Green and energy-efficient extraction of cellulose nano-fibrils from rice straw and its coating to improve functional properties of rice straw paperboard made via refiner mechanical pulping

Abstract

Rice straw is openly burnt in the farms in parts of India as it is not efficiently used as compost or cattle feed. In the present work, a unique approach was used in an attempt to utilize the rice straw grown in the Indian state of Haryana. It was converted into a paperboard of 200 g/m2 and was coated with up to 10 g/m2 cellulose nano-fibrils (CNF) extracted from the rice straw. The CNF of 50 nm size could be extracted via the process which involved a chemical process followed by a two-step mechanical process – 1) high speed homogenization and 2) probe sonication. Subsequent steps of homogenization and probe sonication saved electrical energy by 11.45% than using probe sonication alone. The adapted process did not alter the crystalline arrangement of the cellulose as shown by infrared spectroscopy and x-ray diffractometry, making the process acceptable. Various properties of the coated paperboard were tested and it was found that the coating played a great role toward reducing Bendtsen roughness, water absorption (Cobb60), and porosity; while improving water vapor barrier and grease-resistance.