The ATR FT-IR was employed to investigate the changes of the functional groups on cellulose film after hydrophobic modification by coconut oil. The spectra of both modified and untreated cellulose film are presented in Figure 3. The attachment of coconut oil onto cellulose film can be identified by the presence of ester absorption band at 1744 cm−1. Surface hydrophobicity is evidenced by ATR-FTIR. It is well understood that absorption bands between 3500 cm-1 and 3000 cm-1 represent the hydroxyl absorption band. In case of the modified film, these bands are weak and board, indicating the diminishing cellulose hydroxyl group due to the hydrophobicity modification. On the other hand, the hydroxyl band of unmodified cellulose film shows up strongly which is indicative of its hydrophilic characteristic. ATR-FTIR results are found in a similar manner to wettability test (insert).