GB2471096A

GB2471096A - Laminated composites based on natural materials

Info

Publication number: GB2471096A
Application number: GB0910376A
Authority: GB
Inventors: Timothy Sweatman; Douglas Spinney
Original assignee: ECO MATS Ltd; ECOTECHNILIN Ltd
Current assignee: ECO MATS Ltd; ECOTECHNILIN Ltd
Priority date: 2009-06-16
Filing date: 2009-06-16
Publication date: 2010-12-22
Also published as: WO2010146355A1; GB0910376D0; EP2442976A1

Abstract

A laminated composite material comprises a first layer formed from granulated cork and a binder, and second and optional third layers each comprising a network of plantderived natural fibres, the first layer being sandwiched between and bonded to the second and the optional third layers. The binder used to bind the granulated cork in the first layer is a flame-retardant binder, e.g. a plant-derived material such as a furan resin. The second and third layers are bonded to the first layer by a binder component, typically a furan resin. The plant-derived natural fibres may be hemp, jute, ramie, kenaf, rattan, soya bean fibre, okra fibre, cotton, vine fibre, peat fibre, kapok fibre, sisal fibre or banana fibre. The composite may be used for constructional, acoustical control, fire safety or thermal insulation purposes in buildings or vehicles.

Description

LAMINATED COMPOSITES

BACKGROUND TO THE INVENTION

Field of the invention

The present invention relates to laminated, composite materials, methods for making such materials, and uses of such materials. It is of particular relevance to the use of natural materials, such as natural fibre-based materials.

Related art It have been known for many years that the mechanical properties of wood are limited by the ariisotropic nature of wood. Wood tends to be strong in a direction parallel to the wood grain but relatively weak in a direction perpendicular to the wood grain. Thus, a known method to address this problem is to provide plywood, in which layers (plies) of wood are laid so that the grain direction of one ply is perpendicular to the grain direction of another ply.

The plies are bonded together with an adhesive. Wood-based particle board takes a different approach, by using chips or flakes of wood as a filler and bonding these together using a binder, such as an adhesive. The overall board has substantially isotropic mechanical properties. Similarly, fibreboard (e.g. medium density fibreboard, or MDF) uses

I

wood fibres as a filler, with a binder. These materials (plywood, particle board and MDF) are of use in construction and other applications.

Although it is of great interest to use a renewable material such as wood in the production of construction materials, the materials have several drawbacks. One such drawback is the relatively high density of these materials. Another such drawback is the fire risk provided by the use of wood.

Alternative materials tend to have different drawbacks, in particular cost and environmental drawbacks. It is known, for example, that fibre-reinforced plastics (e.g. carbon fibre reinforced plastics) can have mechanical properties that are far superior to wood-based materials. However, they tend to be relatively expensive and tend to rely on non-renewable materials in their manufacture.

SUNMARY OF THE INVENTION

The present inventors have realised that alternative materials may be provided which are laminated composites, most preferably derived from natural, renewable sources, and which have excellent mechanical properties.

Accordingly, in a first aspect, the present invention provides a laminated composite material comprising at least a first layer and a second layer, the first layer comprising cork and the second layer comprising a network of fibres, preferably natural fibres, the first layer and the second layer being bonded to each other.

In a second aspect, the present invention provides a method for the manufacture of a laminated composite material comprising at least a first layer and a second layer, the first layer comprising cork and the second layer comprising a network of fibres, preferably natural fibres, the method including the step of pressing the first layer and the second layer together to bond these layers together.

In a third aspect, the present invention provides a use of the laminated composite material in a constructional application, e.g. in a building, in a vehicle such as a car or truck, in a railway carriage, etc. In a fourth aspect, the present invention provides a use of the laminated composite material in an acoustical control application, e.g. in a building, in a vehicle such as a car or truck, in a railway carriage, etc. In a fifth aspect, the present invention provides a use of the laminated composite material in a fire safety application, e.g. in a building, in a vehicle such as a car or truck, in a railway carriage, etc. In a sixth aspect, the present invention provides a use of the laminated composite material in a thermal insulation application, e.g. in a building, in a vehicle such as a car or truck, in a railway carriage, etc. Using the invention, it is possible for the natural mechanical advantages of cork (low density, excellent compression properties) to be utilised, whilst the second layer may provide tensile strength to give the composite significantly better properties in tension or bending than would be provided by the first layer alone.

Optional features relating to the present invention will now be set out. These may be combined (either singly or in any combination) with any aspect of the invention unless the context demands otherwise.

Preferably, the material includes a third layer, similar to the second layer, located at an opposing face of the first layer compared with the second layer. The third layer and the first layer are preferably bonded to each other. In this way, it is preferred that the first layer is sandwiched between the second layer and the third layer.

Preferably, the material is in the form of a plate or board, i.e. with dimensions of length and width being significantly (e.g. at least 10 times) greater than the thickness of the plate or board.

The material may have a curved or profiled upper and/or lower surface.

The thickness of the first layer may be at least 1mm.

Typically, the thickness of the first layer is significantly greater than this, e.g. at least 5mm or at least 10mm. The thickness of the second layer (and the thickness of the third layer, if present) is preferably at least 5 times smaller than the thickness of the first layer.

It is known that cork is derived from the bark of specific trees, notably the cork oak tree. The bark is harvested from the tree at regular intervals, with typically 9 to 12 years between each harvest. Cork trees typically live for 200-250 years. After the bark has been harvested from the tree, a new layer of bark regrows. Thus, cork is a naturally renewable material, in the sense that it is renewed by a natural plant growth process, and is replaced within a relatively short period, as indicated above. At present, a significant proportion of cork is used to make bottle closures, typically for wine bottles.

The first layer may further include a binder. In this case, it is typical that the first layer is manufactured from granulated cork which has been mixed with a binder and pressed to form a solid body. The first layer may, for example, be cut from such a solid body. Granulated cork comprises granules of cork material obtainable by shredding or otherwise breaking cork bark. Alternatively, granulated cork may be obtained by recycling cork material, e.g. from used (or unused) bottle closures.

The proportion of binder to cork in the first layer may be as high as 50% by weight. However, it is preferred that the amount of binder in the first layer is lower than this. For example, the proportion of binder to cork in the first layer may be 45% by weight or less, more preferably 40% by weight or less, 35% by weight or less, 30% by weight or less, 25% by weight or less, 20% by weight or less, or 15% by weight or less. The proportion of binder to cork in the first layer may be 1% by weight or more, more preferably 5% by weight or more or 10% by weight or more. Most preferably, the proportion of binder to cork in the first layer is in the range 10-15% by weight.

Preferably, the density of the first layer is not more than 0.4 gcm3 (i.e. not more than 400 grams per litre) . More preferably, the density of the first layer is not more than 0.35 gcm3, more preferably not more than 0.3 gcm3 and is preferably about 0.27 gcm3.

Cork itself is a relatively flame-retardant material. In order to utilise this advantage in the composite, it is preferable that the binder used in the first layer is either used at low levels, or that the binder itself is also flame-retardant, or both of these features. A typical cork binder is polyurethane. Preferably, the binder used in the first layer is a thermosetting binder. Therrnosetting polyurethane can be used, for example. Alternative binders are discussed in more detail below.

Preferred features of the second layer are now set out.

These features are also separately preferred features of the third layer, if present.

Preferably the second layer is in the form of a sheet.

Preferably, the fibres of the second layer are arranged substantially randomly but substantially parallel to a surface of the second layer. The fibres of the second layer may have an average length of at least 10mm, more preferably at least 20mm, at least 30mm, at least 40mm, at least 50mm, at least 60mm or at least 70mm. The fibres may be processed (e.g. cut) to have a maximum length of up to 150mm, for

example.

Preferably, the fibres are natural (i.e. non-synthetic) fibres. In particular, they are preferably plant-derived fibres. Preferably, the plant-derived fibres are one or more selected from the following: hemp, jute, flax, ramie, kenaf, rattan, soya bean fibre, okra fibre, cotton, vine fibre, peat fibre, kapok fibre, sisal fibre, banana fibre or other similar types of bast fibre material. Such plant-derived fibres are fibrous and are flexible. Thus it is preferred that the filler material of both the first layer and of the second layer are plant-derived renewable materials.

Preferably, the second layer has a binder component, in order to form a strong network of fibres. The binder component may be a synthetic binder or a natural binder.

Typically, the binder component may be heat activated. For example, whether the binder is a synthetic material, it may be selected from one or more of: polypropylene, polyethylene, polyester, vinyl, polyvinyl acetate, and other similar binding material. Where the binder is a natural material, it may be selected from one or more of: polylactic acid, starch, furan resin, and other similar binding material.

Further detail relating to binders is set out below.

As mentioned above, the binder component may be heat activated. The binder component is typically a polymer or resin. This may be thermoplastic or thermosetting.

Thermosetting binders are particularly preferred. When the second layer is heated to an activation, or melting, temperature of the binder, inter-fibre bonds are established.

Preferably, the percentage weight of the binder component in the second layer is in the range lwt% to 75wt%. The percentage weight of the binder component in the second layer may be at least lwt%, 5wt%, lOwt%, l5wt%, or 2Owt%.

The percentage weight of the binder component in the second layer may be at most 7Owt%, 65wt%, 6Owt%, 55wt%, 5Owt% or 45wt%. The remaining weight of the second layer is taken up by the fibre content of the second layer.

Preferably, the method of forming the material includes the step of providing a fibre mat and pressing the fibre mat to the first layer, in order to create the second layer and bond the second layer to the first layer in a single step.

This step may include heating. The composite may be heated in this step to a temperature of at least 80 degrees C, more preferably to at least 100 degrees C, at least 120 degrees C, or at least 140 degrees C. Preferably, in this step, the composite is heated to a temperature of 250 degrees C or lower, more preferably 200 degrees C or lower. A typical temperature for this heating step is 160-165 degrees C. In this step, the fibre mat is typically compressed to a greater extent than the first layer. Additionally, after this step the fibre mat typically does not recover its shape but instead is permanently compressed to form the second layer. In contrast, the first layer typically at least partially recovers from the compression. In this step, the density of the second layer at the end of the step is typically at least three times (preferably at least four times or at least five times) the density of the fibre mat at the beginning of the step.

The binder component for the second layer may be incorporated in the fibre mat, e.g. as binder particles.

However, more preferably, the binder component for the second layer is preferably applied to the surface of the fibre mat facing the first layer, and/or is applied to the surface of the first layer facing the fibre mat. This may be applied by sprinkling, spraying, painting, etc. In the method set out above, the first layer is pre-forrned before the second layer is applied to the first layer.

However, it is possible for the first layer and the second layer to be formed substantially at the same time. In this case, the fibre mat and granulated cork (typically with a binder mixed with the granulated cork) are brought into contact, pressed and heated. This allows the granulated cork to be adhered by the binder to form the first layer and, at the same time, allows the second layer to be formed and bonded to the first layer.

Preferably, the fibre mat is formed by needle punching.

Alternatively, air laying may be used. Such fibre mats are non-woven. Non-woven mats are preferred. However, woven mats may be used. The area density of the fibre mat may be in the range 300-3000 grams per square metre (gsm) Preferably, the density of the second layer, is greater than the density of the first layer. For example, the density of the second layer may be at least 0.5 gcm3, more preferably at least 0.6 gcm3, more preferably at least 0.7 gcm3, e.g. about 0.8 gcm3.

Preferably, the binder component used to bond the second layer to the first layer (and also preferably to retain the shape of the second layer after pressing) is a plant-derived material. For example, the binder component may be furfural (furan-2-carbaldehyde) or a derivative of furfural such as furfural alcohol, furan, tetrahydrofuran and tertahydrofurfural alcohol (collectively referred to as furans) . In particular, it is preferred that the binder component is a furan resin. For example, a furan resin may be produced in which furfural replaces formaldehyde in a conventional production of a phenolic resin. The furan resin cross link (cure) in the presence of a strong acid catalyst via condensation reactions. Furfural an aromatic aldehyde, and is derived from pentose (CS) sugars, and is obtainable from a variety of agricultural byproducts. It is typically synthesized by the acid hydrolysis and steam distillation of agricultural byproducts such as corn cobs, rice hulls, oat hulls and sugar can bagase. Further details relating to furan resins whose use is contemplated in the present invention is set out in "Handbook of Thermoset Plastics", edited by Sidney H. Goodman, Edition 2, Published by William Andrew, 1998, ISBN 0815514212, 9780815514213, Chapter 3: Amino and Furan Resins, by Christopher C. Ibeh, the content of which is incorporated herein by reference in its entirety.

Furan resins are of particular interest because they are derived from natural, renewable sources, they bond well to natural fibres and they have good flame-retardancy properties.

The same binder component may be used in the first layer, i.e. to as the binder to bind the cork granules together in the first layer.

Thus, an aspiration of the present invention is to provide a laminate composite material as set out above, which consists essentially only of natural, renewable, plant-derived materials. For example, at least 95% by weight of the laminate composite (and more preferably at least 96% by weight, at least 97% by weight, at least 98% by weight or at least 99% by weight of the laminate composite, and most preferably 100% by weight of the laminate composite) may be natural, renewable, plant-derived materials.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS, ND

FURTHER OPTIONAL FEATURES

Preferred embodiments of the present invention will now be set out, in which further optional features of the invention are described. Such features may be combined either singly or in any combination with any aspect of the invention, unless the context demands otherwise.

Flax plants can be grown with a stem length between 600mm and 800mm. The stem has strong fibre bundles running from root to top. These fibre bundles are disposed outermost in the stem, and in the internal space between the fibre bundles there is a central stalk consisting of wood cells (shives) In comparison, hemp plants have stems which are considerably longer than the stem of the flax plants. They may have stem lengths from 2000mm to 3000mm. Similarly, the hemp stem may comprise outer fibre bundles and a inner wood cells (shives) Traditionally, the flax or hemp fibres are separated from the woody parts of the stem by a retting process. Retting is a microbiological process which partially decomposes the natural fibre. In particular, retting causes hemicellulose and pectin in the natural fibre to bind the fibres together.

Harvesting of flax and hemp for textile production consists of pulling up all of the plant. Pulling up the plants is a slow and work intensive process. After pulling up the plants, the plants are laid aside for retting and the retting process takes place in the field (e.g. dew-retting) The degree of retting is important for determining the properties of the fibres in the making of textile fibres for carding and spinning.

Subsequently, the stems are pressed into bales and transported to a fibre factory. The seeds are torn off in a scutching mill. Scutching is a process of mechanically separating the fibres from the woody part.

Fibre mats may be made using the harvested plant fibres, such as hemp or flax fibres. The fibres may be subjected to carding. Carding the fibres consists of passing the fibres through a card (a comb-like structure), which disentangles the fibres and straightens the fibres. The fibres may be cut to a suitable length, e.g. about 8cm. Thereafter, a fur is formed and finally a needle punching process is performed for making the finished fibre mat. Alternatively, the fibre mat may be formed by air-laying. Alternatively woven natural fibre mats may be used.

In some cases, it may be preferred not to use a retting process. In this case, the plant material may be subjected to a hammer milling process, as described in W02008/107664, the content of which is incorporated herein by reference in its entirety.

According to a first embodiment of the invention, there is provided a laminate composite with a first layer consisting of granulated cork and a polyurethane binder. Such a material is readily available and is typically formed by pressing and heating a mixture of the cork granules and the binder, typically at about 10-15% by weight of binder. This process forms a block, and the first layer can be formed by cutting the block to an appropriate size and shape. For example, the first layer may be in the shape of a board.

The laminate composite of the first embodiment has second and third layers, bonded to opposite faces of the first layer.

Each of the second and third layers is formed from a plant fibre mat. Suitable plant fibre mats include needle punched hemp fibre mats and needle punched flax fibre mats, as described above. Alternatively, air laid fibre mats may be used.

The plant fibre mat may have a binder component already incorporated, such as a polypropylene binder.

The plant fibre mats are placed on either side of the first layer in a heatable press. The arrangement is then heated to a temperature of 160-165 degrees C and pressed. The degree of compression is set to compress the plant fibre mats to a thickness of about one-fifth of their starting thickness, thereby to form the second and third layers.

In order to improve the bonding of the second and third layers to the first layer, an additional binder component may be incorporated at the interface between the first layer and the second layer and at the interface between the first layer and the third layer. This may be, for example, by painting the binder component on to the plant fibre mats and/or on to the surfaces of the first layer. The binder component is furan resin. Furan resin can be obtained, for example, from TransFurans Chemicals bvba, Industriepark Leukaard 2, 2440 GEEL, Belgium. Furan resin can be cured either by heat activation or by cold-cured using a catalyst, depending on the resin used. Based on the weight of the second layer, the proportion of binder component in the second layer is typically about 40% by weight.

After forming, the laminate composite has remarkable stiffness and a low density. The cork first layer provides the laminate with useful thermal insulation and acoustical control properties. Furthermore, the cork first layer is a naturally fire-retardant material, and so the composite may be used in applications where fire-retardancy is required.

A second embodiment of the invention is similar to the first embodiment except that in the heating/pressing step, the composite is not made to be flat. Instead, at least one major surface of the composite is formed to have a curved or undulating surface. For example, an array of strengthening ribs may be formed at one or both major surfaces of the composite.

A third embodiment of the invention is similar to the first embodiment except that the third layer is not provided.

A fourth embodiment of the invention is similar to the first embodiment except that the first layer is formed from granulated cork and furan resin as a binder. In this way, the entire product is formed of natural, renewable, plant-derived materials.

The embodiments set out above have been described by way of example. On reading this disclosure, modifications of these embodiments, further embodiments and modifications thereof will be apparent to the skilled person and as such are within the scope of the present invention.

Claims

CLAIMS1. A laminated composite material comprising at least a first layer and a second layer, the first layer comprising cork and the second layer comprising a network of natural fibres, the first layer and the second layer being bonded to each other.
2. A material according to claim 1 further comprising a third layer, similar to the second layer, located at an opposing face of the first layer compared with the second layer, the third layer and the first layer being bonded to each other, so that the first layer is sandwiched between the second layer and the third layer.
3. A material according to claim 1 or claim 2 wherein first layer is formed from granulated cork and a binder.
4. A material according to claim 3 wherein the binder in the first layer is a flame-retardant binder.
5. A material according to claim 3 or claim 4 wherein the binder in the first layer is a plant-derived material.
6. A material according to claim 5 wherein the binder in the first layer is a furan resin.
7. A material according to any one of claims 1 to 6 wherein the density of the first layer is not more than 0.4 gcm3.
8. A material according to any one of claims 1 to 7 wherein the fibres of the second layer are plant-derived fibres.
9. A material according to claim 8 wherein the plant-derived fibres are one or more selected from the following: hemp, jute, flax, rarriie, kenaf, rattan, soya bean fibre, okra fibre, cotton, vine fibre, peat fibre, kapok fibre, sisal fibre, banana fibre.
10. A material according to any one of claims 1 to 9 wherein the density of the second layer is greater than the density of the first layer.
11. A material according to any one of claims 1 to 10 wherein the second layer further comprises a binder component for bonding to the first layer.
12. A material according to claim 11 wherein the binder component of the second layer is a thermosetting binder.
13. A material according to claim 11 or claim 12 wherein the binder component used to bond the second layer to the first layer is a plant-derived material.
14. A material according to claim 13 wherein the binder component is a furan resin.
15. A method for the manufacture of a laminated composite material comprising at least a first layer and a second layer, the first layer comprising cork and the second layer comprising a network of natural fibres, the method including the step of pressing the first layer and the second layer together to bond these layers together.
16. A method according to claim 15 further comprising providing a third layer, similar to the second layer, and pressing to bond it to an opposing face of the first layer, so that the first layer is sandwiched between the second layer and the third layer.
17. A method according to claim 15 or claim 16 including the step of providing a fibre mat and pressing the fibre mat to the first layer, to create the second layer and bond the second layer to the first layer in a single step.
18. A method according to claim 17 wherein the fibre mat is compressed to a greater extent than the first layer.
19. A method according to claim 18 wherein the fibre mat is compressed to a density at least three times the density of the fibre mat at the beginning of the method.
20. A method according to any one of claims 15 to 19 wherein the second layer is bonded to the first layer via a binder component.
21. A method according to claim 20 wherein the binder component is applied to the surface of the fibre mat facing the first layer, and/or is applied to the surface of the first layer facing the fibre mat.
22. A method according to claim 19 or claim 20 wherein the binder component is a furan resin.
23. A method according to any one of claims 15 to 22 in which the first layer and the second layer are formed substantially at the same time, including the step of bringing the fibre mat and granulated cork and binder into contact, pressing and heating.
24. A method according to claim 23 wherein the binder component is a furan resin.