Preparation And Study On Rheological Mechanism Of Hydrophobically Modified Ethoxylated Urethane Thickeners

Thickeners have attracted wide attention because they can improve the drawback of the environmentally friendly waterborne coatings,such as low viscosity.Hydrophobic modified ethoxylated urethane(HEUR)thickeners,which have thickening mechanism different from that of traditional thickeners,can endow various water-based coating formulas with excellent rheological properties.Further optimization of its own performance by changing the structures of HEUR and investigating rheological rules is still one of the research hotspots In this paper,the Uni-HEUR with strong hydrophobicity,the S-G HEUR with weak hydrophobicity and a new kind of HEUR branched by hydrogenated castor oil were designed and prepared,and the rheological rules in their acqueous solution and waterborne latex were mainly discussed.The contents as follows:Uni-HEUR,including HEURP(X)and HEURP(bY),were synthesized by preparing the prepolymer obtained from the reaction between polyethylene glycol(PEG,Mn=4000,6000,8000)and isophorone diisocyanate(IPDI),the value of NCO/OH was2:1,and then end-capped with liner alkanols(C12,C14,C16,C18)or branched alchols(b C12,b C125(mixed alchols),b C16 and b C18).S-G HEUR,including HEURP(14)-N and HEURP(b16)-N,were synthesized by preparing the prepolymer obtained from the reaction between PEG(Mn=4000,6000,8000)and IPDI,the values of NCO/OH were 3:2?4:3 and 5:4,and then end-capped with liner alkanol(C14)or branched alkanol(b C16).A new type of HEUR,namely HCO-HEUR6(bY)-M,were synthesized by preparing the prepolymer obtained from the reaction between PEG(Mn=4000,6000,8000)and IPDI,the value of NCO/OH was 2:1,then the prepolymers were branched by hydrogenated castor oil,and finally end-capped with branched alkanols(b C13,b C16 and b C18).The structure,molecular weight and polymer dispersity index(PDI)of the above three types of HEURs were characterized by proton nuclear magnetic resonance(¹H NMR),infrared radiation(IR)and gel permeation chromatography(GPC)respectively.It was found that both their acqueous solution and thickened latex behaved mainly as viscous fluid.According to the results of Dynamic light scattering(DLS),the increase of hydrophobic chain length,hydrophilic segments length or concentration is conducive to the formation of larger micelles and multi-size micelle aggregates in aqueous solutions.In aqueous solutions,steady shear and Three interval thixotropy test(3ITT)indicated that compared to Uni-HEURs were substituted by C12?b C12 and b C125,the thickening efficiency of Uni-HEURs that were substituted by C14?C16?b C16 and b C18 was better and the behaviors were shear-thinning,with obvious thixotropy.S-G HEUR aqueous solutions tended to show lower viscosity and at low(?)and weakened thixotropy,but maintained high viscosity at high(?).HCO-HEUR6(bY)-M had higher thickening efficiency than that of HEUR6(bY).In waterborne latex,Uni-HEURs substituted by C14,C16 and C18 showed thixotropic loops,with high viscosity in low shear rate((?))and obvious thixotropy.With hydrophobic chain length increased,the association enhanced,the locations of thixotropic loops(W_loop)moved to low(?)and the surface of HEUR-thickened latex also became rougher.And the thixotropy of the system based on S-G HEUR decreased significantly.The fitting results proved that the viscosity evolution and thixotropy could be predicted by Cross equation and the second order kinetic equation.HCO-HEUR6(bY)-M could effectively improve the viscosity of HEUR6(bY)at low shear rates without changing the viscosity at high shear rates.It was found by scanning electron microscopy(SEM),atomic force microscopy(AFM),3ITT and leveling test that,the surface morphology of Uni-HEUR thickened latex becomes rougher as the length of the terminal group increased and the levelling property of S-G HEUR got better compared to that of Uni-HEUR.For HCO-HEUR6(bY)-M,the branching of prepolymers of HEUR6(bY)did not result in better levelling property.The viscosity of HEUR-thickened latex could reach 36.5 Pa·s(the viscosity of latex is about 0.003 Pa·s)at 1.5%.In production and application,the rules obtained in this paper could be used to adjust the end group,molecular weight or the ratio between hydrophilic and hydrophobic segement of HEUR to meet the requirements of the latex storage and construction technology.