Production of Cellulose Nanofiber (CNF) from wheat straw by carboxylation pretreatment

The current study was carried out to show the possibilities of wheat straw as most important and available agricultural residue for production of the cellulose nanofibers by carboxylation pretreatment. Soda-AQ and ECF bleaching sequences as DEPD were respectively selected as pulping and bleaching processes. TEMPO mediated oxidation as NaClO/NaBr/TEMPO system was applied to introduce carboxyl content on the fiber surface at varying level of 2, 6 and 10 mmol (based on O.D bleached pulp) of oxidant. Two different and applicable methods such as conductometric titration (CT) and fourier transform infrared spectroscopy (FTIR) were used to measure the functional group of carboxyl content. The results showed that the selective oxidation of hydroxyl group at C6 to carboxyl was occurred with increasing the oxidant consumption. The oxidized cellulosic fiber then passed through the high pressure homogenizer (HPH) for four times to produce individualized cellulose nanofibers (CNF). The results showed 58% decrease in viscosity, degree of polymerization (DP) and molecular weight (MW) and 10% decrease in crystallinity of fibers after oxidation and passing through the HPH. In the following, isolated CNF at minimum (two) percent of oxidant (sodium hypochlorite) was used for production of nanopaper via dispersion casting (DC) process. The field emission scanning electron microscope (FESEM) images illustrated that the nanofibers had diameter less than 30 nm. and its nanofiber diameter was measured and it was less than 30 nm by Field Emission Scanning Electron Microscope (FESEM).