水性乳液/聚氨酯模型缔合增稠剂的触变性机理

以异佛尔酮二异氰酸酯(IPDI)与聚乙二醇(PEG,分子量为4000,6000和8000)为原料,以直链醇(C12,C14,C16和C18)为封端剂,合成了疏水改性乙氧基化氨基甲酸酯(HEUR),并将其应用于乳液增稠.采用核磁共振波谱(¹H NMR)、傅里叶变换红外光谱(FTIR)及凝胶渗透色谱(GPC)表征了HEUR的结构、分子量及其分布,研究了其在水性乳液中的流变行为.研究结果表明,当HEUR封端基团为C14,C16和C18,且质量分数增加到1. 0%以上时,增稠的乳液(Latex/HEUR)的流变曲线出现触变环,为触变性流体.当HEUR亲疏水比值(R_h)减小时,疏水性增强,触变环向低剪切速率(γ˙)方向移动,黏度下降率(Δη)增大;当HEUR用量增加时,触变环面积(S_loop)也增大.这些触变性特点归因于HEUR在乳液中的缔合作用、氢键作用及链缠结.利用扫描电子显微镜(SEM)和原子力显微镜(AFM)对Latex/HEUR的聚集态和表面形貌进行了表征.结果表明,随着HEUR封端基团链长增加,Latex/HEUR颗粒...

Thixotropic Behavior of Hydrophobically Modified Ethoxylated Urethane-thickened Waterborne Latex †

Hydrophobically modified ethoxylated urethanes(HEURs) were synthesized by preparing the prepolymers from the reaction between polyethylene glycol(PEG, M_n=4000, 6000, 8000) and isophorone diisocyanate(IPDI), and then end-capping the polymers with liner alkanols(C12, C14, C16, C18). The structure, molecular weight and polymer dispersity index(PDI) of HEUR were characterized by proton nuclear magnetic resonance( ¹H NMR), Fourier transform infrared spectroscopy(FTIR) and gel permeation chromatography(GPC) respectively, and the rheology behaviors of the HEUR-thickened latex were also studied. It was found that the rheological curve of the HEUR-thickened latex(Latex/HEUR) showed thixotropic loops when HEUR were substituted by C14, C16 and C18 and the mass fraction was more than 1.0%, indicating that these Latex/HEUR were thixotropic fluids. The location of thixotropic loops moved to low shear rate and the viscosity of Latex/HEUR dropped sharply with an increase of the ratio between the molecular weight of hydrophilic segment and that of the hydrophobic end. As the amount of HEUR increased, the thixotropic loop area(S_loop) showed the upward trend. These rheological behavior were attributed to the association, hydrogen bonding and chain entanglement of HEUR in latex. Scanning electron microscope(SEM) and atomic force microscope(AFM) were used to characterize the aggregation state and surface morphology of Latex/HEUR. The results showed that the size of Latex/HEUR particles increased and the surface became rough with the increase of the HEUR end group length.