DESCRIPTION

Field of Application

The present invention relates to the technical field of production of panels for the field of construction, means of transport and furniture industry, specifically composite panels.

The invention relates firstly to a plant-based composite panel, more particularly comprising parts of plants of the Posidonia genus and a polymeric material, as well as a process for its production.

Prior art

The need to develop technologies and products as much sustainable as possible is still typical, in all the fields of construction, means of transport and furniture industry, especially in the field of the production of composite panels which are suitable as architectural elements of buildings and/or suitable for constructing structures outside of buildings.

Aluminum skins on composite panels for covering buildings and industrial edifices or for making coverings, for example exterior cladding, building fagades or roofs are well known.

In case of multi-layered composite panels, said panels generally comprise a core of a moderate thickness consisting of plastic material, for example polyethylene, covered with a metal sheet, usually an aluminum sheet, which in turn can be covered by a superficial protective film and / or a paint layer.

Composite panels of the above-mentioned type generally have a moderate compression and tensile strength, a good impermeability and a moderate weather resistance, therefore a moderate resistance to temperature and thermal shocks, a good resistance to ultraviolet radiation and a good chemical resistance.

Depending on the applications, said types of panels could also be capable to insulate, from both the thermal and the acoustic point of view. The panels at issue may also be made from recycled materials, for example recycled plastic or mixtures of virgin and recycled plastic.

In any case - with the exception of panels made of wooden material, such as for example chipboard-based composite panels, which are difficult to use for some types of applications where special mechanical performances are required - the use of composite panels that are based on renewable raw materials and have a low environmental impact, for construction, means of transport and furniture industry is still not very widespread.

Moreover, a fundamental requirement for panels which can be used, in general, in construction and furniture field, is to have an at least moderate fire resistance.

In this sense, it is to say that most of the composite panels made with polymeric resins show a low fire resistance; for this reason, in the known composite panels made with polymeric resins, the latter are mixed with large amounts of flame-retardants.

The patent application WO 2010/000983 relates to an insulating material with flame-resistant characteristics comprising leaves of plants of the Posidonia genus, a binder of the type a glue or a polymeric material, as well as sodium bisulphite.

The material at issue may be used as thermal- or acoustic-proofing for use in the field of industry of construction, means of transport or infrastructure of various type, for example for pipe insulation.

Therefore, the material described in the patent application WO 2010/000983 comprises sodium bisulphite as an agent suitable to hinder the proliferation of microorganisms and molds; however, sodium bisulphite presents toxicity issues on one hand and is potentially corrosive on the other hand.

Indeed, as regards the first aspect, sodium bisulphite may cause release of sulphur dioxide; this substance which irritates lungs and is often associated to allergies; accordingly, such material is not suitable for constructing panels to be used especially in indoor environments.

Moreover, it is noted that the potential corrosive activity of the substance at issue could result in undesired drawbacks, since sodium bisulphite is particularly corrosive to aluminium, a metal which is commonly used in the construction field.

In addition, it can’t be ignored that the material at issue is not suitable to applications which require high performances from the point of view of the mechanical properties, especially in the construction field.

Ultimately, in light of the above-mentioned prior art, the problem underlying the present invention is to provide a composite panel for the transport, construction and/or furniture fields, which is made with waste materials and/or low environmental impact materials, shows both an excellent fire resistance and high insulation properties, at the same time deprived of the drawbacks mentioned above with reference to plant-based panels of the prior art, in particular which is suitable to both the use for applications which require high performances from the point of view of the mechanical properties, especially in the construction field, and indoor applications and, therefore, which is unexceptionable from the point of view of the potential release of substances which are harmful to human beings or to animals in general.

Summary of the invention

Said problem has been solved by providing a process for producing a plant- based composite panel comprising parts of plants of the Posidonia genus, wherein said process comprises the following steps: a) pre-treating said parts of plants of the Posidonia genus, so as to obtain parts of plants of the Posidonia genus which are dried and deprived of dregs; b) mixing said pre-treated parts of plants of the Posidonia genus with a liquid polymeric resin according to a weight ratio of said parts of plants to said liquid polymeric resin between 0.5-5, so as to obtain a mixture comprising parts of plants of the Posidonia genus impregnated with said polymeric resin; c) forming said mixture, thereby inducing curing and solidification of said polymeric resin, obtaining a plant-based composite panel comprising parts of plants of the Posidonia genus, wherein said step a) of pre-treating parts of plants of the Posidonia genus comprises in turn a drying step of said parts of plants of the Posidonia genus at a temperature between 70°C and 100°C.

Preferably, during said step a) of pre-treating said parts of plants of the Posidonia genus said drying step is carried out at a temperature comprised between 70°C and 90°C, more preferably for a time of at least 6 hours, even more preferably for a time between 6 hours and 9 hours.

Preferably, in said mixing step b) said mixture comprising parts of plants of the Posidonia genus impregnated with polymeric resin is completely free of antimicrobial agent, in particular it is free of sodium bisulphite.

Advantageously, the process according to the present invention allows to obtain a plant-based composite panel from a plant-based organic waste material, i.e. parts of plants of the Posidonia genus, which are normally considered as a waste.

In particular, leaves and parts of plants of the Posidonia genus naturally accumulate on stretch of coast and beaches in the Mediterranean basin and on the coasts in the south-east region of the Australian continent; said leaves and parts of plants have to be steadily removed, in contrary case they would accumulate and decompose, resulting in economic damage for the economic entities in tourism field.

Accordingly, besides allowing to obtain a sustainable composite panel, the process according to the present invention allows to develop a high value- added use for a material whose disposal, on the contrary, is generally considered a cost for the community.

Even more advantageously, as it will be better appreciated below, the process according to the present invention allows to obtain a panel with high flame-resistant properties and, at the same time, with enhanced performances from the point of view of the mechanical properties.

Moreover, the process according to the present invention allows to obtain a panel with high performances from the point of view of both thermal and acoustic insulation.

Thanks to the aforementioned drying step, large part of the residual humidity on the outer surface and inside said parts of plants of the Posidonia genus is eliminated, so as to ensure an adequate adhesion of the polymeric resin to said parts of plants and prevent the proliferation of microorganisms and/or molds inside the composite panel which is obtainable by the process according to the present invention in its lifetime.

Indeed, thanks to said drying step, the process according to the present invention allows to obtain a plant-based composite panel comprising parts of plants of the Posidonia genus with a reduced microbial load without the need to add into the mixture obtained in step b) any anti-microbial agent, such as for example sodium bisulphite.

Specifically, thanks to said step a) of pre-treatment of parts of plants of the Posidonia genus and with particular reference to said drying step, the process according to the present invention allows to obtain a plant-based composite panel comprising parts of plants of the Posidonia genus with useful lifetime equal to at least 10 years, preferably equal to at least 15 years.

During said useful lifetime, all the physical and mechanical properties of the panel are maintained, without problems caused by the development and the proliferation of microorganisms.

Advantageously, said step of drying allows, as already mentioned, to decrease the overall content of humidity of the parts of plants of the Posidonia genus, but also allows to make uniform the humidity content among leaves of different age of plants of the Posidonia genus included in the vegetable material, which was previously provided.

In other words, the above-mentioned step of drying allows to reduce the amount of water of the fibres and allows to make uniform the humidity contents of the leaves of plants of the Posidonia genus regardless of their age, thereby ensuring also uniformity of the mechanical behavior of the panel obtained by the present process, both from the point of view of the reproducibility of the mechanical properties among panels which have been obtained from the same batch of leaves of plants of the Posidonia genus, and for what concerns the mechanical characteristics among different portions within the same panel. Indeed, it was proved that the amount of water contained inside leaves of plants of the Posidonia genus varies according to the age of the plant: a young plant contains a higher percentage of water on its total weight compared to a more mature plant.

According to a preferred embodiment of the process according to the present invention, during said step b) said parts of plants of the Posidonia genus may be mixed with said liquid polymeric resin according to a weight ratio of parts of plants to liquid polymeric resin between 0.5 and 3, more preferably between 0.5 and 1.8.

Advantageously, as it will be described in more detail, when the above- mentioned step b) is carried out by mixing said polymeric resin according to a weight ratio of parts of plants to liquid polymeric resin between 0.5 and 3, the process according to the present invention allows to obtain a plant- based composite panel comprising parts of plants of the Posidonia genus with particularly high performances from the point of view of the mechanical properties, which are higher if compared to similar panels obtained by mixing parts of plants of the Posidonia genus with a liquid polymeric resin according to a higher weight ratio of parts of plants to liquid polymeric resin.

In particular, as it will be described in more detail with reference to the detailed description, a plant-based composite panel obtained according to the preferred embodiment, described in the previous paragraph of the process according to the present invention, has a Young's modulus value higher or equal to 400 Mpa, as obtained in conformity with D-790 ASTM test method.

Consistent with the above, said plant-based composite panel has an ultimate tensile strength value which is higher or equal to 25 N, as obtained in conformity with D-790 ASTM test method.

In an equally advantageous manner, when the above-mentioned step b) is carried out by mixing said polymeric resin according to a weight ratio of parts of plants to liquid polymeric resin between 0.5 and 1.8, the process according to the present invention allows to obtain a plant-based composite panel comprising parts of plants of the Posidonia genus with extraordinarily high performances from the point of view of the mechanical properties. In particular, as it will be described in more detail with reference to the detailed description, a plant-based composite panel obtained according to the preferred embodiment, described in the previous paragraph of the process according to the present invention, has a Young's modulus value higher or equal to 500 Mpa, preferably higher or equal to 600 Mpa, more preferably higher or equal to 800 Mpa, as obtained in conformity with D- 790 ASTM test method.

Consistent with what has been reported above, said plant-based composite panel has an ultimate tensile strength value which is higher or equal to 30 N, preferably higher or equal to 35 N, more preferably higher or equal to 45 N, as obtained in conformity with D-790 ASTM test method.

Moreover, when the above-mentioned step b) is carried out by mixing said polymeric resin according to a weight ratio of parts of plants to liquid polymeric resin between 0.5 and 1.8, said step c) of forming the above- mentioned mixture may be carried out in a particularly effective manner, regardless of the average length of said parts of plants of the Posidonia genus.

According to a preferred embodiment, said step a) of pre-treating said parts of plants of the Posidonia genus comprises the following steps:

- providing parts of plants of the Posidonia genus, by recovering parts of plants of the Posidonia genus which are stranded on beaches;

- rinsing with water said parts of plants of the Posidonia genus;

- drying said rinsed parts of plants of the Posidonia genus at a temperature between 70- 100°C, preferably between 70-90°C;

- sifting said dried parts of plants of the Posidonia genus, so as to obtain parts of plants of the Posidonia genus which are dried and deprived of dregs.

In particular, during said step a) of pre-treating said parts of plants of the Posidonia genus, the above-mentioned step of rinsing with water is carried out so as to remove sediments, waste and sea salts absorbed inside the leaves of said plants of the Posidonia genus.

In a totally preferred manner, the above-mentioned rinsing with water may be carried out at the collecting place, using sea water to remove fine anthropic residues and sand. More preferably, said rinsing with sea water may be carried out by means of a sieve.

Advantageously, removing from said parts of the Posidonia genus sand and/or, more in general fine mineral residues, such as shells or calcareous residues of animal origin, for example, at the collecting place, allows to minimize the impact of the process according to the present invention onto the coastal and marine ecosystem.

After said rinsing with sea water, the parts of leaves of Posidonia may be subjected to rinsing with freshwater, more preferably by immersion, so as to remove any salt residue on the outer surface of said parts of plants or also inside the Posidonia leaves (possibly along with or besides fine anthropic residues and sand).

Advantageously, said rinsing with freshwater allows to obtain an essentially raw material free of salts, in particular chloride-free, thereby avoiding problems of metal (aluminum or steel) corrosion in the finished product (for example a composite panel comprising parts of plants of the Posidonia genus and a metal sheet) or at the installation site of the finished product.

Preferably, during said step a) of pre-treating said parts of plants of the Posidonia genus, the above-mentioned step of drying said rinsed parts of plants of the Posidonia genus may be carried out by contacting them with a warm air flow.

During said step a) of pre-treating said parts of plants of the Posidonia genus, the above-mentioned sifting step is carried out in order to separate, from said parts of plants of the Posidonia genus previously dried, possible solid rough residues entrapped in said parts of plants, such as for example pieces of wood, metal, glass or plastic material (for example, cans or bottles).

According to a particular embodiment of the process according to the present invention, said sifting step may be carried out in order to subdivide the leaves of plants of the Posidonia genus depending on their length, preferably said sifting step may be carried out to select leaves of plants of the Posidonia genus with an average length higher or equal to 5 cm. According to a further embodiment of the process according to the present invention, during said step a) of pre-treating said parts of plants of the Posidonia genus, the above-mentioned sifting step may be followed by a step of grinding said parts of plants of the Posidonia genus; preferably, during said grinding step, said parts of plants of the Posidonia genus are reduced into small pieces until reaching an average length shorter or equal to 10 cm, more preferably an average length shorter or equal to 5 cm.

In a totally preferred manner, according to the process of the present invention, said parts of plants may be leaves of plants of the Posidonia genus.

In an equally preferred manner, in accordance with the process according to the present invention, said parts of plants come from members of the Posidonia Oceanica species.

Preferably, said step b) of mixing said parts of plants of the Posidonia genus with a liquid polymeric resin is carried out by mechanically mixing said parts of plants of the Posidonia genus with said polymeric resin, for example by mixing in a screw mixer.

According to a preferred embodiment of the process according to the present invention, said step b) of mixing said parts of plants of the Posidonia genus with a liquid polymeric resin is carried out by spraying said polymeric resin onto said parts of plants of the Posidonia genus.

Specifically, in particular when said mixing step b) is carried out by spraying, the liquid polymeric resin is completely absorbed by the parts of plants of the Posidonia genus, in particular by the leaves, obtaining a mixture substantially comprising leaves of plants of the Posidonia genus impregnated with said liquid polymeric resin.

Advantageously, due to said mixing step b) carried out by spraying, the process according to the present invention allows to mix said liquid polymeric resin with said parts of plants of the Posidonia genus in a particularly efficient manner, ensuring a complete impregnation of the parts of plants of the Posidonia genus and without wasting said polymeric resin.

As it will be appreciated below with reference to the detailed description, when said mixing step b) is carried out by spraying, the process according to the present invention allows to obtain a composite panel with improved mechanical properties.

In said step b) of mixing said parts of plants of the Posidonia genus, said liquid polymeric resin may be a synthetic resin, preferably said resin is any resin selected from the group consisting of epoxy resin, phenolic resin and polyurethane resin.

In a totally preferred manner, in said step b) of mixing said parts of plants of the Posidonia genus with a liquid polymeric resin, said liquid polymeric resin is epoxy resin.

In an equally preferred manner, said step c) of forming said vegetable mixture in a plant-based composite panel comprising parts of plants of the Posidonia genus is carried out by heating, more preferably at a temperature between 45°C and 85°C.

Moreover, said step c) of forming said vegetable mixture in a plant-based composite panel comprising parts of plants of the Posidonia genus is carried out by applying an adequate pressure so as to obtain a composite panel having the desired density characteristics.

The epoxy resin may be a mono-component epoxy resin, i.e. a resin comprising a mixture, which in turn comprises monomers carrying at least one epoxy group, and a compound able to promote the cross-linking reaction, as a hardener (the monomer and the hardener may react when heat is provided).

As an alternative, said epoxy resin may be a bi-component or multi- component epoxy resin, i.e. a resin comprising a first mixture, i.e. the base resin or first component (component A), which in turn comprises monomers and/or oligomers carrying at least one epoxy group, and a second mixture or second component (component B), which in turn comprises a hardener carrying a group able to react with said at least one epoxy group. Preferably, said hardener is a compound with at least one amine functionality.

Preferably, said epoxy resin is a bi-component epoxy resin.

According to a preferred embodiment, said epoxy resin may be an eco- friendly epoxy resin having a bio-based carbon content equal to at least 25%, as obtained in conformity with the test method of the American Society for Testing and Materials, test D6866- 18 ASTM, called “Standard test methods for determining bio-based content of solid, liquid, and gaseous samples using radiocarbon analysis”.

Moreover, said eco-friendly epoxy resin has a volatile organic compound (VOC) content lower than 20 g/L, more preferably lower than 15 g/L, as obtained in conformity with the test method of the American Society for Testing and Materials, test D2369- 10 ASTM, called“Standard test method for volatile content of coatings”.

In accordance with the present invention, with the expression“eco-friendly epoxy resin” is meant an epoxy resin comprising active compounds and / or diluents of natural origin or deriving from renewable raw materials.

In particular, said active compounds and / or diluents of natural origin may derive from wastes resulting from the production of material obtained from renewable raw materials, for example wastes deriving from the production of wood pulp or bio-fuels (for example vegetable oils) .

In particular, said eco-friendly epoxy resin is free of styrene, furfuryl alcohol, phenols and aromatic amines, which are substances well-known to be aggressive and harmful to health.

As it is known, in an epoxy resin, in order to facilitate complete cross-linking between the various monomers and/or oligomers of the base resin (component A) with the second mixture comprising the hardener (component B), (but also in the case of mono-component epoxy resins), during said step c) there is the need to heat said plant-based mixture thereby obtained in said step b), to allow curing and solidification of the polymeric resin. As previously seen, said possibility is envisaged by the process according to the present invention.

Preferably, said step c) of forming a plant-based composite panel comprising parts of plants of the Posidonia genus may be carried out by moulding.

More preferably, said step c) of forming a plant-based composite panel may be carried out by means of a heated mould and/or a heated matching mould.

Alternatively, in an equally preferred manner, said step c) of forming a plant-based composite panel comprising parts of plants of the Posidonia genus may be carried out by lamination.

More preferably, said step c) of forming a plant-based composite panel may be carried out by means of rollers placed inside an oven or by means of heated rollers.

The above-mentioned technical problem was also solved by providing a plant-based composite panel comprising parts of plants of the Posidonia genus and a polymeric material, wherein said composite panel has a density between 0.2-0.6 g/cm ³ and is obtainable by the process according to the present invention.

As it can be understood, said polymeric material is a plastic material formed upon curing and solidification of a liquid polymeric resin previously mixed with parts of plants of the Posidonia genus, in particular during the above- mentioned step b) of the process according to the present invention.

Preferably, said plant-based composite panel comprising parts of the Posidonia genus has a density between 0.3-0.6 g/cm ³ , more preferably between 0.3-0.5 g/cm ³ , even more preferably between 0.35-0.5 g/cm ³ .

Advantageously, when it has a density between 0.3-0.5 g/cm ³ , preferably between 0.35-0.5 g/cm ³ , the composite panel according to the present invention has particularly high performances from the point of view of the mechanical properties, higher compared to similar panels with lower densities.

In any case, the above-mentioned panel according to the present invention has in general marked flame-resistant properties and, at the same time, high performances from the point of view of the mechanical properties.

Moreover, the panel according to the present invention has high performances from the point of view of both thermal and acoustic insulation.

More preferably, the present plant-based composite panel is completely free of antimicrobial agent, in particular it is free of sodium bisulphite.

In equally preferred manner, the present plant-based composite panel has a thermal conductivity comprised between 0.0180 W^m ¹ ·^ ¹ and 0.0450 W^nr ¹ ·^ ¹ , preferably between 0.0220 W^m ¹ ·^ ¹ and 0.0350 W^m ¹ ·^ ¹ .

Moreover, the plant-based composite panel according to the present invention is capable of withstanding temperatures which may occur following some specific applications, for example when the panel according to the present invention is used for covering buildings, where the outside temperature of the fagades may exceed 70°C.

In an equally preferred manner, the plant-based composite panel according to the present invention has a thickness larger or equal to 1 mm, preferably a thickness comprised between 50 mm and 500 mm.

According to a preferred embodiment, said plant-based composite panel further comprises at least a metal sheet, more preferably an aluminum metal sheet or a zinc-coated steel sheet.

In particular, according to the latter embodiment, the plant-based composite panel according to the present invention comprises a first layer comprising parts of plants of the Posidonia genus and a polymeric material and at least a second layer consisting of a second metal sheet.

The composite panel according to the present invention is made so that said first layer has a top surface and a bottom surface. Specifically, said second layer is applied to said top surface or to said bottom surface preferably said second layer is stuck to said top surface or to said bottom surface.

In a totally preferred manner, the plant-based composite panel according to the present invention comprises two metal sheets between which a layer comprising said parts of plants of Posidonia genus and said polymeric material is interlaid.

In other words, the plant-based composite panel according to the present invention comprises a first layer comprising said parts of plants of the Posidonia genus and said polymeric material, a second layer consisting of a metal sheet and a third layer also consisting of a metal sheet, for example a metal sheet identical to the one which constitutes said second layer. According to the latter embodiment, said second layer is applied to said top surface or to said bottom surface; vice versa, said third layer is applied to said bottom surface or to said top surface of said first layer, thereby obtaining a sandwich-structured panel, which has a core, thick and consisting of a plant-based low-density material, and two outer metal sheets or skins, between which said core is enclosed.

Consistently, the above-mentioned technical problem is also solved by using the plant-based composite panel according to the present invention in the field of construction, of means of transport or of furniture industry; preferably, said plant-based composite panel may be used in the field of construction as a construction element of architectural elements of buildings.

Preferably, according to some specific uses, the composite panel according to the present invention may be used as architectural covering, as outer covering panel in ventilated facades, as curtain walls for indoor space separation, as support of photographic reproductions or advertisement in the area of poster design, for creating expository stands or for creating furniture or installations for indoor usage.

The characteristics and the advantages of the present invention will be further highlighted by some embodiments thereof, which are hereinafter explained by way of illustration and not of limitation, with reference to the annexed figures.

Drawings

Figure 1 refers to a graph which shows the results obtained upon a bending test carried out onto specimens, made according to the process of the present invention, in order to determine the behavior of the Young's modulus of said specimens.

Figure 2 refers to a graph which shows the results obtained upon a bending test carried out onto specimens, made according to the process of the present invention, in order to determine the behavior of the ultimate tensile strength of said specimens.

Figure 3 refers to a graph which shows the results obtained upon a thermal conductivity test carried out onto specimens made according to the process of the present invention.

Detailed description

Examples of embodiments of a plant-based composite panel comprising parts of plants of the Posidonia genus, as well as some tests for assessing the technical properties of the plant-based composite panels thereby obtained are shown below.

Example 1

Firstly, 10 kg of leaves of Posidonia oceanica stranded on beaches were provided, which were subjected to a rinsing cycle with freshwater, so as to remove solid residues, such as fine sand, and salt deposits sedimented onto the surface of and absorbed by said leaves.

Downstream of a rinsing cycle, the Posidonia leaves thereby obtained were subjected to a step of draining and drying, by spreading said leaves onto a sieve for about one hour.

Hereafter, a drying step was carried out, which provides for the exposure of the material, placed in an adequate environmental chamber, for 7 hours at a temperature of about 80°C.

Hereafter, the Posidonia leaves thereby dried and stabilized from the microbiological point of view were sifted by means of a vibrating screen, so as to separate the rough dregs, for example residues of anthropic waste or crushed stones, from the leaves.

After having been thereby subjected to sifting, 1.2 kg of dried Posidonia leaves were mechanically mixed with 1 kg of eco-friendly epoxy resin of the Super Sap One System type of the company Entropy Resins, Inc.; a thin flow of polymeric resin was let fall onto the dried Posidonia leaves under strong agitation.

Before being mixed with dried Posidonia leaves, epoxy resin was formulated by mixing the base resin with the hardener and adding the resin thereby obtained to the Posidonia leaves within a preset time (less than 30 minutes) in order to avoid wettability problems due to the increase in viscosity of the resin thereby obtained.

After addition of the polymeric resin to the Posidonia leaves, the resin and the leaves were subjected to mechanical agitation until obtaining a homogeneous mixture which appeared as Posidonia leaves impregnated with and coated with said polymeric resin.

The homogeneous mixture thereby obtained was placed in a wax mould, which was closed again with a matching mould heated to the temperature of 25°C for a time equal to about 24 hours.

The composite panel thereby obtained (Treatment 1) appeared as a board made of solid, compact, translucent and dark material; from the surface of the composite material it was possible to recognize the typical form of Posidonia leaves, although compacted and coated by a thin layer of cured and solidified polymeric resin.

The above-described procedure was repeated 8 more times (Treatment 2-9) according to different ratios of Posidonia leaves to resin, as well as according to different temperature values applied during hot forming of the homogeneous mixture thereby obtained.

On the whole, the procedure for obtaining a composite panel based on leaves of Posidonia oceanica was repeated 9 times according to the values shown in the following table (Table 1).

Table 1 (polymerization temperature = 50°C, polymerization time = 6 hours; polymerization temperature = 68°C, polymerization time = 2 hours)

9 types of panels were made with three different fibre/ matrix ratios and three different polymerization temperatures. From each panel were also obtained specimens (five specimens from each panel) for performing specific tests in order to assess the mechanical properties of each single panel thereby obtained. All the specimens thereby obtained had the same shape and size.

Example 2: assessment of the Young's modulus and of the ultimate tensile strength

The specimens obtained from the preceding Example 1 were subjected to a bending test as obtained in conformity with D-790 ASTM test method. Said test allowed to determine the behavior of Young's modulus and of the ultimate tensile strength of the core in relation to the various vegetable fibre/ polymeric matrix ratios and to the density of the composite panel.

The results obtained for the assessment of the Young's modulus are shown in Figure 1.

As it is known, Young's modulus is a parameter that somehow indicates how stiff a material is, i.e., the higher is its value, the more difficult is the deformation for a given stress.

As can it be noted on the graph shown in Figure 1, the Young's modulus is indirectly proportional to the vegetable fibre / polymeric matrix weight ratio (the thickness and the volume being equal); this means that it is necessary to increase the amount of polymeric matrix, at the expenses of the parts of plants of the Posidonia genus, to obtain increasing values of the Young's modulus.

In particular, the composite panel according to the present invention may therefore show satisfying values of the Young's modulus, comparable to those of a panel having the same thickness and volume and made of only high-density polyethylene.

The results obtained for the assessment of the ultimate tensile strength are shown in Figure 2. It is apparent that the ultimate tensile strength has a trend which is similar to that of the Young's modulus: the ultimate tensile strength is indirectly proportional to the vegetable fibre/ polymeric matrix ratio; therefore, a low vegetable fibre/ polymeric matrix weight ratio, i.e. a lower weight percentage of parts of plants of the Posidonia genus in the panel, the volume being equal, corresponds to a higher ultimate tensile strength.

Therefore, as it is apparent from Figures 1 and 2, the above-analyzed results prove that composite panels which can be made in accordance with the process of the present invention show good mechanical properties, especially suitable for structural applications e.g. in the field of construction industry when the vegetable fibre/ polymeric matrix weight ratio is equal to 1.2 and 2.5 and, in particular, with higher density values (degree of compaction in step c) of forming of the process of the present invention directly proportional, as indicated in Figures 1 and 2, to the so-called “Posidonia amount”, panel volume and thickness being equal).

Example 3: measurement of thermal conductivity

Similarly, the procedure described in Example 1 was repeated in order to obtain three different panels (Treatment 10- 12) having the same thickness equal to 16 cm, but a different vegetable fibre/ polymeric matrix weight ratio.

All the composite panels under analysis were made by carrying out the forming step at the same polymerization temperature, i.e. at a temperature of 25 °C.

The measurement of the characteristics of thermal conductivity was carried out according to the regulation ASTM C 518-02 onto specimens obtained from each composite panel thereby made. The test was carried out first onto a material with known thermal conductivity, so as to be able to calibrate the instrument and, by comparison, the thermal conductivity of the composite panel of the present invention was measured.

Table 2 below shows the parameters used in the process of making the panels from which the above-mentioned specimens for the thermal conductivity test were obtained.

Table 2

As it is apparent also from Figure 3, the thermal conductivity decreases as the vegetable fibre/ polymeric matrix weight ratio increases. From this, one deduces that a panel with good insulating properties should have a moderate thickness and a rather high fibre/matrix weight ratio. This is due to the fibrous structure of Posidonia, which has some air entrapped at the microscopic level, as well as to the air entrapped between the leaves (with increasing amount of Posidonia leaves, the thickness being equal, the gaps between leaves increases, which gaps, at lower vegetable fibre/ polymeric matrix ratios, would be instead occupied by the polymeric matrix) .

Example 4: fire resistance test

Similarly, the procedure described in Example 1 was repeated in order to obtain two different panels (Treatment 13 and 14) having the same thickness equal to 20 cm, but a different vegetable fibre/ polymeric matrix weight ratio.

All the composite panels under analysis were made carrying out the forming step at the same polymerization temperature, i.e. at a temperature of 25°C.

Table 3 below shows the parameters used in the process of making the panels from which the above-mentioned specimens for the thermal conductivity test were obtained.

Table 3

The panel obtained by treatment 13 was subjected to a fire resistance test by applying a flame targeted to a fixed point. The flame was generated by a totally conventional cartridge gas blowpipe, whose burner was placed at a 7 cm distance for 3 min.

After performing the test, the thickness of the carbonized material was measured, thereby finding a thickness of about 2 mm; the composite panel thereby tested proved a high fire resistance, even though it had a vegetable fibre / polymeric matrix weight ratio equal to 1.

Hereafter, the panel obtained by treatment 14 was subjected to a fire resistance test by applying a flame targeted to a fixed point. The flame was generated by a totally conventional cartridge gas blowpipe, whose burner was placed at a 10 cm distance for 10 min.

After performing the test, the thickness of the carbonized material was measured, finding a thickness of about 2 mm; the composite panel thereby tested proved an even higher fire resistance than the one found with reference to the panel obtained by means of treatment 13.

Example 5: production of a composite panel by mixing through spraying

The procedure described in Example 1 was repeated in order to obtain one composite panel according to the invention (Treatment 15) having a thickness equal to 16 cm and a vegetable fibre/ polymeric matrix weight ratio equal to 2.5.

In contrast to the procedure carried out in Example 1, in this case step b) of mixing the Posidonia leaves and the polymeric epoxy resin was carried out by spraying.

Specifically, the Posidonia leaves were placed inside a hopper; later, the Posidonia leaves were gradually let fall from the bottom opening of the hopper.

Said polymeric epoxy resin was sprayed onto the Posidonia leaves as soon as they came out of said bottom opening, the polymeric epoxy resin being simultaneously delivered by four nozzles. The mixture thereby obtained appeared as very moist Posidonia leaves, impregnated and coated with a thin layer of said polymeric resin.

Said mixture was subsequently placed in a wax mould and subjected to said step c) of hot forming at the temperature of 25°C for a time of 24 hours. From the composite panel thereby obtained were obtained three specimens. Each specimen was subjected to a mechanical test for the measurement of the Young's modulus, the ultimate tensile strength and to a thermal conductivity test, respectively.

By means of the above-mentioned tests it was verified that a composite panel, obtained by the process according to the present invention wherein said step b) of mixing is carried out by spraying, has mechanical properties and thermal insulation properties comparable or superior to similar panels in which said step b) of mixing is carried out by mechanical mixing.