| Waterborne polyurethane (WPU) has become an excellent environment-friendly material because of its low VOC and energy saving. However, because the molecules contain hydrophilic groups, the resin has poor water resistance, thermal instability, low hardness and other defects, which limit its use. In order to overcome these shortcomings and improve the practicability of WPU, Chain structure is changed through adding modifiers according to molecular design.Polyester-type WPU emulsions were prepared by 1,4-butanediol (BDO) and bisphenol A as chain extenders, and polyester-polyol with big cohesive energy as soft segment, following a prepolymer mixing process. The effects of raw material formulation and process conditions on the emulsion and film properties were investigated. The results show that when n(-NCO): n(-OH) is 1.5:1, the amount of DMPA is 5～7%, the total amount of BDO and bisphenol A is 5% and the ratio is 3:2, and when the degree of neutralization is 90-100%, the temperatures of the poly early stage, the chain extender stage and the neutralization stage are 85 ℃,80℃ and under 40 ℃ respectively, the emulsion has good appearance and stability and the film has good water resistance prepared by pre-neutralization and inverted dispersion process.Epoxy-modified waterborne polyurethane (EPU) emulsions were prepared with bisphenol A type epoxy resin as a chain extender and a crosslinking agent simultaneously. Ring opening of the epoxy group was demonstrated by FT-IR tracking and the epoxy-modified mechanism was discussed. The effects of the value and amount of epoxy resins on the emulsion and film properties were investigated. The results show that, when the epoxy value is 0.44 and the amount is 8%, the particle size is small, the viscosity is moderate, and the stability is good, the tensile strength of the film is up to 42MPa, the hardness is up to 1H. Compared with the unmodified WPU, the water absorption of the EPU descends from 10.3% to 4.4%, the water contact angle becomes larger, and the temperature improves from 241℃ to 267℃ when the weight loss is 5%.Silicon-terminated modified waterborne polyurethane (Si-WPU) emulsions were prepared with silane coupling agent (KH-550) as a capping agent, which introduced the high-energy Si-O bond into the system by the reaction of-NH2 and-NCO. The effects of the amount of KH-550 on the emulsion and film properties were investigated. The results show that when the amount of KH-550 is 4%, the emulsion has good appearance and stability, the water absorption decreases to 3.3%, the water contact angle increases to 89.46°, and the temperature improves from 241℃ to 279℃ when the weight loss is 5%, as well as the both temperatures of two largest loss rates increase.Composite-modified waterborne polyurethane (Si-EPU) emulsions were prepared with the E-44 as crosslinkers and the KH-550 as capping agents. The effects of the amount of E-44 and KH-550 on the emulsion and film properties were investigated. The results show that when the amount of E-44 is 7%, the amount of KH-550 is 3%, the emulsion and the film have the best performance. The water resistance and heat resistance of Si-EPU are better than the unmodified or single-modified WPU. The water absorption is only 2.3%, and the water contact angle is 93.91°.The temperature raises to 287℃,when the weight loss is 5%. The composite modified waterborne polyurethane emulsions have good overall performance and could be used as high-grade anticorrosive coatings.Waterborne polyurethane anti-rust coatings were prepared with the Si-EPU emulsion, modified composite iron titanium pigments and calcium carbonate fillers as the base materials. The optimal formula was chosen through three factors quadratic regression orthogonal experiment and EXCEL. The film has good anti-rust property. Its adhesion is 0 and its hardness is 2H. |
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