不同酯类单体对缓释型聚羧酸减水剂分散性能及分散保持性能的影响

为探究不同酯类单体对缓释型聚羧酸减水剂分散性能及分散保持性能的影响规律和作用机理,采用不同分子结构酯类单体作为改性原料制备不同缓释型聚羧酸减水剂,并通过水泥浆体经时流动度、Zeta电位、总有机碳、电导率、傅里叶红外光谱、核磁共振氢谱等测试分析其宏观分散性能及分散保持性能与微观结构的变化规律及作用机理。结果表明:采用单酯类单体(丙烯酸羟乙酯、丙烯酸羟丙酯、丙烯酸甲酯)和双酯类单体(马来酸二甲酯)作为功能单体改性的缓释型聚羧酸减水剂分散保持性能较为优异,4 h时流动度相比初始流动度仍有所提升,同时相比未改性空白组,4 h 时流动度显著提升,后期分散性能更为优异。主要机理为:碱性环境下酯基在水泥浆体中缓慢水解出锚固基团羧基阴离子,发挥分散作用;不同分子结构的酯类单体位阻效应和基团电负性存在差异,导致水解速率和水解程度不同,从而使各种缓释型聚羧酸减水剂分散性能及分散保持性能存在差异。

Effects of Different Ester Monomers on Dispersive Performance and Dispersive Retention Performance of Slow-Release Polycarboxylate Superplasticizer

In order to investigate the effects of different ester monomers on the dispersion performance and dispersion retention performance of slow-release polycarboxylate superplasticizer and their action mechanism, different slow-release polycarboxylate superplasticizers were prepared with different molecular structure ester monomers as modified raw materials. The macroscopic dispersion performance and dispersion retention performance, and the microscopic structural change and action mechanism were analyzed by the tests of fluidity of cement paste with time, Zeta potential, total organic carbon, electrical conductivity, Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy. The results show that the dispersion retention performance of slow-release polycarboxylate superplasticizer modified with monoester monomer (hydroxyethyl acrylate, hydroxypropyl acrylate and methyl acrylate) and diester monomer (dimethyl maleate) as functional monomers are superior while the fluidity at 4 h is still improved comparing to the initial fluidity. At the same time, compared with the unmodified control group, the later dispersion performance is better, while the fluidity at 4 h is significantly improved. The main mechanism is as follows: the ester group is slowly hydrolyzed in the alkaline environment of cement paste and produces the anchoring group carboxyl group to achieve the effect of dispersion. The steric hindrance effect and the electronegativity of the contained groups with different molecular structures lead to different hydrolysis rates and degrees of hydrolysis, resulting in different dispersion performance and dispersion retention performance of various slow-release polycarboxylate superplasticizer.