Mechanical pretreatment of cellulose pulp to produce cellulose nanofibrils using a dry grinding method

Cellulose nanofibrils (CNFs) are typically produced via wet milling pretreatment method to facilitate efficient disintegration of cellulose fibers by pre-fibrillation and fiber size reduction. However, the use of high energy and presence of water during wet milling methods leads to the increase in overall energy consumption during CNFs production and pose challenges during storage and handling. The objective of this study is to investigate the dry grinding of cellulose fluff pulp using the shear cutting method to determine the specific energy required to produce cellulose precursors and their characteristics for manufacturing CNFs. The specific energy required to grind cellulose fluff pulp with a screen size of 0.25 mm in three cycles was measured. The ground sample received after each cycle was sampled to characterize its properties and its potential to produce CNF hydrogels. As the number of grinding cycles increased, the specific energy required per cycle decreased with an overall net energy consumption of 894 kWh/Mg for three grinding cycles. The cellulose powder from the third grinding cycle was successfully disintegrated into cellulose nanofibrils with an average diameter of 119 nm without any fiber clogging. In conclusion, the three-cycle shear cutting process was sufficient to produce dry cellulose precursors for CNFs production, while reducing the overall energy consumption and handling and storage problems.