Microstructural and mechanical properties of poly(sialate-siloxo) networks obtained using metakaolins from kaolin and halloysite as aluminosilicate sources: A comparative study

This work focuses on the comparison between the mechanical and microstructural properties of poly(sialate-siloxo) networks based on metakaolins from halloysite and kaolin. Poly(sialate-siloxo) networks were prepared using three metakaolins as aluminosilicate sources. Sodium waterglass from rice husk ash and commercial sodium waterglass were used as chemical reagents. The obtained results showed that metakaolins from kaolins have plate shapes with coarse particle sizes whereas the one from halloysite has a spherical morphology and smaller particle sizes. The IR spectra of poly(sialate-siloxo) networks from calcined halloysite indicate the higher value of the wavenumber of the main band. The XRD patterns of all poly(sialate-siloxo) networks show the broad hump structure with higher intensity between 18 and 40°(2θ). The XRD patterns of poly(sialate-siloxo) networks show the band of the unreacted metakaolin at about 20.45°(2θ). This band is more pronounced on the XRD patterns of geopolymer cements from calcined halloysite. The obtained poly(sialate-siloxo) networks based on metakaolins from halloysite and kaolin have a compact, homogenous and denser microstructures. The compressive strength values of the poly(sialate-siloxo) networks using calcined kaolin are ranging from 58.43 to 66.52 MPa whereas those using calcined halloysite are between 72.29 and 88.50 MPa. The compressive strength values of poly(sialate-siloxo) networks using calcined halloysite are higher compared to those from calcined kaolin. The higher compressive strength values of the geopolymer cements from calcined halloysite could be attributed to the fine and spherical particle sizes of calcined halloysite. This implies that the shape and the fine particle sizes of the raw materials influence the properties of the poly(sialate-siloxo) networks. Metakaolin from halloysite can be used as an aluminosilicate source for producing poly(sialate-siloxo) network with higher mechanical properties.