Synthesis,Characterization And Properties Of Polycarboxylate Superplasticizer By Using An Approach Mechanochemistry

Polycarboxylate superplasticizer(PCE)is currently the most widely used concrete admixture.Adding a small amount of PCE can significantly improve the fluidity and pumpability of concrete and improve the compressive strength,flexural strength and durability of hardened concrete.At present,PCE is mainly prepared by aqueous solution radical polymerization,and the concentration is between 20%and 40%by weight.PCE solutions are not conducive to packaging and transportation,especially when the construction site is too far away.At the same time,PCE solutions cannot be used in the production of building materials such as dry mortar and grout.The mechanochemical method is a synthetic method in which mechanical energy is input by mechanical ball milling to initiate a chemical reaction between substances,with or without a solvent ball milling method and a liquid assisted ball milling method.Mechanochemical method can promote the chemical reaction between reactants quickly and quantitatively,without adding a large amount of solvent to completely dissolve the reactants,and the obtained product has a high solid content,and the concentration is between 90%and 100%by weight,which is a kind of green,convenient and fast synthesis method.In this paper,mechanically,the unsaturated monomer isopentenyl polyoxyethylene ether(IPEG),acrylic acid(AA),sodium methacrylate sulfonate(MAS)and initiator ammonium persulfate(APS)under ball milling Free radical polymerization occurs to synthesize PCE.Solvent-free ball milling polycarboxylate superplasticizer(MPCE)and liquid-assisted ball milling polycarboxylate superplasticizer(LMPCE)were prepared by solvent-free ball milling and liquid-assisted ball milling,respectively.The results of FT-IR and 1H-NMR indicated that the polycarboxylate water reducing agent(TPCE)synthesized by MPCE,LMPCE and traditional aqueous solution free radical polymerization method has similar functional groups and molecular structures.GPC analysis showed that the molecular weight of MPCE and LMPCE was less than TPCE.The solid content of MPCE and LMPCE can reach more than 90%,much higher than TPCE.When the dosage is 0.25%,the cement paste fluidity of MPCE and LMPCE reaches the level of TPCE.When the dosage is 0.3%,the cement paste fluidity of MPCE and LMPCE is higher than that of TPCE.MPCE,LMPCE and TPCE all reduce the surface tension of water.The solid content of LMPCE is slightly lower than that of MPCE,because LMPCE is added to the micro-water assisted ball milling.At the same time,the molecular weight of LMPCE synthesized is higher than that of MPCE,and the conversion rate of LMPCE monomer is lower than that of MPCE.The molar ratio of the raw material acid ether,ie,AA to IPEG,was changed to 2.0:1,2.5:1,3.5:1 and 4.5:1 to synthesize MPCE-A,MPCE-B,MPCE-C and MPCE-D,respectively.As the ratio of acid to ether increases,the monomer conversion rate of the reaction increases,and the molecular weight of MPCE gradually increases.The cement paste fluidity test results show that MPCE-B has the best dispersion performance when the acid-ether ratio is 2.5:1.When the ratio of acid to ether is 3.5:1 and 4.5:1,the dispersion performance of MPCE-C and MPCE-D is worse than that of MPCE-B,mainly because the density of carboxylate increases,the density of MPCE side chain decreases,and the cement particles are reduced.The reaction time,ie,the ball milling time,10 min,20 min,30 min,40 min,50 min,60 min,was used to synthesize MPCE.As the reaction time is extended,the molecular weight and degree of polymerization of MPCE are reduced.When the temperature of the system increases,the decomposition rate of APS initiator increases.Due to the higher concentration of local free radicals in the reaction system,the overall polymerization reaction is more intense,resulting in a decrease in the molecular weight of the product.In addition,due to the increase of reaction time,the mechanical force continuously acts on the molecular shear.The polymerized water reducing agent macromolecular chain is broken and degradation occurs.The results of H-NMR analysis showed that the actual molar ratio of MPCEA-D series was higher than that of the feed acid ether ratio,mainly because the activity of AA was much higher than that of IPEG,and it was easier to participate in the polymerization reaction.Through the rheological property test,the initial viscosity of the cement paste gradually decreases with the ball milling time prolonged,and the new mixed cement paste has a tendency to become thinner as the shear rate increases,mainly because the shearing process is destroyed.The stable flocculation state of cement hydration causes the water in the cement to be released.The mechanical chemical method for the preparation of MPCE and LMPCE solves the problem of low solid content of the traditional synthesis method,which provides a basis for the later powder production and expands its application range.At the same time,the integration of mechanochemistry and organic synthesis has been realized,which has provided new ideas for sustainable development.