GB2244490A

GB2244490A - Buoyancy materials

Info

Publication number: GB2244490A
Application number: GB9111618A
Authority: GB
Inventors: Jacques Jarrin; Eric Robert; Bernard Aubin
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 1990-05-31
Filing date: 1991-05-30
Publication date: 1991-12-04
Anticipated expiration: 2011-05-30
Also published as: GB2244490B; GB9111618D0; NO912069L; FR2662634A1; FR2662634B1; NO912069D0; CA2043724A1; BR9102194A; JPH04232034A

Abstract

Hollow macrospheres made of polypropylene filled with long glass fibres and their use in making buoyancy materials are disclosed. The hollow macrospheres have a diameter of 2 to 20 cm and can be made by assembling two hollow hemispheres obtained e.g. by molding or injecting filled polypropylene. The buoyancy material comprises e.g. from 30 to 60% by volume of such hollow macrospheres, from 0 to 40% by volume of hollow macrospheres from 0.2 to 1.5 cm in diameter, from 20 to 50% by volume of hollow glass microspherules from 5 to 500 microns in diameter and from 10 to 40% by volume of at least one thermoset resin such as a polybutadiene, a polyepoxide, an unsaturated polyester or a polyurethane. The buoyancy materials of the invention have optimum properties of density, resistance to hydrostatic compression and water absorption. They are useful in raising sunken vessels.

Description

LLO MACROSPHERES AND BUOYANCY MATERIALS CONTAINjNC TS The invention is concerned with the field of materials used to give buoyancy to submerged structures.

More particularly, it concerns hollow macrospheres with a lightening effect and buoyancy materials in which these hollow macrospheres are used.

The buoyancy materials are generally made up of a combination of a resin, often a thermosetting one, and fillers with a lightening effect which are resistant to hydrostatic pressure.

The fillers with a lightening effect are most frequently hollow glass microspheres (or microballs), which may be prepared particularly as described in US Patents 2,797,201 and 3,365 ,315. The materials obtained by combining a thermosetting resin and hollow glass microspheres (or syntactic foams) have properties which depend on the quality of resin used and those of the microballs. These materials are prepared by mixing the resin in the liquid state with the highest possible proportion of hollow glass microspherules, and avoiding the appearance of porosity in the resin.

The resin is then thermoset and composite materials are obtained, made up e.g. of 55 to 658 by volume of hollow glass microspherules and 45 to 35% by volume of thermoset resin. The conditions for preparing such syntactic materials are described, for example, in Applicants' French Patent Specifications2,346,403 and 2,361,438 and US Patent 4,107,134.

The properties which these materials are generally acknowledged to have are low density, mechanical properties in hydrostatic compression and low water absorption.

The low density depends on the density of the thermoset resin, the density of the hollow glass microspherules and the proportions (by volume) in which the resin is filled with the microspherules. The resins generally used may be polyepoxides French Patent 2,592,385)1 unsaturated polyesters or polyurethanes, or they may be based on polybutadiene, as described in Applicants' abovearentioned patent specifications or in British Patent Specification 1,195,568.

A general description of the materials is contained in the article by M. Puterman, N. Narkis and S. Rejig entitled: "Syntactic Foams I: preparation, structures and properties".

US Patents 3,353,981 and 3.230.184 also describe the preparation of syntactic foams.

In the following description the densities may be classed as specific mass and will often be given in g/cm3.

The mechanical properties of the syntactic materials in hydrostatic compression depend on the degree to which the thermoset resin is cross-linked, its mechanical properties and those of the hollow glass microspherules incorporated in the resin.

The low water absorption under pressure enables the buoyancy given to the submerged structures to be kept stable with the passage of time.

Some standard properties of syntactic materials described in Applicants' Patent Specifications will be given below, with an indication of the depths at which the materials can be used. The matrixes of the materials are based on entirely hydrocarbon resin.

made up of a thermally cross-linked mixture of one or more styrene monomers and polybutadiene rich in 1,2 units.

The values given as an indication in Table 1 show that this type of material may be used within a depth range from 0 to about 600cm, for densities of 0.43 to 0.59 g/cm3.

TABLE 1 Hollow microspheres K1* B28/75G* D 32/4500* Utilisation depth (m) 1500 2500 6000 Density of syntactic 0.43 0.52 0.59 material (g/cm3) Water absorption (%) < 1 < 1 < 1 after 24 h at (MPa) 15 25 GO * registered trade marks for hollow microspheres marketed by 3M.

The range of utilisation pressures amply covers the potential field of application of these materials. Seabed depths of over 6000 m are relatively rare, and there are no plans to exploit them at present. On the other hand the density of the materials is a very important property to check.

then buoyancy materials are used, the volume submerged must in fact be as low as possible, in order to limit the hydrodynamic strains applied to the structure (currents, effects of a swell) and the costs involved in transporting, handling and positioning the buoyancy elements around the structure. Users are therefore always seeking an optimum compromise between the density of the material and its resistance to hydrostatic compression. They prefer to use lower density materials, particularly in the shallow water range (0 to about 1000 m). These materials may be exparsed foars rade of polyvinylechloride or polyir,ide(US Patent 4 ,433 ,068) .

In this case it is very difficult to obtain an expanded structure with cells which are 100% closed.

This type of material is generally found to have much lower resistance to penetration of water under pressure than syntactic foams; users are again preferring to use syntactic foams, this time made lighter by incorporating hollow lightening macroglobes.

The hollow macroglobes are hollow spheres with a diameter from 1 rrin to about 200 mm, which differentiates them from the hollow microspheres. The preparation of syntactic materials with hollow macroglobes is described, for example, inUS Patent 3,622 ,437.

The lightening macroglobes can be made in various ways. Hollow macrospheres can be made by coating spheres of expanded polystyrene with a thermosetting resin filled with short glass fibres, then cross-linking the resin hot. But in this case the formation of macroglobes larger than about 2 cm in diameter becomes a very delicate operation, whereas if the proportion of filling with lightening material is to be optimised binodal distribution of macroglobes is necessary. Binodal distribution of macroglobes is provided by a set of macroglobes of various diameters, in which the variation in the statistical frequency of the macroglobes as a function of diameter has two clearly differentiated maxima. More particularly it may be a combination of two populations of hollow macrospheres of sufficiently different diameters. The text of the patent published under International Publication No. VX) 87/04 662 describes a method of blowing bubbles of a diameter limited to 10 mm; this therefore has the same disadvantage.

In order to increase the diameter of the macroglobes, methods such as rotational molding or expansion of mixtures of liquid resins filled with glass microspherules have been proposed in US Patent 4,111,713 and 4,482,590. These preparation methods are tricky to carry out owing to the relatively long cycle during the rotational molding and thermal cross-linking of the resins. Moreover it is very difficult to avoid decantation or porosity of the macroglobes thus produced, particularly when the pore forming agents expand. Water absorption by this type of macroglobe is generally much greater than that obtained by sticking or welding hemispheres of filled thermoplastic materials obtained by injection or moulding, as described, e.g. in US Patent 3,622437.

This last method, of injecting then joining hemispheres of thermoplastic materials reinforced with short glass fibres appears to be the most appropriate to form macroglobes from about 2 to 20 cm in diameter.

These macrospheres are characterised by their density (ratio of weight of material used to volume of macrosphere), their resistance to implosion and their absorption of water under hydrostatic pressure as a function of the period of use. They are also characterised by their chemical compatibility with the resins employed in producing syntactic foams, particularly during the hot cross-linking of the materials.

It has now been found that hollow macrospheres can be produced, providing an optimum compromise between the various properties required in the preparation of buoyancy materials. These hollow macrospheres and their use will be described more specifically below.

The hollow macrospheres of the invention may be defined in a general way by the fact that they are made of polypropylene with a 25 to 50% by weight filling of long glass fibres, and that their diameter may range from 2 to 20 cm. Their wall thicknesses are more particularly from 0.5 to 5 mm.

The macrospheres have optimum properties of density and resistance to hydrostatic compression, the latter property being affected as little as possible by prolonged submersion in water.

Polypropylenes which can be used to produce the hollow macrospheres of the invention have a melt index of from 0.2 to 50 g/10 min.

This index is defined in accordance with standard ASItI D-1238; it is none other than a measurement of the mass of polymer which flows at 2300c during a period of 10 min., when the polymer is extruded through a die of standard size and with a diameter of 2.095 nrn under a load of 21.6 N.

Long glass fibres generally have a length of 1 to 10 mm, whereas so-called "short" glass fibres generally have a length of 0.2 to 1 mm.

The hollow macrospheres of the invention may be produced by joining two hollow hemispheres, e.g. by welding or adhesion, the hemispheres themselves being obtained e.g. by lding or injecting filled polypropylene as described above. The welding of the two hemispheres may be carried out by the friction or ultrasonic method, and the adhesion by means of an epoxide, acrylic or neoprene type glue.

The buoyancy materials of the invention are obtained by incorporating, in particular, hollow macrospheres as described above, in thermosetting resin.

They are defined more particularly by the fact that they comprise: from 30 to 60% by volume of hollow macrospheres as defined above; from 20 to 50% by volume of hollow microspherules with a diameter of 5 to 500 microns; and from 10 to 40% by volume of at least one thermosetting resin.

It is also possible, according to the invention, to include a proportion of up to 40% by volume of hollow macrospheres from 0.2 to 1.5 cm in diameter, in order to improve the filling of the resin with lightening fillers. These macrospheres are known in prior art. They may, for example, be hollow macrospheres produced by coating spheres of expanded polystyrene with a thermosetting resin filled with short glass fibres, followed by hot cross-linking of the resin. Such macrospheres are marketed by Emerson & Cumming.

The thermoset resin used as matrix for the buoyancy materials of the invention may be selected from unsaturated hydrocarbon resins (for example polybutadienes), polyepoxides, unsaturated polyesters and polyurethanes.

It is obtained more particularly by cooking a thermosetting resin based on polybutadiene, preferably comprising from 30 to 70% by weight of at least one polybutadiene containing at least 30% of 1,2 units and with a number average molecular weight of less than 20,000, from 29.5 to 69.5% by weight of at least one vinyl monomer selected e.g. from styrene, vinyl toluene, gL-methyl styrene and tertiobutylsytrene, and at least one organic peroxide, as a compound to initiate radical reactions, in a proportion of 0.5 to 5% by weight.

Vinyltriethoxysilane may also be included in the thermosetting resin, for example in a proportion of up to 2% by weight relative to the total weight of resin, to improve the adhesion of the resin to the glass walls of the microspherules.

The thermosetting resin in question may also be obtained by cooking an epoxide resin comprising one or more prepolymers carrying epoxide functions, mixed in substantially stoichiometric proportions with at least one hardener selected from compounds carrying at least one anhydride, amino, alcohol or carboxylic acid function, and the usual catalysts for this type of resin.

The following examples illustrate the invention without restricting its scope. Some materials are described and tested as a comparison.

EXAFfPLE 1: This example compares the properties of hollow macrospheres numbered 1 to 10, made from various materials numbered 1 to 9.

Material 1: expoxy resin filled with short glass fibres; density 1.35 g/cm3 Material 2: acrylonitrile-butadiene-styrene (ABS) polymer resins filled with 20% by weight of short glass fibres; density 1.23 g/cm .

Material 3: polybutylene terephalate (PBT) resin filled with 30% by weight of short glass fibres; density 1.53 g/cm3.

Material 4: polypropylene (PP) resin filled with 40% by weight of long glass fibres: density 1.22 g/cm3.

Material 5: polypropylene (PP) resin filled with 30% by weight of short glass fibres; density 1.14 g/cm3.

Material 6: polyamide resin derived from caprolactam (PA 6); density 1.12 g/cm3 Material 7: polyamide (PA 6) resin filled with 30% by weight of short glass fibres; density 1.37 g/cm3.

Material 8: polyamide resin derived from adipic acid and hexamethylene diamine (PA 6.6) filled with 508 by weight of short glass fibres; density 1.57 g/cm3.

Material 9: polyarylamide resin filled with 50% by weight of short glass fibres; density 1.64 g/cm3.

The e hollow macrospheres made from these materials have the characteristics and properties indicated in Table 2 below.

TABLE 2

Macrospheres Material Diameter Density Resistance to hydrostatic compression (cm) (g/cm ) (MPa) 1 2 0,15-1.3 0,32 7 2 2 5,0 0.22 7.5 3 2 5.0 0,275 10 4 3 5.0 0.29 11 5 4 ,0 0,23 12 6 5 5,0 0.22 7 7 6 5,0 0.21 7 8 7 5,0 0.26 > 10 9 8 5,0 0.30 > 10 10 9 5.0 0.31 > 10 Hallow macrospheres 1 are marked by Emerson & Cumings.

Hollw macrospheres 2 to 10 are prepared by joining hemispheres, obtained by injection from the material 2 to in question.

From the characteristics and properties given in Table 2, the best compromise between resistance to compression and density appears to be obtained with hollow macrospherss 5, made from polypropylone with a 40 % by weight filling of long glass fibres.

EXAMPLE 2.

The collapsing pressure, the absorption of water during various periods of immersion and the collapsing pressure after each period are determined for hollow macrospheres 1, 3, 4, 5, 7, 8, 9 and 10. The results are given in Table 3 below.

TABLE 3 Initial Water absorption Collapsing Hollow collapsing pressure macrospheres pressure after immersion (MPa) after at (%) (MPa) 1 7 10 days 200C 4 4 3 10 2 days 200C 0.7 6 4 10 125 days 200C 0.3 10 5 12 125 days 200C 0.3 12 7 7 10 days 200C 6.2 2.4 14 days 600C 8.6 2.0 8 > 10 10 days 20OC 3.4 6.2 14 days 600C 5.2 5.6 9 > 10 10 days 200C 2.3 8.3 14 days 600C 3.9 6.6 10 > 10 10 days 200C 3.3 7.0 The hollow macrospheres of the invention (No. 5) appear to absorb the minimum of water and to have the same collapsing pressure results before and after a long period of immersion (125 days).

EXAMPLE 3: Buoyancy materials are prepared using the hollow macrospheres numbered 1, 3, 4 and 5 and two different thermosetting resins: an expoxide resin and an unsaturated hydrocarbon resin. The expoxide resin is made up of 41.5% by weight of Epikote 815 (trade mark registered by Shell), 57.5% by weight of dodecylsuccinic anhydride and 1% by weight of tri n-butyl amine.

The thermal cross-linking conditions applied are as follows: 20 hours at 800C 10 hours at l300C The epoxide resin has a density of 1.04 g/cm3 and a viscosity of 350 10-m2/s at 200C.

The unsaturated hydrocarbon resin is made up of: 48% by weight of polybutadiene, marketed by Revertex under the reference Lithene AH (registered trade mark); 48% by weight of vinyl toluene; 1% by weight of tertiobutyl perbenzoate - Trigonox C (trade mark registered by AKZO); 2% by weight of dicumyl peroxide - Perkadox BC 95 (trade mark registered by AKZO); and 1% by weight of vinyltriethoxysilane.

The conditions for thermal cross-linking are as follows: 20 hours at 800C 10 hours at 1400C The resin has a density of 0.98 g/cm3 and a viscosity of 80 10- &commat; 2/s at 2C C.

Each of the two resins used contains hollow glass microspherules with a diameter of 5 to 500 microns, in a proportion of 29 to 33% by weight according to the viscosity of the resin. (The microspherules are marketed by 3M under the name of K1).

For materials A and F (see Table 4) the proportion filled with hollow macrospheres is about 60% by volume, for 40% by volume of resin-microspherule mixture. For materials B, C D, G, H and I the proportion filled with hollow macrospheres is of the order 35% by volume, for 65% by volume of resin-microspherule mixture.

For materials E and J two kinds of hollow macrospheres are used: type 1 hollow macrospheres (mean diameter about 0.5 cm) occupying about 20% by volume and type 5 hollow macrospheres (diameter 5 cm) occupying about 33% by volume, for 47% by volume of resin-microspherule mixture.

The test pieces whose characteristics are determined are cylinders 30 cm high and 15 Cm in diameter.

The characteristics are measured on the test pieces as when they emerge from the mo ld, that is to say, without any external coating. Under these conditions the hollow macrospheres present at the wall are in direct contact with water under pressure when resistance to hydrostatic compression is measured.

It first becomes apparent (material G) that the combination of macrospheres of ABS with hydrocarbon resin is not advisable, since the macrospheres of ABS are much deformed after thermal cross-linking. Syntactic foam G is porous and fragile.

It also becomes apparent that with both types of resins the lowest densities are obtained with macrospheres 5 made of polypropylene reinforced with long glass fibres. Similarly, whatever type of macrospheres is used, the unsaturrated hydrocarbon resin gives the material of lowest density.

Table 4

Syntactic Resistance to hydro Reference Resin Macrospheres material static compression density (MPa) A epoxy 1 0.42 8.3 B " 3 0.40 9.5 C " 4 0.41 11.5 D " 5 0.39 9.5 1 E " 1 0.36 8.3 5 F hydrocarbon 1 0.39 7.5 G " 3 0.38 0 H " 4 0.38 10.7 I " 5 0.36 11.3 1 J " - 0.34 8.2 5 In cases where pieces of smalier volume are made, the filling proportion accessible with macrospheres 5 cm in diameter is still small (about 350), and it is then advantageous to optimise the proportion of macrosphere filling by comining two populations of macrospheres of sufficiently differrent diameters (imaterials E and J). It is found that materials of lower density can be prepared (Material J) by combinig unsaturrated hydrocarbon rasin with polypropylene macrospheres with a 40 % filling of long glass fibres and macrospheres of smaller diameter.

EXAMPLE 4: This example illustrates the characteristics of the macrospheres according to the invention when pieces of larger volume are made.

In this case the proportion filled with macrospheres is larger.

60 litre pieces (cylinders 35 Cm in diameter and 60 cm high) are made with different macrospheres and the unsaturated hydrocarbon resin described in the previous examples, combined with S1 microspherules. The characteristics of the syntactic materials formed are given in Table 5 below: TABLE 5 Density of Resistance to Syntactic Macrospheres syntactic hydrostatic material foam compression (MPa) K 5 0.32 12.3 L 4 0.36 10.5 M 1 0.36 6.5 N

+ 0.30 6.6 5 In this case it is clear that the best results are obtained with macrospheres 5 (material K) or with a combination of these macrospheres with other macrospheres of far smaller diameter (material N).

Claims

1 - Hollow macrospheres, having a diameter of 2 to 20 cm, and made up of polypropylene with a 25 to 50% by weight filling of long glass fibres.

2 - The macrospheres of Claim 1, whose wall has a thickness of 0.5 to 5mum.

3 - The macrospheres of Claim 1 wherein the polypropylene has a melt index, measured in accordance with ASTM standard D-1238 at 2300C and 21.6 N, of 0.2 to 50g/10 minutes.

4 - The macrospheres of Claim 1 wherein the long glass fibres have a length of 1 to 10 mm.

5 - A method of preparing the macrospheres of 1 wherein two hemispheres prepared by molding or injection are joined.

6 - A buoyancy material, comprising 30 to 60% by volume of hollow macrospheres of Claim 1; 0 to 40% by volume of hollow macrospheres with a diameter of 0.2 to 1.5 cm; 20 to 50% by volume of hollow glass microspherules with a diameter of 5 to 500 microns; and 10 to 40% by volume of at least one thermoset resin.

7 - The material of Claim 6 wherein said thermoset resin is selected from unsaturated hydrocarbon resins, polyepoxides, unsaturated polyesters and polyurethanes.

8 - The material of Claim 7 wherein said thermoset resin is obtained by cooking a composition comprising: 30 to 70% by weight of at least one polybutadiene containing at least 30% of 1,2 units and with a number average molecular weight of less than 20,000; 29.5 to 69.5% by weight of at least one vinyl monomer selected from styrene, vinyl toluene,d/-methylstyrene and tertiobutylstyrene; 0.5 to 5% by weight of at least one organic peroxide; and 0 to 22 by weight of vinyltriethoxysilane.

9 - The material of Claim 7 wherein said thermoset resin is obtained by cooking an epoxide resin, containing at least one prepolymer carrying epoxide functions, mixed in substantially stoichiometric proportions with at least one hardener, selected from compounds carrying at least one anhydride, amino, alcohol or carboxylic acid function.