Modification Of Aqueous Polyurethane Dispersion

Aqueous polyurethane dispersions (PUD) display excellent properties and have attracted great interesting in the coatings field due to their controllable of soft and hard blocks. However, PUD possess some shortcomings including low solid content,low hardness and not so good chemisty-resistance, it is necessary to modified PUD.Novel PUDs modified by diisocyanate trimer (TT: trimer of toluene diisocyanate; HT: trimer of hexane diisocyanate) were synthesized via prepolymer mixing process. The effects of the contents of TT on the physic-chemical properties of PUD and films were discussed. The structures and thermal stability of PUD films were characterized by FTIR and thermal gravimetric analysis (TGA). The results showed that introducing 5-10% of HT into PUD improves surface dry rate and crosslinking degree of HPUD films; the HPUD films also display better performance including 45 min of the surface drying time, 80% of the crosslinking degree, 78% and 7% of the alcohol- and water-absorption rate as 10% of HT contents. On the other hand, HPUD possesses faster film hardness increasing rates but slightly lower final films hardness than the common PUDs. DLS analysis showed that the particle sizes and its distributions increase and storage stability decrease with increasing the HT content in the HPUD up to 20% during the storage process. TGA curves indicate that the HPUD films possess good thermal stability. TPUDs have higher hardness and crosslinking degree than the PUD, as well as lower the water/alcohol- absorption, while the storage stability, appearance, adhesive of TPUD films were similar to the PUD as the mass amount of TT≤3%. The TPUD film with 3% of the TT displays excellent physic-chemical properties including 0.75 of hardness, 78% of crosslinking degree and 5% water absorption. TGA curves indicate that the TPUD films modified by TT display better thermal stability than those of the common PUD.PUD and PUA was modified with TMP and HTBN. The effects of the addition process and amounts of TMP on the properties of PUD and PUA were discussed. It was found that the excellent PUD and PUA were achived as 2.5-3% of the amount of TMP, and used mid-added process. The coating performance analysis showed that TMP modification can significantly improve the properties of water-/stain-resistance, while the HTBN modification can make the adhesion much better. The excellent PUD modified with TMP and HTBN was achived and used as the high-grade wood paints.High solid contents waterborne polyurethane-acrylate hybrid emulsions (PUA) were synthesized by emulsion copolymerization of aqueous polyurethane dispersion (PUD) and acrylic monomers including methyl methacrylate (MMA) and butylacrylate (BA) in the present of azodiisobutyronitrile (AIBN), which PUD as an emulsifier and a reactant. The methods of preparation high solid contents emulsions were investigated, the effects of monomer categories and contents on the PUA properties were studied. Meantime, the structures and properties of PUA were characterized by FTIR spectra and thermal gravimetric analysis (TGA). The results indicated that PUA emulsions with high solid contents up to 45% were obtained when PUD/monomers were dispersed by using of 6000 rpm rotation speed for 20min, then thermal polymerized at 70℃for 1-2 h and added 0.70% AIBN as a post-addition initiator. PUA films display good performance including 15.5% water absorption, 6.9% alkali absorption, 22.6% ethanol absorption, 0.75 hardness, and good low temperature crack-resistance (-20℃,72h, film surface no crack) when the mass ratio of PUD/ monomers and MMA/BA are 1:1.2 and 2:1, respectively. TGA curves show that the PUA films containing MMA and BA display good thermal stability.Novel self-emulsifying PUD (NPUD) were prepared by the emulsification of self-emulsifying polymer blends in water, which the polymer blends typically consist of two kind of polyurethane prepolymers, one is a salt group containing polymer (P1), the other is a polymer without salt groups (P2). It was found that the particle diameters NPUD can be controlled by the amount of salt group containing polymer and the concentration of salt groups in the polymer. The properties of conventional PUD and NPUD were compared. The results indicated that the NPUD displays high solid contents, very low VOC contents, and the extremely low content of hydrophilic salt groups, NPUD film possesses high gross up to 95% and excellent water-and solvent-resistance.