Preparation Of Geopolymer Based Waterborne Inorganic Coatings

In this thesis,a kind of waterborne inorganic coatings based on geopolymer technology has been studied.Geopolymer,as a green cementing material,has been widely concerned by researchers because of its superior and unique characteristics such as its special condensed matter network structure,which combines some characteristics of organic polymer,cement and ceramics.As a highly active material,metakaolin contains a large number of amorphous SiO₂and Al₂O₃.The powder is white,under the action of alkali excitation,the geopolymer cementing material is formed,and the special network structure makes it have the characteristics of compact structure,high temperature resistance,early strength and fast hardening.Geopolymer also has a certain low permeability.Furthermore,it is cheap and easy to obtain,green and friendly to environment.Metakaolin(MK)is used as raw material,and water glass(WG)solution is used as alkali activator to prepare geopolymer.The mechanical properties of the coating were improved by adding different kinds of pigments and fillers with different proportions.In order to improve the crack resistance and scrub resistance of the coating,a small amount of silicone acrylic emulsion,mica powder and MgO powder are mixed into it.The results show that when the content of silicone-acrylic emulsion is 19.00%,mica powder is 3.13%,and MgO powder is 2.16%-2.86%,the mechanical properties such as crack resistance and water resistance of the coating are excellent.With the increase of the content of MgO,the scrub resistance of the coating showed a trend that it is first increased and then decreased,which can be ascribed to the enhanced compact of coating and its surface smoothness induced by adding appropriate amount of MgO.In addition,the flame retardancy of the samples was explored through thermal analysis and cone calorimeter.Moreover,the influence of alkali activator modulus on coating performance is systematically investigated.Using metakaolin as raw material,the mixed solution of sodium silicate and sodium hydroxide acts as composite alkali activator,the fixed ratio of 0.5,WG/MK of 0.8,and the appropriate fillers were added to prepare the geopolymer based water-based inorganic coating.It was found that the drying time of the coating increased with the increase of the alkali excitation modulus.The water resistance of the coating also becomes better with the increase of the alkali activator modulus.When the alkali activator modulus is 1.4,the hardness of the coating reaches the maximum.The coating with alkali activator modulus between 1.0 and 1.4 has more than 8500 times of scrub resistance,and the coating has good scrub resistance,which may be due to the enhanced hardness and compact derived from properly increasing alkali activator modulus.The thermal stability of the coating is independent of the modulus of the alkali activator when the modulus of the alkali activator is bigger than 1.