FR3087384A1 - Biodegradable multi-layer film - Google Patents

Abstract

The invention relates to a biodegradable plastic film which can be used in flowpack-type packaging processes, having at least two layers, formed from at least two different polymer materials having a difference in temperature of deflection under load, as well as to a process manufacturing such a film.

Description

The invention relates to a biodegradable plastic film which can be used in flowpack-type packaging processes, having at least two layers, and to at least two different polymer materials, as well as to a process for manufacturing such a film.

The “flowpack” packaging system consists of obtaining an airtight packaging in which the roll of plastic film envelops the product.

It is used in the food industry in particular for the packaging of fresh fruits and vegetables, biscuits, confectionery, the packaging of chocolate, aromatic herbs, spices or cured, but also finds applications in the field. cosmetics, pharmaceuticals, communication (cards, gadgets, printed products, etc.) or industry (pens, cutters, etc.).

This packaging system is used to package products in trays as well as bulk products.

It is particularly suitable for packaging products individually or in small quantities, in particular samples, or sub-packaging in cardboard packaging (biscuits, confectionery, etc.) or in molded cellulose.

This essentially involves forming a sheath around the product by making a longitudinal seal and closing the film by welding the ends of the bag.

Head, foot and back welds are generally waffle welds.

This continuous packaging method can be used at high speed and has a low cost price.

Barrier layer films can be used for perishable food products or those with a long shelf life, and for products packaged in a modified atmosphere or under vacuum.

The films used to date for “flowpack” applications are essentially based on fossil materials, such as, for example, multilayer films made up of PE / PA (Polyethylene / polyamide), PE / PP (Polyethylene / polypropylene), PE / EVOH / PP (Polyethylene / Ethylene vinyl alcohol / Polypropylene), PA / EVOH / PP (Polyamide / Ethylene vinyl alcohol / Polypropylene), and are not recyclable or biodegradable.

2 Current flowpack films for the packaging of fruits and vegetables are mainly coextruded BOPP (bi-oriented polypropylene) films.

Some are laser microperforated to provide breathing.

Other solutions are PET / PE (polyester / polyethylene) laminated films, in which the polyester provides the thermal resistance and the PE the weld.

One of the problems with these films is the requirement of microperforation to allow breathing, these plastics being essentially completely waterproof and airtight.

Thanks to their performance and their specific properties, biodegradable bioplastics are successfully entering certain niche and mass markets: thus, bags, in particular of fruits and vegetables, or mulch films are today essentially biodegradable.

Unfortunately, these materials are still little used for the packaging of food products, and this probably because of their physicochemical properties (sealability, thermal properties, barrier properties, etc.) which are unsuitable when they are used in mono-materials.

Even if additives are starting to be developed on certain dies by manufacturers or universities, they are not necessarily adapted to the constraints of the market or the industrial sector.

20 It is therefore necessary to develop new biodegradable films making it possible to replace the multilayer composite films used to date which are composed of different materials of fossil origin (neither biodegradable nor recyclable), in order to be able in particular to produce food packaging by the method flowpack.

These biodegradable films should consist of at least two layers of different polymers: - A structural layer which provides the desired stiffness, mechanical strength, and which can determine how the package will tear.

This layer provides the overall mechanical properties of the packaging.

It generally exhibits a high melting point, and high temperature sag resistance (also called HDT). - A solder layer, which is intended to allow the film to be sealed by soldering.

This layer should have a low melting point, so that the solder temperature does not lead to the melting of the structural layer, and thus to the maintenance of the integrity of the structural layer.

The ability of a package to be used in flowpack technology lies in its ability to be welded and cut at high speed, and continuously.

For this, the film must have a polymer layer ensuring the welding function, and one or more other so-called structural layers, allowing efficient and clean cutting of each pack.

This or these layers must be sufficiently rigid to ensure the maintenance of the film during its passage through the flowpack machine, and not to melt during the production of the weld, which would cause burrs or the rupture of the weld: the packaging would then lose its integrity and functionality.

Thus, the two polymers must exhibit: A difference in melting temperature to allow soldering - A difference in HDT (resistance to temperature sagging), so that the film can be used in the flowpack method without it being collapses on itself.

In particular, the structural layer must have a high HDT so that the mechanical properties are maintained during the welding operations. - Recrystallization temperatures which are as close as possible to avoid “curling” phenomena during the production of the multilayer film, that is to say the curvature of a layer (high crystallization temperature layer) relative to the other layer if the recrystallization of this other layer (inducing shrinkage of the film) takes place at a temperature too far from that of the layer with a high crystallization temperature.

Temperature deflection resistance (also referred to as HDT, deflection temperature under load, or thermal distortion temperature) is a characteristic of a film which is known in the art and which is measured by standard methods.

This is the temperature at which standardized samples subjected to the action of a given load undergo conventional deformation (begin to soften).

It is preferred to use the international standard ISO 75-2, using loads of 0.45 MPa (method B).

It is thus possible to characterize a film by the HDTB (deflection temperature under load 35 measured by method B of the aforementioned standard). This constant depending on the material (and on the standard used for the measurement) can therefore be considered as reflecting the "Stiffness" of the material as the temperature increases.

Industrially, a normative test known as the temperature of deflection under load (HDT) is used: the test piece is placed on two supports 100 mm apart in a furnace, the temperature rise of which is programmed at 2 ° C./min.

The bending load is applied to the upper part of the sample using a punch.

The international standard ISO 75-2, used to characterize plastics and ebonites, requires loads of 0.45 MPa (HDT B method).

The smallest deflection is 0.25 mm.

We can use the DMA (Dynamic Mechanical Analyzer) tool, and follow the evolution of conservation of the elastic modulus under a temperature ramp: we therefore record the resistance capacity of the material over a wide thermal range, potentially up to the polymer melt, and the value of HDT B is read when the stress reaches 0.45 MPa.

This protocol and this tool are therefore more informative, and richer than the reference ISO test.

The present invention provides a method for making a film for food packaging having at least one of the following characteristics: a.

Be biodegradable under industrial composting conditions, in accordance with standard EN 13432 (see below): the management of this packaging after use is then legitimately done in the bin of fermentable household waste, without the need for incineration or recycling problems . b.

Be composed of several materials and have at least two layers: one of the layers of the film has a lower melting point than the other or the others, and the polymers have an HDT B deviation of at least 20 ° vs.

This thermal difference facilitates machine passage during packaging, with Flowpack technology for example for Fruits and Vegetables.

Indeed, the low melting point layer allows the packaging to be welded around the food, while the higher melting point layer (s) provide the structure and cohesion of the packaging, also allowing a efficient and clean cut between each pack. vs. preferably have sufficient transparency so that the food can be recognized through the packaging, both by the consumer and during checkout. 5 d. possess sufficient mechanical properties for the intended use, and in particular to withstand stresses during use, handling and storage. e. preferably allow controlled respiration of foods by adjusting the barrier properties (water vapor and / or oxygen), depending on the conditioned foods and their industrial cycle (for example, avoiding the creation of dew points).

The transmission of water vapor (WVTR) or oxygen (OTR) makes it possible to measure the permeability of a film.

They can be measured by methods known in the art, such as for example with the standards ASTM E96, DIN 53122 or ISO 2528 for the VVVTR, and the standards ASTMD3985, ASTM F 1927, DIN 53380-3 or JIS K-7126 for the OTR.

In the context of the present invention, the term “biodegradable” is understood to mean any biological, physical and / or chemical degradation, at the molecular level, of substances by the action of environmental factors (in particular enzymes resulting from the metabolism processes of microorganisms. ).

Numerous definitions have been adopted regarding biodegradation (ISO 472-1998, ASTM 20 subcommittee D20-96, DIN 103.2-1993), depending on standardization bodies, techniques for measuring biodegradability and the degradation medium.

However, a consensus has emerged that biodegradation can be defined as the decomposition of organic matter into carbon dioxide, water, biomass and / or methane under the action of microorganisms (bacteria, enzymes, fungi).

We can cite the standard EN 13432 which defines the requirements relating to biodegradable packaging that can be recovered in industrial composting.

The evaluation criteria within the meaning of said standard are as follows: - the material subjected to the test must contain a minimum of 50% of volatile solids - the concentration of toxic and dangerous substances identified in the standard (Zn, Cu, Ni, Cd, Pb, Hg, Cr, Mo, Se, As, Fe) must be less than the threshold stated in the latter - biodegradability must be determined for each packaging material 35 or each significant organic constituent of the packaging material , by 6 significant is meant any organic constituent representing more than 1% of the dry mass of this material - the total proportion of organic constituents whose biodegradability is not determined must not exceed 5% 5 - each material subjected to the The test must be inherently and ultimately biodegradable as demonstrated by laboratory tests (identical to that of ISO 14851: 1999 and 14852: 1999) and must comply with the following criteria and acceptance levels: in mil In aerobic conditions, the percent biodegradation of the test material should be equal to at least 90% total or 90% of the maximum degradation of an appropriate reference substance once a plateau has been reached for both the test material. test material only for the reference substance (eg cellulose).

The duration of the test must be a maximum of 6 months.

In anaerobic environment, the test period should be a maximum of 2 months and the percent biodegradation based on biogas production should be greater than or equal to 50% of the theoretical value applicable to the test material. - each material subjected to the test must disintegrate during a biological waste treatment process: after a composting process of not more than 12 weeks, a maximum of 10% of the initial dry mass of the material subjected to the test screen may be rejected for a 2 mm mesh void. - the final compost must meet European requirements or, failing that, national requirements relating to the quality of the compost.

In a first aspect, the invention thus relates to a method of manufacturing a biodegradable film having at least two layers of different biodegradable polymers, which have a temperature difference of deflection under load of at least 20 ° C, characterized in that the manufacture is carried out by co-extrusion and that the polymer having the lowest temperature of deflection under load has been supplemented by the addition of inorganic fillers or by organic agents so that its recrystallization temperature is increased .

The term co-extrusion means that each polymer layer of the film has been extruded in an independent screw.

In a preferred embodiment, the co-extrusion is an inflation extrusion.

In another embodiment, the co-extrusion is a flat extrusion.

As discussed above, the two polymers must have a temperature difference of deflection under load of at least 20 ° C, in order to be suitable for use in flowpack packaging methods.

However, it is observed that such a difference in flex temperature under load also induces a difference in recrystallization temperature (recrystallization point) (the polymer with lower flex temperature also has a lower melting point and a recrystallization temperature. lower) which can lead to the phenomenon of "curling" described above.

Thus, the polymer is supplemented with fillers as defined above and below.

The Applicants have in fact shown that the addition of such fillers makes it possible to modify (increase) the recrystallization temperature of the polymer, and thus to allow the manufacture of the multilayer film without a curling effect.

It may also be noted that, owing in particular to its components and to the method of manufacture, the film obtained is a biodegradable plastic film, which can also be qualified as plastic, or thermoplastic.

The examples show that there is no need to drastically increase the recrystallization temperature of the low melting point polymer, but that an increase of 10 ° C, preferably 12 ° C or more, more preferably 14 ° C or more, even more preferably 15 ° C or more may be sufficient.

The manufacture is preferably carried out by inflation extrusion.

Swelling extrusion is a known continuous transformation process, in which the granules (compound) enter a heated tube (extruder) fitted with an endless screw.

These granules can be of a single type or of several types when it is desired to produce a mixture.

The homogenized material is pushed, compressed, then passes through a die.

The polymer thus formed is then expanded with compressed air at the extruder / die outlet.

The exit of the extruder is generally vertical, in particular for reasons of space, and to prevent the film from being unbalanced due to gravity.

Compressed air is blown into the melt which swells and rises vertically in a long bubble of film.

After cooling, rollers flatten the film into a flat sleeve which is cooled and wound up on reels.

This method is well known for obtaining films used in the manufacture of packaging, bin bags, freezer bags, medical infusion bags and flexible and thin sheets of horticultural greenhouse liners.

During the implementation by inflation extrusion, the polymer is in the molten state in the screw and the extrusion head: at the outlet of the die, it is still above its 5 Tm (melting temperature), and can be deformed (stretched and inflated) until reaching its Tc (recrystallization temperature).

It then acquires a frozen state and can hardly be deformed any longer.

The polymers recrystallization temperatures are also intrinsic parameters.

In the principle of producing multilayer films, the die is fed by several single-screw extruders, each screw being able to convey one or more materials: this technology therefore makes it possible to superimpose layers of different materials, and finally to assemble their properties for give the final packaging the characteristics essential to its function, such as sealability, rigidity, barrier properties, etc.

It should be noted that, in this co-extrusion process, the same polymer can be used in several different screws, in order to form superimposed layers composed of the same polymer.

This structure can be verified by analysis of a section of the film, in particular by microscopy.

Each screw is regulated in flow rate and in temperature profile according to the polymer worked, independently of the other screws; in fact, each polymer has its own transformation temperature, a function of its melting point.

The position of each extrusion screw will also determine which layer will be on the inside of the bubble, and which layer will be on the outside.

For example, and concerning biodegradable polymers, it is known that the transformation of copolyesters type PBAT (polybutyleneadipate terephthalate) or PBS (poly (butylene succinate)) is carried out around 140 ° C., while the use of polycaprolactones type PCL (e-polycaprolactone), rather around 100 ° C, and that of PLA (polylactic acid) above 160 ° C.

As seen above, the difficulty lies in the isotropic cooling of the different products: the recrystallization of the different materials can generate phenomena of film twisting (curling), which make the product unsuitable for its subsequent use.

It is also necessary to ensure the interface compatibility of the different layers to prevent delamination of one of the layers of the film.

9 The table below gives the values of Tc for some biodegradable polymers, cooled under fast kinetic conditions.

[Table 1] Tm (° C) H DT B Tc (° C) (t) PBATpolybutyleneadipate terephthalate 115 63 56 PLA polylactibe acid 155 55 n.d.

PBS 115 95 68 PBSApolubultylènesuccinateadip 96 96 n.d. ate PCLprolycaprolactone 60 50 14 PHBVpolyhydoxycobutyratecoval erate 145 107 n.d.

Melting and temperature sag resistance and recrystallization temperatures. n.d: not given.

It is recalled that the films used are biodegradable, and may be of fossil origin, that is to say a plastic material and, in particular a thermoplastic material.

It may be chosen from the group consisting of aliphatic polyesters, aromatic aliphatic polyesters, aliphatic-aromatic co-polyesters and in particular butanediol-adipic and terephthalic acid copolyesters, poly-amides, polyester-amides, polyethers, etc. polyesters - ethers - amides, polyesters - urethanes, polyesters ureas and mixtures thereof.

Biodegradable polymers of microbial or plant origin can also be used, rather than a polymer of fossil origin.

This polymer is then chosen in particular from the group consisting of polylactic acid (PLA) or microbial polymers such as polyalkanoates of the polybutyrate (PHB), polyvalerate (PHV) or polyhydroxybutyratevalerate (PHBV) type.

It is also possible to use a polymer from the family of lactones and polycaprolactones, or mixtures of polymers of microbial and fossil origin.

The polymers poly-ecaprolactone, polyethylene and polybutylene-succinate, polyhydroxybutyratehydroxyvalerate, polylactic acid, polyalkylene-adipate, polyalkylene-adipate-succinate, polyalkylene-adipate-caprolactam, polyalkylene-adipate-E-caprolacther-glycidadolactone, polyalkylene adipate-E-caproletheryl-digidadolactone, E-caprolactone / E-caprolactam, polybutyleneadipate-co-terephthalate, polyalkylene-sebacate, polyalkylene-azelate, their copolymers, and mixtures thereof are also useful in the context of the present invention.

PLA is a linear thermoplastic aliphatic polyester; it is produced by several techniques, in particular azeotropic condensation, polymerization by direct condensation, or polymerization by lactide formation (ring-opening), the most widely used on an industrial scale.

Due to the chiral nature of lactic acid, the stereochemistry of PLA is complex.

Since lactic acid exists in two stereoisomeric forms, the dimer obtained from two lactic acids can be in three different enantiomeric forms.

Subsequently, PLA can exist in three stereochemical forms: poly (L-lactide) (PLLA), poly (D-lactide) (PDLA), and poly (DL-lactide) (PDLLA).

L lactic acid is most preferably synthesized by bacteria.

PDLLA is an amorphous polymer, while the PLLA and PDLA forms are semi-crystalline.

For example, PLLA has a crystallinity of about 37%, a glass transition temperature between 50 and 80 ° C, and a melting temperature between 173 and 178 ° C.

The melting temperature of PLLA can be increased by about 50 ° C by mixing PLLA with PDLA, which then forms a highly regular stereo-complex of greater crystallinity.

The semi-crystalline forms and their mixtures are qualified as "thermally resistant".

When it is desired to use a mixture of polymers, a “compound” is used at the inlet of the extrusion screw, rather than each of the polymers.

This term is well known to those skilled in the art of plastics processing and denotes a ready-to-use molten mixture.

In particular, each granule is composed of a mixture of the two polymers, which could be obtained by mixing the polymers in a "compounding screw".

In a preferred embodiment, the polymer exhibiting the highest melting point (i.e. the highest sag resistance) is selected from the group consisting of aliphatic polyesters, aromatic aliphatic copolyesters 11 compounds, and aliphatic polyesters of the polyhydroxyalkanoate family, and mixtures thereof.

Among the aliphatic polyesters, especially preferred are copolyesters, and in particular polybutylenesuccinate.

Among the compounds of aromatic aliphatic copolyesters, polybutyleneadipateterephatalate and thermally resistant polylactic acid are especially preferred (the proportions are chosen by those skilled in the art according to their needs).

Among the aliphatic polyesters of the polyhydroxyalkanoate family, polyhydroxybutyrateco-valerate is particularly suitable.

In a preferred embodiment, the lower flex temperature polymer (which will also have lower melting and recrystallization temperatures than the other polymer) is selected from the group consisting of polylactones, aromatic aliphatic copolyester compounds and amorphous polylactic acid, and compounds of (polycaprolactone and compounds of amorphous PLA and PBAT).

Among the polylactones, especially preferred are E-polycaprolactones. Among the aromatic aliphatic copolyester compounds, those formed by compounding polybutyleneadipateterephatalate and amorphous polylactic acid are preferred.

It is also possible to use compounds of (polycaprolactone and compounds of amorphous PLA and PBAT).

The Applicants have shown that the addition of additives in polymers with a low melting point makes it possible to increase the recrystallization temperature.

These additives are in particular added to the extrusion screw at the same time as the polymer granules.

These additives can be heterogeneous multiamides, such as N, N, 'N "- tricyclohexyl-1,3,5-benzenetricarboxylamide, hydrazides, and in particular benoylhydrazides, such as octomethylenedicarboxyliquedibenoylhydrazyde or decamethylenedicarboxyliquedibenoylhydraz.

These compounds are generally used in low concentration (less than 1% by weight).

Talc, calcium carbonate, microcrystalline cellulose or glycidyl methacrylate can also be used.

These compounds can be added at concentrations ranging from 1% to 10% by weight, generally greater than or equal to 3% or even 4%, and less than or equal to 8%.

It is preferred to choose talc or calcium carbonate for their great industrial availability, their low cost, and also their ability to be so-called reinforcing fillers when their particle size is small, namely a large specific surface area, measured in BET ( ISO 9277) greater than 15 m2 / g.

These fillers are used at concentrations typically less than 10%.

The method described above is particularly suitable for polymers exhibiting flexing temperatures which differ by at least 25 ° C, or even at least 30 ° C, or even at least 35 ° C, or even at least. 40 ° C.

Some embodiments are shown in the table below [Table 2] High Load Polymer Polymer Number of low melting temperature layers melting temperature Film Polybutylenesuccinate (PBS) Aliphatic copolyester compound 2 A aromatic carbonate and 8% calcium Amorphous PLA Film 1 PBS Polycaprolactone 3% talc 3 B 2 Aromatic aliphatic copolyester / highly crystallized PLA Film Aliphatic copolyester Compound aliphatic copolyester glycidylmethacrylate 0.5% 3 C aromatic / aromatic and highly crystallized PLA Amorphous PLA 15 Examples of films obtained by the implementation of the method described above.

In one embodiment, the film has two layers, the high temperature sag layer being formed of polybutylene succinate and the lower temperature sag layer being formed of polycaprolactones supplemented with talc.

In another embodiment, the film has more than two layers.

In particular, it comprises two layers at high temperature of sag, consisting respectively of polybutylenesuccinate, a compound of an aromatic aliphatic copolyester and polylactic acid (generally heat resistant) optionally additivated with glycidyl methacrylate, the layer at more low sag temperature being formed of polycaprolactones additivated with microcrystalline cellulose.

The present method is particularly advantageous for obtaining films that can be used for packaging fruits & vegetables, that is to say films that are waterproof, but allowing breathing (exchanges of water vapor and / or water vapor). oxygen or CO2) with the outside of the packaging, preventing fogging and good preservation of the products.

It is possible in particular to use a film having: A layer: PBAT resin loaded with PLA (thermally resistant) A layer: PCL loaded with talc (which allows good nucleation / crystallization on cooling).

It should be noted that it is not necessary to micro-perforate the films, this permeability property being able to be adjusted by a person skilled in the art by varying the proportions of the parameters, the thickness of the layers, the nature or the concentration of charges ...

Thus, it is advantageous to produce multilayer films by co-extrusion and in particular by inflation extrusion: it is possible to obtain water vapor permeability (VVVTR) of such biodegradable films allowing good gas exchange, in particular during temperature changes. (fridge outlet / inlet), and thus avoiding the appearance of dew points inside the packaging, often leading to the onset of deterioration of the food and less good storage.

It is thus preferred when the films obtained exhibit a transmission of water vapor of between 200 and 1000 g / m '/ 24h at 38 ° C at 90% relative humidity 14 (RH) and / or a transmission of oxygen included. between 2500 and 6000cm3 / m2 / 24h at 23 ° C at 50% relative humidity.

In a particular embodiment, it is also possible to play on the diffraction of the film obtained, that is to say the transparency of the films.

To do this, organic fillers are preferably used, in particular glycidyl methacrylate (ester of methacrylic acid and glycidol) as filler, which can also be added to the barrier film layer (at a higher temperature. sag).

In particular, this filler is suitable when this layer is a compound containing thermally resistant PLA, since it also makes it possible to disperse the PLA phase in the phase of the other, the small size of the PLA in this layer allowing better transparency.

Thus, the method makes it possible to obtain a film which has a transmittance in the visible greater than 80%, preferably greater than 90%, or greater than 95% (400 to 800 nm), which means 80%, 90 % or 95% (respectively) of the visible light passes through the film allowing a good identification of the foods through the biodegradable multilayer film.

Films of varying thicknesses can be made by the co-extrusion methods presented (swelling or flat extrusion).

It is preferred when the total thickness of the film is 10 microns or more.

Preferably, it does not exceed 200 microns.

The layer formed of high temperature load deflection polymer consists of 50% or more (up to 75%) of the thickness of the film.

Accordingly, the layer at the lowest load deflection temperature consists of at most 50%, and generally at least 25%, of the thickness of the film.

These percentages remain valid for all the layers having the same temperature properties of deflection under load, when the film contains several layers.

The invention also relates to a biodegradable multilayer film having and consisting of at least two layers of different polymers, which have a temperature difference of deflection under load of at least 20 ° C, the polymer having the temperature of flexion under load. under the lowest load having been supplemented by the addition of inorganic fillers or by organic agents so that its recrystallization point is increased.

As seen above, these polymers are biodegradable, and are in particular chosen from those listed above.

In a particular embodiment, this film can be obtained by a method as described above.

The films described above and in the examples are thus objects of the invention.

The above films are particularly suitable for use in a flowpack packaging method, for the uses mentioned above, and in particular the packaging of fruits and vegetables.

DESCRIPTION OF THE FIGURES FIG. 1: evolution of the modulus of polymers as a function of temperature.

Dotted line: film A.

Full line: film B.

FIG. 2: evolution of the storage modulus as a function of temperature by dynamic mechanical analysis.

Dotted line: film A.

Full line: film B.

EXAMPLES The examples below are given to illustrate certain embodiments of the invention and to provide those skilled in the art with certain indications for characterizing polymers and obtaining films in accordance with the invention.

To do this, certain polymers may not be specified, if the example aims to illustrate a particular method of selecting polymers.

Those skilled in the art can use these teachings for the choice of polymers and fillers according to the targeted applications.

25 Example 1.

Characterization of polymers The melting point and heat resistance (HDT B) are not correlated.

Some examples are given in Table 1 above for some common biodegradable polymers.

In addition, the thermal behavior over a temperature range is also not identical between 2 polymers having identical or very close HDT B values (Figure 1).

In figure 1, we see that for a value of HDT B close to 50 ° G, the polymer A (dotted lines) will have a more progressive bending at temperature while the polymer B (solid line) will bend very quickly over a range of temperature 16 reduced until it melts at around 60 ° C.

The behavior of polymer B does not allow industrial work because its functional range is too narrow.

Example 2.

Addition of filler in a polymer 5 The introduction of Calcium Carbonate into a matrix composed of a PBAT / PLA mixture does not modify the melting temperatures of the 2 polymers in mixture, respectively around 125 ° C and 170 ° C, but the recrystallization of the whole is clearly modified, going from 55 ° C without Calcium Carbonate to 81 ° C with Calcium Carbonate, introduced at 8% w / w.

10 This is also observed for other polymers: by choosing a PCL (polycaprolactone) with a Tm of 58 ° C, the recrystallization of the pure polymer is at 13 ° C, but passes to 27 ° C when 3% is added. talcum powder.

Thus, the use of specific fillers makes it possible to increase the recrystallization temperature and thus to reduce the structural constraints appearing due to the difference in recrystallization temperatures, and thus to retain functional dimensional properties for use in packaging. food.

Example 3.

Mechanical properties The multilayer film used to produce the packaging must have sufficient mechanical properties for machine passage, flowpack for example, for storage and handling with the packaged food during its life cycle, without deterioration of the product. its integrity.

It must have sufficient rigidity for its good machinability, but not too much at the risk of no longer having plastic elongation capacity and of breaking rapidly.

This function must be provided by the layer (s) of structures, which must in addition have a melting point much higher than the welding layer.

We can choose the best material for the intended application, in particular the 30 packaging Flowpack, by following the evolution of the storage modulus as a function of the temperature from 30 ° C up to more than 100 ° C by dynamic mechanical analysis (DMA ).

FIG. 2 thus shows that, for the same HDT B located at around 90/92 ° C., a polymer A (dotted lines) can prove to be much more rigid at room temperature than a polymer B (solid line).

However, by following the evolution of the modulus, it can be shown that the polymer B, which is more ductile, will exhibit a higher functionality by virtue of its ability to withstand moderate elongation (160% at break) during passage through the machine or at break. handling, without breaking immediately, for a stress level identical to polymer A, close to 25 MPa.

Polymer B may therefore be more suitable for industrial use than polymer A.

Example 4.

Permeability The multilayer swelling extrusion process has the advantage of retaining the barrier properties specific to each layer of the film, which would not be possible if the different polymeric materials were mixed in the same screw, since one would change. then at least the glass transition temperature (induced plasticization effect), and probably the free volume.

Thus, Messin et al (ACS Appl.

Mater.

Interfaces 2017, 9, 34, 29101-29112) 15 report an improvement in permeability for multilayer films obtained by co-extrusion.

Example 5.

Specific examples A.

Three-layer film - bimaterial 20 Polybutylenesuccinate alone: high HDT but mechanical fragility Compound of PBAT and PLA: low HDT B but good elongation Film obtained by inflation extrusion, with a thickness of 110 micrometers, with a layer of 27.5 μm of Compound of PBAT and amorphous PLA and 2 layers of Polybutylenesuccinate for a total thickness of 82.5 μm: the coextruded film 25 has the advantage of having the mechanical and thermal properties of the 2 original polymers, with a high HDT B, and elongation properties of at least 150 ° / ().

In this example, the PBAT layer is not between the two PBS layers which are superimposed.

Regarding the gas permeability properties of the bimaterial three-layer film, the following values are measured, according to the standards defined above: VVVTR: 125 g / m2 / 24h at 23 ° C 50% RH and 625 g / m2 / 24h at 38 ° c 90% RH OTR: 3350 cm3 / m2 / 24h at 23 ° c 50% RH The permeability properties of the most barrier polymer in monolayer film in 25 μm are given by the manufacturer at: 35 WVTR: 500 g / m2 / 24h at 38 ° c 90% RH 18 OTR: 6700 cm3 / m2 / 24h at 23 ° c 50% RH The permeability to water vapor (WVTR) of such a biodegradable film is particularly advantageous because it is used as Flowpack packaging for fruits and vegetables, it will allow a good gas exchange especially during the 5 temperature changes.

B.

Three-layer film - three-material c-polycaprolactone alone: low melting point layer (HDT B around 50 ° C) Compound of PBAT and semi-crystalline PLA alone: first structure layer 10 with good elongation properties Polybutylenesuccinate alone: high point layer melting (HDT B around 95 ° C); 3-layer and three-material coextruded film: the coextruded film has the advantage of having very good mechanical properties and 2 layers having very different thermal behavior, with a difference in HDT B greater than 20 ° C.

The polymer having the highest HDT B will preferably be placed in the central layer of the film, but also with the possibility of being on the outer layer.

In all cases, the polymer with the lowest HDT B will be on the inner layer or on the outer layer of the three-layer film.

The preceding three-layer coextruded film, with a thickness of 30 μm, allows easy processing in a flowpack.

For example, on a ULMA ATLANTIS 23 industrial machine, it is advantageously implemented with the following operating conditions: - 65 ° C long flesh / flesh welding; very good quality and resistance to bursting - Flesh / flesh weld cutter: 90 ° C; very good quality and resistance to bursting Test rate at 25 and 35 cps / min, identical to the traditional non-biodegradable film 30 The low-melting point layer therefore makes it possible to obtain good welding qualities, with good processing above the Tm (50 ° C), but below the Tm of one of the structural polymers (95 ° C).

19 We also note the good transparency of the film, greatly improved by the structure extruded by inflation extrusion rather than monolayer.

Indeed, the coextruded film has a visible transmittance greater than 95% (400 to 800 nm); 95% of the visible light passes through the film 5 allowing good identification of the foods through the biodegradable multilayer film.

vs.

Transparency It is advantageous to manufacture multilayer films by swelling extrusion with different polymers to play on their refractive index, and thus obtain greater transparency of the film.

Thus, a film A obtained by monolayer extrusion by mixing 3 materials (PBAT, PLA and starch) exhibits an average transmittance of 75% in the visible range, whereas a three-layer film B film obtained according to the method according to the invention, and comprising the same isocomposition polymers exhibits a transmittance of greater than 80%.

Claims (11)

CLAIMS 1. Method of manufacturing a biodegradable film having at least two layers of different biodegradable polymers, which have a temperature difference of deflection under load of at least 20 ° C, characterized in that the manufacture is carried out by co-extrusion and that the polymer exhibiting the lowest load deflection temperature has been supplemented by the addition of inorganic fillers or by organic agents so that its recrystallization point is increased. 2. Method according to claim 1, characterized in that the biodegradable polymer at the highest bending temperature under load is chosen from the group consisting of aliphatic polyesters, in particular copolyesters, in particular polybutylenesuccinate, compounds of aromatic aliphatic copolyesters, in particular. polybutyleneadipatetéréphatalate, and thermally resistant polylactic acid and aliphatic polyesters of the polyhydroxyalkanoate family, in particular polyhydroxybutyrateco-valerate, and mixtures thereof. 3. Method according to claim 1 or 2, characterized in that the polymer at the lowest sag temperature under load is chosen from the group consisting of polylactones, in particular s-polycaprolactones, compounds of aromatic aliphatic copolyesters, such as polybutyleneadipatetéréphatalate. (PBAT), and amorphous polylactic acid (PLA), and compounds of (polycaprolactone and compounds of amorphous PLA and PBAT). 4. Method according to one of claims 1 to 3, characterized in that the additives are chosen from the group consisting of heterogeneous multiamides, in particular N, N, 'N "-tricyclohexy1-1,3,5-benzenetricarboxylamide, hydrazides, in particular octomethylenedicarboxyliquedibenoylhydrazyde or decamethylenedicarboxyliquedibenoylhydrazyde, talc, calcium carbonate, microcrystalline cellulose, glycidylmethacrylate and mixtures thereof. 21 5. Method according to one of claims 1 to 4, characterized in that the deflection temperatures under load differ from at least 30 ° C, or even at least 40 ° C. 5 6. Method according to one of claims 1 to 5, characterized in that the coextrusion is an inflation extrusion. 7. Method according to one of claims 1 to 6, characterized in that the film 10 has two layers, the high temperature sag layer being formed of polybutylenesuccinate and the layer at lower sag temperature being formed of polycaprolactones with additives. talc 8. Method according to one of claims 1 to 6, characterized in that the film 15 has more than two layers and that it comprises two layers at high charging temperature, consisting respectively of polybutylenesuccinate, of a compound of a An aromatic aliphatic copolyester and polylactic acid optionally additivated with glycidyl methacrylate, the lower deflection layer being formed of polycaprolactones supplemented with microcrystalline cellulose. 9. Method according to one of claims 1 to 8, characterized in that the film has a transmission of water vapor of between 200 and 1000 g / m2 / 24h at 38 ° C at 90% relative humidity and / or an oxygen transmission of between 2500 and 6000cm3 / m2 / 24h at 23 ° C at 50% relative humidity. 10. Biodegradable multilayer film obtainable by a method according to one of claims 1 to 9. 30 11. Use of a multilayer film according to claim 10 in a flowpack packaging method.