EP2449032A1

EP2449032A1 - Method for producing a biodegradable material

Info

Publication number: EP2449032A1
Application number: EP10742189A
Authority: EP
Inventors: Nadège LIBE; Kareine Rigal
Original assignee: Ulice SA
Current assignee: Carbiolice SAS
Priority date: 2009-07-03
Filing date: 2010-07-02
Publication date: 2012-05-09
Also published as: CN102482499A; BRPI1010196A8; CN102482499B; FR2947557A1; US20120157581A1; IN2012DN00332A; WO2011001128A1; BRPI1010196A2; FR2947557B1

Abstract

The invention relates to a method for developing a biodegradable material, produced from polymers and meal, wherein the meal is processed with a plasticizing agent in a double screw extruder having a diameter D, over a length of at least 6 D.

Description

PROCESS FOR PRODUCING BIODEGRADABLE MATERIAL

The present invention relates to a method of manufacturing a biodegradable material made from polymers and flours, preferably cereals. Such biodegradable materials are intended to replace synthetic polymeric materials traditionally used in applications such as packaging, the manufacture of films, injected parts and other objects.

By "biodegradable" is meant in the context of the present invention any biological, physical and / or chemical degradation, at the molecular level, of the substances by the action of environmental factors (in particular enzymes resulting from the processes of metabolism of microorganisms) . Numerous definitions have been adopted concerning biodegradation (ISO 472-1998, ASTM under committee D20-96, DIN 103.2-1993), according to standardization bodies, biodegradability measurement techniques and degradation medium. There was consensus, however, that biodegradation can be defined as the decomposition of organic matter into carbon dioxide, water, biomass and / or methane by micro-organisms (bacteria, enzymes, fungi).

One can quote the standard EN 13432 which defines the requirements relating to the packagings valorized by composting and biodegradation. The evaluation criteria within the meaning of that standard are as follows:

- the material under test must contain a minimum of 50% volatile solids

- the concentration of the 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 shall be determined for each packaging material or each significant organic constituent of the packaging material, meaning 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%

- each material under test must be inherently and ultimately biodegradable as demonstrated by laboratory tests (identical to NSO 14851: 1999 and 14852: 1999) and must meet the criteria and at the following acceptance levels: in an aerobic environment, the percentage of biodegradation of the test material shall be 90% in total at least 90% of the maximum degradation of an appropriate reference substance plateau has been achieved both for the test material and for the reference substance (eg cellulose). The duration of the test must be at most 6 months. In anaerobic environment, the test period must be a maximum of 2 months and the biodegradation percentage based on biogas production must be greater than or equal to 50% of the theoretical value applicable to the test material.

- each material under test must decay during a biological waste treatment process: after a composting process not exceeding 12 weeks, not more than 10% of the initial dry mass of the test material sieving may be refused for a 2 mm mesh vacuum.

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

The various standards make it possible to determine biodegradability characteristics for particular uses.

Thus, in the context of the present invention, a biodegradable material is understood as a decomposing material according to the definition given above.

The manufacture of biodegradable materials based on mixtures between a synthetic polymer and an isolated natural polymer such as starch, cellulose, hemicellulose, fiber, hemp fiber, or other is known.

US Patents 5,095,054 and EP 327,505 disclose materials made from a synthetic polymer and a destructured starch. In EP 327 505, the starch is previously destructured at temperatures of 130 ^° C. to 190 ^° C. under ⁵ × 10 ⁵ N / m ² . The starch may also be treated with agents such as urea, alkali or alkaline earth hydroxides as described in European Patents EP 400 531 and EP 494 287, or may be subjected to prior chemical treatment to modify its state. surface and make its surface hydrophobic.

The use of this type of starch is described in particular in the US Pat.

6,007,614 and US 5,797,984.

DE 102 30 776 discloses the extrusion of a plasticized cereal flour with a mixture of sorbitol and glycerol with a polyester (paragraph [0016], and especially Example 1). The examples mention the use of a twin-screw extruder, but do not specify its nature. US 2006/0043629 discloses compositions obtained by mixing a soy flour with glycerol, subsequently mixed with a biodegradable polymer (see especially paragraphs [0093] and [0096]). The flour used is not a cereal flour, and thus has strong differences in composition with the flours used in the context of the present invention: the soya flour is richer in lipids and proteins than the cereal flour, which presents a complex composition of carbohydrates.

FR 2,856,405 was filed by the Applicant and is discussed in this application, through the teaching of WO 2004/1 13433, application of the same family. The teaching of WO 2004/113433 serves as a basis for the comparative examples.

DE 198 02 718 (D4) describes the mixture of corn flour with glycerol and a biodegradable polyester. This mixing is carried out at one time, which defines a difference with the object of the process as envisaged, which envisages a plastification of the flour before adding the polymeric agent.

The present invention uses flour, preferably cereal flour as raw material, in place of isolated starch. This flour actually contains starch, but also other compounds that can influence the quality of the materials obtained, such as proteins, lipids and other sugars less complex than starch. Thus, it is likely that the presence of these other compounds affects the mixing capacity of the flour and the synthetic polymer.

The manufacture of biodegradable materials from flour is also known in the art, as described in particular in the application WO 00/14154, which specifies certain conditions for incorporating cereal flour into a polymer matrix. This application mentions in particular that the cereal flours do not undergo any treatment such as, for example, gelatinization or destructuration or modification of the surface of the starches, and that no plasticizers such as urea or glycerol are used.

The application WO 2004/1 13433 also relates to mixtures of cereal fillers and biodegradable polymer. The cereal feed corresponds to flour that has been transformed using a plasticizer to modify its rheological and thermal properties, so that they are similar to those of the biodegradable polymer (obtaining thermoplastic flour). This request thus specifies the conditions for mixing the flour and the plasticizer. Figure 6 of this application shows an example configuration of Screw a twin-screw extruder to prepare a ThermoPlastic Flour (FTP). Thus, WO 2004/113433 is concerned only with the mixture between the flour and the plasticizer, without studying the result obtained when using this product with a biodegradable polymer.

The Applicant has observed that the mixing conditions of flour and plasticizer described in WO 2004/1 13433 do not allow to obtain an optimal mixture between the flour thus transformed and the biodegradable polymer. Thus, the products (films) made from the biodegradable material obtained according to the process described in WO 2004/113433 do not have suitable mechanical properties.

The present invention thus relates to a method for producing a biodegradable material from flour and at least one biodegradable polymer, comprising the step of

a) transforming said flour by the effect of a plasticizer, in order to obtain a transformed flour,

said step a) being carried out in a twin-screw extruder, each screw having the same diameter D, characterized in that said step a) of incorporation of the plasticizer into the flour is carried out over a length of at least 6 times the diameter of the screw (6 x D). Preferably, this incorporation is carried out over a continuous length, that is to say without there being a relaxation phase of the mixture during incorporation. The biodegradable material thus obtained may be called "compound" and is intended to be reworked in the presence or absence of other polymers to obtain biodegradable products, as described in WO 2004/113433 or in WO 2008/003671. it is generally in the form of granules.

Thus, this biodegradable material can be mixed with a biodegradable polymer in a single-screw extruder, for extrusion-inflation processing.

Inflation extrusion is a known continuous process in which the granules (compound) enter a heated tube with a worm. These granules can be of one type or of several types when it is desired to carry out a mixture. The homogenized material is pushed, compressed and then passes through a die. The polymer thus formed is then dilated with the compressed air at the extruder / die exit. Thus, the outlet of the extruder is vertical, and compressed air is blown into the melt which swells and rises vertically into a long film bubble. After cooling, rollers flatten the film into a planar 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 soft and thin sheets of horticultural greenhouses.

In another embodiment, the film is obtained by extrusion of flat film (or cast film). In this method, the polymer falls on a temperature-controlled chill roll at the die outlet. The cold allows recrystallization, and the rotation speed of the rollers allows the adjustment of the thickness.

It is easy to add several layers of material when using this method. It suffices to produce different polymers in several extruders, and to superpose them at the exit of the extruders / dies, just before the inflation phase (inflation extrusion), or drop on the thermostatic cylinder (flat film extrusion).

Twin-screw extrusion is a process known to those skilled in the art. The extrusion machine is more particularly of co-rotating two-screw co-penetrating type, and comprises two screws driven length L and diameter D, rotating about their axes by a motor and a reducer, inside. an elongate envelope forming a sheath, surrounded by heating elements. These screws are provided with helical threads, modular screw elements, which mesh with each other, characterized by their ratio outer diameter (of) on internal diameter (di) determining the free volume of the screw. The inner wall of the sheath forms two intersecting lobes of diameter slightly greater than the outer diameter of the net. The ratios (of / di) and (L / D) are two important features of the extrusion machine. Whatever the diameter chosen, the ratio of the screw length to the diameter is preferably greater than 28, and preferably of the order of 40.

It is thus possible to have a large number of screw elements, making it possible to vary the pitch, the depth, the number and the length of the screw elements on each work zone. The set of elements is called configuration, and is characteristic of the objective to be achieved. Thus, it is possible to use transport elements of the material, and elements that make it possible to provide mechanical energy (shearing of the material). The material advances into the extruder being pushed by the material introduced at the inlet of the extruder, the flow rate being constant.

In general, it provides an energy of between 0.1 and 0.5 kWh / kg, said energy being provided mechanically and / or heat. More preferably, it provides between 0.1 and 0.2 kWh / kg. The heating elements make it possible to maintain a temperature of between 30 and 190 ^° C.

In a preferred embodiment, the extrusion machine comprises continuously, from upstream to downstream in the transfer direction of the material, a plurality of treatment zones, consisting inter alia of:

a zone Z1 for transforming the cereal material (mixed with the plasticizer to obtain a transformed flour),

a zone Z2 for introducing the biodegradable polymer or polymers, a zone Z3 for mixing the transformed flour and the biodegradable polymer (s)

Step a) of the process described in the present application is thus carried out in zone Z1, which represents, in a preferred embodiment, at least 35% of the total length L of the extrusion machine. This zone Z1 comprises an area of introduction of the cereal material (flour) and of the plasticizer, a zone of transport and temperature rise of these two elements, and a mixing zone of these elements, which corresponds to the implementation of step a) of the claimed process.

In a particular embodiment, the total L / D ratio is equal to 40, and the length of the Z1 zone is greater than 16 times D (16D) (for example equal to 18.5 times D (18.5 D)). ).

The modules 1 to 4 of FIG. 6 of WO 2004/113433 correspond to the zone Z1 thus defined. As seen above, no addition of biodegradable polymer is carried out in the extruder described in Figure 6 (which is read in the light of Figure 7) of WO 2004/1 13433. The mixture between the flour and the plasticizer is carried out in module 4. The abbreviations used in this figure correspond to the modular elements carried on the two screws of the extruder: C2F: conjugate with double thread (conveying), MAL2 (bilobal mixers), BL02 (monolobe eccentric on each screw: shear). Thus, in the method described in WO 2004/113433, relaxation ranges (transport materialized by the double-threads) are included during the mixing phase of the flour and plasticizer. Such elements are described in Table 1.19 of the thesis supported by lka Amalia KARTIKA on May 19, 2005 to obtain the title of Doctor of the National Polytechnic Institute of Toulouse, and which is available at http: // ethesis. inp-toulouse.fr/archive/00000159/01/kartika.pdf, reproduced in Figure 1.

In a particular embodiment of the process, the incorporation of the plasticizer in the cereal material is achieved by the use of modular elements having a profile for shearing the cereal flour / plasticizer mixture.

These modular elements will thus lead to a local decrease in the available volume (thus increasing the internal pressure, converted into thermal energy) and an increase in the stress per unit area. Indeed, the modular elements present on the screws also transform the linear flow for transport / conveying due to the modular elements in double-threads in a radial flow.

Such an effect is especially obtained preferably by the use of modular elements having a profile biloba kneaders (MAL2 in the table of Figure 1).

In another embodiment, it is possible to use modular elements carrying monolobe kneaders (FIG. 1), or to set up, in the flour processing zone, various modular elements, some of them being monolobes and other bilobes.

A filling ratio of between 25% and 75% is sought in this zone for processing the flour with the plasticizer. Indeed, the mechanical energy provided by the mixing elements can not be transmitted to the materials if the filling rate is too low, and mixing is not performed for a filling rate too high. The cereal flours that can be used in the context of the present invention are described in WO 2004/1 13433 or WO 00/14154. In particular, T55 wheat flour, whole wheat, corn or any other grain may be used. Cereal flour can also be modified by various techniques, in particular drying, which makes it possible to reduce the humidity or the turboseparation which makes it possible to separate a cereal material into two granulometrically different fractions: a richer in starch (large particles) and a richer in protein (small particles).

The plasticizers used in the present process are molecules of low molecular weight, natural or synthetic, making it possible to lower the melting temperature of a polymer. In particular, it is possible to use water (it is therefore not working at reduced humidity levels), or another plasticizing agent chosen from the group consisting of glycerol and its derivatives such as di- or polyglycerol, from castor oil, linseed oil, rapeseed oil, sunflower oil, corn oil, polyols, sorbitol and its derivatives, ethers and esters of polyols, urea, sodium chloride, alkali or alkaline earth metal halides or hydroxides, and mixtures thereof. However, a person skilled in the art can use any other known plasticizer which makes it possible to offer the cereal material with which it is associated a rheological behavior identical to or at least very close to that of the polymer of the biodegradable material. Plant-based plasticisers are preferably used. Preferably, glycerol, water, or a mixture of glycerol and water is used. A process for obtaining a biodegradable material from cereal flour and a biodegradable polymer, comprising the transformation of the flour by the effect of a plasticizer composed of a mixture of glycerol and water (prior to mixing with the biodegradable polymer) is also an object of the invention. In this specific case, it is possible to use a less shearing screw profile than the profile described above, such as the screw profile described in WO 2004/113433. However, the joint use of the shear screw profile as defined above and the glycerol / water mixture makes it possible to obtain a better result. In this embodiment, the ratio glycerol: water is between 1, 5: 1 and 1 1: 1 (weight for weight), and is preferably between 3: 1 and 5: 1. However, it is also possible to use a ratio glycerol: water equal to 1 (between 0.9 and 1, 1), or between 0.66 and 1, 2.

The term "plasticizer" therefore covers the use of a single compound, or a mixture of several compounds.

The process according to the invention also preferably comprises a step b) of mixing said transformed flour obtained with said biodegradable polymer (s). This step is carried out downstream of zone Z1 in the twin-screw extruder. The biodegradable polymer used in the context of the present process may be a plant material such as wood flour as described in European Patent EP 652 910. It may also be chosen from polyols as described in European Patent EP 575 349, or copolymers of ε-caprolactone and isocyanates as described in European Patent EP 539 541.

As indicated above, one or more biodegradable polymers are used in the process according to the invention.

The biodegradable polymer according to the present invention may 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 copolyesters and in particular butanediol-adipic and terephthalic acid copolyesters, polyamides, polyesteramides, polyethers. , polyesters - ethers - amides, polyesters - urethanes, polyester - ureas and mixtures thereof.

It is advantageously chosen from synthetic polymers of fossil origin: family of butanediol copolyesters, adipic and terephthalic acids, and mixtures of these polymers. Aromatic aliphatic copolyesters are preferably used as described in EP 819 147 in the context of the present invention. In particular, polybutylene adipate terephthalate (PBAT) is particularly suitable.

It should be noted that, in a particular embodiment of the invention, a biodegradable polymer of microbial or vegetable origin is used, rather than a polymer of fossil origin. It is then in particular chosen from the group consisting of polylactic acid (PLA) or microbial polymers such as polyalcanoates of polybutyrate type (PHB), polyvalérate (PHV), or polybutyrate valérate (PHBV). It is also possible to use a polymer of the family of lactones and polycaprolactones, or a mixture of polymers of microbial origin and of fossil origin.

Poly-ε-caprolactone, polyethylene and polybutylene-succinate, polyhydroxybutyrate-hydroxyvalerate, polylactic acid, polyalkylene-adipate, polyalkylene-adipate-succinate, polyalkylene-adipate-caprolactam, polyalkylene-adipate-ε-caprolactone, diglycidyl ether-diphenol polyadipate polymers , poly-ε-caprolactone / ε-caprolactam, polybutylene adipate-co-terephthalate, polyalkylene sebacate, polyalkylene azelate, their copolymers, and mixtures thereof can be used in the context of the present invention. It is also possible to use "mixed" polymers obtained by polymerization of monomers of plant or microbial origin and of monomers of fossil origin.

In a particular embodiment, several biodegradable polymers are used, and in particular the mixture of a biodegradable polymer of fossil origin and a biodegradable polymer of vegetable origin. A mixture of polybutylene adipate co-terephthalate (PBAT) and polylactic acid (PLA) is preferably used. We can thus use Ecovio®, developed by BASF

(Ludwigshafen, Germany), which is a mixture of Ecoflex® and PLA. Ecoflex® is also developed by BASF, and is an aliphatic -aromatic copolyester

(PBAT). A mixture of Ecoflex® and Ecovio® is advantageously used.

In general, the prior art describes a large number of polymers that can be used in the context of the present invention.

Various additives may also be incorporated into the manufactured materials. These additives can be mineral fillers, vegetable fillers, pigments, blocking agents, UV absorbers, stabilizers

UV, carbon black, release agents or any other acceptable additive.

The cereal flours that can be used in the present process are described in particular in the application WO 2004/1 13433. It is thus possible to use maize, wheat, barley, soy, rice or any other cereal flours. The flour used in the process according to the invention usually contains between 65 and 99% starch, 2 and 20% protein, 0.8 and 15% fat and 2 and 15% water. It should be noted that other types of flours containing starch and other polymers such as potato flours could be used.

In carrying out the process, a quantity of flour is preferably used such that the biodegradable material obtained contains between 15 and 80% (by mass) of flour, preferably between 15 and 60%, more preferably between 20 and 50% by weight. %. Depending on the objective, more or less flour is used. If the material is an intermediate material, which must subsequently be mixed with other polymers to form the biodegradable objects (films, molded or blown objects, etc.), it then advantageously contains between 30 and 70% of flour. If the material is directly usable for the production of biodegradable objects, then it usually contains between 15 and 60% flour. In carrying out the process, a quantity of biodegradable polymer (alone or in a mixture) is preferably used such that the biodegradable material obtained contains between 10 and 85% (by weight) of biodegradable polymer (s), preferably between 30 and 80%.

The composition of a material obtained by the implementation of the process comprises between 15 and 80% of cereal flour, between 10 and 85% of biodegradable polymer (s) of fossil origin and / or of plant origin, between 2 and 40% of plasticizer.

More preferably, this material comprises:

- Between 20 and 60% of cereal flour, preferably between 30 to 50%

between 30 and 80% of a biodegradable polymer of fossil origin and / or vegetable origin selected from aliphatic-aromatic copolyesters, polylactic acids, microbial polymers, and mixtures thereof

between 2 and 25% of a plasticizer, preferably about 10 to 20%, between 0 and 5% of urea,

Such a material is also an object of the present invention. It thus relates to a biodegradable material comprising a cereal flour transformed by adding a plasticizer, and at least one biodegradable polymer, characterized in that the reduced specific viscosity of the amylaceous phase of said material (at a concentration of 3 mg / ml), measured by capillary viscometry, is between 15 and 85 ml / g, preferably between 40 and 85 ml / g.

The intrinsic viscosity of starch samples may vary depending on its origin as shown by Narpinder Singh et al. in Structural, thermal and viscoelastic cheracteristics of starches separated from normal, sugary and waxy maize, Food Hydrocolloids 20 (2006) 923-935).

It is therefore possible to calculate the relative reduced specific viscosity of the amylaceous phase (X _ex ), mentioned by van den Einde et al. in Carbohydrate Polymers, 56 (2004) 415-422), which corresponds to the ratio of the reduced specific viscosity measured for the amylaceous phase and the reduced specific viscosity measured for the flour before transformation. (before extrusion). This relative reduced specific viscosity thus reflects well the level of transformation of the flour.

The invention thus also relates to a biodegradable material comprising a cereal flour transformed by adding a plasticizer, and at least one biodegradable polymer, characterized in that the specific viscosity relative reduction of the starch phase of said material (at a concentration of 3 mg / ml), measured by capillary viscometry is between 0.10 and 0.65, preferably between 0.35 and 0.60.

Clearly, such a material is obtainable by a method as described in the present application.

The viscosity of the material is indeed representative of the level of transformation of the cereal flour after contacting with the plasticizer.

Indeed, starch is a natural polymer, in the form of granules of 1 to 100 microns, the size and shape of which vary according to their botanical origin. It is composed of two polysaccharide fractions: amylose (usually 20-30%) and amylopectin (70-80%). Amylose (linear polymer) is characterized by the chain of glucose units linked together by carbohydrate bonds α-1, 4 and is in the form of a helix. Amylopectin is a branched polymer. It is composed of short chains of glucose units linked by α-1, 4 bonds in the linear part and α-1, 6 bonds at the branching points.

In the native state, the starch contained in the cereal flours is in the form of granules.

During its processing, the cereal flour is subjected to a high temperature treatment in the presence of a plasticizer. This transformation is carried out by means of an extruder (usually twin-screw) by subjecting the system to mechanical and thermal energy. The processing of cereal flour takes place in several stages:

- The swelling of the starch granules of the cereal flour when the mixture (plasticizer / cereal flour) reaches its gelatinization temperature. During the swelling of the granules, amorphous amylose solubilizes more or less in the medium. If heating continues, the residual grains burst and disperse, the amylose - lipid complexes form and crystallize. Thus, the morphology of cereal flour after processing in twin-screw extrusion and / or after second transformation (extrusion inflating, for example) can be evaluated by Scanning Electron Microscopy (SEM) after metallization of the samples with gold in order to avoid any phenomenon of electronic discharge that would lead to degradation of the sample analyzed. The acceleration voltage used is rather low: 3kV. partial depolymerization (reduction of the molar masses) by fragmentation of the macromolecules which can be followed by viscometry in solution.

Therefore, the level of processing of cereal flour can be defined by:

- The morphology of the mixture cereal flour / plasticizer / polymer (s) by SEM: it is checked in particular if granules are still present in the mixture.

- the level of degradation of cereal flour by viscosimetry in solution: this analysis is an indicator of the level of molecular weight reduction of amylose and amylopectin.

Indeed, the cooking of the starch takes place in several stages:

- The swelling of the starch granules when the mixture (plasticizer (s) / starch) reaches its gelatinization temperature. This phenomenon results in the loss of the semi-crystalline structure of the starch (characterized by X-ray diffraction (XRD) by type A, B or C diffractograms). During the swelling of the granules, amorphous amylose solubilizes more or less in the medium.

- if the heating continues, the residual grains burst and disperse, and we observe

a) the formation of amylose-lipid complexes which crystallize (type V or E type X-ray diffractograms according to the size of the complexing agent);

b) the partial depolymerization of the starch (reduction of the average molar mass) by fragmentation of the macromolecules. This step is the one that can be followed in viscometry.

It should be noted, however, that during the storage of a composition containing previously heated starch, the crystalline structure of the starch continues to evolve: a continuation of the formation of type V complexes is observed, as well as a possible reorganization amylopectin in type B crystal structures. Consequently, the examination of this composition in XRD is not necessarily representative of the level of transformation of the starch during its mixing with the plasticizer.

Solution viscometry is an analytical technique that makes it possible to evaluate the level of depolymerization of a starch subjected to a thermomechanical treatment (for example of twin-screw extrusion type). At zero concentration, the intrinsic viscosity is a measure of the molar mass of a polymer since:

[r \] = KM ^a

with [η] = intrinsic viscosity (viscosity at zero concentration)

M = Average molecular weight

K = empirical constant depending on the solvent-polymer pair α ≈ constant empirical dependent on the solvent-polymer pair (generally α = 0.5 - 1)

[η] corresponds to the extrapolation for a zero concentration of the curve representing the reduced specific viscosity as a function of the concentration. The reduced specific viscosity corresponds to the specific viscosity brought to concentration (see also below η _S p / c) -

For the products according to the invention, based on starch in 1 M potassium hydroxide (KOH), α = 0.89 and K = 8.4 × 10 ^-2 .

Small differences in molecular weights result in viscosity variations.

Capillary viscometry is a simple analytical technique that provides access to the molecular weight of a polymer by determining the viscosity index. In the claimed material, the variation at a given concentration of the reduced specific viscosity of a dilute solution is quasi-linear as a function of the molecular weight of the polymer (and is therefore related to the level of depolymerization of the starch). It was chosen to follow the reduced specific viscosity and to calculate the relative reduced specific viscosity of a cereal flour solution at a given concentration of 3 mg / ml.

Thus, the measurement of the relative reduced specific viscosity of the starch is indeed an element of characterization of the average molar mass of the starch which has undergone the mechanical and thermal treatment with the plasticizer, and therefore of its level of transformation (depolymerization ). Since the structure of the biodegradable material according to the invention is related to the level of transformation of the starch, the measurement of the viscosity is therefore a relevant parameter of characterization of this material. As seen above, this viscosity measurement is known in the art and routinely used by those skilled in the art.

Since the claimed biodegradable materials consist of a flour / plasticizer / biodegradable polymer (s) mixture, the level of flour transformation (starch depolymerization) is evaluated. 1- Extraction of about 60 mg of the cereal flour, and drying (extraction carried out on film samples). The starch phase is the result of the extraction of cereal flour.

2- Solubilization of the amylaceous phase extracted

3- Measurement of the specific viscosity reduced to a determined concentration

(and calculation of the reduced specific viscosity relative to this concentration).

The protocol for measuring the reduced specific viscosity is as follows:

1 / Extraction and drying of the amylaceous phase

The biodegradable materials according to the invention consist of a mixture cereal flour / plasticizer / polymer (s) biodegradable (s). In order to study the evolution of the reduced specific viscosity of the amylaceous phase, it is necessary to carry out an extraction of the biodegradable polymer (s) present in the mixture. Extraction is performed on film samples produced from the claimed biodegradable materials. This step makes it possible to remove the biodegradable polymer, and to keep only the amylaceous phase.

In order for the evolution of the reduced specific viscosity of the extracted starch phase to reflect the level of processing of the cereal flour in the claimed biodegradable materials, the film samples are produced on the same extrusion line. identical processes (same temperature profile, same crystallization height, same inflation rate, etc.). The results do not depend on the nature of the starting film. Said extraction is carried out by means of a solvent of the polymer (s) constituting the film, which solvent must be a non-solvent of the flour.

The following table (Emmanuelle SCHWACH's thesis: Study of biodegradable multi-phase systems based on plasticized wheat starch Structure relationship - Properties Compatibility approach, defended on 2 July 2004 to obtain the degree of Doctor, Discipline: Chemistry of Materials , University of Reims - Champagne Ardenne, doctoral school: Exact Sciences and Biology) presents different solvents of biodegradable polyesters. These solvents are non-solvents of cereal flour and can therefore be used for the present extraction depending on the biodegradable polymer (s) composing the biodegradable material.

Witt et al., Biodegradation of Aliphatic-aromatic Copolyesters: Evaluation of the Final Biodegradation and Ecotoxicological Impact of Intermediate Degradation, Chemosphere 44 (2001) 289-299 Isolation of the amylaceous phase can be achieved by any means known in the art and in particular by means of a Soxhlet extractor, in particular in the case of biodegradable polymers such as PBAT and PLA. Thus, the PBAT polymer can be extracted with chloroform as described in Emmanuelle SCHWACH's thesis previously cited. After extraction, the amylaceous solid phase is dried.

2 / Solubilization of the extracted amylaceous phase

The solubilization of the amylaceous phase extracted from the films obtained from the biodegradable material according to the invention (at a concentration of 3 mg / ml) is carried out in a solution of potassium hydroxide (KOH) at 1 M with stirring for 1 hour at 60 ^° C.

3 / Measurement of the reduced specific viscosity of the amylaceous phase in solution at 3 mg / ml (and calculation of the reduced specific viscosity relative to this concentration)

Material and conditions of analysis:

- OSTWALD capillary viscometer

- Sample volume introduced into the capillary viscometer: 2mL

- Temperature: 30 ⁰ C

- Conditioning time before measurement: 3min

- Number of measurements per sample: 3

Solvent: KOH 1 M

Principle of the measure: The viscosity of a liquid, or infinitely diluted polymer solutions, is proportional to the flow time of a given volume of solution through a capillary. Therefore, the following quantities can be determined:

the viscosity of the solution relating to the viscosity of the pure solvent:

η t

h h

the specific viscosity reduced to a given concentration (reduced specific viscosity):

with:

- 1 = flow time of the solution through the capillary

- 1 ₀ = solvent flow time through the capillary

- C = the concentration of the solution (in this case C≈ 3 mg / ml).

Calculation of the relative reduced specific viscosity:

As discussed above, the degree of transformation of the cereal flour induced by the biodegradable material production process (twin-screw extrusion) is understood by monitoring the reduced specific viscosity relative to a given concentration of 3 mg / ml, ( X _ex ), calculated as follows:

With:

_{p /} o _c = reduced specific viscosity of the flour at a given concentration (C) after thermomechanical treatment (twin-screw extrusion in our case)

Ηsp _/ c- _to ⁼ reduced specific viscosity of the flour at a given concentration (C) before thermomechanical treatment (twin-screw extrusion in our case)

The invention also relates to plastic films comprising a biodegradable material according to the invention. Preferably, these films are prepared by extrusion-inflating a biodegradable material according to the invention, alone or by adding another biodegradable polymer, as described above.

These films may be single-layer or multi-layer, as described in WO 2008/003671.

The more advanced level of processing of the starch achieved by the process according to the invention greatly improves the quality of the films that can be produced from the biodegradable material thus obtained, and defined above.

Thus, one can obtain films having a Haze profile quite interesting.

By definition, Haze is the haze of a product caused by the scattering of light transmitted through the product. Indeed, the light can be diffused by particles present within the sample (we can cite for example the pigment particles) or by surface defects.

Thus, the optical properties of a plastic film sample can be determined inter alia by measuring the Haze. The latter is defined according to the standard

ASTM D1003 as the amount of light that deflects an average of more than 2.5 ° from the incident light beam. It is expressed as a percentage. A material with a Haze greater than 30% is considered to be diffusing. Haze value is given by:

% Haze = ^^ x 100 with: T = incident beam transmission

The Haze measurement protocol is as follows:

1 / Preparation of samples

Three 10 X 10 cm film samples were cut with a scalpel by reference to be analyzed.

2 / Haze determination

The tests were carried out according to ASTM D1003-07 (1 1/2007) Haze and Light Transmission of Transparent Plastics, Procedure B - Measurement of Haze with a Spectrophotometer.

- Number of test pieces: 3 squares of 50mm side by reference - Pre-conditioning of samples: minimum 4Oh at 23 ° C ± 2 ° C and 50% ± 5% RH

- COLOR-EYE 7000A Spectrophotometer

- Parameters of the spectrophotometer: Illuminant type C, CIE observer 1931

The use of a biodegradable material according to the invention for the production of plastic films and / or sheets is also an object of the invention.

figures

Figure 1: Table summarizing the effects of screw elements in a co-penetrating and co-rotating twin-screw extruder (source: Ika Amalia KARTIKA's thesis).

Examples

Different screw profiles and different formulations are used.

Screw profiles

Screw profile T (control)

Corotative bi-screw extruder, L / D = 40, of / di = 1, 56

Output via a die of 24 holes of 3mm

Configuration of the screw (zone Z1):

Transport, conveying flour: 8D

At L = 8D incorporation of the plasticizer

Transport, conveying of the flour / plasticizer mixture: 4D

Compression, shearing: 2D

Relaxation / conveying: 0,75D

Compression, shearing: 2D

Transport, conveyance of processed flour: 1, 75D

The transformed flour is brought into contact with the biodegradable polymer (s) after a length of 18.5D.

This profile is similar to the profile described in Figure 6 of WO 2004/1 13433.

The flour processing zone thus measures 4.75 D and has a relaxation phase.

Profile A (process according to the invention)

Corotative bi-screw extruder, L / D = 40, of / di = 1, 56

Output via a die of 24 holes of 3mm

Configuration of the screw (zone Z1): Transport, conveying flour: 8D

At L = 8D incorporation of the plasticizer

Transport, conveying of the mixture flour / plasticizer: 2,25D

Compression, shearing: 6.5D

Transport, conveyance of processed flour: 1, 75D

The flour processing zone is therefore 6.5 D and without relaxation phase.

Formulations used

I - Use of glVerol as a plasticizer

Corn flour: 37%

Glycerol: 16%

PBAT: 47%

II - Use of Glvcerol and Water as Plasticizing Agents

Corn flour: 37%

Glycerol: 13.3%

Exogenous water: 2.7%

PBAT: 47%

III - Use of Glvcerol and Water as Plasticizing Agents

Corn flour: 37%

Glycerol: 12%

Exogenous water: 4%

PBAT: 47%

The percentages are given by weight: for example, in Formulation I, 37 g of flour, 16 g of glycerol and 47 g of PBAT are introduced.

In the present case, all the examples were produced from the same cereal flour. Thus, the evolution of the reduced specific viscosity directly translates the level of transformation of the cereal flour. Biodegradable materials are thus produced. These are used for the manufacture of films by extrusion-inflation, according to methods known in the art, and recalled in particular in WO 2008/003671.

The films produced are three-layer films with a thickness of 30 .mu.m, 20/60/20 structure. The outer and inner layers consist of PBAT, and the core layer of the biodegradable material is obtained after extrusion under the above conditions.

In this case, the films were made on a tri-layer extrusion station. The station includes three extruders:

a DOLCI 45 supplying the inner layer: PE type screw, L / D = 22 a REIFENHAUSER 35 supplying the central layer: type screws

PE, L / D = 31, 4

a DOLCI 40 supplying the outer layer: screw type PE, L / D = 32 The process parameters used for the production of all the films studied in the examples are as follows:

Inflation rate = 3.4 - 3.5

- Internal layer temperature profile = 120 - 130 - 140 - 150 ⁰ C

- Central layer temperature profile = 110 - 120 - 125 - 130 ⁰ C

- Temperature profile outer layer = 1 10 - 120 - 130 - 140 - 150 150 - 150 ° C

Filter and die temperature = 155 ° C

The mechanical properties were measured on LLOYD LR5K equipped with a 100N sensor according to the operating parameters below:

no preload

- gap: 80 mm

pulling speed: 100mm / min

width of the specimen: 20 mm

the break is detected when the force drops sharply

% AR = percent elongation at break

Surface analysis of the films is performed on a non-contact surface topography system: AltiSurf®500. The acquisition of three surface profiles was performed in random directions on the analyzed film samples. The acquisition parameters are as follows:

- Probe: 300m

Measured length (X): 4.8mm Resolution: 1 μm

Acquisition rate: 300Hz

- Measuring speed: 300μm / s

We notice :

Ra = Average arithmetic mean deviation of roughness profile

Rq = root mean square deviation of roughness profile

Pt = Total height of the gross profile

The electron microscopy analysis confirms these data.

Example 1

The screw profile T and the formulation I are used.

A film is produced as mentioned above.

The reduced specific viscosity is 99.51 ml / g.

Example 2

The screw profile A is used, and the formulation I

There is thus an improvement in Young's modulus and elongation at break with respect to the film of Example 1. The Haze percentage is lower, which shows that the film of Example 2 is less diffusing (leaves better to pass the light). This result corroborates the topographic analysis which shows a clear decrease in the surface roughness of the film. Similarly, the relative reduced specific viscosity decreases, which is good in the sense of an increase in the level of processing of cereal flour. The reduced specific viscosity is 57.04 mL / g.

Example 3

Screw profile A and formulation II are used

The addition of exogenous water with glycerol notably makes it possible to improve the mechanical properties of the films generated (Young's modulus) as well as their level of cloudiness.

The reduced specific viscosity is 56.57 ml / g.

Example 4

The screw profile T is used, and the formulation III

The reduced specific viscosity obtained is 70.73 ml / g.

This example confirms that the use of exogenous water with glycerol makes it possible to improve the mechanical and cloud level properties of the films generated.

Example 5

The screw profile A is used, and the formulation

The reduced specific viscosity obtained is 49.78 ml / g.

This example shows that a screw profile / plasticizer combination allows the optimization of the mechanical properties, topography and transparency of the films. The level of processing of cereal flour is more advanced, which is reflected in particular by lower surface roughness and haze.

conclusions

It is observed that the use of a screw profile leading to a greater incorporation of the plasticizer into the flour makes it possible to reduce the reduced specific viscosity as well as the relative reduced specific viscosity, which indicates a greater transformation of the cereal flour.

This effect is also observed when using a water / glycerol mixture as a plasticizer, regardless of the screw profile used.

The films made are also of better quality (mechanics, as attested by the Young and Optical Module, as attested by the Haze). The use of a more shearing screw profile and the optimization of the plasticizer make it possible to improve the properties of the films produced.

Claims

claims

A biodegradable material, comprising a cereal flour transformed by incorporation of a plasticizer, and at least one biodegradable polymer, characterized in that the reduced specific viscosity of the amylaceous phase of said material (at a concentration of 3 mg / ml), measured by capillary viscometry is between 15 and 85 ml / g.

2. Biodegradable material according to claim 1, characterized in that it contains between 15 and 80% flour.

3. Biodegradable material according to one of claims 1 or 2, characterized in that it contains between 10 and 85% of biodegradable polymer.

A method of manufacturing a biodegradable material according to one of claims 1 to 3 from flour and at least one biodegradable polymer, comprising the step of:

a) Transforming said flour by the effect of a plasticizer, in order to obtain a transformed flour

said step a) being carried out in a twin-screw extruder, each screw having the same diameter D, characterized in that said step a) of transformation of the flour by the plasticizing agent is carried out over a length of at least 6 times the diameter of the screw (6 x D).

5. Method according to claim 4, characterized in that the incorporation of the plasticizer is achieved by the use of modular elements having a profile for shearing the mixture flour / plasticizer on each of the screws.

6. Method according to claim 4 or 5, characterized in that said modular elements have a profile biloba and / or single-bladed mixers.

7. Method according to one of claims 4 to 6, characterized in that the plasticizer is selected from the group consisting of water, glycerol and its derivatives such as di- or poly-glycerol, castor oil, linseed oil, rapeseed oil, sunflower oil, corn oil, polyols, sorbitol and its derivatives, polyol ethers and esters, urea, sodium chloride, alkali or alkaline earth halides and mixtures thereof.

8. Method according to claim 7, characterized in that the plasticizer is a glycerol / water mixture.

9. Method according to one of claims 4 to 8, further comprising a step b) of mixing said transformed flour obtained said biodegradable polymer.

10. Method according to one of claims 4 to 9, characterized in that the biodegradable polymer is of fossil origin and is selected from the group consisting of aliphatic polyesters, aromatic aliphatic polyesters, aliphatic - aromatic co-polyesters and in particular butanediol-adipic and terephthalic acid copolyesters, polyamides, polyesteramides, polyethers, polyesters-ethers-amides, polyester-urethanes, polyester-ureas and mixtures thereof.

Process according to claim 10, characterized in that the biodegradable polymer is polybutylene adipate co-terephthalate (PBAT).

12. Method according to one of claims 4 to 9, characterized in that the biodegradable polymer is of plant origin and is selected from the group consisting of polylactic acid (PLA) or microbial polymers such as polyalkanoates of the type polybutyrate (PHB), polyvalérate (PHV), or polybutyrate valérate (PHBV).

13. Method according to one of claims 4 to 9, characterized in that the biodegradable polymer is a mixture of biodegradable polymers of fossil origin and of plant origin, or is obtained by polymerization of monomers of plant or microbial origin and of monomers of fossil origin.

14. The method of claim 13, characterized in that the biodegradable polymer is a mixture of polybutylene adipate co-terephthalate (PBAT) and polylactic acid (PLA).

Plastic film comprising a biodegradable material according to one of claims 12 to 14.

The process for preparing a plastic film according to claim 15, comprising extruding - inflating a biodegradable material according to one of claims 12 to 14.

17. Use of a biodegradable material according to one of claims 12 to 14 for the manufacture of plastic films and / or sheets.