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An eco-friendly time indicator (TI) was developed using cellulose-based materials. The TI comprises a dye, copy paper, nanofibrillated cellulose (NFC) film, and filter papers coated with NFC slurry and/or paraffin-free biowax. A suitable dye and its conditions were determined by observing the dye solutions and the migration pattern at the different concentrations. Commercial filter papers were prepared, and the dye migration rate, depending on physical properties, was evaluated. NFC was coated to control the dye migration rate of filter paper. In addition, biowax was used to impart hydrophobicity to filter papers used for supporting NFC films, storing the dye, and allowing the migration of dye. Finally, a TI was fabricated using those components. Methylene blue was selected as a dye for the TI due to its deep color and high solubility. The results showed that the key property of filter paper affecting the dye migration rate was the pore size. The migration rate could be reduced when NFC was coated on both sides of the filter paper. Since biowax modified the hydrophobicity of filter paper surface, it was used to make the NFC film-supporting paper, location for dye storage, and bottom-layer. In conclusion, a multilayered TI could be assembled using cellulose-based materials.

In this study, paper ash generated during the incineration process of paper sludge was applied to measure the bulk, strength, and drying energy reduction of paperboard to assess the possibility of using it as an inorganic additive in paperboard mills. Three types of paper ash were fabricated by incineration, crushed, and fractionated with three different screen sizes, and their physical properties were measured. The fabricated paper ashes were added to Korean old corrugated containers (KOCC) stock to make handsheets, and their physical properties and drying energy reduction were determined. In addition, paper ash particles classified into 200 mesh screens were surface-modified with cationic polyacrylamide (C-PAM), and the handsheets were manufactured to analyze the strength improvement effect of paperboard. The bulk and the drying energy reduction improved as the paper ashes were added into the KOCC stock, but the tensile index, compression index, and burst strength decreased. In particular, the higher the average particle size of the paper ash, the higher the bulk and the drying energy reduction, but the lower the strength. The surface modification of the paper ash with C-PAM was effective in improving the strength. Therefore, paper ash made of paper sludge collected from specialty paper mills is effective in improving the bulk and drying energy reduction of paperboard, and surface modification with C-PAM is required to prevent the deterioration of paper strength.

In this study, we tried to develop techniques to increase coat weight and improve water resistance at a lower number of multilayer barrier coatings with anionic and cationic cellulose nanofibrils (CNFs), which has been reported in previous research. The concentration of CNF slurry was adjusted to increase the coat weight, while alkyl ketene dimer (AKD) was added as an internal sizing agent to the anionic CNF slurry to impart hydrophobicity to the CNFs. After the preparation of CNF slurries, the multilayer barrier coating was applied on never-size base paper. The coat weight, air permeability, and Cobb size degree of the barrier-coated paper were subsequently measured, and the surface of the paper was analyzed via SEM. The coat weight and air permeability of the paper coated four times with CNF slurry at 1.4% concentration were similar to those of the paper coated six times with CNF slurry at 1.0% concentration. In addition, the Cobb size degree of the barrier-coated paper decreased as the AKD addition to anionic CNF at a concentration of 1.4% increased linearly. However, when the addition level of AKD increased more than 5.0%, the Cobb size degree of the barrier-coated paper increased due to the uneven distribution of AKD. Therefore, multilayer barrier coating can be carried out effectively with cationic and anionic CNFs at high concentrations, and AKD improves the water resistance of barrier-coated paper.

In this study, we evaluated the effect of bamboo bleached kraft pulp (BKP) on the strength of the coloring paper used for pear paper bags. The characteristics of bamboo BKP were measured to compare them with those of softwood BKP and hardwood BKP. Handsheets from bamboo and hardwood BKPs were prepared at various mixing ratios, and their strengths were then analyzed. After that, a mill trial was performed to produce a prototype of coloring paper with bamboo BKP, and the effect of bamboo BKP on the strength of the coloring paper was finally determined. The initial freeness and fiber shape of bamboo BKP were similar to those of hardwood BKP, although the average fiber length and curl of bamboo BKP were higher than those of hardwood. As the mixing ratio of bamboo BKP increased, the strength of the handsheets increased, indicating the enhancing effect of bamboo BKP on the strength of coloring paper. As a result of the mill trial of coloring paper in the specialty paper mill, it was found that the tensile strength increased by 27.8% and burst strength by 20.0% when bamboo chemical pulp replaced 20% of the hardwood chemical pulp. Therefore, it was concluded that bamboo chemical pulp can replace and improve the strength of hardwood chemical pulp for manufacturing coloring paper.

The applicability of bleached bamboo kraft pulp (Ba-BKP) was explored as a raw material for the manufacture of nanofibrillated cellulose (EN-NFC) made of enzyme-pretreated pulps and the effects of the EN-NFC on enhancing paper strength. The Ba-BKP was pretreated using an endo-glucanase enzyme at 50 °C and pH 6, after which the EN-NFC was made by micro-grinding. Bleached hardwood kraft pulp (Hw-BKP) was used as a control, and the non-enzymatic refining pretreatment of BKPs was compared with the enzyme pretreatment. The EN-NFC was incorporated into handsheets, and the sheet strengths were measured. The physical properties of the NFC made from the Ba-BKP were similar to those made from the Hw-BKP. The NFC prepared following enzyme pretreatment were smaller and more uniform than those pretreated with refining. The EN-NFC made from the Ba-BKP was effective at enhancing tensile index by 52.7%, and burst index by 210.2% when 2% of EN-NFC was added in the furnish, and those of handsheets containing the EN-NFC made from Hw-BKP showed the similar improvement. Therefore, Ba-BKP can be used as a raw material for the manufacture of EN-NFC that confers similar physical properties and strength enhancement to paper as those made from Hw-BKP.

In this study, we evaluated the applicability of fruit by-products as raw materials for the production of cellulose nanofibril (CNF). The persimmon byproducts generated by pruning persimmon trees were collected and used for the manufacture of bleached kraft pulp and CNFs. The persimmon byproduct bleached kraft pulp (PB-BKP) was made at the optimum pulping and bleaching conditions reported in the previous study and the CNFs were made from PB-BKP and commercial hardwood bleached kraft pulp (Hw-BKP) by refining and micro-grinding processes. After micro-grinding, the particle size, viscosity, zeta potential, and fiber width were evaluated according to the pass number of fibrillation. The appearance of the CNF slurries showed no significant difference between PB-BKP and Hw-BKP. It was found that nanoization of PB-BKP and Hw-BKP proceeded sufficiently when the pass number was five or more. In addition, as the pass number increased, the low shear viscosity of CNF increased, the particle size decreased, and no significant change was observed in the zeta potential. Looking at each pulp, CNF made of PB-KBP had higher fiber width and particle size than Hw-BKP in the initial pass number, but the difference decreased when the pass number was nine. Therefore, CNF made with PB-BKP and CNF made with Hw-BKP showed similar characteristics after the sufficient pass number of micro-grinding. Based on the results, we concluded that persimmon tree by-products can be used as raw materials for the production of CNF.

The goal of this study was to develop an eco-friendly removal technology for fluorescent whitening agents (FWAs) using enzymes suitable for each type of FWA. Internally treated paper with internal FWA (D-FWA) and surface-sized paper with surface-sizing FWA (T-FWA) were made as model papers in a laboratory. The enzymatic treatments were applied to the stock prepared using these model papers by disintegration. Cellulase and (alpha-) amylase treatments were performed at 50 °C under the conditions of pH 3 to 4 and pH 7 to 8, respectively. After disintegration and enzymatic treatments, handsheets were made, and the fluorescence index and FWA reduction of these handsheets were determined for evaluating FWA removal during recycling. Because D-FWA gets strongly attached to cellulosic fibers, it could not be easily separated from the internally treated paper by disintegration. Up to 8.1% of D-FWA was removed by enzymatic treatment with high-activity cellulase. Amylase could not separate D-FWA from cellulosic fibers. In the case of T-FWA, ca. 41% was separated by disintegration, and an additional 24% was detached from surface-sized papers by high-activity amylase treatment. Therefore, cellulase was effective in removing internal FWA (D-FWA), and amylase was required for removing surface-sizing FWA (T-FWA) during recycling.