Use of depolymerised carboxylated celluloses for dispersing and grinding mineral materials

Abstract

The present invention concerns the use of depolymerized carboxylated celluloses as a dispersing agent or grinding aid agent for aqueous suspensions of mineral materials, intended for paint formulations, plastic formulations, detergent formulations, cosmetic formulations, paper formulations or paper coating colors.

Claims

1. A process, comprising grinding, dispersing, or both grinding and dispersing, mineral material in the presence of an aqueous solution of depolymerized carboxylated cellulose, wherein: the aqueous solution of the depolymerized carboxylated cellulose has a solids content ranging from 25 wt % to 40 wt % relative to a total weight of the aqueous solution; and the depolymerized carboxylated cellulose has a molecular weight ranging from 10,000 g/mol to 40,000 g/mol.

2. The process of claim 1, wherein the depolymerized carboxylated cellulose is carboxymethylcellulose.

3. The process of claim 1, wherein the depolymerized carboxylated cellulose has a polydispersity index PI ranging from 2 to 10.

4. The process of claim 1, wherein the depolymerized carboxylated cellulose is partially or completely neutralized with one or more neutralizing agents selected from the group consisting of sodium hydroxide, calcium hydroxide, magnesium hydroxide, potassium hydroxide and an amine.

5. The process of claim 1, wherein the solution of the depolymerized carboxylated cellulose is obtained by a method comprising: 1) depolymerisation, wherein: 1a) a reactor containing water is heated to a temperature between 50 and 85 C. (inclusive), 1b) a carboxylated cellulose to be depolymerized, having a degree of substitution between 0.2 and 2, and a peroxide are added to the reactor gradually and simultaneously, maintaining the temperature according to 1a), and 1c) after adding all of the reactants according to 1b) to form a mixture, the temperature of the mixture is maintained according to 1a) until there is complete consumption of the peroxide; 2) cooling the mixture to a temperature below 75 C.; and 3) optionally neutralizing the mixture.

6. The process of claim 1, wherein the mineral material is selected from the group consisting of natural calcium carbonate, synthetic calcium carbonate, a dolomite, kaolin, talc, gypsum, lime, magnesia, titanium dioxide, satin white, aluminum trioxide, aluminum trihydroxide, a silica, mica and mixtures thereof.

7. The process of claim 1, wherein the mineral material is present in said aqueous solution of the depolymerized cellulose in the form of an aqueous suspension of said mineral material during said grinding, dispersing, or both grinding and dispersing, and wherein said depolymerized cellulose is present in an amount from 0.01 to 8 wt %, based on the total weight of the solids in the suspension.

8. The process of claim 1, wherein the mineral material is present in said aqueous solution of the depolymerized cellulose in the form of an aqueous suspension of said mineral material during said grinding, dispersing, or both grinding and dispersing, and wherein the aqueous suspension of mineral material has a granulometric distribution such that at least 60 wt % of particles have an equivalent diameter less than or equal to 2 m.

9. The process of claim 1, wherein the process produces an aqueous suspension that has a Brookfield viscosity below 1000 mPa.Math.s, as measured just after grinding with a viscosimeter of the Brookfield DVIII type at 25 C. and a speed of 100 rev/min.

10. The process of claim 1, wherein the process produces an aqueous suspension is adapted to function as a paint formulation, a plastic formulation, a detergent formulation, a cosmetic formulation, a paper formulation or a paper coating color.

11. The process of claim 1, wherein the mineral material is calcium carbonate.

12. A composition comprising an aqueous solution of a depolymerized carboxylated cellulose having a solids content between 25 and 40 wt % relative to a total weight of the solution, said depolymerized carboxylated cellulose having a molecular weight ranging from 10,000 g/mol to 40,000 g/mol, and a mineral material present in said aqueous solution of the depolymerized carboxylated cellulose in the form of an aqueous suspension of said mineral material, wherein said mineral material is selected from the group consisting of calcium carbonate, a dolomite, kaolin, talc, gypsum, lime, magnesia, titanium dioxide, satin white, aluminum trioxide, aluminum trihydroxide, a silica, mica and mixtures thereof.

13. The composition of claim 12, wherein the mineral material is calcium carbonate.

14. The composition of claim 12, wherein the depolymerized carboxylated cellulose is carboxymethylcellulose.

15. The composition of claim 12, wherein the depolymerized carboxylated cellulose has a polydispersity index PI ranging from 2 to 10.

16. The composition of claim 12, wherein the mineral material is calcium carbonate, and wherein the aqueous suspension of calcium carbonate has a granulometric distribution such that at least 60 wt % of particles have an equivalent diameter less than or equal to 2 M.

Description

EXAMPLES

Example 1

(1) This example illustrates a method for preparing a solution of depolymerized carboxymethylcellulose (CMC) according to the invention or not according to the invention, as well as the characteristics (viscosity, solids content, Mw, PI) of the solutions thus obtained.

(2) CMC1 (According to the Invention)

(3) Depolymerizalion Step

(4) A 1-liter reactor is charged with 800 g of bi-permuted water and 0.017 g of FeSO.sub.4.7H.sub.2O catalyst. The reactor is heated to 802 C. Then, over the space of 2 h 45 min, a solution of hydrogen peroxide at 35 wt % is injected at 189 mg/min, as well as CMC (Sigma-Aldrich, reference 419281, Mw=250 000 g/mol, DS=1.2) in 25-g aliquots every 15 minutes (continuous method). The reaction is left to continue for 2.5 h after the end of injection. A check that all of the hydrogen peroxide has been consumed is carried out.

(5) Cooling Step

(6) The reactor is cooled to 70 C. The pH as measured in the reactor is 4.4.

(7) Neutralizing Step

(8) A 50% NaOH solution is added so as to reach a pH of 7.4.

(9) CMC2 (not According to the Invention)

(10) The method breaks down into a preliminary step of solubilization of the CMC as well as three subsequent reaction steps.

(11) According to this batch method, all of the CMC is added to the reactor in liquid form before adding peroxide.

(12) Step of Preparation of the Solution of CMC

(13) A beaker is charged with 850 g of bi-permuted water and then 74.4 g of CMC (Sigma-Aldrich, reference 419281, Mw=250 000 g/mol, DS=1.2) is introduced gradually, with stirring.

(14) Depolymerization Step

(15) 870 g of the solution of liquid CMC is transferred to a reactor, which is heated to 802 C. Then injection of a solution of hydrogen peroxide at 35 wt % is started. Then injection of 0.78 g of hydrogen peroxide at 35 wt % is repeated every 2 hours, for 8 hours. The reaction is left to continue after the end of injection until all of the hydrogen peroxide has been consumed.

(16) Consumption of the hydrogen peroxide is checked by a test with titanium oxysulfate(IV)-sulfuric acid (Sigma-Aldrich reference 89532).

(17) Cooling Step

(18) The reactor is cooled to 70 C. The pH as measured in the reactor is 5.4.

(19) Neutralizing Step

(20) A 50% NaOH solution and/or 10% CaOH solution is added, so as to reach a pH of 7.8.

(21) Characterization of the Solution of Depolymerized CMC Obtained

(22) Brookfield Viscosity

(23) The viscosity is measured in the reactor at the start of the process (time t.sub.0) and then that of the solution of CMC obtained, using a Brookfield viscosimeter, model RVT, at 10 rpm using a suitable module.

(24) Molecular Weight (Mw) and Index PI

(25) The molecular weight of the CMC is determined by size exclusion chromatography (SEC), also called gel permeation chromatography (GPC).

(26) This technique employs liquid chromatography apparatus of WATERS mark, equipped with a detector. This detector is a detector of refractometric concentration of WATERS mark.

(27) This liquid chromatography equipment is provided with a size exclusion column suitably selected by a person skilled in the art for separating the different molecular weights of the CMCs investigated. The elution liquid phase is an aqueous phase adjusted to pH 9.00 with 1N soda containing 0.05M of NaHCO.sub.3, 0.1M of NaNO.sub.3, 0.02M of triethanolamine and 0.03% of NaN.sub.3.

(28) In detail, according to a first step, the solution of CMC is diluted to 0.9% dry weight in the solubilization solvent for SEC, which corresponds to the liquid phase for elution in SEC, to which 0.04% of dimethylformamide is added, which performs the role of flow marker or internal standard. Then it is filtered at 0.2 m. 100 L is then injected into the chromatography apparatus (eluent: an aqueous phase adjusted to pH 9.00 with 1N soda containing 0.05M of NaHCO.sub.3, 0.1M of NaNO.sub.3, 0.02M of triethanolamine and 0.03% of NaN.sub.3).

(29) The liquid chromatography apparatus contains an isocratic pump (WATERS 515) whose flow rate is set at 0.8 ml/min. The chromatography apparatus also comprises a furnace, which in its turn comprises the following system of columns in series: a precolumn of the GUARD COLUMN ULTRAHYDROGEL WATERS type with a length of 6 cm and inside diameter of 40 mm, and a linear column of the ULTRAHYDROGEL WATERS type with a length of 30 cm and inside diameter of 7.8 mm. As for the detection system, it is made up of a refractometric detector of the RI WATERS 410 type. The furnace is heated to a temperature of 60 C., and the refractometer is heated to a temperature of 45 C.

(30) The chromatography apparatus is calibrated using standards of sodium polyacrylate powder of different molecular weights certified for the supplier: POLYMER STANDARD SERVICE or AMERICAN POLYMER STANDARDS CORPORATION.

(31) The polydispersity index PI of the cellulose obtained is the ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn.

(32) The results of characterization of the solution of depolymerized CMC obtained are presented in Table 1 below:

(33) TABLE-US-00001 TABLE 1 CMC1 CMC2 V.sub.B at t.sub.0 (mPa .Math. s) =water 18 500 V.sub.B of the solution of depolymerized 725 25 CMC obtained (mPa .Math. s) SC (wt %) 33.9 8 Total process time 4 h 45 >20 h Mw (g/mol) 13 310 14 085

(34) Regarding the method for preparing the depolymerized CMC1, it is noted that the viscosity in the reactor at t0 is that of water, which makes the method for preparing the CMC1 easier to carry out. Moreover, this method gives a solution of depolymerized CMC with high solids content (33.9%), which offers many advantages for use thereof as grinding aid agent or dispersing agent of mineral material.

(35) Moreover, the time for preparation of the depolymerized CMC1 is short (4 h 45 min), relative to batch methods (CMC2), which may take several days to reach a lower solids content. The end product of this transformation is a liquid solution of low viscosity (725 mPa.Math.s).

Example 2

(36) This example illustrates the performance in grinding different solutions of carboxymethylcellulose that have been depolymerized by a method according to example 1. The depolymerized CMCs differ from one another, notably with respect to their molecular weights (see Table 2). The depolymerized CMCs in the following examples were neutralized with a 50% NaOH solution or a 10% suspension of Ca(OH).sub.2.

(37) Grinding efficiency is measured by the amount of mineral material that can be ground in water and the grinding time required, but without the viscosity of the suspension produced making the latter impossible to handle, transport or pump.

(38) Various aqueous suspensions of ground calcium carbonate (GCC), each having a solids content of 751%, are prepared in the presence of 0.35% dry weight of a solution of depolymerized CMC (as grinding aid agent), based on the total amount of solids in the suspension.

(39) The calcium carbonate used is ground calcium carbonate, marble of Italian origin.

(40) The suspensions of coarse calcium carbonate are fed into a DYNO MILL grinding mill, type KDL pilot 1.4 L containing 2500 g of grinding beads ( 0.6-1 mm).

(41) The grinding operations are carried out so as to obtain an aqueous suspension at 75% concentration, in which 60% of particles have an equivalent spherical diameter less than 2 microns.

(42) The grinding efficiency of the solutions of depolymerized CMCs (tests 2-2 to 2-13) is compared with that of a polyacrylic acid polymer of molecular weight 5700 g/mol completely neutralized with sodium marketed by Coatex (test 2-1), tested in the same conditions at 0.26% dry weight based on the total amount of solids in the suspension.

(43) The suspensions obtained are characterized. All the results are given in Table 2 below.

(44) The viscosity (expressed in mPa.Math.s) of each suspension is measured at 25 C. with a viscosimeter of the Brookfield DVIII type. The viscosity values shown are measured just after grinding at a speed of 100 rev/min.

(45) TABLE-US-00002 TABLE 2 Grinding V.sub.B after Mw Index SC time grinding 100 rpm Test (g/mol) PI Neutralization pH (wt %) (min) (mPa .Math. s) 2-1 PA 5500 2.6 Na 8.5 41.0 20 451 2-2 NINV 2180 2.2 Na 8.6 30.1 10 Too viscous 2-3 NINV 3685 3.6 Na 7.4 29.9 7 Too viscous 2-4 NINV 6020 4 Na 7.4 32.0 17 Too viscous 2-5 NINV 9760 4.4 Na 8.0 32.7 17 Too viscous 2-6 INV 10 070 3.9 Na 9.8 33.4 17 832 2-7 INV 11 025 3.9 Na 8.6 32.7 18 658 2-8 INV 13 217 4.0 Ca/Na 8.3 32.3 10 588 2-9 INV 18 800 4.2 Na 9.8 33.8 16 454 2-10 INV 23 010 4.2 Na 10.2 33.3 18 284 2-11 INV 29 695 4.4 Na 9.4 33.4 18 504 2-12 INV 34 520 4.4 Na 32.8 16 555 2-13 NINV 49 085 4.1 Na 10.6 3.0 Too viscous
Na: neutralization with a 50% NaOH solution
Ca/Na: neutralization 10/90 with a 10% suspension of Ca(OH).sub.2 and a 50% NaOH solution

(46) According to the results presented in Table 2, it can clearly be seen that it is essential to adjust the molecular weight of the CMC for the grinding application.

(47) The stability of the suspensions is investigated after storage for 8 days at 25 C. The viscosity values are measured before and after stirring (using equipment of the Rayneri type, for example).

(48) All the suspensions prepared using a depolymerized CMC according to the invention have a Brookfield viscosity at 100 rev/min (before or after stirring) that allows handling in industrial processes.