Preparation And Characterization Of Sulfonated Grafted Starch Water Reducer

The water reducing agent is a concrete admixture that reduces the amount of water used for concrete mixing.As a product of photosynthesis of green plants on the earth,starch has the advantages of renewable,wide source,high yield,non-toxic and low price.What is important is that the special structure of the starch molecular chain makes it possible to modify the starch molecule as a water reducing agent,and find a new way for the preparation of the new water reducing agent.Two kinds of sulfonated grafted starch Water reducing agent were prepared by modifying the molecular structure of corn starch and introducing hydrophilic anionic sulfonic groups into the starch chain.(1)RS-g-SMAS water reducing agent.By using corn starch(RS)as raw material,sodium methallyl sulfonate(SMAS)was used as grafting monomer,ammonium persulfate was used as initiator,graft copolymer(RS-g-SMAS)of SMAS onto RS as a kind of water-reducing agent was prepared through aqueous solution polymerization.Based on fluidity of cement paste(FCP)as the reference standard,single factor and orthogonal test were designed to optimize the process parameters,and the optimum preparation conditions were as follows:initiator dosage 7wtt%,SMAS dosage 1.5wt%,polymerization temperature 65 ? and polymerization time 1 h.FTIR analysis showed that a new absorption peak appeared at 1209 cm-1 of RS-g-SMAS,which proved that the starch molecule had successfully introduced into-SO3-.Structural of reference sample or cement paste mixed with RS-g-SMAS were analyzed by XRD and SEM.The results showed that the initial hydration reaction of RS-g-SMAS mixed with cement slurry was slower than that of reference sample,and the structure of hardened cement was more compact after 28 days.FCP test showed that with the increasing of RS-g-SMAS content,the fluidity increased firstly and then decreased,and when the content of RS-g-SMAS is 0.8wt%,FCP is the largest;setting time test proves that RS-g-SMAS has obvious retarding effect on cement paste;compressive strength test proves that when the content of RS-g-SMAS is 0.4wt%,the compressive strength is significantly higher than that of reference sample.(2)AS-g-SMAS water reducing agent.Acid hydrolyzed corm starch(AS)prepared under certain conditions was used as raw material,SMAS was used as grafting monomer,ammonium persulfate was used as initiator.Graft copolymer(AS-g-SMAS)of SMAS onto AS as a kind of water-reducing agent was prepared through aqueous solution polymerization.The optimum preparation parameters of AS-g-SMAS were obtained through single factor and orthogonal test as followed:acid hydrolysis time 8 h,(NH4)2S2O8 dosage 5wt%,SMAS dosage 10wt%,polymerization temperature 70 ?,polymerization time 3 h.Structural and elemental composition of AS-g-SMAS or cement paste mixed with AS-g-SMAS were analyzed by FTIR,XRD and SEM-EDS.FTIR analysis showed that sulfonic group was successfully introduced onto AS.XRD and SEM showed that the initial hydration reaction of AS-g-SMAS mixed with cement slurry was slower than that of reference sample,and the structure of hardened cement was more compact after 28 days.SEM-EDS elemental analysis confirmed that AS-g-SMAS does not contain chlorine harmful to steel.The setting time test of cement paste shows that when the AS-g-SMAS content increases from 0.2wt%to 1.2wt%,the initial setting,final setting and final and initial setting time difference of cement paste are increased first and then decreased.The best result appears when AS-g-SMAS content is 0.8wt%,and the retarding effect first strengthens and then weakens.