Extrusion pre-treatment of cowpea (Vigna unguiculata (L.) Walp.) lignocellulosic sidestream to produce cellulose fibres

BACKGROUND: Various agricultural sidestreams have been demonstrated as feedstock to produce cellulose. To the best of our knowledge, there is no research work on the potential of agricultural sidestream from cowpea (Vigna unguiculata (L.) Walp.), a neglected and underutilised crop to produce cellulose fibres. Conventional methods to produce cellulose consume large amounts of chemicals (NaOH) and produce a high amount of effluent waste. Herein, we investigated extrusion pre-treatment without and with an alkali followed by bleaching as an alternative method to conventional alkaline pre-treatment followed by bleaching to produce cellulose fibres from cowpea sidestream. RESULTS: Cellulose extracted by extrusion without and with mild alkali followed by bleaching consumed about 20 times less NaOH compared to the conventional method and produced less effluent waste. Extrusion with mild alkali followed by bleaching resulted in higher cellulose yield, purity, and crystallinity compared to extrusion without an alkali followed by bleaching. However, the conventional method resulted in higher cellulose yield, purity and crystallinity compared to extrusion pre-treatment followed by bleaching. Scanning electron microscopy revealed that micro-sized cellulose fibres with an average diameter of 10–15 μm were extracted using both methods. Notably, cellulose fibres extracted using extrusion pre-treatment were shorter than those extracted using the conventional method. CONCLUSION: Extrusion pre-treatment is a promising continuous alternative to alkaline pre-treatment to produce micro-sized cellulose fibres from low-value, underutilised cowpea lignocellulosic sidestream, for potential use as a filler in composite plastics.