Removing silica from oil palm mesocarp fibers

Palm oil production generates oil palm mesocarp fiber (OPMF) as the main lignocellulosic waste from the oil/fruit separation process. The plentiful OPMF can be used for diverse applications, such as reinforcement in polymeric matrix composites or to produce glucose for second-generation ethanol. In both applications, surface properties are essential, and the presence of silica bodies is usually harmful. In the present study, three treatments to remove silica bodies were evaluated as follows: hydrothermal (HT), alkali (AT), and sodium citrate solution (ST). Morphological and structural characteristics of untreated and treated fibers were determined using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Many silica bodies attached to the untreated OPMF surface were observed. The treatments partially removed the silica bodies from the surface. AT was superior, with a removal rate of approximately 91% as quantified by microwave-induced plasma optical emission spectrometry. The crystallinity index increased from 27% in the raw fiber to 40% after all treatments because of the removal of non-crystalline regions of cellulose and extracted material. Thermogravimetric analysis revealed no significant differences in the thermal stability of untreated and treated fibers. Elongation at break was the lowest for AT and HT, and the highest for ST. Removing silica bodies from the OPMF surface can benefit applications where surface properties are critical, adding value to the waste. As far as it is known, the approach used in this study is unprecedented.