| The dissolved and colloidal substances(DCS),also named as anionic trash,are unstable under the effect of temperature and pH change,and will accumulate in the process water with the using of white water closure system in modern paper making factory.The unstable DCS system will have adverse effects on the runnability of paper machine and paper quality.The so-called fixing agents,which are cationic polyelectrolytes with low molecular weights and high charge densities,are commonly used to treat DCS by neutralization and fixation.However,due to their diversity in type and quality,they usually perform differently in effect and mechanism,when they are used to treat different papermaking systems.For instance,the fixing agents with low molecular weight tend to remove colloidal substances by the mechanism of colloidal fixation,which means the colloidal substances are fixed onto fiber as single ones,while the fixing agents with high molecular weight tend to interact with colloidal substances by the mechanism of colloidal agglomeration,which means the colloidal substances are firstly agglomerated and then retained in fiber mats under the treatment of fixing agents.On the other hand,fixing agents with low molecular weight tend more to interact with dissolved substances,while the fixing agents with high molecular weight tend more to interact with colloidal substances.Based on these researches,it can be concluded that combining two different kinds of fixing agents to make compounded agent system may have better effectiveness in controlling DCS.In this study,two kinds of fixing agent,one with low molecular weight while another with high molecular weight,were used to prepare compounded fixing agents to treat dinked pulp.The changes of cationic demand,chemical oxygen demand,turbidity of the filtrates that were separated from dinked pulp after being treated with fixing agents,were used to investigate the effective of compounded fixing agent.Meanwhile,the number,size and size distribution of the particles in the filtrates were measured to study the mechanism of compounded fixing agents.To begin with,an inorganic agent named polymeric aluminum(PAC)and an organic agent named polyamine(PAMo)with moderate molecular were compounded to treat deinked pulp.The results showed that the organic agent PAMo had more effect to remove DCS than the inorganic one,and compounding some ratios of PAC into PAMo could achieve better effect than the pure PAMo,which indicated that PAMo and PAC had significant synergistic effect.Compounding 20%of PAC into PAMo achieved the best effectiveness to remove DCS,which was the optimum ratio.When it came to the behavior of fixing agent,the results showed that PAC removed DCS with the ideal mechanism of colloidal fixation,while PAMo removed DCS with the mechanism of colloidal agglomeration,and with the increase ratios of PAMo in the compounded agents,the phenomenon of colloidal agglomeration would be more obvious.Also,two types of PA synthesized in our own laboratory,one with low molecular weight and charge density,renamed as PAL,and another with high molecular weight and charge density,renamed as PAH,were combined to new compounded agents system to treat dinked pulp.The results showed PAH had more effect to remove DCS than PAL,combining 20%of PAL into PAH didn't reduce the ability of PAH to remove DCS,while combining 20%of PAH into PAL would obviously increase the effect of PAL.Since high molecular weighted PA is difficult to synthesize,combining 20%of PAL into PAH obviously has advantages in reducing product cost and increasing product efficiency.On the mechanism of compounded fixing agent,the PAL reacted with DCS with the ideal mechanism of colloidal fixation,while PAH reacted with DCS with the mechanism of colloidal agglomeration.With the increase ratios of PAH in the compounded fixing agents,the phenomenon of colloidal agglomeration would be more obvious.Again,another two kinds of fixing agents,one as a polyamine synthesized in our own laboratory with medium molecular,another as a kind of commercial fixing agent named as microstickies control agent(MSC),were combined to treat dinked pulp.The results showed that MSC have better performance than the PA on controlling the turbidity and cationic demand of filtrates separated from dinked pulp after being treated with compounded fixing agent,but the PA had the better performance on controlling the chemical oxygen demand of filtrates.In respect of mechanism,the two fixing agents all reacted with DCS with the mechanism of colloidal agglomeration,but the degree of MSC was more obvious.DCS was intensity aggregated when a little ratios of MSC was compounded into the new fixing agents.Finally,the three compounded fixing agents with the optimum ratios in their own group were chosen to treat the same dinked pulp to investigate their effect on removing DCS.The results showed that the compounded fixing agents PAC/PAMo had weaker effect in removing DCS than the other two compounded fixing agents PAL/PAH and PAMe/MSC.When the PAL/PAH and PAMe/MSC were compared,PAMe/MSC had batter performance on controlling the turbidity,chemical oxygen demand and total colloidal counts when the dosages were lower than 0.4%odp.In respect to mechanism,the three compounded fixing agents removed DCS with the mechanism of colloidal fixation at the dosage of 0.1%odp.When the dosages were over 0.1%odp,PAL/PAH and PAMe/MSC turned into colloidal agglomeration,but PAC/PAMo kept the colloidal fixation until the dosages were over 0.5%odp.It was found that 0.4%odp were the optimum dosages for PAMe/MSC compounded fixing agent,if the dosages were over 0.4%odp,then the colloid particles would be re-dispersed. |
PDF Full Text Request