自交联型可再分散苯丙乳胶粉的制备及水分散性与耐水性的协同优化研究

摘要

Self-crosslinking redispersible styrene-acrylate copolymer powder with both excellent water-dispersibility and good water-resistance was prepared via spray drying by adding self-crosslinking monomer, N-Methylolacrylamide (NMA), to the shell of the latex particles. FT-IR, TEM, SEM, Malvern particle size analysis and AFM were adopted to characterize the original emulsion, polymer powder or redispersion emulsion. The neutralization, spray drying and redispersion process of the emulsion were studied respectively and the mechanism of the emulsion having both the properties of water-redispersibility and water resistance was investigated. The self-crosslinking styrene-acrylate emulsion possesses uniform nano-scale soft core/ hard shell structure. The particle sizes of redispersible polymer powders are in the range of 2~20 μm, whereas the average latex particle size of dispersion emulsion is 182 nm, which indicates that the polymer powder possesses excellent water-redispersibility. Thicker“hairy structure”and hydrated shell are formed in the neutralization process because the hydrophobic interaction is weekend by adding NMA monomer into the shell of styrene-acrylate latex particles. During the transient drying process, fusion and crosslinking between different latex particles are impeded because of longer physical distance, and therefore better redispersibility is obtained. The water absorption of polymer film made from self-crosslinking redispersible polymer powder is lower than that of unmodified polymer powder by 40%. Hence both water-redispersibility and water resistance of styrene-acrylate copolymer powder can be improved by the self-crosslinking modification of NMA.%　　软核硬壳结构苯丙乳液壳层引入自交联单体 N-羟甲基丙烯酰胺(NMA)，经喷雾干燥获得水分散性和涂膜耐水性俱佳的自交联型可再分散乳胶粉。采用 FT-IR 光谱、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、马尔文激光粒度分析、原子力显微镜(AFM)等手段对原乳液、乳胶粉、再分散乳液进行表征，研究了乳液中和、干燥和再分散过程，分析了乳胶粉能兼顾再分散性和聚合物涂膜耐水性的机理。研究结果表明，自交联型苯丙乳液具有规整的软核硬壳结构，乳胶粉的粒径在2~20μm，遇水可迅速分散得到平均粒径182 nm 的再分散乳液。乳液壳层添加 NMA 能削弱乳胶粒表面的疏水缔合作用，形成更厚的“绒毛结构”和水化层，因而抑制干燥时的乳胶粒凝聚融合，阻止乳胶粒之间的交联反应，优化了乳胶粉的亲水分散性。自交联作用使可再分散乳胶粉所成聚合物膜的吸水性降低40%以上，因此，采用 NMA 交联改性同时优化了苯丙乳胶粉的水分散性与耐水性。