WO2004113433A1 - Biodegradable material based on polymers and plasticized grain products, method for the production thereof, and uses of the same - Google Patents

Abstract

The invention relates to a biodegradable material comprising a mixture of at least one polymer with at least one grain filler and optionally at least one acceptable additive. The invention is characterised in that the polymer and the grain filler are similar in terms of the rheological and thermal properties thereof. The invention also relates to the use of said biodegradable material and to a method for rendering a grain product compatible with a polymer.

Description

 BIODEGRADABLE MATERIAL BASED ON POLYMERS AND PLASTICIZED CEREAL MATERIALS, MANUFACTURING METHOD THEREOF AND USES THEREOF.

The present invention relates to the field of biodegradability of plastics and relates to the development of composite materials based on polymers and plasticized cereal materials (also called cereal fillers). These biodegradable materials are intended to replace the synthetic plastics used in many fields of activity such as cosmetology, pharmacy, agrifood or agriculture, for example as a packaging product.

Biodegradable materials capable of being substituted for synthetic plastics are known in the prior art. By ^{^} biodegradable "is meant in the context of the present invention, any biological degradation, physical and / or chemical nature at the molecular level of substances by the action of environmental factors (in particular enzymes derived from microorganisms metabolism process) .

First of all, mention may be made of biodegradable materials resulting from a mixture between a polymer and a surface-modified starch, described for example in US Patents No. 1,485,833, and No. 1,487,050, No. 4,021,388 , No. 4 125 495 and European patent No. 45 621. This chemical modification of the surface state of the starch makes it possible to create ether or ester functions or to make the surface of the starch hydrophobic. It has also been proposed materials formed of a polymer and a destructured starch, that is to say having undergone a specific pretreatment with a destructuring agent such as urea, hydroxides of alkali or alkaline earth metals. , as described in European Patent Nos. 437,589, No. 437,561 and No. 758,669, or water as described in US Patent No. 5,095,054. The invention described in European patent No. 535,994 does not use the term destructured starch but that of gelatinized insofar as the starch is heated to 40 ° C in the presence of water, from 1 to 45% by weight, for a time long enough to burst the starch granules.

Methods of obtaining biodegradable materials consisting of starch, polymers other than polypropylene and additives have also been described. These additives can be unsaturated chemical compounds such as natural rubber or elastomers as described in European patent No. 363,383, or vegetable materials such as wood flour or cellulose as described in European patent No. 652,910, or a plasticizer such as polyols, glycerol and / or its derivatives - diglycerol, polyglycerol - calcium chloride or ethers as described in European patents No. 473 726, No. 575 349 and US No. 5,393,804. Among the polymers envisaged, mention may be made of poly (ethylene / vinyl alcohol) and poly (ethylene / acrylic acid) proposed in European patents No. 400 532, No. 413 798 and No. 436 689, or copoly aliphatic erasers and polyesters as proposed in European patent No. 539 541, or polyethylene low density as proposed in PCT patent application No. WO 9115542 and US patent 5,162,392.

Finally, it has been envisaged to prepare biodegradable materials from starch mixed with chemically modified polymers in order to be able to react with the hydroxyl groups of the starch and thus create bonds between the polymer and the starch. These techniques are described for example in European patents No. 554 939 and No. 640 110.

The state of the art also knows biodegradable materials based on polymer and cereal flour. This material, which is the subject of the PCT international patent application published on March 16, 2000 under the number WO00 / 14154, is distinguished from the biodegradable materials of the prior art by the fact that it is obtained from cereal flour and not from starch and that said cereal flour does not undergo any treatment such as total gelatinization, destructuring of the surface of the starches or a modification of this surface.

The process described in international patent application WO 00/14154 consists in mixing together, in a first step, the cereal flour and the polymer. This first step is called "compounding" and is generally carried out by twin-screw extrusion, in the presence of various compatibilizing agents or not.

The Applicant also develops a range of products based on this concept, called FIBERPLAST ^® . For example, by loading polypropylene (PP) with corn flour, it is possible to obtain materials with new properties (Table 1). The name “Fiberplast PP X” means a material containing polypropylene and X% by total weight of corn flour- and obtained according to the process which is the subject of international patent application WO 00/14154.

Table 1

It is found that, in general, the vegetable loads decrease the mechanical resistance of the material (σ max) but greatly increase the rigidity

(Young's modulus) which means that the finished product will have better dimensional resistance to the detriment of its resistance. It follows that not all plastics applications are possible, in particular the formation of plastic films by inflation extrusion which leads to unfavorable characteristics of the product.

The other drawbacks in the method which is the subject of international patent application WO 00/14154 is the compounding stage: it freezes the formulation, raises the cost and subjects the cereal product to undesirable thermal and physical constraints. In addition, the mixture obtained in the compounding step is not homogeneous and has amalgams or lumps. When the biodegradable material thus obtained is used to make a plastic film, the presence of such amalgams or lumps results in a discontinuity of the material, not allowing the film to be produced under industrial conditions, especially for proportions of cereal material greater than 20 %. In addition, the production of plastic parts by the usual methods of plastics processing, in particular injection or extrusion, blowing and calendering, leads to irregular products and even thicker as the cereal load increases.

To this qualitative technical problem which strongly limits the possible uses of the biodegradable material which is the subject of international patent application WO 00/14154, is added a quantitative technical problem. Indeed, in this biodegradable material, it is difficult to obtain a proportion by weight of cereal flour greater than 50%. However, it is obvious that biodegradable materials containing a proportion of cereal flour greater than 50% would make it possible in particular to reduce the cost of said materials.

The Applicant has postulated that the various technical problems cited above were due to the fact that the cereal flours and the polymers used in the biodegradable materials are too far apart. others at the physico-chemical level and that they have different properties. For example, cereal flour is hydrophilic while synthetic thermoplastic polymers are generally lipophilic. Likewise, the size of the particles constituting a cereal flour is between 0.1 and 500 μm while the size of the polymers which can be used is of the order of 2 to 3 mm. Finally, the rheological and thermal characteristics of cereal flour and polymers in the extrusion processes are too different.

The Applicant has hypothesized that the quality of the mixture between the cereal flour and the polymer and its stability at the extruder outlet - single and / or twin-screw - are governed by two laws which are: - thermal similarity in solid phase, according to which the homogeneous mixture of chemically incompatible products is conditioned by an equivalent heat transfer in the solid phase, allowing simultaneous fusion during the extrusion processes; - the rheological similarity, according to which the mixing of two products can only be done if their viscosity is similar at a given temperature.

Consequently, the Applicant, after studying the rheological and thermal behavior of the polymers used, sought to identify a transformation of the cereal material allowing it to approach from the physico-chemical point of view the properties of said polymers with which it is associated in the biodegradable materials. Authors have worked on the production of cereal products, mainly based on starch, which can be used for the production of injected parts. They then use different plasticizers, the objective of which is to obtain a melt of starch during the extrusion. Their work constitutes the starting point for the transformations of the cereal material envisaged by the Applicant.

The work of the Applicant has made it possible, on the one hand, to compare two methods of characterizing a plastic material. The first consists in reading a melting index profile (MFI), a routine analysis for plastics professionals. The analysis of the rheological behavior allowed us to transform the MFI values (for Melting Flow Index) into an evaluation of the viscosity function (WLF equations). The second, heavier and slower, consists of transforming the material into extrusion and recording the pressure drops by capillary rheometry. The treatment of the Navier-Stokes equations for an incompressible fluid in laminar, permanent and established regime, makes it possible to obtain the viscosities of the material as a function of the shear. The results showed the convergence of the 2 methods: it is possible to predict, from an MFI measurement, what will be the viscosity of the material in extrusion for any temperature, shear and pressure.

In a second step, the Applicant sought to prepare a cereal material having a viscosity similar to that of the polymer used during the extrusion. More particularly, it verified that, by prior plasticization of the cereal material, it is possible, during the final extrusion, to compatibilize a polymer with the defined rheology with an adequate cereal material. Biodegradable material thus obtained can be used in particular for industrially obtaining biodegradable films 10 μm thick and exhibits remarkable biodegradability and resistance properties, as described in the examples below.

The present invention therefore relates to a biodegradable material comprising a mixture of at least one polymer with at least one cereal filler and optionally one or more acceptable additives characterized in that the polymer and the cereal filler are close in their rheological and thermal properties.

By "cereal filler" is meant any cereal material plasticized by means of a plasticizer. By “cereal material” is meant, in the context of the present invention, plant materials derived from cereals the compositions of which, according to the various basic ingredients, are as follows (weight percentages): - water between 0 and 20% ,

- carbohydrate compounds between 0 and 85% including starch between 0 and 80%,

- proteins between 0 and 30%,

- fatty acids between 0 and 10%, - minerals between 0 and 5%,

- fibers between 0 and 20%.

By “carbohydrate compounds, proteins, fatty acids, minerals and fibers”, is meant the multiple products and molecules described in a conventional manner by many reference authors in the field of cereal matter compositions. Let us quote for example -. "Food composition. Tables of nutritional values" - Marigold / Fachmann / Kraut - 5 ^th Edition - CRC Press.

International patent application WO 00/14154 describes cereal flours of T55 wheat, whole wheat and corn usable in the context of the present invention.

It is possible to modify the constitution of a cereal material by various techniques. We can cite for example the drying which makes it possible to reduce the humidity or the turboseparation which makes it possible to separate a cereal material into two grain-size fractions: one richer in starch (large particles) and one richer in proteins (small particles). The corn cereal material of the example is a flour obtained following the additional grinding of a coarse corn semolina. The grain size of this corn flour is shown in Figure 5.

With regard to starch, which is an important element in a flour, this consists of a mixture of two glucose polymers: amylose and amylopectin. The ratio between these two molecules is different according to cereals and varieties for the same cereal. In addition, it should be noted that the amylose / amylopectin ratio can be modified by genetic transformations using the nucleotide sequences of the genes involved in the metabolism of starch or by the use of the natural genetic variability of plant species. The biodegradable material of the invention is remarkable in that it comprises all of the constituents of a cereal material and not only of starch. This makes it possible in particular to avoid all the starch extraction techniques but also to use the properties of certain constituents of the cereal material, such as lubrication by fatty acids, improving mechanical strength and flexibility thanks to the cellulose fibers, the natural coloring and aroma due to the partial destruction of proteins during the development of materials.

By “polymer” is meant in the context of the present invention any plastic material and, more particularly, any thermoplastic material. It is advantageously chosen from the following groups: - synthetic polymers: family of polyolefins (high and low density polyethylene, polyprolylene, with MFIs (melting flow index from 0.1 to

60 under 2.16 kg and at 230 ° C), vinyl family

(PVC), family of styrenics (standard PS, expanded or shock), ...

- biodegradable polymers: family of polylactic acids (PLA), family of butanediol copolyester, adipic and tereph alic acids, family of copolyester - starch composites, family of lactones and polycaprolactones, ...

By “plasticizer” in the context of the present invention is meant a natural or synthetic molecule used to lower the melting temperature of a polymer. In the context of the biodegradable material which is the subject of the present invention, the plasticizer makes it possible to plasticize the cereal material. Advantageously, the plasticizers which can be used in the context of the biodegradable material of the invention are chosen from the group consisting of glycerol and its derivatives such as di or polyglycerol, castor oil, linseed oil, rapeseed oil, sunflower oil, corn oil, polyols, urea, sodium chloride and mixtures thereof. However, a person skilled in the art is capable of using any plasticizer known in the implementation of the present invention on the sole condition that the plasticizer used makes it possible to offer the cereal material with which it is associated rheological behavior identical to or at least very close to that of the polymer of the biodegradable material.

By "acceptable additives" in the context of the present invention, more particularly means a natural or synthetic molecule providing a characteristic of appearance to the product, such as color or texture, of rigidity, facilitating the usual plastics processes, such as lecithin serving as a release agent in the injection process, or facilitating the biodegradability of polymers, in particular.

The various tests carried out by the Applicant have made it possible to show that the rate of plasticization of the cereal load must be between 10 and 40%. In fact, when the polymer used is a biodegradable copolyester and the cereal material of corn flour, a rate of plasticization by glycerol of between 20 and 30% is advantageously used, while the use of polycaprolactones as polymers requires '' use a higher plasticization rate, centered on 35%. Those skilled in the art have sufficient teaching in this document to modify the plasticization rates as a function of the polymers used without demonstrating an inventive effort. The present invention also relates to the use of a biodegradable material as defined above for the preparation of plastic films and / or injected plastic parts. Consequently, the present invention relates, on the one hand, to a plastic film made entirely or in part of said biodegradable material and, on the other hand, to an injected plastic object made entirely or in part of said biodegradable material. By way of examples and without limitation, such objects can be cups, bottles, pots, strings, sachets, tubes, etc.

Preferably, the biodegradable material which is the subject of the present invention comprises, for the production of plastic films:

- a content by weight of polymer of between 35 and 94%;

- a content by weight of cereal filler between 5 to 60% and - a content by weight of additives between

1 to 5%.

Preferably, the biodegradable material which is the subject of the present invention comprises, for the production of injected plastic parts:

- a content by weight of polymer of between 0 and 99%;

- a content by weight of cereal filler between 0 to 99% and - a content by weight of additives between

1 to 5%.

The present invention also relates to a method for compatibilizing a polymer with a cereal material in order to produce a biodegradable material as defined above. Said method advantageously comprises the following steps: (i) determining the viscosity of the polymer at a working temperature,

(ii) adapt the viscosity of the cereal material to that of the polymer determined in step (i) at the same temperature and

(iii) verify that the polymer and the cereal material thus adapted have a thermal similarity.

Advantageously, step (i) of the present process is carried out by capillary rheometry. Indeed, the work of the Applicant has made it possible to show that the viscosity of a polymer can be evaluated both in the laboratory by evaluation of the melt index and during the process (ie actual measurements) by online recordings. pressure losses by capillary rheometry.

Step (ii) consists of plasticizing the cereal material using a plasticizer as defined above. The adaptation of the viscosity of the cereal material to that of the polymer can also be influenced by the particle size of said cereal material and / or by the physical state of the starch granules in said cereal material. Thus, before the step of plasticizing the cereal material, a pregelatinization step may be necessary.

The thermal similarity can be assessed in step (iii) by verifying that the polymer and the suitable cereal material exhibit simultaneous melting during the extrusion processes.

The present invention further relates to a process for the preparation of a biodegradable material, a plastic film or an injected plastic object as defined above. Advantageously, such a method comprises a prior step of co-patibilization of the cereal material with the polymer according to a method for compatibilizing a polymer with a cereal material as defined above.

The process for preparing a biodegradable material, a plastic film or an injected plastic object presents at least one additional stage of production of the desired product according to one of the usual processes of the plastics industry with mixing of the compatibilized cereal material and of the polymer.

The process for preparing a biodegradable material which is the subject of the present invention is remarkable in that it makes it possible to avoid the physical step of compounding the processes of the prior art.

Other advantages and characteristics of the invention will appear from the following examples relating to the rheological study of a polymer usable in the context of the present invention, the preparation of a cereal material having a viscosity comparable to that of said polymer and the characterization of the materials thus obtained and which refer to the appended figures in which:

- Figure 1 shows the evolution of the stress at the wall τ _ω as a function of the apparent shear γ ' _a (in log-log); - Figure 2 shows the evolution of the viscosity of the biodegradable copolyester as a function of the actual shear; - Figure 3 shows the comparison of experimental and calculated viscosities of the biodegradable copolyester; FIG. 4 represents the rheogram of the biodegradable copolyester obtained by coupling the MFI values obtained at 150 ° C. under different constraints to the values recorded online;

- Figure 5 shows the grain size of the corn flour used in the experimental part and obtained following additional grinding of a coarse cornmeal; FIG. 6 presents an example of configuration of the screws of a twin-screw extruder to prepare a thermo-elastic flour (FTP) capable of replacing up to 50% w / w of biodegradable copolyester;

- Figure 7 shows a diagram of the process for preparing the thermoplastic flour;

- Figure 8 shows the viscosity-shear rheogram of the thermoplastic flour used in the context of the present invention (clear crosses) and compared to that of a pregelatinized flour at the same rate of plasticization (dark crosses);

- Figure 9 shows the viscosity of FTP obtained at 150 ° C for different shear values; FIG. 10 represents the evaluation of the overall viscosity of the FTP obtained by coupling the values of MFI obtained at 150 ° C. under different constraints to the values recorded online;

- Figure 11 compares the overall viscosity functions of the biodegradable copolyester and an FTP plasticized to 22% at 150 ° C, over the entire shear range; Figure 12 shows the view from two angles (respectively Figure 12A and Figure 12B) of the thermal progression measured for high density polyethylene (black curve) and low density polyethylene

(gray curve). FIG. 13 shows the comparative spatio-temporal visualization between polyester and 10% and 40% glycerol FTP; FIG. 14 shows the comparative spatio-temporal visualization between a FTP at 30% corn oil (black curve), polyester (light gray curve) and low density polyethylene (dark gray curve); - Figure 15 shows the mechanical properties of the 12 μm films obtained from FTP. FIG. 15A shows the evolution of the longitudinal mechanical characteristics of the films as a function of the% of FTP and FIG. 15B shows the evolution of the transverse mechanical characteristics of the films as a function of the% of FTP.

I. Rheological study of the plastic to be loaded. The polymer chosen for the present study is a biodegradable copolyester.

The rheological study of this plastic material is broken down into 2 phases: in the laboratory, with the evaluation of the viscosity function from the melt index, on the process, by online recordings of the pressure drops by capillary rheometry.

The convergence of these 2 approaches will then be checked.

1.1. Study in the laboratory.

1.1.1. Theoretical approach .

We use a device to control the melt index of plastics: the MFI. It is a simple capillary rheometer, the dimensions of which are standardized (DIN 53735). It is therefore necessary to relate the MFI values (g / 10 min) to viscosity values.

We first calculate the representative viscosity:

- V _-. MFI γ = - with V = -

= ^a —.F with F = Mg

8.R..L ^B

This point can be considered as the operating point of the universal viscosity function, and we can then evaluate this function because:

* _lim (7) ^=? 7 _Λ (T) with η _Q : reference viscosity

If we want to know the viscosity at another temperature and under another hydrostatic pressure, we involve the factors of temperature change and pressure with WLF formulas (Williams, Landel and Ferry):

8.86. (T * -T _S ) S.86. (TT _Sp )

„Ιoι.6 + cr ^* -τ _s ) ^ι oi-6 + -τ _s ⁾

^ ₀ (T, P) = 77 ₀ (). 10 ^{û P} where: T * = MFI temperature (in ° C)

Ts = Tg + 50 ° C (Tg = -80 ° C at lBar)

T ≈ temperature (in ° C)

Tsp = Ts + 0.02 P (P in Bars)

où : γ = Cisaillement quelconque (s^"1)

where: γ = Any shear (s ^"1 )

Al = 1.386 ^E -2 A2 ≈ 1.462 ^E -3 α = 0.36

This gives the viscosity in Pa.s.

1.1.2. Experimental results .

The MFI values of the biodegradable copolyester were measured at different temperatures and are collated in Table 2 below (average value of 10 measurements and range (%)).

Table 2

The use of the previous method makes it possible to calculate the viscosities at different temperatures, under their specific constraint. Table 3 below presents these results:

Table 3

On vérifie graphiquement (nomogra me d'évaluation rapide de la fonction viscosité) la cohérence des résultats calculés.

The consistency of the calculated results is checked graphically (nomogra me for rapid assessment of the viscosity function).

This methodology allowed us to assess the viscosity function of the biodegradable copolyester from the MFI values. This remains an assessment, since the regression coefficients used are those of the universal viscosity function. It remains to be seen whether the viscosity values recorded online from the pressure drops converge towards the same values.

1.2. Online registration: capillary rheometry.

1.2.1. Theoretical approach.

The capillary rheometry technique consists in continuously measuring the viscosity of a molten phase <at the output of a twin-screw extruder through a capillary according to the input parameters: temperature, screw speed, flow rate.

The product flows into a capillary of length L = 65 mm and of diameter D = 6 mm (L / D> 10), with a volume flow Qv. The pressure drops ΔP are measured in this capillary by 2 pressure sensors (upstream and downstream).

Starting from the momentum conservation equations:

p = - grad p ^* + μΛ u (Navier - Stokes equation) dt

It is possible under certain assumptions to calculate:

the wall stress (Pa): τ _w = D.ΔP

4L

the apparent shear. (# s -iv): γ ' _a = 32.Q —v - π∑> ~

Les produits pseudoplastiques ne sont pas newtoniens : leur viscosité dépend du cisaillement et leur comportement rheologique peut être évalué par la loi d' Ostwald :Then: 77 = (in Pa. S)

Pseudoplastic products are not Newtonian: their viscosity depends on the shear and their rheological behavior can be evaluated by Ostwald's law:

. (m-l) η = K.γ (rheo-fluidizing fluid)

where: K: consistency index (Pa.s ^m ) m: pseudoplasticity index (m <l)

Thus, from the apparent Newtonian shear rate γ _a , we use the correction of

Rabinowitch to take into account the modification of the speed profiles:

^• (3m + 1) ^{• =} ^ - ^{r «}

The actual viscosity is therefore

η. 4m AP.πX> ⁴

3m + 1128.Qv.L

The initial hypotheses for this study are: - an established permanent flow,

- an incompressible fluid (p = cte, divu = 0), - a laminar regime (Re <2000).

1.2.2. Experimental results.

Table 4 presents the pressure drop records (bars) for a mass flow range from 20 to 60 kg / h, 2 screw speeds, and a temperature of 150 ° C (lots 05.09.02): Table 4

FIG. 1 represents the evolution of the stress at the wall τ _ω as a function of the apparent shear γ _α (in log-log). The slopes indicate the pseudoplasticity indices m. Thus, the pseudoplasticity index at 100 rpm is 0.4872 and at 160 rpm is 0.5827.

By correcting the shear with the Rabinowitch factor, it is then possible to trace the evolution of the viscosity of the biodegradable copolyester as a function of the real shear (FIG. 2).

The behavior of the biodegradable copolyester is very pseudoplastic: decrease in viscosity with shear. The differential behavior due to the screw speed can be explained by a slight depolymerization at high speeds: the difference fades with shear.

With a Reynolds number much lower than 100, the initial hypothesis on the laminar nature of the flow regime is validated.

1.3. Comparison of the two approaches. It is now a question of comparing the laboratory measurements made for weak shears (less than 6 s ^"1 ) and the real measurements carried out on the capillary (shear range between 200 and 800 s ^{" 1} ).

FIG. 3 shows that the viscosity of the biodegradable copolyester changes little for a screw speed of between 100 and 130 rpm, at equivalent shear. Using WLF relationships, it is possible to calculate the theoretical viscosities corresponding to the shears encountered in extrusion (Table 5).

Table 5

On constate que les résultats sont très similaires, ce qui signifie que l'évaluation de la viscosité avec les équations WLF pour des cisaillements, des températures et des pressions quelconques, convergent avec les relevés de pertes de charge sur la ligne . La méthode est très fiable pour des cisaillements supérieurs à 200 s-1, i.e. des débits supérieurs à 20 kg/h. Pour des valeurs inférieures, il existe probablement des fluctuations de remplissage de l'extrudeur, expliquant des résultats un peu différents entre les 2 méthodes .

It is noted that the results are very similar, which means that the evaluation of the viscosity with the WLF equations for any shear, temperatures and pressures, converge with the readings of pressure drops on the line. The method is very reliable for shears greater than 200 s-1, ie flow rates greater than 20 kg / h. For lower values, there are probably fluctuations in the filling of the extruder, explaining slightly different results between the 2 methods.

1.4. Determination of the overall viscosity function of the biodegradable copolyester.

We have seen that it is now possible to determine convergently, by experimental measurements and by calculation, the viscosity of the biodegradable copolyester at low and high shear. A linear regression in log-log coordinates allows us to evaluate the 2 coefficients of the viscosity function of the biodegradable copolyester, according to the Ostwald model. For this, several MFI measurements at 150 ° C under different constraints have been carried out and are grouped in table 6.

Table 6

These values, coupled with those recorded online, allow us to present the following rheogram for the biodegradable copolyester at 150 ° C. The rheogram thus obtained is presented in FIG. 4.

FIG. 4 clearly shows a shear-thinning behavior of the biodegradable copolyester and a correct adequacy between the MFI measurements and those in line, in terms of viscosity continuity. The viscosity function of the biodegradable copolyester responds to:

. - 0.678 η = 17685y with m = 0.322

1.5. Conclusion.

This study allowed us to compare two methods of characterizing a plastic material.

The first consists in reading a melting index profile (MFI), a routine analysis for plastics professionals. The analysis of the rheological behavior allowed us to transform the MFI values into an evaluation of the viscosity function (WLF equations).

The second, heavier and slower, consists of transforming the material into extrusion and recording the pressure drops by capillary rheometry. The processing of Navier-Stokes equations for an incompressible fluid in a laminar, permanent and established regime, allows the viscosities of the material to be obtained as a function of the shear.

The results show the convergence of the 2 methods. It is possible to predict, from an MFI measurement, what the viscosity of the material in extrusion will be for any temperature, shear and pressure.

The same approach will now be applied to the processed cereal material. The aim will be to produce a vegetable material of viscosity similar to the plastic to be loaded, within a defined shear range.

II. Preparation of a cereal material having a viscosity comparable to that of the biodegradable copolyester.

The complete study of the viscosity of the biodegradable copolyester was carried out by 2 analysis methods (MFI and capillary rheometry), and it was concluded that these 2 methods converged. The objective is now to prepare a cereal material having a similar viscosity during xtrusion.

The Applicant wondered whether, by prior plasticization of the flour, it is possible, during the final extrusion, to make a thermoplastic material compatible with the defined rheology with an adequate cereal load. We will qualify these cereal loads in the following by ThermoPlastic Flour (FTP)

The following presentation will answer this question by specifying the operating conditions. II.1. Obtaining FTP.

The most common plasticizer, glycerol (or propanetriol), was used to plasticize the selected cereal flour, i.e. corn flour as detailed in Figure 6.

II.1.1. Twin screw extrusion.

The objective is to achieve a homogeneous mixture of corn flour - glycerol in twin-screw extrusion. The properties of this mixture will be analyzed later.

at. Configuration of the extruder.

The extruder used consists of two co-rotating screws placed in sheaths surrounded by heating elements. This machine allows among other things to mix and melt different constituents thanks to a thermal contribution induced by heating and by mechanical shearing.

The mechanical work is provided by modular screw elements which are positioned on the 2 shafts: the set of elements is called

"Configuration", and is characteristic of the objective to be achieved.

For example, in the case where one wishes to prepare a cereal material capable of replacing up to 50% w / w of biodegradable copolyester for the production of very fine plastic films (10 μm to 20 μm), the detailed configuration is used. in Figure 6, coupled with a specific heating profile.

Likewise, the size of the flour particles is important: it conditions the heat exchange. For the same example (thin films), the particle size distribution corn flour used is shown in the figure

5.

The extrusion conditions are such that there is a Specific Mechanical Energy (SME) of 100 to 300 W.h / kg and a temperature between 80 and 160 ° C for the material leaving the die.

At the exit of the extruder, rods of 3 mm in diameter are obtained and transported on cooling strips before being cut. The granules are stored in sealed bags. The process diagram is presented in Figure 7. We will note a relative compactness of the process, a significant advantage at the industrial level: no post-extrusion drying, but simple cooling.

b. Rheological characterization of FTP.

It is necessary to understand what happens in the extruder when the flour is plasticized. For this, the rheometry capillary is mounted in place of the die and the evolution of the viscosity of the melt is monitored.

The pressure drops are noted for 3 flour flow rates, 2 plasticization levels and 1 screw speed (125 rpm); the temperature of the material leaving the capillary is stabilized between 145 and 150 ° C. The results are presented in Table 7 below.

Table 7

Using an approach similar to that of the biodegradable copolyester, it is possible to determine the viscosity-shear rheogram presented in FIG. 8. Under certain conditions, the viscosity of the FTP is relatively similar to that of the polymer to be loaded. However, respecting the similarity of viscosity of the fuses in the extruder will in part allow a homogeneous mixture.

Thus, the compatibilization of a polymer X and a cereal load, must comply with the following protocol: determine by capillary rheometry the viscosity of the polymer to be loaded into the extruder at a working temperature,

- adapt the viscosity of the cereal melts to that of the polymer to be loaded at the same temperature: role of the plasticizer, the particle size, the physical state of the starch granules, the amylose / amylopectin ratio and the composition of the flour, of the extrusion process.

For the granular state, the rheogram of an FTP produced with a pregelatinized corn flour compared with that of a melt obtained with non-pregelatinized corn flour at the same level of plasticization (22%) and at the same temperature (150 ° C) is as shown in Figure 8.

This melted from a pregelatinized corn flour, by these rheological characteristics, does not allow a sufficiently homogeneous mixture with the biodegradable copolyester, for the production of very fine films (10 to 15 μm). Its rheology will be more suited to a “harder” plastic material, such as HDPE. Thus, the rheological similarity makes it possible to control and adapt the viscosity of the FTP depending on the polymer to be loaded.

However, it can be seen that the characterization and adaptation of the viscosity is not easy.

Indeed, they require direct measurements on the extruder. It would be interesting to see if we can use the universal rheological law (WLF equations) for FTP products.

II.1.2. Characterization in the laboratory of the viscosity of FTP.

Using a methodology similar to thermoplastic, we will use an MFI measurement and transform it into viscosity. We will then see the consistency of these measurements with respect to the pressure drop records on the extruder.

at. Rheological characterization of the fade.

MFI measurements are carried out at 150 ° C. under different constraints. The data are collated in Table 8 below (plasticized FTP at 22%).

Table 8

Figure 9 summarizes these data. The behavior is clearly shear-thinning, in accordance with what has been found by capillary rheometry. Now, it is a question of testing the continuity of the 2 rheological laws (MFI and capillary rheometry) for FTP.

b. Continuity of the rheological law over a wide range of shear.

The alignment of the measurements made by MFI with those by capillary rheometry was carried out to see if a law continues over the whole range of shear could be obtained. The data are shown in Figure 10 (FTP materials at 150 ° C plasticized to 22%).

There is a very good continuity of the 2 laws, proof of the validity of the WLF equations for FTP subjects. Their behavior is indeed thermoplastic, which allows compatibilization with a plastic polymer.

Thus, by an indirect measurement (MFI) at low shear, it is possible for an FTP cereal material, to predict its rheological behavior in extrusion for any shear and temperature. The immediate advantages are a saving of time and material, and the possibility of online control of a production by a deferred measurement.

II.1.3. Comparison viscosity of biodegradable copolyester and FTP.

FIG. 11 compares the overall viscosity functions of the biodegradable copolyester and of a 22% plasticized FTP at 150 ° C., over the whole shear range.

We note that for shears greater than 500 s ^"1 , the viscosities of the 2 products are close, which allows a homogeneous mixture. Plasticized FTP between 20 and 30% can be used for the production of thin films (15 μm) with the biodegradable copolyester. Other percentages are being studied with other polymers: for example, the compatibilization of FTP with polycaprolactones (PCL) requires a level of plasticization centered around

35%. III. Thermal similarity of FTP products.

The first part of the study consisted in studying the rheological behavior of a plastic material and in preparing a cereal material compatible with the polymer to be loaded. In this study, only the melted phases are taken into account. However, as indicated in paragraph I.l.l.a, solid granules obtained from FTP products are used. The characterization of the solid - molten phase passage, which intervenes in the extrusion process, is therefore necessary: it involves the equation of the heat transfer in transient regime.

III.1. Introduction to heat transfer.

Consider a metal bar at a temperature TO. At t = 0, a temperature Tl (> TO) is applied to one end of the bar, and we look at how the temperature increase evolves at the other end of the bar. This image introduces the problem to be solved.

In fact, the rheology of the molten phases was first studied. We must now understand how the transition to the molten phase takes place, and see in particular whether the temperature rise rates are equivalent in the FTP and the polymer. Without a satisfactory thermal similarity, the molten phases will not develop at the same time and the mixture cannot be homogeneous. The homogeneity of the mixture therefore implies 2 distinct physical phenomena: a thermal similarity ensuring an equivalent heat transfer and a coordinated transition to fusion, a rheological similarity allowing the mixing of the molten phases.

To answer the previous question is to solve for the materials concerned, the Laplace equation or heat equation. For reasons of simplification, and due to the spherical geometry of the solid particles on which the study will take place, we will consider only one dimension.

If we note K (m ² / s), the thermal diffusivity of the material, the one-dimensional heat equation is written:

K - = -

Sx ² dt

It is a second order partial differential equation connecting temperature T, time t and position x. The resolution of such an equation requires the use of a formal calculation software: MAPLE V. This will allow us to know how quickly the heat flux in the material progresses, to know the exact temperature at a place and at a particular times. III.2. Modeling of transfer in the polymer and the FTP.

III.2.1 Characteristics of materials.

It is necessary to determine the thermal diffusivity K of the polymer and of the FTP. For this, 3 parameters must be known on solid materials

(granules), because: i

K = p.Cp where λ: thermal conductivity (W / m. ° C) p: density (kg / m ³ )

Cp: specific mass heat (J / kg. ° C)

Basic experimental data are available in "Auslegung von extrusionwerkzeugen. Wortberg, J., Junk, PB., Diesker, A. olloquium desIKV, Aachen. - 1978 ”. For example, the values given in Table 9 below are conventionally found for a polymer such as polyethylene:

Table 9

En prenant les 2 valeurs extrêmes de diffusivité thermique (1,4.10^~7 et 2,96.10^"7 m /s) / il est possible de comparer l'évolution des températures au sein d'une billette de résine (diamètre bille 2 mm) . L'échelle des temps est 180 secondes. Tétha est une température adimensionnelle et représente 1 ' écart à la température finale :

By taking the 2 extreme values of thermal diffusivity (1.4.10 ^{~ 7} and 2.96.10 ^"7 m / s) / it is possible to compare the evolution of temperatures within a billet of resin (ball diameter 2 mm) The timescale is 180 seconds, Tetha is a dimensionless temperature and represents the difference to the final temperature:

T-Tl θ = -

T0-T1

Figure 12 shows the view from two angles

(respectively Figure 12A and Figure 12B) of the thermal progression measured for high density polyethylene (black curve) and low density polyethylene

(gray curve). Thus, the difference in thermal behavior between the 2 products is better assessed: the heat flux progresses more slowly in low density polyethylene, the difference at the final temperature being on average greater. This is also what the thermal diffusivity value tells us.

III.2.2 Study of biodegradable polyester and FTP.

The thermal analyzes carried out on the polyester lead to the results presented in Table 10 below. Table 10

To respect the thermal similarity, it is therefore necessary to develop an FTP having a thermal diffusivity close to 8,15.10 ^"8 m '/ s-

The evolution of the thermal diffusivity of an FTP with increasing glycerol levels is presented in Table 11 below.

Table 11

The comparative spatio-temporal visualization between polyester and 10% and 40% glycerol FTP results in the results presented in Figure 13.

It is found that the heat fluxes are very close, the thermal diffusivity of the polyester being intermediate between a 10% FTP and another 40% glycerol. Combined with the rheological study, it is possible to validate a plasticization close to 27% in glycerol for the production of plastic film with the polyester. Respect for the 2 similarities is therefore an essential technical criterion.

Other FTP can be produced with different plasticizers: di and polyglycerol, glycerol ester, vegetable oils (corn, rapeseed, castor oil, ...). Regardless of the rheological constraints, we can compare the thermal flow of an FTP at 30% corn oil with low density polyethylene and polyester. The result of this study is presented in Figure 14. The curves obtained for FTP at 30% corn oil and for low density polyethylene are very similar. Consequently, the thermal compatibility between these two components is closer than that observed between a 30% FTP of corn oil and polyester. Thus, knowing the thermal properties of the plastic resin to be loaded, and by a judicious choice of the plasticizer, it is possible to comply with the 2 “process” constraints that are thermal and rheological identities.

III.3. Conclusion.

The choice of glycerol as plasticizer therefore appears to be particularly suitable for compatibilizing a cereal flour with polyester. We have seen that an FTP with 27% glycerol allows to achieve a behavioral similarity of flow (rheology) and an efficient thermal transfer management (simultaneous fusion between polyester and FTP). By analogy, it is now possible to copy this reasoning to develop other FTP, with different plasticizers, compatible with other biodegradable plastics or not.

IV. Mechanical properties .

We will characterize the FTP, then secondary transformation products made from FTP.

IV.1. Mechanical characterization of FTP.

The measurements are made with a LLOYD LR5K device, in traction mode: 0.1 N preload, traction speed 100 mm / min, on rods of 4 +/- 0.1 mm in diameter, for a basic length of test tube 80 mm.

The characterization relates to 3 levels of glycerol plasticization; the results are collated in table 12 below.

Table 12

In general, we note that the increase in plasticization decreases the Young's modulus, therefore the rigidity of the material, as well as the stress, but clearly increases the plasticity (elongation). Viscosity and plasticity evolve in the same direction for the plasticization parameter. IV.2. Mechanical characterization of films.

IV.2.1. In the tractio.

The measurements are made with an LLOYD LR5 device, in traction mode: 0.1N preload, traction speed 100 mm / min, for a base length of test tube of 80 mm and a width of 20 mm.

The results on a 12 μm film with loading rates of 30 to 50% are presented in FIGS. 15A and 15B (identical inflation parameters, in particular inflation rate).

There is a certain decreasing linearity of the mechanical properties: the incorporation of FTP reduces the elongation and the tensile strength of the films (σ max), leading to a brittleness of the material. However, it is known that the biodegradation of a film is correlated with the degradation of mechanical properties. We could then consider estimating the durability of a film from its initial mechanical properties.

IV.2.1. Other features.

Two other tests are used to characterize the film obtained: the Elmendorf test

(tear resistance - NF T54-141) and the dart-test

(impact resistance by the free falling punch method - NF T54-109)

Table 13 presents the results observed on a 12 μm film loaded with 40% FTP.

Table 13

On retrouve une résistance plus marquée dans le sens transversal, directement liée à l' extrusion secondaire (gonflage) : traction importante en longitudinal (sens de l'écoulement), et moins de contrainte en transversal (faible taux de gonflage) .

We find a more marked resistance in the transverse direction, directly linked to the secondary extrusion (inflation): significant traction in longitudinal (direction of flow), and less stress in transverse (low inflation rate).

Claims

1) Biodegradable material comprising a mixture of at least one polymer with at least one cereal filler and optionally one or more acceptable additives characterized in that the polymer and the cereal filler are close by their rheological and thermal properties. 2) Biodegradable material according to claim 1, characterized in that said cereal load is a plasticized cereal material by means of a plasticizer. 3) Material according to any one of claims 2, characterized in that said plasticizer is chosen from the group consisting of. glycerol and its derivatives, castor oil, linseed oil, rapeseed oil, sunflower oil, corn oil, polyols, urea, sodium chloride and mixtures of these. 4) Material according to any one of claims 1 to 3, characterized in that said polymer is chosen from synthetic polymers and biodegradable polymers. 5) Material according to any one of the preceding claims, characterized in that it comprises a cereal filler whose plasticization rate is between 10 and 40%. 6) Material according to any one of the preceding claims, characterized in that it comprises: - a content by weight of polymer of between 35 and 94%; - a content by weight of cereal filler between 5 to 60% and - a content by weight of additives between 1 to 5%. 7) Material according to any one of claims 1 to 5, characterized in that it comprises: - a content in: weight of polymer between 0 and 99%; - a content of .-, cereal load weight between 0 to 99% and - a content by weight of additives of between 1 to 5%. 8) Use of a biodegradable material according to any one of claims 1 to 6, for the preparation of plastic films. 9) Use of a biodegradable material according to any one of claims 1 to 5 or 7 for the preparation of injected plastic parts. 10) Plastic film consisting entirely or in part of a biodegradable material according to any one of claims 1 to 6. 11) Injected plastic object consisting wholly or in part of a biodegradable material according to any one of claims 1 to 5 or 7. 12) Method for compatibilizing a cereal material with a polymer, characterized in that said method comprises the following steps: (i) determining the viscosity of the polymer at a working temperature, (ii) adapt the viscosity of the cereal material to that of the polymer determined in step (i) at the same temperature, (iii) verify that the polymer and the cereal material thus adapted have a thermal similarity. '. 13) Method according to claim 12, characterized ^in: that said step (i) is performed by capillary rheometry. ; ^' . 14) Method according to any one of claims 12 or 13, characterized in that said step (ii) consists in plasticizing the cereal material by means of a plasticizer. 15) Method according to any one of claims 12 to 14, characterized in that the thermal similarity is assessed in step (iii) by verifying that the polymer and the suitable cereal material exhibit simultaneous melting during the extrusion processes. . 16) A method for preparing a biodegradable material according to any one of claims 1 to 7, a plastic film according to claim 10 or an injected plastic object according to claim 11 comprising a prior step of compatibilization of the cereal material with the polymer according to any one of claims 12 to 15.