ABSTRACT
A zinc hydroxystannate/sepiolite (SEPZHS) hybrid additive was successfully prepared following a facile wet chemical route synthesis where zinc hydroxystannate (ZHS) nanoparticles were grown on the sepiolite's surface. SEPZHS particles have a fibrillar structure with ZHS nanoparticles homogeneously dispersed and with significantly smaller particle sizes than the synthesized ZHS nanoparticles alone. Sepiolite and SEPZHS were organically modified and introduced in a basic ethylene propylene diene monomer rubber (EPDM) formulation for cable to evaluate the nanocomposite behavior under direct fire sources. The results confirmed the synergistic effect of the hybrid SEPZHS additive in the formation of a most stable and efficient char barrier, thus improving the flame-retardant behavior of EPDM nanocomposite in terms of heat emission, with reductions of more than 40% in the peak of Heat Release Rate (cone calorimeter test), and smoke suppression, with more than 25% reduction in the Total Smoke Production and Smoke Density parameters (smoke chamber test). Moreover, the addition of sepiolite-based additives increased the mechanical properties (hardness) of the nanocomposites, as a result of the matrix reinforcement. This suggests that the SEPZHS hybrid additive may provide a promising option for a new, cost-effective, eco-friendly, yet efficient flame-retardant solution.
ABSTRACT
In the present study, a promising flame retardant consisting of 80 wt% silane-modified nanosepiolites functionalized with 20 wt% graphite (SFG) is used to obtain a synergistic effect principally focussed on the thermal stability of water-blown rigid polyurethane (RPU) foams. Density, microcellular structure, thermal stability and thermal conductivity are examined for RPU foams reinforced with different contents of SFG (0, as reference material, 2, 4 and 6 wt%). The sample with 6 wt% SFG presents a slightly thermal stability improvement, although its cellular structure is deteriorated in comparison with the reference material. Furthermore, the influence of SFG particles on chemical reactions during the foaming process is studied by FTIR spectroscopy. The information obtained from the chemical reactions and from isocyanate consumption is used to optimize the formulation of the foam with 6 wt% SFG. Additionally, in order to determine the effects of functionalization on SFG, foams containing only silane-modified nanosepiolites, only graphite, or silane-modified nanosepiolites and graphite added separately are studied here as well. In conclusion, the inclusion of SFG in RPU foams allows the best performance to be achieved.
