Design,Preparation And Properties Of Polyurethane Dispersions Carrying -NCO Or -OH Groups

Water-based coating has recently become a trend in the world coating industry.Two-component waterborne polyurethane(2K-WPU)is increasingly becoming a research hotspot in this area due to its low VOC contents and excellent film properties.2K-WPU consists of aqueous polymer polyols and aqueous dispersion polyisocyanates,of which the structures,properties,the molar ratio,and their compatibility show major effects on 2K-WPU properties.At present,2K-WPU has some disadvantages including bad storage stability of the polyisocyanates,slow drying rate,poor appearance,poor chemical resistance and low film hardness,seriously restricted its application and development.To solve theses problems,polyurethane dispersions carrying-NCO(WDP)and-OH(OH-PUD)were synthesized respectively,and the influence of various factors on the storage stability of WDP and OH-PUD and film properties were investigated.A series of novel water-dispersible polyisocyanates(WDPs)were synthesized with hexamethylene diisocyanate isoxyanurates(HDI trimer),dimethylol butanoic acid(DMBA),polyethylene glycol monomethyl ether(MPEG-600)and 4-cyclohexanedimethanol(CHDM)as materials.The effects of molar ratios of DMBA/MPEG and CHDM/MPEG and their amounts on properties of WDPs including the water dispersibility,storage stability,film hardness,and water resistance were also investigated.It was found that WDP prepared with DMBA/MPEG displayed good properties while the storage stability decreasing with increase of the DMBA contents.However,the introduction of CHDM could efficiently improve the storage stability,hardness and water resistance of 2K-WPU films due to the rigid cyclic structure and hydrophobicity property of CHDM.WDPs exhibit the good properties with excellent storage stability,short tack-free times,high hardness,good water resistance,excellent surface appearance and gloss of the 2K-WPU films with 3:7:3 of the molar ratio of DMBA/MPEG/CHDM.The high-functionality OH-PUDs were synthesized with sulfonic polyester diol as a hydrophilic chain extender,and alcohol-amine compounds as end-cappers.Effects of factors like synthesis process,SPED contents,soft segment composition and proportion and end-capper types on OH-PUD and its 2K-WPU were investigated.The results are as follow:(1)solid contents of OH-PUD can be improved effectively with SPED as a hydrophilic chain extender.(2)OH-PUD displayed the best stability when the PU prepolymer was blocked after the dispersion step.(3)Polyester-based 2K-WPU films showed higher transparency than that of polyether-based owing to the high polarity of ester groups and improved compatibility with WDP.The film transparency become better with increasing NCO/OH molar ratio and decreasing the molecular weight of polyether diol.(4)OH-PUD exhibits the good properties with 47% of the solid content,0.73 of the pendulum hardness and 3.38% of the water absorption with PCL220 as the soft segment,Tris as the end-capper,40% of the soft segment contents,1.5–1.7 of the NCO/OH molar ratios,12.5% of the SPED contents,40% of the EDA chain extension.