Intrinsically hydrophobic magnesium oxychloride cement foam for thermal insulation material

Abstract To overcome the poor water-resistance, magnesium oxychloride (MOC) cement, was hydrophobically modified with hydroxy-terminated polydimethylsiloxane (PDMS). MOC cement foam was prepared using hydrogen peroxide as the foaming agent. Scanning electron microscope (SEM) images showed that the MOC cement foams contained visible pores with sizes ranging from 150 μm to 600 μm, and the apertures increase with the increase in foaming agent. A lot of acicular phase 5 were observed in the pores, which conferred strength to the materials. Porosity analyses illustrated that the addition of the foaming agent increased the porosity and enlarged the pores, making the materials less dense. The increase in porosity and pore size significantly reduced the thermal conductivity, thereby improving the thermal insulation of the MOC cement foam. The modification of PDMS not only enhanced the water-resistance, but also achieved the superhydrophobicity of MF-1, while the sample with relatively large pores also had good hydrophobic ability. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were used to analyse the samples, explaining the mechanism of the water-resistance enhancement from a microscopic perspective.