro.2021.126017","article-title":"Effect of different ions in assisting protease to open the collagen fiber bundles in leather making","volume":"293","author":"Zhang","year":"2021","journal-title":"J. Clean. Prod."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"10608","DOI":"10.1038\/s41598-025-94531-y","article-title":"Comparative characterization of leather from different tanning processes as a contribution for a sustainable development of the leather industry","volume":"15","author":"Ferraris","year":"2025","journal-title":"Sci. Rep."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"69","DOI":"10.1016\/S0959-6526(01)00015-4","article-title":"Cleaner chrome tanning\u2014Emerging options","volume":"10","author":"Sundar","year":"2002","journal-title":"J. Clean. Prod."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"156","DOI":"10.25082\/MER.2021.01.004","article-title":"Benefits and problems of chrome tanning in leather processing: Approach a greener technology in leather industry","volume":"3","author":"Ahmed","year":"2021","journal-title":"Mater. Eng. Res."},{"key":"ref_5","first-page":"144","article-title":"Use of glucose to improve the environmental aspects of chrome tanning process","volume":"933","author":"Puccini","year":"2014","journal-title":"Adv. Mat. Res."},{"key":"ref_6","unstructured":"Covington, A.D. (2009). Tanning Chemistry: The Science of Leather, Royal Society of Chemistry."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"15","DOI":"10.30574\/gscarr.2023.15.1.0100","article-title":"Reducing chromium discharge in tanning: The salt-free chrome tanning process","volume":"15","author":"Haroun","year":"2023","journal-title":"GSC Adv. Res. Rev."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"2455","DOI":"10.1007\/s10098-017-1442-x","article-title":"Low-chromium- and low-sulphate emission leather tanning intensified by compressed carbon dioxide","volume":"19","author":"Prokein","year":"2017","journal-title":"Clean Technol. Environ. Policy"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"10285\u221210291","DOI":"10.1021\/acssuschemeng.5c02228","article-title":"Valorization of Waste Pickle Liquor from Tanneries: A Greener Approach to Synthesize Azo Dyes","volume":"13","author":"Meganathan","year":"2025","journal-title":"ACS Sustain. Chem. Eng."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"117095","DOI":"10.1016\/j.envres.2023.117095","article-title":"Treatment of salt from hides curing stage by electrocoagulation for use in the pickling stage of the tanning industry","volume":"237","author":"Sarinho","year":"2023","journal-title":"Environ. Res."},{"key":"ref_11","unstructured":"(2025, November 14). Market and Policy Analyses of Raw Materials, Horticulture and Tropical (RAMHOT) Products Team. Trade and Markets Division Food and Agriculture, Organization of the United Nations. World Statistical Compendium for Raw Hides and Skins, Leather and Leather Footwear 1999\u20132015. Available online: https:\/\/openknowledge.fao.org\/server\/api\/core\/bitstreams\/65fff9bf-34c7-4724-9134-9b07c9dfb71e\/content."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"670","DOI":"10.1002\/slct.201802952","article-title":"Mechanism of High Chrome Uptake of Tanning Pickled Hide by Carboxyl-Terminated Hyper-Branched Polymer Combination Chrome Tanning","volume":"4","author":"Yao","year":"2019","journal-title":"ChemistrySelect"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"100175","DOI":"10.1016\/j.jics.2021.100175","article-title":"Improvement of hydrothermal stability and chrome uptake of leather: Amino-terminated hyper-branched polymer as high exhausted tanning auxiliary","volume":"98","author":"Yao","year":"2021","journal-title":"J. Indian Chem. Soc."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"788","DOI":"10.1016\/j.jclepro.2016.08.097","article-title":"Application of an amphoteric polymer for leather pickling to obtain a less total dissolved solids residual process","volume":"139","author":"Jia","year":"2016","journal-title":"J. Clean. Prod."},{"key":"ref_15","first-page":"186","article-title":"THPS Pretreatment Before Tanning (Chrome or Non-chrome)","volume":"93","author":"Plavan","year":"2009","journal-title":"J. Soc. Leather Technol. Chem."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1603","DOI":"10.1016\/j.jclepro.2009.06.004","article-title":"A salt-free pickling regime for hides and skins using oxazolidine","volume":"17","author":"Li","year":"2009","journal-title":"J. Clean. Prod."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"118706","DOI":"10.1016\/j.jclepro.2019.118706","article-title":"A salt-free pickling chrome tanning technology: Pretreatment with the collective polyoxyethylene diepoxy ether and urotropine","volume":"244","author":"Jia","year":"2020","journal-title":"J. Clean. Prod."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"243","DOI":"10.1007\/s10098-003-0240-9","article-title":"Pickle-free chrome tanning using a polymeric synthetic tanning agent for cleaner leather processing","volume":"6","author":"Rao","year":"2004","journal-title":"Clean. Technol. Environ. Policy"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"012024","DOI":"10.1088\/1757-899X\/111\/1\/012024","article-title":"Application of advanced polymeric compounds for development of leather production","volume":"111","author":"Nikonova","year":"2016","journal-title":"IOP Conf. Ser. Mater. Sci. Eng."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"434","DOI":"10.1016\/j.psep.2022.09.024","article-title":"Single pot low float chromium tanning: Cleaner pathway approach to environment friendly leather manufacturing","volume":"167","author":"Ariram","year":"2022","journal-title":"Process Saf. Environ. Prot."},{"key":"ref_21","unstructured":"Puccini, M., Vitolo, S., and Seggiani, M. (2013, January 24\u201325). Development of a Pickle-Free Chrome Tanning to Improve the Eco-Sustainability of Leather Processing. Proceedings of the International Conference on Frontiers of Environment, Energy and Bioscience (ICFEEB 2013), Beijing, China."},{"key":"ref_22","first-page":"370","article-title":"Electrochemical oxidation and reuse of pickling wastewater from tanneries","volume":"103","author":"Sundarapandiyan","year":"2008","journal-title":"J. Am. Leather Chem. Assoc."},{"key":"ref_23","first-page":"279","article-title":"Effect of Pickling Materials on Leather Quality from a Hide Surface Charge Perspective","volume":"117","author":"Yang","year":"2022","journal-title":"J. Am. Leather Chem. Assoc."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1055","DOI":"10.1016\/j.jclepro.2015.07.155","article-title":"A salt-free and chromium discharge minimizing tanning technology: The novel cleaner integrated chrome tanning process","volume":"112","author":"Zhang","year":"2016","journal-title":"J. Clean. Prod."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"1055","DOI":"10.1016\/j.jclepro.2016.06.199","article-title":"A salt-free pickling chrome tanning approach using a novel sulphonic aromatic acid structure","volume":"142","author":"Zhang","year":"2016","journal-title":"J. Clean. Prod."},{"key":"ref_26","unstructured":"(2025, November 21). Safety Data Sheet According to Regulation (EC) No. 1907\/2006 (REACH), Amended by 2020\/878\/EU Toluene-4-Sulfonic Acid Monohydrate \u2265 98%, for Synthesis. Available online: https:\/\/www.carlroth.com\/medias\/SDB-4796-IE-EN.pdf?context=bWFzdGVyfHNlY3VyaXR5RGF0YXNoZWV0c3wzMTE5Njh8YXBwbGljYXRpb24vcGRmfGFEY3dMMmc1Tnk4NU1UZ3hPREF4TXpneE9URTRMMU5FUWw4ME56azJYMGxGWDBWT0xuQmtaZ3wwNDg4MjY1ZjcxNTljZTJlMzcyMTI4ZDNjNTE1MDVjM2RiM2FlMTQ4NDk0OGQxZmRjYjM2ZTBjMzdmZjg5NDcw."},{"key":"ref_27","first-page":"5","article-title":"Modiphitsirovanyi method opredeleniya oksiprolina","volume":"1","author":"Zaides","year":"1964","journal-title":"Biokhimiya"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"265","DOI":"10.1016\/S0021-9258(19)52451-6","article-title":"Protein measurement with the Folin phenol reagent","volume":"193","author":"Lowry","year":"1951","journal-title":"JBC"},{"key":"ref_29","unstructured":"Korosteliovas, P. (1969). Tirpal\u0173 Ruo\u0161imas Analizin\u0117s Chemijos Darbams, Mintis. (In Lithuanian)."},{"key":"ref_30","unstructured":"Golovteeva, A.A., Kutsidi, D.A., and Sankin, L.B. (1982). Laboratornyj Praktikum po Khimiyi i Tekhnologiyi Kozhy i Mekha, Legkaiya i Pischevaiya Prom. (In Russian)."},{"key":"ref_31","unstructured":"Lietuvos Aplinkos Apsaugos Ministerija (1994). Unifikuoti Nuotek\u0173 ir Pavir\u0161ini\u0173 Vanden\u0173 Kokyb\u0117s Tyrimo Metodai. I DALIS, AAM Leidybos Biuras. (In Lithuanian)."},{"key":"ref_32","unstructured":"(2017). Leather\u2014Chemical, Physical and Mechanical and Fastness Tests\u2014Sampling Location (Standard No. Standard ISO 2418:2017)."},{"key":"ref_33","unstructured":"(2015). Leather-Leather\u2014Physical and Mechanical Tests\u2014Determination of Shrinkage Temperature up to 100 \u00b0C (Standard No. Standard ISO 3380:2015)."},{"key":"ref_34","unstructured":"(2011). Leather Physical and Mechanical Tests Determination of Tensile Strength and Percentage Extension (Standard No. Standard ISO 3376:2011)."},{"key":"ref_35","unstructured":"(2009). Leather Chemical Determination of Chromic Oxide Content Part 2: Quantification by Colorimetric Determination (Standard No. Standard ISO 5398-2:2009)."},{"key":"ref_36","unstructured":"(2008). Leather Chemical Tests Determination of Matter Soluble in Dichloromethane and Free Fatty Acid Content (Standard No. Standard ISO 4048:2008)."},{"key":"ref_37","unstructured":"(2018). Leather-Chemical Tests-Determination of pH and Difference Figure (Standard No. Standard ISO 4045:2018)."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"8660","DOI":"10.1021\/acssuschemeng.9b00482","article-title":"PH-sensitive and chromium-loaded mineralized nanoparticles as a tanning agent for cleaner leather production","volume":"7","author":"Li","year":"2019","journal-title":"ACS Sustain. Chem. Eng."},{"key":"ref_39","first-page":"12","article-title":"The Leather Industry: A Chemistry Insight Part I: An Overview of the Industrial Process","volume":"1","author":"Beghetto","year":"2013","journal-title":"Sci. Ca\u2019 Foscari"},{"key":"ref_40","first-page":"435","article-title":"Minimization of chromium discharge in leather processing by using methanesulfonic acid: A cleaner pickling-masking-chrome tanning system","volume":"111","author":"Zhang","year":"2016","journal-title":"J. Am. Leather Chem. Assoc."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"820","DOI":"10.1016\/j.chemosphere.2008.07.036","article-title":"High chrome exhaustion in a non-float tanning process using a sulphonic aromatic acid","volume":"73","author":"Bacardit","year":"2008","journal-title":"Chemosphere"},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"123278","DOI":"10.1016\/j.jclepro.2020.123278","article-title":"A smart high chrome exhaustion and chrome-less tanning system based on chromium (III)-loaded nanoparticles for cleaner leather processing","volume":"277","author":"Zhu","year":"2020","journal-title":"J. Clean. Prod."},{"key":"ref_43","doi-asserted-by":"crossref","unstructured":"Mihai, A., Seul, A., Curteza, A., and Costea, M. (2022). Mechanical parameters of leather in relation to technological processing of the footwear uppers. Materials, 15.","DOI":"10.3390\/ma15155107"},{"key":"ref_44","first-page":"243","article-title":"Effects of vacuum drying variables on the mechanical properties of leather","volume":"96","author":"Liu","year":"2001","journal-title":"J. Am. Leather Chem. Assoc."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"215","DOI":"10.1016\/j.dyepig.2004.12.007","article-title":"Evaluation of modified leather dyeing technique using black dyestuffs from the economical view","volume":"67","author":"Haroun","year":"2005","journal-title":"Dye. Pigment."}],"container-title":["Materials"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1996-1944\/19\/3\/471\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,1,26]],"date-time":"2026-01-26T12:49:01Z","timestamp":1769431741000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1996-1944\/19\/3\/471"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,1,24]]},"references-count":45,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2026,2]]}},"alternative-id":["ma19030471"],"URL":"https:\/\/doi.org\/10.3390\/ma19030471","relation":{},"ISSN":["1996-1944"],"issn-type":[{"value":"1996-1944","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,1,24]]}}}