Polycarboxylate high-performance water reducing agent bai is composed of zhi macromolecular compounds with sulfonic acid groups, carboxyl groups du, amino groups, and polyoxyethylene side chains, etc., in an aqueous solution, synthesized by the principle of free radical copolymerization. Structured polymer surfactants.
The main raw materials needed to synthesize polycarboxylate high-performance water reducing agent are: methacrylic acid, acrylic acid, ethyl acrylate, hydroxyethyl acrylate, sodium allyl sulfonate, methyl methacrylate, 2-acrylamide group -2-methacrylic acid, methoxy polyoxyethylene methacrylate, ethoxy polyethylene glycol acrylate, allyl ether, etc.
The initiators that can be used in the polymerization process are: persulfate initiation Agents, benzoyl peroxide, azobisisobutyl cyanide; chain transfer agents include: 3-mercaptopropionic acid, mercaptoacetic acid, mercaptoethanol and isopropanol.
Polycarboxylic acid polymers have a significant retarding effect on cement, mainly due to the carboxyl group acting as a retarding component. R-COO~ interacts with Ca2+ ions to form complexes, reducing the concentration of Ca2+ ions in the solution and delaying Ca(OH 2) Form crystals, reduce the formation of CHS gel, and delay cement hydration.
Carboxyl (-COOH), hydroxyl (-OH), amino (-NH2), polyoxyalkyl (-OR) n and other polar groups with strong affinity for water are mainly used for surface activity such as adsorption, dispersion, wetting, and lubrication , Provides dispersion and flow properties for cement particles, and increases the workability of fresh concrete by reducing the frictional resistance between cement particles and reducing the free energy of cement particles and water interface.
At the same time, polycarboxylates are adsorbed on the surface of cement particles, and the carboxylate ions give the cement particles a negative charge, thereby causing electrostatic repulsion between the cement particles and dispersing the cement particles, resulting in inhibiting the agglomeration tendency of cement paste (DLVO theory) ) To increase the contact area between cement particles and water to fully hydrate the cement.
In the process of dispersing cement particles, free water surrounded by agglomerates is released, which improves workability and reduces the amount of water mixed.