Extraction and characterization of cellulose and cellulose nanofibers from Citrullus colocynthis seeds

Citrullus colocynthis is a perennial herbaceous plant of the Cucurbitaceae family, cultivated in the Mediterranean basin and tropical countries as a traditional medicinal plant. In this paper, extraction of water-insoluble polysaccharides of Citrullus colocynthis seeds was performed using two chemical extraction processes. The first one involved the deproteinization of grinded Citrullus colocynthis seeds in sodium hydroxide aqueous solution, followed by lipid extraction in the chloroform/methanol solvent. The second process consisted of extracting the lipid material before deproteinization step. Several analytical techniques were used to identify cellulose as the main compound in the water-insoluble extract including ATR-FTIR and IR-Raman spectroscopy, CP/MAS CNMR spectroscopy, X-ray diffraction and TEM. Further, almost 75 wt% of cellulose were obtained from the water-insoluble extract after bleaching process which determines the purification efficiency of cellulose and remove lignin and hemicellulose and the final percentages for this extraction are; 23%, 23%, 40% and 13% for lipids, proteins, cellulose and lignin, respectively. Finally, cellulose nanofibers having needle structure and fibrillar network were prepared by acid hydrolysis.