| Lignocellulose is the most abundant green, renewable resources in terrestrial plants, and which including the first or second most copious organic polymer cellulose and lignin, respectively. The high-value utilization of cellulose and lignin is a promising approach to alleviate fossil energy shortage while improve environment. Alkali lignin with low molecular weight is water insoluable. As one of the effective high value-added application, modified lignin can be used as dye dispersant. However, alkali lignin was modified with the common technologies of sulfomethylation and condensation polymerization cannot have good dispersity when applicated on dye, due to the technologies are difficult to increase sulfonation degree and molecular weight of lignin. Meanwhile, the reduction effect on azo dye and stain effect on fiber caused by lignin dipersant were great limited its application. So, it is significant to study a new modification of improve sulfonate content, increase the molecular weight of lignin, and investigate the adsorption-dispersion mechanism of modified lignin used as dye dispersant to guide the efficient application of lignin. Mechanical fibrillation is the common approach for CNF production but very energy intensive; strong acids can substantially reduce the degree of cellulose polymerization(DP) but that negatively affect its performance for polymer reinforcement; enzymatic treatments can only produce limited energy savings during subsequent mechanical fibrillation and most commercial xylanase typically can only remove 30% xylan. Compared with very low cellulose fiber content of CNF, increase the content of hemicellulose moderately can increase the strength of the fiber. The objective of this study is to achieve mechanistic control in the production of CNF with bleached eucalyptus pulp(BEP) through disk milling with acid hydrolysis pretreatment to facilitate mechanical fibrillation and save energy, and investigate the effect of xylan content in CNF on its properties.A light-colored hydroxypropyl sulfonated alkali lignin(HSAL) was synthesized based on pine AL by grafted-sulfonation with sodium 3-chloro-2-hydroxypropanesulfonate and crosslinking with epichlorohydrin. The reaction was evaluated by GPC, IR and 1H-NMR spectroscopy. The sulfonic group content and the molecular weight(Mw) of HSAL significantly increased while the phenolic hydroxyl groups diminished by around 80% compared to AL. The reducing effects of GSBAL on disperse azo dye had a substantial improvement. The color of HSAL turned to light yellow compared to the dark brown color of AL, that is, it stained less the fiber. The dispersity, heat stability, and dye uptake of dye bath with HSAL was significantly improved compared to sodium lignosulfonate, sulfomethylated AL and dispersants of the naphthalene series.In order to improve the molecular weights of lignin which was limited by formaldehyde polymerization, three hydroxypropyl sulfonated alkali lignin samples(HSALs) with different molecular weights were obtained by controlling the dosage of etherification to crosslink of lignin molecules. The molecular weight of HSAL can be adjusted from 8,100 to 14,830 Da. More than 80% of phenolic hydroxyl groups of HSAL samples were blocked by etherification compared to SAL, and which decrease with increasing of molecular weight. The increasing of molecular weight of HSL causes a considerable reduction in staining effect of HSAL on fiber since the adsorption amount of HSAL on the fiber decreases by reducing phenolic hydroxyl group. HSAL with Mw of 11,020 Da contains 2.10 mmol·g-1 sulfonic group and low as 0.46 mmol·g-1 phenolic hydroxyl group(compared to 2.32 mmol·g-1 of AL) provide an excellent dispersive ability and high temperature stability on dye. More importantly, the dye uptake added HSL with Mw of 11,020 Da is the highest of 85.17% among all dispersants here. Therefore, the etherification modification is a promising approach to increase the molecular weight of lignin and for widespread applications of lignin as highly efficient dye dispersant.In order to reveal its dispersion mechanism on the dye, the adsorption characteristics of sodium lignosulfonate(NaLS) and sodium naphthalenesulfonic acid formaldehyde(SNF) were investigated using a quartz crystal microbalance with dissipation(QCM-D) and an atomic force microscope(AFM). The results showed that the adsorption of dispersant onto the dye film layer was low and unstable without salt, but the adsorption amount of NaSL or NSF onto dye film was increased significantly with the increase in ionic strength. This indicated that hydrophobic effect was the main interaction between dispersant and dye. The adsorption amounts of both dispersants were decreased with the increase in temperature. HSAL exhibited a higher adsorption amount and more viscoelastic adsorption layer than Na LS, this related to that HSAL was gained by the etherification process, which made three-dimensional network structure of molecular conformation more stretch.We prepared a nano disperse dye with average particles size of 94.25 nm by using a hydroxypropyl sulfonated alkali lignin(HSAL) as dispersant. The nano disperse dye had good dispersion, and the particles size of 1.97 μm at 130℃ dye process also showed its good stability at high temperature compared with two milling dye with HSAL and lignosulfonate(NaLS) as dispersant by particle analyzer, SEM, TEM and AFM. The dispersant dosage was used just a half of common milling dye can reduce the reducing effect on dye to 5.39%, caused by HSAL, while its dye uptake reached to amazing of 94.27%. HSAL with high molecular weight can prevent it adsorb into small gap of fiber, the sulfonic group long chain of HSAL also can easy drop of from dye surface to water phase. These factors made it had less adsorption amount onto fiber than NaLS. These factors made it had less adsorption amount onto fiber than NaLS. And since its light color, fiber staining effect caused by HSAL in nano diseperse dye had an essential improvement here. HSAL can provided stronger interaction with dye particles than other dispersants here, so it can be used as a dispersant to prepared composite nano disperse dye.Oxalic acid was used to treat bleached eucalyptus pulp(BEP) fibers to produce cellulose nanofibrils(CNF) by a stone disk grinder. The combined hydrolysis factor(CHFX) of oxalic acid treatment was developed to predict an accurate quantity of xylan hydrolysis. This is because the softable treated reaction with the diluted oxalic acid can control the quantity of xylan hydrolysis easily compare with strong acid such as sulfuric. The impact of xylan removal in BEP on producing CNF was investigated due to the removal of xylan facilitated to produce CNF.Here we used dilute oxalic acid to pretreat a kraft bleached Eucalyptus pulp(BEP) fibers to facilitate mechanical fibrillation in producing cellulose nanofibrils using disk milling with substantial mechanical energy savings. We successfully applied a reaction kinetics based combined hydrolysis factor(CHFX) as a severity factor to quantitatively control xylan dissolution and BEP fibril deploymerization. The fitting parameters were obtained by fitting of CHFX equation, and the results indicated the BEP had fast and slow xylan content of 37.7% and 62.3%, respectively. More importantly, we were able to accurately predict the degree of polymerization(DP) of disk-milled fibrils using CHFX and milling time or milling energy consumption. AFM imaging indicated the degree of polymerization(DP) and energy consumptions was decrease observably with xylan was removed more than 50%. With the increasing in CHFX, the water retention value(WRV) and spectral transmittance of CNF increased while the diameter decreased. In particular the removing of xylan of 72%, CNF diameter were further reduced to approximately 70 nm(50-100 nm) with an even more uniform and narrower distribution. |
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