Modified Polyurethane Waterproof Sealant Preparation, Structure And Performance

Because of the good tensibility and tensile-strength, excellent endurance of water, low temperature, grind, acid and alkali, polyurethane waterproof sealant has been widely used in architecture, water conservancy and public service in America, Japan and other developed countries since 1980s.With the rapid development of architecture and water resource facilities in china, as well as the high requirements of the quality of the project, the demand for high quality waterproof sealant is increasing. However, due to its high price, it is difficult to introduce pure polyurethane waterproof sealant. So during the past several years, we often pad polyurethane waterproof sealant with coal tar. But this kind of waterproof sealant contains many poisonous and harmful substances and it will do harm to people's health, so the government has limited its use.In our country petroleum resin is overstocked in a large volume now, its price is low, it is harmless to environment and has fleet color as well as an excellent ornamental performance, most of all ,it can be compatible with prepolymer of polyurethane .so we can use petroleum resin as a kind of padding to produce a new modified polyurethane waterproof sealant.This research will not only popularize the use of petroleum resin, but also reduce the cost of polyurethane sealant, and decreases pollution. Therefore, it is significant to do research in modified polyurethane waterproof sealant with petroleum resin.In this research, the prepolymer of polyurethane is synthesized with polyether and toluol diisocyanate and NCO% is controlled. Use the prepolymer as component A and component B is made up of petroleum resin, padding and other elements, then use water as extender to synthesize petroleum resin polyurethane waterproof sealant. At the same time the chemical structure, the configuration structure, the mechanical property, the thermal property, the rheological behavior and the water resistant property of the petroleum resin polyurethane waterproof sealant are analysised and researched. The result is shown as following:1. When the reactive temperature is 85±2°C and the reaction time is five hours the prepolymer of polyurethane can be synthesized .It can fully accord with the requirement to use of modified polyurethane waterproof sealant with petroleum resin.2. Petroleum resin modified polyurethane waterproof sealant which has a good mechanical performance is synthesized for the first time with the prepolymer of polyurethane and petroleum resin ,extender, stuffing,activator and other materials. The factors which influence the sealant mechanical performance are discussed such as the content of petroleum resin, padding and -NCO%, as well as the kind of activator and extender and so on. The surface dry time of the polyurethane sealant is less than 24 hours, tensile strength may reach above 1.5MPa; elongation at break can reach above 450%, solid content obtains above 90%. Its property accord with the excellent product requirement of The Industry Standard (JC482-1992 ) .3. Its waterproof property is studied, the water absorption retains below 10% after 3 days immersing at room-temperature, and it can keep its mechanical property. So it has a good waterproof property.4. According to IR and SEM, the structure of modified polyurethane sealant is studied. The result shows that petroleum resin is used as a nonreactive component. Petroleum resin is compatible well with prepolymer of polyurethane.5. According to DSC, TG and DMA, the thermal properties of modified polyurethane waterproof sealant is studied. The result shows that petroleum resin debases Tg of the sealant and adds the plasticity of the sealant in a certain degree.The Tg₁of the flexible segment is about -20°C, while the Tg₂ of the rigid segment is about 80°C. The thermal degradation process of the sealant follows two steps. Through the Coats-Redfern method, the thermal degradation E_a1 of the first phase is 110.9kJ/mol, this process accords with the A₂ Nucleation and growth (Avrami equation (1)) mechanism of the Sigmoidal curves; the thermal degradation E_a2 of the second phase is 168.9kJ/mol , this process accords with the D₃ Three-dimensional diffusion(Jander equation)mechanism of Deceleration curves.6. The rheological behavior of the sealant is studied .The result shows that the sealant is pseudoplastic fluid, its non-newtonian exponent is no more than 1 and will increase with the increase of temperature and decrease with the increase of the petroleum resin content. Its apparent viscosity will decrease with the increase of shear rate and the increase of the temperature. Its flow activation energy is about 7.3kJ/mol in the condition of test, and this shows that the sealant has a preferable fluid capability.