WO2008101538A1

WO2008101538A1 - Preparation of methyl guar

Info

Publication number: WO2008101538A1
Application number: PCT/EP2007/010705
Authority: WO
Inventors: Roland Bayer; Karsten BÖHME; Hans-Jürgen Juhl; Matthias Knarr; Peter Wolbers
Original assignee: Dow Global Technologies Inc.
Priority date: 2007-02-23
Filing date: 2007-12-08
Publication date: 2008-08-28
Also published as: TW200846373A; DE102007008842A1

Abstract

The present invention relates to the preparation of methyl guar and the use in building materials.

Description

PREPARATION OF METHYL GUAR

DE-A 3 602 151 discloses the synthesis and the use of various methylated guar derivatives, such as methyl guar (MG), hydroxypropyl guar (HPG), methylhydroxy- propyl guar (MHPG), hydroxyethyl guar (HEG), methylhydroxyethyl guar (MHEG), in gypsum-based render materials as water retention agents. The effect of the guar derivatives is explicitly attributable to the special preparation process in toluene or tert-butanol. In cement-containing systems, below-average water retention is observed in comparison with cellulose ethers.

The article "Guar gum methyl ethers Part 1. Synthesis and macromolecular characterization" (Polymer, 46 (2005), 12247-12255) discloses, inter alia, the synthesis of methyl guar with degrees of methyl substitution of 0.3, 0.6 and 1.7 by alkylation in an isopropanol or tert-butanol slurry with methyl iodide or dimethyl sulfate.

US 4 169 945 describes a special process for the preparation of guar-based alkyl ethers in the presence of a phase-transfer catalyst.

The preparation of guar ethers or mixed ethers by the conversion of stationary guar split, having guar contents of about 80% by weight, was published in DE-A 3 701 509.

Information on properties and fields of use of such derivatives described in the above references are not mentioned.

Surprisingly, it has now been found that methyl guar derivatives or mixed ethers thereof having a degree of methyl substitution of from 1.0 to 2.0, which are obtained by solvent-free etherification of guar, have a comparatively high water retentivity in gypsum- and cement-bound systems. The present invention therefore relates to a process for the preparation of methyl guar ethers or methyl guar mixed ethers, in which guar is methylated and, if appropriate, alkylated and/or hydroxyalkylated in the absence of a solvent so that a degree of substitution (DS), based on the methyl groups, of from 1.0 to 2.0 results.

Methyl halides or dimethyl sulfate are typically used for the methylation. Mixed ethers of guar having methyl ether groups and further alkyl ether groups and/or hydroxyalkyl ether groups are guar derivatives as may be obtained by methylation and prior, simultaneous or subsequent alkylation and/or hydroxyalkylation.

In the alkylation during the preparation of the mixed ethers, alkyl halides, such as ethyl chloride, are preferably used. In the hydroxyalkylation, alkylene oxides, such as ethylene oxide or propylene oxide, are preferably used.

During the methylation or alkylation, bases, such as sodium hydroxide, are usually concomitantly used.

For avoiding oxidative degradation, the oxygen is expediently removed from the reaction mixture by evacuation and flushing with nitrogen.

The degree of substitution (DS) of the product is controlled via the amount of base used, preferably sodium hydroxide. NaOH can be used as aqueous solution or in solid form (NaOH prills or scales).

Since the etherification reagents are as a rule gaseous under the reaction conditions of the etherification, the reaction is expediently carried out in an optionally stirred autoclave or pressure reactor.

The metering of the reactants can be effected in any desired sequence, over any desired period, completely or divided into a plurality of steps. The reaction temperatures are typically from 45°C to 140⁰C, preferably from 50⁰C to 100°C, particularly preferably from 80°C to 95⁰C.

The reaction times until achieving the desired degree of etherification are typically from 10 to 250 min, preferably from 15 to 60 min.

After the end of the reaction, the guar ethers are suspended in an inert suspending medium, e.g. acetone or toluene, and neutralized with an acid. After temporary crosslinking, for example with glyoxal solution, the salt-containing products are purified by washing with acidic water. The purified guar ethers are then neutralized in an inert suspending medium, dried and, if appropriate, milled.

The methyl guar ethers or the corresponding mixed ethers have a degree of substitution (DS), based on the methylation, of preferably from 1.0 to 2.0, particularly preferably from 1.0 to 1.5.

The methyl guar ethers or the corresponding mixed ethers typically have a degree of substitution (DS), based on the hydroxyalkylation, of from 0.01 to 5, preferably from 0.05 to 3, particularly preferably from 0.1 to 2.5.

For determining the degrees of substitution, the guar ether is reacted with hot, concentrated hydriodic acid (Zeisel cleavage) and the resulting alkyl iodides and alkylenes are gas chromatically separated and analyzed.

The guar ethers of the abovementioned type which are used according to the invention preferably have viscosities at 20⁰C, measured using a rotational viscometer (Thermo Haake) at a shear rate of 2.55 s^"1 with a 2% by weight aqueous solution, of from 1000 to 80 000 mPa-s, particularly preferably from 1500 to 60 000 mPa-s, very particularly preferably from 10 000 to 50 000 mPa-s.

A further subject comprises the methyl guar ethers or methyl guar mixed ethers obtainable by the process according to the invention and building material compositions which contain them. - A -

The methyl guar derivatives according to the invention exhibit pronounced water retentivity.

They are therefore suitable as an additive in "building material compositions", such as mineral- or dispersion-bound systems, such as hand and machine renders, for example based on gypsum, slaked lime or cement, dispersion-bound renders, mortars, cement- and dispersion-bound tile adhesives, air-placed concrete masses, floor leveling masses, cement extrudates and lime-sandstone extrudates, cement-, gypsum- and dispersion-bound joint fillers and filling masses.

In the building material compositions according to the invention, the above- described methyl guar ethers or mixed ethers essential to the invention are present in amounts of from 0.001 to 20% by weight, preferably from 0.001 to 5% by weight. based on the total dry mass.

In a preferred embodiment, exclusively guar ethers of the abovementioned type having methyl ether groups and, if appropriate, alkyl ether groups and/or hydroxyalkyl ether groups are present in the guar ether component in the building material compositions according to the invention.

In addition to the guar ethers essential to the invention the building material compositions may also contain cellulose derivatives, such as methylcelluloses, ethylcelluloses, hydroxypropylmethylcelluloses, hydroxyethylmethylcelluloses, hydroxypropylcelluloses and hydroxyethylcelluloses.

Furthermore, the building material compositions may contain additives and/or modifiers. These may be, for example, hydrocolloids, plastic dispersion powders, defoamer, swelling agents, fillers, lightweight additives, polyacrylates, polyacrylamides, hydrophobizing agents, water repellents, air-pore formers, synthetic thickeners, dispersants, liquefiers, plasticizers, retardants, accelerators or stabilizers. Furthermore, fillers, such as quartz sand, dolomite, lime-sandstone, calcium sulfate dihydrate, are suitable as additives and/or modifiers. The invention furthermore relates to moldings and structures obtainable using the building material compositions according to the invention.

Examples:

The viscosities were measured using a Haake rotational viscometer (Thermo Haake) at a shear rate of 2.55 s^"1 and at a temperature of 20°C with DIN measuring bodies in pure aqueous solution.

Example 1 : Preparation of methyl guar (DS (M) = 0.5) in toluene (analogously to Henkel)

1 mol of guar flour was suspended in 800 g of toluene in a 5 I stirred autoclave and rendered inert 3 times by evacuating and aerating with nitrogen gas. Thereafter, 0.75 mol of a 50% by weight sodium hydroxide solution was added over a period of 5 min and stirring was effected for a further 25 minutes at a temperature of 25°C. After evacuating and aerating with nitrogen gas a further 3 times, 1 mol of methyl chloride was added to the autoclave, heated to 9O⁰C in the course of 30 min and allowed to react at this temperature for 240 min. After the removal of unreacted methyl chloride, the guar ether was removed, adjusted to a pH of 4 in toluene with acetic acid and temporarily crosslinked in the presence of 12.8 g of a 40% by weight aqueous glyoxal solution. After washing with water (pH 4) the purified guar ether was neutralized in toluene with 10% by weight NaOH, dried and milled. The guar ether present as a white powder had a DS, based on the methyl ether groups, of 0.5 and a viscosity of a 2% by weight solution in water (V2 viscosity) of 20 280 mPa-s at 20⁰C. Example 2: Preparation of methyl guar (DS (M) = 1.22) in toluene (analogously to Henkel)

1 mol of guar flour was suspended in 800 g of toluene in a 5 I stirred autoclave and rendered inert 3 times by evacuating and aerating with nitrogen gas. Thereafter, 1.66 mol of a 50% by weight sodium hydroxide solution were added over a period of 5 min and stirring was effected for a further 25 minutes at a temperature of 25°C. After evacuating and aerating with nitrogen gas a further 3 times, 2.2 mol of methyl chloride was added to the autoclave, heated to 9O⁰C in the course of 30 min and allowed to react at this temperature for 240 min. After the removal of unreacted methyl chloride, the guar ether was removed, adjusted to a pH of 4 in toluene with acetic acid and temporarily crosslinked in the presence of 12.8 g of a 40% by weight aqueous glyoxal solution. After washing with water (pH 4) the purified guar ether was neutralized in toluene with 10% by weight NaOH, dried and milled. The guar ether present as a white powder had a DS, based on the methyl ether groups, of 1.22 and a viscosity of a 2% by weight solution in water (V2 viscosity) of 13 880 mPa s at 20⁰C.

Example 3: Preparation of methyl guar (DS (M) = 1.54) in toluene (analogously to Henkel)

1 mol of guar flour was suspended in 800 g of toluene in a 5 I stirred autoclave and rendered inert 3 times by evacuating and aerating with nitrogen gas. Thereafter, 2.33 mol of a 50% by weight sodium hydroxide solution were added over a period of 5 min and stirring was effected for a further 25 minutes at a temperature of 25°C. After evacuating and aerating with nitrogen gas a further 3 times, 3.03 mol of methyl chloride was added to the autoclave, heated to 90⁰C in the course of 30 min and allowed to react at this temperature for 240 min. After the removal of unreacted methyl chloride, the guar ether was removed, adjusted to a pH of 4 in toluene with acetic acid and temporarily crosslinked in the presence of 12.8 g of a 40% by weight aqueous glyoxal solution. After washing with water (pH 4) the purified guar ether was neutralized in toluene with 10% by weight NaOH, dried and milled. The guar ether present as a white powder had a DS, based on the methyl ether groups, of 1.54 and a viscosity of a 2% by weight solution in water (V2 viscosity) of 13 38O mPa-S at 20⁰C.

Example 4: Preparation of methyl quar (DS (M) = 0.48) in MCI (comparative example)

1 mol of guar flour was rendered inert in a 5 I stirred autoclave by evacuating and aerating with nitrogen gas 3 times. Thereafter, 0.65 mol of a 50% by weight sodium hydroxide solution and 5.82 mol of methyl chloride were added to the autoclave and stirred for 30 minutes at a temperature of 25°C. Heating was effected in the course of 30 min to 9O⁰C and stirring was effected at this temperature for 240 min. After removal of unreacted methyl chloride, the guar ether was removed, adjusted to a pH of 5 in acetone with acetic acid and temporarily crosslinked in the presence of 9.1 g of a 40% by weight aqueous glyoxal solution. After washing with water (pH 4), the purified guar ether was neutralized in acetone with 10% by weight NaOH, dried and milled. The guar ether present as white powder had a DS₁ based on the methyl ether groups, of 0.48 and a viscosity of a 2% by weight solution in water (V2 viscosity), of 33 250 mPa-s at 20⁰C.

Example 5: Preparation of methyl quar (DS (M) = 1.23) in MCI

1 mol of guar flour was rendered inert in a 5 I stirred autoclave 3 times by evacuating and aerating with nitrogen gas. Thereafter, 1.88 mol of a 50% by weight sodium hydroxide solution and 5.82 mol of methyl chloride were added to the autoclave over a period of 5 min and stirred for a further 25 minutes at a temperature of 25°C. Heating was effected in the course of 30 min to 80⁰C and reaction was allowed to take place at this temperature for 240 min. After the removal of unreacted methyl chloride, the guar ether was removed, adjusted to a pH of 5 in acetone with acetic acid and temporarily crosslinked in the presence of 11.4 g of a 40% by weight aqueous glyoxal solution. After washing with water (pH 4), the purified guar ether was neutralized in acetone with 10% by weight NaOH, dried and milled. The guar ether present as a white powder had a DS, based on the methyl ether groups, of 1.23 and a viscosity of a 2% by weight solution in water (V2 viscosity) of 30 980 mPa-s at 20⁰C.

Example 6: Preparation of methyl guar (DS (M) = 1.38) in MCI

1.5 mol of guar flour was rendered inert in a 5 I stirred autoclave 3 times by evacuating and aerating with nitrogen gas. Thereafter, 3.0 mol of a 50% by weight sodium hydroxide solution and 5.82 mol of methyl chloride were added to the autoclave over a period of 5 min and stirred for a further 25 minutes at a temperature of 25°C. Heating was effected in the course of 30 min to 80⁰C and reaction was allowed to take place at a temperature of 80⁰C for 30 min. After the removal of unreacted methyl chloride, the guar ether was removed, adjusted to a pH of 4 in acetone with acetic acid and temporarily crosslinked in the presence of 20.4 g of a 40% by weight aqueous glyoxal solution. After washing with water (pH 4), the purified guar ether was neutralized in acetone with 10% by weight

NaOH, dried and milled. The guar ether present as a white powder had a DS, based on the methyl ether groups, of 1.38 and a viscosity of a 2% by weight solution in water (V2 viscosity) of 31 580 mPa-s at 20°C.

Determination of the slump and of the water retentivitv (WR):

The slump is the diameter of a cake of a water/render mixture (gypsum or cement) in mm which forms after demolding and shocking of the mixture by vertical impacts.

For determining the slump (SL) the commercially available unmodified gypsum machine plaster was mixed with 0.21% of the corresponding guar derivative or a commercially available unmodified lime-cement render with 0.08% of the corresponding guar derivative as an additive and stirred in a mortar mixer according to DIN 1164 Sheet 7 with the corresponding amount of tap water at 20⁰C. For this purpose the corresponding amount of water was initially introduced into the mixer and the gypsum plaster was sprinkled in within 15 seconds with the stirrer running at speed 1 and mixed for a further 20 seconds at speed 2. For the lime-cement render, a corresponding amount of water was initially introduced into the mixer and the lime- cement render was sprinkled in within 15 seconds with the stirrer running at speed 1 and mixed for a further 30 seconds at speed 1. Immediately after the mixing, the plaster or render was placed on the slump table with the aid of a slump cone (diameter at top = 100 mm; diameter at bottom = 70 mm, height = 60 mm) and, after removal of the slump cone, was spread according to DIN 1060 by means of 15 vertical impacts. The diameter of the plaster or render was determined using a caliper gauge. The corresponding amount of water was chosen so that a slump of 170 ± 5 mm resulted for the gypsum plaster and a slump of 170 ± 10 mm for the lime-cement render. The resultant water/solid factor is calculated according to

W water/solid factor = — s

where W = amount of tap water used in g and S = amount of dry plaster or render mixture (solid) in g.

The water retentivity of a mineral render is the proportion of water, expressed in percent, which remains in the render after capillary withdrawal of water by the absorptive substrate. For this purpose, the render is brought into contact with a filter sheet for a specified time and the amount of water taken up by the filter paper is then determined.

For determining the water retentivity (WR), the render mixed with water according to the specifications for the slump and stirred was introduced, within 5 seconds after the stirring, into a metal ring (internal diameter = 90 mm, external diameter = 110 mm, height = 15 mm) which rests on a pulp board (diameter = 110 mm) [from Schleicher & Schull, No. 2294]. A release paper (diameter = 110 mm) [from Schleicher & Schull, No. 0980/1] is present between metal ring and pulp board. For the actual measuring process, the ring is filled with the corresponding amount of render, the projecting amount of render is scraped off with a spatula and the amount present in the ring is accurately determined by weighing. In the course of 5 or 30 minutes, the pulp board withdraws water from the render material, which is determined accurately by reweighing the moist cardboard. The release paper serves only for enabling the render to be removed more easily from the board after a suction time of 5 or 30 minutes. The water retentivity (WR) is defined as:

100 - A - H + —

WR [%] =

W

B

A = water absorption of the pulp board and of the release paper in g

B = the amount of render/mortar introduced into the ring in g

A high water retentivity means that the render does not dry out after application and the water required for setting is available to it for a sufficiently long time.

Results of the testing of the performance characteristics

Slump (SL) and water retentivity (WR) of methyl guar in a commercially available gypsum machine plaster

Slump (SL) and water retentivity (WR) of methyl guar in a commercially available lime-cement render

The water retentivity of the guar derivatives according to the invention which were used in the render application is substantially above that of the samples prepared in toluene.

Claims

1. A process for the preparation of methyl guar ethers or methyl guar mixed ethers, in which guar is methylated and, if appropriate, alkylated and/or hydroxyalkylated in the absence of a solvent so that a degree of substitution

(DS), based on the methyl groups, of from 1.0 to 2.0 results.

2. The process as claimed in claim 1 , characterized in that the products have a degree of substitution (DS), based on the methylation, of from 1.0 to 1.5.

3. The process as claimed in claim 1 or 2, characterized in that the products have a degree of substitution (DS), based on the hydroxyalkylation, of from 0.1 to 2.5.

4. A methyl guar ether or methyl guar mixed ether obtainable by a process as claimed in any of claims 1 to 3.

5. A methyl guar ether or methyl guar mixed ether as claimed in claim 4, characterized in that it has a viscosity at 20⁰C, measured using a rotational viscometer at a shear rate of 2.55 s^"1 with a 2% by weight aqueous solution, of from 10 000 to 50 000 mPa-s.

6. A building material composition containing methyl guar ether or methyl guar mixed ether as claimed in claim 4 or 5.

7. A molding or structure obtainable using methyl guar ethers or methyl guar mixed ethers as claimed in claim 4 or 5.