WO1997039083A1

WO1997039083A1 - Ammonium polyphosphate slurries

Info

Publication number: WO1997039083A1
Application number: PCT/EP1997/001799
Authority: WO
Inventors: Richard Malcolm Clapperton
Original assignee: Albright & Wilson Uk Limited
Priority date: 1996-04-13
Filing date: 1997-04-10
Publication date: 1997-10-23
Also published as: GB9707384D0; AU2384297A; GB2311939B; GB2311939A; AU2695197A; WO1997039101A1

Abstract

Ammonium polyphosphate fire retardant comprising material of low solubility is suspended in an aqueous structured surfactant preferably containing a more soluble ammonium polyphosphate in solution.

Description

AMMONIUM POLYPHOSPHATE SLURRIES

Introduction

The present invention provides pourable, stable, concentrated aqueous based slurries of ammonium polyphosphate comprising, typically, at least 35% by weight of polyphosphate. The slurries find particular application as fire retardants, which are present in an easily handleable form.

The invention is applicable to the preparation of slurries comprising the orthophosphate, pyrophosphate, triphosphate, tetraphosphate and or higher polyphosphates and metaphosphates of ammonium. In particular it is applicable to ammonium polyphosphate mixtures having a low solubility component (e.g. less than 5% in water at 20°C).

Ammonium polyphosphates are used as fire retardants. Their solubility in water depends on the degree of polymerisation. Ammonium polyphosphates are sold either as aqueous solutions of relatively soluble (lower molecular weight) products containing mainly ortho-, pyro- and tripolyphosphates, or as relatively water-insoluble higher molecular weight polyphosphates typically having mean molecular masses greater than 1000 amu up to and even greater than 1,200,000 amu The aqueous solutions are primarily used in applications such as impregnation of timber panel products for which a liquid is required and the solids in products such as intumescent paints for which a substantially anhydrous material is preferred.

Aqueous solutions of ammonium polyphosphates are often applied to products such as fibre board which are subjected to hot pressing. The lower molecular weight ammonium polyphosphates are liable to decompose at the temperatures employed for pressing such panels. It has been discovered that the higher molecular weight ammonium polyphosphates are stable at such temperatures. However, since they are insufficiently water-soluble, it has not been considered possible to apply them. Aqueous ammonium polyphosphates are limited in respect of their concentration by the solubility ofthe product. This results in solutions which are bulky, and expensive to store and transport. Solid polyphosphates are inconvenient to handle and may give rise to problems of dust, which may constitute a health hazard.

There is a need to provide concentrated, pourable, stable, aqueous ammonium polyphosphate slurries which can supply high levels of polyphosphates both in a weight on weight and weight on volume basis in a convenient form to avoid the cost of transporting dilute solutions, and to avoid the problems typically associated with handling the solid form.

There is a particular need to provide a fluid product which can be used to impregnate timber with an ammonium polyphosphate that does not decompose in the course of hot pressing.

The problem is therefore to provide arnmonium polyphosphate in a form:

(a) which contains more high molecular weight polyphosphate than could be obtained in aqueous solution;

(b) which is pourable and stable at normal storage temperatures (e.g.. 0 to 40°C) ; and

(c) which contains an economically viable concentration of phosphate per unit volume.

(d) that is more easily handled than the conventional powdery or granular solids;

In particular it is a specific object of the invention to obtain products meeting some or preferably all of the following criteria :

(i) They contain more than 20% w/w of undissolved polyphosphate, and preferably the maximum amount consistent with (ii) below; W

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(ii) They have a viscosity less than 3 Pas preferably less than 2 Pas at ambient temperature (e.g. 20°C) and 21 sec^"' shear;

(iii) They do not sediment on standing e.g. for 24 hours, preferably for 1 week most preferably for 3 months, at 20°C or at normal storage temperatures;

(iv) They do not contain ingredients which are extraneous to the desired end formulation in proportions relative to the phosphate which would be greater than is desirable in the end formulation;

(v) They contain a total weight of ammonium polyphosphate per unit volume at least comparable with the undiluted solids.

Discovery

We have now discovered that pourable, stable, concentrated, aqueous slurries which solve the above problem and which meet at least some of the above criteria may be prepared by suspending insoluble ammonium polyphosphates in a structured surfactant wherein the surfactant and dissolved electrolyte (typically dissolved ammonium polyphosphate) are sufficient to provide a solid-suspending spherulitic system.

Prior Art

Structured surfactants and in particular spherulitic systems are known in the detergent art. Detergent composition typically require the presence of high concentrations of surfactant and may also require a solid such as an abrasive and or an insoluble builder.

It has been found (see. for example, GB 2 153 380) that surfactants when present in sufficiently high concentrations, and, in the presence of sufficient quantities of dissolved electrolyte, form structured systems comprising a surfactant mesophase interspersed with an aqueous electrolyte phase. The surfactant mesophase is typically present, at least partly, in the form of spherulites having a diameter ofthe order of 0.05 to 20 microns (usually 0.1 to 10 microns) and comprising a plurality of concentric shells of surfactant, alternating with shells of aqueous phase. The surfactant shells are in the form of bilayers of surfactant molecules all arranged with their hydrophilic groups on the outer faces of the bilayer and their hydrophobic groups in the interior.

The spherulites can interact with one another to form weak structures which will immobilise and suspend solid particles indefinitely in the manner of a gel, but which break under the shear stresses imposed when the suspension is poured, permitting it to flow like a mobile liquid. Such systems are referred to as spherulitic. They may usually be identified by optical microscopy, using a polarising microscope when the spherulites typically appear as bright discs bearing dark extinction crosses, by scanning electron microscopy when the spherulites are usually directly visible and/or by small angle x-ray diffraction, when they often exhibit a peak corresponding to the repeat spacing between successive surfactant bilayers. This usually corresponds to a repeat spacing between 3 and 15nm, typically 5 to lOnm, often with a smaller second order peak at double the angle of the first, indicating lamellar symmetry.

Further details of structured surfactant systems are to be found in GB 2259519 and GB 2279080 which describes the use of certain surfactants to avoid flocculation of the spherulites. EP 0414549 describes the preparation of spherulitic structured surfactant systems in the absence of dissolved electrolytes.

The Invention

According to a first embodiment the present invention provides a stable, pourable, aqueous phosphate slurry comprising: water; at least 35% w/w of ammonium polyphosphate comprising a component having a solubility of less than 10% by weight in water at 20°C. said polyphosphate being at least partly present as suspended solid particles; and a surfactant system, adapted, in the presence of any dissolved proportion of phosphate or other surfactant-desolubilising electrolyte present in the slurry to foπn a spherulitic solid-supporting structure. Preferably according to this embodiment the amount of surfactant is sufficient, with the dissolved electrolyte, to form a structure capable of suspending, or inhibiting the sedimentation of, the particles, and in particular of preventing sedimentation over periods of at least three months.

According to a preferred embodiment the invention provides a composition consisting essentially of: (i) water; (ii) from 20 to 40% by weight of a solid ammonium polyphosphate having a mean molecular mass greater than 2,000amu ; (iii) from 30 to 60% by weight of dissolved ammonium polyphosphate having a mean molecular mass less than 800amu; (iv) from 1 to 5% by weight of surfactant said surfactant being sufficient to form a spherulitic structured surfactant capable of suspending said solid ammonium polyphosphate; and (v) from 0 to 2% by weight of foam inhibitors.

References herein to mean molecular mass shall whenever the context permits be construed as references to the weight average molecular mass.

Phosphate

The solid polyphosphate is preferably a relatively low solubility product, e.g. having a solubility less than 10%, especially less than 5% e.g. less than 3% w/w at 20°C in water. Typically the insoluble phosphate has a mean molecular mass greater than 3.000 amu and usually greater than 9,000 amu. For example products with molecular masses in the range 9,000 to 230,000 amu are often used, having a solubility of about 3%. However, ammonium polyphosphates are available with molecular masses in excess of 1 million amu and a solubility less than 1% w/w. Such products are also suitable for use according to the invention.

The soluble ammonium polyphosphate preferably consists of at least 50% by weight selected from mixtures of orthophosphate, pyrophosphate and tripolyphosphate, with a minor proportion of tetraphosphate and higher polyphosphates. The soluble polyphosphate preferably has a mean molecular mass less than 1 ,000 amu more preferably less than 800 amu, most preferably less than 500 amu usually between 150 and 450 e.g. between 200 and

400 amu. The soluble polyphosphate has a solubility greater than 20% w/w, more usually greater than 30% w/w/ especially greater than 40%, preferably greater than 50% more preferably greater than 55% e.g. greater than 60% w/w. Typically the aqueous phase ofthe slurry is saturated with respect to at least the major phosphate species present. Ammonium polyphosphate slurries for use as e.g. fire retardants may, for example, be formed by slurrying the solid ammonium polyphosphate in a solution (usually a saturated solution) of the more soluble ammonium polyphosphate. In general the total amount of suspended solid is at least

20% by weight ofthe composition more usually at least 30%, especially 20 to 40%, but for some purposes concentration of solid above 40%, e.g. more than 50% by weight are required.

In general the total amount of solid is preferably the maximum which can be slurried using the selected surfactant system, without the viscosity exceeding a desired level, e.g. 3 Pas, more preferably 2 Pas at 20°C and 21 sec^"'.

It is preferred that the total amount of soluble ammonium polyphosphate is from 20% to saturation, more preferably greater than 50% e.g. 30 to 60%.

It is preferred that the slurries comprise at least 45% w/w total phosphate, more preferably at least 50% w/w. most preferably at least 52% w/w e.g. at least 60%. In some cases levels of up to 70% or even 75% w/w total phosphate may be used.

Surfactant

The surfactant is generally present in a total concentration of from 1 to 10% by weight, more usually 1 to 5% especially 2 to 4%, preferably 2.5 to 3% by weight based on the total weight of slurry. We prefer that the weight ratio of phosphate to surfactant is greater than 4, more preferably greater than 6, especially 10 to 30 e.g.. 15 to 25.

The surfactant is preferably selected to form a spherulitic structured system in the presence of the electrolyte in the slurry. According to the conventional technology, hitherto employed in preparing liquid detergents a surfactant system has been selected such that when the concentration of dissolved electrolyte in an aqueous micellar solution of the surfactant is progressively increased from zero, keeping the surfactant to water ratio constant, the electrical conductivity ofthe system first rises to a maximum and then falls, passing, if the electrolyte is sufficiently soluble, through a minimum. The conductivity may subsequently pass through a second maximum. The two maxima define a trough within which the system is turbid and forms optically anisotropic spherulites. A space filling system has been selected within the conductivity trough. The behaviour is described in detail in GB 2 153 380.

For systems containing low levels of dissolved electrolyte it has sometimes been preferred to use surfactants of a type which form spherulites in the absence of electrolyte or in the presence of relatively low concentrations of electrolyte. A typical surfactant of this type is isopropylamine alkyl benzene sulphonate. Such systems are described in more detail in EP 0 414 549. When electrolytes are added to such surfactants the conductivity does not increase to an initial maximum, but instead may show an initial fall in conductivity on adding electrolyte, followed by a rise, ifthe electrolyte is sufficiently soluble.

For convenience, where the conductivity ofthe aqueous surfactant passes tluough a minimum on addition of a sufficiently soluble electrolyte, the range of electrolyte concentrations containing the minimum and extending between the next lowest maximum, (or in the case where there is no initial maximum, zero) and the next highest maximum (where present) will be referred to as the conductivity trough. Some surfactants may exhibit a plurality of troughs, associated with different, stable, suspending structures.

When an aqueous surfactant which exhibits a conductivity trough, is mixed with an electrolyte which causes a fall in conductivity, but reaches saturation before the minimum value is reached the saturation value is deemed for the purposes of this specification to fall within the conductivity trough which would notionally be formed if the concentration of the dissolved electrolyte could be increased further. The conventional spherulitic systems as described in the above prior art are not always applicable to suspending relatively large amounts of phosphate in the presence of relatively small amounts of surfactant as preferred in the present invention. When a large volume of solid phosphate is to be suspended, it may not be necessary to have such a large volume fraction of surfactant mesophase present in order to form a space filling system. Moreover adjusting the electrolyte content is not generally the most convenient way of obtaining a stable phase. In most cases the concentration of dissolved electrolyte is determined by the saturation concentration ofthe phosphates. Lower concentrations are not possible in the presence ofthe solid phosphate, whereas higher concentrations can be achieved only by adding a more soluble extraneous electrolyte. This is not generally preferred.

One way of identifying suitable surfactant combinations is to make up a mixture of two surfactants. Typically one surfactant is relatively water-insoluble, e.g. an alkylbenzene sulphonate, and the other is relatively water-soluble, e.g. an alkyl ether sulphate, a 10 to 50 mole ethoxylated alcohol or an alkyl polyglycoside. A series of compositions may be prepared at a constant total surfactant concentration and a constant (saturated) dissolved phosphate concentration, but containing the two surfactants in varying proportions. At sufficiently high concentrations, a plot of conductivity will usually reveal a minimum corresponding to the optimum mixture of surfactants.

Taking the optimised surfactant mixture, compositions spanning a range of total surfactant concentrations are prepared in saturated phosphate, in order to determine the optimum surfactant concentration.

When two or more conductivity troughs are observed, each associated with a stable structured system, we generally prefer to use concentrations of surfactant such that the saturation concentration of the electrolyte falls within the lower or lowest of the troughs.

The surfactant concentration may be adjusted such that the saturation concentration of the phosphate present in the slurry is greater than the concentration corresponding to the first maximum (where present) but below that which would be required to pass any second EP97/01799

- 9 - maximum and also, preferably, below that required to pass the minimum. Thus if addition of the phosphate to the aqueous surfactant system causes the conductivity to pass tiirough the conductivity minimum before the saturation concentration is reached, the surfactant level may be decreased until, on addition of the phosphate, the saturation concentration of the phosphate (or the total concentration of dissolved electrolyte actually present in the slurry) is reached before the conductivity passes through the minimum. Conversely if on addition to the surfactant ofthe electrolyte present in the aqueous phase of the slurry, one reaches the saturation point before the first conductivity maximum value has been passed, the concentration of surfactant may be increased, tending to shift any conductivity features to lower electrolyte concentrations, until the position ofthe trough is such that the electrolyte concentration present in the slurry is sufficient to take the conductivity past the first maximum but not past the first minimum.

Instead of increasing the surfactant concentration the same effect can be achieved by increasing the electrolyte concentration, e.g. by adding a more soluble salt to the slurry. Alternatively the composition of the surfactant mixture may be adjusted using the same amount of a less soluble surfactant to achieve the same effect as increasing the surfactant (or electrolyte) concentration, or of a more soluble surfactant to achieve the same effect as lowering the surfactant concentration.

Less soluble surfactants typically include sodium alkyl benzene sulphonates, and alcohol ethoxylates having a low degree of ethoxylation.

The more soluble surfactants typically include alkyl ether sulphates, alcohol higher ethoxylates and alkyl polyglycosides. Alkyl sulphates are generally more soluble than alkyl benzene sulphonates but less soluble than alkyl ether sulphates. They are preferably used as the more soluble component in combination with alkylbenzene sulphonates. It is, however, possible to use them as the less soluble component in conjunction with ether sulphates and higher alkylethoxylates. In order to achieve a non-flocculated surfactant system, especially where the dissolved electrolyte concentration is high, it is sometimes desirable to use small amounts of a deflocculant, which is preferably a deflocculating surfactant. The deflocculant is typically an alkyl polyglycoside or a polyacrylate capped at one end by an alkyl thiol. Deflocculating surfactants are described in detail in EP 0 623 670. Alternatively deflocculating polymers may be used, such as are described for instance in EPO 301 883 EP A 0 346 993 EP A 0 346 994 EP A 0 41568 WO91/09102 and WO91/09932. Generally only small amounts, e.g. less than 0.5% by weight or less of such deflocculents are required. Conventional deflocculants for the suspended solids are not normally required, however, since the surfactant itself is normally sufficient to prevent or inhibit the flocculation of the phosphate, to the extent required to form a stable, mobile slurry.

In general the surfactant system is usually a mixture of two or more surfactants selected from anionic, amphoteric and/or nonionic surfactants.

We prefer that the active system comprise at least one anionic surfactant, especially a sodium linear alkyl benzene sulphonate. Other anionic surfactants include alkyl sulphates, alkylether sulphates, parafin sulphates, oiefin sulphonates, fatty ester sulphonates, isethionates, soaps, taurides, salts of alkyl phosphonic acids, sulphosuccinates and sulphosuccinamates. In each case the surfactant has at least one C_g.₂₀ aliphatic hydrocarbon group e.g. a straight or branched chain alkyl or alkenyl group and the counter ion is preferably sodium but could also be potassium, lithium, an alkaline earth metal such as calcium, ammonium or an organic base such as isopropylamine or an alkanolamine. References to "ether" herein imply, unless the context requires otherwise, a polyoxyethylene group containing from 1 to 80 ethylene oxy groups more usually 2 to 50 groups e.g. 3 to 20 groups, said groups optionally containing a minor proportion of oxypropylene groups and/or a glyceryl group.

The surfactant may additionally or alternatively contain one or more non-ionic surfactants especially straight or branched chain C_8-20 alcohol ethoxylates having from 1 to 80 preferably 2 to 50 e.g. 3 to 20 ethyleneoxy groups. Other non ionics which may be present include ethoxylated C_g.20 carboxylic acids, ethoxylated C₈.₂₀ alkyl glycerides, ethoxylated C_8.20 sorbitan esters, alkyl polyglycosides, alkanolamides such as coconut mono and diethanolamide, sugar esters and amine oxides.

The surfactant may optionally comprise amphoteric surfactants, for example betaines, which are typically tertiary amines having one C₈.₂₀ alkyl group, which have been quatemised with chloracetic acid. Other surfactants which may be used include, sulphobetaincs and carboxymethyl ated imidazolines, or amidoamines. Less preferably the surfactant may comprise cationic surfactants such as quaternary ammonium surfactants. The counter-ions of the cationic surfactants are typically chloride, bromide, iodide, hydrosulphate, phosphate, citrate, acetate, formate, lactate or tartrate.

We normally prefer that cationic surfactants should not be used in conjunction with anionic surfactants.

The surfactant is preferably present in an amount sufficient to provide a surfactant structure which inhibits or preferably prevents the sedimentation ofthe particles. The structures preferably comprise spherulites, which are formed of concentrically arranged bilayers of surfactant, or domains of lamellar or other mesophase dispersed in the aqueous medium. The spherulites typically have a size in the range 0.05 to 20 microns, e.g. 0.1 to 10 microns.

The amount of surfactant is preferably adjusted to provide a non-sedimenting system. However, excess of surfactant may give rise to undesirably high viscosity. The amount of surfactant generally depends on the nature ofthe surfactant and the amount of suspended solid and dissolved electrolyte in the aqueous medium. The more solid phosphate present, and the more electrolyte in solution, the less surfactant is required to structure the composition. Rheology and Stability Requirements

We prefer that the slurries of our invention should be physically stable. The total amount of surfactant, is preferably adjusted to provide a composition which can be stored for at least 24 hours, preferably at least 1 week, more preferably at least 3 months at ambient temperature and preferably also at 0°C and 100°C without sedimentation, i.e. less than 5% v/v separation, preferably less than 3% v/v separation most preferably no visible separation of solids during storage at these temperatures.

The slurries of the present invention are preferably pseudoplastic. That is the viscosity is dependent on the applied shear, falling as the shear rate increases. There is preferably a yield point, or minimum shear force which must be applied before the slurry commences to flow. It has been found that the total concentration of surfactant, as well as the phosphate content, influence the rheology ofthe slurries. The particle size and morphology of the crystals is also found to influence the rheological behaviour ofthe slurries.

The zero shear rate viscosity ofthe slurries is determined by extrapolation ofthe viscosity measured by a stress/shear rate flow curve for the slurry. It should be sufficiently high to ensure that the slurry remains physically stable on storage as defined above.

The viscosity of the slurries at 21 sec^'1 over the temperature range 3°C to 40°C. should not be such than an unpourable slurry at any temperature in said range is produced. Preferably the zero shear rate viscosity of the slurries is within the range 100 Pa s to 5000 Pa s, most preferably 700 Pa s to 2000 Pa s. The viscosity at 21 sec^"1 ofthe slurries is preferably substantially constant over the temperature range 3°C to 40°C. Typically the viscosity at 21 sec^"1 shear rate will remain within the range of 0.4 Pa s to 5 Pa s, preferably 0.5 Pa s to 3 Pa s, e.g. 0.56 Pa s to 2 Pa s at all temperatures between 3°C to 40°C.

Immediately after the preparation ofthe slurries their viscosity at both 21 sec^"' and zero shear rate, is sometimes lower than the above preferred values. However, upon standing, e.g. after 2 to 6 hours, the viscosity usually rises to the above mentioned values, at which it typically remains substantially constant.

Other Components

Generally the slurries of our invention consist essentially of water, phosphate and surfactant. However it is sometimes useful to include other ingredients.

Ammonium polyphosphate slurries ofthe invention may contain auxiliary fire retardants such as red phosphorous, as well as foam inhibitors and biocides.

Other components which may be useful in an ammonium polyphosphate slurry include: antifoaming agents, such as silicone based antifoams or mineral oils, which may be present in amounts of up to 2% by weight, more preferably up to 1% by weight, especially up to 0.5% by weight, e.g. 0.01 to 0.4% by weight and which help to lower viscosity by releasing entrained air; thickeners such as gums and polymers e.g. guar gum or xanthan gum, which may sometimes be present in amounts up to about 2% by weight; suspending agents such as sodium carboxymethyl cellulose which are typically present in amounts up to 2%, more usually 0.1 to 1% e.g. 0.2 to 0.5%; electrolytes other than phosphate, such as chlorides, carbonates, silicates, citrates or alkali metal hydroxides, which may assist in structuring the slurry or in providing alkalinity, and which if so required may be present in concentrations up to saturation, but which are generally otherwise undesirable; auxiliary deflocculents such as lignin sulphonate, which are not normally required; biocides or preservatives to prevent microbiological contamination; and hydrotropes or solvents.

Preparation

Preferred methods of preparation ofthe slurries of the invention include continuous, e.g. loop processes, cascades, or a batch process. The invention will be further described with reference to the following examples:

Example 1

Seven formulations were made up from the following ingredients with the surfactant consisting of CIO-14 alkylpolyglycoside having a mean DP of 1.5 (APG) and sodium C10-14 alkylbenzene sulphonate (Na LABS) in varying proportions.

% a.i. Low Molecular Wt. 45% w/w soluble ammonium polyphosphate (sold under the registered Trade Mark "Amgard" WL) 29.59

High Molecular Wt, low solubility (<4%) ammonium polyphosphate

("Amgard" MC) 27.88

Silicone antifoam 0.15

Surfactant (APG + NaLABS) 2.55

Water 39.83

The viscosities and yield points ofthe samples were measured at 20°C and their phases observed using a polarising microscope. The results are recorded in Table 1. The relative proportions of APG and LABS is given by:

[APG]

[APG] + [NaLABS] TABLE 1

Example 2

The samples of Example 1 were centrifuged at 20,000G for 30 mins and the upper, aqueous surfactant layers were separated. Viscosity and yield point were measured and are recorded in Table 2.

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TABLE 2

Example 3

The three compositions set out in Table 3 were prepared. In each case the balance of the composition was water with 0.15% by weight, based on the weight ofthe composition, of silicone antifoam. The compositions were all stable and pumpable.

TABLE 3 w ve

v

Claims

1. A stable, pourable, composition comprising; water; at least 35% w/w ammonium polyphosphate comprising a component which has a solubility of less than 10% w/w in water at 20°C, which is present as suspended solid; and surfactants, adapted in the presence of any dissolved electrolyte present in the slurry to form a spherulitic, solid- supporting structure.

2. A composition according to claim 1 comprising (i) water; (ii) at least 20% by weight of ammonium polyphosphate having a solubility less than 10% w/w in water at 20°C; and (iii) from 20% by weight to saturation of ammonium polyphosphate having a solubility of greater than 20%> w/w in water at 20°C.

3. A composition according to either of claims 1 and 2 containing at least 20%) by weight of ammonium polyphosphate having a mean molecular mass of greater than 2,000 amu.

4. A composition according to claim 3 comprising at least 20%> by weight of ammonium polyphosphate having a mean molecular mass of greater than 9000 amu.

5. A composition according to claim 4 comprising from 30 to 40% by weight of ammonium polyphosphate having a mean molecular mass greater than 9,000.

6. A composition according to any foregoing claim comprising at least 30%_> by weight of ammonium polyphosphate having a mean molecular mass less than 900 amu.

7. A composition according to claim 6 comprising at least 30% by weight of ammonium polyphosphate having a mean molecular mass of from 150 to 450 amu.

8. A composition according to any foregoing claim containing from 1 to 10%) by weight of surfactant.

9. A composition according to claim 8 containing from 2 to 5% by w eight of surfactant.

10. A composition according to any foregoing claim consisting essentially of: water; 20 to 40%_> by weight of ammonium polyphosphate having a mean molecular mass greater than 9000 amu and/or a solubility of less than 10% by weight in water at 20°C; 30 to 60% by weight of ammonium polyphosphate having a mean molecular mass of 150 to 450 amu and/or a solubility of more than 20%> by weight in water at 20°C; from 1 to 10% by weight of surfactant; and from 0 to 2% by weight of a foam inhibitor.