Synthesis of polycarboxylic superplasticizer by Co2+, Ni2+ and Zn2+ catalysted NaHSO3-H2O2 initiation system
Polycarboxylate superplasticizer (PCA) as a new type of high performance water reducing agent, has many excellent properties, but still faces the problems of poor water slurry dispersion, early strengthening flowability, water reducing rate and fluidity of cement paste. In order to further improve the comprehensive performance of Polycarboxylate superplasticizer, optimize the synthesis process and reduce production cost, it is of great theoretical and practical significance to develop a new cost-effective composite initiator system of Polycarboxylate superplasticizer. In this paper, Co2+, Ni2+ and Zn2+ catalysted NaHSO3-H2O2 initiation system were designed as redox initiators to synthesis Polycarboxylate superplasticizer, leading to PCA (Co2+), PCA (Ni2+) and PCA (Zn2+), respectively. The complexes were characterised by FTIR, GPC, zeta potential, XRD, TG, SEM and HPLC methods. When the folded solid content was 0.15%, compared with PCA0, the functional group type of PCA was unchanged and the molecular weight of PCA was slightly reduced. The transition metal ions coordinated with the carboxyl group (-COO-) of acrylic acid, which shifted the carbon-carbon double bond conjugated electron cloud in the monomer to the carbonyl carbon, enhanced the double bond activity, and promoted the polymerization reaction. When the double bond retention rate of the raw material isopentenol polyoxyethylene ether (TPEG) was 94.34%, the conversion rate of the large monomer could increase to 93.82%, which was 16.48% higher than that of PCA0 (77.34%), and the dispersion and retention ability of the cement slurry were improved. PCA (Co2+), PCA (Ni2+) and PCA (Zn2+) are more conducive to the early hydration of cement slurry than PCA0. Compared with PCA0, the water reduction rates of PCA in modified synthesis all increased by at least 3%. Compared with PCA0, the fluidity of the modified PCA cement paste was improved by 51mm.