Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
  • C08K3/20—Oxides; Hydroxides
  • C08K3/22—Oxides; Hydroxides of metals

Definitions

• the present invention relates to new nanostructured particulate alumina and its use for improving the fire resistance in composite polymer systems.
• the overall concept of fire safety however also comprises the concept of fire resistance, i. e. the property whereby a composite material retains its physical integrity both during and as a consequence of a fire situation.
• fire resistance i. e. the property whereby a composite material retains its physical integrity both during and as a consequence of a fire situation.
• aluminium hydroxide is only partially successful. When heated above 200 °C, it releases ca. 34.5% of its weight as water vapour. Despite this loss of weight, the particles retain their external form and shape.
• Composite materials based on systems which promote pronounced charring of the organic polymer will promote fire resistance.
• Such systems may involve the synthetic resin itself (e. g. phenolic resins where the fire load is relatively low) or additives based on phosphorus or phosphorus in combination with nitrogen containing compounds to create an intumescent effect.
• These macro charring systems have a major disadvantage however, they raise substantially the toxicity of the gases released in a fire situation.
• aluminium hydroxide is not compatible with such char forming systems for two reasons. Firstly, the release of fire fighting water vapour interferes with the ability of the organic system to build a stable char. Secondly, aluminium hydroxide in converting to the aluminium oxide goes through a pronounced 'active' phase which catalyses the oxidation of carbonaceous material to gaseous carbon dioxide with minimum little or no formation of the highly toxic intermediate, carbon monoxide. What is needed in the art is a means of imparting fire resistance to aluminium hydroxide containing composite materials without recourse to the use of inherently toxic char promoting additives.
• Object of the present invention therefore is to provide a material which does not comprise the drawbacks of the systems known in the art and which imparts excellent fire resistance properties to composite polymer systems.
• the nanostructured alumina is characterised by an average particle size in the 50% range (d 50 ) of 1 ⁇ m to 5 ⁇ m, a specific surface area according to BET of 10 m 2 /g to 350 m 2 /g, preferably 10 m 2 /g to 200 m 2 /g, and by structural channels having a width of 1 to 100 nm, preferably of 10 to 50 nm.
• the nanostructured alumina can further be characterised by a particle size in the 10% range (d ⁇ o) of 0.1 ⁇ m to 2 ⁇ m and in the 90% range ( ⁇ i 0 ) of 2 ⁇ m to 10 ⁇ m and by a loss on ignition at 1000 °C (LOI) of 1 to 15%.
• the main mineralogical form of aluminium hydroxide is gibbsite, with the chemical formula Al(OH) 3 .
• the crystal habit of naturally occurring gibbsite is usually pseudohexagonal, tabular, while that of synthetic gibbsite (produced by the Bayer process) is determined by the conditions of crystallisation.
• the material is in fact highly polycrystalline and composed of crystallites of a significantly smaller size. Even so, it is at the atomic level that the key features of aluminium hydroxide as a base for creating a nanostructured material become evident. Millions (per cm 2 ) of structural channels within the crystal lattice both parallel and perpendicular to the c-axis provide the preferred routes for the removal of water which forms at temperatures above 200 °C. It was found that the structural channels already present in the aluminium hydroxide open up when the system is heated with the progressive loss of water causing the structure to shrink since the loss of mass is not accompanied by a decrease in the external dimensions of the particles.
• any boehmite aluminium monohydroxide, A1OOH which may have formed during the heating process will have decomposed endothermically thereby releasing its associated water of crystallisation and stabilising the nanostructure.
• Preparation of the nanostructured alumina of the present invention may accordingly be accomplished by a heat treatment at a temperature between 100 °C and 1000 °C, preferably between 300 °C and 750°C, of an aluminium hydroxide having an average particle size in the
• the aluminium hydroxide preferably used as starting material can further be characterised by a particle size in the 10% range (dio) of 0.1 ⁇ m to 2 ⁇ m and in the 90% range (d 90 ) of 2 ⁇ m to 10 ⁇ m. Good results have been achieved with standard aluminium hydroxides obtained from the Bayer process, e. g. the MARTINAL types of Alusuisse Martinswerk, Bergheim,
• Heat treatment as a rule takes place in such a manner that the starting aluminium hydroxide is slowly heated, e. g. at a controlled rate of 1 to 20 K/min, from ambient temperature to a maximum temperature of 100 °C to 1000 °C, preferably 300 °C to 750 °C, most preferably 400 °C to 700 °C, and then kept at this temperature for 10 to 60 min.
• the heating usually takes place in air at normal pressure or under reduced pressure.
• the heat treatment is carried out under reduced pressure, the reduced pressure more preferably being 100 mbar or less, most preferably 50 mbar or less.
• nanostructured alumina according to the invention can be filled into synthetic polymer systems using methods known to the person skilled in the art and in amounts sufficient to impart fire resistance to the polymer system.
• thermoplastic and thermosetting polymer systems can be filled with the nanostructured alumina of the invention.
• Suitable thermoplastic polymer systems are based on polyacrylates, polymethacrylates, polyesters or polyolefins like polyethylene and polypropylene.
• Suitable thermosetting polymer systems are epoxides, polyurethanes, unsaturated polyesters, vinyl esters or acrylic resins.
• the nanostructured alumina and the additional flame retardant(s) (if any) may be mixed either with the thermoplastic polymer or with an appropriate polymer precursor (mono- or oligomer) which is subsequently polymerised (cf. examples).
• the nanostructured alumina and the additional flame retardant(s) (if any) have to be mixed with an appropriate polymer precursor before curing.
• the filling level is in the range of 1 wt.% to 50 wt.%, preferably 2 to 40 wt.%, most preferably 5 to 15 wt.%.
• Most preferred additional flame retardant is aluminium hydroxide and/or magnesium hydroxide.
• 335 g of a nanostructured alumina was obtained with a specific surface area (BET) of 48 m 2 /g and a loss on ignition (at 1000 °C/2 h) of 2.5 wt.%.
• the particle size distribution of the nanostructured alumina remained unchanged from the starting aluminium hydroxide according to laser scattering measurement with Cilas ® 850.
• X-ray diffraction indicated the absence of boehmite.
• Scanning electron microscopy revealed the existence of the nanostructure with delaminations up to 40 nm parallel to the (001) crystal faces observed and a random pattern of channels up to 10 nm in width on the (001) faces and hence running parallel to the prismatic side faces of the pseudohexagonal crystals.
• methyl methacrylate monomer 20 g of the nanostructured alumina prepared as described above was added and fully dispersed in a dispersing unit (Dispermat ® CA from VMA) at 500 rpm at ambient temperature for 1 to 2 minutes. Then 80 g of MARTINAL ® ON 901 (Alusuisse Martinstechnik GmbH, Bergheim, Germany) was added to this mixture and the mixture was further dispersed for 2 minutes. Curing was effected by the addition of 0.5 wt.% tcrt-butylcyclohexyl peroxydicarbonate at a temperature of 60 °C.
• the solidified, translucent composite was cooled to room temperature.
• the solidified, opaque composite was cooled to room temperature.
• Fire resistance testing was accomplished according to BS 6853 small-scale alcohol test whereby the specimen was held 15 cm above a methanol flame for 5 minutes.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
• Compositions Of Macromolecular Compounds (AREA)

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Citations (3)

• 2000
  • 2000-08-29 WO PCT/EP2000/008425 patent/WO2001019732A1/en active Search and Examination
  • 2000-08-29 JP JP2001523323A patent/JP2003509319A/ja not_active Withdrawn
  • 2000-08-29 AU AU68417/00A patent/AU6841700A/en not_active Abandoned
  • 2000-08-29 EP EP00956497A patent/EP1233929A1/en not_active Withdrawn
  • 2000-08-29 CA CA002383079A patent/CA2383079A1/en not_active Abandoned

Patent Citations (3)

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