Tomato plant residue as new renewable source for cellulose production: extraction of cellulose nanocrystals with different surface functionalities

With the aim of identifying new sources for cellulose manufacturing, post-harvest tomato plant residue (TPR) was proposed in this study as a viable and sustainable source for the extraction of cellulose derivatives, namely cellulose microfibers (CMF) and cellulose nanocrystals (CNC). Pure CMF with an average diameter of 20 µm were successfully produced by subjecting the raw TPR to chemical treatments and then characterized in terms of their morphology and physico-chemical characteristics. By subjecting CMF to sulfuric, phosphoric and citric/hydrochloric acid hydrolysis, sulfated CNC (S-CNC), phosphorylated CNC (P-CNC) and carboxylated CNC (C-CNC) have been successfully produced. This was done to produce CNC with different characteristics and surface functionalities depending on the inserted functional groups during the acid hydrolysis process. By using several characterization techniques, it was found that all the extracted CNC characterized by cellulose I structure, with a crystallinity index of 81–89, 81 and 78%, an aspect ratio of 40–49, 98 and 67 and zeta potential of − 27.8 to − 37.3, − 36.9 and − 22.3 mV for S-CNC, P-CNC and C-CNC, respectively. The determined thermal stability of all extracted CNC is relatively higher than that generally obtained for S-CNC from other sources, which suffer from limited thermal stability. The produced CNC with different surface functionalities formed stable colloidal suspensions in polar solvents such as water and dimethyl sulfoxide. The production of CMF and CNC from this underutilized waste has the potential to add value to the post-harvest tomato plant, which is produced annually as waste in vast quantities throughout the world, in addition to significantly reducing the volume of cumulative waste in the environment.