Vol.:(0123456789) 1 3 Biomass Conversion and Bioreﬁnery https://doi.org/10.1007/s13399-023-05027-6 ORIGINAL ARTICLE A facile, low‑thermal, and environmentally friendly method to improve the properties of lignin‑containing cellulose nanocrystals (LCNCs) and cellulose nanoﬁbrils (LCNFs) from bagasse unbleached soda pulp Saleh Ghahramani 1 · Sahab Hedjazi 2 · Soheila Izadyar 1 · Steﬀen Fischer 3 · Ali Abdulkhani 1 Received: 20 June 2023 / Revised: 12 October 2023 / Accepted: 17 October 2023 © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2023 Abstract Using novel treatments before lignin-containing nanocelluloses (LNCs) production from agricultural residues is a growing ﬁeld of fondness due to environmental, economic, and bioreﬁnery issues. So, in this study, cold caustic extraction (CCE) was utilized as a facile, low-thermal, bleaching-free, environmentally friendly, and light alkaline post-treatment of bagasse unbleached soda pulp before lignin-containing cellulose nanocrystals (LCNCs) and lignin-containing cellulose nanoﬁbrils (LCNFs) manufacturing processes. The optimum conditions of CCE post-treatment of pulp were 10% sodium hydroxide at 20 °C for 60 min. The production of LCNCs was performed with an acid hydrolysis method using sulfuric acid (64 wt%), and LCNFs were manufactured via microﬂuidizer. Morphological analysis clearly indicated that the average diameter of LCNCs and LCNFs reduced after CCE post-treatment. Furthermore, Fourier transform infrared spectroscopy conﬁrms the reduction of hemicelluloses and lignin on the ﬁber surface after CCE post-treatment. X-ray diﬀraction results show that CCE post-treatment increases the crystallinity of LNCs. The thermal analyses also showed that the generated LCNCs and LCNFs from CCE post-treated pulps had obviously higher thermal stability than untreated ones. The manufactured nanoﬁlms after CCE post-treatments also exhibited outstanding mechanical and appearance properties. In general, this study elucidates that the chemical, morphological, and thermal features of LNCs as well as mechanical and appearance properties of manufactured nanoﬁlms can be signiﬁcantly improved by CCE post-treatment of the unbleached pulp with an easy, aﬀordable, and environmentally friendly method instead of bleaching or other expensive and non-eco-friendly methods, especially for heat-resistant nano biopolymers and composite applications. Keyword Lignin-containing cellulose nanocrystals (LCNCs) · Lignin-containing cellulose nanoﬁbrils (LCNFs) · Cold caustic extraction (CCE) · Nanoﬁlm · Soda pulp · Bagasse 1 Introduction Although wood is the most plentiful resource of lignocellulosic in nature, excessive and inconsiderate harvesting of trees results in deforestation with a radical negative eﬀect on the environment worldwide. Hence, it causes an imbalance in the ecosystem [1]. The Global Forest Review reports show that the world has lost 459 million hectares (Mha) of tree cover since the turn of the century, equivalent to about 12% of global tree cover in 2000. It is important to note that this trend of tree cover loss has been on the rise in recent years, increasing from 13.4 Mha in 2001 to 22.8 Mha in 2022 [2]. Furthermore, the United Nations Food and Agriculture Organization estimates that Highlights • Cold caustic extraction (CCE) as a novel and low-thermal post- treatment of unbleached pulp was used to produce lignocellulosic nanocrystals (LCNCs) and nanoﬁbrils (LCNFs), LCNC ﬁlms, and LCNF ﬁlms. • LCNCs and LCNFs with excellent homogeneity, crystallinity, and thermal stability were produced by CCE post-treatment of unbleached pulp. • LCNC and LCNF ﬁlms with outstanding mechanical and appearance properties were manufactured from CCE post-treated pulps and untreated pulps. • The inﬂuence of CCE post-treatment on pulps leads to diﬀerent properties in produced LCNCs, LCNFs, LCNC ﬁlms, and LCNF ﬁlms. Extended author information available on the last page of the article