甲基丙烯酸对聚合物乳胶粉再分散性影响机理

采用半连续种子乳液聚合法,以甲基丙烯酸(MAA)为壳层亲水功能单体,合成了丙烯酸酯原乳液,并通过喷雾干燥法制得具有可再分散性的聚合物乳胶粉.讨论了原乳液粒子粒径随pH值和MAA量的变化关系;重点研究了MAA量对乳胶粉水分散液稳定性、再分散乳液zeta电位、乳胶粒粒径分布及乳胶粉内部微观形貌的影响,并分析其作用机理.研究结果表明:原乳液粒子粒径随pH值的增大逐渐增大,且MAA含量越高,粒径增幅越大;随MAA量增加,再分散液稳定性增强,zeta电位绝对值增大,平均粒径逐渐变小,乳胶粉再分散性显著改善.透射电子显微镜(TEM)结果显示:当MAA含量较高时,乳胶粉内部出现较大孔径的中空微孔结构.中空微孔结构提供水分向乳胶粉内部扩散通道,因而优化其水分散性,再分散乳液的"绒毛结构"与较高的zeta电位赋予其优异的分散稳定性.

Influencing Mechanism of Methacrylic Acid on the Redispersion Properties of Redispersible Polymer Powders

Acrylic polymer emulsions were synthesized by semi-continuous seeded emulsion polymerization and the corresponding redispersible polymer powders were prepared by spray drying. Methacrylic acid (MAA) was used as the hydrophilic shell monomer. The influences of the amount of MAA on the average particle size of the original emulsion, the dispersion stability, zeta potential, and size distribution of the redispersion emulsion were investigated. The results show that with an increase in the amount of MAA, the particle size of original emulsion, the dispersion stability, and the zeta potential of the redispersion emulsion increased significantly. The size distribution of the redispersion emulsion with a high amount of MAA was unimodal and similar to the original emulsion indicating excellent water-redispersibility. Transmission electron microscopy (TEM) was used to characterize the internal microtopography of the redispersible polymer powder, and results showed that with a higher amount of MAA, millipores with larger pore sizes were present in the transection of the redispersible polymer powder. When polymer powders are redispersed in an aqueous phase, large micropores provide a more convenient channel for water permeation, which optimizes the redispersibility. The hairy structure and higher zeta potential endow the redispersion emulsion with excellent redispersion stability.