WO2000015007A1

WO2000015007A1 - A plastics material in combination with a paramagnetic silicate

Info

Publication number: WO2000015007A1
Application number: PCT/GB1999/002975
Authority: WO
Inventors: Allan Ernest Churchman
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-09-09
Filing date: 1999-09-08
Publication date: 2000-03-16
Anticipated expiration: 2001-03-09
Also published as: GB9819546D0; AU5752099A

Abstract

Plastics material in combination with paramagnetic silicate is disclosed. The silicate may be ferrosilicate, copper silicate or aluminium silicate. The silicate heats upon being exposed to an RF field to melt the plastics, an adjacent plastics material or accelerate the curing of the plastics material. The plastics material (15) may be used to bond materials or articles (10, 12) together. The material may also be used to seal leaks in, for example, pipes or vessels. A further use of the plastics material is to allow detection of an article made of or attached to the plastics material.

Description

A PLASTICS MATERIAL IN COMBINATION WITH A PARAMAGNETIC SILICATE

The invention relates to bonding and sealing materials. Such materials are useful for joining objects made of, for example, thermoplastic material, such as gas pipes, or other

mouldings. The invention further relates to the use of materials of the invention for

tracking and detecting, for example, pipes, and as high friction materials, and the

production of reinforced thermoplastic pieces or members using pultrusion processes.

Paramagnetic materials, such as tungsten, zirconium, copper or iron have the property of trying to align themselves with a magnetic field applied to them. When an oscillating magnetic field (known as "magnetic induction") is applied to the materials, heat is produced as the material tries to align with the changing magnetic field. Such materials

tend also to have the property that they resonate and produce heat upon application of

radio to microwave (known hereafter as "RF") electromagnetic radiation.

WO 93/10962 discloses the use of heat produced from a paramagnetic material to which

microwave energy has been applied, to melt a thermoplastic to produce a seal or weld.

The document discloses a composite bonding material having a thermoplastic matrix

which contains a plurality of microwave susceptor particles. The susceptor particles

comprise a substrate of materials such as glass, mica, ceramic or a polymer, which is coated with one or more coatings of a conductive or semi-conductive material such as tungsten, zirconium, copper or iron. The composite bonding material is used to seal

joints between, for example, gas pipes. A strip or sleeve of the composite material is placed around the adjacent ends of two gas pipes. Microwave energy is applied to the composite bonding material so that the bonding material is heated until it melts. The molten composite bonding material forms a seal between the adjacent gas pipes.

The susceptor particles themselves, are the subject of EP-A-0479438.

The susceptor particles used in WO 93/10962 are complex and relatively difficult to produce.

The inventors have now unexpectedly found that paramagnetic silicate, such as

ferrosilicate, can be used instead of such microwave susceptor particles. The preferred silicate used, ferrosilicate, is a waste product of known industrial processes. As such, the ferrosilicate is relatively inexpensive and is readily available. Furthermore, ferrosilicate may be used in its waste form without any further processing, thus allowing

a thermoplastic bonding material to be produced relatively easily and at relatively low

cost.

Silicates such as ferrosilicate also have advantages over prior art material containing, for example, iron or copper, since the iron in ferrosilicate is maintained within a silicate

matrix, and is chemically inert. Furthermore, ferrosilicate has been found to mix readily

with a wide variety of plastics materials such as thermoplastics, thermosetting plastics

and resins so making a wide variety of thermoplastic bonding materials to be produced. Ferrosilicate can also be used to heat plastics to over 250°C, thus allowing a wide variety of plastics to be used with the material. A first aspect of the invention provides a plastics material in combination with paramagnetic silicate.

Preferably, the plastics material is a thermoplastic, thermosetting plastics or a resin.

The paramagnetic material may be bound to the surface of the plastics material and/or

may be mixed within the plastics material. The plastics material is preferably for use as a thermoplastic bonding material. By thermoplastic bonding material, we mean a

material which may melt upon being exposed to RF and cause one or more adjacent materials to bond to it o to another material.

The term "paramagnetic silicate" is intended to mean a silicate which is capable of absorbing RF to produce heat.

The silicate is preferably ferrosilicate which may be provided as substantially pure

ferrosilicate or as a commercially available material such as Myranite which is available from Powder Services Limited, Billingham, Cleveland, United Kingdom.

Commercially available ferrosilicate material typically contains 25-50% by weight of

iron as Fe₂ O₃ and Fe₃ O₄ and 25-50% by weight of silica. The commercially available material may also comprise up to 25% of contaminants such as tin, lead, zinc, copper, manganese, calcium oxide, potassium oxide, aluminium oxide and/or other contaminants. The paramagnetic silicate, such as ferrosilicate, may be blended with ferromagnetic

and/or other metal or paramagnetic materials to form a ferrosilicate mixture. This

achieves optimum heating characteristics when energised by an RF source of an application specific frequency. The ferromagnetic, metal and paramagnetic materials

may be selected from one or more of low cost steels, aluminium alloys, nickel alloys,

brasses and bronze powders, which may be pretreated for specific applications. Such alloys may be low cost waste alloys resulting in cost advantages. This also allows the RF frequency at which the ferrosilicate heats up to be fine tuned to a particular frequency. Hence, this allows two or more joints to be made using different silicates

which heat at different frequencies. This allows the joints to be selectively joined or

detached using specific RF frequencies without affecting adjacent joints.

This allows replacement and repair of old and worn parts, and allows disassembly and recycling of materials.

Optimised powder plastic mixtures may be produced that result in an enhanced response to a narrow spectrum of frequencies, allowing the use of lower levels of particulate in

the junction, thus lessening the impact of the powder on the physical properties of the plastics material.

This plastics material may be achieved by the careful selection of a range of metal and

non-metal powders to be compounded into the plastics that then develop a reluctance

equal to the peaks of the exciting waveform thereby resulting in an effect at the centre frequency of having twice the amplitude applied to the work-piece and therefore nearly twice the heat is produced by the increased losses in the plastics material.

The action of the silicate, such as ferrosilicate, is to widen the response curve thus allowing less stringent setting up procedures to be employed in the course of

manufacture and use of the jointing mediums.

Preferably the silicate such as ferrosilicate is blended with up to 20% by weight of

ferromagnetic, metal or paramagnetic material to form a silicate, especially ferrosilicate

mixture. These materials may be pretreated, for example the added material may be

oxidised on the surface of the powder. Alternatively, they may be phosphated by reacting with phosphoric acid to produce a metal-phosphate coating. This latter process prevents, for example, iron powders reacting with moisture and rusting. Surfactants may also be added to improve the wetting of the added material by the plastics.

Other silicates such as aluminium or copper-silicate could also be used instead of or in addition to. ferrosilicate.

The plastics material may be selected from any known thermoplastic, such as cellulose derivatives, vinyl polymers (such as PVC), polystyrenes, polyamides (such as nylon),

acrylic resins (such as methacrylate) and polythenes (such as high, medium or low density polythenes). The thermoplastic material used may be one or several different thermoplastic materials. This allows, for example, the temperature at which the thermoplastic material melts to be varied, or alternatively it allows the chemical properties of the thermoplastic material to be varied to enable the thermoplastic material

to be compatible with different substrates to which the thermoplastic material may be attached.

An alternative method of making the plastics material compatible with different

substrates is to incorporate one or more compatibilisers into the plastics material. Such

compatibilisers are well known in the art. Accordingly, preferably the plastics material according to the first aspect of the invention contains up to 10% by weight of one or

more compatibilisers.

Preferably the plastics material is produced by compounding a mixture of one or more

thermoplastic materials with paramagnetic silicate such as ferrosilicate or a ferrosilicate mixture as defined above and, for example, where the lower melting point polymer may permit the bonding of dissimilar granular materials thus forming a polymer

conglomerate. The mixture of thermoplastic materials may be an impure, recycled material contaminated with plastics having a higher melting point than the bulk

material, e.g. polyethylene with PET impurities. This allows recycled material to be

used.

The conglomerate acts like aggregate in concrete to form a plastics material having

improved strength characteristics.

The term ferrosilicate is intended to include pure ferrosilicate and commercially available ferrosilicate with impurities as described above. Preferably the amount of ferrosilicate added to form the ferrosilicate mixture is between 10 and 95% ferrosilicate by total volume, especially 20-80%), 30-60%), most preferably 40%> by volume ferrosilicate.

The thermoplastic material may have sufficient paramagnetic silicate added for the paramagnetic silicate to heat and soften or melt the thermoplastic upon exposure to RF.

The amount of paramagnetic silicate to the thermoplastic may be between 10 and 95%, especially 20 to 80%, 30 to 60% most preferably 40% by volume.

The paramagnetic silicate enables functions such as removing and refitting components as in the process of repair and replacement or for disassembly or recycling at the end of a component's/construction's life cycle.

Alternatively, the paramagnetic silicate may be coated onto the surface of the plastics

material, for example, by pressing the crystalline silicate into the surface of the

thermoplastic material. This may be achieved by subjecting the silicate to RF to heat it

and cause it to melt the plastics around it. Such surface coated thermoplastic material may be used as bonding or sealing material, as described below. Alternatively, the paramagnetic silicate material has been observed to produce a surface with a high

coefficient of friction. Hence, such a surface may be used for abrasive or high friction purposes.

Thermoplastic materials can be repeatedly heated and shaped. However, in an alternative embodiment of the invention the thermoplastic material may be replaced by a thermosetting plastics material, which, once heated, irreversibly cures and cannot be

remelted or be reshaped. Thermosetting plastics are known in the art. This enables moulded thermosetting plastics to be cured or achieve accelerated cure by RF heating.

Paramagnetic silicate may also be mixed with resins such as epoxy resins. The resin may be used as an adhesive, with one or both surfaces to be joined being coated with the

resin, prior to joining. The resin is then subjected to RF to heat the paramagnetic silicate and accelerating the curing of the resin.

The plastics material according to the invention, may be compounded into pellets and

then may be extruded by an extrusion machine of the type known in the art, to produce formed plastics material.

Preferably the plastics material, such as the formed plastics material, is a thermoplastic

material and may be used as a thermoplastic bonding material.

Preferably, the formed plastics material may be in the form of a tape, cordage or a sheet. Such a tape, cordage or sheet of material may be placed between, for example, two

layers of one or more materials such as plastics material, and melted by means of an RF field. The tape, cordage or sheets may comprise one or more layers of conventional adhesive to maintain the tape or sheet in position prior to heating. Apparatus for producing RF fields are known in the art. Typical RF frequencies which are suitable for use in the invention are those between 500 Khz and 5 GHz, more typically 3 MHz to 6 MHz.

The RF causes the paramagnetic silicate, such as ferrosilicate, within the plastics material to heat. This melts, for example, thermoplastics material within the plastics

material, which then melts at least the adjacent surface of the thermoplastic material which requires bonding. This results in a "weld" of the thermoplastic material to be

joined. The thermoplastic weld becomes solid upon removal of the RF.

The plastics material may be selected so that the melted material acts as an adhesive between adjacent layers of plastic. For example EVA blended with ferrosilicate can be

placed between two dissimilar layers of plastics, melted with RF and cooled to form an adhesive layer holding the two dissimilar layers together.

The amount of heating to which the plastics, such as thermoplastic bonding material, is

subjected can be varied by controlling the power input and/or the time which the thermoplastic material is subjected to the RF energy.

In a preferred embodiment, a sheet, cordage or tape made of plastics material, such as

thermoplastic bonding material, may be used to join two sections of pipe, such as gas pipe or water pipe, together. Preferably, two ends of pipe are placed adjacent, end on end, to one another and typically a moulding of the plastics material placed between them. Alternatively, one or more pieces of plastics material, such as thermoplastic bonding

material, are then placed adjacent to the part of the pipes to be joined, and a sleeve of a

thermoplastic material is placed over the formed plastics material. The joint is then subjected to RF to melt the adjacent thermoplastic material.

This results in a strong water and gas tight seal. This has also been found to have the advantage that the ends of the pipes to be joined do not need to be smooth or entirely

free of contamination. The plastics material or thermoplastic material melts and fills any gaps or irregularities between the pipes and/or the layer of thermoplastic materials surrounding the plastics material.

Alternatively, the plastics material may be moulded into a collar which simply is placed

around the ends of the pipes to be joined. This collar is then subjected to RF and the

collar melts to seal the joint between the pipes.

A tape or sheet of plastics material may also be used to seal leaks in, for example, pipes

by simply placing the plastics material in the form of a tape or sheet over the aperture

producing a leak in the pipe, and subjecting the tape to RF thus melting the plastics material so that it melts and plugs the leaking portion of the pipe. The plastics material may also be used to mend leaks in other objects, such as vessels or tanks.

The plastics material may be used to achieve bonding between the wall of a pipe, vessel or tank and a similar or dissimilar patching material effecting a repair or strengthening on a radius, flat surface or over a complex topology with the plastics material performing both a seal and a bridge between surfaces.

A further use of a tape, cordage or sheet of plastics material according to the invention

is in the attachment of two or more long or continuously extruded formings. Accordingly, two or more continuous thermoplastic extrusions are produced by methods

known in the .art. A tape of plastics material is placed between the continuous extrusions, and the tape is subjected to RF to join the two or more extrusions. The tape

may be supplied by means of a reel, or alternatively be produced in situ as an extrusion

at the same time that the extrusions to be joined are produced.

A further embodiment of the invention is the production of one or more mouldings comprising at least a portion of plastics material. The plastics material portion of the moulding may then be placed adjacent to another moulding made of, for example, a

thermoplastic, and the plastics material subjected to RF in order to join the mouldings.

This is particularly advantageous where the mouldings are complicated, and it would be

difficult to. bond the surface of one moulding to the surface of a second moulding. The plastics material may be provided by coextruding the plastics material at the same time as a second thermoplastic material so that the plastics material is placed against the surfaces of the moulding ready to be joined. Such coextrusion methods are known in

the art. Alternatively, a thermoplastic moulding may simply be produced and then

plastics material be provided as a tape, cordage or sheet which is simply cut to size and attached to the surface of the moulding. Plastics containing paramagnetic silicate according to the invention absorb RF.

Accordingly, this property can be used for the detection, tracking or marking of articles such as gas pipes. Accordingly, a further aspect of the invention provides the use of a

plastics material in combination with paramagnetic silicate, as previously defined, as a marker material.

Preferably the material is attached to the article to be marked by, for example, providing the material, for example, as tape and attaching the tape by adhesive or by heating the

tape with an RF field, as discussed previously. Alternatively, the article to be marked may simply have paramagnetic silicate incorporated into it.

For example, a gas pipe may be made of a plastics compound with paramagnetic

silicate. The paramagnetic silicate enables the covered pipe to be traced from above ground by means of, for example, the type of detectors usually used to detect buried

metal gas pipes.

Furthermore, the plastics material may be used as a sheath for, for example, optical fibres, enabling the optical fibres to be traced within the walls or ceiling of a building.

A still further aspect of the invention provides a plastics material in combination with a

paramagnetic silicate according to the first aspect of the invention, in combination with one or more reinforcement fibres. This allows reinforced plastics material to be produced that can be melted using RF fields.

Preferably the reinforcement fibres are glass, carbon, kevlar or natural fibres such as

hemp, sisal or jute. The reinforcement fibres may be co-mingled with plastics fibres.

Preferably the plastics used is a thermoplastic. The reinforcement fibres may be co-mingled with the plastics fibres at either the filament, fibre, roving or twine level.

Methods of producing co-mingled glass and polymer filaments, for example, are known

in the art.

The incorporation of paramagnetic silicate enables the plastics to be melted using RF. The melted plastics and fibres may then be pulled through a dye, rollers and/or guides

prior to forming into a profile. Such a system is known as "thermoplastic pultrution".

Before cooling, paramagnetic silicate may be introduced onto the surfaces of the formed material so that the full material may be joined to other components using microwaves or oscillating magnetic fields as described above.

The use of reinforcing fibres allows very long strength members to be produced either by the processed profile alone, by combining the profiles made by welding or by

introduction of the profiles as stiffening members to other non- or slightly-reinforced thermoplastic members. The invention also provides within its scope products comprising a plastics material

according to the invention.

The invention will now be described by way of example with reference to the accompanying figures:

Figures 1, 2, 3 and 4 show preferred embodiments of the invention in which two

separate mouldings are joined by means of a plastics material according to the

invention.

Figure 5 shows the use of a plastics material according to the invention as to

effect local repair or strengthening.

Figure 6 shows the use of a plastics material according to the invention to join

one or more mouldings.

Figure 7 shows an alternative use of the plastics material according to the

invention for joining all elements or continuously extruded mouldings.

Figure 8 shows a method of producing a plastics material according to the invention. Figure 9 shows the use of a plastics material according to the invention for joining thermoplastic pultruded members or other fibre reinforced members to

each other, for example to continuously extruded moulding.

In the following example, a plastics material, according to the invention, was produced

by compounding 40%> by volume of ferrosilicate with polyethylene. The ferrosilicate

was provided with a form of a powder with the chemical analysis of the typical composition of that shown in Table 1 :

TABLE 1

Chemical Analysis

Symbol Name % Contents

Sn Tin 0.2

Pb Lead 0.3

Zn Zinc 4.0

As Arsenic <0.1 Trace

Cu Copper 0.9

Ni Nickel <0.1 Trace

Fe Iron as Fe₂ O₃ or ] 25 to 50

Mn Manganese 0.5

Sb Antimony <0.1 Trace

CaO Calcium Oxide 9.0

K₂O Potassium Oxide 0.1

Al₂O₃ Aluminium Oxid 4.5 SiO₂ Silica 25 to 50

P2O5 Phosphorus Pentoxide <0.2 s Sulphur <0.2

MnO Manganese Oxide 1.9

Cd Cadmium <0.1

Cr Chrome <0.1 Trace

Bi Bismuth <0.1 Trace

Ferrosilicate such as Myranite is provided as a powder and was mixed with powdered

polyethylene and compounded into pellets. These pellets were then placed into an

extrusion machine, of the type known in the art, and extruded into sheets of plastics material which were approximately 3 mm thick.

Sheets of plastics material were then used to join two lengths of standard pipes of the

type used to transport natural gas. The arrangement used is shown generally in Figure 1.

Two lengths of gas piping made of medium density polyethylene (10, 12) and of 90 mm diameter and 8 mm thickness were placed end to end. Several sheets of plastics material (14) were placed at roughly equal distances around the circumference of the

pipes (10, 12). A premoulded collar (16) of medium density polyethylene, 95 mm

diameter and 8 mm thickness was then placed around the circumference of the pipe (10, 12) to be joined (18) and the layer of bonding material (14). The arrangement was then subjected to RF for 4-20 minutes with the RF operating at

650 watts at a frequency of 2.45 GH_Z. This resulted in the melting of the plastics

material. Cross-sections of the finished joined article afterwards indicated that the plastics material melted to completely seal any gaps between both the sheets of the thermoplastic bonding material (14) and gaps between the thermoplastic bonding

material (14) pipes (10, 12) and the collar (16). Thermoimagery of the pipe as it was

heated indicated that the temperature of the plastics material exceeded 192°C, that is well in excess of the melting temperature of the plastics material.

Figure 2 shows an alternative arrangement in which the plastics material (14) is

premoulded into a ring having flanges (15). The flanges serve to guide and hold the

pipes 10, 12 in position, whilst the pipes are sealed together. Alternatively, as shown in

Figure 3 the plastics material (14) may simply be in the form of a ring of material placed between the pipes (10, 12).

Figure 4 shows a method of attaching a plastics pipe in the form of a saddle. A first plastics pipe (68) has an aperture cut in its wall. A second pipe (70) is cut to fit around

the aperture. A layer of plastics material (72) according to the invention is placed between the pipes (68, 70) and heated by RF. This melts the pipes (68, 70) to form a weld between them.

Figure 5 shows a repair patch or strengthening patch. The pipe (74) comprises an aperture (shown as ghost) (76). A patch (78) of plastics material according to the invention is placed over the aperture (76) and heated by RF to seal the patch (78) to the pipe (74).

Figure 6 shows an alternative use of a plastics material according to the invention. Two

moulded portions of plastics material (20, 22) are provided. These may be produced by conventional moulding techniques such as injection moulding. A layer of plastics material (24) is placed between the interfaces between the mouldings (20, 22) and the moulding is subjected to RF to soften and melt the thermoplastic bonding material.

This produces a strong weld between the mouldings (20, 22).

The thermoplastic bonding material may be provided in the form of a tape, cordage or sheet which has an adhesive surface placed upon one or both sides to enable it to be maintained in the correct position prior to melting with RF. Alternatively, the

thermoplastic bonding material may be placed into one or other of the moulds which

produce the mouldings (20, 22) prior to filling the mould with thermoplastic.

Figure 7 shows the use of a plastics material according to the invention to weld two continuous weldings or long elements (30, 32).

Mouldings (30, 32) may be produced by continuous extrusion or alternatively produced

by injection moulding. The structural elements are welded by providing a tape or thermoplastic bonding material between the faces of the elements to be joined. Plastics material may be provided from a reel of tape which may have one or more surfaces coated with an adhesive to secure the tape to the moulding (30, 32). Alternatively, the

tape may be extruded at the same time that the mouldings are extruded.

Mouldings (30, 32) may be made of different thermoplastic materials. The plastics material of the invention is then formulated to ensure that it is compatible with both

types of thermoplastic material used for the mouldings (30, 32). This may be achieved

by altering the mixture of thermoplastics within the plastics material or alternatively providing one or more compatibilisers to ensure that the plastics material produces a

secure weld between the two mouldings (30, 32).

Figure 8 discloses the production of a pultruded product according to the invention (40).

The Figure shows reels of thermoplastic fibres (42) and reinforcement fibres (44). The

thermoplastic fibres comprise a paramagnetic silicate such as ferrosilicate or Myranite.

Fibres are pulled from the reels, thermoplastic fibres being shown as (46) and reinforcement fibres as (48). The fibres are then co-mingled are passed through a

preheater (50) in order to achieve uniform heating. The preheater (50) may use a first

RF frequency to heat the core of the material. The preheated material (52) is then passed through a primary heater (54) which may use a different RF frequency to further heat the material. The melted thermoplastic fibres and co-mingled reinforcement fibres are then pulled through a heated dye, rollers and/or guides (56). The material is formed

into a profile and cooled on exit from the dye, roller or guide. The apparatus may also utilise a pulling mechanism (58) in order to pull the fibres through the system. A saw (60) is shown which separates the final cooled material into pieces.

Before cooling, ferrosilicate powder or material such as Myranite, or another

paramagnetic silicate may be introduced into the surfaces in order that the surface may

be joined to other components using the microwaves or oscillating magnetic fields.

It should be noted that the thermoplastic fibres (46) may be pre-compounded with

paramagnetic silicate or alternatively may have paramagnetic silicate introduced into the

co-mingled fibre bundle prior to heating.

Figure 9 shows the joining of pultruded members, for example, to form a continuously extruded thermoplastic member. It shows the bonding of a first plastics layer (80) to a second plastics layer (84) via a plastics material (82) according to the invention. The

plastics material (82) is heated by RF to melt the plastics layers (80, 84) and join them

together.

Claims

1. A plastics material in combination with a paramagnetic silicate.

2. A plastics material according to claim 1 selected from a thermoplastic, a

thermosetting plastic or a resin.

3. A plastics material according to any preceding claims, wherein the paramagnetic

silicate is bound to the surface to the plastics material and/or is mixed with the plastics

material.

4. A plastics material according to any preceding claim, wherein the paramagnetic

silicate is selected from one or more of ferrosilicate, copper silicate and aluminium

silicate.

5. A plastics material according to any preceding claim, wherein additionally comprising one or more steel, aluminium alloy, nickel alloy, brass and/or bronze

powders.

6. A shaped or extruded material comprising a plastics material according to any preceding claim.

7. A shaped or extruded material according to claim 6, wherein the shaped or

extruded material is in the form of tape, cordage or a sheet.

8. The use of a plastics material according to any one of claims 1 to 5 as a thermoplastic bonding material.

9. A method of joining two or more pieces of material comprising the steps of:

(i) placing a portion of plastics material according to any one of claims 1 to 5 between the parts of the pieces of material to be joined;

(ii) optionally sandwiching a thermoplastic material between the plastics

material and a part of the pieces of material to be joined;

(iii) subjecting the plastics material to RF to melt at least one of the plastics material, a part of the pieces of material to be joined and/or thermoplastic

material; and

(iv) allowing to cool to form a joint between the pieces of material to be

joined.

10. A method of joining two or more pieces of material comprising the steps of:

(i) placing the parts of the pieces of material to be joined adjacent each other; (ii) placing a portion of plastics material according to any one of claims 1 to over or around the parts of the pieces of material to be joined;

(iii) optionally placing a sleeve or cover of thermoplastic material over plastics material;

(iv) subjecting the plastics material to RF to melt at least one of the plastics material, part of the pieces of material to be joined and/or thermoplastic

material; and

(v) allowing to cool to form a bond between a joint between the pieces of

material to be joined.

11. A method according to claim 9 or claim 10, wherein the plastics material is a

thermoplastic material which melts when subjected to RF.

12. A method according to any one of claims 9 to 11, wherein the pieces of material

to be joined are two pieces of pipe.

13. A method according to any one of claims 9 to 11, wherein the pieces of material

to be joined are two or more extrusions or mouldings of thermoplastic material.

14. A method according to claim 13, wherein the extrusions are continuous extrusions.

15. A method of joining two adjacent pieces of material, comprising the steps of:

(i) providing a moulded, extruded or protruded portion of a plastics material according to any one of claims 1 to 5;

(ii) placing the plastics material adjacent to a second piece of material;

(iii) subjecting to RF to melt at least a portion of the plastics material and/or second piece of material; and

(iv) allowing to cool to form a joint between the plastics material and the

second piece of material.

16. A method according to claim 15, wherein the plastics material is moulded or extruded to form a sheet or tape which is used to seal a leak in the second piece of

material.

17. A method of curing a plastics material according to any one of claims 1 to 5 comprising subjecting the plastics material to RF.

18. The use of a plastics material according to any one of claims 1 to 5 as a marker

material.

19. The use of a plastics material according to any one of claims 1 to 5 of a high friction material or as an abrasive.

20. An article comprising a plastics material according to any one of claims 1 to 5.

21. An article according to claim 20 which is a gas pipe or an optical fibre.

22. An article according to claim 20 or claim 21 comprising a plastics material

according to any one of claims 1 to 5 in combination with one or more reinforcement

fibres.