Synthesis Of Anionic Starch By Dry Method And Their Properties As Water-reducing Agents

Water-reducing agent is a commonly used additive for cement and concrete.The addition of water-reducing agents to concrete can improve the fluidity of the concrete,while reducing the water needed to mix with the concrete.In this paper,SAS and SAMAS were synthesized and as water reducing agents based on native starch which is a kind of natural polymers.The reaction conditions to prepare SAS and SAMAS as well as their water reducing performance were studied in detail.In this paper,SAS was prepared by dry method in the presence of small amount of water,and corn starch was used as raw material,sulfamic acid as sulfonation reagent,and urea as catalyst.The effects of various reaction condition on the preparation of SAS were investigated in detail.The results showed that the dosage of sulfamic acid,the reaction temperature and the amount of water had a large influence on the substitution degree of sulfate groups and the efficiency of sulfamic acid reaction.The optimum conditions for the dry preparation of SAS can be concluded from the single-factor experiments.The optimum conditions were n（NH₂SO₃H）:n（AGU）1.5:1,dosage of water 20wt%（based on the dry weight of starch）,reaction temperature 110°C,reaction time 4h.Under optimal conditions,SAS had a sulfate group substitution degree of 0.65,a carbamate group substitution of 0.12.In this paper,SAMAS was prepared by dry methods in the presence of small amount of water,and hydrochloric acid degraded starch was used as raw material,maleic anhydride as esterification reagent,sulfamic acid as sulfonation reagent,and urea as catalyst.The effects of various reaction condition on the preparation of SAMAS were investigated in detail.The results showed that the dosage of maleic anhydride and sulfamic acid,the dosage of urea and the reaction temperature had a larger influence on the substitution degree of maleate groups and the efficiency of maleic anhydride reaction,and the dosage of sulfamic acid had a larger influence on the substitution degree of sulfate groups and the efficiency of sulfamic acid reaction.The optimum conditions for the dry preparation of SAMAS can be concluded from the single-factor experiments.The optimum conditions were n（MA）:n（SA）=1:1,n（Acid）:n（AGU）=1:1,n（Urea）:n（AGU）=0.5:1,dosage of water 20wt%（based on the dry weight of starch）,reaction temperature 120°C,reaction time 4h.Under optimal conditions,SAMAS had a maleate group substitution degree of 0.128,a sulfate group substitution degree of 0.35,a carbamate group substitution of 0.20.In this paper,the properties of SAMAS and SAS as dispersing agent was studied based on the fluidity of cement paste（FCP）and the time needed for cement setting,and compared with commercially available naphthalene-based superplasticizer（PDN）and polycarboxylate superplasticizer（PC）,and the results showed that the dispersing ability to cement:PC>SAMAS>SAS>FDN,and the FCP of SAMAS or SAS dosed with 0.3%was close to PC.The prepared starch-based water reducing agent had excellent dispersion effect with a maximum FCP of 227 mm.The setting time of cement slurry doped with SAS,SAMAS and Bn SAS was studied,and the results showed that SAMAS had a weak retarding effect on cement slurry,and SAS had a strong retarding effect on cement slurry,and it corresponded to the characterization results of XRD and SEM.