“Greener” homogeneous esterification of cellulose isolated from Stipa tenacissima plant located in the Eastern region of Morocco using ionic liquids as reaction medium

Homogeneous esterification of cellulose isolated from Stipa tenacissima plant located in the eastern region of Morocco, using anhydride and acid chloride compounds has been performed in ionic liquids (ILs) prepared in our laboratory as reaction mediums. ILs were chosen as solvents due to their green character and ability to disperse native cellulose compared to other solvents. [C₄mim]OAc showed the highest solubility percentage of cellulose (15 wt%). Other principles of green chemistry were applied herein such as the uses of biomass, catalysts, and green solvents. The formed cellulosic esters were analyzed for structural, surface, and thermal properties by various analytical techniques: FTIR-ATR, NMR, XRD, TGA, and DSC. The esterificating agents were varied in this study to obtain different cellulose derivatives. Notably, high degrees of substitution (DS) were achieved for cellulose propionate (2.91) and cellulose butyrate (2.76). However, cellulose phthalate and cellulose laureate were obtained with low DS values, which affect their solubility in different solvents depending on their DS values. The effect of esterification on cellulose properties, on one hand, decreases the crystallinity index (C_Ir) and crystallite size, however, on the other hand, increased the surface area and pore volume. The contact angle measurements revealed an enhancement in the hydrophobicity of the cellulose esters. Particularly, cellulose propionate with high DS exhibited a significantly elevated contact angle, reaching 142.5°. This emphasizes that the hydrophobic nature of the modified cellulose can be improved by raising the DS, rather than solely relying on the length of the carbonyl chain.