Novel high-consistency forming of all-cellulose composites: The role of sodium hydroxide solvent system on fiber swelling/dissolution and composite properties

In this study, we introduce a novel manufacturing technique for producing all-cellulose composites (ACCs) using a sodium hydroxide (NaOH) solvent system during a roll-forming process. We address the impact of varying NaOH concentrations on the swelling and dissolution of cellulose microfibrils. NaOH concentration changes from 2 % to 20 %, causing different phenomena at each consistency, including swelling, partial or complete dissolution of cellulose microfibrils. These phenomena are evaluated by measuring the crystallinity and rheology of the furnish, the enthalpy of the reaction, and microscopy imaging of composites. The process utilizes a high-consistency fibrillated cellulose material produced from enzymatic hydrolysis of pulp fibers. The cellulose is swollen by the addition of NaOH. The furnish is then roll-formed into sheets at 20 % wt solids, followed by a freezing step that promotes dissolution and fiber sintering. After the freeze–thaw step, the web is dewatered using our previously developed cyclic pressing method, yielding dense, semi-transparent composites. This process allows efficient dewatering and enhances mechanical properties by enabling fiber welding. Our findings underscore the significant impact of NaOH concentrations on the structural and mechanical characteristics of ACCs. The NaOH concentration should be tailored to the specific application since this affects the swelling and dissolution of microfibrils. A freezing step, particularly at 8–12 % NaOH/Water concentration, enhances the dissolution. This study highlights the pivotal role of NaOH treatment in reshaping interactions within cellulose structures and provides practical insights for developing advanced cellulose-based materials for diverse applications.