Aluminum-containing layered double hydroxides: the thermal, mechanical, and fire properties of (nano)composites of poly(methyl methacrylate)

Abstract

Hydrotalcite-like anionic clays or layered double hydroxides (LDHs IntroductionIn recent years, polymer-inorganic nanocomposites have been the subject of extensive research. Previous studies on the layered materials have mainly focused on the layered silicates and polymerlayered silicate nanocomposites, 1 because of the relatively low layer charge density and the easy exfoliation of montmorillonite (MMT)-type layered silicate compounds. Anionic clays are also of interest as they may have properties that are parallel to or divergent from those of the cationic clays. The most well-known anionic clays are the hydrotalcitelike layered double hydroxides or LDHs. 2 LDHs have a much higher charge density than MMT in the interlayer and a stronger interaction among the hydroxide sheets than layered silicates, which makes the exfoliation of LDHs much more difficult. 3 Recently, a number of reports on the exfoliation of LDHs 4 and NOT THE PUBLISHED VERSION; this is the author's final, peer-reviewed manuscript. The published version may be accessed by following the link in the citation at the bottom of the page. Chemistry, Vol. 18, No. 26 (2008): pg. 3091-3102. DOI. This article is © Royal Society of Chmistry and permission has been granted for this version to appear in e-Publications@Marquette. Royal Society of Chmistry does not grant permission for this article to be further copied/distributed or hosted elsewhere without the express permission from Royal Society of Chmistry. Journal of Materials3 polymer-LDH exfoliated nanocomposites 5 have been published. These synthetic anionic clays are emerging as potential fire retardants. 6 Layered double hydroxides consist of positively charged metal hydroxides sheets with anions (along with water) located between the layers to compensate the charge on the layers. 7 The LDH structure is described with the ideal formula [ , and various carboxylates, etc.; intra and inter denote the intralayer domain and the interlayer space, respectively. The LDH structure consists of brucite-like layers constituted of edge-sharing M(OH)6 octahedra. 8 Partial M III for M II substitution induces a positive charge on the layers, balanced by the presence of the interlayer anions. LDHs then consist of a stacking of positively charged layers with anions intercalated in the interlayer region, usually referred to as the gallery space, together with water molecules. LDHs exhibit anion-exchange properties 9 and their interlayer spacing can change depending on the size of the intercalated anions. 10 When heated above about 600 °C, these materials lead to mixed oxides. 11The presence of an organic moiety in the LDH gallery space plays an important role in the preparation of the LDH-polymer nanocomposites. Pinnavaia et al.12 reported a Mg 2+ /Al 3+ /Cl -LDH with a gallery height of approximately 2.97 Å. The size of the interlayer space was calculated from a basal spacing of 7.74 Å (indicated by X-ray powder diffraction) and the thickness of the brucite layer (4.77 Å). The gallery distance between each ...

Polymer nanocomposites using zinc aluminum and magnesium aluminum oleate layered double hydroxides: Effects of LDH divalent metals on dispersion, thermal, mechanical and fire performance in various polymers

“…This clearly shows that aluminum is present in the cone residue before calcination, but it is in an amorphous form, not detectable by XRD. Introducing ZnAl in different polymers (PMMA and PEBuA) did not change the identity of the crystalline phases in the residue, identified with XRD either after cone calorimetry, or after further calcinations at 1000 °C for 12 h. The same materials can be identified in the chars from PMMA/ZnAl and PEBuA/ZnAl; these have also been observed in previous work after burning PMMA containing a zinc aluminum undecenoate LDH [17].…”

“…In previous work from these laboratories, it was found that the variation of the divalent metal cations in a series of aluminumcontaining LDHs affects dispersion, thermal and fire properties of their PMMA composites as measured by the cone calorimetry [17]. The combustion behavior of PMMA/LDH composites showed better improvement in fire properties relative to what has usually been obtained for PMMA/layered silicate nanocomposites, and this behavior was found to correlate with the type of the charge balancing anion in the LDH precursor (e.g.…”

Comparative study on the flammability of polyethylene modified with commercial fire retardants and a zinc aluminum oleate layered double hydroxide

“…[11]. These LDH nanomaterials were recently found to be particularly effective fire retardants for polar polymers like poly(methyl methacrylate) rather than non-polar polystyrene [12]; the performance of LDHs in PMMA was found to be comparable with that of the layered silicates when evaluated by the reduction in PHRR [12] and [13]. It was also observed that the identity of the divalent or trivalent metal cation [13] and the anion chain length [14] does play a role in the amount of reduction obtained.…”

“…The time to ignition is decreased as more LDH is added to PE. Just after ignition, the heat release rate curves of PE/LDH systems increase much more quickly than in the pristine polymer and a compact carbonaceous layer which is a mixture of metal oxide and/or spinel [13] and [20] is quickly formed on the surface of the polymeric sample. This mixture of metal oxides resulting from the decomposition of the LDH effectively protects the polymer from heat and explains for example the plateau observed in the HRR curves of these composites at both 10 and 20% loadings.…”

The role of the trivalent metal in an LDH: Synthesis, characterization and fire properties of thermally stable PMMA/LDH systems

“…), anion sizes, crystallite sizes, stoichiometry and the polymer. The variation of the divalent metal cation in an LDH has an influence dispersability and fire properties of the corresponding polymer (nano)composites [19]. Finally, the length of the carboxylate chain has been varied and the dispersability of the LDH and fire properties assessed with both PMMA and PS; the dispersion is much better with PMMA but there is still a substantial reduction in the peak heat release rate even with the LDH poorly dispersed in PS [20].…”