Method for preparing poly-beta-hydroxyalkanoate film

Abstract

This application relates to a method for preparing a PHA film, comprising the steps of: a) mixing PHA in powder form with an aqueous solution to obtain a PHA suspension; b) allowing the PHA suspension to stand, whereby a part of the PHA precipitates to obtain pellets and a supernatant floats thereon; c) collecting at least a part of the supernatant; d) applying the collected supernatant to at least one flat and horizontal part of the surface of a first substrate; e) evaporating water from the applied supernatant; f) heating at least one region of the part of the surface of the first substrate to which the supernatant has been applied, whereby a first substrate having the at least one region covered with a PHA film is obtained. Using this method, a PHA film with a thickness of 1 to 60 μm can be obtained.

Description

Technical Field

[0001] The present invention relates to a method for preparing poly-β-hydroxyalkanoate (PHA) films that can be particularly used for manufacturing paper or cardboard-based packaging.

Background Art

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

[0003] PHA can be converted into a film by deposition of a PHA solution in an organic solvent onto a substrate. The film is formed by evaporation of the solvent. This technique is generally referred to as the "solvent casting method" and can obtain very thin films of about 20 microns.

[0004] The main drawback of this technique is that PHA is only soluble in very toxic chlorine-based solvents (i.e., dichloromethane, chloroform). Evaporation has to be carried out at a relatively high temperature of about 80 °C for a relatively long time in the range of 8 to 24 hours. Therefore, the formation of PHA films from chlorine-based solutions requires special equipment in addition to personnel trained to handle this type of product. Considerable additional costs are incurred for these health constraints to limit the risk of contamination and poisoning of both the handler and the environment. To ensure that it is harmless to the end-user, it is necessary to ensure complete evaporation of the chlorine-based solvent from the film.

[0005] There are few methods for preparing PHA films from aqueous solutions. Application WO 91 / 13207 discloses - a step of applying a latex containing 15 to 25% by mass of PHA in water to a substrate, in particular paper, - a step of evaporating water from the latex, - A step of forming a film by heating and melting PHA A method for preparing coated paper or impregnated paper is described, which includes

[0006] This latex is a colloidal suspension of PHA in water, and the PHA particles have a particle size of 0.2 - 1.5 μm.

[0007] However, this method results in the acquisition of thick PHA films, thereby limiting their use as packaging.

[0008] The main difficulty encountered with PHA is the thickness of the resulting film, which according to the literature is more than 100 μm. Since the required film must have a thickness of at least one-fifth, i.e., about 20 microns, this limits the industrial use of PHA for the manufacture of PHA-based paper / cardboard packaging.

[0009] There are two sources for obtaining thick PHA films. The first is commercially available PHA granules, which usually have an average particle size of 0.5 - 2 mm, and the melting of these results in the formation of thick films. Second, methods of producing films by injection or extrusion of PHA also result in thick films.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0011] There is a need to develop thinner PHA films that can be obtained by methods that do not use chlorine-based solvents.

Means for Solving the Problems

[0012] For this purpose, the present invention provides a method for preparing a PHA film, comprising: a) PHA in powder form having the following formula (I): H-[CHR-CH2-COO] n -H (I) (wherein - each R independently represents a linear or branched alkyl containing 1 to 12 carbon atoms, - n is an integer value of 2 or more representing the number of PHA units) is mixed with an aqueous solution to obtain a suspension containing 0.5 to 15% by mass, preferably 3 to 10% by mass of PHA based on the mass of the aqueous solution; b) allowing the PHA solution to stand (usually for 10 seconds to 16 hours), thereby precipitating a part of the PHA to obtain a pellet with a supernatant floating thereon containing 0.1 to 1.0% by mass of PHA based on the mass of the aqueous solution; c) collecting at least a part of the supernatant; d) applying the collected supernatant to at least one flat and horizontal portion of the surface of a first substrate; e) evaporating water from the applied supernatant; f) simultaneously with or after step e), at least one region of the portion of the surface of the first substrate to which the supernatant is applied is preferably - higher than (specific melting point of PHA + 5°C), preferably higher than (specific melting point of PHA + 15°C), and - lower than (decomposition temperature of PHA - 10°C) heated to a temperature to obtain a first substrate having at least one region covered with a PHA film. The method comprises the steps.

[0013] The method includes step a) of mixing PHA and an aqueous solution to obtain a suspension.

[0014] This mixing step can be carried out by any method, for example, by magnetic stirring or ultrasound.

[0015] The PHA used in step a) has the following formula (I): H-[CHR-CH2-COO] n -H (I) (wherein, - each R independently represents a linear or branched alkyl containing 1 to 12 carbon atoms, particularly 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, - n is an integer value of 2 or more representing the number of units of PHA) and has.

[0016] The PHA may be a homopolymer. In this case, all R groups of the polymer units are the same. Examples of homopolymers are PHB (poly(β-hydroxybutyrate)) (where R represents methyl at this time), and PHV (poly(β-hydroxyvalerate)) (where R represents ethyl at this time).

[0017] The PHA may be a copolymer. In this case, the PHA contains at least two different Rs. For example, PHBV is a copolymer of poly(β-hydroxybutyrate) and poly(β-hydroxyvalerate). Preferably, the PHA is a copolymer of poly(β-hydroxybutyrate) and poly(β-hydroxyvalerate) containing 1 to 20% by mass of hydroxyvalerate units.

[0018] The PHA is typically used in a powdery form having an average particle diameter of 0.1 to 1 μm as measured by an electron microscope (SEM). Such PHA is commercially available, for example, from NaturePlast under the reference number PHI 003.

[0019] The use of PHA granules having an average particle size of 0.5 to 2 mm in step a) in a measurement by light diffraction should be excluded because no supernatant is formed when the suspension is allowed to stand in step b). The granules are too large and settle, and the concentration of PHA in the supernatant is zero or almost zero.

[0020] By the step of mixing PHA in powder form in an amount of 0.5 to 15% by mass (relative to the mass of the aqueous solution) with an aqueous solution, when the suspension is allowed to stand, a suspension can be formed that forms a supernatant containing 0.1 to 1% by mass of PHA (1 g / L to 10 g / L, since 1% by mass is recognized as representing 10 g / L in the case of water) relative to the mass of the aqueous solution.

[0021] The aqueous solution used in step a) usually does not contain a chlorine-based solvent and preferably does not contain an organic solvent. Preferably, the method does not use a chlorine-based solvent, and particularly preferably does not use an organic solvent.

[0022] An advantage of this method is the use of water as a solvent (in this case, since PHA is insoluble in water, it is used as a non-solvent). This involves no risk of poisoning to the user (handler, consumer) and no risk of environmental pollution, and a substantial reduction in production costs compared to methods using chlorine-based solvents.

[0023] The aqueous solution used can - contain one or more components selected from polymers, such as pectin, such as polysaccharides, - surfactants, preferably surfactants of biological origin, and / or - salts, especially alkali ions, alkaline earth or metal salts, such as calcium or magnesium ions.

[0024] Preferably, the solubility of the component (or, if a plurality of them are present, each of the components) in water is greater than 1 g / L at 25°C. It is preferred to use components soluble in water so that the components are uniformly arranged in the formed PHA film at the final stage of the method. ​

[0025] The presence of ions can affect the crystallinity of the PHA film obtained by this method. Preferably, the crystallinity is 40% or less. Amorphous PHA films are actually preferred because they are more flexible.

[0026] The presence of ions may also affect the precipitation reaction rate during step b).

[0027] Generally, monovalent ions have no effect on the precipitation rate of PHA or on the size of PHA particles. 2+ ) and calcium (Ca 2+ Divalent ions such as ) can accelerate the precipitation of PHA and change the size of the PHA particles. Finally, a combination of divalent and monovalent ions can produce results similar to those presented. Whatever the ion, it is preferable to use only ion concentrations below 0.01M. Above this, ion deposits can form, which tend to significantly alter the mechanical and barrier properties of the PHA film.

[0028] Preferably, the solution used in step a) is water, such as tap water, demineralized water or mineral water.

[0029] It is difficult or even almost impossible to prepare a suspension of PHA with a PHA content of less than 0.5% by weight relative to the weight of the aqueous solution. This is because PHA is hydrophobic and the incorporation of small amounts of PHA into an aqueous solution leads to the formation of large agglomerates of PHA, which almost immediately all coalesce to form pellets with a supernatant that contains almost no PHA. For this reason, the method described in application WO 91 / 13207 uses a suspension of PHA of 15 to 25% by weight in water (referred to in the application as latex).

[0030] However, the inventors found that when a saturated solution of PHA, i.e., a suspension of PHA at 0.5 to 15% by mass with respect to the mass of the aqueous solution, is prepared, a significant proportion of the PHA precipitates in pellet form, but some of the PHA remains in the supernatant in suspended form for about 16 hours.

[0031] This method includes step b) of allowing the PHA suspension to stand, whereby a part of the PHA precipitates to obtain pellets, and floating a supernatant containing 0.1 to 1.0% by mass of PHA thereon.

[0032] The mass ratio of PHA in the supernatant is usually 0.1 to 1.0% by mass with respect to the mass of the aqueous solution. This is the ratio of PHA immediately after step b) of standing is carried out, and thus is also the ratio of PHA in the supernatant collected in step c).

[0033] The period of step b) of standing can be changed. The period is usually from 10 seconds to 16 hours. A period of less than 10 seconds usually results in a supernatant in which the mass concentration of the PHA seems to be too high. The film formed in the final stage of this method seems to be too thick for most of the required applications, especially for use as packaging. When the suspension is allowed to stand for more than 16 hours in step b), the mass ratio of PHA in the supernatant becomes too small and control becomes difficult.

[0034] The duration of step b) depends on the solution used in step a). When deionized 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. Some components of the aqueous solution can affect the precipitation reaction rate of PHA. For example, calcium and / or magnesium ions accelerate the precipitation reaction rate. 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 precipitation reaction rate in terms of the aqueous solution used, and it is recognized that the duration of step b) must be less than or equal to the end point when all the PHA has precipitated (the concentration of all PHA in the supernatant is zero at this time).

[0035] The PHA particles with particle size D90 present in the supernatant collected in step c) are usually 40 μm or less as measured by light diffraction. The PHA particles with particle size D50 present in the supernatant collected in step c) are usually 10 μm or less as measured by light diffraction.

[0036] This method includes step c) consisting of the step of collecting at least a part of the supernatant, and then step d) consisting of the step of applying the collected supernatant to at least the flat and horizontal part of the surface of the first substrate, and then step e) consisting of the step of evaporating the water of the applied supernatant.

[0037] The evaporation step e) can be accelerated by a heating step, for example, by placing the first substrate in an oven or on a hot plate. The heating temperature is preferably less than 100 °C to avoid boiling of water which is considered to affect the uniformity of the deposited PHA powder.

[0038] A uniform powder deposit is formed on the part of the surface where the supernatant was applied after the water has been evaporated. The surface of the first substrate on 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 uniformly arranged.

[0039] It is necessary to proceed with a melting process to solidify this powder, whereby it becomes possible to form a film usually having a thickness of 10 to 60 μm. This method, therefore, preferably involves at least one region of the surface portion of the first substrate coated with the supernatant, - higher than (the inherent melting point of PHA + 5°C), preferably higher than (the inherent melting point of PHA + 15°C), and - lower than (the decomposition temperature of PHA - 10°C) heating to a temperature, thereby obtaining a first substrate having the at least one region covered with a PHA film which comprises step f).

[0040] Preferably, the duration of step f) is less than 5 minutes so as not to degrade the formed PHA film.

[0041] Steps e) and f) may be simultaneous. In this case, the steps of evaporation and heating are carried out simultaneously. The heating temperature can exceed 100°C at this time. Then, without forming PHA powder, the supernatant is directly converted into a film. For example, it becomes possible to perform steps e) and f) simultaneously by applying a hot press or calender roller to the region of the first substrate.

[0042] The region of the first substrate heated in step f) may coincide with the entire surface on which the supernatant is coated. In this case, the film formed in step f) will have the shape of the surface portion of the substrate on which the supernatant is coated. Then, all of the PHA deposited on the surface is converted into a film.

[0043] Alternatively, the area heated in step f) may be further restricted compared to the surface portion of the substrate on which the supernatant is applied. The film is formed only in the heated area, and the PHA remains in powder form in the non-heated area. Step f) can be carried out, for example, using a laser and targeting only the required single or multiple areas. With this option, such a pattern can be obtained.

[0044] Advantageously, the PHA film obtained by the method 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 a thickness is particularly suitable for packaging. When the thickness is 30 μm or less, the film is usually transparent. At larger thicknesses, the film has a slightly brownish color.

[0045] The method may include a step of recovering the film, i.e., step g) which consists of separating the film from the first substrate. It is preferable to leave the film standing at room temperature (about 20 °C) for at least 60 minutes between steps f) and g). This period makes it possible to crystallize the PHA of the film, thereby advantageously facilitating its detachment from the surface of the first substrate.

[0046] Advantageously, the pellets formed in step b) can be used as a source of PHA to form a PHA suspension and the method can be carried out. Thus, there is no loss of material. In one embodiment in this way, the method is a') After step c), mixing the pellets, optionally with a portion of the supernatant not collected in step c), with an aqueous solution to obtain a second suspension containing 0.5 to 15% by mass, preferably 3 to 10% by mass of PHA based on the mass of the aqueous solution, b') Leaving the PHA solution standing for 10 seconds to 16 hours, thereby obtaining a second pellet on which a second supernatant containing 0.1 to 1.0% by mass of PHA based on the mass of the aqueous solution is floating, c') Collecting at least a portion of the second supernatant, d') applying the collected second supernatant to at least one flat and horizontal portion of the surface of the second substrate; e') evaporating water from the applied second supernatant; f') simultaneously with or after step e'), heating at least one region of the portion of the surface of the second substrate to which the second supernatant has been applied, preferably - higher than (the inherent melting point of PHA + 5°C), preferably higher than (the inherent melting point of PHA + 15°C), and - lower than (the decomposition temperature of PHA - 10°C) to obtain a second substrate having at least one region covered with a PHA film; The process comprises the steps constituted thereby.

[0047] The above and below embodiments regarding the first substrate and the first supernatant also apply to the second substrate and the second supernatant.

[0048] According to a first option of the method, the first substrate is paper or cardboard. At the end of step f), a composite material made of paper or cardboard with at least one region thereof covered with a PHA film is obtained.

[0049] By this film, the paper or cardboard acquires barrier properties (water, oil and / or gas) and is particularly suitable for use as packaging.

[0050] This composite material is completely biodegradable into industrial compost. The composite material can serve as a source of food for strains of bacteria that produce PHA. It is a pure life cycle that forms part of a circular and sustainable and responsible economic activity.

[0051] The disadvantage of using paper or cardboard as the first substrate is that during step d), the step of applying the supernatant to at least a part of its surface may cause wetting of the paper or cardboard and deteriorate some of its properties.

[0052] Therefore, according to the second option of the method, the first substrate is neither paper nor cardboard. Then typically, the method includes, after step f), step h) which consists of moving the PHA film onto a substrate having properties different from those of the first substrate.

[0053] This movement can h1) heating the first substrate, at least one region of which is covered with the PHA film; h2) placing at least a part of the surface of a substrate having properties different from those of the first substrate onto the film so that a multilayer material is obtained which is located between the first substrate and the substrate having properties different from those of the first substrate; h3) removing the first substrate from the multilayer material, thereby obtaining a substrate having properties different from those of the first substrate and at least a part of its surface being covered with the PHA film. The process may include steps composed of.

[0054] For example, the first substrate is made of glass, ceramic, vulcanized or Teflon-coated paper, or metal, and the substrate having properties different from those of the first substrate is made of paper or cardboard. Using a first substrate made of vulcanized or Teflon-coated paper is advantageous in that the film is easily detachable and its recovery is promoted.

[0055] In the final stage of the method according to this second option, therefore, a composite material consisting of paper or cardboard, at least a part of the surface of which is covered with the film, is also obtained. The advantages mentioned above remain valid. One additional advantage is that the paper or cardboard is not wetted during the method.

Embodiments for Carrying Out the Invention

[0056] The following examples illustrate the method according to the invention.

[0057] In the following examples, the PHA was obtained from NaturePlast under the reference number PHI 003.

[0058] The scanning electron microscope used was the SEM-FEG Ultra 55 sold by Zeiss.

Example

[0059] Method for preparing a PHA film on an aluminum cup The following procedure was followed. - Step of preparing a 5% by mass PHA suspension in water by mixing 1.5 g of PHA with 30 g of water and stirring the suspension until a uniform milky appearance is obtained (Step a)) - Step of allowing the suspension to stand for 3 minutes (Step b)) - Step of collecting the supernatant (Step c)) - Step of depositing the supernatant on the bottom of the aluminum cup (first substrate) until the surface of the bottom of the cup is entirely covered with the supernatant (Step d)) - Evaporation step (for example, it takes about 36 hours to completely evaporate 6 g of the supernatant at room temperature (20 °C)) (Step e)) - Alternatively, a step of accelerating evaporation by placing the cup on a hot plate or in an oven

[0060] Once the supernatant has evaporated, a white PHA deposit appears. - Step of preheating the hot plate to 200 °C - Step of placing the cup containing the PHA deposit on the hot plate for a maximum of 5 minutes, thereby forming a film (Step f)) - Step of cutting the contour of the cup to retain only the bottom with the film thereon - Step of recovering the film, if necessary, by removing the bottom of the cup (Step g))

[0061] The obtained PHA film was 7.75 μm thick (average value of three measurements determined by a scanning electron microscope using a magnification of 500 times).

Example

[0062] Transfer of the film of Example 1 onto paper was carried out according to the following procedure. - Step of cutting its outer shape and placing a cup with a film at its bottom on a hot plate stabilized at 200 °C (step h1)) - Immediately after the film melted, placing paper on the melted film to obtain a multi-layer material of aluminum / PHA film / paper (step h2)) (the substrate different from the first substrate is, therefore, paper in this example) - Step of applying a roller to one side of the surface of the paper - Step of removing the aluminum / PHA film / paper multi-layer material from the hot plate and leaving it to stand for at least 60 minutes to cool to room temperature (20 °C) (the time for PHA to crystallize works advantageously for its detachment from aluminum) - Step of removing aluminum to obtain paper whose surface is covered with a PHA film (step h3))

[0063] In the first three steps, the action of a hot press machine is encouraged. In an industrial context, the use of a hot press machine or calender rollers is preferred.

Example

[0064] Influence of the concentration of PHA in the suspension prepared in step a) and the period of step b) on the concentration of PHA in the supernatant The mass concentration of PHA in the supernatant was - the mass concentration of PHA in the suspension prepared in step a), and - the period of the standing step b) (the period between the preparation of the suspension and the collection of the supernatant) determined by.

[0065] The results are shown in Table 1.

[0066]

Table 1

[0067] Table 1 (Table 1) shows the initial concentration of PHA in the suspension prepared in step a) and the mass concentration of PHA in the supernatant according to the period of step b) (expressed as %wt of PHA relative to the mass of water).

[0068] 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).

[0069] When there is no standing step b) (period of 0 minutes: immediately after preparing the suspension, the supernatant is collected), the concentration of PHA in the supernatant changes almost linearly in accordance with the initial mass concentration of PHA in the suspension prepared in step a).

[0070] On the other hand, after standing for 3 minutes, regardless of whether the initial mass concentration of PHA in the suspension prepared in step a) is 3% or 5% with respect to the mass of the aqueous solution, the same concentration of PHA of about 0.35 mass% (i.e., 3.5 mg / ml) was obtained in the supernatant.

[0071] This means that a suspension with an initial concentration of 5 mass% PHA can be prepared, and until the concentration of the suspension drops to 3%, the concentration of PHA in the supernatant remains unchanged, and the collected supernatant and pellet can be reused to reform the suspension.

[0072] To demonstrate the low concentration of the supernatant, a suspension of 5% PHA by mass was prepared by mixing 1.5 g of PHA with 30 g of water (i.e., a concentration equivalent to 50 mg / ml). In the supernatant, after standing for 3 minutes, the concentration was 3.6 mg / ml, i.e., 1 / 14 of the concentration.

[0073] To obtain a suspension of PHA at 3.6 mg / ml in water, it seems that a step of mixing 85 mg of PHA with 30 g of water is required. However, due to the immiscibility of PHA with water, 85 mg of PHA could not be uniformly mixed with water. Such a low concentration of PHA could only be obtained by first preparing a much denser concentrated suspension, allowing it to stand, and collecting the supernatant.

[0074] This demonstrates the advantage that a suspension of low-concentration PHA that cannot be prepared by other methods can be obtained by first preparing a concentrated suspension and then recovering the supernatant.

[0075] PHA films obtained from suspensions of 3% or 5% PHA by mass relative to the mass of the aqueous solution were approximately 10 micrometers thick as measured by SEM.

Example

[0076] 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 The dry PHA powder used as the starting product contains an agglomerate of particles having a size range of approximately 100 micrometers to less than 1 micrometer as measured by an electron microscope (SEM).

[0077] When preparing the suspension (step a)), the maximum size of the PHA particles in the suspension depends on the mineralization of the water. The more mineralized the water is, the smaller the size of the PHA particles when preparing the suspension.

[0078] On the other hand, when using mineral water, after standing for 3 minutes, the PHA particles in the supernatant become larger.

[0079] The size of the particles in the supernatant becomes independent of the mineralization of the water used after standing for 5 minutes.

[0080] Table 2 shows the change in the maximum size of the particles as a function of the standing period in step b) and the mineralization of the water. The initial concentration of PHA in the suspension prepared in step a) was 5% by mass relative to the mass of the aqueous solution in all cases.

[0081]

Table 2

[0082] The maximum size of the particles in the supernatant was obtained from a 5% wt PHA suspension with respect to the mass of the aqueous solution.

[0083] These results indicate that the mineralization of water affects the particle size, but from a precipitation time of 5 minutes, the same particle size can be obtained regardless of the aqueous solution used. As a conclusion, it is possible to add inorganic substances to the PHA solution without changing the procedure, which has advantages in terms of cost and production time.

Example

[0084] Precipitation reaction rate as a function of water mineralization The suspension was prepared as described in Example 1. The suspension was stirred and then placed in a dark room. The suspension was uniformly illuminated with light, and photographs were taken at regular time intervals. For each photograph, the brightness was measured on a vertical line. When the PHA precipitated in the form of pellets, its color changed from white to black, enabling the precipitation of the PHA to be observed. The extracted brightness values were each plotted on a graph with the X-axis representing time and the Y-axis representing brightness. Thus, a time mapping of the precipitation was formed in this way. The precipitation was regular and linear with respect to time and matched the conventional profile of the precipitation of immiscible solid particles, the so-called "barometric". The precipitation ended after 16 - 17 hours.

[0085] The experiment was reproduced for the suspension whose aqueous phase was an aqueous solution of CaCl2. A suspension of PHA in a 0.1 M aqueous solution of CaCl2 could be obtained following the procedure of Example 1, except that 0.3 mL of a 1 M solution of CaCl2 was added to the water during step a). The precipitation reaction rate was similarly followed. In this case, the precipitation ended after 30 minutes.

[0086] Ions, especially "heavy" ions (Ca 2+ , Mg 2+) The addition of accelerates precipitation during step b). Without being bound by any particular theory, the inventors presume that these ions create a bond between two PHA molecules. As a result, larger, i.e., heavier aggregates are created, and therefore, they precipitate more rapidly.

[0087] The precipitation period therefore depends on the properties of the aqueous solution. The optimal period for step b) also depends on the properties of the aqueous solution. The supernatant must be collected before precipitation is complete.

Claims

1. a) The following formula (I): H-[CHR-CH 2 -COO] n -H (I) (wherein - Each R independently represents a linear or branched alkyl containing 1 to 12 carbon atoms, - n is an integer value of 2 or more representing the number of units of the PHA) A PHA in powder form having and An aqueous solution Are mixed to obtain a suspension containing 0.5 to 15% by mass, preferably 3 to 10% by mass of PHA based on the mass of the aqueous solution, b) The PHA solution is allowed to stand (usually for 10 seconds to 16 hours), whereby a part of the PHA is precipitated to obtain a pellet, and a supernatant containing 0.1 to 1.0% by mass of PHA based on the mass of the aqueous solution floats thereon. Obtaining a pellet, c) Collecting at least a part of the supernatant, d) Applying the collected supernatant to at least one flat and horizontal part of the surface of the first substrate, e) Evaporating water from the applied supernatant, f) Simultaneously with or after step e), at least one region of the surface portion of the first substrate on which the supernatant is applied is preferably - Higher than (intrinsic melting point of PHA + 5 ° C), preferably higher than (intrinsic melting point of PHA + 15 ° C), and - Lower than (decomposition temperature of PHA - 10 ° C) Heating to a temperature to obtain a first substrate having at least one region covered with a PHA film A method for preparing a PHA film, comprising the steps constituted by

2. The method according to claim 1, wherein the PHA in powder form used in step a) has an average particle diameter of the PHA particles of 0.1 to 1 μm as measured by an electron microscope (SEM).

3. The aqueous solution used in step a) is - A polymer (for example, a polysaccharide (for example, pectin)), - A surfactant, preferably a surfactant of biological origin, and / or - A salt, particularly an alkali ion, alkaline earth or metal salt (for example, calcium or magnesium ion) The method according to claim 1 or 2, comprising one or more components selected from

4. The method according to any one of claims 1 to 3, wherein the PHA film 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 a scanning electron microscope.

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

6. The method according to any one of claims 1 to 4, comprising step g) which is constituted by a step of recovering the PHA film after step f).

7. The method according to any one of claims 1 to 4, comprising step h) which is constituted by a step of moving the PHA film onto a substrate having properties different from those of the first substrate after step f).

8. Step h) comprises h1) a step of heating the first substrate in which at least one region is covered with a PHA film; h2) a step of placing at least a part of the surface of a substrate having properties different from those of the first substrate on the PHA film to obtain a multilayer material in which the film is disposed between the first substrate and a substrate having properties different from those of the first substrate; h3) a step of removing the first substrate from the multilayer material, thereby obtaining a substrate having properties different from those of the first substrate, at least a part of the surface of which is covered with a PHA film The method according to claim 7, comprising the step thus constituted.

9. The first substrate is made of glass, ceramic, sulfuric acid paper or Teflon-coated paper, or metal, The method according to claim 7 or 8, wherein the substrate having properties different from those of the first substrate is made of paper or cardboard.

10. a') After step c), the pellets are optionally mixed with a part of the supernatant not collected in step c) and an aqueous solution to obtain a second suspension containing 0.5 to 15% by mass, preferably 3 to 10% by mass of PHA based on the mass of the aqueous solution; b') The PHA solution is allowed to stand for 10 seconds to 16 hours, thereby obtaining a second pellet on which a second supernatant containing 0.1 to 1.0% by mass of PHA based on the mass of the aqueous solution floats; c') a step of collecting at least a part of the second supernatant; d') a step of applying the collected second supernatant to at least one flat and horizontal part of the surface of the second substrate; e') a step of evaporating water from the second supernatant; f') Simultaneously with or after step e'), at least one region of the surface part of the second substrate on which the second supernatant is applied is preferably - higher than (the intrinsic melting point of PHA + 5°C), preferably higher than (the intrinsic melting point of PHA + 15°C), and - lower than (the decomposition temperature of PHA - 10°C) A step of heating to a temperature to thereby obtain a second substrate having the at least one region covered with a PHA film The method according to any one of claims 1 to 9, comprising the steps constituted thereby.

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