Phosphorus and Silicon Containing Low-Melting Organic-Inorganic Glasses Improve Flame Retardancy of Epoxy/Clay Composites

New low-melting organic-inorganic glassy polymers containing phosphorus and silicon are synthesized by the reaction between phenylphosphonic acid and methyltrichlorosilane or methyltriethoxysilane. They possess both low-softening points and high onset decomposition temperatures, which are favorable for preparing flame retardant composites. Although the glass by itself is sensitive to water, the composites are not significantly affected in that way. For glass/clay/epoxy composites glass transition temperature (T(g)) as well as storage modulus increase with the glass amount. The glasses improve flame retardancy significantly due to flame inhibition and the formation of fire residue working as protection layer during burning. The total heat evolved is reduced by 23-28% for using 5-15 wt.% glass and the maximum HRR even by 58-48%. The latter effect decreases with increasing glass amount due to an adulterate residue deformation. The combination of glass and clay is proposed as a possible route to enhance flame retardancy.