Preparation Of Block Copolymer P(AM-DMBAC) And Its Sludge Dewatering Properties

Cationic polyacrylamide(CPAM)has a high share in the synthetic organic polymer flocculant,which is characterized by its good solubility,high molecular weight and prominent flocculation efficiency.However,the traditional CPAM preparation methods usually focus on improving the molecular weight of the polymer,and there is a problem that the cationic monomer unit of the product is not concentrated,randomly distributed,and can not fully exert the advantages of the neutralization.The influence of the sequence structure on the flocculation and dehydration performance of CPAM is less concerned,and such studies are rarely seen.At the same time,the initiation speed of the UV light is fast and the pollution will not be caused before and after the reaction.The operation is simple and the activation energy of this kind of reaction is low,which has the advantages of energy saving and can reduce the amount of initiator and has good development prospect.The purpose of this paper is to develop a new CPAM flocculant with high purity,good linearity and good solubility by using soap-free emulsion polymerization of surface active monomer with hydrophobic group and hydrophilic group and acrylamide monomer based on ultraviolet light initiation.And to explore the effect of the molecular chain block structure on its properties.Here,we adopted a surface active monomer benzyl dimethyl 2-(methacryloyloxy)ethyl ammonium chloride(DMBAC)to copolymerized with acrylamide(AM)monomer under UV irradiation,and a novel cationic hydrophobically associating polyacrylamide flocculant P(AM-DMBAC)(PAB)was synthesized.At the same time,a cationic monomer methacrylatoethyl trimethyl ammonium chloride(DMC),which is structurally similar to the DMBAC monomer but has less hydrophobic benzyl group,is selected to prepare another copolymer P(AM-DMC)(PAD)and compared with the same environment.Based on the microstructures of the copolymer molecular chains,the monomer reactivity ratio,composition structure,sequence length,thermal stability of the copolymers were investigated in the copolymer PAB and PAD.The effects of total monomer mass fraction,urea,EDTA-2Na,reaction system pH,UV light initiation time,monomer molar ratio,initiator dosage on the intrinsic viscosity and conversion of polymerization were investigated.And compared with commercially available CPAM products to study the effect of copolymer PAB sequence on its flocculation performance.By comparing and analyzing the calculation of reactivity ratio,the equation of copolymer composition and the sequence distribution structure of monomer.It was found that the reactivity ratios of AM monomer and DMC monomer were less than 1 in the PAD polymer,which showed the random copolymerization in the polymerization.In the PAB polymer,AM reactivity ratio is less than 1,the reactivity ratio of DMBAC is higher than 1,indicated that AM tends to copolymerization,while DMBAC tends to be homogeneous,which shows that the surface active monomer DMBAC is a block structure in the polymer backbone.And when the feed ratio is the same,the cationic degree of DMBAC is higher,the block length is longer,and the charge distribution of cation is more concentrated.Single factor experiment and response surface method was used to optimize the conversion rate and viscosity of PAB in the polymerization.It shows that the best synthesis conditions for the UV irradiation time is 1h,the concentration of initiator is 0.03%,the urea concentration is 2%,the reaction system pH is 4,the EDTA-2Na concentration is 0.4% and the cationic monomer molar ratio of n(DMBAC): n(AM)=1:9,the total monomer mass fraction is 40%.At this point,the conversion rate of PAB is 99.17%,the intrinsic viscosity is 10.86dL/g.The molecular structure and thermodynamic stability of copolymer PAD and PAB were analyzed by means of Fourier transforms infrared spectroscopy(FTIR),magnetic resonance spectrometer(1H NMR)and thermal gravimetric analysis(DSC-TGA).The results showed that two kinds of copolymers PAD and PAB were successfully synthesized under UV irradiation,and they had similar chemical structure.The copolymer PAD and PAB have good thermal stability at room temperature and the polymer PAB has a micro block structure.The flocculant PAB was subjected to sludge dewatering experiment to investigate the effect of dosage and sequence structure on the flocculation and dehydration performance.Compared with PAD and commercially available CPAM,it can be seen that the sludge dehydration performance of the copolymer PAB with micro-block structure is the best,and the trend of Zeta potential is combined to show that the dehydration performance of the flocculant PAB can be enhanced under the combined conditions of the charge neutralization and adsorption bridging.FCMC,SRF and RTS reached the minimum(68.7%,2.4 × 1012 m / kg,2.6NTU)when the amount of flocculant PAB was 40 mg / L.By investigating the changes of SEPS in the flocculation and dehydration experiments,it is shown that the cationic micro-block structure can enhance the electrical neutralizing ability and bridging ability of the copolymer PAB,so that the total protein(PN)in the SEPS can be removed more effectively,which helps to reduce sludge viscosity and compressibility.Scanning electron microscopy(SEM)and flocs morphological properties showed that the floc formed by the copolymer PAB was larger and denser,and it was not easily broken when exposed to high shear force.The floc regeneration ability was higher than that of the other three flocculant conditioning.