Title: Compressed biocomposite material, method for the production of such material and products obtained when using the material

Technical Field

The present invention relates to a compressed layered biocomposite material consisting of a core material, which on each side is covered by a structural layer and optionally a surface coating. Furthermore, the invention relates to a method for the production of such material as well as the use of the material for the production of materials or ob- jects within several industries such as furniture industry, automobile industry and construction industry.

Background

All over the world, in Europe, Asia and North America in particular, there is a growing interest in the development of new composites, in which both the strengthening fibres and the matrix material (plastic) are based on sustainable and renewable biomaterials. This interest is due to a number of factors aiming at replacing synthetic and inorganic fibres such as glass, metallic and mineral fibres with natural fibres and at the same time replacing the plastic with a biopolymer in various products. By replacing synthetic and inorganic fibres, such as glass fibre, with plant fibres and similarly replacing the matrix material, such as epoxy and polypropylene, with a biopolymer the following advantages in particular are obtained:

- natural fibres and biopolymers come from sustainable sources and are available in large quantities; natural fibres and biopolymers are not based on fossil fuels;

- biocomposites based on natural fibres and biopolymers are potentially CO ₂ neutral and therefore easier to dispose of; - most biocomposites are fully compostible; and

- when it comes to disposal it is possible to burn the material and utilise the heat for energy-winning.

There is a long tradition of using wood veneer for the production of furniture. In order to compensate for the directional characteristics of wood veneer the individual layers are crossed during the laying-up in the same way as known from plywood. This known type

of furniture veneer allows only to a limited degree for double curved surfaces and sharp edges. At the same time, variations in thickness of the material are difficult to achieve when shaping the products.

If the same characteristics in terms of strength, tenability and flexibility can be obtained as those characterising composite materials including synthetic and inorganic fibres, biocomposite materials will be an attractive alternative to the composite materials known so far for a large number of uses.

It has now surprisingly turned out that it is possible to manufacture a product, a chair in particular, on the basis of a layered biocomposite material, which after a so-called "sandwich" stacking is made subject to a pressing operation during which the material is shaped. In doing so, materials with both sharp edges and double curved surfaces may be manufactured and the thickness of the material may vary. In addition, it is pos- sible to add threaded bushings and inserts in connection with the press consolidation. A specific characteristic of the present invention is that the production process counts fewer stages compared to the conventional production methods for furniture veneer, the cycle time can be reduced substantially, the amount of waste can be reduced and an attractive working environment can be established.

Prior art

The prior art is quite extensive when it comes to composite products, also including products completely or partly based on biomaterials.

JP 2001-335710 A discloses a biodegradable, fibre-reinforced composite material and a method for the production hereof. Thermoplastic resin and vegetable cellulose fibre, such as Manila hemp or henequen, are hot-pressed at 100-300 ⁰ C.

In JP 2005-280361 A a biodegradable composite material is disclosed. The composite material consists of at least three layers, of which the two outer layers are made of a mixture of a polylactic acid base polymer and a crystalline-nucleating agent and of which one or more intermediate layers are made of a biodegradable aliphatic polyester. The material is produced using vacuum pressing.

WO 2005/042222 A discloses a moulding product consisting of a plant material that has been soaked and a thermoplastic resin. The product is shaped by means of hot- pressing.

WO 2004/094509 A discloses a sheet with excellent biodegradability and satisfactory characteristics in terms of formability and mechanical strength. The material is moulded into a sheet at a temperature of 120-180 ⁰ C. Furthermore, JP 2004-255833 A discloses a biodegradable fibre laminate which is produced by pressing. The material appears to be a cotton-like material on the basis of bamboo fibre and polylactic acid fibre, which in a specific weight proportion is pressed into its shape at a temperature, which does not affect the features of the bamboo fibres and which is higher than the melting point of polylactic acid fibres.

EP 1600288 A1 describes a method for the production of a fibre-reinforced decorative laminate, in which the stacked layers having been resin-impregnated are pressed and cured under heat and pressure.

WO 2005/105435 A1 discloses a thermoplastic composite sheet with excellent features not only when it comes to mechanical features, such as bending strength, modulus of elasticity, impact strength and linear thermal expansion coefficient, but also in terms of further processability suitable for moulding into various structures, for example for building materials and automobile parts. The material produced by melt-extruding a thermoplastic resin and providing a reinforcing fibre layer, after which the layers are compressed, is not based on a material with biopolymers.

US 5.635.123 A describes a fibre-reinforced protein-based material in the form of particles including a thermosetting resin obtained from legumes which together with cellulose fibre are pressed for the production of rigid biocomposite materials. Preferably, a secondary thermosetting adhesive such as an isocyanate is used.

Moreover, a large part of the patent literature within the field of biocomposite materials relates to the manufacturing of products for surgical use, such as bone prostheses for implantation. Such products and production methods are for example described in JP 2125827 A and in US 5.084.051 A.

Patents relating to the production of chairs in particular are GS 774322 A, which describes the production of backs and seats of chairs using traditional veneer pressing and JP 2000-004992 describing the production of chair parts, i.e. seats and backs from a laminate with a thermoplastic core covered by a textile-like layer.

Composites Science and Technology, Volume 63(9), 1287-1296 (2003) describes the production of a biocomposite material by pressing, particularly pre-consolidation of the layers, contact heating under vacuum and press consolidation. Biocomposites in the form of flax fibre-reinforced biopolymers are described in Composites Science and Technology, Volume 67(3-4), 462-470 (2006), which indicates that biocomposites produced by press consolidation might be able to be used for building matters.

The ever growing interest in biocomposite materials is for example reflected in the article "Composites turn green!" (e-Polymers no. T 002, 2002), which in short explains how entirely recyclable polymer composites are under development with a view to be used in the automobile and construction industry. Pressing machines and know-how for this purpose are developed and sold by the company R+S Technik GmbH among others offering a so-called "one-shot" process based on natural fibres (disclosed at 5th Global World and Natural Fibre Composites Symposium, April 2004, Kassel, Ger- many). This company uses short cycle times, but generally hot pressing too.

WO 03/047955 A1 discloses a composite material for a skateboard deck, preferably comprising two structural layers bonded to either side of a light flexible core, largely made of renewable biomaterials. The core, however, is not made of a thermoplastic polymer - which would allow yielding - but rather of a thermosetting polymer.

US 6.682.673 A describes fibre composite materials made from renewable resources, said materials being useful for the manufacture of sandwich elements for furniture or furniture parts. Again, the core polymer is not thermoplastic and yielding is therefore not obtainable.

EP 0687711 A2 discloses a composite material, which is biodegradable. The possibility of using natural fibres is mentioned and so is the possibility of using a matrix material based on a biopolymer. A sandwich stacking with a flexible core, which may undergo yielding during consolidation is, however, neither claimed nor suggested.

The closest prior art within the field of composites may thus be characterised in that it does not include a sandwich stacking of biomaterials, that it only to a limited extent makes use of real biomaterials and that the production of furniture veneer is usually done by hot pressing, where the retention time in the press is conditional on the time necessary for the glue, e.g. urea-formaldehyde, to cross-link and cure.

In contrast, the present invention includes a pressing process, in which a sandwich stacking is heated separately, shaped and cooled down in the press. Therefore, the retention time in the press may typically be reduced to about one third and the biologic raw materials used for the method according to the invention give enormous advantages in terms of raw material consumption (widely available raw materials), working environment and last but not least elimination of waste disposal issues since the material is compostible and potentially CO ₂ neutral.

Detailed description of the Invention

As mentioned before, the invention relates to the production of a layered compressed biocomposite material and products obtained when using the material. More specifically, the invention relates to a compressed layered biocomposite material character- ised in (a) that it is made from a sandwich stacking consisting of a structural layer (2) in the form of one or more layers with oriented fi-bres or veneer and a thermoplastic core material (3) possibly reinforced with short fibres and/or fillers, which allow for yielding, both consisting of materials based on renewable resources, and optionally a surface coating (1), the layers (1) and (2) optionally being replaced with a pre-consolidated skin layer (4), and (b) that the matrix material in (2) and (3) is a biopolymer.

The biocomposite material referred to consists of a core material, which on each side is covered by one or more structural layers and optionally a surface coating. The biocomposite material is made from raw materials, which are abundantly available and the method for production hereof includes a pressing process in the form of cold pressing, where the material is shaped and cooled down in the pressuring unit. The biocomposite material referred to and the method for production hereof distinguishes itself by enabling the production of materials with both sharp edges and double curved surfaces, while the thickness of the material may vary. Furthermore, the invention makes it pos- sible to manufacture materials in a considerably more rational way, since the production process counts fewer stages compared to conventional production methods for

moulded furniture veneer. In addition, the cycle time of the material can be reduced substantially compared to known production methods, which means higher productivity of the pressing machine.

A preferred embodiment of the present invention is the production of shell seats. Traditionally, veneer shell seats are produced by a method including hot pressing. Then, the edges of the seat are trimmed, polished and varnished before the chair is assembled. Typically, the polishing varnishing will have to be repeated at least two times in order to obtain a satisfying result.

Using the method according to the invention, the traditional hot pressing of furniture veneer is replaced with a pressing, in which the material cools down during the shaping process. This means that the retention time (in the pressing machine) is reduced substantially and the cycle time is thus reduced accordingly.

Another advantage is that composite materials tend to open up more opportunities in terms of design compared to furniture veneer as far as double curved surfaces and sharp edges and corners are concerned.

The pressed layered biocomposite material according to the invention may be covered with a surface coating, which may be relevant for example when the material has to be used for the production of chairs. In this case, the surface coating will typically be in the form of a foil, which eliminates the need for environment-unfriendly and costly surface treatments such as varnishing. The surface foil may vary in shine, colour and pattern.

Brief Description of the Drawings

The method according to the invention may be carried out in a number of embodiments based on a sandwich stacking as described below and shown in Fig. 1. The stacking is as follows:

1. Surface foil with finish

2. Structural layer with oriented fibres

3. Core material with short fibres, which allows for yielding

In the structural layer 2 the oriented fibres have the effect that the composite material gets the required strength.

The outermost structural layer 2 can also be one single layer of furniture veneer, even a 3-D furniture veneer, if the requirements for the double curved surfaces and sharp edges of the material allow for it.

In a first embodiment a stacking as shown in Fig. 1 is established and heated, for example by means of a belt press or by means of infrared radiation. Afterwards, the ma- terial is shaped and consolidated in a press mould while cooling down.

Another embodiment, particularly suited for the production of chairs, includes placing preformed and pre-consolidated skin layers in a pressing machine. The pre- consolidated layers 1 and 2 together constitute layer 4 as shown in Fig. 1. Along with the skin layers it is possible to mount threaded bushings and inserts or similar devices for subsequent embedment.

A melted core layer 3 is then placed between the pre-consolidated skin layers 4 in the pressing machine. During the pressing process the core layer may be subject to yield- ing and constitute a core with varying thickness. Finally, the material is consolidated in a press mould while cooling down. Here, the layers get their final shape while being joined.

"Yielding" in the sandwich stacking means a condition in which the heated biopolymer is more or less molten. Hereby, the polymer assumes a viscous or elastic state, in which especially the core material is allowed to be shaped under pressure. Normally the stacking is heated in a plane state with uniform material thickness. The heated stacking is shaped under pressure in a mould allowing yielding to proceed until the plastic material solidifies and the composite material has been consolidated. Subse- quently, the thickness of the composite material may vary along the surface which is an advantageous feature, because it gives a higher degree of design freedom and makes it easier to adapt the individual parts to each .other.

The biocomposite material produced distinguishes itself by consisting exclusively of biological, i.e. vegetable, material and by having surprising and unexpected characteristics in terms of strength, tenability and flexibility. In practice, the biocomposite mate-

rial is a plastic material produced on the basis of for example maize, which is reinforced with for example flax fibre. The vegetable material for biopolymers may be chosen from a wide range of materials like maize, potatoes, wheat or biowaste. Natural fibres for the structural layers will typically be plant fibres of the bast type with a high cellulose con- tent, such as flax and hemp, in order to obtain good mechanical characteristics. However, sisal, jute, straw and wood fibre may also be used. When it comes to the core material, the requirements are not so precise as regards characteristics, but materials such as wood fibre from saw dust, pulp from the production of bioethanol, seaweed and waste products from earlier or other production, which can be used as fillers, which are not necessarily fibres, are also good alternatives. The raw materials distinguish themselves by being CO ₂ -neutral and are thanks to their nature available in huge quantities. ^{' "}

The biocomposite material according to the invention has turned out to be particularly well-suited for the production of formable sheets and semi-finished products, which may be used separately, but are also appropriate for further processing. The material is particularly suited for the production of chairs and other furniture in a potentially cost- effective way, because the method for the manufacture of the products is considerably simplified compared to the methods used so far.

One example of a chair made out of the biocomposite material according to the invention is shown in Fig. 2. The seat shell is produced in two stages: the stacking is pressed as described above and then the edges are trimmed. As soon as the seat shell leaves the press mould, the surface is ready since it does not need varnishing, painting or any other surface treatment. Consequently, the environment-unfriendly surface treatments necessary when dealing with traditional veneer chairs are avoided. The chair depicted in Fig. 2 has a surface, which is both water and dirt repelling and can be obtained with a high-lustre finish in all kinds of colours and patterns.

The method according to the invention distinguishes itself by a significant reduction of the cycle time as described above. This means that more objects can be produced per unit of time with a set of pressing machines resulting in an increase in productivity. Surface treatments like for example varnishing are replaced with a surface foil. In short, apart from potentially financial advantages, substantial environmental advantages are obtained in terms of raw material consumption, reduced or even no waste at all and a better physical working environment. For disposal of the product, for example a seat

shell, composting may be used since the material is entirely vegetable-based and therefore CO ₂ -neutral. This is a clear advantage in countries, such as Denmark, in which waste is not burned.

The method of the invention and the biocomposite material produced according to this method may not only be used for the manufacture of chairs, but also more generally for the production of shell components, for example bodywork parts and other components for the automobile industry, plywood-like construction materials and similar materials.

The biocomposite material according to the invention can be made of natural fibres in the broadest sense, for example maize, and reinforced with fibre made of for example flax, which gives good rigidity. As mentioned before, the invention is not limited to the use of these plant materials. It is thus possible to use many other plant materials with an appropriately high content of starch.