Study On The Synthesis Process Of Phosphate-Polycarboxylate Superplasticizer

Polycarboxylate superplasticizer(PC)is a kind of dispersant which is consisted of poly carboxylic acid backbone and side chains with specific functions,and they have been widely used in concrete additive industry because of its low dosage,high water reducing rate and good dispersing performance during the industrial process.However,the temperature of the traditional polycarboxylate superplasticizer synthesis process is relatively higher and it is not easy to control the temperature of the reaction kettle during large-scale production,which leads to many problems such as difficult operation,high energy consumption,and high cost.At the same time,sulfate and polycarboxylate superplasticizer can competitively attach to the surface of cement particles,thus reduce the water-reducing effect of polycarboxylate superplasticizer.The competitive adsorption of SO42-ions can be restrained by the introduction of phosphate group.Therefore,carboxylic group,phosphoric acid group and sulfonic acid group were introduced into the structure of polycarboxylate superplasticizer based on molecular design and phosphate-polycarboxylate superplasticizer was synthesized in the redox system at a lower temperature.Firstly,the mechanism of polycarboxylate superplasticizer synthesis at a lower temperature and the action mechanism of phosphoric acid group in cement were studied,which theoretically provided a basis for low temperature synthesis of poly carboxylic acid water-reducing agent and the introduction of phosphoric acid group.Secondly,the kind and the molecular weight of the monomer,the chain transfer agent,and the redox system were determined.The results showed that poly carboxylic acid reducing agent was synthesized by a molecular weight of 2400 isopentenol polyoxyethylene ether macromonomer and other small monomer under the action of initiating agent ammonium persulphate-ascorbic acid,chain transfer agent 3-mercaptopropionic acid,which exhibited excellent performance.Finally,the best monomer molar ratio of polycarboxylate superplasticizer was methyl acrylic acid(MAA):methyl allyl sulfonate(SMAS):unsaturated phosphate monoester(UPE):isoamyl alcohol polyoxyethylene ether(TPEG)= 3.87:0.29:0.49:1 obtained by the single factor experiment and response surface analysis.The optimized synthesis condition was that the dosage of oxidation-type initiator ammonium persulphate,reducing-type initiator ascorbic acid and chain transfer agent was respectively 4%(mole fraction,similarly hereinafter),0.35% and 3% of the total monomer molar,that the reaction temperature was 35?,the reaction time was 4 h,and the feeding mode was constant dropping.The original fluidity of cement paste of the synthetic water reducing agent was 310 mm,the water reducing rate reached 30%,and the solid content reached 39% under the above process conditions.In addition,the effect of monomer molar ratio on the performance of water reducing agent was n(MAA):n(TPEG)> n(UPE):n(TPEG)> n(SMAS):n(TPEG)by response surface analysis.The synthetic phosphate-polycarboxylate superplasticizer has a strong ability of dispersion and good solubility with cement,and it is energy saving and environmentally friendly in the process,which is significant in the guidance of polycarboxylate superplasticizer industrial production.