Nanocellulose Board: Study on the performance of cold pre-pressing and physical properties of the Board

Background and Objective: According to the literature, cellulose nanostructures possess much better properties compared to cellulose microstructures. One of promising products previously made from cellulose nanostructures is nanocellulose sheet or nanopaper. All fabricated nanocellulose sheets had thickness below 100 µm, but in this study, nanocellulose board was made purely from cellulose nanofibers, for the first time. Then, the physical properties of specimens including dimensional and density changes during fabrication process and long-term water absorption and thickness swelling behaviour were investigated. The performance of pre-pressing system was also investigated. 
Materials and Methods: Cellulose nanofibers or nanocellulose (NC) were provided from Nano Novin polymer Co. (Iran). The NC-board has been produced through a wet process without using resin. To make NC-mat, a special pre-pressing apparatus was designed and fabricated containing piston and cylinder made of polyethylene as main components. Piston made pressure on the NC gel in the cylinder and the water inside the gel went out through a screen with mesh size of 300, resulted in NC-mat. During vacuum oven drying at 70 °C for 24 h, NC-board was produced. The board was cut to proper sizes (2.8× 20 ×20 mm) for long-term water absorption and thickness swelling tests.
Results: The results of using pre-pressing system showed that the gel concentration increased from 6 wt% to 40 wt% and mat thickness and density reached 5.5 mm and 0.54 g/cm³ (based on dry weight of NC), respectively. After drying in vacuum oven, the thickness and density of the board obtained 2.8 mm and 1.35 g/cm³, respectively. The results of water absorption and thickness swelling during 240 hours demonstrated that these properties rapidly increased to 52% and 44% respectively over 24 hours immersion in water and then did not show significant changes over immersion time longer than 24 hours.
Conclusions: The performance of pre-pressing system was quite suitable to make nanocellulose mat with desirable properties. Since cellulose nanofibers are super absorbent material with high specific surface area, the values of water absorption and thickness swelling increased during the first 24 hours and then the values were not changed significantly over immersion time longer than 24 hours.