The Preparation Of Waterborne Polyurethane Dispersions With Hydroxyl Groups And The Study Of Structure And Properties

Two-component waterborne polyurethane(2K-WPU) coatings have both the characteristics of excellent properties of two-component polyurethane coatings and Low VOC of waterborne polyurethane coatings, It has been the focus of research in each country during the near decade. 2K-WPU is composed by two components: water-dispersible resin with hydroxyl groups and polyisocyanates. This paper has prepared the polyurethane dispersions with hydroxyl groups, paying attention on the relation of structure and properties of waterborne dispersions.First, We have prepared the waterborne polyurethane dispersions with hydroxyl groups by prepolymer process, analyzed their chemical structure, researched the particle diameter and distributing of the waterborne dispersions and their influencing ingredients, discussed the rheology properties and their influencing ingredients and analyzed the relation of particle diameter, particle distributing and rheology properties. The results indicate: With the increase of DMPA content, the particle average diameter minishes, the particles distributing gets narrow, stability gets well; viscosities of system ascend and intrinsic viscosities also ascend. With the increase of mol ratio of [NCO]/[OH], the particle average diameter increases, the particle distributing gets wide, stability gets bad; the viscosities of system gradually descend and intrinsic viscosities also descend. The stability of waterborne dispersions is good with the use of chain extenders; with the increase of the content of diethylene-glycol, the viscosities of system gradually ascend; with the increase of the content of 1,4-butylene-glycol, the viscosities of system gradually descend. In addition, the prepolymer process is fit for the condition of leaning alkalescence, when the PH value is smaller than 8, with the increase of PH value, the particles decrease quickly; when the PH value is larger than 8, with the increase of PH value, the particles nearly immovable; and with the increase of PH value, the specific viscosities increase.In addition. We have prepared the waterborne polyurethane dispersions with hydroxyl groups by one-step process, analyzed their chemical structure, researchedthe particle diameter,distributing of the waterborne dispersions and their influencing ingredients. The results indicate: With the increase of DMPA content, the particle average diameter decreases, the particle distributing gets narrow and stability gets well; At the same condition, the average particle of waterborne dispersions prepared by 307110 polyester are smaller than the average particle of waterborne dispersions prepared by 308110 polyester. With the increase of mol ratio of [NCO]/[OH], the particle diameter first decreases then increases; the particle distributing first gets narrow then gets wide; The particle diameter is smallest when the mol ratio of [NCO]/[OH] is 0.9, and the stability is best in this condition. The different neutralization reagents have different functions, When we use the NaOH and NH₃·H₂O as the neutralization reagents, the particle diameters are big, and the stability isn't good; When using the TEA as the neutralization reagents, the appearance and stability are both good, It is the best choice for neutralization reagents.To the waterborne polyurethane dispersions with hydroxyl groups prepared by prepolymer process and one-step process, The effects of DMPA content on the particle diameters and distributings are same; but effects of the mol ratio of [NCO]/[OH] are not all same.