| Silane coupling agent(SCA) is widely used in organic-inorganic composites owning to its special molecular structure and chemical properties. It can enhance the compatibility between the organic materials and inorganic materials so as to greatly improve various properties of composite materials. In the polymer cement waterproof coating system, the compatibility and combination between the organic polymer emulsion and inorganic components(e.g., cement, fillers) is rather poor, which restricts the improvement of coating performance. SCA is a good solution for this issue, but its character of easy hydrolysis in water makes it difficult to be applied.Silane coupling agent microcapsule(SCAM) was prepared by spray drying process. SCA C2287 was used as core material and two kinds of material in polyvinylpyrrolidone(PVP), polyvinyl alcohol(PVA), maltodextrin(MD) and water-soluble starch(WS) were pair combined as wall material to prepare emulsion. The results indicated that the emulsion prepared by using PVP and MD as wall material had the smallest particle size, best stability and highest yield. Encapsulation efficiency was relatively high when the mass ratio of PVP and MD was 1:4. The effect of emulsion solid content, emulsion oil concentration, inlet air temperature of spray drying and atomizer rotation speed on the encapsulation efficiency, microcapsule average size and moisture content were investigated by central composite design. A series second-order models were established to fit the experimental results and response surface methodology was employed to analyze the model. According to the model, encapsulation efficiency was strongly influenced by emulsion solid content and emulsion oil concentration. The primary factor affecting average particle size was the emulsion solid content and atomizer rotation speed was the second factor. Moisture content was mainly affected by inlet temperature, followed by emulsion solid content and atomizer rotation speed. The lowest EC(the cost of raw material of encapsulate 1 kg of core material) was got at emulsion solid content of 48.9%, emulsion oil concentration of 29.8%, inlet air temperature of 180 °C and atomizer rotation speed of 27000 r/min. The SCAM with unbroken surface and good shape were obtained under these optimized conditions. The encapsulation efficiency, average particle size, moisture content and EC of the SCAM was of 82.7%, 21.3 μm, 0.93%, 191.1 RMB/kg, respectively. These experimental values agree well with the model prediction with relative error less than 5%.The prepared SCAM was added to polymer cement waterproof coating in order to improve the performance of the coating. The tension strength, elongation at break and water absorption rate of the coating with four kinds of fillers(ground calcium carbonate, talc powder, mica powder and light calcium carbonate) were determined. The results showed that the coating had the best overall performance(tension strength 2.652 MPa, elongation at break 191.2%, 7 d water absorption rate 9.12%) when ground calcium carbonate was used as filler and 2 wt% SCAM was added. Durability test showed that the SCAM could improve the performance of water resistance, alkali resistance, heat resistance and weather resistance of the coating. |
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