Study On Preparation And Application Of Fiber-Based Retention And Drainage Aids For Papermaking

Most of papermaking wet-end retention and drainage aids are cationic polymers, the effect is impacted by the salt accumulation resulted from closed circle of white water, aluminium sulfate used in acidic papermaking system. Also, the transition from anionic to cationic environment due to their excessive usage makes a new exclusion. The increase of viscosity of white water resulted from soluble cationic polymers makes paper machine operation become difficult. To resolve these problems, modified cationized pulp fibers (CPF) can substitute the cationic polymers. Cationic pulp fibers (CPF) were prepared by the adsorption, deposition and grafting processes in this study. They are fiber-based papermaking retention and drainage aids (CPF₁, CPF₂, CPF₃, CPF₄). The preparation conditions were optimized, their application properties as wet end additives were evaluated, and they were characterized by FT-IR, SEM and XPS. Also, a comparison of their preparation conditions, retention and drainage properties, physical properties of paper, and production cost were made.In the adsorption process, cationic ester quaternary ammonium salt (31441) and polydimethyl dially ammomium chloride (PDMDAAC) were adsorbed onto Canadian bleached softwood kraft pulp fibers (CKF). The composites were named as CPF₁ and CPF₂ respectively. The optimized conditions for the CPF-1 preparation were 80℃, 30min, and 4% 31441 (based on oven-dry pulp). Under the conditions of 50℃and 0.5h, the suitable dosage of PDMDAAC with polymerization degree of 10000 is 5% for the preparation of CPF₂. CPF₁ and CPF₂ could improve the retention of precipitated calcium carbonate (PCC) filler significantly. With 0.9% CPF₁ (based on oven-dry pulp), the retention of PCC increased from 57.53% to 72.21%. With 7% CPF₂, the retention of PCC increased 6.6%, whereas the increase of PCC retention was 6.1% with 0.05% CPAM. The tensile and burst strength of the paper with CPF₁ and CPF₂ were higher than those with CPAM significantly, not lower than those with untreated CKP. CPF₁ and CPF₂ addition had also a positive effect on the improvement of stock drainage.In the deposition process, deposits of fiber-CS (CPF₃) were prepared by depositing the chitosan (CS) dissolved in 5% acetic acid onto CKF. The suitable preparative conditions were: 0.5% CS, 4% NaOH, 20℃and 30 min. CPF₃ could improve the retention of PCC filler significantly. With 5% CPF₃, the retention of PCC increased from 67.72% to 71.47%. The tensile and burst strength of the paper with CPF₃ were higher than those with CPAM significantly, not lower than those with untreated CKF. CPF₃ addition also had a positive effect on the improvement of stock drainage.In the grafting process, fiber-EPI-DMA (CPF₄) was prepared by grafting epichlorohydrin dimethylamine (EPI-DMA) to CKF. The optimized conditions for the CPF₄ preparation were 75℃, 30 minutes and 6g/L of EPI-DMA with polymerization degree of 10⁴. CPF₄ could improve the retention of PCC filler significantly. With 2% CPF (based on oven-dry pulp), the retention of PCC increased from 61.09% to 83.42%, and was better compared to CPAM. The physical properties of paper were also slightly improved. The tensile and burst strength of the paper with CPF₄ were higher than those with CPAM. CPF₄ addition could also improve the stock drainage.The comparison of CPF₁, CPF₂, CPF₃ and CPF₄ showed that the preparation of CPF₁, CPF₂ and CPF₃ are easier to prepare, have little impact on tensile and burst strength. Compared with CPF₄, the retention and drainage properties of CPF₁, CPF₂ and CPF₃ are common. CPF₄ has the best retention and drainage properties, and little impact on tensile and burst strength, as well as it is not difficult to prepare.Compared with conventional cationic polymer retention aids, CPF is more effective in improving retention and drainage, neutralizing anionic trash and reducing the white water load, as well as it is also biodegradable. Therefore, CPF has an advantage in application. The related studies can further enrich papermaking theories and are important valuable in research and application.