GB2078752A - Syntactic Thermosetting Resin Foam Compositions Containing Fly- ash - Google Patents

Abstract

A syntactic foam composition having a low specific gravity and a high resistance to hydrostatic compression is made by curing a mixture comprising fly-ash and a thermosetting resin formulation including at least one conjugated diene polymer. The fly-ash consists of hollow non-combustible particles transported by the smoke from boilers burning powdered coal. It can be used as a lightweight construction material and is particularly useful for marine floats, oil-drilling installations and other submerged articles resistant to hydrostatic compression.

Description

SPECIFICATION Syntactic Foam Compositions Containing Flyash, for Use Particularly as Buoyancy Materials The invention concerns new buoyancy materials for use at great depths, particularly in oil drilling installations.

Various techniques which are carried out in and under the sea are known to make use of materials with a set of special properties, particularly low density, high resistance to hydrostatic compression and low capacity for absorbing water.

Under the generic name of "syntactic foam", a number of materials have already been proposed in prior art, comprising compositions of polymeric resins which are made lighter by the inclusion of hollow spheres made of thermoplastic or thermosetting resins or borosilicate glass, silica or carbon. Typical examples of the hollow spheres used in previous methods are hollow microspheres or "microballs", made of borosilicate glass and generally from 10 to 250 microns in diameter, and hollow macrospheres or "macroballs", made of resins (possibly reinforced with glass or carbon fibres) and generally from 1 to 50 mm in diameter.

Apart from the poor resistance to hydrostatic compression which some of the hollow bodies have, the main disadvantage of using prior art micro- or macroballs is their very high cost; consequently, in spite of their intrinsic qualities, applications of this type of syntactic foam are still limited by the unfavourable economic factor.

As a way of avoiding these disadvantages, syntactic foams have already been proposed in prior art, with the hollow glass microspheres replaced by "fly-ash",which consists of small, hollow, non-combustible particles transported by the smoke from boilers burning powdered coal, and collected in electrostatic dust removers before being discharged through the chimneys (see e.g. "les Cendres Volantes" by A. Jarrige, Editions Eyrolles).

The dimensions of the grains are generally from 0.5 to 200 microns, and the average apparent mass per unit volume of the grains of fly-ash is e.g. from approximately 190 to 340 kg/m3 (specific gravity 0.19 to 0.34).

The elemental chemical composition of the flyash varies according to where the coal is obtained from. It usually contains silica, alumina, iron, aikaline earth metals and alkali metals, generally in complex combinations; it may further contain unburnt residues resulting from incomplete combustion of the coal. Fly-ash is virtually insoluble in water.

Thus the syntactic foams previously described contained fly-ash enclosed in matrices consisting of phenolic resins, polyepoxides and polyesters.

However, syntactic foams formed in this way have a number of disadvantages; in particular, their density and their buoyancy reserve are insufficient to meet requirements for the applications envisaged for these materials.

The invention proposes new syntactic foams which inter alia have very good properties of resistance to hydrostatic compression. They also have the advantage of low cost. Futhermore, they have much reduced density and hence a high "buoyancy reserve", which is maintained down to great depths. Finally, all their physical and mechanical properties are retained for long periods of time.

The syntactic foam compositions of the invention may be generally defined as resulting from the hardening of a mixture comprising flyash and a thermosetting resin formulation comprising at least one conjugated diene polymer.

More particularly; the conjugated diene polymer used consists of a polybutadiene, the microstructure of which is made up of 20 to 98% of 1, 2 units, of which from 5 to 40% may be in cyclised form, the complement of unsaturation being in the form 1, 4 cis or trans; the polybutadiene has an average molecular weight, as a number, less than 100,000.

In effect the use of a resin based on 1, 2 polybutadiene associated with fly-ash has the economic advantage of producing a material which is an interesting compromise between low density and high resistance to compression.

The resin can further be diluted or fluidised by the addition of one or more liquid unsaturated monomers. It contains one or more agents for initiating thermal cross-linking, such as aliphatic or aromatic peroxides, or peresters, which provide free radicals at the resin curing state. It is also possible to use mixtures of radical producing compounds in combination with accelerating compounds well known in the art, such as metallic derivatives or amines.

As an illustration of a particularly appropriate formulation for a thermosetting resin the composition may contain from 30 to 99% by weight of polybutadiene: from 0 to 69% by weight of a liquid monomer which can be polymerised by radicals, such as styrene, a-methylstyrene, ethylstyrene, vinyltoluene or t-butylstyrene:- and 1 to 5% by weight of a compound producing free radicals, such as an organic peroxide or perester compound.

According to the invention, the fly-ash is preferably used dry, since it then has a fluid flow.

It generally has a specific gravity in the region of 0.4, e.g. from 0.35 to 0.43.

The quantity of fly-ash included in the syntactic foams of the invention may vary and will be determined by the properties required for the final weight-reduced material. Generally speaking from 5 to 60 parts by weight of fly-ash is used per 95 to 40 parts by weight of resin. These respective proportions are preferably from 1 5 to 50 and from 85 to 50.

Without going beyond the scope of the invention, it is possible to use fly-ash mixed with other hollow fillers such as inorganic or organic micro- or macro-balls, or with other fillers, in powder or fibre form, e.g. expanded glass or reinforcing glass, asbestos or carbon fibres. From 2 to 25 parts by weight are then generally used per 100 parts by weight of foam.

The strength of the syntactic foam according to the invention may equally be improved by adding to the resin a substance which will encourage adhesion between the resin and the fly-ash, such as vinylsilane, vinyltriethoxysilane or vinyl tris (2methoxyethoxy) silane.

Preparation of the syntactic foams according to the invention is relatively simple. Taking a liquid mixture of a polydiene resin containing one or more radical producing compounds, the required quantity of dry fly-ash is gradually added, and possibly other weight reducing or reinforcing fillers. Mixing is continued until a homogeneous consistency is obtained. It is then desirable to degas the mixture of constituents, while keeping it at low pressure for a period ranging from 30 minutes to 2 hours, so as to remove the enclosed air. The mixture is then poured into a mould ofthe final shape required for the foam, and is thermoset by heating in a heat controlled oven, which may possibly be ventilated.

The temperature and baking time for syntactic foams according to the invention vary and will be determined particularly by the type of free radical generator used and by the composition of the resin. Generally speaking, thermal cross-linking is carried out at a temperature from 25 to 2000C for a period of 1 to 48 hours.

The syntactic foam is preferably cured in several stages, by gradual heating. This gives better control over the reaction and prevents microcracks from forming, particularly in the manufacture of foam particles of large dimension and large cross-section.

The syntactic foams of the invention have a reduced specific gravity e.g. reduced to values below 0.8 and in some cases as little as 0.5.

They may have various applications. They form excellent lightweight construction materials. They can preferably be used for articles intended to come into contact with water, such as pipes running under the sea or pipework used to exploit the heat energy of the sea. They are more particularly intended for buoyancy materials which have to be resistant to hydrostatic compression, such as submarines or floats used at great depths, or the extension tubes used in producing oil at sea.

The following examples are given as an illustration of the invention, but should in no way be regarded as imposing any limitations on it.

Example 2 is given as a comparison. The fly-ash used has dimensions of approximately 30 to 120 microns.

Example 1 A solution is prepared, consisting of 1 65 g of a polybutadiene, the microstructure of which is made up of 75% of 1, 2 units, and the average molecular weight of which, as a number, is equal to 5,000, with 3.3 g of tertiobutyl perbenzoate and 3.3 g of dicumyl peroxide, in 165 g of vinyltoluene. 296 g of dry fly-ash is stirred gradually into the solution. The fluid mixture is degassed for 30 minutes at low pressure, before being poured into a baking mould. It is heated in a heat controlled oven, at 850C for 16 hours then at 1 300C for 24 hours. The syntactic foam thus obtained has a density of 0.73 and a resistance to breaking by hydrostatic compression of 830 bars.

Example 2 (comparative) An equal quantity of an epoxy resin is prepared, i.e. 330 g, by adding equal quantities of a liquid epoxy binder derived from bisphenol A diglycidylether and a hardener based on tetrapropenylsuccinic anhydride.

An equal quantity, i.e. 296 g, of dry fly-ash is stirred gradually into, the liquid mixture.

The fluid mixture is de-gassed for 30 minutes at reduced pressure before being poured into the baking mould. It is heated in a heat controlled oven at 400C for 8 hours, 800C for 8 hours and 1000C for 24 hours.

The density of the syntactic foam obtained is 0.94 and its resistance to hydrostatic compression is 640 bars.

Example 3 A solution is prepared, consisting of 267 g of a polybutadiene containing 85% of 1,2 units with 25% in cyclised form and with an average molecular weight, as a number, equal to 1,800; 16 g of vinyltriethoxysilane; 5.5 g of benzoyl peroxide and 5.5 g of dicumyl peroxide, in 267 g of vinyltoluene. 18 g of short carbon fibres, 110 g of dry fly-ash and 94 g of glass microballs sold by Minnesota Mining and Manufacturing Co. under reference B28-750 are added to the solution. The mixture is de-gassed for 1 hour at reduced pressure. Thermal cross-linking is carried out at 700C for 8 hours and 1 500C for 20 hours. The density of the syntactic foam thus obtained in 0.64 and its resistance to breaking by hydrostatic compression is 815 bars.

Example 4 A solution of 300 g of polybutadiene is prepared, containing 60% of 1,2 units with 15% in cyclic form and with an average molecular weight, as a number, equal to 1,300, 6.6 g of tertiobutyl perbenzoate and 6.6 g of dicumyl peroxide in 300 g of vinyltoluene. A mixture of 260 g of selected fly-ash (apparent density in the region of 0.4) and 300 g of glass microballs (apparent density in the region of 0.28) are stirred into the solution. The mixture is de-gassed for 30 minutes at reduced pressure and injected into a mould, which is heated in a stove, successively at 700for7 hours, 1000Cfor2 hours, 1 150for2 hours and 1 300C for 10 hours. The density of the foam obtained is 0.55 and its resistance to breaking by uniaxial compression is 640 bars.

Example 5 1 75 g of fly-ash and 50 g of macroballs, sold by Emerson and Cumming under the name of Eccospheres EP 300, are mixed with 275 g of a polybutadiene resin of the formulation described in Example 1.

The mixture is gradually heated to 650C for 4 hours, 800C for 4 hours and 1 200C for 8 hours.

The density of the syntactic foam obtained is below 0.50. Its resistance to hydrostatic compression is nevertheless over 400 bars.

Claims (12)

Claims

1. A syntactic foam composition that results from curing a mixture comprising fly-ash and a thermo-setting resin formulation including at least one conjugated diene polymer

2. A composition as claimed in Claim 1, in which the conjugated diene polymer is polybutadiene, the micro-structure of which is made up of 20 to 98% of 1,2 units, the complement of unsaturation being in the form 1, 4 cis or trans, and the polybutadiene having an average number molecular weight less than 100,000.

3. A composition as claimed in Claim 2, in which from 5 to 40% of the 1, 2 units of the polybutadiene are in cyclised form.

4. A composition as claimed in any one of Claims 1 to 3, in which the thermosetting resin formulation comprises from 30 to 99% by weight of polybutadiene, 0 to 69% by weight of at least one free-radical-polymerisable liquid monomer, and 1 to 5% by weight of at least one free-radicalproducing compound.

5. A composition as claimed in any one of Claims 1 to 4, in which the fly-ash has particles whose size is in the range 0.5 to 200 microns and its mean specific gravity is approximately 0.4.

6. A composition as claimed in any one of Claims 1 to 5, in which the said mixture comprises from 5 to 60 parts by weight of fly-ash, and from 95 to 40 parts by weight of the said thermosetting resin formulation.

7. A composition as claimed in Claim 6, in which the said mixture comprises from 1 5 to 50 parts by weight of fly-ash and from 85 to 50 parts by weight of the thermosetting resin formulation.

8. A composition as claimed in any one of Claims 1 to 7, that further contains from 2 to 25 parts by weight of micro- and/or macro-balls and/or inorganic or organic reinforcing fibres per 100 parts by weight of foam.

9. A composition as claimed in Claim 1 substantially as hereinbefore described in any one of Examples 1 to 5.

10. A method of preparing a composition as claimed in any one of Claims 1 to 8, in which the mixture of at least the fly-ash and a thermosetting resin composition is heated to a temperature in the range 25 to 2000C in the presence of at least one compound producing free radicals.

11. Marine floats, oil-drilling installations and other submerged articles resistant to hydrostatic compression in which a syntactic foam composition as claimed in any one of Claims 1 to 9 has been used as a construction material.

12. Lightweight building construction components in which a syntactic foam composition as claimed in any one of Claims 1 to 9 has been used as a construction material.