WO2011128537A1

WO2011128537A1 - Process for modifying plasticized flour and compositions comprising said flour

Info

Publication number: WO2011128537A1
Application number: PCT/FR2011/050461
Authority: WO
Inventors: Jérôme GIMENEZ; Didier Lagneaux; Anne-Carine Brosse
Original assignee: Setup Performance
Priority date: 2010-04-14
Filing date: 2011-03-04
Publication date: 2011-10-20
Also published as: FR2958937A1; FR2958937B1; EP2558505A1

Abstract

One subject of the present invention is a process for modifying a composition comprising at least one plasticized flour according to which, in an extruder, at least said plasticized flour is reacted with at least one organic anhydride, the amount of organic anhydride incorporated representing between 30 and 670 parts by dry weight per 100 parts by dry weight of flour.

Description

PROCESS FOR MODIFICATION OF PLASTIFIED FLOUR AND COMPOSITIONS COMPRISING SAID FLOUR

FIELD OF THE INVENTION

The invention relates to a method for modifying previously plasticized flour and the compositions thus obtained.

Flours plasticized and modified by the process according to the invention can find an application especially in the preparation of partially or fully biosourced thermoplastic compositions.

PRIOR STATE OF THE ART The chemical modification of the flour or starch makes it possible to modify the properties inherent to the latter. It is generally carried out by esterification or acetylation reaction. These reactions make it possible to envisage and develop new applications for these flour or starch derivatives. For example, in WO9310187 A1, starch acetate is prepared by esterification of the flour. This is an acetylation reaction which is carried out in batch reactor (batch reactor) in the presence of an acetylating agent and a catalyst in particular. These are respectively a mixture of acetic acid / acetic anhydride and a strong acid.

The modification of starch by esterification or acetylation is also known to those skilled in the art ("Starch: Chemistry and Technology", Second Edition, edited by Roy L. Whistler et al, Chapter X, Starch Derivatives: Production and Uses by MW Rutenberg et al, Academy Press, Inc., 1984 ").

In general, the low or high degree of substitution of the starch is responsible for the modified properties of the starch. By degree of substitution, DS is understood to mean the number of substitutions carried out on the three hydroxyl groups present in a starch unit.

Thus a DS equal to 1 means that 1 OH group is substituted for each starch unit. In other words, 1 OH group on 3 is substituted. On the other hand, a DS equal to 0.1 means that 0.1 OH group is substituted for each starch motif. In other words, 1 of 30 OH groups is substituted.

It has been reported that a low degree of acetylation of the starch results in a decrease in the gelatinization temperature. The starch thus has a better thermal stabilization during cooking and does not undergo retrogradation after cooking. Thus, acetylated starch having a DS between 0.1 and 0.2 may find an application particularly in the food field. Even though this acetylation is mainly carried out in a "batch" reactor, it can, however, be carried out in an extruder ("Starch esterification by reactive extrusion, V. D. Miladinov and M. A. Hanna, Industrial Crops and Products 11 (2000) 51-57).

On the other hand, obtaining starch with high degrees of substitution (DS between 1.5 and 2.5) makes it possible to envisage non-food applications, particularly in biosourced plastics that are not very sensitive to water. The acetylation reaction of starch with acetic anhydride, in the solvent phase (glacial acetic acid, pyridine), is well known to those skilled in the art (RL Shogren, "Preparation, thermal properties, and extrusion of high- amylose starch acetates, Carbohydrate Polymers 29 (1), (1996) 57-61 "W. Jarrenko" Acetylated starch and miscellaneous organic esters ", Ch.4, in: Modified Starches: Properties and Uses, OB Wurzburg Ed .; Press Inc., Boca Raton, FL, USA, 1986, 55-78 ").

The plasticized flour obtained by the techniques of the prior art is partially or completely soluble in water. This plasticized flour is insoluble in organic solvents such as ethanol, ethyl acetate, propyl acetate, butyl acetate, triethyl citrate, dibasic esters, dimethylsulfoxide (DMSO) or glycerol triacetate.

WO 03/046082 A1 discloses a method of manufacturing a biodegradable plastic material comprising proteins, starch, pentosans and fats. This composition may further comprise a plasticizer. Although the obtained material is intended to be dissolved in water, its hydrophobic character can be improved by the addition of 10% organic anhydride (relative to the weight of the flour) or by mixing the initial formulation with water. hydrophobic oil. Thus the duration of use of these materials can be increased, their lifetime can vary from a few weeks to several months depending on the nature of the hydrophobic agent introduced.

The method according to the invention makes it possible to overcome these disadvantages by modifying the previously plasticized flour in order to render it organosoluble and not very soluble or even insoluble in water. By organosoluble is meant soluble in an organic solvent. The modification of the plasticized flour makes it possible to change the chemical nature of the flour and its constituents but also that of the plasticizer.

SUMMARY OF THE INVENTION The Applicant has developed a process for preparing plasticized and modified (esterified) flour which is partially or completely organosoluble and poorly soluble or even insoluble in water.

This modification is carried out by strong esterification of the flour by means of an organic anhydride in an extruder. In general, the extruder may be a co-rotating or counter-rotating mono-screw or bis-screw, with a screw length to screw diameter ratio greater than 30, preferably greater than 40, and even more preferably greater than 50. Applicant has thus developed a method for modifying a composition comprising at least one plasticized flour according to which, in an extruder, at least said plasticized flour is reacted with at least one organic anhydride. By flour is meant a biobased material resulting from the milling

- cereals such as, wheat, rye, triticale, maize, barley, sorghum or rice;

- tubers such as cassava or potato;

- legumes such as soybeans or peas;

whose compositions according to the basic vegetable materials are as follows

(percentages by weight)

- water content between 0 and 20%

- content of carbohydrate compounds between 0 and 85% including starch content between 0 and 80%

- protein content between 0 and 30%

- fatty acid content between 0 and 10%>

- mineral content between 0 and 5%

- fiber content in 0 and 20%.

By carbohydrate compounds, proteins, fatty acids, minerals and fibers are meant the multiple products conventionally described by many reference authors in the field of compositions of cereal materials. For example: "The composition of food. Tables of nutritional value "- Souci / Pachmann / Kraut - ^5th Edition - CRC Press.

Table 1 shows, by way of example, vegetable flours that can be used according to the invention: wheat flours (type T55), maize and whole wheat flour.

Table 1: Non-limiting examples of vegetable flours that can be used according to the invention. Thus, flours within the meaning of the invention can generally contain up to 20% by weight of moisture. They consist mainly of crude cellulose and lignocellulose, starch, proteins, lipids and minerals. The flours within the meaning of the invention may also be starch-enriched flours by purification of the flours resulting from the milling, in particular making it possible to extract a portion of the proteins, fatty acids and minerals.

The vegetable meal in the sense of the invention advantageously contains between 10 and 95% by weight of starch, preferably between 20 and 80% by weight of starch, more preferably between 35 and 70% by weight of starch.

By plasticized flour is meant a flour that has been previously obtained by plasticizing either:

(a) adding, in the extruder, prior to the addition of the organic anhydride, at least one flour and at least one first plasticizer; or (b) according to the techniques known to those skilled in the art, by reacting the flour with a first plasticizer flour, especially in a reactor. The method according to the invention mainly comprises two embodiments, [A] and [B]. In the process [A], plasticization and modification are carried out continuously in the extruder whereas the method [B] comprises two discontinuous steps ([B1] and [B2]) in which the plasticization of the flour (step [B1] ) is performed prior to the modification of the plasticized flour (step [B2]).

The first preferred embodiment (Method [A]) according to the invention makes it possible, during a single extrusion, to plasticize the flour and to modify the plasticized flour. The screw profile according to the method [A] is the following:

transport zone (1) for incorporating at least one flour and at least one first plasticizing agent for flour at a temperature of less than 100 ° C. and preferably less than 80 ° C .;

zone (2) for mixing and shearing to laminate the flour with an increasing temperature profile up to 200.degree. C., preferably 160.degree. C. and even more preferably 130.degree. - Zone (3) sealed transport to dehydrate the medium at a temperature below 200 ° C and preferably below 160 ° C;

- Transport zone (4) for incorporating at least one organic anhydride and optionally an esterification catalyst and at least one second plasticizer at a temperature below 200 ° C, preferably below 160 ° C and even more preferably 130 ° C ;

zone (5) for mixing and shearing to carry out the esterification reaction with an increasing temperature profile up to 250.degree. C., preferably 200.degree. C. and even more preferably 160.degree.

- Zone (6) sealed transport for optionally removing the volatiles from the reaction medium by exposing it to a reduced pressure at a temperature below 200 ° C, preferably below 160 ° C and more preferably 130 ° C. The flow rate and rotational speed of the screw (s) are adjusted according to the level of plasticizing agent of flour and the level of organic anhydride incorporated and so as to ensure a thermomechanical mixture sufficient for the plastification of the flour and a time of maximum residence time (50 seconds to 7 minutes) for the esterification reaction. On leaving the die, after the process [A], the plasticized and esterified flour is cooled in water, granulated or milled and dried.

Advantageously, the flour is plasticized with at least one first plasticizer of flour selected from the group comprising:

- diols;

- the triols;

polyols such as glycerol, polyglycerols, isosorbide, sorbitans, sorbitol, mannitol, and hydrogenated glucose syrups;

salts of organic acids such as sodium lactate;

- urea;

a mixture of these compounds.

The first plasticizer advantageously has a molar mass of less than 5000 g / mol, preferably less than 1000 g / mol, and in particular less than 400 g / mol. The first organic plasticizer naturally has a molar mass greater than 18 g / mol, ie it does not include water. Typically, the amount of the first plasticizer is from 10 to 150 parts by weight per 100 parts by dry weight of flour, preferably from 25 to 120 parts by weight and in particular from 40 to 120 parts by weight. The incorporation into the zone (1) of at least one first plasticizing agent for flour may be carried out before, simultaneously with or after the incorporation of the flour. As already indicated, this step is followed by a thermomechanical plastification step of the flour in a zone of mixing and shearing of the extruder (zone 2). Advantageously, the plasticization of the flour is carried out in the extruder before the addition of the organic anhydride, from at least one flour and at least one first plasticizer.

The flour thus plasticized is then dehydrated continuously before the addition of the organic anhydride, exposing the reaction medium to a reduced pressure in a second sealed transport zone of the extruder (zone 3). In this dehydration zone, the drying of the plasticized flour is carried out up to a residual moisture content of less than 5% by weight, preferably less than 1%, and in particular less than 0.1%.

A third transport zone (zone 4) succeeding the dehydration zone makes it possible to incorporate at least one organic anhydride.

Advantageously, the organic anhydride is chosen from the group comprising the following compounds or families of compounds:

- acetic anhydride, propanoic anhydride, butyric anhydride, heptanoic anhydride, palmytic anhydride;

cyclic anhydride such as maleic anhydride, succinic anhydride, n-octyl succinic anhydride;

mixed anhydride such as propanoic acetic anhydride or adipic acetic anhydride;

a mixture of these compounds.

Advantageously, the amount of organic anhydride incorporated represents between 30 and 670 parts by dry weight per 100 parts by dry weight of flour, preferably between 130 and 300 parts and even more preferably between 150 and 200 parts. In a particular embodiment, the amount of anhydride is between 1 and 320 parts by dry weight per 100 parts by dry weight of flour, preferably between 110 and 260, and even more preferably between 110 and 170 parts.

The reaction of the organic anhydride on the plasticized flour in the zone of mixing and shearing (zone 5) advantageously makes it possible to chemically modify by esterification the flour and its constituents but also the first plasticizer.

Advantageously, at least one catalyst capable of accelerating the esterification reaction between the plasticized flour and the organic anhydride can be added to the extruder (zone 4). Said catalyst is advantageously a strong base, preferably sodium hydroxide. Advantageously, the amount of catalyst represents between 0.2 and 10 parts by weight per 100 parts by dry weight of flour.

Typically, the addition of the catalyst and the anhydride are simultaneous.

As already indicated, it should be noted that the modification of the plasticized flour can be carried out advantageously in the presence of another plasticizer, said second plasticizer. In the extruder, at least a second plasticizer is added to said plasticized flour with or after the organic anhydride.

Preferably, said second plasticizing agent is chosen from the group comprising:

methyl, ethyl or fatty esters of organic acids such as lactic, citric, succinic, adipic and glutaric acids;

the acetic or fatty esters of monoalcohols, diols, triols or polyols such as ethanol, diethylene glycol, glycerol and sorbitol;

a mixture of these compounds.

By way of examples, mention may be made of glycerol diacetate (diacetin), glycerol triacetate (triacetin), isosorbide diacetate, isosorbide dioctanoate, isosorbide dioleate, isosorbide dilaurate, esters of dicarboxylic acids or dibasic esters ("Dibasic esters" or "DBE"). Said second plasticizer advantageously has a molar mass of less than 5000 g / mol, preferably less than 1000 g / mol, and even more preferably between 150 and 400 g / mol. Typically, the total amount of plasticizer (first plasticizer and second plasticizer included) is from 20 to 180 parts by weight of plasticizer per 100 parts by dry weight of flour, preferably from 35 to 150 parts by weight and in particular from 50 to 150 parts by weight. After esterification in the mixing and shearing zone (zone 5), the plasticized and modified flour is transported and optionally dried in a tight transport zone of the extruder (zone 6) in order to eliminate the volatiles by exposing the reaction medium to reduced pressure. In a particular embodiment, method [A] comprises an additional zone for incorporating and mixing the second plasticizer when it is not incorporated in zone 4.

The rods obtained at the outlet of the die are cooled in water, granulated or milled. The granules or grinds of esterified plasticized flour may then be dried in order to remove the adsorbed surface water during the passage of the rods in the water.

The other preferred embodiment (process [B]) according to the invention comprises two discontinuous steps ([B1] and [B2]) in which the plasticization of the flour (step [B1]) is carried out prior to the modification of the plasticized flour (step [B2]).

In step [B2], at least one previously plasticized and dehydrated flour is added to the extruder with at least one organic anhydride. Stage [B1] of process [B] is carried out beforehand, advantageously in an extruder having the following profile:

zone (2) for mixing and shearing to laminate the flour with an increasing temperature profile up to 200.degree. C., preferably 160.degree. C. and even more preferably 130.degree. - Zone (3) sealed transport to optionally dehydrate the medium by exposing it to a reduced pressure at a temperature below 200 ° C and preferably below 160 ° C. The flow rate and rotational speed of the screw or screws are adjusted according to the level of plasticizer incorporated flour and so as to ensure a thermomechanical mixture sufficient for the plasticization of the flour.

At the outlet of the die, after step [B1], the plasticized flour is cooled in an inorganic or organic liquid or in air, granulated or milled and dried under a flow of dry air possibly hot.

Advantageously, the drying of the plasticized flour is carried out (a) by dehydration of the reaction medium (in zone 3) and / or (b) by exposing the granules or ground materials to a flow of dry air possibly hot. The drying makes it possible to obtain a dried plasticized flour whose residual moisture content is less than 5% by weight of the plasticized flour, preferably less than 1%, and in particular less than 0.1%.

Of course, the step [B1] making it possible to obtain a plasticized flour may be carried out in a batch type reactor.

Step [B2] of the process [B] concerns the modification of the plasticized flour in an extruder according to the following profile:

transport zone (4) for incorporating at least one dried plasticized flour whose moisture content is less than 5% by weight of the plasticized flour, at least one organic anhydride and optionally an esterification catalyst and at least one second plasticizer at a temperature below 200 ° C, preferably below 160 ° C and even more preferably 130 ° C;

- Zone (6) sealed transport for optionally removing the volatiles from the reaction medium by exposing it to a reduced pressure at a temperature below 200 ° C, preferably below 160 ° C and more preferably 130 ° C. The flow rates and rotational speed of the screw (s) are adjusted according to the level of incorporated organic anhydride and so as to ensure a maximum residence time (50 seconds to 7 minutes) for the esterification reaction. In a particular embodiment, the step [B2] comprises an additional zone for incorporating the second plasticizer when it is not incorporated in the zone (4).

At the end of the die, after step [B2], the plasticized and esterified flour is cooled in water, granulated or milled and dried under a flow of dry air that may be hot.

The present invention also relates to any thermoplastic composition comprising a modified plasticized flour obtainable according to the process according to the invention.

Thus, the invention allows the modification of plasticized flour to make it thermoplastic, organosoluble and insensitive to water.

EXAMPLES OF REALIZATION

The invention and the advantages thereof will become more apparent from the following figures and examples.

FIG. 1 represents an extruder comprising the transport (1, 4, 6), transport and drying (3) and mixing / shearing zones (2, 5) used to modify a plasticized flour by the method [A].

The extruder zones are defined as follows:

transport zone (1) for incorporating the flour and a first plasticizing agent for flour;

zone (2) for mixing / shearing to carry out the plasticization of the flour;

- Zone (3) sealed transport to dehydrate the medium;

transport zone (4) for incorporating the organic anhydride and optionally an esterification catalyst and a second plasticizer;

zone (5) of mixing / shearing to carry out the esterification reaction;

- Zone (6) sealed transport to eliminate the volatiles. FIG. 2 shows two extruders comprising a transport (1 or 4), transport and drying (3 or 6) and mixing / shearing zone (2 or 5) used for plasticizing a flour and modifying the plasticized flour by the process [ B].

The extruder zones are defined as follows:

For step [Bl]

zone (2) for mixing / shearing to carry out the plasticization of the flour;

- Zone (3) sealed transport to dehydrate the medium;

For step [B2]

transport zone (4) for incorporating the plasticized flour, the organic anhydride and optionally an esterification catalyst and a second plasticizer;

zone (5) of mixing / shearing to carry out the esterification reaction;

- Zone (6) sealed transport to eliminate the volatiles.

Five compositions were prepared in a twin-screw co-rotating extruder with a diameter of 26 mm and a ratio (screw length / screw diameter) of 50 D.

Composition 1 was prepared according to method [B1].

Compositions 2, 4 and 12 were prepared according to method [A].

Composition 3 was prepared according to process [A] without the addition of organic anhydride in zone 4.

Composition 5 was prepared according to the method [B] ([B1] + [B2]).

The compositions 6 to 11 were prepared according to the method [A], in the presence of sodium hydroxide. Flour type 55 contains 70% starch and 15% water while Wheat Oatmeal contains 45% starch and 15% water.

Compositions 6 and 8 illustrating the prior art (WO 03/046082 A1) comprise 10 parts of acetic anhydride relative to 100 parts of flour. For these compositions, the DS obtained is of the order of 0.1%. Examples wheat flour tri acetate glycerol anhydride

(process) type 55 glycerol acetic acid

Composition 1

70 shares 30 shares 0 0

[Bl]

Composition 2

70 shares 30 shares 0 80 shares [A]

Composition 3

70 shares 20 shares 10 shares 0

[AT]

Composition 4

70 shares 20 shares 10 shares 80 shares [A]

Composition 5

70 shares 30 shares 0 90 shares [B]

Composition 6 7 (+2 parts of type 55/70 Glycerol / 30 0

[A] soda)

Composition 8 9 (+2 parts of type 55/92 Sorbitol / 8 0

[A] soda)

Composition 9,150 (+2 parts type 55/92 Sorbitol / 8 0

[A] soda)

Composition 10 208 (+2 parts type 55/66 Sorbitol / 34 0

[A] soda)

Composition 11,138 (+2 parts type 55/54 Sorbitol / 46 0

[A] soda)

Composition 12

Oatmeal / 92 Glycerol / 8 0 36

[AT]

Table 2: Examples of plasticized and optionally modified flour compositions.

Temperatures (° C) Speed of

Flow Examples

Zone Zone Zone Zone Zone Zone Vis

(process) kg / h

1 2 3 4 5 6 (rpm)

Composition 1 80 to

<80 150 - - - 150 3 [Bl] 150

Composition 2 80 to

<80 150 100 130 150 150 5.4 [A] 150

Composition 3 80 to 130 to

<80 150 100 150 150 3 [A] 150 220

Composition 4 80 to 130 to

<80 150 100 150 150 5.4 [A] 150 220

Composition 5 80 to 130 to 150 * 3 *

<80 150 100 150

[B] 150 220 150 ** 5.4 **

Composition 6 80 to 130 to

<80 150 100 150 150 5.4 150 220

Composition 7 80 to 130 to

<80 150 100 150 150 5.4 150 220

Composition 8 80 to 130 to

<80 150 100 150 150 5.4 150 220

Composition 9 80 to 130 to

<80 150 100 150 150 5.4 150 220

Composition 10 80 to 130 to

<80 150 100 150 150 5.4 150 220

Composition 11 80 to 130 to

<80 150 100 150 150 5.4 150 220

Composition 12 80 to 130 to

<80 150 100 150 150 5.4 150 220

Table 3: Extrusion parameters used to prepare the plasticized and optionally modified flour compositions (* Step [B1] / ** Step [B2]) At the extruder outlet, the compositions 1 and 3, prepared according to the prior art , can not be cooled in water at the end of step [Bl] or [A]. The materials absorb very quickly water. The surface of the rushes becomes sticky and the plasticized flour dissolves in the water. On the other hand, when the rushes obtained from these plasticized flours, cooled in the air and dried, are immersed in water at 23 ° C, they disintegrate strongly after two hours of immersion. On the other hand, at the outlet of the extruder, the compositions 2, 4-5, 7, 9-12 prepared according to the invention (process [A] and [B]) can be cooled in water. The surface of the rushes is not affected.

When the rushes obtained from these plasticized and modified flours according to the invention, cooled in water and then dried, are immersed in water at 23 ° C, they retain their shapes and initial dimensions after 2 hours of immersion. . In addition, their surface is not altered. Flour plastified and modified according to the invention thus have a very low sensitivity to water. On the other hand, the same rods immersed in the organic solvent Rhodiasolv® Dibasic ester, are strongly disintegrated after two hours of immersion and almost solubilized after 24 hours. This result indicates that the plasticized and modified flours are organophilic. The insoluble levels measured (Table 4) show that the compositions prepared according to the prior art (without added acetic anhydride or with only 10% of anhydride) remain sensitive to water, whereas the compositions having more than 30 parts of anhydride make it possible to obtain a material that is not very sensitive to water.

Examples Insoluble rate after immersion in water

at 22 ° C for

2 hours 24 hours

Composition 1 84.5 69.4

Composition 2 99.5 98.8

Composition 3 89.9 72.3

Composition 4 99.8 99.3

Composition 5 99.7 99.1

Composition 6 86.3 71.3

Composition 7 99.5 99.0

Composition 8 95.2 92.8

Composition 9 99.9 99.9

Composition 10 99.8 99.4

Composition 11 99.6 99.1

Composition 12 99.9 99.9

Table 4: Insoluble levels of the plasticized and possibly modified arine compositions In fact, the composition 6 based on wheat flour (70 parts), plasticizer (30 parts), and acetic anhydride (7 parts + 2 parts of soda) has similar results to composition 1 also comprising 70 parts of wheat flour and 30 parts of glycerol. On the other hand, compositions 2, 5 and 7 comprising the same proportions of flour and of glycerol but also comprising at least 80 parts of anhydride and possibly of sodium hydroxide, have significantly higher properties with a level of insoluble material after immersion in water. water greater than 99%.

Claims

A method of modifying a composition comprising at least one plasticized flour in which, in an extruder, at least said plasticized flour is reacted with at least one organic anhydride, the amount of incorporated organic anhydride being between 30 and 670 parts by weight dry for 100 parts by dry weight of flour.

Process according to Claim 1, characterized in that the flour is chosen from the group comprising the flours of:

- cereals such as, wheat, rye, triticale, maize, barley, sorghum or rice;

- tubers such as cassava or potato;

- legumes such as soybeans or peas.

Process according to Claim 1, characterized in that the organic anhydride is chosen from the group comprising the following compounds or families of compounds:

mixed anhydride such as propanoic acetic anhydride or adipic acetic anhydride;

a mixture of these compounds.

Process according to Claim 1, characterized in that the amount of organic anhydride incorporated represents between 130 and 300 parts by dry weight per 100 parts by dry weight of flour, preferably between 150 and 200 parts.

Process according to Claim 1, characterized in that at least one catalyst capable of accelerating the reaction between the plasticized flour and the organic anhydride is added to the extruder.

6. Method according to claim 5 characterized in that the catalyst is a strong base, preferably sodium hydroxide and the amount is between 0.2 and 10 parts by weight per 100 parts by dry weight of flour. Process according to Claim 1, characterized in that the plastification of the flour is carried out in the extruder before the addition of the organic anhydride, starting from at least one flour and at least one first plasticizing agent.

Process according to Claim 7, characterized in that the said first plasticizing agent is chosen from the group comprising:

- diols;

- the triols;

salts of organic acids such as sodium lactate;

- urea;

a mixture of these compounds.

Process according to Claim 7, characterized in that the quantity of the first plasticizing agent represents from 10 to 150 parts by weight per 100 parts by dry weight of flour, preferably from 25 to 120 parts by weight and in particular from 40 to 120 parts by weight. weight.

Process according to Claim 1, characterized in that at least one second plasticizer is added to the extruder.

Process according to claim 10 characterized in that said second plasticizer is selected from the group consisting of:

a mixture of these compounds.

Process according to Claims 7 to 8, and 10 to 11, characterized in that the total amount of plasticizing agents (first plasticizing agent and second plasticizer included) represents from 20 to 180 parts by weight of plasticizer per 100 parts by weight dry flour, preferably from 35 to 150 parts by weight and in particular from 50 to 150 parts by weight.

13. The method of claim 1 characterized in that dehydrates the plasticized flour continuously by exposing the reaction medium to a reduced pressure before the addition of the organic anhydride.

14. The method of claim 1 characterized in that at least one flour is added before plasticized and dehydrated in the extruder with at least one organic anhydride.

15. Thermoplastic composition comprising a modified plastic flour obtainable by the method according to one of the preceding claims.