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Peroxide bleaching stage. The peroxide bleaching was done after removing transition metal by the complexing treatment (Q-stage). The Q-stage was performed using 0.3% diethylenetriamine penta acetic acid (DTPA) and 1 mol l −1 H 2SO 4 at 65 °C for 60 min to remove transition metals. 35 The metal content in the pulp before and after Q-stage was analyzed by ICP-OES (Optima 3000, PerkinElmer) after hydrolysis with nitric acid in a microwave oven, according to Janzon et al. 36
Y. Dong, H. Ji, C. Dong, W. Zhu, Z. Long and Z. Pang, Preparation of high-grade dissolving pulp from radiata pine, Ind. Crops Prod., 2020, 143, 111880, DOI: 10.1016/j.indcrop.2019.111880.X. Jiang, Y. Bai, X. Chen and W. Liu, A review on raw materials, commercial production and properties of lyocell fiber, J. Bioresour. Bioprod., 2020, 5(1), 16–25, DOI: 10.1016/j.jobab.2020.03.002. Soda pulping is the chemical process of using sodium hydroxide as the active chemical to produce pulp from lignocellulosic materials. Soda pulping only makes up a minor share of the commercially used pulping techniques for wood pulping but is the preferred process for pulping annual plants. 24 Soda pulping utilizes sodium hydroxide (NaOH) as an active chemical under high pressure and temperatures well above the boiling point of the cooking liquor, commonly between 150–170 °C. 25 This achieves swelling of the fibers to increase the accessibility of the cooking chemicals and for better penetration into the raw material. 25 The pulps from 100 °C O-stage showed slightly higher bleachability in the subsequent peroxide bleaching, as shown in Fig. 4B. The positive effect of the higher temperature in the O-stage on brightness remains effective after both P stages ( Fig. 4B). The brightness of PH soda pulp after the P 1 stage was better than P 2 stage by 3% and 2.8% for steaming severity of 3.83 and 4.13, respectively. On the other hand, the pulp viscosity was lower by 37 ml g −1 and 53 ml g −1 ( Fig. 3B). However, the negative effect of O-stage on viscosity is equalized in the P-stage, at least for pulps with high PH severity. This indicates that with a high temperature in the O-stage and a high peroxide charge (P 1), good bleaching efficiency can be obtained by simple OQP 1 sequence reaching a brightness of 83.2% and a viscosity of 424 ml g −1 for the PH soda pulp with the severity of 4.13. Moreover, extensive research on innovative techniques for dissolving grade pulp production directly from lignocellulose biomass or paper-grade pulp has also been investigated in response to environmental and cost considerations. But, the typical processes for commercial uses of wood are still the prehydrolysis kraft (PHK) and acid sulfite (AS) processes. 13,14 Soda pulping is solely used for processing monocotyledons and especially cotton linter. The AS process is better suited than the regular kraft process due to the spontaneous cleavage of glycosidic bonds in the hemicellulose chain under the acidic condition. 13 An acidic prehydrolysis is added to the kraft process to achieve a comparable result by removing the hemicelluloses before the alkaline cooking process. 9
A. Michud, M. Hummel and H. Sixta, Influence of molar mass distribution on the final properties of fibers regenerated from cellulose dissolved in ionic liquid by dry-jet wet spinning, Polymer, 2015, 75, 1–9, DOI: 10.1016/j.polymer.2015.08.017. Fig. 4 ISO brightness of pulps before and after oxygen (O) bleaching (A) after OQP 1 and OQP 2 (B), after OQP 2P 2 and OQP 2P 3 (C) and after OQP 2D (D) (temperature of O-stage in the sequences are indicated by for 90 °C and for 100 °C).The amount of lignin increased from 11.6% to 16.6% with steaming intensity, as shown in Fig. 1B. The increase of lignin content in steamed fibers is mainly due to a shift of composition due to the removal of hemicelluloses. This underlines that only minor lignin solubilization occurs during steaming. On the other hand, some generation of pseudo-lignin might occur under high-severity conditions contributing to the high lignin content. It results from the re-polymerization of carbohydrate degradation products and condensation of lignin components. 12,17,38 The oxygen-bleached pulp was then subjected to a complexing step using 0.3% DTPA before the peroxide bleaching stages. In this one you can see a tiny bit of sugar has crystallised at the bottom because it's a bit cooler. But this one, look how much sugar is actually in the bottom. The sugar behaves like most solids - the solubility increases as the temperature of the solvent does.
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