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Moderate decreases in polarity were obtained, as observed by the solubility of the esterified lignins in toluene and ethanol. Three reaction mechanisms involving one, two, or three of the carboxylic acids in citric acid are proposed. For both biomass sources, increasing the concentration of citric acid increased the <jats:italic>M<\/jats:italic><jats:sub>W<\/jats:sub> (and <jats:italic>T<\/jats:italic><jats:sub>g<\/jats:sub>) of the lignin, whereas increasing the catalyst, sodium hypophosphite (SHP), beyond 1\u20132\u2009wt%, decreases the <jats:italic>M<\/jats:italic><jats:sub>W<\/jats:sub> due to an unwanted side reaction between citric acid and SHP. In fact, for HPL, the highest <jats:italic>T<\/jats:italic><jats:sub>g<\/jats:sub> is obtained with no added catalyst, thus creating a green process that uses only renewable feed materials to build the <jats:italic>M<\/jats:italic><jats:sub>W<\/jats:sub> and <jats:italic>T<\/jats:italic><jats:sub>g<\/jats:sub> of lignin.<\/jats:p>","DOI":"10.1002\/cssc.202500311","type":"journal-article","created":{"date-parts":[[2025,4,15]],"date-time":"2025-04-15T11:07:47Z","timestamp":1744715267000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":7,"title":["Interlinking Lignin Molecules with Citric Acid: The Effect of Reaction Conditions on Lignin Properties"],"prefix":"10.1002","volume":"18","author":[{"ORCID":"https:\/\/orcid.org\/0009-0002-4683-9234","authenticated-orcid":false,"given":"Oreoluwa Rebecca","family":"Agede","sequence":"first","affiliation":[{"name":"Chemical and Biomolecular Engineering Clemson University  206 South Palmetto Blvd. Clemson SC 29634\u20100909 USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2833-485X","authenticated-orcid":false,"given":"Mark C.","family":"Thies","sequence":"additional","affiliation":[{"name":"Chemical and Biomolecular Engineering Clemson University  206 South Palmetto Blvd. Clemson SC 29634\u20100909 USA"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2025,5,12]]},"reference":[{"key":"e_1_2_9_2_1","doi-asserted-by":"publisher","DOI":"10.1039\/D2NR00203E"},{"key":"e_1_2_9_3_1","doi-asserted-by":"publisher","DOI":"10.1021\/acssuschemeng.8b01170"},{"key":"e_1_2_9_4_1","first-page":"223","volume":"2","author":"Xie Y.","year":"2023","journal-title":"Resour. 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