Process for preparing poly-β-hydroxyalkanoate film

Abstract

Process for preparing a poly-β-hydroxyalkanoate film. The application relates to a process for preparing a PHA film comprising the steps of: a) mixing powdered PHA with an aqueous solution to obtain a PHA suspension, b) allowing the PHA suspension to stand, thereby sedimenting a portion of the PHA and forming a pellet, above which a supernatant floats, c) taking at least a portion of the supernatant, d) applying the taken supernatant to at least one flat, horizontal portion of a surface of a first substrate, e) evaporating the water from the applied supernatant, f) heating at least one area of ​​the portion of the first substrate surface to which the supernatant has been applied, thereby obtaining a first substrate, at least one area of ​​which is covered with a PHA film. PHA films with thicknesses of 1 to 60 µm can be obtained with this process. Figure for abstract: None

Description

Title of the invention: Process for preparing poly-p-hydroxyalkanoate film

[0001] The present invention relates to a process for preparing poly-[3-hydroxyalkanoate (PHA) film usable in particular for the manufacture of paper or cardboard-based packaging.

[0002] The development of packaging made from bio-based and recyclable materials is required for environmental reasons. In this context, PHA is an interesting bio-based and recyclable film-forming material. Generally, PHA powder is bio-based, produced by bacteria.

[0003] PHA can be transformed into a film by depositing a solution of PHA in an organic solvent onto a substrate. Evaporation of the solvent forms a film. This technique is commonly called "solvent casting" and allows for the production of very thin films, on the order of 20 microns.

[0004] The major drawback of this technology is that PHA is soluble only in chlorinated solvents (i.e., dichloromethane, chloroform), which are highly toxic. Evaporation must take place at relatively high temperatures, on the order of 80°C, over relatively long periods, ranging from 8 to 24 hours. The formation of PHA films from chlorinated solutions therefore requires specific equipment, in addition to personnel specially trained to handle this type of product. These health and safety requirements result in significant additional costs to limit the risks of pollution and poisoning for both the handlers and the environment. Finally, it is essential to ensure that the chlorinated solvent is completely evaporated from the film to guarantee non-toxicity for the end user.

[0005] Processes for preparing PHA films from aqueous solutions are rare. Application WO 91 / 13207 describes a process for preparing coated or impregnated paper comprising:

[0006] - the application to a substrate, in particular paper, of a latex comprising 15 to 25% in weight of PHA in water,

[0007] - the evaporation of water from the latex,

[0008] - heating to form a film by melting the PHA.

[0009] This latex is a colloidal suspension of PHA in water, the PHA particles having a diameter of 0.2 to 1.5 pm.

[0010] However, this process leads to the production of thick PHA films, which is a hindrance to its use as packaging.

[0011] The main difficulty encountered with PHA is the thickness of the films obtained, su greater than 100 pm according to the literature. This hinders the industrial use of PHA to manufacture PHA-based paper / cardboard packaging, because the desired films must have a thickness at least 5 times less, i.e. around 20 microns.

[0012] Obtaining thick PHA films has two sources: On the one hand, commercially available PHA granules generally have an average diameter of 0.5 to 2 mm, and melting them leads to the formation of thick films. On the other hand, film production methods by injection or extrusion of PHA also result in thick films.

[0013] There is a need to develop thinner PHA films that can be obtained by a process not using chlorinated solvents.

[0014] To this end, the invention relates to a method for preparing a PHA film comprising the steps of:

[0015] a) mix a PHA in powder form and of the following formula (I):

[0016] H-[CHR-CH2-COO]nH (I)

[0017] in which

[0018] - each R independently represents a linear or branched alkyl comprising 1 to 12 carbon atoms,

[0019] - n is an integer greater than or equal to 2 representing the number of units in the PHA,

[0020] to an aqueous solution to obtain a suspension comprising 0.5 to 15% by weight, preferably 3 to 10% by weight, of PHA relative to the weight of aqueous solution,

[0021] b) allowing the PHA suspension to stand, generally from 10 seconds to 16 hours, whereby some of the PHA settles and a pellet is obtained, above which floats a supernatant comprising 0.1 to 1.0% by weight of PHA relative to the weight of aqueous solution,

[0022] c) to take at least a portion of the supernatant,

[0023] d) apply the supernatant taken from at least one flat and horizontal part of a surface of a first substrate,

[0024] e) evaporate the water from the applied supernatant,

[0025] f) simultaneously with step e) or after step e), heat at least one area of ​​the portion of the surface of the first substrate to which the supernatant was applied, preferably to a temperature:

[0026] - higher than the (specific melting point of PHA + 5 °C), preferably su above the (specific melting point of PHA +15 °C), and

[0027] - lower than the (degradation temperature of PHA - 10°C),

[0028] by which a first substrate is obtained, of which said at least one zone is re- covered with a PHA film.

[0029] The process includes a step a) of mixing a PHA and an aqueous solution to obtain a suspension.

[0030] This mixing can be done by any method, for example by magnetic stirring or ultrasound.

[0031] The PHA used in step a) has the following formula (I):

[0032] H-[CHR-CH2-COO]nH (I)

[0033] in which:

[0034] - each R independently represents a linear or branched alkyl comprising 1 to 12 carbon atoms, in particular 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, and

[0035] - n is an integer greater than or equal to 2 representing the number of units in the PHA.

[0036] PHA can be a homopolymer. In this case, the R groups of all the units of the polymer are identical. Examples of homopolymers are PHB (poly([3-hydroxybutyrate) (R then representing a methyl)) and PHV (poly([3-hydroxyvalerate) (R then representing an ethyl).

[0037] PHA can be a copolymer. In this case, PHA comprises at least two different Rs. For example, PHBV is a copolymer of poly([3-hydroxybutyrate]) and poly([3-hydroxyvalerate]). Preferably, PHA is a copolymer of poly([3-hydroxybutyrate]) and poly([3-hydroxyvalerate]) comprising from 1 to 20% by weight of hydroxyvalerate units.

[0038] The PHA is used in powder form, with an average particle diameter typically of 0.1 to 1 pm as measured by electron microscopy (SEM). Such a PHA is commercially available, for example from NaturePlast under the reference PHI 003.

[0039] The use of PHA granules with an average diameter of 0.5 to 2 mm as measured by light diffraction in step a) is to be avoided because they do not allow the formation of a supernatant when the suspension is left to stand in step b). The granules are too large and settle, the concentration of PHA in the supernatant is then zero or almost zero.

[0040] Mixing 0.5 to 15% by weight (relative to the weight of aqueous solution) of a PHA in powder form with an aqueous solution results in the formation of a suspension capable of forming a supernatant comprising 0.1 to 1% by weight (from 1 g / L to 10 g / L, knowing that 1% by mass represents 10 g / L for water) of PHA relative to the weight of aqueous solution, when the suspension is left to stand.

[0041] The aqueous solution used in step a) is generally free of chlorinated solvents, preferably free of organic solvents. Preferably, the process does not introduce It uses chlorinated solvents, and in a particularly preferred manner, it does not use organic solvents.

[0042] The advantage of the process is the use of water as a solvent (in this case, as a non-solvent, since PHA is insoluble in water). This implies the absence of any risk of poisoning for users (handlers, consumers), any risk of environmental pollution, and a substantial reduction in production costs compared to processes using chlorinated solvents.

[0043] The aqueous solution used may comprise one or more components selected from:

[0044] - polymers, for example polysaccharides, such as pectin,

[0045] - surfactants, preferably bio-based surfactants, and / or

[0046] - salts, in particular salts of alkali, alkaline earth or metallic ions, by example of calcium and magnesium ions.

[0047] Preferably, the water solubility of the (or each of the components when there are several) is greater than 1g / L at 25°C. The use of water-soluble components is preferred so that they are distributed homogeneously in the PHA film formed at the end of the process.

[0048] The presence of ions can affect the crystallinity of the PHA film obtained by the process. Preferably, the crystallinity is less than or equal to 40%. An amorphous PHA film is indeed preferred because it is more flexible.

[0049] The presence of ions can also impact the sedimentation kinetics during step b).

[0050] Generally, monovalent ions do not influence either the sedimentation kinetics of PHA or the size of PHA particles. In contrast, divalent ions, such as magnesium (Mg2+) and calcium (Ca2+), accelerate PHA sedimentation and can modify the size of PHA particles. Finally, a combination of divalent and monovalent ions gives results similar to those presented. Regardless of the ions used, it is preferable to use ion concentrations below 0.01 M. Above this concentration, ion deposits may form, which can significantly alter the mechanical and barrier properties of the PHA film.

[0051] Preferably, the solution used in step a) is water, for example tap water, demineralized water or mineral water.

[0052] It is difficult, if not virtually impossible, to prepare PHA suspensions with PHA contents below 0.5% by weight relative to the weight of aqueous solution. This is because PHA is hydrophobic; suspending small quantities of PHA in aqueous solution leads to the formation of large PHA agglomerates, which almost immediately clump together to form a pellet with a supernatant that is almost entirely free of PHA. Therefore, the process described in application WO 91 / 13207 uses a suspension (named latex in the application) of 15 to 25% by weight of PHA in water.

[0053] However, the inventors discovered that, when a saturated solution of PHA is prepared, i.e. a suspension of 0.5 to 15% by weight of PHA relative to the weight of the aqueous solution, a substantial proportion of the PHA settles as a pellet, but some of the PHA remains suspended in the supernatant for about 16 hours.

[0054] The process includes a step b) where the PHA suspension is left to stand, whereby some of the PHA settles and a pellet is obtained, above which floats a supernatant comprising 0.1 to 1.0% by weight of PHA.

[0055] The weight proportion of PHA in the supernatant is generally between 0.1 and 1.0% by weight relative to the weight of the aqueous solution. This is the proportion of PHA once step b) of resting has been carried out, but therefore also the proportion of PHA in the supernatant taken in step c).

[0056] The duration of step b) resting is variable. It is generally from 10 seconds to 16 hours. A resting time of less than 10 seconds generally results in a supernatant with a PHA mass concentration that is too high. The film formed at the end of the process will be too thick for most intended applications, particularly for use as packaging. If the suspension is left to rest for more than 16 hours in step b), the weight proportion of PHA in the supernatant becomes too low and difficult to control.

[0057] The duration of step b) depends on the solution used in step a). When demineralized water is used, the duration is preferably from 10 seconds to 16 hours, preferably from 30 seconds to 1 hour, typically from 1 minute to 20 minutes. Certain components of the aqueous solution can affect the sedimentation kinetics of PHA. For example, calcium and / or magnesium ions accelerate it. When an aqueous solution containing calcium and / or magnesium ions is used in step a), the duration of step b) is preferably from 10 seconds to 30 minutes, typically from 30 seconds to 15 minutes. The appropriate duration for step b) can be determined by studying the sedimentation kinetics with respect to the aqueous solution used, bearing in mind that the duration of step b) must be less than or equal to the time after which all the PHA has sedimented (the concentration of PHA in the supernatant being then zero).

[0058] The diameter D90 of the PHA particles present in the supernatant collected in step c) is generally less than or equal to 40 pm, as measured by light diffraction. The diameter D50 of the PHA particles present in the supernatant collected in step c) is generally less than or equal to 10 pm, as measured by light diffraction.

[0059] The process includes a step c) consisting of taking at least a portion of the supernatant, then a step d) consisting of applying the taken supernatant to at least a flat and horizontal part of a surface of a first substrate, then a step e) consisting of evaporating the water from the applied supernatant.

[0060] Step e) of evaporation can be accelerated by heating, for example by placing the first substrate in an oven or on a hot plate. The heating temperature is preferably below 100°C to avoid boiling the water, which would affect the homogeneity of the deposited PHA powder.

[0061] After evaporation of the water, a homogeneous powder deposit forms on the part of the surface to which the supernatant has been applied. The surface of the first substrate to which the collected supernatant is applied must be flat and horizontal; otherwise, the supernatant will flow into the lowest or hollow areas and will not be distributed uniformly.

[0062] In order to solidify this powder, a melting step is necessary, which forms a film typically 10 to 60 µm thick. The process therefore includes a step f) consisting of heating at least one area of ​​the portion of the surface of the first substrate onto which the supernatant has been applied, preferably to a temperature:

[0063] - higher than the (specific melting point of PHA + 5 °C), preferably su above the (specific melting point of PHA +15 °C), and

[0064] - lower than the (degradation temperature of PHA - 10°C),

[0065] by which a first substrate is obtained, of which said at least one zone is re covered with a PHA film.

[0066] Preferably, the duration of step f) is less than 5 minutes so as not to degrade the PHA film formed.

[0067] Steps e) and f) can be simultaneous. In this case, evaporation and heating occur at the same time. The heating temperature can then exceed 100°C. The supernatant is then directly transformed into a film, without the PHA powder being formed. For example, applying a heat press or a calendering roller to the area of ​​the first substrate allows steps e) and f) to be carried out simultaneously.

[0068] The area of ​​the first substrate heated in step f) can correspond to the entire surface to which the supernatant was applied. In this case, the film formed in step f) will have the shape of the portion of the substrate surface to which the supernatant was applied. All the PHA deposited on the surface is then transformed into a film.

[0069] Alternatively, the heated area in step f) can be smaller than the surface area of ​​the substrate to which the supernatant was applied. The film forms only in the heated area, and the PHA remains in powder form in the unheated area. Step f) can, for example, be implemented with a laser, which targets only the desired area(s). This alternative makes it possible to obtain patterns.

[0070] Advantageously, the PHA film obtained by the process according to the invention has a thickness of 1 to 60 µm, typically 2 to 50 µm, particularly 3 to 30 µm, preferably 5 to 25 µm, as measured by scanning electron microscopy (SEM). Such thicknesses are particularly suitable for packaging. The film is generally transparent when its thickness is less than or equal to 30 µm. It has a slightly brownish color for greater thicknesses.

[0071] The process may include a step g) consisting of recovering the film, i.e., separating it from the first substrate. It is preferable to let the film rest for at least 60 minutes at room temperature (around 20°C) between steps f) and g). This time allows the PHA in the film to crystallize, which promotes its detachment from the surface of the first substrate.

[0072] Advantageously, the pellet formed in step b) can be used as a source of PHA to form the PHA suspension and implement the process. Thus, there is no loss of material. Therefore, in one embodiment, the process comprises the steps of:

[0073] a') after step c), mix the pellet, optionally with the portion of the supernatant not having been collected in step c), with an aqueous solution to obtain a second suspension comprising 0.5 to 15% by weight, preferably 3 to 10% by weight, of PHA relative to the weight of aqueous solution,

[0074] b') let the second PHA suspension stand for 10 seconds to 16 hours, this whereby a second pellet is obtained, above which floats a second supernatant comprising 0.1 to 1.0% by weight of PHA relative to the weight of aqueous solution,

[0075] c') to take at least a portion of the second supernatant,

[0076] d) apply the second supernatant taken from at least one flat part and ho ricental of a surface of a second substrate,

[0077] e') evaporate the water from the second applied supernatant,

[0078] f') simultaneously with step e') or after step e'), heat at least one zone of the part of the surface of the second substrate to which the second supernatant was applied, preferably at a temperature:

[0079] - higher than the (specific melting point of PHA + 5 °C), preferably su above the (specific melting point of PHA +15 °C), and

[0080] - lower than the (degradation temperature of PHA - 10°C), which is obtained a second substrate of which said at least one area is covered with a PHA film.

[0081] The embodiments described above and below for the first substrate and for the first supernatant also apply to the second substrate and for the second one to float on.

[0082] According to a first alternative of the process, the first substrate is paper or cardboard. At the end of step f) a composite material made of paper or cardboard is obtained, at least one area of ​​which is covered with a PHA film.

[0083] Thanks to this film, the paper or cardboard acquires barrier properties (water, oil and / or gas), which makes it particularly suitable for use as packaging.

[0084] This composite material is fully biodegradable in industrial compost. The composite material can serve as a food source for PHA-producing bacterial strains. This is a virtuous life cycle within a circular, sustainable, and responsible economy.

[0085] The disadvantage of using paper or cardboard as a first substrate is that the application of the supernatant to at least part of its surface during step d) leads to wetting the paper or cardboard, which can degrade some of its properties.

[0086] Thus, according to a second alternative of the process, the first substrate is neither paper nor cardboard. Typically, the process then comprises, after step f), a step h) consisting of transferring the PHA film onto a substrate of a different nature than the first substrate.

[0087] This transfer may include the steps of:

[0088] hl) heat the first substrate, at least one area of ​​which is covered with a PHA film,

[0089] h2) place at least a portion of the surface of a substrate of a different nature from the first substrate on the PHA film so as to obtain a multilayered material in which the film is located between the first substrate and a substrate of a different nature than the first substrate,

[0090] h3) remove the first substrate from the multilayer material, thereby obtaining a substrate, of a different nature than the first substrate, and of which at least part of the surface is covered with a PHA film.

[0091] For example, the first substrate is made of glass, ceramic, parchment or Teflon-coated paper, or metal, and the second substrate, which is different in nature from the first, is made of paper or cardboard. Using a first substrate made of parchment or Teflon-coated paper is advantageous because the film is easy to peel off, thus facilitating its recovery.

[0092] At the end of the process according to this second alternative, a composite material made of paper or cardboard is also obtained, at least part of whose surface is covered with the film. The advantages mentioned above remain valid. An additional advantage is that the paper or cardboard has not been wetted during the process.

[0093] The following examples illustrate the method according to the invention

[0094] In the examples below, the PHA was sourced from NaturePlast, under the reference PHI 003.

[0095] The scanning microscope used was a SEM-FEG Ultra 55, marketed by the company Zeiss.

[0096] Example 1: Method for preparing a PHA film on an aluminum cup

[0097] The following protocol was followed:

[0098] - Prepare a 5% by weight suspension of PHA in water by mixing 1.5 g of Add PHA to 30 g of water and shake the suspension until a homogeneous milky appearance is obtained (step a))

[0099] - Let the suspension rest for 3 minutes (step b))

[0100] - Collect the supernatant (step c))

[0101] - Deposit the supernatant at the bottom of an aluminum dish (first substrate), until the surface at the bottom of the dish is completely covered with supernatant (step d))

[0102] - Allow to evaporate (e.g., 6 g of supernatant takes approximately 36 hours to evaporate completely) at room temperature (20°C) (step e))

[0103] - Alternatively, place the cup on a hot plate or in an oven to accelerate evaporation

[0104] Once the supernatant has evaporated, a deposit of white PHA is visible.

[0105] - Preheat a hot plate to 200°C

[0106] - place the cup containing the PHA deposit on the hot plate for a Maximum time of 5 minutes, by which a film is formed (step f))

[0107] - Cut out the contours of the cup so as to keep only the base on which it rests the film

[0108] - If necessary, retrieve the film by removing the bottom of the cup (step g)).

[0109] The PHA film obtained was 7.75 pm thick (average of three measurements determined by scanning electron microscopy with a magnification of x 500).

[0110] Example 2: Transfer of the film from example 1 onto paper

[0111] The following protocol was followed:

[0112] - Place the cup whose contours have been cut out and on the bottom of which rests the film on a heated plate stabilized at 200°C (step h 1))

[0113] - Once the film has melted, place paper on the melted film to obtain a material multilayer aluminium / PHA film / paper (step h2)) (the substrate, different from the first substrate, is therefore paper in this example)

[0114] - Roll a roller over the surface of the paper

[0115] - Remove the aluminum / PHA film / paper multilayer material from the plate heated, and let it cool to room temperature (20°C) for at least 60 minutes (the time it takes for the PHA to crystallize, facilitating its detachment from the aluminum)

[0116] - remove the aluminum to obtain a paper whose surface is covered with a film of PHA (step h3)).

[0117] The first three steps simulate the action of a heat press. In an industrial context, the use of a heat press or calendering rollers is preferred.

[0118] Example 3: Impact of the concentration of PHA in the suspension prepared in step a) and of the duration of step b) on the concentration of PHA in the supernatant

[0119] The mass concentration of PHA in the supernatant was determined as a function of:

[0120] - the mass concentration of PHA in the suspension prepared in step a) and

[0121] - of the duration of step b) rest (duration between the preparation of the suspension and the sampling of the supernatant).

[0122] The results are provided in Table 1.

[0123] [Tables 1] Initial mass concentration of PHA in the suspension prepared in step a) (as %wt PHA) Duration of step b) 0 minutes 3 minutes 0.5 0.24 0.11 1 0.43 0.17 3 1.55 0.34 5 2.1 0.36 10 6.3 0.8

[0124] Mass concentration (in %wt PHA relative to the weight of water) of PHA in the supernatant as a function of the initial concentration of PHA in the suspension prepared in step a) and the duration of step b).

[0125] The results show that the mass concentration of PHA in the supernatant depends on the initial mass concentration of PHA in the suspension prepared in step a).

[0126] When step b) of rest is absent (duration of 0 min: the supernatant is taken immediately after preparation of the suspension), the concentration of PHA in the supernatant evolves almost linearly with the initial mass concentration of PHA in the suspension prepared in step a).

[0127] On the other hand, after three minutes of rest, an identical PHA concentration of the order of 0.35% mass (i.e. 3.5 mg / ml) in the supernatant is obtained, whether the initial mass concentration of PHA in the suspension prepared in step a) is 3% or 5% relative to the weight of aqueous solution.

[0128] This means that a suspension having an initial concentration of PHA of 5% by weight can be prepared, the supernatant taken, and the pellet reused to reform a suspension until the concentration in the suspension falls to 3%, without the concentration of PHA in the supernatant being changed.

[0129] To demonstrate that the concentration in the supernatant is low, a 5% PHA suspension by weight was prepared by mixing 1.5 g of PHA with 30 g of water, resulting in a concentration equivalent to 50 mg / ml. In the supernatant, after 3 minutes of rest, the concentration was 3.6 mg / ml, a concentration 14 times lower.

[0130] Obtaining a 3.6 mg / ml PHA suspension in water would require mixing 85 mg of PHA with 30 g of water. However, the 85 mg of PHA could not be homogeneously mixed with the water due to the immiscibility of PHA in water. Such a low concentration of PHA could only be obtained by preparing a much more concentrated suspension initially, allowing it to stand, and then collecting the supernatant.

[0131] This demonstrates the advantage of preparing a concentrated suspension initially, and then recovering the supernatant in order to obtain a low concentration PHA suspension, which cannot be prepared otherwise.

[0132] The PHA films obtained from a suspension of 3 or 5% PHA by weight relative to the weight of aqueous solution were approximately 10 micrometers thick as measured by SEM.

[0133] Example 4: Size of PHA particles in the supernatant as a function of the time of step b) and the mineralization of the water used to prepare the suspension

[0134] The dry PHA powder used as a starting product contains agglomerates of particles with sizes ranging from hundreds of microns to sizes below one micrometer, measured by electron microscopy (SEM).

[0135] During the preparation of the suspension (step a)), the maximum size of the suspended PHA particles depends on the mineralization of the water. The more mineralized the water, the smaller the PHA particle size during the preparation of the suspension.

[0136] On the other hand, the PHA particles in the supernatant are larger after 3 minutes of rest when mineral water is used.

[0137] The size of the particles in the supernatant becomes independent of the mineralization of the water used after 5 minutes of rest.

[0138] Table 2 shows the evolution of the maximum particle size as a function of the resting time in step b) and the water mineralization. The initial concentration of PHA in the suspension prepared in step a) was 5% by weight relative to the weight of aqueous solution in all cases.

[0139] [Tables2] Resting time of step b) (min) Demineralized water Tap water (Equivalent to demineralized water containing 0.01M (approximately 0.5g / L) of CaCl2 dihydrate) Mineral water (containing 0.1M (approximately 2g / L) of CaCl2 dihydrate) 0 140 103.5 89 1 108.2 74.8 65 3 12.2 7.7 35.5 5 10.4 10.4 10.4 10 10.4 12.2 8.9

[0140] Maximum particle size in the supernatant obtained from a 5%wt PHA suspension relative to the weight of aqueous solution.

[0141] These results show that water mineralization impacts particle size, but that from a sedimentation time of 5 minutes, it is possible to obtain the same particle size regardless of the aqueous solution used. In conclusion, it is possible to add minerals to the PHA solution without having to modify the protocol, which is an advantage in terms of cost and production time.

[0142] Example 5: Sedimentation kinetics as a function of water mineralization

[0143] A suspension was prepared as described in Example 1. The suspension was stirred and then placed in a dark chamber. The suspension was uniformly illuminated, and photographs were taken at regular time intervals. In each photograph, the intensity was measured along a vertical line. As the PHA settles in the pellet, the color changes from white to black, allowing the PHA sedimentation to be tracked. Each intensity measurement was plotted on a graph where the x-axis represents time and the y-axis the intensity value. This thus forms a temporal map of the sedimentation. The sedimentation was regular and linear over time, and consistent with a classic, so-called "barometric," sedimentation profile of immiscible solid particles. Sedimentation was complete after 16 to 17 hours.

[0144] The experiment was reproduced for a suspension in which the aqueous phase was an aqueous solution of CaCl2. The protocol of Example 1 was followed, except that 0.3 mL of a CalCl2 solution was added to the water in step a), resulting in a suspension of PHA in a 0.1 M aqueous CaCl2 solution. The sedimentation kinetics were monitored in the same way. In this case, the sedimentation The meeting was completed after 30 minutes.

[0145] The addition of ions, and in particular "heavy" ions (Ca2+, Mg2+), accelerates sedimentation during step b). Without wishing to be bound by any particular theory, the inventors suppose that these ions create a bond between two PHA molecules. This results in the creation of larger, and therefore heavier, aggregates, which then sediment more quickly.

[0146] The sedimentation time therefore depends on the nature of the aqueous solution. The optimal duration of step b) also depends on this. The supernatant must be collected before sedimentation is complete.

Claims

Demands

1. A process for preparing a PHA film comprising the steps of: a) mixing powdered PHA of the following formula (I): H-[CHR-CH2-COO]nH (I) wherein: - each R independently represents a linear or branched alkyl group comprising from 1 to 12 carbon atoms, - n is an integer greater than or equal to 2 representing the number of units in the PHA, and an aqueous solution to obtain a suspension comprising 0.5 to 15% by weight, preferably 3 to 10% by weight, of PHA relative to the weight of the aqueous solution, b) allowing the PHA suspension to stand, generally from 10 seconds to 16 hours, whereby a portion of the PHA settles and a pellet is obtained, above which floats a supernatant comprising from 0.1 to 1.0% by weight of PHA relative to the weight of the aqueous solution, c) taking at least a portion of the floating,d) apply the supernatant taken from the sample to at least one flat, horizontal portion of a surface of a first substrate, e) evaporate the water from the applied supernatant, f) simultaneously with step e) or after step e), heat at least one area of ​​the portion of the surface of the first substrate to which the supernatant has been applied, preferably to a temperature: - above the (specific melting point of PHA + 5 °C), preferably above the (specific melting point of PHA + 15 °C), and - below the (degradation point of PHA - 10 °C), thereby obtaining a first substrate of which said at least one area is covered with a film of PHA.

2. A method according to claim 1, wherein the PHA in powder form used in step a) is such that the average diameter of PHA particles is 0.1 to 1 pm as measured by electron microscopy (SEM).

3. A method according to any one of claims 1 to 2, wherein the aqueous solution used in step a) comprises one or more components selected from: - polymers, for example polysaccharides, such as pectin, - surfactants, preferably bio-based surfactants, and / or - salts, in particular salts of alkali, alkaline earth or metallic ions, for example calcium or magnesium ions.

4. A method according to any one of claims 1 to 3, wherein the PHA film has a thickness of 1 to 60 pm, typically 2 to 50 pm, in particular 3 to 30 pm, preferably 5 to 25 pm, as measured by scanning electron microscopy.

5. A method according to any one of claims 1 to 4, wherein the first substrate is paper or cardboard.

6. A method according to any one of claims 1 to 4, comprising, after step f), a step g) of recovering the PHA film.

7. A method according to any one of claims 1 to 4, comprising, after step f), a step h) of transferring the PHA film onto a substrate of a different nature from the first substrate.

8. A method according to claim 7, wherein step h) comprises the steps of: h1) heating the first substrate, at least one area of ​​which is covered with a PHA film, h2) placing at least a portion of the surface of a substrate of a different nature than the first substrate on the PHA film so as to obtain a multilayer material in which the PHA film is located between the first substrate and the substrate of a different nature than the first substrate, h3) removing the first substrate from the multilayer material, thereby obtaining a substrate, of a different nature than the first substrate, of which at least a portion of the surface is covered with a PHA film.

9. A method according to claim 7 or 8, wherein the first substrate is made of glass, ceramic, parchment or Teflon paper or metal and the substrate of a different nature from the first substrate is made of paper or cardboard.

10. A method according to any one of claims 1 to 9, comprising the steps of: a') after step c), mixing the pellet, optionally with the portion of the supernatant not collected in step c), with an aqueous solution, to obtain a second suspension comprising 0.5 to 15% by weight, preferably 3 to 10% by weight, of PHA relative to the weight of aqueous solution, b') allowing the second PHA suspension, generally 10, to stand seconds at 4 p.m., whereby a second pellet is obtained, above which floats a second supernatant comprising 0.1 to 1.0% by weight of PHA relative to the weight of aqueous solution, c') take at least a portion of the second supernatant, d') apply the second supernatant taken to at least a flat, horizontal portion of a surface of a second substrate, e') evaporate the water from the second supernatant, f') simultaneously with step e') or after step e'), heat at least an area of ​​the portion of the surface of the second substrate to which the second supernatant has been applied, to a temperature above the melting point of PHA, preferably to a temperature: - greater than the (specific melting point of PHA + 5 °C), preferably greater than the (specific melting point of PHA + 15 °C), and - lower than the (PHA degradation temperature - 10°C), whereby a second substrate is obtained, of which said at least one area is covered with a PHA film.