Research On The Mechanism Of Water Diffusion And Waterproof Structure Of Rigid Polyurethane Foam Material

LNG(Liquefied natural gas)vessels building is one of the key point of national 11th Five-Year Plan. However, the thermal insulation material applied under -163℃, which used on the liquid tank, is totally depends on importation. We are entrusted by the Shanghai Hudong-Zhonghua Shipbuilding (Group) Company to carry out the research in the localization of the thermal insulation material which also has good low temperature resistance. The material preparation and molding has already been completed, but some problems have been found during the use period. Water has a great influence on coefficient of heat conductivity and the service life for the material.However, there are no reports about the distribution and trajectory of water in the polyurethane material both at home and abroad until now. Firstly, water is a small molecule substance that is hard to be observed directly, secondly, the complex structures of polyurethane after foaming makes it even more difficult. In the past, gravimetric method is often used to research the diffusion absorption of water in polyurethane foam. However, the trajectory of water diffusing in the polyurethane material can not be observed directly, and the conclusion of the research is conjecture by theory, its reliability cannot be guaranteed. Therefore, the method we adopt to study the trajectory of water diffusing in the polyurethane material is the key point to lower the coefficient of heat conductivity and the prolong service life.In this paper, the method that remark the water path in an indirect way is used to solve the problem mentioned. Firstly, dissolove NaCl in water, use the microtechnique to observe the distribution of NaCl in polyurethane, and then conjecture the path of the water. At the same time, optical microscope and electrochemical impedance spectroscopy have been used to research the dynamic diffusion process on the surface and internal of the polyurethane foam, and the water transmission model has been brought up. Based on this foundation, we summarized the relevant research for internal and abroad, and took the two fundamental theories which influenced the foaming—reducing the surface tension and increasing the nucleation points as basis to select siloxane with different surface activity and laminal filler--sericite and its modifiers which was featured by heterogeneous nucleation to study. EIS,SEM,TG,FT-IR,Shore A durometer and metalloscope were used to characterize the modified foam system. Then establish relations between molecular structure and effect through the connection between the molecular structure and preventing water effect. This thesis came to the conclusion that,1) The problem of the adsorption sitesand and trajectory of water in the foam system were solved by using the NaCl tracer, EIS and electrochemistry together. The special capillary structure has been found in water transmission. The dynamic mechanism model of water collapse diffusion has been put forward combining with the result of dynamic diffusion process on the surface and internal of the polyurethane foam;2) Adding silane coupling agent can effectively extend the time for water diffusion resistant. The resistance value of the material added by KH550 and KH560 is above 108?*cm2 after 900h-immersion, far longer than the pure polyurethane foam system which value drop down below 108?*cm2 after 48h. However, due to the increase of the phase interface and the decrease of the porosity by closed pore, flake sericite system is poor at waterproof effect.3) The foam structure is an important factor that affects the water diffusion. The whole bubble could prevent the water diffusion, but the marginal matrix resin would have high hydroscopicity.4) The relationship between HLB value of silane coupling agent and the time for water diffusion resistant is quadratic function, T= 952.37268+ 28.71987X- 6.47857X2; T stands for the time of water diffusion resistant of foam system whose impedance value is above 108?*cm2, X stands for the HLB value of silane coupling agent.5) By analysis the infrared spectrum technology combined with the chemical reaction theory, the hydrolytic crosslinking of siloxane did well in waterproof. And the waterproof model has been established in the foam system. The–NH in the ammonia ester bond and urea linkage in the molecular chain of the resin has a great influence on water absorption, and we can the lower water absorption rate by reduce the number of active hydrogen.