Synthesis Of A Novel Lignin-based Branched Polycarboxylate Cement Dispersant And Its Application

Polycarboxylate cement dispersant is widely used in modern industrial production and applications for itsadvantages,such as low dosage,high water reduction rate,high dispersion,and security environmental protection.However,due to its compatibility problems with other admixtures and gel materials,problems such as bleeding and segregation often arise in production applications.As the first generation of water reducing agent,lignin is often used as compound products in the admixtures field for its good performance of molding.In order to solve the problem of easy bleeding and eduction of polycarboxylate cement dispersant,the molecular structure of the polycarboxylate was designed to introduce lignin into the molecular structure of the polycarboxylate to optimize the performance of these two types of water reducing agents.In this paper,lignin-modified monomers(KL-TPEG)and lignosulfonate-modified monomers(LS-TPEG)were prepared from kraft lignin(KL)and sodium lignosulfonate(LS).The modified lignin-based polycarboxylate cement dispersant were prepared by these two kinds of lignin-based polyether monomers,and the application performance was studied.The main research methods and conclusions are summarized as follows:(1)Modified kraft lignin-based polyether monomers(KL-TPEG)with different grafting rates were synthesized by kraft lignin,and appropriate monomer(KL-TPEG3)was selected to synthesize kraft lignin-based polycarboxylate(PCE-L).The branched structure of PCE-L were characterized by FT-IR,~1H NMR and GPC.The dispersibility test showed that under the same dosage of 0.15%,the fluidity of the cement paste dispersed by ordinary polycarboxylate water reducer(PCE-B)had dropped to 280mm in 90min,while the fluidity of PCE-L dispersed cement paste could keep above 300mm.PCE-L had better dispersibility and stability according to rheological test.The adsorption of PCE-L on cement particles was consistent with the Langmuir isotherm adsorption model and the pseudo-secondary adsorption kinetic model.The adsorption amount of PCE-B on the surface of cement particles was about 1.6 times that of PCE-L,but PCE-L exhibited good dispersibility due to its branching molecular structure and strong"spherical effect".(2)In addition,lignosulfonate-modified monomers(LS-TPEG)monomer were synthesized sodium lignosulfonate(LS).After characterization and testing,PCE-LS were synthesized by LS-TPEG1 as a monomer.The dispersion test and rheological test showed that PCE-LS has better dispersibility and stability.Zeta potential analysis showed that Zeta potential of PCE-LS hadincreased from-5 mV to-20 mV,and still increased with the content of LS,as well as the adsorption capacity onto the cement particles.PCE-L exhibited good dispersion properties for its special branched molecular structure,space resistance,electrostatic repulsion.The introduction of lignin to the polycarboxylate cement dispersant did not reduce the dispersibility of the polycarboxylate cement dispersant,but improved its dispersibility and stability.The relationship between the properties and structure of lignin-based polycarboxylate cement dispersant was established in this dissertation,and the special functions of lignin were studied,which will provide theoretical guidance for the research and application of polycarboxylate cement dispersant.