Production of Porous Poly(phospho-siloxo) Networks for Thermal Insulations Using Low-Value Calcium-Rich Wastes as Pore-Forming Agents

This study focuses on the preparation of porous poly(phospho-siloxo) networks for thermal insulation applications using commercial calcium carbonate and calcium-rich wastes such as oyster shell, snail shell and eggshell powders as pore-forming agents. The control and porous poly(phospho-siloxo) networks were prepared by adding phosphoric acid (4 M) as a chemical ingredient to metakaolin containing 0 and 15 wt% of each foaming agents. The final products were monitored using the X-ray diffractometry, infrared spectroscopy, apparent density, absolute density, thermal conductivity, optical microscopy, scanning electron microscopy and mercury intrusion porosimetry. The results show that the thermal conductivity of the control and porous poly(phospho-siloxo) network from commercial calcium carbonate are 0.35 and 0.20 W/mK, respectively. They were higher compared to those from snail shell (0.17 W/mK), eggshell (0.15 W/mK) and oyster shell (0.14 W/mK). The cumulative pore volumes are 211.4, 365.5, 380.6, 389.7 and 393.3 mm 3 /g for the control and porous specimens from chicken eggshell, commercial calcium carbonate, snail shell and oyster shell powders, respectively. Their total porosity measured by mercury intrusion porosimeter are 30.9, 45.5, 46.0, 45.9 and 45.4%, respectively, whereas those calculated with apparent and true density measured by pycnometer are 34.48, 45.25, 52.74, 50.84 and 52.60%, respectively. The concentrated pore size diameter of the porous sample from eggshell is highest compared to the others. It can be seen that the total porosities measured by mercury intrusion porosimeter of porous specimens are nearly the same trend as well as the thermal conductivity. It was found that the low-value calcium-rich wastes could be used for producing porous poly(phospho-siloxos) networks which could be utilized for thermal insulation applications. Graphic Abstract