Pore Structure Regulation of Carboxyethylated Microfibrillated Cellulose Films

Carboxyethylation is a recent chemical pretreatment for preparation of microfibrillated cellulose (MFC). The carboxyethylated MFC film prepared by coating method has compact structure and high mechanical properties. In order to expand its application, three approaches including using organic solvents, different drying methods and cationic additives, have been adopted in this paper to enrich and regulate the pore structure of MFC film. The results show that all the approaches can improve the pore structure but decrease the mechanical properties of MFC film. When organic solvents such as ethanol, isopropanol and n-butanol were used to replace the water in MFC suspension or pre-dried MFC film, the pore structure of films were increased. Additionally, the film obtained by freeze-drying or air-drying after freezing in liquid nitrogen or freezer has high porosity but poor strength. The best drying process is to rewet dry MFC film, freeze in liquid nitrogen and then freeze-dry. Moreover, the addition of cationic polyelectrolytes or alkene ketone dimer (AKD) in MFC suspension can also significantly increase the film's porosity. Through the above approaches, the porosity of carboxyethylated MFC film can be regulated between 20% and 90%.