Study On Room Temperature Synthesis And Clay Sensitivity Of Polycarboxylate Superplasticizer

Polycarboxylate superplasticizer had the advantages of high water-reducing rate,good slump retention and strong designability of molecular structure.It had been developed rapidly in recent years and was widely used in various kinds of concrete.Due to its simple synthesis process,pollution-free and short production cycle,it had attracted many domestic manufacturers to join,and the competition for low-level homogenization had become increasingly fierce.What's more,the actual engineering application found that the clay in the gravel seriously inhibited the performance of the polycarboxylate superplasticizer.It seriously affected the quality of the concrete and restricted the further promotion and application of the polycarboxylate superplasticizer.In order to reduce the reaction temperature and save production cost,this paper explored the process and influencing factors of synthesizing polycarboxylate superplasticizer at room temperature with acrylic acid?AA?and three macromonomers?4-hydroxybutyl polyethylene glycol vinyl ether VPEG,isopentyl polyethylene glycol ether TPEG,methyl allyl polyethylene glycol ether HPEG?with higher polymerization activity.It was found that the redox initiator system of H₂O₂-VC was more suitable for the initiation of polycarboxylate superplasticizer polymerization at room temperature.The amount of initiator had the greatest influence on the structure and properties of the product,followed by the ratio of acid to ether and the concentration of the reactant,and the reaction temperature had the least effect on the properties of the product.With the increased of initiator dosage and reaction temperature,and with the decreased of acid-ether ratio,the intrinsic viscosity of the product decreased,and the dispersion of cement increased first and then decreased;with the increased of reactant concentration,the intrinsic viscosity of the product and the dispersion of cement increased first and then decreased.The dispersibility of polycarboxylate superplasticizer to cement paste was proportional to its molecular weight.The optimum process for preparing polycarboxylate superplasticizer from three macromonomers at room temperature were as follows:?1?The dosage of H₂O₂ was 10.0 mol%of the total monomer,the polymerization temperature was 30?,the reactant concentration was 60 wt.%,n?AA?:n?VPEG?=2.5:1;?2?The dosage of H₂O₂ was 10.0 mol%of the total monomer,the polymerization temperature was 35?,the reactant concentration was 35 wt.%,n?AA?:n?VPEG?=3.0:1;?3?The dosage of H₂O₂ was 7.5 mol%of the total monomer,the polymerization temperature was 35?,the reactant concentration was 40 wt.%,n?AA?:n?VPEG?=3.0:1.The three optimized process products all have good cement dispersion.Compared with TPEG and HPEG,VPEG used in the synthesis of polycarboxylate superplasticizer needed less acrylic acid,lower reaction temperature,shorter reaction time,higher solid content and slightly better dispersibility.The main reason that clay inhibits polycarboxylate superplasticizer was that it adsorbs most of the polycarboxylate superplasticizer molecules which should have adsorbed dispersed cement particles.In order to reduce the sensitivity of clay,this paper attempted to enhance the adsorption of polycarboxylate superplasticizer on cement by grafting anionic groups with stronger electronegativity on the main chain of polycarboxylate superplasticizer molecule.The results showed that grafting a small amount of anionic functional monomer 2-acrylamide-2-methylpropionic sulfonic acid?AMPS?could improve the dispersibility of the product,but the sludge resistance decreased;the dispersion of the product decreased when grafting more AMPS,but showed a certain anti-sludge effect.This might be related to the fact that the adsorption of polycarboxylate superplasticizer on montmorillonite was slightly enhanced after grafting AMPS,but it was significantly enhanced on cement.Grafting of 2-hydroxyethyl methacrylate phosphate?HEMAP?significantly reduced the dispersibility and clay resistance of the product.Polycarboxylate superplasticizers with different molecular weights were obtained by ultrafiltration or by changing the amount of initiator.It was found that the polycarboxylate superplasticizer with a larger molecular weight not only had better dispersing properties,but also had lower clay sensitivity.Adsorption studies also showed that the adsorption amount of polycarboxylate superplasticizers on cement and montmorillonite increased with the increase of molecular weight.The paper also studied the effect of the side chain structure of polycarboxylate superplasticizer on its clay sensitivity.It was found that the adsorption amount of PEG on montmorillonite was very large,and the adsorption amount of PEG on montmorillonite decreased with the increase of PEG molecular weight,and the adsorption amount of the same molecular weight of polyethylene glycol monomethyl ether?mPEG?was lower than PEG.It indicated that polyether side chains with small molecular weight and strong hydrophilicity might decrease the sludge resistance of polycarboxylate superplasticizer.In this paper,the normal temperature synthesis process of polycarboxylate superplasticizer and the effects of anion composition,molecular weight and side chain structure of polycarboxylate superplasticizer on clay sensitivity were investigated.This study could be conducive to the development of anti-mud polycarboxylate superplasticizer.