Study of Cellulose Extraction from Robusta Coffee Husk Using NaOH Solution

Abstract

This study reports on manufacturing cellulose from robusta coffee husks through a solid-liquid extraction process. A high yield of cellulose can be achieved by extraction using 3.5% HNO₃ at a temperature of 100 ^oC with a gain of 35.4%. Meanwhile, the extraction process with 4.5% HNO₃ at a temperature of 80 ^oC only achieved a yield of 32.8%. From the results of this study, it can be seen that the smaller the concentration of HNO₃ used and the higher the temperature, the greater the yield of cellulose produced. The X-ray diffraction pattern shows high peaks appearing at an angle of 2θ around 22.5^o; this area is a typical peak of the cellulose structure. High crystallinity was obtained at a concentration of 3.5% HNO₃ at a temperature of 100 ^oC at 82.47%, while the lowest crystallinity was found at a 5.5% HNO₃ concentration at a temperature of 100 ^oC at 74.27%. The decrease in crystallinity was caused by the high temperature and concentration of HNO_3, which caused the acid to penetrate quickly into the cellulose tissue layer and hydrolyze the crystalline regions of cellulose. FT-IR analysis showed a high absorption area at 3314 cm^-1 and a low absorption area at 1028 cm^-1, typical of Robusta coffee husk cellulose. The absorption located around the 3314 cm^-1 bands is a stretch of the –OH group and the absorption in the 1028 cm^-1 band is related to the -CH₂ group. SEM can show the morphology of cellulose with smaller and uniform crystal dimensions with a scale of 20 µm.