Kyujeong Sim

Structural characteristics of nanofibrillated cellulose mats: Effect of preparation conditions

Nanofibrillated cellulose (NFC) mats, which have porous or dense structures, were prepared in this study. The effects of the number of grinding passes, suspension solids content, and drying conditions on the structural changes of the NFC mats were investigated. Water removal in the NFC suspensions for forming the mats was carried out using pressurized dewatering equipment. The field-emission scanning electron microscope observation showed that the nanofibrils were preserved by solvent exchange drying, whereas the partial aggregation of nanofibrils occurred by freeze drying. Properties such as shrinkage, density, porosity, and specific surface areas of the NFC mats changed depending on the preparation conditions of the NFC mats. The NFC mats, which have low density and high porosity, could be prepared by solvent exchange drying and freeze drying. Porosity of the NFC mats varied from 76 % to 96 %. The specific surface area of the NFC mat increased to 175 m2/g with an increase in the number of grinding passes.

Flocculation behavior of cellulose nanofibrils under different salt conditions and its impact on network strength and dewatering ability

Flocculation of cellulose nanofibrils (CNF) was induced by charge neutralization with different types and concentrations of salt, and its effects on the network strength and dewatering ability of the CNF suspension were investigated. Aggregation of the CNF suspension was evaluated by measurement of light transmission using Turbiscan equipment. This procedure enabled us to characterize the aggregation and sedimentation behavior of nanofibrils under different salinity conditions. Aggregation and sedimentation of CNF occurred on salt addition because the degree of compression of the electrical double layer was changed by adsorption of cations onto the CNF, depending on the type and concentration of salt. The changes in network strength of the CNF suspension due to flocculation were evaluated using a conventional oscillatory rheometer. The viscosity, storage modulus, and yield stress of the CNF suspension increased with an increase in the ionic strength of the suspension. Microrheology measurements using the dynamic light scattering technique were also adopted to characterize the viscoelastic properties of the CNF suspension, revealing that CNF suspension containing a high concentration of salt showed more solid-like behavior. In addition, the aggregation degree of the CNF affected the dewatering ability of the CNF suspension. Bivalent cations were more effective for increasing the network strength and dewatering for a small amount of added salt compared with monovalent cations.

Effect of salt concentration in polyelectrolyte multilayering on properties of modified GCC and filled paper - OPEN ACCESS

This study investigated the effects of salt concentration in polyelectrolyte multilayering (PEM) treatment on the properties of ground calcium carbonate (GCC) and the mechanical strength of the filled paper with the PEM treated GCC. Polydiallyldimethyl-ammonium chloride (PDADMAC) and poly(sodium 4-styrene sulfonate) (PSS) were used as cationic and anionic polyelectrolyte, respectively, for the PEM treatment. The PEM treatment was performed in 0 0.1 M NaCl solutions. Polyelectrolyte multilayers could be formed without flocculation of the PEM treated GCC particles, which was confirmed by the zeta potential and particle size of GCC. The amount of polymer adsorbed onto GCC showed different behavior depending on salt concentration. At relatively higher salt concentration (0.1 M NaCl) in this study, more adsorption of polyelectrolytes occurred, which resulted in a thick multilayer on GCC. In addition, it provided strength improvement of the filled paper when the PEM treated GCC was used as filler. As a results, salt concentration during PEM treatment affected both of properties of the PEM treated GCC and mechanical properties of filled paper. ADDRESSES OF THE AUTHORS: Jegon Lee (ljg234@snu.ac.kr), Kyujeong Sim (sim0828@gmail.com), and Hye Jung Youn (page94@snu.ac.kr), Department of Forest Sciences, College of Agriculture and Life Sciences, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826 Corresponding author: Hye Jung Youn