GB2400107A

GB2400107A - Montmorillonite flame retardant polyurethane

Info

Publication number: GB2400107A
Application number: GB0404892A
Authority: GB
Inventors: Graham Clayton Lees; Christopher Mark Liauw; Arthur Norman Wilkinson; Alexander Mcintyre; David Burrows
Original assignee: Kay Metzeler Ltd
Current assignee: Kay Metzeler Ltd
Priority date: 2003-03-04
Filing date: 2004-03-04
Publication date: 2004-10-06
Anticipated expiration: 2024-03-04
Also published as: GB2400107B; GB0404892D0; GB0304834D0

Abstract

A method for the preparation of flame retardant polyurethane materials comprising the steps:- adding, to a mixture comprising at least one polyol and at least one poly isocyanate, at least one modified and/or unmodified layered material and curing the resulting mixture to form a polyurethane material, characterised in that the layered material such as montmorillonite is added to the mixture as an aqueous blend.

Description

. 24001 07

METHOD FOR THE PRODUCTION OF POLYMERIC MATERIAL

The present invention relates to a method for the production of polymeric material and in particular flame retardant polyurethane foam Polyurethane (PU) foam because of its relatively low cost and attractive property profile is used in a variety of applications such as automotive seating, upholstery and bedding, packaging and medical applications. However, due to its low density and open cellular structure polyurethane foam has a large surface area and high air permeability and is therefore highly flammable upon the application of a sufficient ignition source and oxygen.

Accordingly, it is necessary to minimise the rate and level of mass loss during combustion, particularly for the most demanding applications such as mass transport.

Therefore, flame retardants are often added to reduce the flammability. The choice of flame retardant is largely dependent upon the intended application of the foam and the specific flammability requirements that the foam has to comply with. The type of flame retardant used and the level of addition will influence the ease of ignitability, ability to create a char, burning rate and smoke evolution.

Several small scale test methods are used to classify the combustion behaviour of flexible polyurethane foam ea. California TB 117A, ASTM D2683, FMVSS 302, BS 5852 part 2. Generally flame retardants employed for domestic furniture in the U.K. are based on melamine and halogenated liquid compounds to ensure that the government regulations ( which are based on BS5852 part 2) are met. Halogenated compounds particularly of the brominated type are increasingly coming under the microscope of À ce. ct: ce' : : ce. : :e various environmental groups and regulatory pressures are being placed on certain halogenated compounds.

At low foam densities e.g. 20 kg/m3 a substantial amount of flame retardant is required in the foam formulation to ensure that the government regulations are met. The high flame retardant levels also mean that the physical properties of the foam are markedly reduced compared to a non-flame retardant foam of equivalent density.

More recently it has become known to reduce the flammability of foam by way of char promoting agents, which interfere with the free-radical mechanism of combustion.

Such char promoting agents can be used in combination with a flame retardant as described above or with a phosphate or boron based system.

As described in GB 2 168 706 B1, US 5 169 876 and US 4 698 369 expandable graphite is one of the most successful char promoting agents and is manufactured by the oxidation of graphite flake in sulphuric acid. The layered platelet structure of the graphite flake permits it to absorb the acid readily to create an intercalated graphite which, when exposed to ignition sources, expands due to vaporization of the intercalatant and creates a char layer. Creation of the char layer dramatically reduces the heat release, mass loss, smoke generation and toxic gas emission.

Another approach to the production of flame retardant PU foam is to use high levels of aluminium trihydroxide (ATH). The levels of ATH required are such that a post-treatment technique is used to produce the foam i.e. an open-celled PU foam is passed through a polymer latex slurry containing high levels of ATH together with other additives. The treated foam is cured by way of a curing oven. However, due to the large :;:: 'see:. ee:e amounts of ATH required to render the foam flame retardant, physical properties of the foam such as tear resistance, abrasion and dynamic fatigue are unsatisfactory.

A recent development in composite technology is the use of so-called nanoscale particles to form so-called nanocomposites i.e. composites based on a matrix and nano- scale particles.

Nano scale particles can be derived from minerals that have a layered structure, these are typically kaolinites and montmorillonites, it is also possible to use layered minerals of the illite group. Preferred layered minerals are often referred to as 2:1 layered silicate minerals, which can include materials such as muscovite, vermiculite, saponite, hectorite and montmorillonite. The most widely used nano-scale particles are derived from montmorillonite. Montorillonite consists of octahedral alumina sheets sandwiched between two tetrahedral silica sheets. In the alumina sheet some of the aluminium cations are replaced by magnesium cations, this results in these alumino- silicate sheets (known as layers) having a net negative charge. This negative charge is balanced by hydrated inorganic cations positioned in the space between the alumino- silicate layers. These spaces are known as galleries. In order to form nano-scale particles from clays the clay is chemically modified such that the chemical intercalates between the layers. This increases the spacing between the layers such that the attractive force between them is reduced, this can lead to delamination (exfoliation) either before or during incorporation of the clay into the polymer or polymerising system. Delamination leads to the production of nano-scale particles.

À d. I: I.: :e.e 't. À:' 'c. :e The primary objective for production of polymer matrix nano-composites was high reinforcement coupled with low mass. It was soon realised however, that the combustion behaviour was also modified by the presence of these very high surface area to volume ratio particles. The combustion modification afforded by the presence of nanoscale particles ultimately led to research focused on these characteristics. This is referred in NIST report 6531, J. W. Gilman et al. For reference, in order that reinforcing particles are defined as nanoscale particles one of the dimensions must be less than 100 nm.

These nano-scale particles have been most widely applied to polyamide matrices due to their high polarity. However, their use has met with limited success when applied to polyolefins due to their non-polarity. Derivatised olefinic co-polymers such as ethylene vinyl acetate (EVA) have enjoyed more success, as exemplified in M. Alexandre et al., Macromol. Rapid Comm., 2001, 22, 643.

Thermosetting polymers such as epoxies and polyurethanes have been investigated as matrices for nanocomposites. US 6 017 632 and US 2002 0 037 953 both refer to the use of non-cellular polyurethane matrices for nanocomposites. Elastomeric polyurethane matrices are described by K.J. Yao et al., Polym. Comm., 2001, 43, 1017.

This reference also refers to soaking the layered material, which has been modified using quaternary ammonium salts, in polyols prior to the polymer forming reaction. However, nano-scale particles have not been used in conjunction with a cellular polyurethane matrix. This is due to the difficulty of achieving the exfoliated (delaminated) state within the short time period required for expansion of the foam and "elation, and the high 4 c tt :. I:: mini s surface area of the platelets which, affects the surface tension characteristics/stability of the rising foam.

Surprisingly, it has been found that by introducing the layered material into the reaction mixture as an aqueous blend the combustion behaviour properties of the foam, and indeed polymeric materials generally, are enhanced relative to foams where the layered material has been introduced as a non-aqueous system.

According to a first aspect of the present invention there is provided the use of an aqueous blend of at least one modified and/or unmodified layered material in the preparation of flame retardant polymeric materials.

The blend of the present invention can be used to prepare a wide range of polymeric materials such as films, coatings, adhesives and cellulose materials, but is preferably used for the preparation of polyurethane materials.

Thus, and in accordance with the second aspect of the present invention there is provided a method for the preparation of flame retardant polyurethane materials comprising the steps:- adding, to a mixture comprising at least one polyol and at least one polyisocyanate, at least one modified and/or unmodified layered material and curing the resulting mixture to form a polyurethane material, characterized in that the layered material is added to the mixture as an aqueous blend.

By modified it is meant organically modified for example the ions that exist between the alumino-silicate layers can be exchanged with quaternary ammonium salts such as tetraalkyl/aryl ammonium halides.

le t lestedit By unmodified it is meant a material in the state in which it naturally occurs, or a material that has had calcium ions, that exist between the alumino-silicate layers, replaced by sodium ions.

By aqueous blend it is meant a composition comprising the said layered material and water for example a paste, a gel or a suspension.

Advantageously the method of the present invention gives rise to material having a composition whereupon ignition charring of the material is promoted. In fact, upon ignition of material produced in accordance with the present invention substantial char formation occurs. This charring gives rise to a significant reduction in the burn rate relative to established fire retardant foam systems.

Advantageously, it is not necessary to modify the layered material in order to achieve material, which exhibits substantial char formation upon ignition. Therefore, the method of the present invention provides a cheaper route for obtaining PU materials and in particular cellular polyurethane foams which have improved combustion properties than established fire retardant foam systems.

Advantageously, the use of layered materials gives rise to excellent flame retardancy without using environmentally damaging compounds, in particular halogenated compounds. A further advantage of the use of layered materials lies with the fact that only a minimal amount of the layered material is required to obtain the desired flame retardant properties. e À

e e e À À e À c e e e e e À e À A still further advantage of the present invention is that the mechanical properties of the PU foam can be greatly improved due to the reduced solids in the foam formulation hence giving improved physical properties.

It has been found that polyurethanes make particularly good matrices for nano- scale composites as the starting materials from which they are manufactured i.e. isocyanates and alcohols are liquid in nature. These liquids penetrate the layered materials much more easily than macromolecules due to their higher mobility.

Typical PU foams are prepared from the reaction between an isocyanate and an alcohol to form a urethane, as exemplified by Scheme 1 below: o R-N=CO + Rat CH2OH À R-N-C-O-CH2-R

H

Scheme 1 When extended to polyfunctional reactants i.e. polyols and polyisocyanates, this reaction provides a direct route to cross-linked PU polymers.

To prepare a PU foam the polymer must be expanded or blown by the introduction of bubbles and a gas. A convenient source of gas is the carbon dioxide, which is produced from the reaction of the isocyanate group with water. The intermediate product of this reaction is the thermally unstable carbamic acid, which spontaneously decomposes to an amine and carbon dioxide. Diffusion of the carbon dioxide into bubbles previously nucleated in the reacting medium causes the expansion of the medium to make foam. Again if the isocyanate and amine molecules cee À:: À:: :: e À ce. À : : a:: À À arepolyfunctional a cross-linked PU will result. Blowing can also be achieved by the physical addition of a low boiling non-reactive solvent to a foam formulation.

Vaporisation of these solvents by heat from the exothermic reactions produces gas molecules, which diffuse into nucleated bubbles and contribute to foam expansion, an alternative to the use of low boiling solvents is to use liquid carbon dioxide or other such liquefied gases.

Preferably the polyols of the present invention are polyether or polyester type polyols.

Polyesters tend to be used for the manufacture of foam for specialised applications such as fabric lining and packaging, and are generally not used in seating applications.

Preferably the polyesters of the present invention will have a molecular weight of from about 800 to about 5000 but more preferably from between 2000 to 4000.

Suitable polyesters are derived from adipic acid and diethylene glycol, optionally other all-acids and glycols can be included, these polyesters may be optionally branched typical branching agents include pentaerythritol, glycerol or trimethylol propane.

Alternatively the polyols of the present may be a polyether type polyol with a molecular weight range from 500 to 15000 and preferably from 1000 to 8000.

Suitable polyether type polyols include any of the following either alone or in combination:- polyoxypropylene dials, trials, tetrols and higher analogues; ethylene oxide capped dials, trials, tetrols and higher analogues; and random and block polymers ee e:: e:: :: a. e À À À:e e: : : eae of the aforesaid polyethers in which the polyol is made with both ethylene and propylene oxides.

"Modified polyetherpolyols" which, contain organic fillers formed by the in- situ polymerization of suitable monomers are also suitable for use in the present invention. Three classes of polyol are identified namely: (1) Polymer polyols. (2) PHD polyols. (3) PIPA polyols. In such polyols in addition to the polyether polyol itself the polyol contains at least one other polymer dispersed therein. Thus, a polymer polyol additionally includes a vinyl polymer dispersion, formed in-situ in the polyol, as well as the reaction product of the polyol and a vinyl monomer. A PHD polyol contains a dispersion of a polyurea in a polyether polyol, formed in-situ by polymerization of a all-amine and an isocyanate, while a PIPA ( Polyisocyanate polyaddition) polyol contains a polymer dispersion formed by the reaction of an alkanolamine with an isocyanate.

That said, a comprehensive review of polyols which are suitable for use in the present invention can be found in: Chapter 9 (Polyols for Polyurethane Production) of "Telechelic Polymers: Synthesis and Applications", Ed. E.J. Goethals, CRC Press Inc. Florida 1989.

Polyisocyanates which are suitable for use on the present invention may be any compound having two or more isocyanate groups and which may be aromatic, aliphatic or cycloaliphatic.

Preferably the polyisocyanates of the present invention are derived from toluene di-isocyanate (TDI), diphenyl methane di-isocyanate (MDI), modified and polymeric diphenyl methane di-isocyanate and isophorone diisocyanate (IPDI) and mixtures thereof.

9: Be: .: ::e À À e À À e e e When the isocyanate is TDI, it may be the pure 2,4 isomer however, generally it is a mixture of 2,4 and 2,6 isomers with a ratio of 80:20 or 65:35. These isomers have a high reactivity and TDI is the standard diisocyante which, is used for the manufacture of flexible PU foam. Such blends are commercially available e.g. VORANATE_ series available from Dow and the LUPRANATE_ series available from Elastogram UK Ltd. Blends of TDI and MDI may also be utilised in the present invention. i.e from O to 100% of either type.

The aqueous blend of the layered material, of the present invention may be in the form of a gel, paste, dispersion or any other suitable form.

Preferably the layered material of the aqueous blend is unmodified i.e. the layered material remains chemically unchanged upon addition to the reaction mixture. Where the layered materials are modified they are preferably modified using compounds such as tetraalkylammonium halides, amine terminated poly(dimethyl siloxane), and poly (hydromethylsiloxane) and phosphorous and/or boron containing compounds.

Modifying the layered materials in this way gives rise to an intercalated layered structure.

The layered materials of the present invention may be layered minerals, and are preferably layered silicates, both natural and synthetic. Montorillonite may be the preferred type but fluorohectories and laponites could also be used as could synthetic micas and fluoro micas.

The preferred layered silicate for use in the present invention is a sodium exchanged montmorillonite.

:e c.: e.. :e À:. aces The layered material shall constitute from 0.1 to 45 % and preferably from 2 to 30% by weight of the composition of the present invention.

In addition to the polyol and polyisocyanate typically a reaction mixture for foam manufacture can include any one or more of the following components:- water, auxiliary blowing agent, amine catalyst, tin catalyst, surfactant, filler, chain extender, cross-linker, stabiliser, anti- static additive, colourant, anti-oxidant or flame retardants.

The PU foam composition of the present invention may also comprise flame retardant additives which include any of the following either alone or in combination:- melarhine, aluminium trihydroxide (ATH), ammonium polyphosphate, expandable graphite or halogenated phosphates or zinc berates.

Preferably the PU foams of the present invention have foam densities ranging from about 8 kg/m3 to about 300 kg/m3.

The method described herein can be used to prepare cellular semi-rigid and rigid PU foams. However, it is preferable that the method described herein is used to prepare flexible flame retardant PU foam. By flexible it is meant a PU foam that falls within the definition according to ASTM D1056 1985 i.e. a cellular structure which will not rupture within 60 seconds when a specimen 200 x 25 x 25 mm is bent round a mandrel at a uniform rate of one lap in 5 seconds in the form of a helix at a temperature between 18 and 29 C.

The PU foam may be produced from a commercially available polyol, isocyanate prepolymer or from discrete polyols and polyisocyantes which, are combined in situ or even a combination of the two.

ce c:: À e:: :: e À . :: À. À.: Once prepared, PU foam reaction mixtures of the present invention may be manufactured using standard foaming techniques i.e. slabstock, cold cure and hot cure processes.

In order that the present invention be more readily understood the composition of the present invention will now be described further by way of example only with reference to the following examples: Example F l Control Component Function Quantity by Weight (g) Hypol 2002 Pre- polymer 300 Water Initiator 300 + Cloisite Na Nano-scale particles 0 Silicone L620 Surfactant 1.35 Silicone B3640 Surfactant 0 * Hypol 2002 is a commercially available pre-polymer available from Dow Polyurethane Systems. The NCO pre-polymer is a reaction product of a mixture of diisocyanate and polyol having unreacted isocyanate groups which in the presence of a suitable initiator, such as water, will react to produce carbon dioxide thereby forming expanded PU foam.

The control foam above was prepared by mixing the pre-polymer with the Surfactant using a propeller type mixer. Water was then added to the aforesaid mixture with continued stirring at 2000 rpm for 6 seconds. The mixture was then poured into a box mould 380 x 110 x 120 mm in size. The resultant foam was then placed in an oven ct ec:a: À: te À À:: :: c:e.:À . À' . set at 60 C until it was tack free - approximately 10 minutes. The foam was then placed in a forced convection oven at 70 C in order to remove the excess moisture. The weight of the foam was monitored until a steady dry weight was observed - approximately 5 hours.

Example F2

Component Function Quantity by Weight (g) Hypol 2002 Pre-polymer 300 Water Initiator 300 Cloisite Na+ Nano-scale particles 30 Silicone L620 Surfactant Silicone B3640 Surfactant 1.35 The nano-composite was prepared as follows:- Cloisite Na+ was added to the water in order to produce a slurry. This slurry was then added to the pre-polyrner. The stirrer was switched on and simultaneously the Surfactant was added to the mixture and mixed for 6 seconds at 2000 rpm. Curing and drying of the nano-composite was carried out as described above with respect to the control.

The flammability properties of the two foams were assessed using FMVSS 302: A flame height of 38 mm is set using the regulating valve on a Bunsen burner, and the centre of the burner tip should be 19 mm below the centre of the bottom edge of the specimen at the open end of the clamp which holds the specimen.

:e;;' ceas:e À:. Àe The foam sample is exposed to the Bunsen flame for 15 seconds and then the gas supply is turned off. Timing of burning commences when any part of the flame front reaches a point 38 mm from the edge of the specimen exposed to the flame. If the flame front does not reach the 38 mm mark, the material is classed as self extinguishing.

Results Parameter Foam Type Control Nano-composite Dry Foam Density (kg/m') 110 96 FMVSS 302 Burn Rate Self extinguishing 18 (mm/min) The control foam did not burn more than 38 mm from the edge of the foam exposed to flame, therefore could be classified as self extinguishing. The reason that the control foam did not support burning was that the control foam melted away from the Bunsen flame. However, when the Bunsen flame was not extinguished and was allowed to follow the melting foam front, then the foam was totally consumed i.e. burnt.

The foam containing the Cloisite Na+ did not melt away from the ignition flame, but burned at a very slow rate (18 mm/min) and formed a hard biscuit like char.

Breaking the char showed that the foam beneath the char layer was still intact and that the char layer acted as a barrier to protect the rest of the foam. X-ray diffraction (XRD) measurements indicated that a nanocomposite type foam had been produced.

Further examples in which 100 is equivalent to 600g of polyol, the remaining are expressed as a ratio relative to this: :e c: ce':e À:e À.

Component Amount added (ratio of components) F3 F4 F5 F6 F7 F8 F9 Polyol (1) 100 lOO 100 lOO 100 100 100 Catalyst (2) 0.30 0.30 0.30 0.30 0.30 0. 30 0.30 Surfactant (3) 1.20 1.20 1.20 1.20 1.20 1.20 1.20 Water 4.60 4. 60 4.60 4.60 4.60 4.60 4.60 Tin Catalyst (4) 0.25 0.25 0.25 0.25 0.25 0. 25 0.25 Isocyanate (5) 58.20 58.20 58.20 58.20 58.20 58.20 58.20 Modifier (6) 0 6.90 0 0 0 0 0 ATH (7) 0 0 6.90 0 0 0 0 Melamine (8) 0 0 0 6. 90 0 0 0 PTFE Powder (9) 0 0 0 0 6.90 0 0 Graphite (10) 0 0 0 0 0 6.90 0 Liquid Fire Retardant (11) 0 0 0 0 0 0 6.90 Foam Density (kg/m') 20.0 20. 4 23.4 23.7 23.9 22.3 22.4 FMVSS 302 Burn Rate (mm/min) 148 150 118 149 110 102 102

Table 1

(1) Arcol 1104 - 3000 molecular weight polyether polyol available from Bayer; (2) Desmorapid DMEA (2-dimethylamino ethanol amine) - catalyst available from Bayer; (3) Niax L620 surfactant - a polyaLkylene oxide methyl siloxane copolymer available from Osi Crompton; (4) Dabco T9 (stannous-2-ethylhexanoate) - tin catalyst available from Air Products; (5) Desmodur T80 (toluene diisocyanate) - available from Bayer; (6) Calcium carbonate filler- available from Croxton and GalTy Ltd.; (7) Aluminium trihydroxide FRF 40 - available from Alcan Chemicals; a. ':: c:: ::e ea. c, a À (8) Melamine- available from DSM; (9) PTFE powder- type 636-N available from DuPont; (10) Graphite - exfoliated graphite available from Nordman Rassman; and (11) Fyrol PCF (Tris(2-chloroisopropyl) phosphate) available from Akzo Nobel.

The examples referred to in Table 1 above were prepared as follows: Step 1 - The polyol, catalyst, surfactant and one of the fire retardant additives numbered 7 to 11 were weighed out and mixed together at 2000 rpm for 60 seconds using a propeller type stirrer; Step 2 - The tin catalyst was added and the mixture was stirred for a further 20 seconds; Step 3 - The isocyanate was added and the mixture was stirred for a further 8 seconds following which the reaction mixture was transferred into a 40 x 40 x 40 cm open box mould; Step 4 - The reaction mixture was allowed to expand completely and the mould was then placed in an oven at 60 C for 10 minutes or until the foam was tack free: and Step 5 - The resulting PU foam was left for a minimum of 4 days prior to the cutting of samples for laboratory testing.

Table 1 shows the burn rates achieved with various flame retardant additives incorporated into a 3000 molecular weight propylene oxide based polyether polyol foamed using 4.6 parts of water. Modifier (Ca(CO3)2) was added to F4 as it is often added to PU foams to reduce formulation costs. The additives numbered 7 to 11 can all be used as flame retardants in PU formulations :e;: Àe:e e.:s À.

The best burn rates were achieved by the use of exfoliated graphite (F8) and halogenated phosphate (F9). All of PU foams F3 to F9 showed signs of melting and dripping except for F8 where char formation was observed.

Component Amount added (ratio of components) F10 F11 F12 F13 F14 F15 F16 Polyol (1) 100 100 100 100 100 100 100 Catalyst (2) 0.30 0.30 0.30 0.30 0. 30 0.25 0.30 Surfactant (3) 0 1.20 1.20 0 1.20 0 0 Surfactant (4) 1. 20 0 0 1.20 0 1.20 1.20 Water 4.6 0 4.6 0 0 0 4.6 Tin Catalyst (5) 0.25 0. 25 0.25 0.40 0 0.46 0.25 Tin Catalyst (6) 0 0 0 0 0.16 0 0

_ __

Isocyanate (7) 58.2 58.2 58.2 58.2 58.2 58.2 58.2 Na+ Paste (4.6 H2O:6.5 Na+) 0 0 0 - 0 11.5 11.5 0

_

Na+ Powder (8) 0 0 0 0 0 0 0 QPN Paste (4.6 H20:4.6 QPN) 0 9.2 0 9. 2 0 0 0 QPN Powder (9) 0 0 4.6 0 0 0 0 Graphite 0 0 0 0 0 5.0 5.0

_ _

Density (kg/m') 19.8 21.3 22.0 22.2 22.5 21.8 20.6 FMVSS 302 Burn Rate (mm/min) 135 77 180 95 81 97 127

Table 2

ete ce. .. : :e ce.e.: ease:e À . (1) Arcol 1104 - 3000 molecular weight polyether polyol available from Bayer; (2) Desmorapid DMEA (2-dimethylamino ethanol amine) - catalyst available from Bayer; (3) Niax L620 surfactant - a polyalkylene oxide methyl siloxane copolymer available from Osi Crompton; (4) Tegostab B8234 - available from Goldschmidt (DeGussa) (5) Dabco T9 (stannous-2-ethylhexanoate) - tin catalyst available from Air Products; (6) Fomrez UL28 {dimethyl bis[(10-oxoneodecyo)oxy]stannane} - available from Osi Crompton; (7) Desmodur T80 (toluene diisocyanate) - available from Bayer; (8) Cloisite Na+ clay powder - available from Southern Clay Corporation (USA); and (9) QPN clay powder - available from Colin Stewart-Minchem.

The Na+ and QPN pastes referred to in table 2 were prepared as follows: Water and Na+ clay were weighed out in the ratio shown in table 2 and mixed with a small propeller mixer at 500 rpm until a homogeneous mixture ensued. During its preparation the viscosity increases therefore to facilitate the procedure a proportion of the total amount of polyol is added to the mix.

Table 2 shows burn rates achieved when two types of clays, which are in accordance with the present invention, were incorporated into a 3000 molecular weight polyether polyol foamed using 4.6 parts of water.

The best bum rates were achieved where the clays were introduced into the PU formulation as a gel or paste. Both PU foams F 11 and F 14 burnt with much slower burn rates than the flame retardant containing foams referred to in table 1. Furthermore, F11 and F 14 exhibited good char formation and no melting or dripping was observed.

Where the QPN was added to the formulation as a powder (F12) the burn rate increased dramatically. Char formation was not observed, instead the foam melted and dripped to a large degree.

d e e : À : : : À 1 The most commonly used techniques for the characterization of nano-composites are X-ray diffraction (XRD) and transmission electron microscopy (TEM).

X-ray diffraction allows the determination of the spaces between the layers or platelets of the silicate by utilising Bragg's Law: Sin = n 2 d The processes which occur during the formation of a nanocomposite are intercalation (the penetration of the PU foam components between the layers of the layered structure), followed by delamination/ exfoliation which increases the distance between the platelets and for complete exfoliation separates them into nano-scale particles. Indeed it is these changes which, indicate that a nano-composite has been formed. A reductionin the diffraction angle corresponds to an increase in the d- spacing i.e. the distance between the platelets.

XRD measurements on PU foams Fll and F14 showed that the d-spacing had increased indicating that a nano-composite had formed, this was not the case for F12 el. '$: aft: e' . :el Component Amount added (ratio of components) F17 F18 Fl9 F20 F21 F22 F23 Polyol (1) 100 100 100 100 100 100 100 Catalyst (2) 0.30 0.30 0.30 0.30 0.30 0.30 0.30 Surfactant (3) 1.20 1. 20 1.20 1.20 1.20 1.20 1.20 Water 4.60 4.60 4.60 4.60 4.60 4.60 4.60 Tin Catalyst (4) 0.25 0.25 0.25 0.25 0.25 0.25 0.25 Isocyanate (5) 58.20 58. 20 58.20 58.20 58.20 58.20 58.20 Modifier (6) 0 6.90 0 0 D O O ATH (7) 0 0 6.90 0 0 0 0 Melamine (8) 0 0 0 6.90 0 0 0 PTFE Powder (9) 0 0 0 0 6. 90 0 0 Graphite (10) 0 0 0 0 0 6.90 0 Liquid Fire Retardant (11) 0 0 0 0 0 0 6.90 Foam Density (kg/m) 20.0 22.4 23.7 23.7 Z2.6 23.8 22.3 FMVSS 302 Burn Rate (mm/min) 140 203 174 120 153 95 110

Table 3

(1) Alcupol F-4811 - 3500 molecular weight polyether polyol available from Repsol Quimica SA; (2) Desmorapid DMEA (2-dimethylamino ethanol amine) catalyst available from Bayer; (3) Niax L620 surfactant - a polyalkylene oxide methyl siloxane copolymer available from Osi Crompton; (4) Dabco T9 (stannous-2-ethylhexanoate) - tin catalyst available from Air Products; (5) Desmodur T80 (toluene diisocyanate) - available from Bayer; (6) Calcium carbonate filler- available from Croxton and Garry Ltd.; (7) Aluminium trihydroxide FRF 40 - available from Alcan Chemicals; (8) Melamine- available from DSM; (9) PTFE powder- type 636-N available from DuPont; (10) Graphite - exfoliated graphite available from Nordman Rassman; and (11) Fyrol PCF (Tris(2-chloroisopropyl) phosphate) available from Akzo Nobel.

The formulations referred to in table 3 are similar to those referred to in table 1 i À 1 i Except the formulations of table 3 utilise a 3500 molecular weight polyol with an ethylene oxide content of approximately 12-13 %.

The best burn rates were achieved for F22 which contained exfoliated graphite and F23 which contained a halogenated phosphate. All of PU foams F17 to F23 burnt exhibiting melting and dripping except for F22 where char formation occurred Component Amount Added (ratio of components) F24 F25 F26 F27 F28 F29 F30 F31 Polyol (1) 100 100 100 100 100 100 100 lOO Catalyst (2) 0.300.30 0.30 0.15 0.30 0. 30 0.30 0.30

_

Surfactant 1 (3) 2 50 2.50 2.40 0 2.50 0 2.50 2.40 Surfactant 2 (4) 0 0 0 1.50 0 0 0 0 Surfactant 3 (5) 0 0 0 0 0 1.20 0 0 Water 4.60 4.60 4. 60 0 0 0 0 4.60 Tin Catalyst (6) 0.25 0.25 0.25 0.50 0.25 0.25 0.25 0.25 Isocyanate (7) 58.2 58.2 58.2 58.2 58.2 58.2 58.2 58.2 Na+ Blend 0 0 20 20 20 20 0 0 + _ __.

Na Gel 0 0 0 11.5 11.5 11.5 11.5 0 (4.6 H2O:6.9 Na+) Na+ Powder (8) 0 0 0 0 0 0 0 20 Cloisite 30B Powder (9) 0 6.90 0 0 0 0 0 0 Density (kg/m3) 20.5 22.9 22.8 24.0 23.6 23.5 22.7 23. 0

_ _

FMVSS 302 Burn Rate (mm/min) 142 106 95 90 87 90 76 110

Table 4

(1) Alcupol F-4811 - 3500 molecular weight polyether polyol available from Respol Quimica SA; (2) Desmorapid DMEA (2-dimethylamino ethanol amine) catalyst available from Bayer; (3) Niax L620 surfactant - a polyalkylene oxide methyl siloxane copolymer available from Osi Crompton; (4) Tegostab B8234- available from Goldschmidt (De Gussa); (5) Tegostab B8680 available from Goldschmidt (De Gussa); Àe as: eee: Àe.e À. es:e À À (6) Dabco T9 (stannous-2-ethylhexanoate) - tin catalyst available from Air Products; (7) Desmodur T80 (toluene diisocyanate) - available from Bayer; (8) Cloisite Na+ clay powder - available from Southern Clay Corporation (USA); and (9) QPN clay powder - available from Colin Stewart-Minchem.

The Na+ blend referred to in table 4 is a 1:5 ratio of Na+ :polyol and it is prepared as follows: Na+ was mixed with the polyol using a Silverson mixer for 8 minutes to give a good finely distributed blend, free of agglomerates. In order that the polyol could soak into the Na+ the mixture was then allowed to stand for at least one week before the PU foam was prepared. The blend was mixed on alternate days to prevent settling.

Table 4 shows burn rates achieved with two types of clay incorporated into a 3500 molecular weight polyol foamed with 4.6 parts of water.

The two types of clay used were: Cloisite Na+ (an unmodified clay) and Cloisite 30B (an organically modified clay) The best burn rates and charring were observed for F30 where the clay had been introduced as a water based paste (as described above). F27, F28 and F29, which were made with a combination of Cloisite Na+ blend and Cloiste Na+ paste, had slightly higher burn rates than F30 but the char obtained was denser due to the extra clay in the blend.

The Cloisite 30B was added to F25. However the Cloisite 30B was not added as a paste. F25 was found to have a higher burn rate and only exhibited a slight sign of charring compared to the char formed on F30. Therefore, it would seem that unmodified clays produce a better char in compositions of the type depicted in table 4.

c c ceeÀ e: a:. eve ase: Component Amount added (ratio of components)) F32 F33 F34 Polyol (1) [Blend] 100 lOO 100 Catalyst (2) 0.30 030 0.30 Surfactant 1 (3) 2.50 1.25 0 Surfactant 2 (4) 1.25 Water [Blend] 4.60 4. 60 4.60 Na+ Clay (5)[Blend] 20 20 20 Tin Catalyst (6) 0.25 0.25 0.25 Isocyanate (7) 58.2 58.2 58.2 Density (kg/mJ) 20.1 21.3 21.8 FMVSS 302 Burn Rate (mm/min) 82 92

Table 5

(1) Alcupol F-4811 - 3500 molecular weight polyether polyol available from Respol Quimica SA; (2) Desmorapid DMEA (2-dimethylamino ethanol amine) catalyst available from Bayer; (3) Niax L620 surfactant - a polyalkylene oxide methyl siloxane copolymer available from Osi Crompton; (4) Tegostab B8234- available from Goldschmidt (De Gussa); (5) Cloisite Na+ clay available from Southern Clay Corporation (USA); (6) Dabco T9 (stannous-2-ethylhexanoate) - tin catalyst available from Air Products; and (7) Desmodur T80 (toluene diisocyanate) - available from Bayer Table 5 shows burn rates for foams where the Cloisite Na+ was introduced into the formulation as a soaked polyol water blend..

À cee' ;:: cee. :e cerise eeee À . In contrast to the blend used in the formulations of table 4, the blend used in the formulations of table 5 contained water. In fact the blend contained a 100:20:4.6 ratio of polyol:Na+ clay:water.

When F32, F33 and F34 were burnt they produced a good strong char and had burn rates comparable to F27, F28 and F29 where a polyol blend and Cloisite Na+ was used.

Component Amount Added (ratio of components) F35 F36 F37 F38 F39 F40

_

Polyol (1) 100 100 100 100 100 100 Catalyst (2) 0.40 0.40 0.40 0.40 0. 40 0.40 Catalyst (3) 0.10 0.10 0 10 0.10 0.10 0.10 Water 5.0 5.0 5.0 5. 0 5.0 5.0 Surfactant 1 (4) 0.30 0.30 0 0 0 0 Surfactant 2 (5) 0.30 0. 0. 60 0.60 0.60 0.60 Cell Opener (6) 2.0 2.0 0 2.0 D O Isocyanate (7) 31. 8 31.3 31.8 31.8 81.8 81.8 Na Gel (8) 7.5 0 0 7.5 0 7.5 QPN (9) 0 7. 5 0 0 7.5 0 Graphite (10) 0 0 7.5 7.5 7.5 7.5 Liquid Fire Retardant (11) 0 0 0 0 D 2.0 Density (kg/m) 33.2 33.5 32.7 35.0 35.1 35.0 FMVSS 302 Burn Rate (mm/min) 77 79 49 40 46 31

Table 6

(1) Specflex NC635 - 6000 molecular weight polyol available from Dow; (2) Dabco 33LV - 33% Triethylene diamine in dipropylene glycol available from Air Products; (3) Niax A1 - 70 % bis (N,N-dimethylamino ethyl) ether in dipropylene glycol available from Osi Crompton; (4) B4690 Surfactant high resilient foam surfactant available from Goldschmidt (De-Gussa); eeÀ A Àa.

(5) B8680 Surfactant - high resilientfoam surfactant available from Goldschmidt (De-Gussa); (6) CP1421 - high ethylene oxide polyol available from Dow; (7) UK 721 - solvent free modified isocyanate based on 4,4diphenylmethane di isocyanate (MDI) available from BASF; (8) Cloisite Na+ clay powder - available from Southern Clay Corporation (USA); (9) QPN clay powder - availale from Colin Stewart (Minchem); (10) Exfoliated graphite available from Nordman Rassman; (11) Fyrol PCF (Tris(2-chloroisopropyl)phosphate available fro Akzo Nobel.

Table 6 shows burn rates achieved for formulations containing QPN and Cloisite Na+ clays. Table 6 also shows burn rates for formulations which contain a combination of QPN and/or Cloisite Na+ and exfoliated graphite.

A char was produced when all of F35 to F40 were burnt. However, a stronger, denser char was observed for F38, F39 and F40, which contained a combination of QPN and/or Cloisite Na+ and exfoliated graphite.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiments, which are described by way of example only. e

Claims

Claims 1. The use of an aqueous blend of at least one modified and/or

unmodified layered material in the preparation of flame retardant polymeric materials.
2. A method for the preparation of flame retardant polyurethane materials comprising the steps: adding, to a mixture comprising at least one polyol and at least one polyisocyanate, at least one modified and/or unmodified layered material and curing the resulting mixture to form a polyurethane material, characterised in that the layered material is added to the mixture as an aqueous blend.
3. A method according to claim 2, wherein the polyol is a polyether type polyol.
4. A method according to claim 3, wherein the polyether type polyol has a molecular weight ranging from SOD to l SOOO.
S. A method according to claim 4, wherein the polyether type polyol has a molecular weight ranging from 1000 to 8000.
6. A method according to any of claims 3 to 5, wherein the polyether type polyols, is selected from polyoxypropylenes dials, trials, tetrols and higher analogues; ethylene oxide capped dials, trials, tetrols and higher analogues; and random and block polymers of the aforesaid polyethers in which the polyol is made with ethylene and propylene oxides and mixtures thereof.
7. A method according to claim 2, wherein the polyol is a polyester type polyol.

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8. A method according to claim 7, wherein the polyester type polyol has a molecular weight in the range from 800 to 5000.
9. A method according to claim 8, wherein the polyester type polyol has a molecular weight in the range from 2000 to 4000.
10. A method according to any of claims 7 to 9, wherein the polyesters are derived from adipic acid and diethylene glycol.
l l. A method according to any of claims 7 to 10, wherein optionally branched polyester type polyols are derived from all-acids and glycols are added.
12. A method according to claim 11, wherein the branching agent is selected from pentaerythritol, glycerol or trimethylol propane.
13. A method according to any of claims 2 to 12, wherein the polyisocyanate has two or more isocyanate groups.
14. A method according to any of claims 2 to 13, wherein the polyisocyanate is aromatic, aliphatic or cycloaliphatic.
lS. A method according to any of claims 2 to 14, wherein the polyisocyanate is derived from to luene di-isocyante (TD I) , diphenyl methane di-isocyanate (MDI) , modified or polymeric diphenyl methane diisocyante and isophorone di-isocyante (IPDI).
16. A method according to any of claims 2 to 15, wherein the polyisocyanate is a ratio of 80: 20 to 65:35 of pure 2,4 TDI: 2,6 TDI.
17. A method according to any of claims 2 to 16, wherein the aqueous blend of the layered material is in the form of a gel, paste or dispersion.

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18. A method according to any of claims 2 to 17, wherein the layered material is unmodified.
19. A method according to any of claims 2 to 18, wherein the layered material comprises layered minerals.
20. A method according to any of claims 2 to 19, wherein the layered material is sodium exchanged montmorillonite.
21. A method according to any of claims 2 to 20, wherein the layered material constitutes from 0.1 to 45% by weight of the total composition.
22. A method according to claim 21, wherein the layered material constitutes from 2 to 30% by weight of the total composition.
23. A method according to any of claims 2 to 22, wherein the following additional ingredients are added to the mixture and these are selected from water, auxiliary blowing agent, amine catalyst, tin catalyst, surfactant, filler, chain extender, cross-linker, stabiliser, anti-static additive, colourant, anti-oxidant, flame retardant and mixtures thereof.
24. A method according to claim 23, wherein the flame retardant is selected from melamine, aluminium trihydroxide (ATH), ammonium polyphosphate, expandable graphite or halogenated phosphates or zinc berates.
25. A method according to any of claims 2 to 24, wherein the polyurethane has a foam density in the range from 8kg/m3 to 300 kg/m3.