WO2020079202A1

WO2020079202A1 - Multilayer biodegradable film

Info

Publication number: WO2020079202A1
Application number: PCT/EP2019/078310
Authority: WO
Inventors: Laurent Massacrier; Jean Mattieu BROUILLAT; Joseph THIBIERGE
Original assignee: Cdl; Leygatech
Priority date: 2018-10-20
Filing date: 2019-10-18
Publication date: 2020-04-23
Also published as: FR3087384A1; EP3867056A1; FR3087384B1

Abstract

The invention relates to a biodegradable plastic film that can be used in flow pack type packaging methods, having at least two layers, formed of at least two different polymer materials having a difference in deflection temperature under load, and also to a method for manufacturing such a film.

Description

MULTI-LAYER BIODEGRADABLE FILM

The invention relates to a biodegradable plastic film usable in flowpack-type packaging processes, having at least two layers, and at least two different polymeric 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 wraps 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 salting, but also finds applications in the field cosmetics, pharmaceuticals, communication (cards, gadgets, printed products ...) or industry (pens, cutter ...).

This packaging system is used to package products in trays as well as bulk products. It is particularly suitable for packaging single or small quantities of products, in particular samples, or sub-packaging in cardboard packaging (cookies, confectionery ...) or in molded cellulose.

It is essentially a question of forming a sheath around the product by carrying out a longitudinal weld and of closing the film by welding of the ends of the sachet. The head, foot and back welds are generally embossed welds.

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

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

The films used to date for flowpack applications are essentially based on fossil materials, such as for example multilayer films made 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. Current Flowpack films for fruit and vegetable packaging are mainly coextruded BOPP films. Some are laser microperforated to provide breathing. Other solutions are PET / PE (polyester / polyethylene) laminated films, in which the polyester provides thermal resistance and the PE the weld. One of the problems with these films is the requirement for microperforation to allow breathing, these plastics being essentially completely waterproof and hermetic.

Thanks to their performance and their specific properties, biodegradable bioplastics successfully penetrate certain niche and mass markets: bags, in particular fruit 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 matrices by industrialists or universities, they are not necessarily adapted to the constraints of the market or the industrial sector.

It is therefore advisable 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 flowpack method.

Patent application JP 2004114582 describes a method of manufacturing a packaging film having at least two layers of different polymers. These films (PET and PEN) have a deflection temperature difference under load of at least 20 ° C, and the production is carried out by flat co-extrusion. Inorganic particles are added to what is called "polyester resin raw material", that is to say the layer (C) of PEN, which exhibits the highest deflection temperature under load. Furthermore, the polymers used in this patent application (PET and PEN) are not biodegradable. WO2009014313A1 describes a biaxially oriented and biaxially oriented biodegradable laminated film comprising at least a first layer of resin and at least a second layer of resin which are laminated together alternately, the first and second layers of resin containing as main components respectively a polymer based on polylactic acid and a polyester-based aromatic resin, which exhibit biodegradability, flexibility, increased gas barrier property and thermal resistance, useful for ecological packaging.

WO2017207662A1 relates to a heat-shrinkable multilayer thermoplastic film which forms a barrier to gases, suitable for the manufacture of packaging and comprising a first outer sealing layer, a second outer polyester layer, an inner barrier layer, no layer (s) polyamide or polyester inner (s), no polyolefin layers placed between the barrier layer and the sealing layer and at least one bulk polyolefin layer of specific relative thickness placed between the inner barrier layer and the polyester layer outside.

These biodegradable films must consist of at least two layers of different polymers:

A layer of structure that achieves the desired stiffness, mechanical strength, and that can determine how the package will tear. This layer provides the overall mechanical properties of the package. It generally has a high melting point, and a high resistance to flexing at temperature (also called HDT).

A layer of solder, which is intended to allow the film to be closed by soldering. This layer should have a low melting point, so that the welding 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 for 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 layer of polymer ensuring the sealing function, and one or more other so-called structural layers, allowing an effective and clean cutting of each pack. This or these layers must be rigid enough to maintain the film during its passage through the Flowpack machine, and not melt during the production of the weld, which would cause burrs or rupture of the seal: the packaging would then lose its integrity and functionality.

Thus, the two polymers must have:

A difference in the melting temperature to allow welding A difference in HDT (resistance to deflection at temperature), so that the film can be used in the flowpack method without it collapsing 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 the phenomena of “curling” during the production of the multilayer film, that is to say the bending of a layer (layer at high crystallization temperature) relative to to the other layer if the recrystallization of this other layer (inducing a shrinkage of the film) takes place at a temperature too far from that of the layer at high crystallization temperature.

The deflection resistance at temperature (also called HDT, deflection temperature under load, or temperature of thermal distortion) is a characteristic of a film which is known in the art and which is measured by standardized methods. This is the temperature at which normalized 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). We can thus characterize a film by HDTB (deflection temperature under load measured by method B of the aforementioned standard). This material-dependent constant (and the norm used for the measurement) can therefore be considered to reflect the “rigidity” of the material as the temperature increases.

Industrially, a normative test known as deflection temperature under load (HDT) is used: the test piece is placed on two supports 100 mm apart in an oven whose temperature rise 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 charges of 0.45 MPa (HDT B method). The the lowest deflection is 0.25 mm. We can use the DMA (Dynamic Mechanical Analyzer) tool, and follow the evolution of conservation of the elastic module under a temperature ramp: we therefore record the resistance capacity of the material over a wide thermal range, potentially up to the melting of the polymer, 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 referent ISO test.

The present invention provides a method for manufacturing 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 trash of fermentable household waste, without the need for incineration or the problem of recycling .

b. Be composed of several materials and have at least two layers: one of the film layers has a lower melting point than the other or the others, and the polymers have a HDT B difference of at least 20 ° C . This thermal difference facilitates machine passage during packaging, with Flowpack technology for example for Fruits and Vegetables. Indeed, the layer with low melting point allows the packaging to be welded around the food, while the layer (s) with the highest melting point ensure the structure and cohesion of the packaging, also allowing cutting efficient and clean 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.

d. have sufficient mechanical properties for the intended use, and in particular to withstand the stresses during its use, handling and storage.

e. preferably allow controlled breathing of food by adjusting the barrier properties (water vapor and / or oxygen), depending on the packaged food and its 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 with standards ASTM E96, DIN 53122 or ISO 2528 for WVTR, and standards ASTMD3985, ASTM F 1927, DIN 53380-3 or JIS K-7126 for the OTR.

By “biodegradable” is meant in the context of the present invention any biological, physical and / or chemical degradation, at the molecular level, of substances by the action of environmental factors (in particular enzymes derived from the metabolism processes of microorganisms) . Many definitions have been adopted for biodegradation (ISO 472-1998, ASTM subcommittee D20-96, DIN 103.2-1993), depending on the 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). Thus, this term is known in the art and polymers can be classified according to their biodegradability or not. In particular, some fossil polymers are clearly non-biodegradable.

Mention may be made of standard EN 13432 which defines the requirements relating to biodegradable packaging which can be reused in industrial composting, to be used within the scope of the invention. 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 lower than the threshold indicated in the latter

- the biodegradability must be determined for each packaging material or each significant organic component of the packaging material, by significant is meant any organic component 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% - each material subjected to 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 criteria and levels of following acceptance: in aerobic environment, the percentage of biodegradation of the test material must be at least 90% in total or at least 90% of the maximum degradation of an appropriate reference substance once a plateau has been reached both for the test material and for the reference substance (eg cellulose). The duration of the test must be a maximum of 6 months. In an anaerobic environment, the test period must be a maximum of 2 months and the percentage of biodegradation based on the production of biogas must 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 12 weeks at most, a maximum of 10% of the initial dry mass of the material subjected to the test sieving can be refused for a mesh vacuum of 2 mm.

- the final compost must meet European requirements or, failing this, national requirements relating to the quality of the compost.

A certain number of polymers and in particular those mentioned below meet the conditions of this standard and are therefore biodegradable polymers, in general, and more particularly in connection with standard EN 13432.

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 deflection temperature difference 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 deflection temperature under load has been supplemented by addition of inorganic fillers or with organic agents so that its recrystallization temperature is increased.

The term co-extrusion means that each layer of polymer in 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 seen above, the two polymers must have a deflection temperature difference under load of at least 20 ° C, in order to be used in flowpack packaging methods. However, it is observed that such a difference in deflection temperature under load also induces a difference in recrystallization temperature (recrystallization point) (the polymer at lower deflection temperature also has a lower melting point and a recrystallization temperature weaker) 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 the curling effect.

It can also be noted that, due in particular to its components and the manufacturing method, the film obtained is a biodegradable plastic film, which can also be described as plastic, or thermoplastic.

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

The manufacturing is preferably carried out by inflation extrusion. Extrusion inflation is a known process of continuous transformation, in which the granules (compound) enter a heated tube (extruder) provided with a worm. 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 outlet of the extruder / die. The outlet 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 molten material which swells and rises vertically in a long bubble of film. After cooling, rollers flatten the film into a flat sheath which is cooled and wound on reels. This method is well known for obtaining films used in the manufacture of packaging, garbage bags, freezer bags, medical bags for infusion and flexible and thin sheets of coatings for horticultural greenhouses.

During processing 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 Tf (melting temperature), and can be deformed (stretched and swollen) until reaching its Te (recrystallization temperature). It then acquires a frozen state and can almost no longer be deformed. The recrystallization temperatures of the polymers 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 to confer in the final packaging the characteristics essential to its function, such as sealability, rigidity, barrier properties ...

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 adjusted in flow rate and temperature profile according to the polymer worked, independently of the other screws; indeed, each polymer has its own transformation temperature, a function of its melting temperature. The location of each extrusion screw will also determine which layer will be inside the bubble, and which layer will be 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 at 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 various products: the recrystallization of the various materials can generate phenomena of film twisting (curling), which render the product unsuitable for its subsequent use. It is also important to ensure the interface compatibility of the different layers to prevent delamination of one of the layers of the film. The table below gives the Te values for some biodegradable polymers, cooled under rapid kinetic conditions.

[Table 1]

Melting temperatures and resistance to deflection at temperature and recrystallization n.d: not given.

It will be recalled that the films used are biodegradable, and can be of fossil origin, that is to say a plastic material, and in particular a thermoplastic material. It can be chosen from the group consisting of aliphatic polyesters, aromatic aliphatic polyesters, aliphatic-aromatic co-polyesters and in particular copolyesters of butanediol-adipic and terephthalic acids, polyamides, polyester-amides, polyethers , polyesters - ethers - amides, polyesters - urethanes, polyesters - ureas and their mixtures.

Biodegradable polymers of microbial or vegetable 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 origin and of fossil origin. Polymers poly-e-caprolactone, polyethylene and polybutylene-succinate, polyhydroxybutyrate-hydroxyvalerate, polylactic acid, polyalkylene-adipate, polyalkylene-adipate- succinate, polyalkylene adipate-caprolactam, polyalkylene adipate-e- caprolactone, diglycidyl ether-diphenol polyadipate, poly-e-caprolactone / e- caprolactam, polybutylene adipate-co-terephthalate, polyalkylene-sebacate, polyalkylene, polyalkylene their mixtures can also be used in the context of the present invention.

PLA is a linear thermoplastic aliphatic polyester; it is produced by several techniques, notably azeotropic condensation, polymerization by direct condensation, or polymerization by lactide formation (ring-opening), the most used on an industrial scale. Due to the chiral nature of lactic acid, the stereochemistry of PLA is complex. As lactic acid exists in two stereoisomeric forms, the dimer obtained from two lactic acids can be present 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 very preferentially synthesized by bacteria.

PDLLA is an amorphous polymer, while the PLLA and PDLA forms are semi-crystalline. For example, PLLA has a crystallinity of around 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 approximately 50 ° C by mixing PLLA with PDLA, which then form a highly regular stereo-complex with greater crystallinity. Semi-crystalline forms and their mixtures are described as “thermally resistant”.

When we want to use a mixture of polymers, we use a "compound" at the entry of extrusion screws, rather than each of the polymers. This term is well known to those skilled in the art of the plastics industry and designates 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 having the highest melting point (that is to say the highest flexural strength) is chosen from the group consisting of aliphatic polyesters, copolyester compounds aromatic aliphatics, and aliphatic polyesters of the polyhydroxyalkanoate family, and mixtures thereof.

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

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

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

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

Among the polylactones, e-polycaprolactones are particularly preferred,

Among the compounds of aromatic aliphatic copolyesters, 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 notably 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 benoylhydrazydes, such as octomethylenedicarboxyliquedibenoylhydrazyde or decamethylenedicarboxyliquedibenoylhydrazides. low concentration (less than 1% by weight).

Talc, calcium carbonate, microcrystalline cellulose or glycidylmethacrylate can also be used. These compounds can be added to 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%.

We prefer to choose talc or calcium carbonate for their high 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, measure in BET (ISO 9277) greater than 15 m ² / g.

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

The method described above is particularly suitable for polymers having deflection temperatures which differ from 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 presented in the table below

[Table 2]

Examples of films obtained by the implementation of the method described above. In one embodiment, the film has two layers, the high deflection temperature layer being formed of polybutylene succinate and the lower deflection temperature layer being formed of talc additive polycaprolactones.

In another embodiment, the film has more than two layers. In particular, it comprises two layers at high deflection temperature, consisting respectively of polybutylenesuccinate, of a compound of an aromatic aliphatic copolyester and of polylactic acid (generally with thermal resistance) optionally additive with glycidyl methacrylate, the lower layer deflection temperature being formed of polycaprolactones with microcrystalline cellulose additive.

The present method is particularly advantageous for obtaining films which can be used for the packaging of fruit & vegetables, that is to say films which are waterproof, but which allow breathing (exchanges of water vapor and / or oxygen or C0 ₂ ) with the outside of the packaging, preventing fogging and good preservation of the products.

One can use in particular a film having:

One layer: PBAT resin loaded with PLA (heat resistant)

A layer: PCL loaded with talc (which allows good nucleation / crystallization during 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 load concentration ...

Thus, it is advantageous to produce multilayer films by co-extrusion and in particular in inflation extrusion: it is possible to obtain a permeability to water vapor (WVTR) of such biodegradable films allowing good gas exchange in particular during temperature changes ( exit / entry fridge), and thus avoiding the appearance of dew points inside the packaging, often leading to the start of degradation of the food and less good conservation.

It is thus preferred when the films obtained have a water vapor transmission of between 200 and 1000 g / m ² / 24h at 38 ° C. at 90% relative humidity (RH) and / or oxygen transmission between 2500 and 6000cm ³ / m ² / 24h at 23 ° C at 50% relative humidity.

In a particular embodiment, one can also 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 higher temperature deflection). In particular, this charge 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 from 80%, 90% or 95% (respectively) of visible light passes through the film allowing good identification of food through the biodegradable multilayer film.

Films of various thicknesses can be made by the co-extrusion methods presented (inflation or flat extrusion). It is preferred when the total film thickness is 10 microns or more. Preferably, it does not exceed 200 microns. The layer of polymer under high temperature deflection under load consists of 50% or more (up to 75%) of the film thickness. Consequently, the layer at the lowest deflection temperature under load consists of at most 50%, and generally at least 25% of the film thickness. These percentages remain valid for all the layers having the same deflection temperature properties 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 deflection temperature difference under load of at least 20 ° C., the polymer having the deflection temperature under lowest charge having been supplemented by addition of inorganic fillers or with organic agents so that its recrystallization point is increased. As well as seen above, these polymers are biodegradable, and are chosen in particular from those listed above.

In a particular embodiment, this film is capable of being 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

Figure 1: evolution of the polymer module as a function of temperature. Dotted line: film A. Solid line: film B.

Figure 2: evolution of the conservation module as a function of temperature by dynamic mechanical analysis. Dotted line: film A. Solid 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, some 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 lessons for the choice of polymers and fillers according to the intended applications.

Example 1. Characterization of polymers

The melting temperature 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 with identical or very similar HDT B values (Figure 1).

In FIG. 1, it can be seen that for an HDT B value close to 50 ° C., the polymer A (dotted lines) will have a more progressive bending at temperature while the polymer B (solid line) will flex very quickly over a range of temperature reduced until it melts 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

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.

This is also observed for other polymers: by choosing a PCL (polycaprolactone) with a Tf of 58 ° C, the recrystallization of the pure polymer is at 13 ° C, but goes to 27 ° C when adding 3% of talc.

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

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 foodstuff during its life cycle, without deterioration of its integrity.

It must have enough rigidity for its good machinability, but not too much at the risk of no longer having a plastic elongation capacity and of breaking quickly. This function must be provided by the layer or layers 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 Flowpack packaging, by following the evolution of the preservation module according to the temperature from 30 ° C to more than 100 ° C by dynamic mechanical analysis (DMA) .

FIG. 2 thus shows that, for the same HDT B situated around 90/92 ° C., a polymer A (dotted lines) can prove to be much more rigid at ambient temperature than a polymer B (solid line). However, following the evolution of the module, we can show that polymer B, which is more ductile, will have superior functionality due to its ability to resist moderate elongation (160% at break) during machine passage or handling, without immediately breaking, for a level of stress identical to polymer A, close to 25 MPa.

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

Example 4. Permeability

The multilayer inflation extrusion process has the advantage of retaining the barrier properties of each layer of the film, which would not be possible if the different polymeric materials were mixed in the same screw, since we would then change minimum 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) report an improvement in permeability for multilayer films obtained by co-extrusion.

Example 5. Specific examples

A. Three-layer film - bi-material

Polybutylenesuccinate alone: high HDT but mechanical brittleness

Compound of PBAT and PLA: weak HDT B but good elongation

Film obtained by swelling extrusion, with a thickness of 1 10 micrometers, with a layer of 27.5 μm of amorphous PBAT and PLA compound and 2 layers of Polybutylenesuccinate for a total thickness of 82.5 μm: the coextruded film has 1 '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 layers of PBS which are overlapped.

Concerning the gas permeability properties of the two-layer three-layer film, the following values are measured, according to the standards defined above:

WVTR: 125 g / m ² / 24h at 23 ° c 50% RH and 625 g / m ² / 24h at 38 ° c 90% RH

OTR: 3350 cm ³ / m ² / 24h at 23 ° c 50% RH

The permeability properties of the most barrier polymer in single-layer film in 25 μm are given by the manufacturer to:

WVTR: 500 g / m ² / 24h at 38 ° c 90% RH OTR: 6700 cm ³ / m ² / 24h at 23 ° c 50% RH

The water vapor permeability (WVTR) of such a biodegradable film is particularly advantageous because when used as flowpack packaging for fruits and vegetables, it will allow a good gas exchange, especially during temperature changes.

B. Three-layer film - three-dimensional

e-polycaprolactone alone: layer with low melting point (HDT B around 50 ° C)

Compound of semi-crystalline PBAT and PLA alone: first layer of structure with good elongation properties

Polybutylenesuccinate alone: layer with high melting point (HDT B around 95 ° C);

Coextruded 3-layer and three-layer film: the coextruded film has the advantage of having very good mechanical properties and 2 layers with very different thermal behaviors, with an HDT B difference 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 located on the outer layer. In all cases, the polymer having the lowest HDT B will be located 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 implementation in Flowpack. For example, on an ULMA ATLANTIS 23 industrial machine, it is advantageously used with the following operating conditions:

• Flesh / long flesh weld: 65 ° C; very good quality and burst resistance

• Flesh / flesh sealer: 90 ° C; very good quality and burst resistance

• Cadence: tests at 25 and 35 cps / min, identical to the traditional non-biodegradable film

The layer with a low melting point therefore makes it possible to obtain the good welding qualities, with applications well above the Tf (50 ° C.), but below the Tf of one of the structural polymers (95 ° C). The good transparency of the film is also noted, greatly improved by the structure extruded by inflation extrusion rather than in monolayer.

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

C. Transparency

It is advantageous to manufacture multilayer films by inflation 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) has an average transmittance of 75% in the visible range, while a three-layer film B film obtained according to the method according to the invention, and comprising the same isocomposition polymers has a transmittance greater than 80%.

Claims

1. Method of manufacturing a biodegradable film having at least two different layers of biodegradable polymers, which have a deflection temperature difference 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 deflection temperature under load has been supplemented by addition of inorganic fillers or with organic agents so that its recrystallization point is increased.

2. Method according to claim 1, characterized in that the biodegradable polymer at deflection temperature under the highest load is chosen from the group consisting of aliphatic polyesters, in particular copolyesters in particular polybutylenesuccinate, compounds of aromatic aliphatic copolyesters, in particular polybutyleneadipateterephatalate, and thermally resistant polylactic acid and aliphatic polyesters of the family of polyhydroxyalkanoates, in particular polyhydroxybutyrateco-valerate, and their mixtures.

3. Method according to claim 1 or 2, characterized in that the polymer at the lowest load deflection temperature is chosen from the group consisting of polylactones, in particular e-polycaprolactones, aromatic aliphatic copolyester compounds, such as polybutyleneadipateterephatalate (PBAT), and amorphous polylactic acid (PLA), and compounds of (polycaprolactone and amorphous PLA and PBAT compounds).

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 "-tricyclohexyl-1, 3,5-benzenetricarboxylamide, hydrazides, in particular octomethylenedicarboxyliquedibenoylhydrazyde or decamethylenedicarboxyliquedibenoylhydrazyde, talc, calcium carbonate, microcrystalline cellulose, glycidylmethacrylate and mixtures thereof.

5. Method according to one of claims 1 to 4, characterized in that the deflection temperatures under load different from at least 30 ° C, or even at least 40 ° C.

6. Method according to one of claims 1 to 5, characterized in that the co-extrusion is an inflation extrusion.

7. Method according to one of claims 1 to 6, characterized in that the film has two layers, the high deflection temperature layer being formed of polybutylenesuccinate and the lower deflection temperature layer being formed of polycaprolactones with talc additives

8. Method according to one of claims 1 to 6, characterized in that the film has more than two layers and that it comprises two layers at high loading temperature, consisting respectively of polybutylenesuccinate, of a compound of a copolyester aromatic aliphatic and polylactic acid optionally additive glycidyl methacrylate, the layer at lower deflection temperature being formed of polycaprolactones additive microcrystalline cellulose.

9. Method according to one of claims 1 to 8, characterized in that the film has a transmission of water vapor between 200 and 1000 g / m ² / 24h at 38 ° C at 90% relative humidity and / or an oxygen transmission between 2500 and 6000cm ³ / m ² / 24h at 23 ° C at 50% relative humidity.

10. Biodegradable multilayer film capable of being obtained by a method according to one of claims 1 to 9.

1 1. Use of a multilayer film according to claim 10 in a flowpack packaging method.