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.
Highlights
The distinctive combination of low weight, low thermal conductivity and good mechanical properties makes rigid polyurethane (RPU) foam an indispensable thermal insulating material in buildings, insulated transport, refrigerators and pipelines, among other applications [1]
A promising halogen-free flame retardants (FRs) consisting of 80 wt% silane-modified nanosepiolites functionalized with 20 wt% graphite (SFG) was incorporated into water blown RPU foams
The morphology of the Silane-modified nanosepiolites functionalized with graphite (SFG) particles was observed by SEM (Figure 3), confirming the particle sizes supplied by the manufacturer and the functionalization of the nanosepiolites with graphite
Summary
The distinctive combination of low weight, low thermal conductivity and good mechanical properties makes rigid polyurethane (RPU) foam an indispensable thermal insulating material in buildings, insulated transport, refrigerators and pipelines, among other applications [1]. The halogenated FRs, which cover all organic compounds containing in their composition the elements of group 17, have been extensively used for many years due to their high efficiency in flame retardancy They have a major drawback in that a large amount of toxic polluting gases are generated during their combustion. Its fire-retardant properties are based on the charred layer formed during combustion, which acts as a thermal insulator prior to the degradation of the polymeric matrix This effect is due to the small air spaces between individual layers of graphite [9]. Sepiolite is a natural clay mineral of the structural family known as the 2:1 phyllosilicates, with (Si12 Mg8 O30 )(OH) (OH2 )4 ·8H2 O as theoretical unit cell formula [23] It exhibits a microfibrous morphology formed by two layers of tetrahedral silica and a central layer of magnesium oxide-hydroxide. This work was designed in the expectation that the synergistic effects of nanosepiolites and graphite together might be effective for enhancing the thermal stability of PU materials
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