A zero-waste one step method to produce carboxy nanocellulose from the untreated barley and wheat straws

Abstract

A zero-waste simple method was developed to produce carboxy nanocellulose directly from the untreated barley and wheat straw by treating with nitric acid (55%) and sodium nitrite at 40 °C for 12 h. This method significantly reduced the need for toxic chemicals such as TEMPO ((2,2,6,6-tetramethylpiperidin-1-yl)-oxyl) and radical generating chemicals. The process also reduced the usage of corrosive bases and acids and energy demand during the pretreatment process for the multi-step acid hydrolysis of biomass. Moreover, the by-product can be easily neutralized with the addition of NaOH, and the neutralized solution can be concentrated to obtain sodium nitrate which can be utilized as a fertilizer. The current method produces rod shaped and spherical particles of carboxy nanocellulose from the barley and wheat straw respectively with lower crystallinity (ca. ⁓30% of crystallinity index) than the barley and wheat straw itself (ca. ⁓60% of crystallinity index) as evidenced from the grazing incidence X-ray diffraction (GIXRD) technique. The conductometric titration revealed a high concentration (ca. ⁓2.6 mmol/g) of surface carboxylic (-COOH) acid groups and this result is supported by the high zeta potential value (ca ⁓-40mV) for the synthesized carboxy nanocellulose.