Preparation of hemp nanofibers from agricultural waste by mechanical defibrillation in water

Industrial hemp is a green economic plant for biogas and fuel. It is also used mainly in construction, paper, and textile industries. After harvested, the stubs of hemp are left as wastes. Therefore, the added value of this part is considered in this study. Mechanical defibrillation is an interesting method which does not require any harmful chemicals to be involved for size reduction. In this work, high-pressure homogenization by microfluidizer was carried out to defibrillate hemp fibers. Three investigating parameters, which were chemical pretreatment (delignification and hemicellulose removal), fiber concentration, and defibrillation time, were studied. It was found that chemical pretreatment enhanced capability of mechanical defibrillation in which nanofibrillated cellulose could be obtained shortly by microfluidizer (starting from only 15 min defibrillation to obtain 20-50 nm fiber diameters). Higher fiber concentration during defibrillation provided greater degree of polymerization and slightly higher thermal degradation temperature. Meanwhile, longer defibrillation time resulted in smaller and more uniformity of size of nanofibers and provided significant lower degree of polymerization and minor decrease in thermal degradation temperature. However, no significant change on crystallinity was observed. From the obtained results, 0.7% w/v of fiber concentration and 120 min defibrillation time using chemi-mechanical method provided the most uniformity of fiber size and the highest transparency of an aqueous suspension as well as its cast film. (C) 2016 Elsevier Ltd. All rights reserved.