WO2005025827A2

WO2005025827A2 - Fibre-plastics composite

Info

Publication number: WO2005025827A2
Application number: PCT/GB2004/003896
Authority: WO
Inventors: Kim Lloyd
Original assignee: Timbaplus Products Limited
Priority date: 2003-09-16
Filing date: 2004-09-10
Publication date: 2005-03-24
Also published as: GB0321699D0; WO2005025827A3

Abstract

The invention relates to methods of producing fibre-plastics composites, using fibrous cellulosic material and plastic material. The cellulosic material may be moist and dried prior to mixing. Additionally, or alternatively, the material may be passed through an extruder (13), the extruder (13) tapering between the entrance (10) to the extruder and the exit (14) of the extruder (13). Products produced by the methods of the invention are also provided. The products produced are especially useful for the production of door frames, window frames or staircases. Additionally, scaffold boards may be produced by the method of the invention. The application also provides fibre-plastic composite scaffold boards.

Description

Fibre-Plastics Composite

The invention relates to methods of producing fibre-plastic composites, to compositions containing mixtures of fibrous cellulosic material and plastics materials, to fibre-plastic composites produced by the methods and to apparatus for producing fibre-plastic composites.

Conventional structural manufacture, for example of windows and doors or building furniture such as skirting board, has used vinyl, wood and metal components for forming the structural members. Wood has been used for many hundreds of years and has been shaped into structural components. Wooden structure, whilst structurally strong, can suffer problems under certain circumstances related to the deterioration of the wood components. Wood windows also suffer from cost problems related to the availability for suitable wood for construction.

Further, plastic polyvinyl chloride (PVC) has been combined with wood members, or used instead of wood members, for many years. A problem with plastic materials has been that the plastic materials, such as PVC, often do not have sufficient strength, thermal expansion, elasticity or workability properties to allow them to be successfully used. Furthermore, plastics and wood products have conventionally been expensive.

There is therefore a need to provide a cheaper product. Efforts were therefore made to combine wood by-product materials, such as sawdust, with recycled thermoplastic products, such as recycled PVC. Eventually, these materials had been burned for their heat value and electrical power generation or were shipped to landfill sites for disposal.

It is known that it is possible to form a replacement for a wood structural member by forming structural members from a polymer and a wood fibre composite material. For example, US 5,406,768 discloses combining PVC with wood sawdust material in a typical concentration of 60 wt.% PVC with 40 wt.% sawdust. This material is extruded or injection moulded into a linear member with a hollow profile. The wood fibre normally used by manufacturers of fibre-plastic composites is finely powdered to a substantially flour-like consistency. This is because those manufacturers have conventionally thought that finely powdered wood fibre produces a "better" finish on the fibre-plastic composites. Furthermore, the use of sawdust, and especially finely powdered sawdust that has been milled to produce a fine flour-like consistency, is potentially dangerous because of the risk of powder-explosions should a spark be allowed to ignite the wood-powder. This has meant that the wood fibre is often pre-pelletised, either cellularly or in combination with the plastics material and stored, prior to being used in either injection moulding or extrusion processes to create pellets which have reduced fallibility. Conventionally the wood fibre is milled to a flour-like consistency, dried in a kiln, mixed with plastics material and then extruded and cut to pellets. Typically, the pellets are cylindrical with a radius of 1-5 mm. and a length of 1-10 mm.

An alternative method that has been used to reduce the fire risk is to use wood fibre of a minimum size of length and width of at least 1 mm. because wood flour tends to be explosive at certain wood-to-air ratios. This is the proposal put forward in US 5,441,801. The patent also suggests that the fibres could be up to 3 cm. in length and 0.5 cm. in thickness.

The current application identifies an improved method of processing the moist fibres directly into the moulding process, without the need for pelleting and without the need to sift out the fine powder from, for example, a source of sawdust.

Typically, at least 40% PVC is used in combination with 60% or less fibre. High concentrations of PVC have been required in order to produce composites with sufficiently high structural strength. The application provides an improvement on the conventional extrusion process that results in composites with improved strength, and allows the use of concentrations of fibrous material above 60% to 70% or even 80% concentration of wood fibre. This reduces the amount of plastics material that needs to be used.

A first aspect of the invention provides a method of producing a fibre-plastics composite comprising the steps of: (a) Providing a mixture comprising fibrous cellulosic material and a plastics material;

(b) Heating the mixture and extruding the heated mixture through a die to produce a heated extrusion; and

(c) Passing the heated extrusion through hollow cooling means to form a cooled extrusion wherein the cooling means comprises: (i) a first aperture for receiving the heated extrusion, and (ii) a second aperture through which the cooled extrusion exits the cooling means, and wherein a diameter inside of the cooling means tapers between at least a part of the distance between the first aperture and the second aperture so that the heated extrusion is compressed.

An extruder is typically used to produce the heated extrusion. The extruder usually uses one or more screws that rotate and force a powdered or pelletised material past one or more heaters to melt the plastics material and then forces the heated, at least partially liquefied or molten material, past a die to form the heated extrusion.

Conventionally, extruded materials are cooled by, for example, passing through a water bath and pulling them out at the other end with a pair of rollers. Alternatively, extrusions can be extruded onto a moving belt and cooled with jets of air.

The Applicants have identified that where a mixture of fibrous cellulosic material and a plastics material is used, it is possible to compress the heated extrusion whilst being cooled to create a cooled extrusion with improved strength. This improvement in strength appears empirically to be in the region of +20%.

This improvement in strength is especially noticeable where the cooled extrusion is hollow. Formally, it is preferred that the cooled extrusion comprises at least one cavity within it. This may be produced by means of a mandrel which extends at least partially into the cooling means to support the heated extrusion whilst it is being cooled to a low enough temperature to support itself. The mandrel creates one or more walls surrounding at least a portion of the cavity. The cavity may be any shape, but is typically cylindrical or rectangular along the length of the extrusion.

Typically, the amount of taper used in the method from the first aperture to the second aperture is 5-15%, preferably 7-12%, most preferably 9-10% of the thickness of the wall from the outside of the heated extrusion to the cavity.

Usually, the cooling means has one or more walls which taper. For example, the cooling means could be substantially circular in cross-section, with the tapered part of the cooling means having a substantially frusto-conical internal surface, or have one or more substantially planar walls. For example, the cooling means may comprise four walls. Two of the walls are substantially parallel to each other, the other two opposite walls taper towards each other to compress the heated extrusion in one direction. Alternatively, the cooling means may have four walls, each of the walls being tapered in a substantially frusto-pyramidal manner so that the heated extrusion is compressed whilst it is being cooled from both top and bottom and from the sides.

Preferably, the tapered walls of the cooling means comprises one or more channels containing a cooling fluid. The cooling fluid may be a chilled fluid such as water, oil, gas (such as a refrigerant, e.g. a chlorofluorocarbon) or indeed an oil/water mix.

Typically, the heated extrusion is cooled sufficiently to allow a surface crust to form on the exterior of the composite, whilst still allowing some expansion of the inside of the extrusion to occur in the direction of the cavity after leaving the end of the mandrel.

Typical temperatures of the heated extrusion will vary depending on the thermoplastic used. However, the temperature will be less than the decomposition temperature of wood fibre, which whilst varying from source to source is typically less than 450°C. Most preferably, the temperature used is between 140°C - 220°C.

The fibrous cellulosic material and/or plastic material used is preferably in a particulate form, although it also may be used in the form of pre-combined pellets of plastics material and wood material of the type known in the art.

Preferably, the fibrous material is provided as a moist fibrous material and is passed through a drying chamber to produce dried fibrous cellulosic material, prior to mixing with at least one plastics material to form the mixture comprising fibrous cellulosic material and a plastics material.

Accordingly, a further aspect of the invention comprises the steps of:

(a) Providing moist, fibrous, cellulosic material;

(b) Passing the moist, fibrous, cellulosic material through a drying chamber to produce dried cellulosic fibrous material;

(c) Mixing the dried, fibrous, cellulosic material with at least one plastics material to form a mixture; and

(d) Moulding the mixture to form a fibre-plastics composite.

The mixture may be moulded by heating the mixture and passing the heated mixture through a die to form a heated extrusion or alternatively may be moulded by injection moulding methods known in the art.

Preferably, the drying chamber is a heated auger, the heated auger comprising a housing, the housing having a first aperture for receiving moist fibrous material and a second aperture for removing the dried fibrous cellulosic material, and a helical screw which rotates to move the fibrous material between the first aperture to the second aperture. The pitch of the helical screw may be constant through the length of the screw. However, if the pitch is greater towards the first aperture than towards the second aperture, it has been found to decrease the risk of blockages forming in the heated auger. Any suitable method may be used to heat the auger. However, using trace heaters to heat a wall of the auger has been found to be particularly effective.

If more radiant heat, for example from heated walls of the auger, is used, it is preferable that a large proportion of the moist fibrous material is in contact with the wall of the auger. This can be increased by having a wide cylindrical central core to the auger with the width of the screw being reduced to increase the amount of sawdust which is directly in contact with the surface of the wall of the auger.

Preferably, a plurality of heater augers mounted consecutively in series to progressively dry the moist, fibrous, cellulosic material is used. Typically, three augers are used.

The moist, fibrous material may be passed directly from the drying chamber to the rest of the apparatus. Alternatively, the dried material may be passed to a holding chamber. The holding chamber is simply used as a buffer to allow sufficient dried cellulosic fibrous material to be built up to continuously supply the extrusion process, whilst still allowing, for example, a new delivery of moist, fibrous cellulosic material to be delivered to the drying chamber.

Having the drying chamber in the same chain as the rest of the extrusion process reduces the amount of dried fibrous material available to cause dust explosions. This improves the safety of the process.

Preferably, the fibrous, cellulosic material is combined with a plastic material on a vibratory table. This has been found to be particularly advantageous as it allows an accurate measurement of the amount of fibrous material entering the extrusion process to be determined. The plastics material may be delivered onto the vibratory table either before, during or after the delivery of the fibrous cellulosic material onto the vibratory table. Additionally, one or more additives may be added to the mixture.

Typically, the plastics material and fibrous, cellulosic material (optionally with one or more additives) are mixed in a ribbon blender.

The mixture of fibrous cellulosic material and plastics material may be transported to one or more extruders by a powder flight conveyor of the type known in the art.

Preferably, the mixture of fibrous cellulosic material and plastics material is compressed without melting the plastics material to exclude air. The compressed material is then passed to an extruder where it is heated and passed through a die to form the heated extrusion. Compressing the mixture has been found to reduce the number of air voids within the extruded product, thus improving the quality of the final fibre-plastics composite. This compression process may be applied to other methods of producing extruded fibre-plastic composites.

Hence, a further aspect of the invention provides a method of producing a fibre-plastic composite comprising:

(i) Providing a mixture comprising a fibrous, cellulosic material and a plastics material;

(ii) Compressing the mixture to form a compressed mixture without melting the plastics material:

(iii) Passing the compressed material into an extruder;

(iv) Heating the compressed material in the extruder; and

(v) Passing the heated material through die to form a heated extrusion. The compressed material, according to the invention, may be compressed for example by a rotating screw within a compression chamber.

The Applicant has realised that under certain circumstances it is necessary to be able to further improve the structural properties of the material, either structurally or for resilience to abrasion from, for example, people walking on the product. Accordingly, the cooled extrusion may be further co-extruded with a mixture of a plastic material with glass fibres to coat the cooled extrusion with a layer of the plastics material with glass fibres therein. By glass fibres, we mean any conventional glass fibres or mineral fibres known in the art. The glass fibres act to improve the structural and wear-resistant properties of the plastics material and strengthen the plastic material coating. The plastics material itself may be the same or different to the plastic material used in the cooled extrusion.

This coating step may equally be applied to other composites produced by extruding the fibrous, cellulosic material and plastics material.

A further aspect of the invention provides a method of producing reinforced plastic composite comprising:

(i) Producing an extrusion of a mixture comprising fibrous cellulosic material and a plastics material; and

(ii) Co-extruding the extrusion with heated mixture comprising a plastics material and glass fibres to form a coated reinforced fibre-plastic composite.

The methods of the invention are suitable for use with a range of different concentrations of fibrous cellulosic material and plastic material. However, it has been found that the method allows concentrations of at least 50% by weight of fibrous cellulosic material and less than 50% by weight of plastics material. More preferably, the amount of fibre cellulosic material is at least 60%, at least 65%, at least 70%, at least 75% or at least 80% by weight of fibre cellulosic material and less than 40%, less than 35%, less than 30%, less than 25%, more preferably less than 20% by weight of plastics material. Accordingly, a further aspect of the invention provides a mixture comprising at least 60% by weight of a fibre cellulosic material; and less than 40% by weight of plastics material. Preferably, the amount of fibre cellulosic material is at least 65%, at least 70%, at least 75%, more preferably at least 80% by weight of fibre cellulosic material and less than 40%, less than 35%, less than 30%, less than 25%, especially less than 20% by weight of plastics material.

The fibre cellulosic material, according to any aspect of the invention, may be provided by taking the raw material and passing it through a 5 mm. diameter mesh screen to remove particles having a diameter of greater than 5 mm. More preferably, the mesh screen is less than 4 mm, less than 3 mm, less than 2 mm, more preferably 1 mm in diameter. Metal contaminants are preferably removed from the fibre cellulosic material, for example, by the mesh screen or by use of a magnet.

Preferably, no further sizing of the material is used. A further screen to remove particles of less than 0.5 mm. or 0.1 mm. is preferably not used. That is, the material contains particles which range in size from fine dust-like particles to particles having a diameter which just allows them to pass through the screen. These larger particles may have longer lengths than the diameter of the screen, for example may have a 1 mm. diameter to pass through a 1 mm. diameter screen, but still have a length of 3-5 mm.

This simple screening method considerably reduces the cost of the fibrous material product. No further processing is required. For example, the material is not normally pulverised in a ball mill to reduce the size of the particles any further. Furthermore, the powderous material is not normally removed.

Typically, the fibrous cellulosic material is delivered to the moulding equipment containing 10-20%o moisture. The moisture has to be removed to prevent the formation of steam bubbles upon formation of the heated extrusion product. As indicated above, drying finely powdered material considerably increases the fire-risk associated with the product. However, in the case of the current invention, the Applicants dry the material in situ on the same moulding equipment as the extruder. That is, the drying equipment is part of a substantially continuous chain passing the moist fibre to the extruder, via the dryer. This considerably reduces the amount of dried fibrous cellulosic material available and reduces the fire-risk. This allows the use of "crudely" sifted material. That is, the fine powdered material of less than 1 mm. in length, especially less than 0.5 mm, less than 200 mm, most preferably less than 100 mm. in length, does not need to be removed.

Accordingly, preferably the method and mixture comprises the use of fibrous cellulosic material comprising at least 50% weight of particles of at least 100 μm diameter, more preferably at least 60%, at least 70%, at least 80%, or at least 90% by weight of particles of at least 100 μm in diameter.

Preferably, the fibrous cellulosic material comprises less than 50%, less than 40%, less than 30%, less than 20%, more preferably less than 90%, but more than 1% fibrous cellulosic material of less than 100 μm diameter. Preferably, the particles are less than 100 μm diameter are less than 50 μm diameter.

The weight percentages referred to above refer to the dried weight of the fibrous cellulosic material. Typically, the dried weight of fibrous cellulosic material means that it contains less than 5%, especially less than 2% by weight moisture content.

The fibrous cellulosic material may comprise, in addition to the fibrous cellulosic material, contaminants such as paint, plastics coatings or preservatives that have been used with the source of the fibrous material. Preferably, the contaminants are less than 10% by total weight of the plastic material used, especially less than 7%, less than 5% or less than 2% by weight.

Preferably, the fibrous cellulosic material is sawdust from soft- or hardwood. However, cellulosic material may be obtained from, for example, recycled cloth, cotton waste, straw from, for example, barley or maize, seed husks and nuts, hemp, jute, rice and sugarcane waste, or recycled paper. The concentrations of the fibrous cellulosic material may vary from source to source, as different sources of fibrous cellulosic material have different properties. For example, softwoods contain a high concentration of lignins, but lower concentrations of hemicellulose than hardwoods. By cellulosic material, we mean a material that contains a cellulose polymer or a derivative of a cellulose polymer such as hemicellulose.

The plastics material may be in the form of a virgin plastics material, that is one that has not been used for other purposes before. This virgin plastic may be as a polymeric form or be in the form of monomers. Monomers are especially used where the plastics material is a thermosetting polymer. Thermoplastic materials, such as polyethylene, PVC and polystyrene are materials that can be softened by heating and then which harden again on cooling. However, thermosetting materials which first soften on heating and then with further heating set hard and there afterwards cannot be softened again by heat may also be used.

Preferably, the plastics material is waste plastics material. That is, the material has been used for other purposes and then recycled. This plastics material may be chipped, prior to mixing with the fibrous cellulosic material. Waste material may be also comprise one or more contaminants, such as paints, waxes, stearate, foaming agents, bulking agents, titanium dioxide, stabilisers, master batch, colorants, talcs, surfactants and/or preservatives.

Preferably, the plastics material is selected from a polyolefine, uPVC, polypropylene, polyethylene, polyamide, poly(meth)acrylates, acrylonitrile-butadiene-styrene (ABS), polystyrene, polyphenylene oxides, polyhydroxy- butyrate (PHB), polyhydroxyvalerate, or copolymers or mixtures thereof, or monomers of the polymers.

A combination of uPVC and polyethylene is particularly preferred.

Polyhydroxybutrate (PHB) and co-polymers with polyhydroxyvalerate are especially preferred. Such polymers are so-called "biopolymers". They have been produced for a number of years by means of microbial and plant systems which have been engineered to produce the polymers. Therefore, these polymers are perceived to be environmentally friendly, thus improving the marketability of the product. The mixture of the fibrous cellulosic material and plastics material may comprise one or more of waxes, stearate, foaming agents, bulking agents, titanium dioxide, stabilisers, master batch, colorants, talcs, surfactants and/or preservatives. Preferably, less than 10%, less than 5%, especially less than or equal to 2% of the total amount of the mixture of cellulosic material and plastics material, with the additives, by weight, is additive material.

Preferably, 100% of the plastics material is recycled. However, preferably less than 50%, less than 40%, less than 30%, less than 10% by weight of the plastics material used in the method or mixture is virgin plastics material. This virgin plastics material may be incorporated to improve the structural properties of the plastic-fibre composite, although in practice the Applicants have found that this is not normally required.

Mixtures of different plastics materials and/or mixtures of fibrous cellulosic materials may be used.

The claimed methods allow the use of cheap recyclable materials and allows a reduction in the cost of operating the moulding systems used to mould the fibre-plastic composites.

The invention also provides fibre-plastic composites obtainable by the methods of the invention or containing the mixture of the invention.

Preferably, the fibre-plastic composite is a part of a door frame, window frame or a staircase.

The fibre-plastic composite may comprise a rail, a jamb, a style, a sill, a track, a stop-sash, or a trim element such as a skirting board, grid, cove, quarter-ran, etc.

The fibre-plastic composite may be attached to other structural elements made from other materials, such as metal or wood. The Applicants have realised that the fibre-plastic composites are especially useful for producing inexpensive products such as scaffold boards. Preferably the scaffold boards comprise a coating of glass-fibre reinforced plastics material. This allows the scaffold board to be durable, whilst still being relatively inexpensive.

The use of the mandrel means that the scaffold board comprises at least one hollow aperture running along the length of the scaffold board. This has been adapted so that the aperture can be used to attach adjacent scaffold boards via a connector. The connector itself may be made by an extrusion process according to the invention, or alternatively be made by injection moulding. The connector may be made from a wood-plastics composite material, or alternatively be made from a metal, for example aluminium. The connector connects scaffold boards either lying adjacent to one another or scaffold boards placed end to end by engaging with at least one of the hollow apertures of each scaffold board and holding them together, for example by means of a friction-fit. The connector may be adapted so that it can attach both adjacent boards running parallel to one another and also scaffold boards placed end to end. Accordingly, the connector preferably comprises a cross-member and a plurality of engaging members, each substantially perpendicular to the cross-member, the engaging members arranged to engage a hollow aperture of a scaffold board or composite according to the invention. Preferably, the connector comprises a plurality of the engaging members on opposite sides of the cross-member. The cross-member and engaging members are preferably in the same plane, and the cross-member additionally comprises attached to it one or more members in the extending part of the plane for connecting with one or more scaffold poles. For example, the member extending out of the plane may be sized to fit into the hollow end of a scaffold pole. Alternatively, one or more of the members may comprise a clamp for attaching onto a scaffold board.

Additionally, the connector or composite may comprise one or more additional engaging means, for example at an end of the cross-member in the same plane to attach the cross-member to the scaffold poles. Again the connector may comprise, for example, a clamp for attaching the cross-member to a scaffolding pole. The invention also includes within its scope, scaffold and comprising a composite, scaffold board and/or connector according to the invention.

A still further aspect of the invention provides an apparatus for moulding a fibre-plastics composite comprising a heater for heating a mixture comprising a fibrous, cellulosic material and a plastics material, a die for extruding the mixture to form a heated extrusion, and hollow cooling means, the cooling means comprising a first aperture for receiving the heated extrusion and a second aperture through which the cooled extrusion can exit, wherein the diameter of the inside of the cooling means tapers between at least a part of the distance between the first and second apertures so that a heated extrusion passing through the cooling means is compressed.

Preferably, the apparatus comprises one or more mandrels which extend at least partially into the cooling means for creating a cavity within the cooled extrusion. Preferably, the mandrel is positioned to form one or more walls surrounding at least a portion of the cavity.

The taper from the first aperture to the second aperture is preferably 5-15% of the thickness of the wall formed by the mandrel when in use, especially 7-12%, most preferably 9-10% of the thickness of the wall.

The inside of the cooling means preferably forms a tapered wall which is arranged to be in contact with the heated extrusion when in use. The tapered wall may be frusto-conical, with a substantially circular cross-section. Alternatively, it may contain three or more walls. For example, the cooling means may comprise four walls. Two walls run substantially parallel to one another and the two other walls which are opposite to each other are arranged to taper towards each other to compress the heated extrusion when in use. Alternatively, all four walls may taper towards each other so that, when in use, the composite material is compressed both at the sides and top and bottom. That is, the four walls form a frusto-pyramidal shape. The tapered wall may comprise one or more cooling channels containing a fluid liquid, as described above.

Preferably, the apparatus comprises a hopper for supplying a fibrous, cellulosic material to a drying chamber for drying the fibrous, cellulosic material, and supply means for supplying at least one plastics material to the dried, fibrous, cellulosic material to form a mixture of fibrous cellulosic material and plastics material. This apparatus may be used independently with a number of different moulding system. Accordingly, a further aspect of the invention provides an apparatus for producing a fibre-plastics composite comprising means for supplying a moist, fibrous, cellulosic material to a drying chamber, for drying the moist, cellulosic, fibrous material, means for supplying at least one plastics material to the dried, fibrous, cellulosic material and moulding means to form a fibre-plastics composite. The moulding means may be, for example, an extruder or an injection moulder. The drying chamber may comprise a heated auger, the heated auger comprising a housing, the housing having a first aperture for receiving the moist, fibrous material and a second aperture for removing the dried, fibrous, cellulosic material, and a helical screw which is rotatable to move the fibrous material between the first aperture and the second aperture. The construction of the heated auger in its preferred form has been described above.

Preferably, the apparatus comprises a holding chamber for receiving the dried, cellulosic, fibrous material before it is mixed with a plastics material. Again, this has been described in more detail above.

The apparatus according to the invention further comprises a vibrating table for combining fibrous, cellulosic material with plastics material and may additionally comprise means for supplying one or more additives to the mixture of fibrous, cellulosic material and plastics material.

Preferably, the apparatus comprises a ribbon blender for mixing the fibrous, cellulosic material and the plastics material. A powder flight conveyor is preferably used for transporting the mixture of fibrous, cellulosic material and plastics material to one or more extruders. The apparatus preferably additionally comprises means for compressing the mixture of the cellulosic material and plastics material prior to passing to an extruder, the extruder comprising a die through which the heated mixture may be passed to form a heated extrusion. This is described in more detail above. However, preferably the means for compressing the mixture is a rotating helical screw.

Again, this arrangement is applicable to other methods for other types of apparatus for making fibre-plastics composite. Hence, a further aspect of the invention provides an apparatus for producing a fibre-plastics composite comprising means for supplying a mixture of particulate fibrous, cellulosic material and plastics material, means for compressing the mixture to form a compressed mixture without melting the plastics material and means for passing the compressed material into an extruder, the extruder comprising means to heat the compressed material and pass the heated material through a die to form a heated extrusion.

A still further preferred embodiment of the invention provides an apparatus of the invention additionally comprising a co-extruder for coating a cooled extrusion with a mixture of plastics material and glass-fibre. Co-extrusion is, itself a known technique in the art.

The invention also provides a method of forming a fibre-plastic composite comprising the use of an apparatus according to the invention.

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

FIGURE 1 shows a schematic diagram illustrating the process of the invention. FIGURE 2 shows a longitudinal cross section of an extruder for use in the invention. FIGURE 3 shows a transverse cross section of the extruder.

FIGURE 4 shows a view of the mode of interaction of the connector with the scaffold boards as a perspective view (a) and a schematic plan view (b). Figure 1 depicts the apparatus for preparing the fibre-plastics composite according to the invention. The fibrous cellulosic material is provided as a moist fibrous cellulosic material and is transferred into a drying chamber comprising heated wood-drying augers (1), which possess a first aperture (2) to receive the moist fibrous cellulosic material and a second aperture (3) for the removal of the dried fibrous cellulosic material. Helical screws (4) rotate within the augers in such a way to allow the fibrous cellulosic material to be moved along the length of the augers while a heat source is applied through the walls of the augers to dry the material, with the pitch of the helical screw being greater towards the first aperture than towards the second aperture. Trace heaters are particularly effective heating means. Upon exiting the augers, the dried material may be passed directly from the drying chamber to the rest of the apparatus for immediate processing, or alternatively may be moved into a holding chamber (also called a "day bin" (5)) prior to mixing.

The day bin is a temporary holding tank. This allows a continuous feed of material to be passed through to the rest of the system, whilst, for example, an additional batch material is passed into the dryers. The additional material may be passed to the dryers (1) via a screw (25), from a walking floor trailer (A) (26) or a second trailer (B) (28).

The fibrous cellulosic material passes along onto the vibratory table conveyor (6), onto which is supplied a plastics material(29), and also optionally additive substances (30), for combination with the fibrous cellulosic material. The plastics material may be delivered onto the vibratory table either before, during or after the delivery of the fibrous cellulosic material onto the vibratory table. The vibratory table allows the material to be consistently mixed and easily weighed.

The mixture with comprising fibrous cellulosic material and plastics material is then moved into a "U"-trough mixer, or ribbon blender (7), where the mixture is homogenised. This now-homogeneous mixture is transported to one or more extruders (9) by means of the powder flight or aeroflight conveyor (8). Prior to entry into the extruders, the homogeneous mixture is compressed, and the compressed material is delivered to an extruder where it is heated and passed through a die to form the heated extrusion material. Figure 2 depicts a non-schematic side view of an extruder (9), showing the compressed material entering the extruder via a first aperture (10), and one of the mandrels (11) passing through the length of the material being extruded (12). It can be seen that the inner walls of the extruder (13) are so arranged that the diameter of the inside of the cooling means tapers to compress the heated extrusion as it passes through the extruder before exiting the second aperture (14), and that the material is constantly in contact with the inner walls of the extruder. Please note that the taper is exaggerated for the purposes of clarity.

Figure 3 shows a non-schematic cross section view of an extruder (9). The plurality of mandrels (11) extend at least partially into the cooling means to support the heated extrusion material (12) whilst it is being cooled to a low enough temperature to support itself. In the tapered extruder wall surrounding the heated extrusion product are the holes (15) through which the cooling fluid is passed.

Figure 4 shows a non-schematic view of the connector (16) and its method of engagement with the hollow apertures (20) of one or more scaffold boards (18) through a plurality of engaging members (17) in the same plane. A clamp may be present on the end (19) of the connector for attachment to a scaffold board or scaffold pole. The connector (16) may comprise a raised, enlarged centre cross-piece portion (34) to reduce the gap between adjacent scaffold boards. The connector may extend so that several adjacent pairs of boards (18) may be connected as shown schematically in Figure 4(b).

Claims

1. A method of producing a fibre-plastics composite comprising the steps of:

(a) Providing a mixture comprising fibrous cellulosic material and a plastics material;

2. A method according to claim 1, wherein the die comprises a one mandrel which extends at least partially into the cooling means to produce a cavity within the cooled extrusion.

3. A method according to claim 2, wherein the mandrel forms one or more walls surrounding at least a portion of the cavity.

4. A method according to claim 3, wherein the taper from the first aperture to the second aperture is 5 to 15% of the thickness of the wall from the outside of the heated extrusion to the cavity.

5. A method according to any preceding claim comprising at least one tapered wall in contact with the heated extrusion.

6. A method according to claim 5, wherein the tapered wall comprises one or more cooling channels containing a cooling fluid.

7. A method according to any preceding claim, wherein the fibrous cellulosic material and/or plastics material are particulate prior to mixing together.

8. A method according to any preceding claim, wherein:

(i) the fibrous material is provided as moist fibrous material;

(ii) the particulate moist fibrous material is passed through a drying chamber to produce dried fibrous cellulosic material and

(iii) is mixed with at least one plastics material to form the mixture comprising fibrous cellulosic material and a plastics material.

9. A method of producing a fibre-plastics composite comprising the steps of:

(a) Providing moist, fibrous, cellulosic material;

(d) Moulding the mixture to form a fibre-plastics composite.

10. A method according to claim 9 wherein the mixture is moulded by heating the mixture and passing the heated mixture through a die to form a heated extrusion.

11. A method according to claim 9 wherein the mixture is moulded by injection moulding.

12. A method according to any one of claims 8 to 11, wherein the dry chamber comprises having the housing having the first aperture for receiving the moist, fibrous material and a second aperture for removing the dried, fibrous, cellulosic material, and a helical screw which rotates to move the fibrous material between the first aperture to the second aperture.

13. A method according to claim 12, wherein the pitch of the helical screw is greater towards the first aperture, than towards the second aperture.

14. A method according to any of claims 12 or 13, wherein the housing comprises a wall, the wall having one or more trace heaters to heat and dry the fibrous, cellulosic material.

15. A method according to any of claims 12 to 14, comprising a plurality of heated augers mounted consecutively in series to progressively dry the moist fibrous, cellulosic material.

16. A method according to any of claims 8 to 15, wherein the dried, cellulosic, fibrous material is moved into a holding chamber prior to bring mixed with the plastics material.

17. A method according to any preceding claim, wherein the fibrous, cellulosic material is combined with the plastics material on a vibratory table.

18. A method according to any preceding claim additionally comprising the step of adding one or more additives to the mixture.

19. A method according to any preceding claim wherein the plastics material and fibrous cellulosic material are mixed in a ribbon blender.

20. A method according to any preceding claim, wherein the mixture of fibrous cellulosic material and plastics material are transported to one or more extruders by a powder flight conveyor.

21. A method according to any preceding claim comprising:

(i) Compressing the mixture to form a compressed mixture without melting the plastics material:

(ii) Passing the compressed material into an extruder;

(iii) Heating the compressed material in the extruder; and

(iv) Passing the heated material through a die to form the heated extrusion.

22. A method of producing a fibre-plastics composite comprising:

(iii) Passing the compressed material into an extruder;

(iv) Heating the compressed material in the extruder; and

(v) Passing the heated material through a die to form a heated extrusion.

23. A method according to claim 21 or claim 22 wherein the mixture is compressed by a rotating screw.

24. A method according to any preceding claim additionally comprising the step of co-extruding the cooled extrusion with a mixture of a plastics material and glass fibres to coat the cooled extrusion with the glass fibres.

25. A method of producing a reinforced fibre-plastic composite comprising:

26. A method according to any preceding claim wherein the mixture comprises at least 60% by weight of fibrous, cellulosic material and less than 40% of plastics material.

27. A method according to claim 26, wherein the fibrous, cellulosic material comprises at least 50% by weight of particles of at least 100 μm diameter.

28. A mixture comprising:

(i) >60 wt.% of a fibrous cellulosic material; and

(ii) <40 wt.% of a plastics material;

wherein the fibrous cellulosic material comprises at least 50% wt. of particles of at least 100 μm diameter.

29. A method or a mixture according to any preceding claim, wherein the fibrous, cellulosic material is from wood, corn, nuts, straw, hemp, jute, rice stalks, seed husks, cotton, paper and/or sugar cane.

30. A method or a mixture according to any preceding claim wherein the plastics material is virgin plastics material, recycled plastics material or a mixture thereof.

31. A method or a mixture according to any preceding claim comprising a virgin thermosetting plastics material which is provided as manomeric plastics material.

32. A method or mixture according to any preceding claim wherein the plastics material is selected from a polyolefine, uPVC, polypropylene, polyethylene, polyamide, poly(meth)acrylates, acrylonitrile-butadiene-styrene (ABS), polystyrene, polyphenylene oxides, polyhydroxy- butyrate (PHB), polyhydroxyvalerate, or copolymers or mixtures thereof, or monomers of the polymers.

33. A method or mixture according to any preceding claim wherein the plastics material is a combination of uPVC and polyethylene.

34. A method or mixture according to any preceding claim wherein the mixture of fibrous cellulosic material and plastics material additionally comprises one or more of waxes, stearate, foaming agents, bulking agents, titanium dioxide, stabilisers, master batch, colorants, talcs, surfactants and/or preservatives.

35. A fibre-plastic composite obtainable by a method according to any one of claims 1 to 27 and 29 to 34 or containing a mixture according to claim 28.

36. A fibre-plastic composite which is a part of a door frame, window frame or a staircase.

37. A fibre-composite according to claims 34 or 35 comprising a rail, a jamb, a style, a sill, a track, a stop sash, a trim element.

38. A fibre-plastic composite according to claim 35, which is a scaffold board.

39. A fibre-plastic composite according to claim 38, wherein the scaffold board comprises a hollow aperture running through the length of the scaffold board.

40. A fibre-plastic scaffold board comprising a hollow aperture running through the length of the scaffold board.

41. A composite according to claim 39 or a scaffold board according to claim 40 comprising a plurality of apertures.

42. A composite or scaffold board according to claims 39 to 41 comprising a coating of glass-fibre reinforced plastics material.

43. A composite according to claim 34 which is a connector for connecting two or more scaffold boards or composites according to any of claims 39 to 42 by engaging the hollow aperture of a first scaffold board with a hollow aperture of an adjacent board.

44. A connector for connecting two or more scaffold boards or composites according to any of claims 39 to 42 by engaging the hollow aperture of a first scaffold board with a hollow aperture of an adjacent scaffold board.

45. A connector or composite according to claim 43 or claim 44 comprising a cross member and a plurality of engaging members, each substantially perpendicular to the cross member, the engaging members arranged to engage a hollow aperture of a scaffold board or composite according to any of claims 39 to 42.

46. A connector or composite according to claim 45 comprising a plurality of said engaging members on opposite sides of the cross member.

47. A connector or composite according to claims 45 or 46, wherein the cross member and engaging members are in the same plane, and the cross member additionally has attached to it one or more members extending out of the plane for connecting with one or more scaffold poles.

48. Scaffolding comprising a composite, scaffold board and/or connector according to any one of claims 39 to 47.

49. An apparatus for moulding a fibre-plastics composite comprising a heater for heating a mixture comprising a fibrous, cellulosic material and a plastics material, a die for extruding the mixture to form a heated extrusion, and hollow cooling means, the cooling means comprising a first aperture for receiving the heated extrusion and a second aperture through which the cooled extrusion can exit, wherein the diameter of the inside of the cooling means tapers between at least a part of the distance between the first and second apertures so that a heated extrusion passing through the cooling means is compressed.

50. An apparatus according to claim 49 additionally comprising one or more mandrels which extends at least partially into the cooling means for creating a cavity within the cooled extrusion.

51. An apparatus according to claim 50, wherein the mandrel is positioned to form one or more walls surrounding at least a portion of the cavity.

52. An apparatus according to claim 51, wherein the taper from the first aperture to the second aperture is 5-15% of the thickness of the wall formed by the mandrel.

53. An apparatus according to any one of claims 49-52 comprising at least one tapered wall positioned to be in contact with the heated extrusion.

54. An apparatus according to claim 53 wherein the tapered wall comprises one or more cooling channels containing a cooling fluid.

55. An apparatus according to any one of claims 49-54 comprising a hopper for supplying a fibrous, cellulosic material to a drying chamber for drying the fibrous, cellulosic material and supply means for supplying at least one plastics material to the dried, fibrous, cellulosic material to form a mixture of fibrous, cellulosic material and plastics material.

56. An apparatus for producing a fibre-plastics composite comprising means for supplying a moist, fibrous, cellulosic material to a drying chamber, for drying the moist, cellulosic, fibrous material, means for supplying at least one plastics material to the dried fibrous, cellulosic material and a moulding means to form a fibre-plastics composite.

57. An apparatus, according to claim 56, wherein the moulding means is an extruder.

58. An apparatus, according to claim 56, wherein the moulding means is an injection moulder.

59. An apparatus, according to any one of claims 55-58 comprising a heater auger, the heated auger comprising a housing, the housing having a first aperture for receiving the moist, fibrous material and a second aperture for removing the dried, fibrous, cellulosic material, and a helical screw which is rotatable to move the fibrous material between the first aperture and the second aperture.

60. An apparatus, according to claim 59, wherein the pitch of the helical screw is greater towards the first aperture than towards the second aperture.

61. An apparatus, according to claims 59 or 60, wherein the housing comprises a wall, the wall having one or more trace heaters for drying the fibrous, cellulosic material.

62. An apparatus, according to any one of claims 59-61, comprising a plurality of heated augers mounted consecutively in series for progressively drying the moist, fibrous, cellulosic material.

63. An apparatus, according to any one of claims 55-62, comprising a holding chamber for receiving the dried, cellulosic, fibrous material before it is mixed with a plastics material.

64. An apparatus, according to any one of claims 49-63, comprising a vibratory table for combining fibrous, cellulosic material with plastics material.

65. An apparatus, according to any one of claims 49-64, comprising means for supplying one or more additives to the mixture of fibrous, cellulosic material and plastics material.

66. An apparatus, according to any one of claims 49-65, wherein a ribbon blender is provided for mixing the fibrous, cellulosic material and the plastics material.

67. An apparatus, according to any one of claims 49-66, additionally comprising a powder flight conveyor for transporting the mixture of fibrous, cellulosic material and plastics material to one or more extruders.

68. An apparatus, according to any one of claims 49-67, comprising means for compressing the mixture of the cellulosic material and the plastics material prior to being passed into an extruder, the extruder comprising a die through which heated mixture may be passed to form the heated extrusion.

69. An apparatus for producing a fibre-plastics composite comprising means for supplying a mixture of particulate fibrous, cellulosic material and plastics material, means for compressing the mixture to form a compressed mixture without melting the plastics material and means for passing the compressed material into an extruder, the extruder comprising means to heat the compressed material and pass the heated material through a die to form a heated extrusion.

70. An apparatus, according to any one of claims 49-69, additionally comprising a co-extruder for coating a cooled extrusion with a mixture of a plastics material and glass fibres.

71. A method of forming a fibre-plastics composite comprising the use of an apparatus according to any of claims 49 to 70.