Synthesis Of Polycarboxylate Ethers And Their Application In Cement And Gypsum Formulation

Efficient cement, concrete and ceramic plaster mold all have the requirements for fairlyhigh strength. In this experiment, Polycarboxylate macromolecules (PMs) were synthesisedwith radical aqueous solution polymerization through molecular design. The syntheticproducts were studied for the fluidity of construction cement and the gypsum’s strength whichwere used as admixture时of construction cement and ceramic mold gypsum，respectively.The main contents and results are as follows:1. In this study, modified iodometric method was investigated. The results showed thattribromide strategy is suitable for the double bond determination of those substanceswhich were used in the experiments. The monomers contained acrylic acid (AA),methacrylate (MA), allyl polyoxyethylene ether (APE) and allyl polyoxyethylenepolyoxypropylene ether (APPE), and so on. Monomer reactivity ratios were investigatedand then we found that AA and MA were easier to occur self-polymerization reactionthan APE, APPE and sodium methallyl sulfonate (SMS). However, SMS was easy tooccur copolymerization reaction with other monomers and APE was easier to react withSMS than APPE. We optimized the synthesis conditions of PMs, AA and MA mixedsolution was added dropwise with aqueous solution of SMS and APE (or APPE) while thereaction was carried out,85oC, addition time was2.5h, the ratio of initiator APS weight toall monomers’ weight was1.1%. Lastly, when we use APE and APPE as themacromolecular monomers, the conversion rate were97.3%and99.5%, respectively, thereaction time was8hours.2. The performance of PM-1were investigated with the fluidity of cement paste as index,85oC, the ratio of initiator APS weight to all monomers’ weight was0.9%and the dosage ofPM-1was0.6%were optimum conditions. The optimized reaction formula was nSMS: nAPE:nMA: nAA=20:12:6:62, obtained via orthogonal test. At0.29W/C, the30s fluidity ofcement paste was279mm. PM-1had stable and reliable performance but cement pastefluidity decreased22.2%after2h. PM-1had good thermal stability, the weight loss of300oC and400oC was5.1%and45.9%, respectively.3. It was found that the performance of modified gypsum was poor with early experimentproducts. Via single factor experiment, the gypsum’s performance was well when thecontent of AAwas less than54mmol, SMS was20mmol, APE was14mmol and ester toacid ratio was0.13in the formula of PM-2, while the content of AA, SMS and APPE were35mmol,20mmol and9mmol in the formula of PM-3. The orthogonal experiment wasdesigned, we found the optimum synthetic formulation of PM-2was nAA: nMA: nSMS:nAPE=30:36:25:9,1.1wt%APS. As the same to PM-2, nAA: nMA: nSMS: nAPPE=32:49:9:10,1.4wt%and85oC was optimized formula of PM-3via orthogonal experiment.4. PM-2and PM-3all prolonged the gypsum plaster’s setting time. In this study, theoptimized dosage of PM-2was0.2wt%. It presented an increase of bending strength andcompressive strength of31.1%and32.6%in24h, respectively. At the same measurementconditions, the plasters containing0.2%PM-3had an increase of bending strength andcompressive strength of48.9%and27.8%, respectively. The bending strengrh of PM-3 modified gypsum was50.0%higher than PM-2modified gypsum. The water absorptionrate of the PM-2and PM-3modified plaster was22.0%and22.8%, respectively, so it waseasy to find that the water absorption rate of PM-2and PM-3modified plaster were9.1%and5.9%lower than that of pure plaster. The water absorption rate of PM-3modifiedplaster were3.8%lower than that of PM-2modified plaster. At300oC, the weight loss ofPM-2was6.3%while PM-3was4.2%. At400oC, the weight loss of PM-2and PM-3were46.4%and38.9%, respectively. The weight loss of PM-3was less than PM-2, so thethermal stability of PM-3was a little better than PM-2. Compared to commerciallyavailable PMs SP-8CN and Julong94, the strength and water absorption rate of PM-3modified gypsum was better.