Study of supercritical carbon dioxide pretreatment processes on green coconut fiber to enhance enzymatic hydrolysis of cellulose

•Supercritical CO2 (200 bar, 70 °C) with rapid depressurizing caused cell damage.•Polarity modifier and supercritical CO2 exposure time intensify the fiber damage.•Supercritical CO2 reduced steric hindrance and weakened cellulose-liginin bond.•Supercritical CO2 didn’t enhance cellulose enzymatic hydrolyses.•Moisture and flexibility of the fibers could affect CO2 supercritical delignification. Green coconut fiber was treated by supercritical CO2 with the aim to enhance hydrolysis of its enzymatic cellulose. To this end, different static conditions of CO2 contact times (3 and 5 h) and polarity modifiers (NaOH, NaHSO4, ethanol) were evaluated at 20 MPa, 70 °C and 1 h of dynamic extraction followed by fast depressurization. After supercritical CO2 exposition, SEM images showed fiber damage and FTIR spectra showed decreases of phenolic and wax contents, including a reduction in the degree of the hydrogen bond established between lignin and cellulose. Despite the apparent delignification, supercritical CO2 did not enhance cellulose enzymatic hydrolyses. Fiber exposed to supercritical CO2 (5 h) demonstrated that the highest sugar content (540.9 μmol glucose likely limited supercritical CO2 delignification; however, green coconut in natura can be an innovative substrate for fermentation in alcohol production.