Preparation,Modification And Research Of Performance Of Waterborne Polyurethane Coatings

In the past, market demands for high performance and appearance were the pacemaker in the development of coatings. Mainly solventborne systems were in use. Today, a major change in coatings technology is caused by the restrictions on volatile organic compounds (VOC) in coatings. These government regulations combined with performance advantages are the key to the success of waterborne polyurethane. The preparation of waterborne PU, compared to solventborne systems, is more challenging because of working in the aqueous phase. Requirement for coatings with higher performance, formerly set by solventborne coatings, could not be matched by waterborne systems. Recently, the production and chemistry of waterborne PU have been studied successfully in overseas, and the waterborne PU coatings with good properties have been obtained from aliphatic diisocyanate. However in china, the aromatic diisocyanate (TDI etc.) is the main material to produce PU, and the study on waterborne system is still at initial stage.In this paper, the anionic waterborne polyurethane was obtained from toluene diisocyanate (TDI), polypropylene glycol (PPG), and dimethlolpropionic acid (DMPA), following a emulsification process. The reaction condition was determined and the effect of DMPA content, chain extender content, NCO/OH ratio on the state of dispersion and mechanical properties of the cast films were discussed in detail. IR spectrum showed that hydrogen bonds existed between the hard segments and the soft segments, which played a very important role on the mechanical properties. The existence of the hard segments gave PU an excellent mechanical strength, and the soft segments contributed to a good flexility.And the epoxy modified polyurethane dispersion was prepared by the grafting of epoxy resin with polyurethane. The effects of epoxy content and its addition mode on the state of dispersion and mechanical properties of the cast films were studied. IR spectrum showed that the chemical bond was formed between PU and EP. Compared with non-modified polyurethane, the water resistance, solvent resistant and mechanical properties of the epoxy modified polyurethane were greatly improved.