Use of a transparent composition for photobioreactors

The present invention relates to photobioreactors and more particularly relates to the use of a transparent composition based on at least one methacrylic polymer for the construction of installations intended for the culture of photosensitive organisms. This composition can be in the form of films, plates or cylinders such as tubes. A subject of the invention is also a transparent multilayer structure comprising at least one layer of a methacrylic polymer for the culture of photosensitive organisms.

A photobioreactor is a system in which biological interactions take place, in the presence of light energy, which one seeks to control by controlling the culture conditions. Within it, a biochemical photosynthetic reaction takes place with the aim of producing plant biomass from photosynthetic microorganisms, light, carbon dioxide and a minimum of mineral elements. During the photosynthetic mechanism, most of the organic components are produced (carbohydrates, lipids and proteins).

Microalgae, photosynthetic under solar radiation, allow in aquaculture the production of a biomass whose composition depends on the species chosen, and which can reach in energy value, according to estimates, twenty to one hundred times that of plants on the ground. There are several thousand genera of microalgae divided into species, some of which represent a large group potentially supplier of compounds that can be used as biofuels or in the fields of cosmetics, pharmacy, or even the food industry.

Some species are rich in lipids, it is possible to extract the oils (triglycerides) giving more or less directly a biodiesel. The residues can also be valorized, for example by a fermentation producing bioethanol. The lipid-rich microalgae thus become a technical solution to the energy problems linked to the depletion of oil deposits and the replacement of raw materials of fossil origin with renewable materials. In addition, algae production is accelerated by bubbling CO₂ resulting for example from a polluting industry such as a thermal power plant with flame, thus avoiding the immediate release of this greenhouse gas. Microalgae also constitute an alternative to obtaining biofuels from vegetable crops (for example rapeseed, beets, wheat) which require large cultivable areas. According to American scientists, certain microalgae are capable of synthesizing 30 times more oil per hectare than land plants used for the manufacture of biofuels. Moreover, the use of this raw material as a source of biofuels avoids the problems of seasonality and supply characteristic of the use of terrestrial plants.

Composed mainly of proteins, some species have a good food precedent because they are rich in vitamins, polyunsaturated fatty acids and trace elements. They find applications in agriculture and horticulture through the use of seaweed extracts which play a role not only as a fertilizer but also as an accelerator and protector of crops.

Other species represent a productive potential applicable in the fields of health, for the synthesis of drugs or biocosmetics from extracts of substances with biological or therapeutic activities, in the food industry by the extraction and manufacture of pigments, natural dyes or gelling agents. Microalgae can constitute potential sources of molecules that are difficult to access by chemical synthesis.

Microalgae can be directly involved in the production of new and renewable energy, in particular the production of biofuels such as hydrogen. Some species can produce hydrogen under the action of enzymes present such as hydrogenases.

The culture of microalgae offers an interesting alternative for the treatment of wastewater (urban, industrial or agricultural effluents). It allows tertiary biotreatment coupled with the production of potentially recoverable biomass. As a purifying agent, microalgae play various roles such as the simultaneous elimination of nutrient salts (NH⁴⁺, NO³',

PO₄³'), the purification of secondary effluents by producing oxygen which is used by bacteria to degrade residual organic compounds, a bactericidal action reducing the survival of pathogenic germs contained in secondary effluents. This technology has the advantage of being based on the principles of natural ecosystems and is therefore safe for the environment.

The growth of microalgae can be carried out on the surface of open solar ponds or under greenhouses, which constitute photobioreactors of limited investment. However, this technology is limited to the use of hardy species, which can resist variations in temperature or sunlight or viruses. The production of biodiesel from the biomass thus obtained has not proved to be economically competitive compared to petroleum products.

For more stable or more intensive production, closed solar photobioreactors with transparent walls are used. These devices are generally of plane geometry (flat photobioreactors) or of cylindrical geometry (tubular photobioreactors). It is also possible to use photobioreactors with a more particular geometry such as structures of the hollow section type in the shape of an “H” or an “I” for example.

A flat photobioreactor consists of two transparent parallel panels, with variable surfaces and between which resides a thin layer of culture with a depth of a few centimeters.

A tubular photobioreactor consists of one or more transparent tubes, of varying diameters and lengths, of various configurations and within which the culture can circulate. The configuration variants are numerous:

- a wide and vertical tube forming a column,

- two tubes of different diameters arranged one inside the other forming an annular chamber,

- a tube placed on the ground and of moderate diameter but of considerable length, arranged in the form of a coil,

- a tube of small diameter and long length wound helically around a tower,

- several small diameter tubes arranged parallel and vertically.

The peculiarity of a photobioreactor derives, in addition to the usual needs common to all bioreactors, to the need to supply photonic energy to the microorganisms to be cultivated, in particular microalgae, this contribution being essential for carrying out photosynthesis. From a technological point of view, the enclosure of the system must therefore be transparent and be designed in such a way as to provide sufficient light intensity for the microalgae.

To meet this requirement, photobioreactors are generally made from a material exhibiting high transparency in the visible range, such as glass or polycarbonate (PC).

The use of glass, which in addition must be of high purity, has many drawbacks, however: it is a heavy, expensive, rigid material which breaks easily and which is difficult to machine. Glass also has poorer light diffusion than methacrylic polymers such as PMMA. Its implementation limits the choice of the geometry of the reactor: arrangements in the form of loops or coils are difficult to produce, the tubes connected to each other by pipes or fittings are sources of leaks; in order to maintain correct access of light, reactors must be cleaned very often due to the formation of a biofilm on their walls. The optimization between a large length of tube, a reduced surface area on the ground and the accessibility of light to the culture medium proves to be difficult.

Polycarbonate is a product which has little resistance to UV over time, and whose light transmission is lower than that of PMMA. Furthermore, for photobioreactors which require very thick walls, PC becomes very fragile. Finally, PC has low chemical resistance to washing products such as hydrochloric acid, bleach and ozone.

The geometry of the reactor should as much as possible favor a high ratio of the illuminated surface to the culture volume, while limiting the bulk and remaining in line with the objectives of the desired biomass concentration and the physiological needs of the microorganisms cultivated. A hydrodynamic / regulation compromise should also be sought to ensure sufficient mixing and control of parameters such as CO consumption.₂, release of oxygen, temperature.

Access to light must be optimized in all cases, so that the light actually available is significant and homogeneous within the culture. Different variations are used, for example tilting the flat reactors to improve the use of solar irradiance, placing the reactors on reflective surfaces in order to increase the incidence of the radiation by reflection, placing the artificial light sources in tubes at the heart of the culture medium, etc.

Photobioreactors give rise to numerous publications, for example the following documents describe different configurations for carrying out photosynthetic reactions from microorganisms: EP 112,556; EP 239,272; WO 99/20736; WO 00/12673; WO 00/23562; FR 2,907,311; WO 07/025145; WO 08/040828; US 2005/064577.

The state of the art does not specify the nature of the transparent materials used to develop the culture zones, tubes or reaction chambers for the photosynthesis of microorganisms.

The object of the present invention is to provide a transparent material capable of replacing glass or polycarbonate for the culture of photosensitive organisms in photobioreactors, which makes it possible to avoid the aforementioned technical problems and drawbacks encountered with the current use of glass or polycarbonate, and improves its efficiency and lifespan.

The efficiency of the reactor will be all the higher as the material which constitutes it will allow light to pass through and as this light diffusion remains high over time. Furthermore, during cleaning operations, it is necessary to avoid scratching the surface of the reactor and to ensure that the reactor will not crack or break by chemical attack on the material by the washing products.

The object of the present invention is to provide a light and easily transportable thermoplastic material, transparent in the visible range (between 400 and 800 nm), resistant over time, in particular under the effect of prolonged exposure to the sun or to sunlight. humidity, exhibiting high mechanical strength, good chemical resistance to washing products, convertible into different shapes, in particular flexible and connectable.

Another object of the present invention is to provide transparent films, plates, profiles or tubes intended for the construction of installations of various geometries and configurations for the culture of photosensitive organisms.

More specifically, the present invention relates to the use of a transparent composition based on at least one methacrylic polymer for the construction of installations intended for the culture of photosensitive organisms, such as microorganisms, microalgae, photosynthetic bacteria or plankton.

By methacrylic polymer is meant PMMA, homopolymer of methyl methacrylate MAM - or a copolymer of methyl methacrylate (MAM), comprising by weight at least 50% of MAM. The copolymer is obtained from MAM and at least one comonomer which can be copolymerized with MAM.

Preferably, the copolymer comprises by weight from 70 to 99.9%, advantageously from 90 to 99.9%, preferably from 95 to 99.9% of MAM for respectively from 0.1 to 30%, advantageously from 0, 1 to 10%, preferably 0.1 to 5% of comonomer.

Preferably, the comonomer which can be copolymerized with MAM is a (meth) acrylic monomer or a vinyl aromatic monomer such as, for example, styrene or substituted styrenes.

The comonomer can be chosen, for example, from the list of:

• acrylic monomers of formula CH₂= CH-C (= O) -O-Ri where Ri denotes a hydrogen atom, a linear, cyclic or branched C1-C40 alkyl group optionally substituted by a halogen atom, a hydroxy, alkoxy or cyano group, amino or epoxy such as for example acrylic acid, methyl, ethyl, propyl, n-butyl, isobutyl, tert-butyl, 2-ethylhexyl, glycidyl acrylates, hydroxyalkyl acrylates , acrylonitrile;

• methacrylic monomers of formula CH2 = C (CH₃) -C (= O) -O-R2 where R2 denotes a hydrogen atom, a linear, cyclic or branched C2-C40 alkyl group optionally substituted by a halogen atom, a hydroxy, alkoxy, cyano or amino group or epoxy such as, for example, methacrylic acid, methyl, ethyl, propyl, n-butyl, isobutyl, tert-butyl, 2ethylhexyl, glycidyl, hydroxyalkyl methacrylates, methacrylonitrile;

• vinyl aromatic monomers such as, for example, styrene, substituted styrenes, alpha-methylstyrene, monochlorostyrene, tertbutyl styrene.

The comonomer can also be a crosslinking agent, that is to say a molecule or an oligomer having at least two ethylenic unsaturations, polymerizable with MAM by a radical mechanism. The crosslinking agent can be difunctional. It may be, for example, ethylene glycol di (meth) acrylate, hexanediol, tripropylene glycol, butanediol, neopentyl glycol, diethylene glycol, triethylene glycol, dipropylene glycol, allyl or divinyl benzene. The crosslinking agent can also be trifunctional. It may be, for example, tri (meth) acrylate of tripropylene glycol, of trimethylol propane, of pentaerythritol. The crosslinking agent can also be tetrafunctional, such as for example pentaerythritol tetra (meth) acrylate or hexafunctional such as dipentaerythritol hexa (meth) acrylate.

Preferably, the comonomer is an alkyl (meth) acrylate, in particular methyl, ethyl, propyl or butyl acrylate, or butyl methacrylate.

PMMA may advantageously be a copolymer of MAM and acrylic and / or methacrylic acid. This type of PMMA offers thermomechanical resistance as well as improved scratch resistance compared to a PMMA not containing it.

Preferably, the methacrylic polymer has a weight molecular weight (M_w) ranging from 90,000 g / mol to 170,000 g / mol, advantageously from 110,000 to 170,000 g / mol, preferably from 140,000 g / mol to 160,000 g / mol (PMMA standard).

The methacrylic polymers marketed under the Altuglas® brand, in particular the HCR-3 grade, are perfectly suited for the invention.

The composition based on at least one methacrylic polymer according to the invention can be reinforced on impact using at least one impact modifier. Advantageously, an extruder is used to produce the mixture. The impact modifier can, for example, be an acrylic elastomer. The acrylic elastomer can be a block copolymer having at least one elastomeric block. For example, it may be a styrenebutadiene-methyl methacrylate or methyl methacrylate-butyl acrylate-methyl methacrylate copolymer. The impact modifier can also be in the form of fine multilayer particles, called core-shell (core-shell), having at least one elastomeric (or soft) layer, that is to say a layer formed of a polymer having a T_g below -5 ° C and at least one rigid (or hard) layer, that is to say formed of a polymer having a T_g above 25 ° C.

The composition according to the invention may further comprise additives conventionally used chosen from thermal stabilizers, for example terdocecyldisulfide (DtDDS) or Irganox® 1076; lubricants, for example stearic acid or stearyl alcohol; flame retardants, for example antimony trioxide or a brominated or chlorinated phosphate ester; organic or inorganic pigments; UV stabilizers, for example Tinuvin® P; antioxidants, such as hindered phenolic compounds; antistatic.

Advantageously, the composition according to the invention comprises at least one antifouling and / or antistatic additive in order to avoid the phenomena of adhesion and soiling in the presence of the culture medium and / or in the presence of air. The use of such additives to the methacrylic composition also makes it possible to use concentrated culture media without seeing the problems of attaching photosensitive organisms to the walls in contact with the organic medium and / or in contact with the. air.

As antifouling and / or antistatic additive, use may in particular be made of a copolymer containing polyamide blocks and polyether blocks (also called PEBA according to the IUPAC).

PEBA or Polyether-Block-Amide, such as those marketed by the company Arkema under the name Pebax®, result from the polycondensation of PA polyamide blocks with reactive ends with PE polyether blocks with reactive ends, such as, among others:

1) polyamide blocks with diamine chain ends with polyoxyalkylene blocks with dicarboxylic chain ends.

2) polyamide blocks with dicarboxylic chain ends with polyoxyalkylene blocks with diamine chain ends, obtained by cyanoethylation and hydrogenation of aliphatic polyoxyalkylene alpha-omega dihydroxyl blocks called polyetherdiols

3) polyamide blocks containing dicarboxylic chain ends with polyetherdiols, the products obtained being, in this particular case, polyetheresteramides.

The polyamide blocks containing dicarboxylic chain ends originate, for example, from the condensation of polyamide precursors in the presence of a dicarboxylic acid chain limiter.

The polyamide blocks having diamine chain ends originate, for example, from the condensation of polyamide precursors in the presence of a chain-limiting diamine.

The molar mass in number Mn of the polyamide blocks is in the range from 400 to 20,000 g / mol, preferably from 500 to 10,000 g / mol, and more preferably from 600 and 6,000 g / mol.

Polymers containing polyamide blocks and polyether blocks can also comprise units distributed randomly.

The polyamide blocks can contain homopolyamides or copolyamides.

Three types of polyamides can be used in the composition of these PA blocks.

According to a first type, the polyamide blocks come from the condensation of at least one dicarboxylic acid (aliphatic, cycloaliphatic or aromatic) in particular those having from 4 to 36 carbon atoms, preferably those having from 6 to 18 carbon atoms and of at least one diamine (aliphatic, cycloaliphatic or aromatic) chosen in particular from those having from 2 to 20 carbon atoms, preferably those having from 6 to 15 carbon atoms.

As examples of aliphatic diacids, mention may be made of butanedioic, adipic, suberic, azelaic, sebacic, dodecanedicarboxylic, myristic, tetradecanedicarboxylic, hexadecanedicarboxylic, octadecanedicarboxylic and dimerized fatty acids.

As examples of cycloaliphatic diacids, mention may be made of 1,4cyclohexyldicarboxylic acid.

As examples of aromatic diacids, mention may be made of terephthalic (T) and isophthalic (I) acids.

As examples of aliphatic diamines, mention may be made of tetramethylenediamine, hexamethylenediamine, 1,10decamethylenediamine, dodecamethylenediamine, trimethylhexamethylene diamine.

By way of example of cycloaliphatic diamines, mention may be made of the isomers of bis- (4-aminocyclohexyl) -methane (BACM or PACM), bis- (3methyl-4-aminocyclohexyl) methane (BMACM or MACM), and 2-2 -bis- (3-methyl4-aminocyclohexyl) -propane (BMACP), isophoronediamine (IPDA), 2,6-bis (aminomethyl) -norbornane (BAMN) and piperazine (Pip).

Advantageously, the copolymer comprises at least one PA block based on PA 4.4, PA 4.6, PA 4.9, PA 4.10, PA 4.12, PA 4.14, PA 4.16, PA 4.18, PA 4.36, PA 6.4, PA 6.6, PA 6.9, PA 6.10, PA 6.12, PA 6.13, PA 6.14, PA 6.16, PA

6.18, PA 6.36, PA 9.4, PA 9.6, PA 9.10, PA 9.12, PA 9.14, PA 9.18, PA 9.36, PA 10.4, PA 10.6, PA 10.9, PA 10.10, PA 10.12, PA 10.13, PA 10.14, PA 10.16, PA 10.18, PA 10.36, PA 10.T, PA BMACM.4, PA BMACM.6, PA BMACM.9, PA BMACM.10, PA BMACM.12, PA BMACM.14, PA BMACM.16, PA BMACM.18 , PA BMACM.36, PA PACM.4, PA PACM.6, PA PACM.9, PA PACM.10, PA PACM.12, PA PACM.14, PA PACM.16, PA PACM.18, PA PACM.36 , PA Pip.4, PA Pip.6, PA Pip.9, PA Pip.10, PA Pip.12, PA Pip.14, PA Pip.16, PA Pip. 18 and / or PA Pip. 36, and mixtures thereof.

According to a second type, the polyamide blocks result from the condensation of one or more alpha omega-aminocarboxylic acids and / or of one or more lactams having from 6 to 12 carbon atoms in the presence of a dicarboxylic acid having from 4 to 12 carbon atoms or a diamine.

As examples of lactams, mention may be made of caprolactam, oenantholactam and lauryllactam.

As examples of alpha omega amino carboxylic acid, mention may be made of aminocaproic, 7-amino-heptanoic, 11-amino-undecanoic and 12-amino-dodecanoic acids.

The dicarboxylic acids or the diamines can be chosen from those mentioned above.

Advantageously, the polyamide blocks of the second type are made of polyamide 11, of polyamide 12 or of polyamide 6.

According to a third type, the polyamide blocks result from the condensation of at least one monomer of the first type with at least one monomer of the second type. In other words, the polyamide blocks result from the condensation of at least one alpha omega-aminocarboxylic acid (or a lactam), with at least one diamine and one dicarboxylic acid.

In this case, the PA blocks are prepared by polycondensation:

- aliphatic, cycloaliphatic or aromatic diamine (s) having X carbon atoms;

- dicarboxylic acid (s) having Y carbon atoms; and

of the {Z} comonomer (s), chosen from lactams and alpha-omega-aminocarboxylic acids having Z carbon atoms;

- in the presence of a chain limiter chosen from dicarboxylic acids or diamines or of an excess of dibasic acid or diamine used as structural unit.

Advantageously, the dicarboxylic acid having Y carbon atoms, which is introduced in excess relative to the stoichiometry of the diamine (s), is used as chain limiter.

According to another variant (case of copolymers, that is to say copolyamides), the polyamide blocks result from the condensation of at least two different alpha omega-aminocarboxylic acids or of at least two different lactams having from 6 to 12 carbon atoms or of a lactam and of an aminocarboxylic acid not having the same number of carbon atoms in the possible presence of a chain limiter.

As examples of polyamide blocks of the third type, mention may be made of those formed by the following polyamides (copolyamides):

. PA 6 / 6.6 in which 6 denotes caprolactam and 6.6 denotes a monomer resulting from the condensation of hexamethylenediamine with adipic acid.

. PA 6.6 / Pip. 10/12 in which 6.6 denotes a monomer resulting from the condensation of hexamethylenediamine with adipic acid. Pip.10 denotes a monomer resulting from the condensation of piperazine with sebacic acid. 12 denotes lauryllactam.

. PA 6.6 / 6.10 / 11/12 in which 6.6 denotes monomer resulting from the condensation of hexamethylenediamine with adipic acid. 6.10 denotes a monomer resulting from the condensation of hexamethylenediamine with sebacic acid. 11 denotes 11-amino-undecanoic acid. 12 denotes lauryllactam.

As examples, we can also cite PA 10.10 / 11, PA 6.10 / 11, PA10.12 / 11, PA 10.10 / 11/12, PA 6.10 / 10.10 / 11, PA 6.10 / 6.12 / 11, PA 6.10 /6.12/10.10.

In PEBAs, the polyether blocks can represent 1 to 99%, and preferably 5 to 90% by weight of the copolymer containing polyamide and polyether blocks, even more preferably from 10 to 50% by weight. The molar mass Mn of the polyether blocks is in the range going from 100 to 6000 g / mol and preferably from 200 to 3000 g / mol, even more preferably from 250 to 2000 g / mol.

By polyether blocks (hereinafter abbreviated PE) is meant polyalkylene ethers polyols, in particular polyalkylene ether diols, such as poly (ethylene glycol) (PEG), poly (1,2-propylene glycol) (PPG), polytetramethylene ether glycol (PTMG), polyhexamethylene glycol, poly (1,3-propylene glycol) (PO3G), poly (3-alkyl tetrahydrofuran) in particular poly (3-methyltetrahydrofuran (poly (3MeTHF)), and their mixtures. It is also possible to envisage a PE block of the block or random “copolyether” type containing a sequence of at least two types of PE mentioned above. The polyether blocks can also comprise blocks obtained by oxyethylation of bisphenols, such as for example bisphenol. A. These latter products are described in EP 613 919.

The polyether blocks can also include ethoxylated primary amines. These blocks are also advantageously used. By way of example of ethoxylated primary amines, mention may be made of the products of formula:

H - (OCH₂CH₂)_m —N - (CH₂CH₂O)_not—H (ch₂) x ch₃ in which m and n are between 1 and 20 and x between 8 and 18. These products are commercially available under the brand NORAMOX® from the company CECA and under the brand GENAMIN® from the company CLARIANT.

Thus, the chain ends of the PE blocks can be diOH, diNH₂, diisocyanate or diacid according to their method of synthesis.

NH chain end PE blocks₂, can be obtained by cyanoacetylation of aliphatic polyoxyalkylene alpha-omega dihydroxyl sequences called poletherdiols such as Jeffamines® D300, D400, D2000, ED-600, ED-900, ED2003, Elastamines® RP-409, RP-2009, RT1000, RE-600, RE-900, RE-2000, HT-1700, HE-180 from the Huntsman company. Such blocks are described in patents JP 2004346274, JP 2004352794 and EP1482011.

The preparation of copolymers with polyamide block (s) and PEBA polyether block (s) comprises any means making it possible to attach the polyamide blocks (PA block) and polyether blocks (PE block) according to the present invention. In practice, essentially two processes are used, one said in 2 stages, the other in one stage.

The general two-step preparation method for PEBA copolymers having ester bonds between the PA blocks and the PE blocks is known and is described, for example, in French patent FR 2 846 332. The general method for preparing PEBA copolymers having amide bonds between the PA blocks and the PE blocks is known and described, for example in European patent EP 1 482 011.

Advantageously, the two-step or one-step methods described in document WO 01/18111 are used.

According to the invention, the following are advantageously used as antifouling and / or antistatic additives:

- copolymers with polyamide blocks and polyether blocks essentially comprising ethylene oxide units and in which the polyamide blocks are copolyamides resulting from the condensation of at least one alpha omega-aminocarboxylic acid (or one lactam), at least one diamine and at least one dicarboxylic acid, as described in document EP 1 046 675,

- Poyletheresteramides having polyamide blocks comprising dicarboxylic acid sulfonates either as chain limiters of the polyamide block, or associated with a diamine as one of the constituent monomers of the polyamide block and having polyether blocks consisting essentially of oxide units of alkylene, as described in WO 01/29113.

- A mixture of a copolymer with polyamide blocks and polyether blocks and of a polymer or oligomer comprising in its chain at least one ionic function and chosen from polyamides, copolymers with polyamide blocks and polyether blocks, polyesters or thermoplastic polyetheramides, copolymers containing polyester blocks and polyether blocks, polyethers and polyurethanes, as described in document EP 1 262 527.

According to a preferred embodiment of the invention, copolymers having polyamide 12 blocks and polyether blocks essentially comprising ethylene oxide units are used as antifouling and / or antistatic additives. In particular, it is possible to use Pebax®MV 1074 having polyamide 12 blocks with a number average molar mass of 1500 and PEG blocks with a number average molar mass of 1500.

The antifouling and / or antistatic additives described above are preferably used at a content which may range from 3 to 15% by weight relative to the total composition. Depending on the additive content, it is possible to obtain a methacrylic polymer exhibiting antifouling properties or a methacrylic polymer exhibiting antistatic properties. By way of example, a PMMA composition comprising from 5% to 10%, more particularly from 6% to 8% of a PEBA, results in a composition exhibiting good antistatic properties. Preferably, to obtain a methacrylic polymer exhibiting antifouling properties, the additive will be present in a content ranging from 10% to 15% by weight relative to the total composition.

The antistatic and / or antifouling property of a polymer can be measured by its surface resistivity. By way of example, a film of 500 μm of PMMA alone with a molecular mass equal to 150,000 g / mol, has a surface resistivity of 126 10⁺¹⁵ Ohm. The addition of 7% by weight and 10% by weight of PEBAX® MV1074 in the PMMA respectively makes it possible to obtain surface resistivities measured on a film of 500 μm of 136 10⁺¹² and 47 10⁺¹² Ohm, the surface resistivity measurements having been carried out using a cell

Keithley connected to an electrometer, according to ASTM D257, with a measurement voltage of 500 Volts.

According to a variant of the invention, a fluoropolymer is used as an antifouling additive which makes it possible to provide antifouling properties, but also good resistance, in particular to UV and to chemicals. This denotes any polymer having in its chain at least one monomer chosen from compounds containing a vinyl group capable of opening in order to polymerize and which contains, directly attached to this vinyl group, at least one fluorine atom, a fluoroalkyl group. or a fluoroalkoxy group.

By way of example of a monomer, mention may be made of vinyl fluoride; vinylidene fluoride (VDF, CH₂= CF₂); trifluoroethylene (VF₃); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); peril uoro (alkyl vinyl) ethers such as perfluoro (methyl vinyl) ether (PMVE), peril uoro (ethyl vinyl) ether (PEVE) and periluoro (propyl vinyl) ether (PPVE); perfluoro (1,3-dioxole); perfluoro (2,2dimethyl-1,3-dioxole) (PDD); the product of formula CF₂= CFOCF₂CF (CF₃) OCF₂CF₂X where X is SO₂F, CO₂H, CH₂OH, CH₂OCN or CH₂OPO₃H; the product of formula CF₂= CFOCF₂CF₂SO₂F; the product of formula F (CF₂)_notCH₂OCF = CF₂ where n is 1, 2, 3, 4 or 5; the product of formula R₁CH₂OCF = CF₂ in which R₁ is hydrogen where F (CF₂) z and z is 1, 2, 3 or 4; the product of formula R₃OCF = CH₂ in which R₃ is F (CF₂)_z- and z is 1, 2, 3 or 4; periluorobutyl ethylene (PFBE); 3,3,3trifluoropropene and 2-trifluoromethyl-3,3,3 -trifluoro-1-propene.

The fluoropolymer can be a fluorinated homopolymer or a fluorinated copolymer which can also comprise non-fluorinated monomers such as ethylene or propylene.

By way of example, the fluoropolymer is chosen from:

- homo- and copolymers of vinylidene fluoride (VDF, CH₂= CF₂) containing at least 50% by weight of VDF. The comonomer of VDF can be chosen from chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF₃) and tetrafluoroethylene (TFE);

- copolymers of TFE and ethylene (ETFE);

- homo- and copolymers of trifluoroethylene (VF₃) ;

- copolymers of the EFEP type combining VDF and TFE (in particular EFEP from Daikin);

- copolymers, and in particular terpolymers, combining the residues of chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TFE), hexafluoropropylene (HFP) and / or ethylene units and optionally VDF and / or VF units₃.

Advantageously, the fluoropolymer is a homo- or copolymer PVDF. This fluoropolymer indeed has good chemical resistance, in particular to UV and to chemicals, and it is completely miscible in a methacrylic polymer matrix. Preferably the PVDF contains, by weight, at least 50% of VDF, more preferably at least 75% and better still at least 85%. The comonomer is advantageously HFP.

Thus, the PVDFs marketed under the KYNAR® brand, in particular grades 710, 720 or 740 are perfectly suited for this formulation.

The fluoropolymer is preferably present in a content which may range from 5 to 60% by weight relative to the total composition, preferably from 20 to 40%.

The composition according to the invention can be prepared by the usual thermoplastic techniques such as, for example, by extrusion or using twin-screw mixers or alternatively using an apparatus of the Buss® Ko-kneader type.

The composition according to the invention can be provided in the form of powder, granules or pellets.

The composition according to the invention can be put in the form of films, plates, hollow profiles in the shape of an “H” or of an “I” for example, or of cylinders such as tubes according to the conventional extrusion or extrusion processes. injection.

According to a variant of the invention, the antifouling and / or antistatic additive is used in the form of a thin layer on the surface of the methacrylic polymer.

Thus, the invention also relates to a transparent multilayer structure comprising at least one layer of a methacrylic polymer and a layer comprising at least one antifouling and / or antistatic additive, as well as to its use for the construction of installations intended for the culture of photosensitive organisms, such as microorganisms, microalgae, photosynthetic bacteria, plankton.

Advantageously, the multilayer structure comprises at least:

- a layer of at least one methacrylic polymer as defined above

a layer comprising at least one antifouling additive capable of being in contact with a culture medium, the layers being arranged one on top of the other.

Advantageously, the layer in contact with the culture medium consists of either an antifouling methacrylic polymer defined in the present invention by a methacrylic polymer as defined above, with at least one antifouling additive chosen from polyamide block copolymers and polyether blocks or the fluorinated polymers defined above, or of a polymer having antifouling properties chosen from the fluorinated polymers defined above.

Preferably, the multilayer structure comprises in order at least:

- a layer comprising at least one antistatic additive capable of being in contact with air or the external environment

- a layer of at least one methacrylic polymer as defined above

- a layer comprising at least one antifouling additive capable of being in contact with a culture medium.

Advantageously, the layer in contact with the air or the external medium consists of an antistatic methacrylic polymer, defined in the present invention by a methacrylic polymer with 5 to 10% of an antistatic additive chosen from polyamide block copolymers and polyether blocks.

The single or multilayer structure has a thickness of between 200 μm and 12 mm, preferably between 500 μm and 7 mm.

The antistatic or antifouling layer has a thickness of between 50 μm and 2 mm, and preferably between 100 μm and 1 mm.

The multilayer structures can be coextruded, hot pressed, coextruded-laminated, and preferably are coextruded, making it possible to obtain multilayer tubes or plates.

The invention also relates to a multilayer pipe which may have a diameter of 2 to 100 cm, preferably 10 to 60 cm, and a length of 1 to 10 50 meters.

The invention also relates to a plate which may have a thickness of 1 to 100 mm and a width and length of 1 to 50 meters.

The invention also relates to an installation for cultures of photosensitive organisms comprising films, plates, profiles or transparent tubes based on at least one methacrylic polymer.