Fig. 2B shows the differences in chemical functionality in the ATR-FTIR spectra of phos-CNFSL, phos-CNCSL, CNCBE and CNCSL. All samples showed characteristic bands of cellulose; the broad bands in the region between 3650 and 3000 cm−1 ha tag OH stretching vibrations, peaks at 2900 cm−1 correspond to CH stretching vibrations, and peaks at around 1650 cm−1 due to the deformation vibration of water molecules. Absorption bands in the 1500–800 cm−1 spectral region, attributed to the CH, OH, CO and COC vibration on the glucosidic ring, represent the fingerprint of cellulose. The main differences can be observed between phosphorylated and non-phosphorylated samples. For the phos-CNFSL and phos-CNCSL three new bands were detected; at 2360 cm−1, 1210 cm−1 and 930 cm−1, assigned to the PH stretching vibration mode , the PO stretching mode , and the POH stretching vibration mode, respectively, of the incorporated phosphate groups . For phos-CNCSL, beside phosphate groups, also carboxylate groups were confirmed with new detectable band at 1600 cm−1. This could be attributed to the partial oxidation of the cellulose units during the phosphorylation process . Negatively charged phosphate as well as carboxylate functionalities highly diminish agglomeration in water by counterbalancing the attractive hydrogen-bond interactions exerted by the abundant hydroxyl cellulose groups. A minor band at 1600 cm−1 for the presence of carboxylate functionalities was also identified for CNCBE.