TEMPO-modification Of Nanocrystalline Celllose And Its Improvements In Pulp Performence

With increasing of the paper machine running speed, recycled fiber untilization andwater closed circulation, how to more efficiently increase the retention of fine fibers andfillers and improve the runnability of the paper machine are becoming more importantin the paper industry. Micro-particle retention and drainage aid system is widely usedin high-speed paper machines, due to it not only increases the fines and fillers retention,improves the pulp drainage, but also provieds produced papers with a better formationand air permeability. The particle size and the charge density of nano-crystalline cel-lulose (NCC), which prepared from renewable lignocellulose resources, can be con-trolled during the preparation process. The attributes of NCC can be further improvedthrough modification treatments so that it can be used more effecient as a micro-particleretention and drainage system in papermaking processes. In this study, nanocrystallinecellulose is prepared from a bleached hardwood kraft pulp, and it then be modified bythe2,2,6,6-tetramethyl-piperdine-1-oxyl (TEMPO). The characteristics of the mod-ified nanocrystalline cellulose and its improvement to pulp properties are investigated.Firstly, how the NaClO consumption, reaction temperature and time affect themorphology, carboxyl group content, charge density and yield of TONCC were investi-gated. The results showed that the carboxyl groups were introduced onto the cellulosesurface during the TEMPO-mediated oxidation, while the cellulose remained in the typeof crystalline cellulose I. Increase the addition of NaClO, raise the reaction tempera-ture or extend the reaction time improved the carboxyl group content, the oxidation de-gree and the charge density, increased the dispersion of the TEMPO oxidated products,but decreased to some extent its yield. Sulfuric acid groups on the NCC surface werebasically unstable and easily removed under mild alkaline condition. However, theTEMPO-mediated oxidation improved significately the stability of its surface carboxylgroups under the mild alkaline condition.Next, micro-particle retention and drainage aid systems were consisted of the NCCor TONCC with cationic polyacrylamide at neutral pH, and the effectiveness to improvethe pulp drainage and fines retention were examined, furthermore, their application tothe inforcement of hansheets strength properties were investigated. The results showthat both of the NCC and TONCC improved the fine fiber retention, though the pulpdrainage decreased to some extent. In addition, the TONCC with a high charge densi- ty demonstrated a higher effect on the performance of retention and drainage, the reten-tion increased by about5.2%but the filtration spead cecreased by12.5%, respectively.A micro-particle retention and drainage aid system, which consisted of the NCC or theTONCC with cationic polyacrylamide, improved not only the fines retention but alsothe pulp drainage. The system consisted of high charge density TEMPO oxidatedNCC and cationic polyacrylamide demonstrated a better retention and drainage perfor-mances. The fines retention increased by about3.1%, and the filtration spead de-creased by11.8%, respectively. Applied the NCC/anionic polyacrylamide, and theTONCC (with low, middle or high charge density)/anionic polyacrylamide to the pulp,the tensile strength of handsheet papers increased by8.7%,13.1%,13.6%,14.3%and6.8, respectively, the tear strength improved25.6%,31.6%,35.0%,36.8%and26.5%,respectively, and the endurance raised14.8%,8.4%,16.4%,19.3%and16.9%, respec-tively.Finally, the NCC was prepared by using the TEMPO to oxidize the bleachedhardwood kraft pulp fibers. The influences of NaClO dosage on the morphology, car-boxyl group content, charge density and producet yield were investigated. The pre-pared TONCC combined with CPAM to compose micro-particle retention and drainageaid system, and being used in a Kaolin suspension to examine the effect on flocculationbehavior. The results showed that the TONCC were acquired bu suing the TEMPOmodifying bleached hardwood kraft pulp fibers. Carboxyl groups were introduced inthe produced TONCC, and the cellulose remained in the typs of crystalline cellulose I.Generally, the Zeta potential, polymerization degree, and product yield of the producedTONCC decreased with increase the NaClO dosage, but improved its dispersion, andimproved the carboxyl group content and the oxidation degree of TONCC product.The Zeta potential of TONCC product decreased with increasing the pH value duringthe preparation. The flocculation of the small flocs in Kaolin suspension was mainlycaused through the mechanism of particle bridging and charge neutralization. For themicro-particle retention and drainage aid system composed of cationic polyacrylamidewith TONCC, a higher shear force will be beneficial to improve the flocculation per-formance of Kaolin suspension.