Compared with the traditional water reducing agent, polycarboxylic acid high-performance water reducing agent has many characteristics:
1. In the synthesis process, polycarboxylic acid high-performance water reducing agent is synthesized by unsaturated monomer copolymerization rather than polycondensation used in traditional water reducing agent. Therefore, there are many synthetic raw materials of this kind of water reducing agent, such as polyethylene glycol, (methyl) acrylic acid, allyl alcohol polyoxyethylene ether, etc.
2. In terms of molecular structure, the molecular structure of polycarboxylic acid high-performance water reducer is linear comb structure, rather than the single linear structure of traditional water reducer. There are many different active groups polymerized on the main chain of this kind of water reducer, such as carboxylic acid group (- COOH), hydroxyl group (- OH), sulfonic acid group (- SO3Na), which can produce electrostatic repulsion effect; Its side chain has hydrophilic nonpolar active groups and has high steric effect.
Due to its wide source of raw materials and unique molecular structure, it has incomparable advantages over the previous two generations of water reducing agents. In addition, it does not use formaldehyde in the synthesis process. It is a green environmental protection product. Therefore, it has become one of the key and hot spots in the research field of concrete admixtures.
In the synthesis of polyester polycarboxylic acid series high-performance water reducer, the synthesis of polyethylene glycol monomethyl acrylate is the key factor to determine the performance of water reducer. Therefore, we should determine the best esterification process and achieve the esterification rate of more than 95% through the study of different molecular weight polyethylene glycol and methacrylic acid under different molar ratio, different reaction temperature, different amount of polymerization inhibitor, different amount of catalyst and different reaction time.
The optimum polymerization process was determined by studying the experimental conditions such as different amount of initiator, different amount of molecular weight regulator, different reaction temperature and different reaction time.
About pH control. The pH value is better in the range of 6-7: when the pH value is lower than 4, the polymer is turbid, and its net slurry fluidity and concrete slump are free; When the pH value is higher than 9, the net slurry fluidity and concrete slump begin to decrease.
The development and application of polycarboxylic acid based high-performance water reducer is a milestone in the development history of concrete admixture. Because of its large adjustability of molecular structure, we should give it higher performance by changing the type and number of functional groups in the molecular structure. Such as low temperature early strength type, high slump retention type, anti shrinkage type, low viscosity type and so on. Undoubtedly, polycarboxylic acid high-performance water reducing agent will become the development direction of concrete admixture technology, and its market will also face a great development opportunity.
