| The reuse of deinked pulp in paper industry is a typical example of circular economy, due to its significant reduction in the loading of emissions and use of raw materials. With the development of high-speed, large-scale, intelligence and other modern techniques in papermaking engineering, deinked pulp shows much more dependence on functional additives. However, with the shortage of non-renewable resources and the requirements of environment protection, the traditional fossil paper-based functional additives are not suitable to be used in the deinked pulp. So the new bio-based and multi-functional additives and their multivariate complex bio-based retention and drainage system are attractive choses in modern papermaking additives, which is an effective way to solve the unrenewable and nonbiodegradable problems in papermaking additives.The content of this study is a part of national science and technology support program(2013BAC01B03) titled by Development and application of biomass-based green and renewable waste paper additives. According to the purposes of this project and the systematically research on the commercially available bio-based retention and drainage aids, cationic guar gum(CGG) is an excellent bio-based papermaking retention and drainage aids, which is needed to be further studied. Therefore, the synthesis and optimization of cationic guar gum by an organic solvent method was studied in this paper. The application of CGG in individual or complex wet system of deinked paper was also evaluated. The purpose of this study was to develop an eco-friendly wet retention and drainage system, which is suitable to be used as the additives in the recyclation of the waste paper. The fouding of this study was also a basis to industrial preparation of CGG.In this paper, guar collagen powder was used as substrate and the ethanol was used as the dispersion medium. The technological parameters which would affecting synthesis of cationic guar gum through the method of organic solvent were studied. In view of DS, zeta potential, reaction efficiency of modified products, the optimum conditions for synthesis of cationic guar gum were found out as the followings: 2% of alkali dosage, 70% of ethanol volume fraction, 1:3 of liquid ratio, 2h of reaction time, 60℃ of reaction temperature, molar ratio 1.0 of etherification agent and guar gum. Under this condition, the substitution degree of cationic guar gum was up to 0.39. FT-IR spectrum was analyzed in order to confirm the chemical structure of cationic guar gum. The application of cationic guar gum in wet end system of deinked pulp was also discussed. The results showed that the cationic guar gum with a higher DS value exhibited a higher retention for waste paper. The ultrasound solubilization could effectively improve the performance of cationic guar gum. When the dosage of cationic guar gum swith a DS value of 0.392 was 0.5%, the zeta potential of deinked pulp system was-6.8 mV. And the solids retention and filler retention was thigh up to 95.7% and 87.3%, respectively. Compared with controlled sample, they were increased14.1% and 68.5%, respectially. Meanwhile, beating degree of pulp system was highly decreased by 18 oSR.Compared with traditional PA(polyamide) and PAC, quaternary ammonium salt of chitosan with low molecular weight(HACC) is an effective bio-based anionic trash trapping agent(ATC). When the dosage of HACC was 0.1%, more than 70% the anionic trash in deinking pulp was effectively removed while the surface Zeta potential of fibers was nearly unchanged. In addition, HACC has some favorable properties such as large amount of hydroxyl groups, special amine structure and fiber directness, which would effectively enable residual ink and fines to be fixed onto the surfaces of pulp fiber, and reduce the content of the wet end sediment. The 2# HACC with higher molecular weight was more suitable to be used as ATC than 1# HACC. Compared with the traditional ATC, it was more effective to remove the negative effects of anionic trash on the physical properties of handsheets and runnability of paper machine.The addition of HACC can improve the chemical environment of deinking pulpwet-end system. The binary system consisting of equal dosage of CGG and HACC had a better result in Zeta potential and contribute fines retention than CGG single system, confirming that the addition of ATC in wet-end system was must in front of the cationic retention agent.The effect of particle retention and drainage system consist of CGG, HACC and anionic particles with low molecular weight such as SiO2, soy protein and bentonite was studied in this paper. The result showed that CGG particles combined with bentonite particle retention and drainage system had an ideal effect than other systems. With the 0.1% dosage of HACC, 0.3% dosage of CGG and 1.0% dosage of bentonite, the fines retention efficiency was high up to 68.9% while the beating degree decreased 24.5 oSR. SiO2 particle system had a controllable contribution on retention effect, but it can effectively improve the drainage performance of pulp. Unmodified isolated soy protein had a poor effect in pulp retention and drainage.The commercially available cationic starch(HCS) with a higher degree of substitution would have a greater effect in the Zeta potential and retention of slurry system. The binary system including commercial HCSwith a 0.14 substitution degree(DS) and anionic particles was applied in the wet-end system of pulp. The results showed that that dosage amount of HCS and particles are both important factors to affect the retention of fines. The effect in retention was increased with increasing their dosage.The system with HCS and bentonite was better than HCS and SiO2. The system including 0.1% HACC, 0.8% HCS and 1.2% bentonite, would get a 72% retention of fines and 20.5 oSR of beating degree.The results of bentonite particle system including CGG and HCS showed that: the two dosage proportions, which were 0.1% HACC, 0.1% CGG, 0.6% HCS, 1.2% bentonite and 0.1% HACC, 0.2% CGG, 0.4% HCS, 1.2% bentonite, respectively, had a similar retention of fines. Hoewer, thebeating degree was different, which were 24.5 oSR, 22 oSR(46.5 oSR for control sample). It was ovserved that the addition of HCS was possible to reduce the dosage of CGG in order to ensure the same fines retention. The increasing dosage of CGG wouldimprove the performance of the sheet drainage. In addition, the optimal biomass-based compound particles system including CGG, HCS, CGG associate with HCS particle system, can be comparable with the industrial system applied in Huatai, whose fines retention rate was 72.6% and beating degree was 23 oSR.Under the optimum conditions of wet method, the large-scale preparation of CGG showed that: the degree of substitution of synthetic CGG with expansion of 50 times experiment was slightly higher than smaller experiment sbut Zeta potential was considerable, indicating that the experimental synthesis process in chamber obtained has a good reproducibility and high feasibility. |
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