Bleaching Of Chlorine Dioxide Of Cotton Linter Pulp And Its Degradation Technology

Cotton linter pulp was mainly used to produce viscose and cellulose-derivatives product due to its high performance of pulp, such as high cellulose content, low impurity content, and value-added product potential. The brightness and degree of polymerization (DP) was critical for cotton linter pulp. In this context, the environmentally friendly ClO2 bleaching sequence and chemical/mechanical treatment were studied in this thesis. In addition, the cellulose qualities and structures were also characterized based on advanced technologies.The optimal bleaching sequence was DED based on the comprehensive studies. The optimal condition was:D1 stage, ClO2 dosage= 1%, T= 70℃, t= 120 min, pulp consistence= 8%, initial pH= 4, E stage, NaOH dosage= 2%, T= 70℃, t= 90 min, pulp consistence= 8%, D2 stage, ClO2 dosage= 1%, T= 70℃, t= 120 min, pulp consistence= 8%, initial pH= 4. The pulp with brightness of 82%ISO was obtained under the optimal condition, while the DP was decreased slightly. The lignin in pulp was oxided and degreed specifically by ClO2 bleaching, whereas the cellulose was hardly affected based on the FTIR, SEM and X-RD analyzed.Varied treatment technologies including NaOH, NaOH/02, and ball milling/NaOH were studied to de-polymerize the cotton linter pulp. Results showed that the DP and brightness of pulp was decreased ～17% and 5.6%ISO, respectively, under the NaOH treatment condition of NaOH dosage= 4%, T= 120℃, and t= 120 min. For NaOH/O2 treatment, the DP was decreased ～41%and the brightness was kept constant under the condition:NaOH dosage= 4%, O2 pressure= 0.5 MPa, T= 120℃, t= 120 min. For ball milling/NaOH treatment, the DP was significantly decreased to 500 under the condition: t= 30 min, NaOH dosage= 4%, T= 120℃, t= 120 min. The fiber qualities were characterized by GPC, FQA, SEM, FTIR, and X-RD. Results showed that the DP of cellulose was decreased and the molecular weight distribution was much more uniform after NaOH, NaOH/O2, and ball milling/NaOH treatment. In comparison with NaOH treatment, the pulps were improved for those from NaOH/O2, and ball milling (30 min)/NaOH treatment, including the smoother of fiber surface, the increase of curling and kinking index. Although the DP was decreased for treated pulp, the characteristic absorption band was not changed, indicating that the cellulose structure was remained. X-RD analyzed suggested that the crystalline structure of cellulose was cellulose-1 crystalline. The cellulose CryI was decreased, while the crystal size increasing after NaOH/02 treatment. As a comparison, the pulp CryI and crystal size were increased after ball milling (30 min)/NaOH treatment. As a conclusion, all the treatment could enhance the reactivity of cotton linter pulp.