Preparation Of Hydrophobic CPAM Through Ultrasonic-Template Method And Its Flocculation Study

Along with social development and urbanization process,the rapid increasing of both municipal and industrial water consumption brings not only pressure on water supplying,the abundant generation and discharge of both municipal and industrial sewage also bring serious water environment pollution.The water pollution has become a main reason which hinders the development of society and improving of people's life.As one of the most widely utilized water treatment methods,there is no doubt that the flocculation process has played an important role in controlling water pollution and improving the water environment.The design and development of new and highly efficient flocculants,the heart of the flocculation process,is critical to improving water treatment efficiency and quality.Cationic polyacrylamide?CPAM?is widely used in water treatment due to its synergistic effect between bridging and charge neutralization effect in flocculation.However,the cationic units dispersively arranged in the traditional CPAM polymer chain,so that,the utilization efficiency of positive charge is reduced,and charge neutralization ability and flocculation performance are consequently limited.Focused on the aforementioned drawbacks of conventional CPAMs,this study employed template copolymerzation technology to artificially control the cationic units centralized distributing in polymer chain to form cationic microblock structure,which can improve the charge neutralization ability of polymers.Furthermore,the introduction of hydrophobic units in polymer chain makes it amphiphilic and behaves obvious hydrophobic association behavior in solution,which promotes the interaction between flocculant molecular and hydrophobic pollutants,and also improves the phase transformation ability of flocs.This thesis built a ternary copolymerization system using acrylamide monomer?AM?,cationic monomer acryloxyethyl trimethylammonium chloride?DAC?and hydrophobic monomer lauryl acrylate?LA?.The target amphiphilic copolymer product TP?AM-DAC-LA?with cationic microblock structure was synthesized with the dosage of anionic template molecular sodium polyacrylate?NaPAA?using a novel ultrasonic initiation technology,the flocculation behavior of which was also investigated.Currently,there are very limited work related to cationic flocculants preparation through template copolymerization,the reserch about flocculant that combines both cationic microblock structure and hydrophobic association hasn't been reported yet.The main research works and conclusions are as follows:?1?The effects of copolymerization conditions,including ultrasonic power,ultrasonic irradiation time period,total monomers concentration,cationic monomer concentration,reaction system pH value,initiator concentration,and template reagent dosage,on molecular weight of copolymers and monomers conversion rates are well investigated.The ultrasonic irradition can complete the initiation of copolymerization system in 20 min.The optimal molecular weight and monomers convertion rate of the final product TP?AM-DAC-LA?of template copolymerization achived 3.45×10⁶ Da and98.2%,respectively.The established RSM model accurately predicted the molecular weight of the product,which can be a good guide to copolymer production.?2?Instrumental characterizations were employed for the comparative analysis of TP?AM-DAC-LA?and its corresponding non-template copolymer P?AM-DAC-LA?.The FTIR results indicate that both of them are copolymers from AM,DAC and LA.The introduced template molecular NaPAA didn't join into the copolymerization reaction or change the chemical composition of copolymers.The ¹H NMR results confirm not only the chemical composition of copolymers,but also the formation of DAC cationic microblock structure.The significant weakened of disappeared interference protons resonance signals belong to sidechain functional groups indicate that the DAC units were sited in a chemical environment that is more similar to its homopolymer.DSC-TGA analysis confirmed good thermal stability of both copolymers.The three separate heat adsorption peaks of TP?AM-DAC-LA?during the backbone thermal decomposition stage indicate that the AM,DAC and LA units all arranged in a form of block structure in the TP?AM-DAC-LA?polymer chain.SEM images showed the formation of a three-dimensional network due to the hydrophobic association of amphiphilic polymer chains.?3?The kinetics study of template copolymerization indicates that the relations between R_p and C_TM and C_I were R_p?C_TM^1.7733 and R_p?C_I^0.6322,respectively,which accorded with the classic free radical polymerization theory.Polymerization pH affects R_p by affecting the electrostatic interaction between cationic monomers and templates.The effects of template dosage on kinetics proved that the interaction force between cationic monomers and templates was mainly electrostatic attraction,which is consistent with the type I ZIP reaction mechanism.The binding constant between cationic monomers and templates achieved K_M=17.63 indicated that approximately 78.9%of the cationic monomers had been pre-adsorbed on the templates,which is another solod evidence that the template copolymerization system established in this work follows the type I ZIP reaction mechanism.?4?The copolymerization mechanism of TP?AM-DAC-LA?was discussed based on the rules of classic free radical polymerization and type I ZIP reaction mechanism of template copolymerization,according to the copolymer characterization and kinetics study.The template copolymerization reaction involves template pre-adsorption and micelle solubilization processes prior to initiation,chain initiation,growth,and termination accompanied by chain transfer.Biradical disproportionation termination is the main mode of chain termination.The electrostatic adsorption of template moleculars to DAC monomers and the solubilization effect of micelle to LA monomers are the main reason of the formation of DAC segments and LA segments,respectively.?5?The association behavior of the copolymer in solution was evaluated based on an apparent viscosity investigation.The results show that the introduction of hydrophibic groups makes the copolymer to behave obvious hydrophobic association effect in solution.The intermolecular association can connect the macromolecular chains with each other to form a three-dimentional net-like structure,which can greattly increase the hydrodynamic volume,thereby increasing the solution apparent viscosity.This association effect would be favorable for the enhancement of bridging and sweeping ability of flocculants.?6?The TP?AM-DAC-LA?and its corresponding non-template copolymer and hydrophilic binary copolymer were utilized in municipal sludge dewatering experiments.The results show that the cationic microblock structure and hydrophobic association can together improve the sludge flocculation efficiency.The FCMC and SRF reached 67.2%and 3.84×10¹22 m·kg^-1 using TP?AM-DAC-LA?at its optimal dosage of 2.5 mg·g^-1,which are better than that of the samples flocculated by other polymers.Cationic microblock structure effectively enhanced charge neutralization and electrostatic patching effect to obtain a compacter inner structure of flocs,which means a higher mechanical strength and stronger shear resistance ability.Therefore,the strong flocs can play as a skeleton structure and make the filter cake less compressable to maintain the porous and permeable of which in mechanical dewatering.Therefore,the strong flocs can maintain the porous and permeable structure of filter cake in mechanical dewatering.Furthermore,hydrophobic association can enlarge floc size to obtain better solid-liquid separation oerformance.Besides,hydrophobic association,as a physical reversible effect,can improve the regrowth ability after flocs breakage.?7?The copolymers were further utilized in simulating oily wastewater flocculation.The optimal oil and turbidity removal rates of 91.2%and 92.9%,respectively,were obtained by TP?AM-DAC-LA?at the dosage of 40mg/L,which is better than the other copolymers which means it can act as an effective pretreatment method in oily wasterwater treatment.The introduction of hydrophobic units evidently imcreased oily wastewater flocculation efficiency.In addition,the flocculation efficiency was not significantly affected when the solution was positively charged by the overdosaged polymer,which indicate that bridging and hydrophobic association are the main mechanism in oily wastewater treatment.Cationic microblocks made the flocs compacter while hydrophobic association enlarged the oily flocs size.Furthermore,the amphiphilic macromolecular chain decreased the mechanical strength of emulsified interfacial film by competitive emulsification effect,which accelerated the demulsion process and increased the flocculation efficiency.The competitive emulsification and hydrophobic association brought by hydrophobic monomers introduction were the main reason for the better flocculation efficiency obtained by amphiphilic flocculants.