Preparation And Properties Of Associative Waterborne Polyurethane Thickener

Hydrophobically modified ethoxylated urethane(HEUR)is often used to adjust the rheological properties of coatings,and can improve the anti-sagging performance of coatings,prevent cracks and enhance the storage stability of coatings.The present HEUR has some disadvantages including poor thickening effect,poor anti-solvent interference performance,and containing organic tin and organic solvents.Herein,this paper explored the environmental friendship process of HEUR,synthesized hydrophobic end branched HEUR and silicone modified HEUR,and characterized their properties.The main contents are as follows:(1)In order to realize the environmental friendship HEUR,a series of environment-friendly linear HEUR were prepared by the reaction of PEG6000 and hexadecanol with HDI in the molar ratio of-NCO:-OH=1.02.The effects of catalyst and cosolvent on the properties of HEUR were studied.It was found that using bismuth carboxylate as catalyst instead of DBTDL and isododecanol polyoxyethylene ether as cosolvent instead of organic solvent,environmental friendship HEUR could be prepared.The viscosity,thickening efficiency,thixotropy,molecular weight and its distribution of the product were very close to the present linear HEUR(L-HEUR),and could completely replace L-HEUR.(2)In order to improve the thickening efficiency of associating waterborne polyurethane thickener,monohydric alcohol with two hydrophobic long chains was prepared by the reaction of glycerol and octadecyl isocyanate in the molar ratio of-NCO:-OH=1:1.31,and then branched hydrophobic terminal modified HEUR(B-HEUR)with four hydrophobic long chains was prepared by the reaction of PEG 6000 and HDI in the molar ratio of-NCO:-OH=1.08:1.The critical micelle concentration,thickening performance and acid-base stability of B-HEUR and L-HEUR were tested.It was found that B-HEUR had lower critical micelle concentration,thickening efficiency of B-HEUR was 2.35 times that of L-HEUR,and thixotropic index of B-HEUR was high up to 4.42.In addition,B-HEUR has good film-forming properties.(3)In order to improve the anti-solvent interference ability of HEUR,three kinds of silicon modified HEUR(Si-HEUR)were prepared with different hydroxyl(amino)double ended PDMS.The aggregation behavior of Si-HEUR in aqueous solution and the rheological behavior of Si-HEUR in polymer emulsion system were characterized,and the thickening properties and solvent-resistance of three kinds of Si-HEUR were also studied.It was found that the thickening efficiency of Si-HEUR(300)was 1.26 times of B-HEUR and 2.96 times of L-HEUR.The results show that the anti-solvent performance of Si-HEUR(300)is 3 times higher than that of non-silicon HEUR,and it displays outstanding anti-solvent interference performance.