Totally biodegradable composite material based on a thermoplastic matrix and natural plant fibres, method of manufacturing thereof and medical devices made of said composite material

Abstract

Composite material based on stacked alternate layers of: - a matrix based on a polymer of natural origin derived from renewable sources in the form of thin films; said matrix can be PolyLactic Acid (PLA) or Polybutylene Succinate (PBS); - natural plant fibres, preferably flax, hemp, jute. In a first embodiment, such natural plant fibres are in the form of a fabric provided with a warp and weft perpendicular to each other. In a second embodiment, such natural plant fibres are in the form of unidirectional windings of tapes obtained through filament winding technique. The present invention further comprises two methods for the preparation of the first and of the second embodiments, respectively. The composite materials according to the present invention can be used to produce medical devices intended for supporting patients.

Description

“Totally biodegradable composite material based on a thermoplastic matrix and natural plant fibres, method of manufacturing thereof and medical devices made of said composite material”* * * *

[0001] The present invention relates to a composite material based on stacked alternate layers of- a matrix based on a polymer of natural origin derived from renewable sources in the form of thin films; said matrix can be PolyLactic Acid (PLA) or Polybutylene Succinate (PBS);- natural plant fibres, preferably flax, hemp, jute.

[0002] In a first embodiment, the present invention relates to a composite material made of stacked layers of- a matrix based on a polymer of natural origin derived from renewable sources in the form of thin films; said matrix can be PolyLactic Acid (PLA) or PolyButylene Succinate (PBS);- sheets of a natural plant fibre fabric, preferably flax, hemp, jute.

[0003] In a second embodiment, the present invention relates to a composite material made of stacked layers of- a matrix based on a polymer of natural origin derived from renewable sources in the form of thin films; said matrix can be PolyLactic Acid (PLA) or PolyButylene Succinate (PBS);- layers of natural plant fibres, preferably flax or hemp or jute, wherein the natural fibres are provided with a unidirectional orientation, as they were produced by winding a natural fibre tape around a winding plate by using the filament winding technique.

[0004] Moreover, the present invention relates to the manufacturing method of said composite material and medical devices obtainable by using said composite material. Said components of the composite material undergo hot compaction inside a compression moulding machine or heated press. Saidcomposite material is obtained starting from renewable natural materials and is totally compostable and recyclable.

[0005] In the context of the present invention, distinguishing between thermoplastic and thermosetting materials is worthwhile. Thermoplastic materials are hot formed and can be re-processed many times. The matrixes used for thermoplastic materials are provided in the form of pellets or film and, in their molten state, are very viscous. Thermosetting materials are provided in the form of fluid resins that can be polymerized through heat or even at room temperature; once such materials have been polymerized, they cannot be re-processed.

[0006] Currently, research is pointing towards materials provided with three very desirable features: a) materials of natural origin, derived from renewable sourcesMaterials should allow to avoid the use of components of fossil origin, in particular derived from petrol; b) compostabilityOnce their service life is expired, materials should be totally composted, without leaving any toxic residue; c) recy cl abilityMaterials should be able to be totally recycled.

[0007] Polylactic acid is the polymer of lactic acid, which is obtained through several passages from maize or other sources of starch. Optionally, polylactic acid can be obtained from plant-derived waste. There are provided two enantiomeric forms (L and D). Often the racemate is used.

[0008] Polybutylene succinate is a biodegradable aliphatic polyester, obtainable e.g. from cereal fermentation.

[0009] The natural plant fibre is obtained from crops, e.g. flax or hemp or jute. It is worth pointing out that, throughout the description and in the claims, when speaking about natural fibres, natural plant fibre is meant,indeed obtained from flax, hemp or jute, and never reference is made to polylactic acid fibres.

[0010] In the first embodiment, said plant fibres are in the form of fabrics, well known in the art, e.g. plain fabric (made of just one thread for warp and weft), twill (two threads for each of warp and weft), wherein warp and weft are parallel to each other. All the warp threads are parallel to each other, while all the weft threads are parallel to each other.

[0011] In the second embodiment, the tapes for winding are provided with fibres in the form of tapes that can be provided with a linear density indicatively comprised between 300 tex to 3000 tex. In the plant industry, the tex is a unit of the universal measurement for yams: a yam has a title of 1 tex when 1,000 m of that yarn weigh 1 g (1 tex is equivalent to 0.11 den).

[0012] Several patents describe materials comprising natural fibres (among which flax) and polylactic acid. Nonetheless, most of the materials described in such documents make use of non-woven felts, while as will be shown in the following, the orientation of the natural fibre is paramount in order to confer the desired mechanical properties to the final composite material.

[0013] CA2168209A1 describes an absorption mat, comprising at least a biodegradable bottom layer which is impermeable to fluid, a biodegradable intermediate layer with odour absorbing and fluid-absorbing constituents, and a biodegradable top layer which is permeable to fluid, which absorption mat during decomposition, in particular during incineration, does not release hazardous waste substances. Said absorption mat has an absorbency of at least 4 litres of body fluid per square metre of absorption mat; with the proviso that when the odour absorbing constituent is natural fibre the fluid absorbent is not a hydroexpansible polymer powder or a natural fibre. Said mat can be used as a removable cover for an operating table, dissecting table or stretcher, that is as a medical device.

[0014] DE202022103585U1 discloses a geosynthetic mat comprisingoutermost layers of a biodegradable barrier film and covering layers of woven material, comprising biodegradable fibres and biodegradable thermoplastic materials, and comprising a five-layer material wherein the outer layers comprise a film material.

[0015] US9186868B2 describes a method for manufacturing biopolymer architectural or building panels made of biopolymers, comprising positioning a plurality of biopolymer sheets adjacent to one another, and subjecting them to a laminating temperature that exceeds the glass-transition temperature of the sheets for a time period sufficient to achieve lamination.

[0016] US20220316133 Al describes a synthetic leather made of layered materials, that includes a layer of a biodegradable polyurethane, a backing layer, and an adhesive layer. The layered material is formed by bonding a first surface of the biodegradable polyurethane layer to a first surface of the layer of the bamboo fibre through the adhesive layer. In some embodiments, the biodegradable synthetic leather is formed solely from ingredients of plants.

[0017] CN115302867B describes a preparation process of carbon fibre / hemp fibre reinforced thermoplastic composite panels. The panel consists of a surface layer and a core layer. The surface layer is a carbon fibre braid, while the core layer is a multi-layer structure obtained by stacking a carbon fibre braid and a hemp fibre thermoplastic composite felt. The carbon fibre is one or more combinations of braids obtained by using plain weave, twill, satin or three-dimensional weaving methods. The hemp fibre contains a thermoplastic resin chosen from the group comprising polypropylene PP, nylon PA6, polylactic acid (PLA), polyetheretherketone (PEEK), polyethersulfone (PES), and nylon PA66 or polyethylene terephthalate (PET) fibres. The presence of carbon makes the material non-compostable.

[0018] FR2964064B1 describes a biocomposite material for domestic objects comprising a superimposition of renewable materials comprising a minimum of two layers. One layer is made of unidirectional fibres. One of thecited components is natural fibres, in particular flax. One of the biodegradable polymers is polylactic acid. The material can be hot-formed. Said material is used to produce domestic objects.

[0019] The thesis "Polylactic Acid Fibre Reinforced Biodegradable Composites" submitted on 1 January 2015 to the University of Manchester for the degree of Doctor of Philosophy in the faculty of Engineering and Physical Sciences by Weiwei Jia describes a self-reinforced composite comprising just polylactic acid, both in the form of fibre and matrix, wherein the fibres of polylactic acid are aligned through filament winding. Two kinds of composites are described: four-stack composites and five-stack composites (pages 75-76, figure 4.6). The four-stack composite is made by superimposing a first outer PLA film, a first unidirectional layer of PLA fibres, a second unidirectional layer of PLA fibres, a last outer PLA film. The five-stack composite is made by superimposing a first outer PLA film, a first unidirectional layer of PLA fibres, an intermediate PLA film, a second unidirectional layer of PLA fibres, a last outer PLA film.

[0020] CN110884170A describes a pipe, a pipe manufacturing system and a method thereof, in particular a continuous fibre-reinforced thermoplastic pipe. Preferably, between the inner thermoplastic resin layer and the outer thermoplastic resin layer, a reinforcement layer is provided. Preferably, the fibre is glass fibre / carbon fibre / basalt fibre / polyester fibre / nylon fibre / cotton fibre / aramid fibre.

[0021] US20150337094A1 describes a biodegradable film and an enhanced biodegradable fabric and laminate prepared by laminated biodegradable films, which mainly comprise PBAT or PBS, or a mixture thereof, PLA and other degradable high molecular polymers, such as PBSA, PCL, PCL-BS and PHA, to prepare PLA, and a new mixture of PLA and PH As, or a mixture of PLA with PBAT and PBS, or a mixture of PLA and PHAs with PBAT and PBS or other degradable high molecular polymers.

[0022] CN217553178U describes a device for preparing a standardsample for testing the mechanical strength of a layer formed through filament winding, having the fibres oriented in a given direction, so as to obtain samples having a consistent thickness and therefore more accurate measurements. The document describes the use of a winding die that rotates on itself, around which a prepreg wire (thermosetting material) is wound; the windings of the prepreg wire are provided with a parallel orientation and a consistent thickness. Once the desired thickness of 1-2 mm is reached, the so obtained layer still wound around the winding die is polymerized inside an oven, and finally cut using a cutting groove on the short side of the winding die.

[0023] WO2019173745(Al) describes a device for winding fibres of glass, carbon, graphite, boron, ceramic, silicon carbide thermoplastic material o PEEK suitably impregnated in a bath with a resin before winding them around the winding matrix. Alternatively, the fibre is wound dry around a mandrel and impregnated with an epoxy resin (thermosetting material) in a following moment, when the winding structure is already formed. The winding shape can be planar or have a three-dimensional form (e.g. cylinder, cube). Once the desired winding structure is formed, it can be inserted into a mould for polymerization.

[0024] Using plastic materials for the production of sundry medical devices is known, e.g. extrication boards for extracting patients involved in a major accident trapped in the wreckage parts deriving from the accident (e.g. a car accident), but also stretchers and possibly wheelchairs. At present, such medical devices, well known in the art, are manufactured by using e.g. thermoformed ABS, which is produced starting from components of fossil origin. Obviously, such devices must be able to support the weight of a patient, which can reach 137 kg. Heavier patients are considered bariatric patients and special medical devices must be produced for such patients, who can reach a weight of even 350 kg. Nonetheless, at the end of their service life, the disposal of such materials is problematic. Biodegradable andcompostable plastics are destined to acquire an increasingly significant market share.

[0025] Aim of the present invention is producing a composite material of natural origin, totally compostable and totally recyclable, provided with suitable mechanical properties, and that can be used for manufacturing medical devices.

[0026] Such aim is reached through a composite material having the features described in claim 1 or in claim 2, and two manufacturing methods thereof having the features defined in claim 11 and in claim 16.

[0027] The matrix according to the invention is derived from crops, e.g. maize or other sources of starch for polylactic acid, and from cereal fermentation for polybutylene succinate. The fibres are natural fibres, e.g. flax, hemp, jute and others; all the components are renewable materials of natural origin.

[0028] According to the first embodiment, at least one film of matrix and at least one sheet of a natural fabric are sandwiched, for a number of layers that can reach 60 overall layers. With the increase of the number of layers the thickness of the composite material increases, as much as the mechanical properties of the manufactured article. With a low number of layers (up to 10) a material provided with some flexibility is obtained, while beyond 10 layers the rigidity of the manufactured article increases.

[0029] According to the second embodiment, a unidirectional winding of natural fibre produced through filament winding is called layer, while a winding of natural fibre coupled with film of matrix is called lamina. With winding structure, a sandwich of matrix films and layers of natural fibre is meant, each layer of natural fibre having a unidirectional orientation of fibres, which did not undergo compression moulding yet. Vice versa, once the compression moulding has taken place, a semi-finished product is obtained.

[0030] According to the second embodiment, at least one film of matrix and at least a layer of natural fibre are sandwiched, for a number oflaminae that can reach an overall number of thirty. With the increase of the number of layers the thickness of the composite material increases, as much as the mechanical properties of the manufactured article.

[0031] It is worth mentioning that the films of PLA and PBS have a very thin thickness, in the order of 0.1 mm. Optionally, when the sandwiched structure is formed, more than one matrix film can be stacked, e.g. two or more matrix films, between two consecutive layers of fabric or winding of natural fibre. The numerosity of the matrix films depends on the thickness of the films themselves. In particular, in the second embodiment, the percentage in volume of the natural fibres is about 30-35% with respect to the total volume fibres+matrix.

[0032] In a preferred embodiment, layers of fabric or natural fibre windings and matrix films are sandwiched leaving at the outer extremes at least one matrix film. Such structure, made of stacked layers of matrix film and of fabric or of natural fibre windings, is then compression-moulded in a compression moulding machine or heated press forming a semi-finished product. In order to prevent that the adhesion of the matrix to the press, a film of release material is used, e.g. Kapton® or polytetrafluoroethylene Teflon® placed between the moulding machine and the two outermost matrix films for the first embodiment. For the second embodiment, a sheet of release material is placed between the winding plate and the first matrix film. Analogously, a sheet of release material is placed between the mould and the outermost matrix sheets.

[0033] In the first embodiment, the thickness of the final composite material obtainable in this way is 7-8 mm, as with higher thicknesses the homogeneous heating of the semi-finished product becomes difficult.

[0034] In the second embodiment, the thickness of the final composite material obtainable in this way is 5-6 mm, as with higher thicknesses the homogeneous heating of the semi-finished product becomes difficult.

[0035] In the second embodiment, the tapes for winding used in thepresent invention are provided with fibres in the shape of tape having a linear density ranging 500 tex to 1500 tex.

[0036] In the second embodiment, the natural fibre consists of layers obtained through the filament winding technique starting from tapes, which technique allows to obtain fibres that are all oriented in the same direction, with a desired level of tension. The tape of natural fibre is wound around a winding plate so obtaining a pre-determined thickness (a first layer); after this, at least one matrix film is superimposed to the first layer. Now over the matrix film a new tape is wound, in a unidirectional way, so obtaining a second layer of natural fibre, then superimposing at least a new matrix film and repeating this operation up to the obtaining of the desired thickness. It is worth mentioning that the orientation of the fibres in the superimposed unidirectional laminae can be equal or different: e.g. the first layer can have fibres arranged with a first winding angle, the second layer can have fibres arranged with a second winding angle, the third layer can have fibre arranged with a third winding angle. Advantageously, by choosing suitably the winding angle of the tape with respect to the longitudinal axis of the winding plate, e.g. -45° and +45°, a semi-finished product can be obtained having laminae with an orientation of fibres perpendicular to each other.

[0037] PLA melts at 155°C. PLA moulding temperatures range 160- 190°C. For PBS moulding temperatures are slightly lower, 150-180°C. For both matrixes the moulding pressures range 10-50 bar.

[0038] The compression moulding of the sandwich according to the first embodiment or of the winding structure (layers of natural fibre + matrix film) according the second embodiment occurs in compression moulding machines or heated presses which are provided with two metal shells heated through cartridge heaters. The press must be uniformly heated, and must also cooled in a controlled way.

[0039] The compression moulding process can be provided with variations, in particular in the compression moulding machines temperatureramps and pressure ramps can be set, e.g. preferably the process provides a pre-heating at the desired temperature (e.g. 180°C) for some minutes, followed by the effective compacting step at one or two levels of pressure (10- 30 bar). Once the process is over, the semi-finished product can be brought back to room temperature through a cooling at a speed that can be about 10°C / min. The compression moulding machines used in the process must be controllable both in the increasing and in the lowering of temperature, because the compression moulding temperature affects the final properties of the material, in that it can damage the flax natural fibres, and can affect the degradability of the final material.

[0040] The degree of residual humidity in the pressed material during the forming technological process affects the biodegradability of the material: the higher the humidity content, the more easily and quickly the resulting composite material is biodegradable. The degree of humidity of the compression moulded composite material tends to balance with ambient humidity.

[0041] In order to obtain mechanical properties and durability of the composite material, the starting materials (matrix film and / or natural fibres) may undergo a drying pre-moulding process. In order to obtain the desired durability properties, the humidity in the pre-moulding materials must be lower than 250 ppm for the PLA matrix composite and lower than 700 ppm for the PBS matrix composite.

[0042] In particular, although in principle both matrix films and / or sheets of fabric or layers of natural fibres can be dried, experimentally it was found out that with respect to the degradability of the material at the end of its service life, the degree of humidity of the matrix is more important than the degree of residual humidity in the fabric or in the layers of natural fibre. This because a higher humidity in the matrix allows the water molecules to perform a partial hydrolysis of the polymer during the compression moulding process, so determining a more rapid degradation and affecting its final mechanicalproperties. In the first embodiment, both matrix films and sheets of fabric are placed in an oven, indicatively at 60-80°C for at least 8-10 hours. In the second embodiment, the winding structure is formed (made of windings of tape and matrix films wound around the winding plate), and the complete winding structure is placed in an oven, indicatively at 60-80°C, for at least 8- 10 hours. In an alternative embodiment, just the matrix films are dried at the same conditions.

[0043] Once the composite material according to the invention has completed its service life, it can be biodegraded / composted. Alternatively, said material can be ground and recycled by mixing it in a percentage of 5- 30% with virgin matrix in order to use it in standard technological processes of thermoplastic materials.

[0044] It is worth pointing out that also the compression moulding temperatures can affect the biodegradability of the material; in particular, too high compression moulding temperatures lead to more biodegradable composite materials, as the natural fibre is damaged. This nonetheless affects also the mechanical properties of the semi-finished product and of the final product.

[0045] The compostability time is under testing at the moment. Compostability tests in an industrial environment are under way; at the moment, it is believed that in the industrial compost the degradation time of the material according to the present invention can be estimated in three months at most.

[0046] The material according to the invention, if left in the environment, obviously has longer degradation times. Nonetheless, it is worth underlining that both materials - matrix and natural fibres - are such that none of them can cause damage to flora and fauna.

[0047] It was observed that the orientation of the natural fibres in the compression moulded composite material is relevant for the mechanical properties of the final product.

[0048] In the first embodiment, the method for obtaining the composite material according to the present invention comprises the following steps: a) providing a plurality of natural fibre sheets having warp and weft that are perpendicular to each other, each sheet having a thickness ranging 0.5-0.8 mm and dimensions corresponding to that of the compression moulding machine to be used; b) providing a plurality of matrix films; c) alternately arranging said sheets of natural fibre fabric and said matrix films inside said compression moulding machine, taking care of leaving matrix films as outermost layers of the resulting semi-finished product; d) preheating the compression moulding machine containing the natural fibre fabric sheets and the matrix films at 175-185°C for 1-10 minutes; e) compacting said layers at a temperature of 180-190°C for 5 minutes at two different levels of applied pressure, preferably 10 and 30 bar; f) cooling the semi-finished product inside said compression moulding machine maintaining the applied pressure and setting a cooling ramp of 10°C / min up to room temperature.

[0049] In an embodiment, the stacked sheets of fabric are all oriented in the same way, i.e. the warp is always vertical and the weft is always horizontal. In an alternative embodiment, the stacked sheets of fabric are differently oriented, e.g. the first sheet of fabric has a vertical warp and a horizontal waft, while the second fabric sheet has its warp and weft oriented obliquely with respect to those of the first sheet of fabric. E.g., the first sheet of fabric has a vertical warp and a horizontal waft, while the second fabric sheet is rotated of 45° with respect to the first fabric sheet; optionally, theinclination angle can be different from 45° and for the following fabric sheets different angles can be chosen.

[0050] In the second embodiment, the method for obtaining the composite material according to the present invention comprises the following steps: a) optionally placing a sheet of release material on both sides of a winding plate; b) stacking on said sheet of release material at least a first film of matrix on both sides of said winding plate; c) winding a first layer of natural fibre tape with unidirectional orientation so obtaining two first layers, one for each side of said winding plate; d) repeating steps b) and c) for the number of times needed to obtain the desired thickness, obtaining a winding structure that has a matrix film as its two outermost layers; e) optionally placing a sheet of release material in direct contact with the compression moulding machine provided for the compression moulding; f) preheating said compression moulding machine at 175- 185°C for 1-10 minutes; g) compacting the winding structure at a temperature of 180-190°C for 5 minutes for each level of applied pressure, preferably 10 and 30 bar, so obtaining a semi-finished product; h) cooling the semi-finished product inside said compression moulding machine maintaining the applied pressure and setting a cooling ramp of 10°C / min up to room temperature; i) cutting the semi-finished product along the edges of the winding plate, so obtaining two distinct semi-finished products.

[0051] It is worth pointing out that in the pressing process, all thewinding structure, including the inside winding plate, is placed in the compression moulding machine and heated.

[0052] In an embodiment, the winding plate, too, is provided with an own heating system that can be actuated while the winding structure is inside the compression moulding machine. This allows to heat the sandwich of matrix film and of natural fibre layers both from the outside (through the compression moulding machine) and from the inside (through the winding plate), and therefore to obtain winding structures with a thickness higher than that obtainable with the heating performed through the compression moulding machine only.

[0053] The winding plate is provided with two edges covered with non-impregnated tape. With cutting along the edges of the winding plate, the cutting of the portions of non-impregnates tape along the edges of the plate itself is meant (see figure 10).

[0054] In an embodiment, the orientation of the natural fibres of two consecutive layers (obviously with the interposition of at least one matrix film) is different. E.g., if the even layers of natural fibre are provided with a first angle of winding (e.g. -45° with respect to the longitudinal axis of the winding plate), the odd layers of natural fibre are provided with a second angle of winding (e.g. +45° with respect to the longitudinal axis of the winding plate), so that in the winding structure the fibres have a perpendicular orientation of the different layers.

[0055] In an embodiment, the natural fibre layers have even different orientations: horizontal, vertical, and +45° and -45° in equal number, so as to obtain a symmetric laminate. This disposition of the natural fibre has the advantage to have analogous mechanical properties in all the directions when the composite is stressed in different directions.

[0056] In a preferred embodiment, the matrix films are not in direct contact with the compression moulding machine and / or with the winding plate, but on the surface of the compression moulding machine in contact withthe sandwich and on the winding plate in contact with the matrix films there is provided a sheet of release material.

[0057] In an embodiment, at least two semi-finished products obtained through the above-described methods, each semi-finished product having a maximum thickness of 7-8 mm for the first embodiment and a maximum thickness for 5-6 mm for the second embodiment, are stacked and further hot- pressed. In the second embodiment, the two layers 5-6 mm thick can be provided with a different fibre orientation. In this step, a shape different from the planar shape can be given to the final composite product.

[0058] In an embodiment, before the compression moulding step, said sheets of fabric or said layers of natural fibre and / or said matrix films, preferably under the shape of winding structure for the second embodiment, are dried, bringing the two components to a humidity degree lower than 250 ppm for the PLA matrix composite and lower than 700 ppm for the PBS matrix composite. Indicatively, this requires a drying at 60-80°C for at least 8-10 hours for both kinds of matrix.

[0059] In the second embodiment, the peripheral portion of the pressed semi-finished product, after having been cut and removed from the winding plate, is cut along the edges in order to obtain two perfectly homogeneous semi-finished products provided with uniform mechanical properties. The scraps can be further processed or recycled.

[0060] It is worth pointing out that the matrix has a paramount importance in determining, on the one hand, the durability of the material and on the other hand its compostability. E.g. the use of amorphous PLA leads to a final composite material provided with a higher compostability and lower durability; vice versa, the use of semi-crystalline PLA leads to a final composite material provided with a lower compostability and a higher durability.

[0061] In an embodiment, the composite material so obtained is used for producing medical devices, in particular extrication boards, stretchers orwheelchairs. Such medical devices must be able to support a patient’s body, which indicatively can reach a weight of 137 kg.

[0062] The first advantage of the present invention is providing a composite material of natural origin, capable of replacing plastic materials of different nature obtained from non-renewable resources, still retaining comparable mechanical properties.

[0063] The second advantage of the present invention is providing a composite material that at the end of its service life is totally recyclable and totally biodegradable / compostable.

[0064] The third advantage of the present invention is that the composite material can be recycled by adding a reduced percentage (5-30%) of the composite material to virgin polylactic acid in order to obtain a starting material that can be hot-pressed through the standard technologies of thermoplastic materials.

[0065] A fourth advantage is the possibility to provide materials that have a different degree of biodegradability by acting on the degree of precompression moulding humidity of the components (matrix and / or natural fibres).

[0066] The fifth advantage of the second embodiment is that with just one process two distinct compression moulded semi-finished products are obtained.

[0067] A sixth advantage of the second embodiment is that the scraps of material obtained in the processing can be recycled in their turn.

[0068] Further advantages and properties of the present invention are disclosed in the following description, in which exemplary, non-limiting embodiments of the present invention are explained in detail based on the drawings: first embodiment figure 1 A shows an example of plain fabric, while figure IB shows an example of twill fabric; such kinds of fabrics are known in the art;figure 2 shows an example of two starting materials; in particular, figure 2A shows an example of twill and figure 2B an example of matrix film used for preparing the composite material according to the invention; figure 3 shows an example of the compression moulded material obtained according to the present invention; figure 4 shows two examples of cut (at 0° and at 45°) of the composite material, in order to characterize it from a mechanical point of view; in particular, figure 4A shows a cut made at 0°, while figure 4B shows a cut made at 45° with respect to the warp and weft of the fabric; figure 5 shows three series of samples obtained by cutting the compression moulded composite material at 0° (figure 5A) and at 45°C (figure 5B) respectively, with respect to the warp and weft of the fabric; second embodiment figure 6 shows the device used to produce the semi-finished products through filament winding according to the present invention, before starting the process for obtaining said semi-finished product; figure 7 shows the device used to produce the semi-finished products through filament winding according to the present invention, wherein on the winding plate a first layer of natural fibre was wound; figure 8 shows a detail of the device used to produce the semifinished products through filament winding, wherein a first matrix film was stacked on the first unidirectional layer of natural fibre; figure 9 shows a winding structure made of a plurality of natural fibre layers with interposed matrix films, inserted in a compression moulding machine for compression moulding; figure 10 shows a compression moulded semi-finished product, before the cut allowing to separate the two semi-finished products from the winding plate; figure 11 shows a compression moulded semi-finished product after cutting, which cutting separated it from the winding plate, but before thesemi-finished product was freed from scraps; figure 12 shows a schematic diagram of a winding structure inserted in a heated press.

[0069] Although tests were performed on flax fabrics and fibres, the other natural plant fibres are provided with similar features. Process conditions (temperature, pressure), are mainly dictated by the matrix.

[0070] It is worth pointing out that the length of the natural fibre affects the mechanical properties of the composite material. In particular, continuous fibres allow to obtain better mechanical properties in comparison to long fibres (from 1 to 5 cm) and short fibres (up to 1 mm).

[0071] For the first embodiment, figure 1 A shows an example of plain fabric, while figure IB shows an example of twill fabric. In both figures, the white stroke indicated by the vertical arrow represents the warp, while the black stroke indicated by the horizontal arrow represents the weft. As can be easily observed, in the plain fabric one warp thread is alternated with one weft thread, while in the twill fabric two warp threads are alternated with two weft threads, creating a more complex pattern. Such kinds of fabric are well known in the art.

[0072] Figure 2A shows an example of twill fabric, while figure 2B shows an example of a matrix film, starting components used to prepare the hot-pressed composite material according to the first embodiment. From figure 2B is easy to observe the extreme thinness of the matrix film, which is almost transparent.

[0073] Figure 3 shows an example of the compression moulded composite material obtained according to the present invention. Indicatively, the dimensions of the sample shown in figure 3 are 15x4 cm, for a thickness of about 7 mm. The stacked layers of the sample shown in figure 3 are 54, 44 films of polylactic acid and 10 sheets of flax fabric. In the sample, the warp and weft of the flax twill fabric are well visible, as much as the fact that the sample was cut about parallel to warp and weft.

[0074] Figures 4A, 4B show the way wherein the sample shown in figures 5A, 5B were cut out, respectively, in relation to the warp and weft of the flax fabric. In particular, figure 5A shows a sample cut out parallel to the warp and weft of the flax fabric (parallel sample), while figure 5B shows a sample cut out at 45° with respect to the warp and weft of the flax fabric (oblique sample).

[0075] Figure 5A shows three parallel samples, while figure 5B shows three oblique samples. On such samples, mechanical resistance tests were performed, measured according to ASTM D3039 standard.

[0076] EXAMPLE 1In this test, compression moulded composite material samples were used, obtained starting from a 250 g flax Twill fabric produced by Safilin (Bethune, France), while the PLA matrix film was provided by Peruzza s.r.l (Mareno di Piave, TV, Italy) under the form of a 30 cm large and 20 micron thick reel. From the semi-finished products obtained from the compression moulding, the samples were cut through laser. Samples with fibres oriented at 0° (parallel samples) and at 45° (oblique samples), having dimensions of 110 x 20 x 3 mm were prepared. Traction tests were performed according to ASTM D3039 standard, using a dynamometer (INSTRON 4467, USA) and a 30 kN load cell. The samples had previously been dried for at least 10 hours, at 60°C. Five samples were tested for each orientation, at room temperature conditions and with a cross-head speed of 2 mm / min. The modules were evaluated through an extensometer (INSTRON 2620 601, USA, 12.5 mm gauge length).Table 1 - Properties of the material; standard deviation in brackets

[0077] As expected, the parallel samples have better mechanical properties than oblique samples. This occurs both in terms of strength G and Young’s modulus E.

[0078] For the second embodiment, figure 6 shows a device 1 for filament winding. Such device and such technique are known in the art. 2 indicates a winding plate, provided with a (dotted) longitudinal axis 4, which is also the axis on which the plate itself rotates during the winding of a natural fibre tape. The winding of the natural fibre tape occurs through the presence of at least a mandrel 3. The winding plate 2 is provided with four lateral edges; the cutting of tape windings occurs along the edges indicated with 13.

[0079] Figure 7 shows the device 1 used to produce the semi-finished products according to the present invention, wherein a first layer 7 of natural fibre tape 5 is wound with a winding angle of about 90° with respect to the rotation axis 4 (shown in figure 1) of the winding plate 2. Said tape 5 is withdrawn from a reel 6; the tape is suitably tensioned through passages around rollers, using solutions well known to the skilled person. Said winding 7 of the tape 5 on the winding plate 2 builds two first layers of natural fibre, one for each side of the winding plate 2. In this embodiment, a tape having a width of about 4 mm was used.

[0080] Figure 8 shows a winding plate 2 around which a winding 7 of natural fibre was wound, so obtaining two layers, one for each side of the winding plate 2. Between the winding plate 2 and the first matrix film there was interposed a sheet 9 of release material. In this embodiment, a tape 5having a width of about 5 mm was employed. As it is apparent from the figure, this allows to obtain an aligned and uniform winding layer. A matrix film 8 was stacked on said winding 7. In this case, too, the orientation of the fibres is about 90° with respect to the longitudinal axis of the winding plate 2. This figure shows a winding structure ready to be inserted into a compression moulding machine.

[0081] Figure 9 shows a winding structure, comprising several layers 7 of wound tape, and several matrix films 8, inserted in a heated press 10. There are provided two sheets 9 of release material interposed between the two plates of the compression moulding machine 10 and the winding structure.

[0082] Figure 10 shows the semi-finished product 11 still wound around the winding plate 2, after the compression and moulding in the compression moulding machine 10.

[0083] Figure 11 shows the composite material of figure 10 after cutting, that freed it from the winding plate. This figure shows only one semifinished product of the two semi-finished products obtained by cutting the semi-finished product shown in figure 10 along the lateral edges 13. By observing the figure, the outer non-impregnated area of the matrix film 8 with respect to the winding 7 of natural fibre is well visible. In addition to the need of cutting along the edges of the winding plate 2 in order to free the semifinished product from the winding plate 2 itself, this image also clarifies the need to trim the semi-finished product, so as to obtain a semi-finished product free from scraps 12 (i.e. a semi-finished product not provided on its sides with windings of natural fibre that were not impregnated by the matrix film).

[0084] Figure 12 shows a schematic representation of a winding structure or sandwich according to the second embodiment, comprising said winding plate 2, on the two sides of which there are optionally provided two sheets of release material 9. In contact with said release material there is a first matrix film 8, followed by a first natural fibre winding 7. In this figure thereare shown three layers of winding 7 of natural fibre and four layers of matrix film 8, but as said the number can vary up to about 15 layers of natural fibre winding for each side of the winding plate. Moreover, in this figure just one matrix film 8 is shown interposed between two windings 7, but the number of matrix films interposed between two layers of winding can be higher (e.g. 2, 3, 4, etc.). With just one compression moulding there are obtained two semifinished products, each comprising up to 15 layers of natural fibre winding, i.e. 30 layers for a winding structure, with a variable number of matrix films interposed between windings, as above explained. Another optional sheet of release material 9 is interposed between the last matrix film 8 and the press 10. As explained above, each of the winding layers 7 of natural fibre can have a different orientation; e.g. the first layer could have a fibre orientation of 0°, the second layer could have a fibre orientation of 90° with respect to the first layer, the third layer could have a fibre orientation of 45° with respect to the first layer, etc.

[0085] In an alternative embodiment, there is provided that in a single winding structure like the one shown in figure 12, at least one of the tape windings 7 can be replaced with a sheet of natural fibre fabric, e.g. plain fabric or twill fabric, provided with a warp and a weft. Such fabrics are well known in the art.

[0086] The method according to the second embodiment comprises the following steps: a) optionally placing a sheet of release material 9 on both sides of a winding plate 2 of a device 1 (visible in figure 6) for performing filament winding; b) stacking on said sheet of release material at least a first film 8 of matrix on both sides of said winding plate 2; c) winding a first layer of natural fibre tape 5 (visible in figure 7) with unidirectional orientation obtaining two first layers 7, one for each side of said winding plate 2;d) repeating steps b) and c) for the number of times needed to obtain the desired thickness, obtaining a winding structure that has a matrix film 8 as its two outermost layers; e) optionally placing a sheet of release material 9 in direct contact with the compression moulding machine 10 (visible in figure 9) provided for the compression moulding; f) preheating said compression moulding machine at 175- 185°C for 1-10 minutes; g) compacting the winding structure at a temperature of 180-190°C for 5 minutes for each level of applied pressure, preferably 10 and 30 bar, so obtaining a semi-finished product; h) cooling the semi-finished product inside said compression moulding machine maintaining the applied pressure and setting a cooling ramp of 10°C / min up to room temperature; i) cutting the semi-finished product along the edges 13 of the winding plate, so obtaining two distinct semi-finished products.

[0087] EXAMPLE 2In this test, a 1000 tex Lincore tape produced by Depestele (Le Bocasse, France), and a Luminy LX175 PLA matrix film produced by Corbion Total (Gorinchem, The Netherlands) having a thickness of 0.2 mm were used. The semi-finished products (like the one shown in figure 11) were cut through a band saw (Sabre-250, Record Power Ltd, Chesterfield, UK), from the semi-finished product obtained through compression moulding. Samples with fibres oriented at 0° and at 90°, having dimensions of 120 x 15 x 4 mm were prepared. Traction tests were performed according to ASTM D3039 standard, using a dynamometer (INSTRON 4467, USA) and a 30 kN load cell. The samples had previously been dried for at least 10 hours, at 60°C. Five samples were tested for each orientation, at room temperature conditions and with across-head speed of 2 mm / min. The modules were evaluated through an extensometer (INSTRON 2620 601, USA, 12.5 mm gauge length).Table 2 - Properties of the material; standard deviation in brackets

[0088] EXAMPLE SIn this test, a 1000 tex Lincore tape produced by Depestele (Le Bocasse, France), and an INGEO 325 ID PLA matrix film produced by Natureworks (Minnetonka, Minnesota, USA) having a thickness of 0.2 mm were used. The semi-finished products (like the one shown in figure 11) were cut through a band saw (Sabre-250, Record Power Ltd, Chesterfield, UK), from the semi-finished product obtained through compression moulding. Samples with fibres oriented at 0° and at 90°, having dimensions of 120 x 15 x 4 mm were prepared. Traction tests were performed according to ASTM D3039 standard, using a dynamometer (INSTRON 4467, USA) and a 30 kN load cell. The samples had previously been dried for at least 10 hours, at 60°C. Five samples were tested for each orientation, at room temperature conditions and with a cross-head speed of 2 mm / min. The modules were evaluated through an extensometer (INSTRON 2620 601, USA, 12.5 mm gauge length).Table 3 - Properties of the material; standard deviation in brackets

[0089] As expected, the samples characterized in the direction longitudinal to the fibres are provided with mechanical properties that are better in comparison to the mechanical properties transversally characterized. This occurs both in terms of strength G and Young’s modulus E.

[0090] It is worth pointing out that the length of the natural fibre affects the mechanical properties of the composite material. In particular, continuous fibres allow to obtain better mechanical properties in comparison to long fibres (from 1 to 5 cm) and short fibres (up to 1 mm).

[0091] For both embodiments, the mechanical properties of the composite material are very good. In particular, its rigidity is only slightly lower than that of a glass fibre composite. Anyway, the material shows a performance suitable for producing products provided with structural or semi- structural functions, like e.g. extricating boards. Moreover, the material can be a valid replacement for ABS components, in that its mechanical properties are markedly better both in terms of rigidity and of resistance.

[0092] As known in the art, and as can be observed from Tables 1-3 in the present application, the mechanical properties of the composite material obtained are much better when measured parallel to the direction of the natural plant fibres. As a consequence, according to the object to be produced, and in particular according to the mechanical loads that the object undergoes when in use, natural plant fibres can be oriented just in one direction: when the object undergoes mechanical loads according to just one direction, fibres can be oriented just in that direction. On the other hand, when the final object mustundergo mechanical loads according to more directions, a plurality of windings of natural plant fibre will be used, each winding being unidirectional, but stacked with different orientations. When an object is provided with more unidirectional windings of fibres, each winding being perpendicular to the other, using fabric sheets or unidirectional windings perpendicular to each other will produce very similar results.

[0093] It is worth specifying that the first embodiment is less onerous, easier to produce; nonetheless, as can be observed through the comparison of Table 1 on one side and Tables 2 and 3 on the other, the second embodiment allows to provide products having more performing and more customizable mechanical properties. As a consequence, the choice between the first and the second embodiment depends on the mechanical properties required in use.1. Device for filament winding2. Winding plate3. Mandrel4. Longitudinal axis of the winding plate 5. Tape6. Tape reel7. Tape winding8. Matrix film9. Release material sheet 10. Compression moulding machine11. Moulded composite12. Scraps13. Edges of the winding plate

Claims

CLAIMS1. Totally compostable and recyclable composite material of natural origin comprising stacked alternate layers of-films of a matrix made of a polymer of natural origin,-sheets of a natural plant fibre fabric, wherein the two outermost layers are made of matrix, characterized in that said natural fibre fabric is provided with a warp and a weft that are perpendicular to each other.

2. Totally compostable and recyclable composite material of natural origin comprising stacked alternate layers of-films of a matrix made of a polymer of natural origin,-layers of a natural plant fibre wherein the fibres of a single layer are unidirectional, wherein the two outermost layers are of matrix film, characterized in that said natural fibre layers were obtained through filament winding.

3. Composite material according to claim 1 or 2, wherein the natural plant fibre fabric or the layers of natural plant fibre is / are obtained from flax, hemp, jute, while the matrix is polylactic acid (PLA) or polybutylene succinate (PBS).

4. Composite material according to one or more of the preceding claims, wherein two or more matrix films are interposed between two consecutive sheets of natural plant fibre fabric or two consecutive layers of natural fibre fabric.

5. Composite material according to one or more of the preceding claims, wherein the degree of humidity of the matrix film and of the natural fibre fabric before film stacking is lower than 250 ppm for PLA composite material and lower than 700 ppm for PBS composite material.

6. Composite material according to claim 1, wherein the sheets ofnatural fibre fabric have a thickness of 0.5-0.8 mm, while the matrix films have a thickness of 0.1 mm.

7. Composite material according to claim 1, comprising an overall number of layers of natural fibre fabric and matrix film comprised between 10 and 60.

8. Composite material according to claim 2, wherein the matrix films have a thickness of 0.1-0.2 mm, while the percentage in volume of the fibres is about 30-35% with respect to the overall fibres+matrix volume.

9. Composite material according to claim 2, comprising an overall number of natural fibre layers ranging 5-15 for each semi-finished product, with a suitable number of matrix films interposed between the various layers of natural fibre.

10. Medical devices comprising the composite material according to claims 1 to 9, preferably extrication boards, stretchers, wheelchairs.

11. Method for the preparation of the composite material according to claims 1 and 3 to 7, said method comprising the following steps: a) providing a plurality of natural fibre sheets having warp and weft that are perpendicular to each other, each layer having dimensions corresponding to that of the compression moulding machine to be used; b) providing a plurality of matrix films; c) alternately arranging said sheets of natural fibre fabric and said matrix films inside said compression moulding machine, taking care of leaving matrix films as outermost layers of the resulting semi-finished product; d) preheating the compression moulding machine containing the natural fibre fabric sheets and the matrix films at 175-185°C for 1-10 minutes; e) compacting said layers at a temperature of 180-190°C for 5 minutes at two different levels of applied pressure, preferably 10 and 30 bar, so obtaining a semi-finished product; f) cooling the semi-finished product inside said compressionmoulding machine maintaining the applied pressure and setting a cooling ramp of 10°C / min up to room temperature.

12. Method for the preparation of the composite material according to claim 11, further comprising the step, before step a), of drying said matrix films natural and / or fibre fabric sheets before stacking, bringing them to a humidity content lower than 250 ppm for PLA composite material and lower than 700 ppm for PBS composite material.

13. Method for the preparation of the composite material according to claim 11 or 12, wherein between the sandwich made of fabric and matrix and the compression moulding machine two sheets of release material are interposed, preferably polytetrafluoroethylene.

14. Method for the preparation of the composite material according to one or more of claims 11-13, further comprising, after step f), the step of stacking at least two semi-finished products having a maximum thickness of 7-8 mm and performing a step of hot compression moulding.

15. Method for the preparation of the composite material according to one or more of claims 11-14, wherein in the stacking of different layers, the orientation of warp and weft of the different sheets of stacked natural fibre fabric is arranged always in the same way or differently.

16. Method for the preparation of the composite material according to claims 2 to 5 and 8-9, said method comprising the following steps: a) optionally placing a sheet of release material on both sides of a winding plate (2) of a device (1) suitable for performing filament winding; b) stacking on said sheet (9) of release material at least a first film of matrix (8) on both sides of said winding plate (2); c) winding a first layer of natural fibre tape (5) with unidirectional orientation obtaining two first layers (7), one for each side of said winding plate; d) repeating steps b) and c) for the number of times needed toobtain the desired thickness, obtaining a winding structure that has a matrix film (8) as its two outermost layers; e) optionally placing a sheet of release material (9) in direct contact with the compression moulding machine (10) provided for the compression moulding; f) preheating said compression moulding machine at 175-185°C for 1-10 minutes; g) compacting the winding structure at a temperature of 180- 190°C for 5 minutes for each level of applied pressure, preferably 10 and 30 bar, so obtaining a semi-finished product; h) cooling the semi-finished product inside said compression moulding machine maintaining the applied pressure and setting a cooling ramp of 10°C / min up to room temperature; i) cutting the semi-finished product along the edges (13) of the winding plate, so obtaining two distinct semi-finished products.

17. Method for the preparation of the composite material according to claim 16, further comprising the step of drying said natural fibre fabric sheets and said matrix films, preferably already stacked in the winding structure but before inserting them into the compression moulding machine, bringing them to a humidity content lower than 250 ppm for PLA composite material and lower than 700 ppm for PBS composite material.

18. Method for the preparation of the composite material according to one or more of claims 16-17, further comprising, after step f), the step of stacking at least two semi-finished products having a maximum thickness of 7-8 mm and performing a step of hot thermoforming.

19. Method for the preparation of the composite material according to one or more of claims 16-18, wherein consecutive layers of natural fibre have a different orientation of the fibres, obtained by winding the natural fibre tape with desired different angles on the winding plate.

20. Method for recycling the composite material according toclaims 1-9, wherein said composite material, once it reached its end-of-life, is ground and added in a percentage ranging 5-30% to virgin matrix in order to use it in procedures of injection moulding.

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