Study On Polyurea Coating Systems And Their Tribological Properties

Towards the protection of concrete structures of hydraulic architecture in hydropower construction of China, the feasibility and the key technology of the application of polyurea coatings to the protective concrete structures of hydraulic construction are studied. Based on the deep analysis of anti-sediment-flow erosion of concrete structures of hydraulic architecture and the properties of polyurea coatings the coatings of polyurea and polyaspartic ester are developed, and the composite coating systems are designed, which are suitable for the protection of concrete surface, according to the requirements of wear resistance and adhesion strength in the concrete surface; Through a series of mock tests (including the erosion, wet adhesion, physical and chemical properties and surface analysis) under the hydraulic conditions, the wearing and adhesion mechanism of these coatings under the condition of erosion by sand aquifer flow at a high speed are discussed. The main contents and the significant new results are shown as follows:1. From the special demand of anti-erosion protection of hydraulic construction surface, the ingredients of polyurea A, B components, their preparation, and their relationship with the performance of the coatings are studied intensively. Thereby, a new polyurea coating has been developed. The mechanical and physical properties of the new polyurea coating are excellent.2. The polyaspartic acid ester by the use of the domestic raw materials (poly propylene oxide diamine and diethyl maleate) is synthesized. The structure of polyaspartic acid ester and its coating are characterized by using NMR, IR and DSC curves, and the synthesis process is optimized. The polyaspartic acid ester coating has good adhesion, mechanical physical and chemical media properties. However, its wear-resistant performance is not good as the conventional polyurea coatings in the erosion wear conditions or dry conditions.3. The tribological properties of the polyurea coatings are studied intensively. The erosion performances of the coatings are evaluated by using the high pressure jet impact erosion testing machine firstly, and the erosion mechanism is explored. Studies showed: (1) The effect of polyurea coating compositions on erosion-resistant performance of the coatings is mainly reflected in the influence of bubbles arising during the preparation of the polyurethane-urea coatings. The key to improve their wear resistance is to decrease the bubbles of the coatings by adjusting the material compositions and spray process. (2) The polyurea coatings have superior wear performance than polyurethane/polyurea hybrid coating systems and display an excellent performance of anti-erosion under both conditions of dry friction and erosion and also an improved sensitivity on the erosion angle. (3) Under the dry-friction condition, the oxidation-wear process occurs on spray polyurea surface, while such a process does not easily happen under the high-speed water jet sandy condition. (4) The polyurea coating is provided with higher damping, hardness and thermal stability, which makes it withstand the heating created by high inner friction; the heat can be transmitted to the test fluid in time so that the coating has an excellent wear-resistance performance. (5) On the basis of Bitter's erosion theory of ductile materials, the erosion model of polyurea is established, the erosion behaviors of ductile materials at different impact angle and velocity are described, and the erosion law is also proposed, which holds that the maximal cutting wear is at the impact angle about 31.5°and the maximal deformation wear at the impact angle close to 90°.4. The wet-adhesion measurement was first applied to measure the adhesion strength of the polyurea coating on the surface of concrete, which provides important scientific data and finds a better solution to characterize the adhesion strength between the polyurea coating and the concrete surface. The solvent-free epoxy sealing coating is developed with an excellent adhesion by choosing liquid epoxy resin, reactive diluents and curing agent. This solvent-free epoxy sealing coating improves the adhesion of the coating system and enhances the strength of the concrete surface. The failure of the adhesion resulted from the damage of the physical adhesion between the polyurea coating and concrete. However, the failure of "solvent-free epoxy sealing coating + polyurea coating" system results from both the damage of the physical adhesion between the coating and concrete and the damage of cohesion of the sealing coating itself.5. The "polyaspartic acid ester + polyurea coating" composite polyurea coating system on the surface of the concrete sample was proposed and prepared firstly as the protective coating system of hydraulic concrete construction. The polyaspartic acid ester coating can enhance the adhesion of the coating system and the strength of the concrete surface. The composite polyurea coating system exhibits an excellent erosion resistance so as to be more suitable for the protection against the erosion under the hydraulic condition.