Studies On Gel Retention Mechanism Of Nonionic Retention And Drainage System

In this thesis, gel retention and drainage mechanism was put forward on the basis of many experiments, and a mechanism model was established too. Polyethylene oxide(PEO)-phenolic resin(PR) retention system was used to inspect and verify gel retention and drainage mechanism. A new dual PEO-silica sol two-component retention and drainage aids system was successfully developed along the idea of gel retention mechanism. In the end of the thesis, gel retention and drainage mechanism was summarized and popularized, it will gain a broader range of applications and provide a reference direction for future researches.1. Experiments showed that the materials which could gelate all had a flocculation effect on pulp under the same conditions. But their flocculation effects were different due to various influence factors. For example PEO-PR gel system, PEO-silica gel system and PEO-bentonite gel system had good flocculation effect. And they can/have become effective retention systems. Polyacrylate sodium(PAAS)-PEO system and methylcellulose(MC) both had perfect flocculation effect on pulp too, but PAAS was very sensitive to metallic ion and MC didn't gain a good flocculation before the pulp temperature reached the gelatum temperature of MC(which is about 63℃) or above, so PAAS-PEO system and MC used for retention system was more difficult than PEO-PR system. And flocculation effect of PAAS-PEG gel system was poor.2. Retention and drainage effect of PEO-PR resin system was related to the nature of PEO-phenolic resin gel itself: if the consistency of PEO was assured most gel amount was gained when the dosage of PR was about 5 times as much as the amount of PEO; and the biggest fines retention was obtained as phenolic resin was just 5 times the dosage of PEO. In acidic condition, strength of PEO-PR gel was poor, while in neutral and alkaline conditions the shear resistance of PEO-PR retention system was preferred to in acidic condition.3. According to gel retention and drainage mechanism, PEO-silica system was found obvious flocculation effects on pulp; further research showed that this system had good retention and drainage effects at low dosage. When the dosage of PEO was 0.01% and silica was 0.1%, the beating degree reduced from 54°SR to 31°SR; fines retention and filler retention reached 90%. In addition, this retention system affected little on the paper evenness, strength and whiteness. 4. It is known that changes in the external environment are the root cause of dehydration and shrinkage of gel and the gel retention mechanism. However, under the given external environment, gel retention mechanism is directly related to gel amount the systems produce (amount of gel is related to concentration, molecular weight and mixture ratio of gel components and so on), the gel contraction and dehydration time, gel strength and elasticity and other factors. From this point of view, humid part of paper is suitable for thermo-responsive hydro gel and pH sensitive gel which respond to changes of temperature or pH and then dehydrate and shrink, such as Hydroxypropylcellulose(HPC) which gelatum temperature is 40-45℃is likely to produce a flocculation effect as MC, and polyvinyl pyrrolidone (PVP) forms complex compound with many chemical compound in neutral or acidic condition. These gels are the new research directions of retention and drainage mechanism.5. During the gel retention and drainage retention mechanism, cationic retention systems and particulate retention systems work with fiber and filler to form a special three-dimensional network structure via electrostatic coupling or chelating, which achieve the filtering purposes and broaden application ranges of gel retention and drainage mechanism.