METHOD FOR MODIFYING POLYSACCHARIDE MATERIAL BY SEQUENCED HOMOGENEOUS CHEMICAL FUNCTIONALISATION

Abstract

The present invention concerns a method for modifying a polysaccharide material, preferably an amylaceous material, involving a first step of homogeneous solubilisation of said polysaccharide material in an aqueous solvent, followed by a step of homogeneous chemical functionalisation comprising at least one non-crosslinking chemical modification, or at least one crosslinking chemical modification, or a sequence of at least one non-crosslinking chemical modification and at least one crosslinking chemical modification. Secondly, the present invention concerns a modified polysaccharide material, in particular obtained by the method according to the invention, characterised in that it has a novel distribution of the chemical substituents attached to the hydroxyl functions of the anhydroglucose units of said polysaccharide material. The novel starches can be used as organic adjuvants for dry mortars made from cement or made from gypsum, in particular as a binder for a dry mortar made from cement or as a thickening agent for a mortar made from plaster.

Claims

1-15. (canceled)

16. A process for modifying a polysaccharide material including anhydroglucose units, comprising the dissolution, preferentially the total dissolution, of this polysaccharide material, and homogeneous chemical functionalization of the dissolved polysaccharide material, characterized in that: a. the dissolution is performed before the chemical functionalization, b. the chemical functionalization consists of a sequence of at least two non-crosslinking esterifications chosen between hydroxyalkylation and carboxyalkylation.

17. The process for modifying a polysaccharide material as claimed in claim 16, wherein a non-crosslinking esterification is a hydroxyalkylation, performed until the polysaccharide material has a degree of substitution of between 0.05 and 2.

18. The process for modifying a polysaccharide material as claimed in claim 17, wherein a non-crosslinking esterification is a hydroxyalkylation performed until the polysaccharide material has a degree of substitution of between 0.1 and 1, preferentially between 0.15 and 0.6.

19. The modified polysaccharide material as claimed in claim 16, wherein a non-crosslinking chemical esterification is a hydroxyalkylation and wherein the hydroxyalkyl group is chosen from hydroxypropyl or hydroxyethyl, preferentially hydroxypropyl.

20. The process for modifying a polysaccharide material as claimed in claim 16, wherein the non-crosslinking esterification is a carboxyalkylation, performed until the polysaccharide material has a degree of substitution of between 0.03 and 2.

21. The process for modifying a polysaccharide material as claimed in claim 16, wherein the non-crosslinking esterification is a carboxyalkylation, performed until the polysaccharide material has a degree of substitution of between 0.03 and 1, preferentially between 0.03 and 0.3.

22. The process for modifying a polysaccharide material as claimed in claim 16, wherein a non-crosslinking chemical esterification is a carboxyalkylation and wherein the carboxyalkyl group is carboxymethyl.

23. The process for modifying a polysaccharide material as claimed in claim 16, wherein the chemical functionalization consists of a sequence of at least two non-crosslinking esterifications wherein the hydroxyalkylation preceeds that carboxyalkylation.

24. The process for modifying a polysaccharide material as claimed in claim 16, wherein a non-crosslinking chemical modification is a hydroxyalkylation, performed until the hydroxyalkyl groups substituting the hydroxyl functions of the anhydroglucose units of the polysaccharide material are distributed in the following manner: at most 68%, preferentially at most 65%, very preferentially at most 64% in position 2, and/or at least 15%, preferentially at least 17%, very preferentially at least 17.5% in position 3, and/or at least 15%, preferentially at least 17%, very preferentially at least 18% in position 6, the sum of the percentages of the hydroxyalkyl groups substituting the hydroxyl functions being equal to 100% and these percentages being measured by proton NMR.

25. The process for modifying a polysaccharide material as claimed in claim 16, wherein a non-crosslinking chemical modification is a carboxyalkylation, performed until the carboxyalkyl groups substituting the hydroxyl functions of the anhydroglucose units of the polysaccharide material are distributed in the following manner: at least 75.5%, preferentially at least 76.5% in position 2, and/or at most 20%, preferentially at most 19% in position 3, and/or at least 4%, preferentially at least 5% in position 6, the sum of the percentages of the carboxyalkyl groups substituting the hydroxyl functions being equal to 100% and these percentages being measured by proton NMR.

26. A modified polysaccharide material including anhydroglucose units, preferentially a modified starch, which is totally water-soluble, the hydroxyl functions of said anhydroglucose units being substituted with at least one hydroxyalkyl chemical group and characterized in that the hydroxyalkyl groups substituting the hydroxyl functions are distributed in the following manner: at most 68%, preferentially at most 65%, very preferentially at most 64% in position 2, and/or at least 15%, preferentially at least 17%, very preferentially at least 17.5% in position 3, and/or at least 15%, preferentially at least 17%, very preferentially at least 18% in position 6, the sum of the percentages of the hydroxyalkyl groups substituting the hydroxyl functions being equal to 100% and these percentages being measured by proton NMR.

27. The modified polysaccharide material as claimed in claim 26, the hydroxyl functions of said anhydroglucose units being substituted with at least one carboxyalkyl chemical group and characterized in that the carboxyalkyl groups substituting the hydroxyl functions are distributed in the following manner: at least 75.5%, preferentially at least 76.5% in position 2, and/or at most 20%, preferentially at most 19% in position 3, and/or at least 4%, preferentially at least 5% in position 6, the sum of the percentages of the carboxyalkyl groups substituting the hydroxyl functions being equal to 100% and these percentages being measured by proton NMR.

28. The modified polysaccharide material as claimed in claim 26, characterized in that the hydroxyalkyl group is chosen from hydroxypropyl or hydroxyethyl, and is preferentially hydroxypropyl.

29. The modified polysaccharide material as claimed in claim 26, characterized in that the hydroxyalkyl group is a hydroxypropyl group, and characterized in that its degree of hydroxypropyl substitution is between 0.05 and 2, preferentially between 0.1 and 1 and most preferentially between 0.15 and 0.6.

30. The modified polysaccharide material as claimed in claim 26, characterized in that the carboxyalkyl group is carboxymethyl.

31. The modified polysaccharide material as claimed in claim 26, characterized in that its degree of carboxymethyl substitution is between 0.03 and 2, preferentially between 0.03 and 1 and most preferentially between 0.03 and 0.3.

32. The modified polysaccharide material as claimed in claim 26, characterized in that it is in the form of a powder which has a volume-mean diameter, measured by dry-route laser scattering, of between 10 μm and 1 mm, preferentially between 50 μm and 500 μm.

33. The modified polysaccharide material as claimed in claim 26, characterized in that it is soluble without heating, preferentially at least 95% amorphous, more preferentially at least 98% amorphous and most preferentially totally amorphous.

34. A dry mortar composition, preferentially a dry mortar for tile adhesive, and most preferentially a mortar for ceramic tile adhesive, comprising an organic adjuvant comprising the modified polysaccharide material obtained according to the method of claim 16.

35. A gypsum-based mortar, preferentially in a spraying plaster or in a plasterboard plaster, comprising the modified polysaccharide material obtained according to the method of claim 16.

Description

FIGURES

[0238] FIG. 1: location of the hardness measurement points on a plasterboard

[0239] FIG. 2: graph of comparison of the hardnesses at 5 mm (N) of plasterboards

EXAMPLES

Example 1: Preparation of Starch Modified According to the Process of the Prior Art

[0240] The example that follows describes the process for preparing a modified starch according to the prior art.

[0241] Modification Process:

[0242] This example of implementation of the process according to the prior art is performed in a Druvatherm DVT10 reactor from the manufacturer Lödige Process Technology. It is a jacketed, horizontally positioned cylindrical reactor, the stirring device of which is suitable for fluids with a viscosity which may be up to 1000000 mPa.Math.s. The stirring device consists of a main mixer with plowshare paddles arranged along the central horizontal axis, and a secondary mixer with rotating knives arranged close to the inner wall of the reactor. Each mixer can rotate at its own adjustable speed.

[0243] For all the operations performed in this example, the stirring is set at 100 rpm for the main mixer and at 1000 rpm for the secondary mixer.

[0244] The first step is the preparation of a starch milk. To do this, 2500 g of dry potato starch are spread into 3750 g of water at 39° C., 725 g of sodium sulfate powder are then dissolved in this starch milk and the pH of the milk is adjusted to 8 with aqueous 5% sodium hydroxide solution.

[0245] The second step is granular-phase hydroxypropylation, catalyzed with sodium hydroxide, to reach a degree of substitution of 0.25. 800 g of aqueous 5% sodium hydroxide solution, i.e. 40 g of dry sodium hydroxide, are introduced into the milk. This amount of sodium hydroxide is the catalyst for the hydroxypropylation reaction. 260 g of liquid propylene oxide are introduced while maintaining a pressure of less than or equal to 3 bar in the reactor. The reaction medium is then maintained at 39° C. for 16 hours, until the propylene oxide has been totally consumed, without regulating the pressure. During this hydroxypropylation, the starch conserves its granular structure, by means of the sodium sulfate present and at a temperature below the gelatinization temperature of potato starch (about 65° C.).

[0246] The third step is the cooking, i.e. gelatinization, of the hydroxypropylated starch to obtain a starch adhesive. The temperature of the reactor is increased to 80° C. and maintained for 60 minutes to obtain a homogeneous adhesive of stable viscosity.

[0247] The fourth step of the starch modification is carboxymethylation catalyzed with sodium hydroxide. 803 g of aqueous 50% sodium hydroxide solution, i.e. 401.5 g of dry sodium hydroxide, are introduced into the starch adhesive: this amount of sodium hydroxide is the catalyst for the carboxymethylation. 900 g of dry sodium monochloroacetate are introduced in a single portion into the starch adhesive. The reactor is stirred at 80° C. for 5 hours to reach the end of the reaction.

[0248] The next step in the modification of the gelatinized and carboxymethylated hydroxypropylated starch, i.e. the fifth step in this process, is crosslinking catalyzed with the excess sodium hydroxide introduced during the preceding reactions. The crosslinking agent is sodium trimetaphosphate. 2.5 g of this salt are introduced in dry form into the reaction medium. The reactor is stirred at 80° C. for 3 hours.

[0249] Drying Protocol:

[0250] The modified starch gel obtained on conclusion of the three chemical substitutions is then transformed into a solid by passing through a drying drum from the manufacturer Andritz Gouda, at a spin speed of 7.5 rpm, the cylinders of which are heated to 90-100° C. with steam at 10 bar. Flakes of a solid starch are thus obtained. These flakes are successively milled in a hammer mill from the manufacturer Retsch, equipped with a 2 μm grate, at 1500 rpm, and then in a Septu brand ultra-fine mill set at 50 Hz, at a spin speed of 3000 rpm. This results in a fine whitish powder. The volume-mean diameter of this powder is 37 μm.

[0251] The degrees of substitution of the starch are: 0.25 of hydroxypropyl functions, and 0.36 of carboxymethyl functions, and 1000 ppm of trimetaphosphate. This starch is referenced EDT 4.

[0252] Three other starches according to the prior art are prepared by partly following the prior art process.

[0253] Two starches are prepared by performing the hydroxypropylation, gelatinization and carboxymethylation, but not the crosslinking: EDT 3 is prepared with a degree of hydroxypropyl substitution of 0.2 and of carboxymethyl substitution of 0.1 by using 260 g of propylene oxide and 300 g of sodium monochloroacetate; EDT 2 is prepared with a degree of hydroxypropyl substitution of 0.7 and of carboxymethyl substitution of 0.2 by using 910 g of propylene oxide and 600 g of sodium monochloroacetate. A starch, denoted EDT 1, is prepared by performing only the hydroxypropylation with 650 g of propylene oxide to achieve a degree of substitution of 0.5.

TABLE-US-00001 TABLE 1 starches prepared according to the process of the prior art DS with DS with DS with Base hydroxy- carboxy- tri- D43 Reference starch propyl methyl metaphosphate (μm) EDT 1 Potato 0.5 0 0 37 EDT 2 starch 0.7 0.2 0 35 EDT 3 0.2 0.1 0 40 EDT 4 0.25 0.36 1000 42

Example 2: Preparation of Starches Modified According to the Process of the Invention

[0254] The example that follows describes the process for preparing a modified starch according to the invention.

[0255] Modification Process:

[0256] This example of implementation of the process according to the invention is performed in a Druvatherm DVT10 reactor from the manufacturer Lödige Process Technology, identical to the reactor used for example 1 of the process according to the prior art.

[0257] First, a starch gel is prepared by performing the gelatinization of the native starch under the effect of heat in the presence of sodium hydroxide. To do this, 2500 g of dry potato starch are spread in 5833 g of water at 20° C. with stirring at 100 rpm for the main mixer and at 1000 rpm for the secondary mixer, and the temperature of the reaction medium is then gradually increased to about 80° C. at about 10° C./hour. During this heating, when the temperature reaches 65° C., the stirring speed of the main mixer is increased to 200 rpm and that of the secondary mixer to 2000 rpm, and 80 g of aqueous 50% sodium hydroxide solution are then added to the starch suspension over 5 minutes, i.e. 40 g of dry sodium hydroxide, to facilitate the splitting of the starch grains. After reaching the temperature of 80° C., the starch gel is kept stirring at this temperature for 1 hour to obtain a homogeneous gel. The starch gel obtained does not contain any whole or split grains: the starch is dispersed in its entirety in the form of a hydrocolloid.

[0258] Secondly, the chemical modifications are performed, conserving the stirring parameters used previously: namely, a speed of 200 rpm for the main mixer, and a speed of 2000 rpm for the secondary mixer.

[0259] The first chemical modification of the gelatinized starch is hydroxypropylation catalyzed with sodium hydroxide. No additional amount of sodium hydroxide is added. 294 g of liquid propylene oxide are introduced while maintaining a pressure of 3 bar in the reactor. The reaction medium is then maintained at 80° C. for 4 hours, until the propylene oxide has been totally consumed. On conclusion of this hydroxypropylation, a starch referenced ROQ 1 may be isolated in solid form by following the drying protocol below.

[0260] The second modification is carboxymethylation catalyzed with sodium hydroxide. 214 g of aqueous 50% sodium hydroxide solution, i.e. 107 g of dry sodium hydroxide, are introduced into the starch adhesive: this amount of sodium hydroxide is the catalyst for the carboxymethylation. 240 g of dry sodium monochloroacetate are introduced in a single portion into the starch adhesive. The reactor is stirred at 80° C. for 5 hours to reach the end of the reaction. On conclusion of this carboxymethylation, a starch referenced ROQ 2 is prepared in solid form by following the drying protocol below.

[0261] The third modification step is crosslinking catalyzed with the excess sodium hydroxide introduced during the preceding reactions. The crosslinking agent is sodium trimetaphosphate. 2.5 g of this salt are introduced in dry form into the reaction medium. The reactor is stirred at 80° C. for 3 hours. A modified starch ROQ3 is prepared in solid form by following the drying protocol below.

[0262] A modified starch ROQ4 is prepared according to the same modification protocol as ROQ 1 above, this time using a potato starch/pea starch mixture in a 50/50 ratio. 1250 g of potato starch are mixed with 1250 g of pea starch for a total of 2500 g of starch. A modified starch ROQ5 is prepared according to the same modification protocol as ROQ3 above, this time using a potato starch/pea starch mixture in a 50/50 ratio. 1250 g of potato starch are mixed with 1250 g of pea starch for a total of 2500 g of starch.

[0263] Drying Protocol:

[0264] As for the modified starch of example 1, the modified starch gel obtained on conclusion of the three chemical substitutions is then transformed into a solid by the same operations, of drying on a drying drum and of successive milling, as those performed in example 1, resulting in a fine whitish powder. The volume-mean diameter of this powder is 35 μm.

[0265] The degrees of substitution of the starch are: 0.2 of hydroxypropyl functions, and 0.1 of carboxymethyl functions, and 1000 ppm of trimetaphosphate.

TABLE-US-00002 TABLE 2 starches prepared according to the process of the invention DS with DS with DS with hydroxy- carboxy- tri- D43 Reference Base starch propyl methyl metaphosphate (μm) ROQ 1 Potato 0.2 0 0 35 ROQ 2 starch 0.2 0.1 0 37 ROQ 3 0.2 0.1 1000 ppm 40 ROQ 4 50/50 0.2 0 0 38 ROQ 5 starch 0.2 0.1 1000 ppm 32 potato/pea

Example 3: Sliding Resistance and Setting Time of Adhesive Mortars

[0266] According to the standard NF EN 12004-2: 2017-04, tile adhesives are prepared according to the instructions of paragraph 6, starting with dry mortars of composition chosen by the Applicant to be discriminating between the mortars. These adhesives are used to bond ceramic tiles 10 cm×10 cm in size, in order to compare the sliding resistances thereof, according to the instructions of point 8.2 of said standard.

[0267] Preparation of the Dry Mortar:

[0268] The composition of the dry mortar is 40 parts of CEM I Portland 52.5N CP2 cement supplied by Equiom, 59 parts of sand 0.1-0.4 μm in size supplied by Société Nouvelle du Littoral, 0.50 part of the redispersible powder Vinnapas 5010N supplied by Wacker, 0.50 part of the cellulose ether Walocel MKX 6000 supplied by Dow, and 0.05 part of modified starch, according to the prior art or according to the invention. The masses of products making it possible to prepare 847.9 g of dry mortar satisfying this composition are given in table 3. All the components are in the form of dry powders.

[0269] The required masses of these powders are mixed in a L01.M03 planetary mixer from the manufacturer Euromatest Sintco, at a stirring speed of 140 rpm for the rotor speed and of 62 rpm for the planetary movement, for 15 minutes.

TABLE-US-00003 TABLE 3 composition of the dry mortar for tile adhesive Parts Commercial by dry Mass Components references weight (grams) CEM I (Portland) CEM I - 52.5N - CP2 from Equiom 40 339 0.1-0.4 μm sand Société Nouvelle du Littoral 59 500 Redispersible powder Vinnapas 5010N from Wacker 0.50 4.24 Cellulose ether Walocel MKX 6000 from Dow 0.50 4.24 Starch Variable according to the tests 0.05 0.42

[0270] The 0.1-0.4 μm sand is composed of particles with a diameter ranging from 0.1 μm to 0.4 μm, and the particle size of which is characterized by a D.sub.10 of 171 μm, a D.sub.50 of 270 μm, a D.sub.90 of 418 μm and a D.sub.4.3 of 284 μm.

[0271] Preparation of the Mortar Adhesive (Mixing Operation):

[0272] A tile adhesive is prepared from the dry mortar, adhering to a ratio of the mass of water to the mass of cement of 0.7. Thus, 237.3 g of water and 847.9 g of dry mortar prepared according to the composition of table 3 are mixed according to the procedure of point 6 of the standard NF EN 120004-2, the only difference being that only one mixing operation is performed, instead of the two envisaged by the standard. Thus, the mass of water is poured into the tank of an L01.M03 automatic mortar mixer from the manufacturer Euromatest Sintco in accordance with the standard EN 196-1: 2016. The mass of dry mortar is then dispersed in the water, and mixing is then applied for one minute at a spin speed of 285±10 rpm and a planetary movement of 125±10 rpm. On conclusion of this single mixing operation, the adhesive is used immediately in a sliding resistance test.

[0273] Method for Measuring the Sliding Resistance

[0274] The materials and the apparatus are those of the standard NF EN 12004-2: 2017-04. The adhesive mortars are prepared according to example 3. The procedure is that of paragraph 8.2.3 of said standard.

[0275] Implementation of this procedure leads to an amount per unit area of adhesive used ranging from 2.5 to 3.5 kg of adhesive per m.sup.2 of concrete.

[0276] Method for Measuring the Setting Time

[0277] The method for measuring the setting time is that described in the standard NF EN 480-2:2006-11, using a PA8 automatic setting meter from the manufacturer Acmel, equipped with a Vicat needle 1.13 mm in diameter and 50 mm long, and a Vicat frustoconical mold with a base diameter of 80 mm, a top diameter of 70 mm and a height of 40 mm. Unlike in the standard, all the steps required for preparing and performing the setting time test are performed in an atmosphere at 23° C.±2° C. and a relative humidity of 50%±5%.

[0278] Results:

[0279] The sliding values and setting onset time measured for various adhesives prepared from dry mortars differing in the nature of the starch present are presented in table 4.

TABLE-US-00004 TABLE 4 comparison of the sliding results measured Sliding value Setting onset measured time Starch Chemical according to according Sliding used modifications NF EN to NF test in the dry Starchy HP CM TMPNa 12004-2 EN 480-2 reference mortar base (DS) (DS) (ppm) (mm) (hours) G0 Without — — — — 150 16 starch G1 EDT 1 Potato 0.5 — — 62.7 21.8 G2 EDT 2 (pot) 0.7 0.2 — 6.4 19.7 G3 EDT 3 0.2 0.1 — 12.7 n.d. G4 EDT 4 0.25 0.36 1000 150 21 G5 ROQ 1 0.2 — — 1.7 20.7 G6 ROQ 2 Potato 0.2 0.1 — 7.1 15.8 G7 ROQ 3 (pot) 0.2 0.1 1000 4.5 17.1 G8 ROQ 4 50/50 0.2 — — 1.7 n.d. G9 ROQ 5 pot/pea 0.2 0.1 1000 4.2 n.d.

[0280] When only hydroxypropylation is performed (tests G1, G5 and G8), the improvement in the sliding resistance is just as large: the modified starch EDT 1 leads to a sliding value of 62.7 mm, whereas the modified starches ROQ1 and ROQ4 give sliding values of 1.7 mm. Such a low sliding value is moreover less than that of the market reference product Casucol 301, which has a sliding value of 6.4 mm.

[0281] When the three chemical substitutions are performed (tests G4, G7 and G9), the effect of the process according to the invention relative to the process of the prior art is flagrant: the modified starch EDT4 leads to a maximum sliding value of 150 mm, which is unacceptable, whereas the modified starches ROQ 3 and ROQ 5 both lead to sliding values of 4.5 mm and 4.2 mm, which are entirely acceptable.

Example 4: Gypsum-Based Spraying Mortar

[0282] The modified starches according to the invention may be used as binding organic adjuvant in the gypsum-based spraying mortar formulation according to table 5.

TABLE-US-00005 TABLE 5 spraying mortar composition Parts Commercial by dry Mass Components references (supplier) weight (grams) Gypsum Beta plaster of Paris (Dislab) 66 450 Hydrated lime a 63 hydrated lime (Lhoist France) 3 20.5 Calcium carbonate Mikhart 5 - 5 μm (Provencal S.A) 30 204.6 Retardant Tartaric acid (Merck) 0.2 1.36 Cellulose ether Culminal ® MHEC 15000 PFR (Ashland) 0.1 0.68 Air entraining agent Berolan LP-W 1 (Berolan) 0.01 0.070 Light aggregate Perlite 0-1 mm 0.8 5.5 Starch Variable according to the test 0.02 0.14

[0283] The Beta plaster of Paris sold by Dislab® is composed of 60% of beta-calcium sulfate hemihydrate, 20% of anhydrite II and 10% of calcium sulfate dihydrate. It is a fine powder, the particle size of which is characterized by a D.sub.10 of 2.9 μm, a D.sub.50 of 24.5 μm and a D.sub.90 of 99 μm, as measured by dry-route laser scattering particle size analysis on a Malvern Mastersizer particle size analyzer.

[0284] All the components of the formulation, stabilized beforehand at 23° C.±2° C. and under an atmosphere at 50%±5% relative humidity, are weighed out in a reclosable 1-liter glass jar.

[0285] This powder mixture is homogenized in a L01.M03 planetary mixer from the manufacturer Euromatest Sintco, at a stirring speed of 140 rpm for the rotor speed and of 62 rpm for the planetary movement, for 15 minutes. The dry spraying mortar is thus obtained.

[0286] 400 g of drinking water at 23° C.±2° C. are placed in another L01.M03 automatic mortar mixer from Euromatest Sintco, in accordance with the standard NF EN 196-1. All 682.85 g of the dry spraying mortar are poured into the water without stirring. Immediately after this addition, the stirring of the mixer is started at a slow speed for 10 seconds, and then at a fast speed for 50 seconds. Following this mixing, the mortar is immediately sprayed onto a concrete wall. The layer of mortar adheres correctly to the concrete support, and does not collapse.

Example 5: Thickener for Plasterboard Plaster

[0287] The starches modified according to the process of the invention have thickening properties for plasterboard plasters. The thickening properties of various modified starches according to the invention are compared according to a Vicat spreading measurement according to paragraph 4.3.2 entitled “Dispersion method” of the standard NF EN 13279-2 (revision of February 2014) entitled “Liants-plâtres et enduits à base de plâtre pour le bâtiment—Partie 2: méthodes d'essais [Binding plasters and plaster-based renderings for construction—Part 2: test methods]”.

[0288] Preparation of the Wet Plaster:

[0289] The modified starches according to the invention may be used as binding organic adjuvant for forming wet plasters for plasterboards. According to the formulation of table 6, several starches modified according to the process of the invention are tested.

TABLE-US-00006 TABLE 6 composition of the plasterboard Commercial Mass Components references (supplier) (grams) Gypsum Beta plaster of Paris (Dislab) 300 Starch Variable according to the test 0.3375 Water Drinking water 210

[0290] A wet plaster is prepared by pouring all of the dry mixture of the components, homogenized beforehand in an L01.M03 planetary mixer from the manufacturer Euromatest Sintco, at a stirring speed of 140 rpm for the rotor speed and 62 rpm for the planetary movement, for 15 minutes, onto a mass of water and mixing using a whisk in a figure-of-eight movement for 45 seconds, in order to obtain a lump-free homogeneous paste. On concluding the mixing, the wet plaster is engaged in the spreading measurement.

[0291] Spreading Measurement:

[0292] A Vicat frustoconical ring with a base diameter of 75 mm is filled with a wet plaster preparation according to the formulation of table 6, taking care to pour the plaster slowly into the ring so as not to incorporate any air bubbles, and leveling off the free surface with a blade. This filling operation generally takes about 15 seconds. Immediately on conclusion of the filling, the Vicat ring is abruptly raised vertically in order to release the plaster, which can then spread onto the support glass plate, to form a puddle of wet plaster. 15 seconds after removing the ring, the spreading has generally stabilized, and the mean maximum diameter of the puddle of wet plaster is measured.

TABLE-US-00007 TABLE 7 comparative of the spreading values measured for starches according to the invention Viscosity according to test Reference of the A: at 10% solids starch used in Starch/ Spreading in water, at 20° C. the plaster modifications (mm) (mPa .Math. s) Without starch / 171 na EDT 5 Amidon M-B-065 R starch sold by Roquette 172 Not available Freres (native corn starch)/no modification ROQ 1 Potato/hydroxypropylated DS = 0.2 78 5 000 ROQ 2 Potato/hydroxypropylated DS = 0.2 and 138 1 300 carboxymethylated DS = 0.1 ROQ 3 Potato/hydroxypropylated DS = 0.2; 76   500 carboxymethylated DS = 0.1 and crosslinked TMPNa 1000 ppm ROQ 8 Pea/hydroxypropylated DS = 0.2 157 23 300  ROQ 9 Pea/hydroxypropylated DS = 0.2; 134  8800 carboxymethylated DS = 0.1 ROQ 10 Pea/hydroxypropylated DS = 0.2; 76  2500 carboxymethylated DS = 0.1 and crosslinked TMPNa 1000 ppm

[0293] Without starch or with a native corn starch Amidon M-B-065-R from Roquette Frères, the spreading achieved exceeds 170 mm, which illustrates the total absence of thickening of the wet plaster.

[0294] As regards the starches modified using potato starch, the starch ROQ 1 gives a spreading value of 78 mm, i.e. only 3 mm more than the diameter of the Vicat ring base. This demonstrates that a starch modified by means of the process according to the invention, the only chemical modification being a hydroxypropylation with a DS of 0.2, allows strong thickening of the wet plaster. The addition of a carboxymethylation with a DS of 0.1 (starch ROQ 2) gives a spreading value of 138 mm, which demonstrates degradation of the thickening effect. This might be due to the decrease in viscosity of the starch according to test A to 1300 mPa.Math.s. Surprisingly, the addition of a carboxymethylation with a DS of 0.1 and crosslinking with sodium trimetaphosphate at 1000 ppm (starch ROQ 3), makes it possible to regain the thickening power of the starch ROQ 1 which is only hydroxypropylated. This is all the more surprising since the viscosity according to test A of the starch ROQ 3 per se was, however, further decreased to 500 mPa.Math.s relative to ROQ 2. The regain of thickening power is thus not due to the viscosity of the modified starch, but to the interactions once again made possible by virtue of the spatial structure imposed by the crosslinking.

[0295] As regards the starches modified using pea starch, the starch ROQ 8 only substituted by hydroxypropylation with a DS of 0.2 leads to a high spreading value, of 157 mm, despite a high viscosity according to test A, of 23300 mPa.Math.s. This spreading value is reduced to 134 mm by addition of a carboxymethylation with a DS of 0.1 (starch ROQ 9). However, for these two starches, there is clearly no thickening effect on the wet plaster. Surprisingly, for the starch ROQ 10 which has additionally undergone crosslinking with 1000 ppm of trimetaphosphate, the spreading value is virtually equal to the diameter of the Vicat ring, which indicates that the wet plaster has virtually not spread, and thus that the thickening power of the starch ROQ 10 is high. This is all the more surprising since the viscosity of the starch ROQ10 according to test A is less than that of the starches ROQ 8 and ROQ9. In the case of the pea starch, the short-distance crosslinking thus made it possible to reveal the thickening power of the triply modified starch: the short-distance crosslinking gave a spatial structure which makes the hydrogen interactions of the hydroxypropyl groups efficient.

Example 6: Core Reinforcement of Plasterboards

[0296] This example illustrates the increase in “core” mechanical strength by the starches according to the invention for plasterboards prepared from the gypsum-based plaster formulation of example 5 (table 6).

[0297] One way of characterizing the core mechanical strength of a plasterboard is to measure the force required, expressed in newtons (N), to make a point penetrate therein to a certain depth, such as with an Instron® 9566 reference rheometer. According to this way of working, the Applicant measured the force required for a geometry point of “circular-based pyramid” type to penetrate 5 mm into the plasterboard at a speed of 10 mm/minute, at a temperature of 20° C. The dimensions of the point are: circular base diameter equal to 4 mm, height equal to 2.5 cm, and thickness of the top of the point equal to 1 mm.

[0298] The hardnesses of the plasterboards prepared with starches according to the invention, namely the starches ROQ 1 and ROQ 3, are thus compared with the hardnesses of plasterboards prepared without starch, with native starches (corn starch, pea starch) or with a pregelatinized starch (Roquette commercial starch M-ST 310).

[0299] Preparation of the Plasterboards:

[0300] Plasterboards of length×width×thickness dimensions equal to 15 cm×7.5 cm×1 cm are each prepared according to the following protocol. When starch is added, only one type of starch is added. There is no mixture of starches.

[0301] A wet plaster paste is prepared according to the same protocol as in example 5, with a modification included: 0.33 g of accelerator is added to the dry mixture of gypsum and starch. The accelerator is a powder consisting of plaster, obtained from a commercial plasterboard free of its cardboard faces, which has been manually ground with mortar and dried in an oven at 110° C. for 1 hour.

[0302] Immediately on conclusion of its preparation, all the approximately 510.67 g of paste is poured in excess onto a rectangular “plasterboard” cardboard placed in a rectangular steel mold, and covering the entire surface of the mold (15×7.5 cm), the assembly resting on a plastic plate. The term “excess” means that the mass of plaster paste is greater than the mass that the mold can receive, which thus ensures that all the available volume is filled with plaster paste. The rectangular cardboard at the bottom of the mold constitutes the lower face of the plasterboard. Once the casting of the plaster in the mold is complete, a rectangular cardboard (15×7.5 cm) is placed on top of the paste, the concave part of the rectangular cardboard being placed in contact with the paste. This second cardboard constitutes the upper face of the plasterboard. A second plastic plate is then placed on top of this rectangular cardboard, so as to cover the entire surface of the mold.

[0303] A 10 kg mass is then placed on the upper plastic plate so as to uniformly cover the surface of the upper cardboard face, for a period of 5 minutes. During the application of this mass, the excess mass of plaster paste spills out at the sides. The mass is then removed, and the assembly is then left as is, to rest in a horizontal position for 4 minutes, after which the plasterboard is stripped from the mold and placed on its edge in the vertical position of its longer edge, for 10 minutes. The plate is then dried standing on its edge, in an oven saturated with water, at 180° C. for 20 minutes, and then in another oven not saturated with water, at 110° C. for 20 minutes, and finally in an oven not saturated with water, at 45° C. for 12 hours. The plasterboard thus obtained is stabilized in a room conditioned at 23° C.±2° C. and humidity of 50%±5% for at least 2 days.

[0304] Protocol for Measuring the Hardness of the Plasterboard:

[0305] The hardness of each plasterboard is measured by means of the resistance to the penetration of a punch to a depth of 5 mm at a speed of 10 mm/minute with an Instron® 9566 machine. This “5 mm” hardness is expressed in newtons (N). For each plate, five penetration measurements are taken distributed over the surface of the plasterboard according to FIG. 1 so as to take into account any inhomogeneities of the plasterboard: the 5 mm hardness is a mean value of these five measurements, and the standard deviation is given for information (in newtons).

[0306] 5 mm Hardness Results:

[0307] Compared with a plasterboard prepared with a starch-free plaster paste, the results (table 8 and FIG. 2) show an increase in hardness of about 7% by virtue of the addition of native starch to the plaster paste, and of about 10% by virtue of the addition of Roquette M-ST 310 pregelatinized starch. The increase in hardness reaches about 26% with the starches ROQ 1 and ROQ 3 according to the invention. The starches ROQ 1 and ROQ 3 according to the invention are thus efficient for increasing the hardness of a plasterboard, i.e. they make it possible to increase the core mechanical strength of the plasterboard.

TABLE-US-00008 TABLE 8 results of the 5 mm hardness measurements 5 mm Standard Nature of hardness deviation the starch (newtons) (±) Without starch 194.5 13 Native corn starch 208.5 4 Native pea starch 206.6 11 Roquette M-ST 310 213.6 11 pregelatinized starch ROQ 1 starch 245.1 13 ROQ 3 starch 245.8 7

Example 7: Characterization of the Starches According to the Invention by Proton NMR

[0308] In this example, it is explained how to exploit proton NMR measurements on a starch which has undergone two successive chemical modifications: in a first stage, a hydroxypropylation, a sample of which, denoted as “Ech_HP”, is analyzed; and then, in a second stage, a carboxymethylation, a sample of which, denoted as “Ech_HP+CM”, is analyzed by means of the preceding analysis of the hydroxypropylated sample “Ech_HP”, notably by subtracting the signals of the H1 protons due to the hydroxypropylation.

[0309] The present method is an adaptation of the method disclosed in the article “Determination of the level and position of substitution in hydroxypropylated starch by high-resolution 1H-NMR spectroscopy of alpha-limit dextrins”, from A. Xu and P. A. Seib, published in the Journal of Cereal Science, vol. 25, in 1997, on pages 17 to 26.

[0310] Proton NMR Method for the Identification and Quantification of the Positions of the Hydroxypropyl Groups of the Sample Ech HP:

[0311] This method is valid for a starch modified only with hydroxypropyls.

[0312] The analysis is performed by proton nuclear magnetic resonance, NMR, at 25° C. in deuterium oxide solvent, D.sub.2O, with a purity of at least 99.8%, and deuterium chloride, DCI, on a Brüker Spectrospin Avance III spectrometer, operating at 400 MHz, using NMR tubes 5 mm in diameter.

[0313] A solution of sample to be analyzed is prepared by diluting about 15 mg, to within a mg, in 750 microliters of D.sub.2O+100 microliters of 2N DCI, in an NMR tube. The 2N DCI is a solution of deuterium chloride at a double-normality concentration, in deuterium oxide. The sample is heated on a boiling water bath until dissolution is complete and a clear, fluid solution is obtained. The NMR tube is allowed to return to room temperature.

[0314] The proton nuclear magnetic resonance spectrum is then acquired at 25° C. at 400 MHz.

[0315] With reference to the article by Xu and Seib, the anhydroglucose (denoted as AGU) H1 protons are identified as follows: [0316] at 5.61 ppm and 4.64 ppm: the H1 protons of the alpha-reducing and beta-reducing terminal AGUs, [0317] at 4.95 ppm: the H1 protons of the alpha-(1,6) bonded AGUs, [0318] at 5.67 ppm: the H1 protons of the AGUs whose hydroxyl in position 2 is etherified; the surface area is denoted as S_OR2_HP, [0319] at 5.52 ppm: the H1 protons of the AGUs whose hydroxyl in position 3 is etherified; the surface area is denoted as S_OR3_HP, [0320] at 5.40 ppm: the H1 protons of the AGUs alpha-(1,4) bonded and the H1 protons of the AGUs whose hydroxyl in position 6 is etherified [0321] at 1.15 ppm: this doublet represents the methyl protons of all the attached hydroxypropyl groups; the surface area is denoted as S_CH3_HP,

[0322] As stipulated in Xu and Seib, it is considered that the etherification of one hydroxypropyl group with another hydroxypropyl group is negligible. The number of attached hydroxypropyls per 100 AGUs is equal to the surface area S_CH3_HP divided by 3.

[0323] The surface area S_OR6 representing the number of H1 protons of the AGUs whose hydroxyl in position 6 is etherified is calculated as follows: S_OR6_HP=(S_CH3_HP)/3−S_OR2_HP−S_OR6_HP.

[0324] The sum of the surface areas of the signals of protons H1 whose hydroxyl is etherified, denoted as S_OR_HP_tot, is calculated: S_OR_HP_tot=S_OR2_HP+S_OR3_HP+S_OR6_HP.

[0325] The proportions of the three different hydroxypropyl ethers (denoted as HP) as a percentage of the AGU is then calculated: [0326] % of AGU HP-substituted in position 2=100×S_OR2_HP/S_OR_HP_tot [0327] % of AGU HP-substituted in position 3=100×S_OR3_HP/S_OR_HP_tot [0328] % of AGU HP-substituted in position 6=100×S_OR6_HP/S_OR_HP_tot

[0329] Proton NMR Method for the Identification and Quantification of the Positions of the Carboxymethyl Groups of the Sample Ech HP+CM:

[0330] This method is valid for a starch modified first with hydroxypropyls and then second with carboxymethyls, and whose NMR spectrum after hydroxypropylation and before carboxymethylation was analyzed according to the preceding method (method for Ech_HP).

[0331] The analysis is performed by proton nuclear magnetic resonance, NMR, at 25° C. in deuterium oxide solvent, D.sub.2O, with a purity of at least 99.8%, and deuterium chloride, DCI, on a Brüker Spectrospin Avance Ill spectrometer, operating at 400 MHz, using NMR tubes 5 mm in diameter.

[0332] A solution of sample to be analyzed is prepared by diluting about 15 mg, to within a mg, in 750 microliters of D.sub.2O+100 microliters of 2N DCI, in an NMR tube. The 2N DCI is a solution of deuterium chloride at a double-normality concentration, in deuterium oxide. The sample is heated on a boiling water bath until dissolution is complete and a clear, fluid solution is obtained. The NMR tube is allowed to return to room temperature.

[0333] The proton nuclear magnetic resonance spectrum is then acquired at 25° C. at 400 MHz. With reference to the article by Xu and Seib, the anhydroglucose (denoted as AGU) H1 protons are identified as follows:

[0334] With reference to the article by Xu and Seib, the anhydroglucose (denoted as AGU) H1 protons are identified as follows: [0335] at 5.61 ppm and 4.64 ppm: the H1 protons of the alpha-reducing and beta-reducing terminal AGUs, [0336] at 4.95 ppm: the H1 protons of the alpha-(1,6) bonded AGUs, [0337] at 5.67 ppm: the H1 protons of the AGUs whose hydroxyl in position 2 is etherified; the surface area is denoted as S_OR2_HP+CM, [0338] at 5.52 ppm: the H1 protons of the AGUs whose hydroxyl in position 3 is etherified; the surface area is denoted as S_OR3_HP+CM, [0339] at 5.40 ppm: the H1 protons of the AGUs alpha-(1,4) bonded and the H1 protons of the AGUs whose hydroxyl in position 6 is etherified [0340] at 1.15 ppm: this doublet represents the methyl protons of all the attached hydroxypropyl groups; the surface area is denoted as S_CH3_HP, [0341] at 4.22 ppm: this doublet represents the protons of all the attached carboxymethyl groups; the surface area is denoted as S_CH2_CM,

[0342] The number of attached hydroxypropyls per 100 AGUs is equal to the surface area S_CH3_HP divided by 3. The number of attached carboxymethyls per 100 AGUs is equal to the surface area S_CH2_CM divided by 2.

[0343] The signals OR2 and OR3 representing all of the ethers in positions 2, 3 and 6, whether they are hydroxypropyl or carboxymethyl, are integrated. To determine the amount of carboxymethylated ether for each position, the results obtained for the analysis of the sample that is only hydroxypropylated Ech_HP are taken into account. Thus, the surface areas corresponding to the H1 protons of the AGUs whose hydroxyl is carboxymethylated are thus calculated: [0344] In position 2: S_OR2_CM=S_OR2_HP+CM−S_OR2_HP [0345] In position 3: S_OR3_CM=S_OR3_HP+CM−S_OR3_HP [0346] In position 6: S_OR6_CM=(S_CH3_HP)/3+(S_CH2_CM)/2−S_OR2_CM−S_OR3_CM-S_OR6_HP

[0347] The sum of the surface areas of the signals of protons H1 whose hydroxyl is etherified, denoted as S_OR_CM_tot, is calculated: S_OR_CM_tot=S_OR2_CM+S_OR3_CM+S_OR6_CM.

[0348] The proportions of the three different carboxymethyl ethers (denoted as CM) as a percentage of the AGU is then calculated: [0349] % of AGU CM-substituted in position 2=100×S_OR2_CM/S_OR_CM_tot [0350] % of AGU CM-substituted in position 3=100×S_OR3_CM/S_OR_CM_tot [0351] % of AGU CM-substituted in position 6=100×S_OR6_CM/S_OR_CM_tot

[0352] Comparative Results:

[0353] A starch modified by means of the process of the prior art (such as in example 1) by hydroxypropylation to DS 0.26 (denoted as EDT5) is compared with starches prepared by means of the process according to the invention (such as in example 2) by hydroxypropylation to DS 0.20 (denoted as ROQ1) or DS 0.57 (denoted as ROQ 11). The three modified starches were analyzed by means of the proton NMR method for determination of the positions of the substituents on the HP sample. The percentages of hydroxypropyl groups attached in position 2, in position 3 and in position 6 were thus quantified (table 9).

[0354] It is found that the starches modified by means of the process according to the invention have a quite different distribution of the hydroxypropyl substituents from that of the starch modified according to the process of the prior art, namely: [0355] Position 2 has a percentage of substitution that is at least 6% lower [0356] Positions 3 and 6 have percentages of substitution that are at least 3% higher.

TABLE-US-00009 TABLE 9 comparative of the positions of the hydroxypropyl substituents according to the prior art and according to the invention Chemical Distribution of the hydroxypropyl modifications groups (proton NMR) Reference of the HP CM Position 2 Position 3 Position 6 modified starch (DS) (DS) (%) (%) (%) EDT5 0.26 — 70.9 14.2 14.9 ROQ1 0.20 — 63.6 17.7 18.7 ROQ11 0.57 — 62.6 19 18.4

[0357] The starch prepared by means of the process according to the invention (as in example 2) by hydroxypropylation to DS 0.20 (preceding ROQ1) was then modified by carboxymethylation to DS 0.27 (denoted as ROQ 12).

[0358] The two modified starches were analyzed by means of the proton NMR method for determination of the positions of the substituents on the HP+CM sample. The percentages of hydroxypropyl groups attached in position 2, in position 3 and in position 6 were thus quantified (table 10).

[0359] It is found that the starches modified by means of the process according to the invention have a quite different distribution of the carboxymethyl substituents from that of the starch modified according to the process of the prior art, namely: [0360] Position 2 has a percentage of substitution that is at least 1.5% higher, [0361] Position 3 has a percentage of substitution that is at least 2% lower, [0362] Position 6 has a percentage of substitution that is at least 4% higher.

TABLE-US-00010 TABLE 10 comparative of the positions of the carboxymethyl substituents according to the prior art and according to the invention Chemical Distribution of the carboxymethyl modifications groups (proton NMR) Reference of the HP CM Position 2 Position 3 Position 6 modified starch (DS) (DS) (%) (%) (%) EDT6 0.26 0.15 75 20.7 3.4 ROQ12 0.20 0.27 76.9 18.5 8