HK1071148B - Cellulose derivatives having gel-like rheological properties and process for the preparation thereof - Google Patents

Description

Cellulose derivatives having gel-like rheological properties and process for their preparation

The present invention relates to cellulose derivatives having gel-like rheological properties and to a process for their preparation.

Cellulose derivatives are widely used, for example, as thickeners, adhesives, binders and dispersants, water-retaining agents, protective colloids, stabilizers and suspending agents, emulsifiers and film formers, owing to their excellent properties and physiological safety.

Conventional commercially available water-soluble cellulose derivatives, such as methylhydroxyethylcellulose, methylhydroxypropylcellulose and hydroxyethylcellulose, have characteristic rheological curves which can be characterized on the basis of the material function of the aqueous cellulose solution. Aqueous solution here means a substance comprising water, for example tap water, cellulose derivative and, if present, salts and accompanying cellulose derivative.

The material function in question is generally a function of the viscosity η describing the flowability as a function of the shear rate γ, the storage modulus G' and the loss modulus G ″ describing the linear viscoelasticity as a function of the angular frequency ω, respectively.

The symbols used here follow the recommendations of the following documents: c.l.sieglasff: "nomenclature recommendations for steady-state shear flow and linear viscoelasticity", proceedings of the rheology, 20: 2(1976)311-317.

With regard to viscosity, usually not the complete function η (γ) is given, but a representative viscosity value, which is determined under the specified conditions, including the concentration of the aqueous solution of the cellulose derivative, the temperature, the shear rate, and the measurement instrument used and the instrument condition set points. This method is well known to those skilled in the art. It is also generally known that in most cases the viscosity of aqueous solutions of cellulose derivatives decreases with increasing shear rate; the aqueous solution thus exhibits pseudoplastic flow properties.

The linear viscoelasticity is measured in a shear flow oscillating at small amplitude and variable angular frequency. The values of G' and G "here depend to a large extent on the concentration of the aqueous solution of the cellulose derivative and on the value of its representative viscosity. Therefore, only the course of the change of G 'and G' with respect to the increase of the angular frequency ω is considered later. The cellulose derivatives G 'and G' have the following characteristics at a concentration of 1.5-2 parts by weight of cellulose derivative per 100 parts by weight of aqueous solution and a temperature of about 20 ℃: at low angular frequencies ω, the storage modulus G 'is less than the loss modulus G ", but as the angular frequency increases, G' increases faster than G". It may also happen that, above a certain angular frequency, G' eventually exceeds G ", so that the solution is mainly elastic at high angular frequencies.

Thus, for conventional aqueous solutions of cellulose derivatives, G' is much more dependent on angular frequency than G ″; specifically, when the angular frequency ω is 0.1s^-1-1s^-1In the range, the linear viscoelastic material functions as a function of storage modulus G 'and loss modulus G' as a function of angular frequency

(1)G’∝ωⁿ(storage modulus is proportional to the angular frequency to the power n.)

(2)G”∝ω^m(loss modulus proportional to the m power of angular frequency)

The indices n and m in the above relation differ considerably, the ratio of n to m being greater than 1.2 for the cellulose ethers of the prior art.

In addition to the possibility of using cellulose derivatives to increase the viscosity as much as possible, gel-like properties are also required to achieve optimum rheology of the aqueous systems. Here, for example, methylhydroxyethylcellulose or methylhydroxypropylcellulose, which have a thermal flocculation point in water, offer the possibility of forming gels, the formation of which is dependent on the temperature, see n.sarkar: "kinetics of thermal gelation of methylcellulose and hydroxypropyl methylcellulose in aqueous solution," Carbohydrate Polymers, 26(1995) 195-203. In gel-like systems, G 'is no longer much more dependent on angular frequency than G'.

The gel-like nature can only be achieved with a thermal flocculation point in a set temperature range, which means that the use of cellulose derivatives will be greatly limited in two respects: first, when such a cellulose derivative is used, it is necessary to set a temperature suitable for achieving the gel-like property with a certain effort; secondly, the choice of cellulose derivative limits the products having a flocculation point in the desired temperature range.

Partial or complete replacement of cellulose derivatives with other hydrocolloids capable of forming gel-like properties is often not feasible because, as a result of this, certain properties of the cellulose derivatives, such as good water retention, are not fully available. Also, such hydrocolloids are not generally based on renewable raw materials and are also not biodegradable.

Thus, there is a need for cellulose derivatives which have gel-like rheological properties in aqueous solutions, but do not require the addition of other substances, nor do they require special temperature conditions.

British patent 514917 has described a process for preparing water-soluble crosslinked cellulose ethers using bifunctional reagents. The object of british patent 514917 is to prepare cellulose ethers having a particularly high viscosity in water. Preferably, the product is capable of increasing the viscosity by 400%.

Us patent 4321367 also describes a process for preparing crosslinked cellulose ethers, again with the aim of providing products with increased viscosity in aqueous solution. Preferably, the viscosity of a 2% strength by weight solution increases by at least 50%; in the best case, the viscosity of a 2% strength by weight solution increases by at least 100%.

Among the added substances, surfactants are added as additives to the reaction mixture, so that the reactants are uniformly distributed.

Some of the processes described in these patent publications are multi-step, require other additives such as surfactants, and are relatively low in yield with respect to the crosslinking agent. The viscosity of the above-mentioned cellulose ethers is greatly increased compared to the uncrosslinked cellulose ethers, as a result of which the experimental results of these methods are practically not reproducible.

For these reasons, no commercially viable product has been produced according to this group of patents.

The object of the present invention is to develop corresponding cellulose derivatives which, when water without further additives is used as solvent, have gel-like rheological properties at temperatures of 20 ℃. + -. 1 ℃ in a concentration of 1.5 to 2.0 parts by weight of cellulose ether per 100 parts by weight of solution; more precisely, said gelatinous properties are obtained directly at a temperature at which the cellulose derivative is capable of forming a solution. Furthermore, no additional substances are required to obtain the gel-like nature of the solution.

The term "gel-like rheology" is defined herein by the dependence of the storage modulus G' and loss modulus G "on the angular frequency ω of the linear viscoelastic material function on the basis of the" gel point "as can be found in the articles Chambon and Winter [ see: chambon and h.h.winter: "Linear viscoelasticity of stoichiometrically unbalanced crosslinked PDMS at the gel point", Journal of Rheology, 31(8) (1987)683-697 ]; in this context, the gel point is defined as the point at which the angular frequency dependence of G' and G "can be described by the following relation:

(1)G’∝ωⁿ(storage modulus is proportional to the angular frequency to the power n.)

(2)G”∝ω^m(loss modulus proportional to the m power of angular frequency)

Where the indices n and m are equal, or n/m is 1. The G 'and G' values may be different, the only important being ln G 'and ln G'The slope of the straight line is the same for ln ω, and only the range of angular frequency ω is considered to be 0.1s here^-1-1s^-1. According to this definition, the n/m of cellulose derivatives having gel-like rheological properties is close to 1, or more significantly close to this value than conventional cellulose derivatives; specifically, n/m should be less than or equal to 1.2. In order to satisfy the requirement that n/m is close to 1, n/m should be greater than or equal to 0.8. It was therefore an object of the present invention to develop cellulose ethers having n/m of from 0.80 to 1.20 under the abovementioned conditions.

The above requirements are now surprisingly met by the preparation of specific irreversibly crosslinked cellulose derivatives.

The present invention thus relates to cellulose ethers having gel-like rheological properties in aqueous solution, which are obtainable by the following process:

1) alkalizing cellulose with an aqueous alkali metal hydroxide solution in the presence of a suspension medium,

2) the alkalized cellulose is reacted with one or more alkylene oxides,

3) then reacting with the halogenated alkane in the suspension medium,

4) the alkalized cellulose is subsequently or simultaneously reacted with 0.0001 to 0.05 equivalents of a crosslinking agent, the unit "equivalents" representing the molar ratio of the crosslinking agent relative to the Anhydrous Glucose Units (AGU) in the cellulose used,

5) if appropriate after further addition of alkali metal hydroxide and/or alkylating agent, the resultant irreversibly crosslinked cellulose derivative is isolated from the reaction mixture, if appropriate purified and dried.

The cellulose ethers having gel-like rheological properties according to the invention are distinguished in that water is used as solvent without further additives in a concentration of 1.5 to 2.0 parts by weight per 100 parts by weight of solution of the cellulose ether at a temperature of 20 ℃. + -. 1 ℃ and an angular frequency omega of 0.1s^-1-1s^-1Its linear viscoelastic material function storage modulus G' and lossThe modulus G' is a function of angular frequency and satisfies the relation

(1)G’∝ωⁿ(storage modulus is proportional to the angular frequency to the power n.)

(2)G”∝ω^m(loss modulus proportional to the m power of angular frequency)

Wherein the indices n and m are almost identical, n/m being from 0.80 to 1.20 for the cellulose ethers of the present invention.

The linear viscoelastic material functions G' and G "of the aqueous cellulose ether solutions were determined in an oscillatory mode using commercially available rotary and oscillatory rheometers. A rheometer of this type is a measuring instrument with which the relation between mechanical deformation and mechanical stress of a sample, such as the cellulose ether solution herein, can be determined, the deformation or stress being preset and another parameter being determined, depending on the type of rheometer. For this purpose, an appropriate amount of the cellulose ether solution is placed in a measuring device. Particularly suitable measuring devices are of the plate cone or plate type. The use of beakers and cylinders is in principle also a suitable measuring device, but it is not ideal when measuring in the rocking mode, since the moment of inertia of the rotating body is generally high.

After the addition of the cellulose ether solution, it is heated for a certain period of time, establishing certain boundary conditions for the measurement.

The measurement of the wobble pattern is then carried out: by means of a rheometer controller, a sample is first subjected to a certain shear deformation gamma', which oscillates sinusoidally with time (time denoted by symbol t), characterized by a deformation amplitude gamma₀And angular frequency ω:

γ^*＝γ₀sin(ωt)

amplitude of deformation gamma₀Representative of the maximum deformation during oscillation, i.e. gamma in one oscillation cycle^*At extreme value + gamma₀And-gamma₀To change between. The period of a complete oscillation cycle is 2 pi times the inverse of the angular frequency omega, i.e. the higher the set angular frequency, the oscillation periodThe shorter the time of.

Mechanical stress sigma generated in the process^*Also in the stress amplitude σ₀And is subjected to deformation gamma^*The same angular frequency varies in a similar sinusoidal fashion over time, but shifted by a phase angle δ:

σ^*＝σ₀sin(ωt+δ)

depending on the viscoelasticity of the sample, the value of the phase angle δ is between 0- π/2, δ -0 being the limit case for ideal pure elasticity, and δ - π/2 being the limit case for ideal pure viscosity.

To determine the linear viscoelastic material function, the deformation amplitude gamma needs to be determined in advance₀For the sample to be measured, a linear relation exists between the deformation amplitude and the stress amplitude, and the phase angle does not change along with the deformation amplitude in practice. These conditions are usually easily fulfilled if the deformation magnitude is chosen small enough.

Next, the data obtained can be directly converted into the linear viscoelastic material functions storage modulus G' and loss modulus G ":

G’＝σ₀/γ₀cos delta (storage modulus equals stress amplitude divided by deformation amplitude multiplied by cosine of phase angle)

G”＝σ₀/γ₀sin delta (storage modulus equals stress amplitude divided by deformation amplitude multiplied by the sine of the phase angle)

At constant temperature, G 'and G' for a given cellulose ether solution are a function of only the angular frequency ω. According to the process that the storage modulus G 'and the loss modulus G' of a linear viscoelastic material function change with the angular frequency omega, the conventional cellulose ether and the cellulose ether with gel-like rheological property can be clearly distinguished.

It was surprisingly observed that not only the aqueous solution without further additives has a gel-like rheology but also a solution of a solvent comprising 98 parts by weight of water and 2 parts by weight of sodium hydroxide per 100 parts by weight of solvent for the cellulose ether of the invention.

Here, the cellulose ether solutions of the invention show the following relationships

(1)G’∝ωⁿ(storage modulus is proportional to the angular frequency to the power n.)

(2)G”∝ω^m(loss modulus proportional to the m power of angular frequency)

Wherein the index n/m is in the range from 0.80 to 1.20, in particular in the range from 0.85 to 1.20. For the preferred cellulose ethers of the present invention, n/m is from 0.88 to 1.18, particularly preferably from 0.90 to 1.15. More preferred cellulose ethers have an n/m of from 0.95 to 1.15; most preferred cellulose ethers have an n/m between 0.98 and 1.12.

It is also surprising that the n/m change is small when the solvent is changed. In this case, the solvent is used

A: water (W)

Or B: the choice of 98 parts by weight of water and 2 parts by weight of sodium hydroxide per 100 parts by weight of solvent has little effect on the ratio of the two indices n and m. Under the same other conditions, the difference in n/m between solvent A and solvent B is less than 20% of the average value of n/m between solvent A and solvent B. For the preferred cellulose ethers of the invention, the corresponding difference is less than 15%, particularly preferably less than 10%, most preferably less than 8%, of the average of n/m for solvent A and n/m for solvent B.

Cellulose derivatives irreversibly crosslinked by one or more polyfunctional agents (also known as crosslinkers) may have such rheological properties. The crosslinking can be carried out before or after the etherification reaction to give the water-soluble cellulose derivative. However, it is preferred to carry out the etherification reaction simultaneously with the crosslinking agent and the agent which subsequently imparts water solubility.

Unlike the irreversible crosslinking reaction using a crosslinking agent, the reversible crosslinking reaction with aldehydes (e.g., glyoxal) is abandoned again during water dissolution. If appropriate, the irreversibly crosslinked cellulose derivatives according to the invention can additionally undergo reversible crosslinking, thereby slowing down the dissolution process.

The crosslinking agent which can be used is a polyfunctional compound, and a compound containing a halogen or an epoxy group or an unsaturated group is preferably used so that ether bonds are connected in the reaction. It is preferred to use difunctional compounds selected from the group consisting of 1, 2-dichloroethane, 1, 3-dichloropropane, dichlorodiethyl ether, diglycerol phosphate, divinyl sulfone. Compounds with two different functional groups can also be used, examples of which are glycerol methacrylate, epichlorohydrin and epibromohydrin. A particularly preferred crosslinking agent is epichlorohydrin.

The amount of cross-linking agent used is between 0.0001 and 0.05 equivalents, where the unit "equivalent" represents the molar ratio of cross-linking agent relative to the Anhydrous Glucose Units (AGU) of the cellulose units used. The amount of the crosslinking agent is preferably 0.0005 to 0.01 equivalent, particularly preferably 0.001 to 0.005 equivalent.

The cellulose derivative of the present invention is preferably a cellulose ether whose water solubility is achieved by etherification with hydroxyalkyl and/or alkyl groups. Preferably, the cellulose derivative is a derivative of hydroxyethyl cellulose (HEC) or Methyl Cellulose (MC). Specifically, MC used is preferably a mixed ether with a hydroxyalkyl group (methylhydroxyalkylcellulose). Methyl cellulose ethers which may be mentioned in particular here are methyl hydroxyethyl cellulose (MHEC), methyl hydroxypropyl cellulose (MHPC) and methyl hydroxyethyl hydroxypropyl cellulose (MHEHPC).

In cellulose ether chemistry, alkyl substitution is generally characterized by DS, which is the average number of substituted hydroxyl groups per anhydroglucose unit. For example, methyl substitution may be described as DS (methyl) or DS (m).

Typically, hydroxyalkyl substitutions are characterized by MS. MS is the average number of moles of etherifying agent used to link to synthesize the ether per anhydroglucose unit. For example, etherification with the etherifying agent ethylene oxide may be described as MS (hydroxyethyl) or MS (HE). Etherification with the etherifying agent propylene oxide is correspondingly denoted as MS (hydroxypropyl) or MS (HP).

Pendant groups can be identified by Zeisel's method (cf. G.Bartelmus and R.Ketterer, Z.anal.Chem., 286(1977) 161-190).

If irreversibly crosslinked HEC is prepared as the cellulose derivative, the degree of substitution MS (HE) is preferably set to 1.5 to 4.5, in particular, the degree of substitution MS (HE) is set to 2.0 to 3.0.

However, preference is given to crosslinking with mixed ethers of methylcellulose, where, in the case of MHEC, the DS (M) value is advantageously set to 1.2 to 2.1 and the MS (HE) value to 0.05 to 0.75. In particular, in the case of MHEC, the DS (M) value is preferably set to 1.3 to 1.7 and the MS (HE) value is preferably set to 0.15 to 0.45. In the case of MHEC, the DS (M) value is preferably set to 1.35-1.60 and the MS (HE) value is set to 0.20-0.40.

In the case of MHPC as the mixed methyl cellulose ether, the DS (M) value is preferably set to 1.2 to 2.1 and the MS (HP) value is preferably set to 0.1 to 1.5. In particular, in the case of MHPC, the DS (M) value is preferably set to 1.3 to 2.0 and the MS (HP) value is preferably set to 0.2 to 1.2.

Suitable etherification materials are finely ground wood pulp and finely ground cotton staple cellulose or mixtures thereof.

The invention also relates to a process for preparing irreversibly crosslinked methylhydroxyalkylcelluloses from cellulose and an alkylating agent in the presence of alkali metal hydroxide and one or more suspension media, followed by isolation and purification of the reaction product, preferably by washing with hot water or with an organic medium.

The invention therefore relates to a process for preparing cellulose derivatives, characterized in that

1) Alkalifying cellulose with an aqueous alkali metal hydroxide solution in the presence of a suspension medium,

2) the alkalized cellulose is reacted with one or more alkylene oxides,

3) reacting with halogenated alkane in the presence of a suspension medium,

4) the alkalized cellulose is subsequently or simultaneously reacted with 0.0001 to 0.05 equivalents of a crosslinking agent, where the unit "equivalents" denotes the molar ratio of the crosslinking agent to the anhydroglucose units (AGU) of the cellulose used,

5) if appropriate after further addition of alkali metal hydroxide and/or alkylating agent, the resultant irreversibly crosslinked cellulose derivative is isolated from the reaction mixture, if appropriate purified again and dried.

The cellulose is alkalized (activated) with aqueous solutions of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, preferably with sodium hydroxide solutions having a concentration of 35% to 60% by weight, particularly preferably with sodium hydroxide solutions having a concentration of 48% to 52% by weight. However, alkali metal hydroxide solids, such as granular (prill) solids, may also be used.

The alkalization reaction is preferably carried out in a suspension medium. Among the suspension media which may be used are dimethyl ether (DME), C₅-C₁₀Alkanes (e.g. cyclohexane or pentane), aromatic hydrocarbons (e.g. benzene or toluene), alcohols (e.g. isopropanol or tert-butanol), ketones (e.g. butanone or pentanone), open-chain or cyclic ethers (e.g. dimethoxyethane or 1, 4-dioxane), or mixtures of the above suspension media in different proportions. A particularly preferred suspension medium is dimethyl ether (DME).

If appropriate, the suspension medium may already contain, during the alkalization, certain amounts of the alkylating agent, preferably the haloalkane, which are required in the subsequent alkylation.

Suitable alkylating agents are unbranched or branched C₁-C₆Halogenated alkanes, such as methyl chloride (MCl), ethyl chloride, ethyl bromide, and halogenated propanes, such as propyl iodide, are preferred. Methyl chloride and ethyl chloride are preferred, and methyl chloride is particularly preferred. Alkylating agents containing ionic functional groups, such as monochloroacetic acid, N- (2-chloroethyl) diethylamine and vinylsulphonic acid, may likewise be used. Suitable reagents for introducing hydroxyalkyl groups are Ethylene Oxide (EO), Propylene Oxide (PO), Butylene Oxide (BO) and acrylonitrile. Ethylene oxide and propylene oxide are particularly preferred.

The alkalized cellulose is then reacted at a temperature above 65 ℃ with one or more alkylene oxides and an alkyl halide, preferably methyl chloride, present in the suspension medium.

The alkalized cellulose is simultaneously reacted with one or more polyfunctional reagents. The cross-linking agent may be added to the reaction mixture at different times. Thus, it can be added before, during or after basification, but it can also be added in the heating stage or in the hydroxyalkylation stage. The crosslinking agent is preferably added to the reaction mixture before or after basification.

The crosslinking agent may be added neat or diluted with an inert suspending medium or with a haloalkane or hydroxyalkylating agent. Preferably, the added crosslinking agent is dissolved beforehand in the inert suspension medium or in methyl chloride or in a mixture of inert suspension medium and methyl chloride.

After hydroxyalkylation, the haloalkane is added in an amount of at least the difference between the equivalent amount of haloalkane already added per AGU and the total amount of alkali metal hydroxide per AGU, this amount being at least 0.2 equivalent/AGU. If appropriate, further alkali metal hydroxide, preferably in the form of an aqueous alkali metal hydroxide solution, may be added. In this case, the alkali metal hydroxide may also be added prior to the addition of the second portion of haloalkane.

When methyl chloride (MCl) is used, the first portion of the haloalkane added thereafter with the suspension medium is also referred to as MClI, and the second portion of the haloalkane in the hydroxyalkylation solution is subsequently added, also referred to as MCl II.

The cellulose derivative obtained is separated from the reaction mixture and, if appropriate, purified.

The cellulose derivative is then converted into a powder product using prior art methods.

In practice, the process is carried out by charging milled or fiberized cellulose, usually under inert conditions. The cellulosic substrate is then suspended in a DME/MCl I mixture, wherein the DME/MCl I weight ratio is from 90/10 to 20/80, preferably from 80/20 to 40/60, particularly preferably from 70/30 to 50/50. In the first process step, the amount of mcii is characterized in that the unit "equivalent" denotes the molar ratio of the respective starting material relative to the anhydroglucose units (AGU) of the cellulose used: the minimum equivalent MCl I is equivalent NaOH/AGU-1.4 and the maximum equivalent MCl is equivalent NaOH/AGU + 0.8. In the first process step, the preferred amounts of mci are: the minimum equivalent MClI is equivalent NaOH/AGU-1.0 and the maximum equivalent MCl I is equivalent NaOH/AGU + 0.3. In the first process step, particularly preferred amounts of mci are: the minimum equivalent MCl I is equivalent NaOH/AGU-0.5 and the maximum equivalent MCl I is equivalent NaOH/AGU + 0.1. In the first process step, the most preferred amount of mci is: the minimum equivalent MCl I is equivalent NaOH/AGU-0.5 and the maximum equivalent MCl I is equivalent NaOH/AGU-0.1.

The crosslinking agent epichlorohydrin is preferably dissolved in MCl or DME/MCl mixture and then added to the reaction mixture together with the remaining suspension medium. The amount of MCl or DME/MCl mixture used to dissolve the crosslinker should be subtracted from the suspension medium beforehand.

The cellulose used is alkalized with 1.5 to 5.5 equivalents of NaOH/AGU, preferably with 1.9 to 3.0 equivalents of NaOH/AGU, particularly preferably with 2.2 to 2.9 equivalents of NaOH/AGU. In general, the alkalization reaction is carried out at 15 to 50 ℃ for 20 to 80 minutes, preferably 30 to 60 minutes. The concentration of the aqueous NaOH solution used is preferably from 35 to 60% by weight, particularly preferably from 48 to 52% by weight.

After the alkalization stage, a hydroxyalkylating agent, for example Propylene Oxide (PO) or Ethylene Oxide (EO), is added and heated to promote the reaction, if appropriate. The hydroxyalkylating agent may also be added during the heating stage. For example, the reaction of the hydroxyalkylating agent, the crosslinking agent and MCl I is carried out at 60 to 110 ℃, preferably 70 to 90 ℃ and particularly preferably 75 to 85 ℃. The amount of hydroxyalkylating agent added may be adjusted as the case may be, depending on the degree of substitution desired. The amount of hydroxyalkylating agent employed is from 0.1 to 5 equivalents per AGU, preferably from 0.2 to 2.5 equivalents per AGU. The alkylene oxide can be added to the reaction system in one step or in several portions in a plurality of steps, preferably in one step, particularly preferably in one step directly after the alkalization stage.

After the first etherification phase, the amount of MCl II required to complete the predetermined methyl substitution, characterized as follows, is added without significant cooling: minimum equivalent MCl II-equivalent NaOH-equivalent MCl I +0.3, if the amount of MCl II calculated from the previous formula is less than 0.2 equivalents MCl/AGU, then the minimum equivalent MCl II-equivalent MCl/AGU is 0.2 equivalents MCl/AGU. Preferably, 1 to 3.5 equivalents of MCl II are used per AGU, particularly preferably 1.5 to 2.5 equivalents of MCl per AGU. The amount of MCl II is added at a temperature above 65 ℃, preferably between 75 and 90 ℃ or at the end of the hydroxyalkylation stage. If appropriate, further alkali metal hydroxide, preferably an aqueous solution of alkali metal hydroxide, may be added. In this case, the alkali metal hydroxide can also be added before the addition of MCl II.

At the end of the second etherification phase, all volatile constituents are distilled off, if appropriate under reduced pressure. The resulting product is purified, dried and ground by methods conventionally used in cellulose derivatization processes.

The following examples illustrate the process of the invention and describe the products obtained, without restricting the invention in any way.

Examples

Example 1 (comparative example)

A400L reactor was evacuated and charged with nitrogen gas to place 17.7kg of finely ground wood pulp (moisture: 3.6% by weight; intrinsic viscosity in Culene glycol solution: 1558ml/g) and 17.7kg of finely ground cotton staple (moisture: 4.2% by weight; intrinsic viscosity in Culene glycol solution: 1753ml/g) in an inert atmosphere. 52.9kg of dimethyl ether and 2.0mol equivalents of methyl chloride are then metered into the reaction vessel. 2.2mol equivalents of sodium hydroxide in the form of a 50% strength aqueous sodium hydroxide solution are then sprayed onto the cellulose and stirred for about 10 minutes. The reaction system was continuously stirred throughout the reaction. Basified for another 35 minutes. The addition of alkali metal hydroxide solution and subsequent basification is carried out during a temperature increase from about 28 ℃ to 38 ℃. Then, 0.66mol equivalent of ethylene oxide was added to the reaction vessel over about 25 minutes. During this process, the temperature rose from 60 ℃ to 63 ℃. After stirring at this temperature for a further 25 minutes, the mixture was heated from 78 ℃ to 82 ℃ over a period of 25 minutes. The reaction was continued at this temperature for a further 60 minutes. At this temperature, 2.0mol equivalents of methyl chloride were added to the reaction vessel over 8 minutes. The reaction was continued at the same temperature for an additional 12 minutes. Volatile components are distilled off and the reaction vessel is evacuated.

The crude product was washed with hot water, then dried and ground.

The methyl-hydroxyethyl cellulose thus obtained had a degree of substitution by methyl groups (DS-M) of 1.48 and a degree of substitution by hydroxyethyl groups (MS-HE) of 0.40. The NaCl content was 2.3% by weight.

Example 2

The procedure as described in example 1, but after basification 0.001mol equivalent of epichlorohydrin dissolved in 2.5L of dimethoxyethane was added to the reactor within 5 minutes.

The degree of substitution by methyl groups (DS-M) and the degree of substitution by hydroxyethyl groups (MS-HE) of the resulting irreversibly crosslinked methylhydroxyethylcellulose was 1.42. The NaCl content was 3.6% by weight.

Measurement of examples

Methylhydroxyethylcellulose (MHEC) of example 1 (measurement 1) and example 2 (measurement 2) was dissolved in water in an amount of 1.5 parts by weight of MHEC and 98.5 parts by weight of water.

The dissolution process was the same for all measurements and examples: at room temperature, the weighed weight of cellulose ether was slowly dispersed in the previously weighed weight of solvent, and stirred to avoid agglomeration. The round glass container used to hold the solution was tightly sealed with a cap and shaken several times by hand to disperse the cellulose ether that had not dissolved. Further dissolution was carried out for 24 hours, during which the round glass container was slowly rotated in the horizontal direction about its longitudinal axis. In this manner, all of the locations within the glass container are continuously wetted by the liquid.

After the dissolution operation, the glass vessel containing the cellulose ether was allowed to stand for several hours to allow the bubbles distributed in the solution to rise and to be dispersed from the surface of the solution.

Then performing rheological measurement of the cellulose ether solution; the procedure is the same for all measurements and examples: the glass container is opened just before the measurement with the rheometer, the desired amount of cellulose ether solution is sucked from it, loaded into the measuring device of the rheometer, and the measuring device is placed in the place where the measurement is to be made. Standing for a certain time to allow the cellulose ether solution in the measuring device to reach a temperature of 20 ℃ before starting the measurement; the temperature is controlled according to the temperature display of the rheometer. Errors due to inaccuracies in the calibration of the temperature measurements are small, showing a maximum error of + -1 deg.C at a temperature of 20 deg.C. The maximum change in temperature during the measurement was ± 0.2 ℃.

During the measurement, at 0.1s^-1-1s^-1A total of 6 measurement points are taken over the angular frequency ω of (a). In this case, the deformation amplitude γ₀Between 0.0025 and 0.0075, this is sufficiently small in all viewing situations that the storage modulus G 'and the loss modulus G' of the material function can be reliably determined in the linear viscoelastic range.

The rheological measurement structure of example 1 (comparative) is listed in table 1:

measurement 1:

table 1: changes of storage modulus G 'and loss modulus G' with angular frequency omega of linear viscoelastic material of methylhydroxyethyl cellulose obtained in example 1 (comparative example)
			ω unit: s-1	G' unit: pa is	G' unit: pa is
0.1	6.64	13.2
			0.159	9.78	17.9
0.251	14.8	23.4
			0.398	21.5	30.4
0.632	30.6	37.7
			1	42.4	47.6
A rheometer: universal Dynamic Spectrometry UDS 200 measuring device available from Physica Messtechnik GmbH, Stuttgart, Germany: cone/plate with diameter of 50mm, cone angle of 1 degree and cone top flattened by 0.05mm

The data are further processed, i.e. the logarithm of the storage modulus G '(log G') is regression-analyzed in relation to the logarithm of the angular frequency ω (log ω), the slope of the straight line corresponding to the index n, and the logarithm of the storage modulus G "(log G") is regression-analyzed in relation to the logarithm of the angular frequency ω (log ω), the slope of the straight line corresponding to the index m, to determine the indices n and m in the following relations:

(1)G’∝ωⁿ(storage modulus is proportional to the angular frequency to the power n.)

(2)G”∝ω^m(loss modulus proportional to the m power of angular frequency)

The results of the regression analysis of example 1 (comparative) are given in table 2:

table 2: regression analysis of log G '-log ω and log G' -log ω of methylhydroxyethyl cellulose obtained in example 1 (comparative example) and the data G ', G' and ω are from Table 1
				logω	log G’	logω	log G”
-1	0.8222	-1	1.1206
				-0.7986	0.9903	-0.7986	1.2529
-0.6003	1.1702	-0.6003	1.3692
				-0.4001	1.3324	-0.4001	1.4829
-0.1993	1.4857	-0.1993	1.5763
				0	1.6273	0	1.6776
Slope: 0.8107R: 0.9992 the slope corresponds to the exponential n regression analysis in equation (1) using the known principle of least sum of variance. R is the regression mass coefficient and should always be greater than 0.95.		Slope: 0.5528R: the 0.9982 slope corresponds to the index m in formula (2). Regression analysis is performed using the known principle of least sum of variance. R is the regression mass coefficient and should always be greater than 0.95.
				For the methylhydroxyethylcellulose obtained in example 1 (comparative example), this analysis gave an n/m of 1.47(0.8107/0.5528), so that the product was obtainedThe mass has no gel-like rheological properties.

Measurement 2:

the results of the rheological measurements for example 2 are given in table 3:

table 3: example 2 variation of the Linear viscoelastic Material of methylhydroxyethyl cellulose As a function of the storage modulus G 'and loss modulus G' with the angular frequency omega
			ω unit: s-1	G' unit: pa is	G' unit: pa is
0.1	26.5	17.8
			0.159	31.6	20.9
0.251	38.1	25.6
			0.398	45.1	29.9
0.632	54.3	35.7
			1	64.5	41.3
A rheometer: universal Dynamic Spectrometry UDS 200 measuring device available from Physica Messtechnik GmbH, Stuttgart, Germany: cone/plate with diameter of 50mm, cone angle of 1 degree and cone top flattened by 0.05mm

The results of the regression analysis performed for measurement 2 are given in table 4:

table 4: regression analysis of log G '-log ω and log G' -log ω of methylhydroxyethyl cellulose obtained in example 2, the data G ', G' and ω being from Table 3
				logω	log G’	logω	log G”
-1	1.4232	-1	1.2504
				-0.7986	1.4997	-0.7986	1.3201
-0.6003	1.5809	-0.6003	1.4082
				-0.4001	1.6542	-0.4001	1.4757
-0.1993	1.7348	-0.1993	1.5527
				0	1.8096	0	1.6160
Slope: 0.3873R: the 0.9999 slope corresponds to the exponential n regression analysis in equation (1) using the known principle of least sum of variance. R is the regression mass coefficient and should always be greater than 0.95.		Slope: 0.3706R: the 0.9991 slope corresponds to the index m in equation (2). Regression analysis is performed using the known principle of least sum of variance. R is the regression mass coefficient and should always be greater than 0.95.
				For the methylhydroxyethylcellulose obtained in example 2, this analysis gave an n/m of 1.05(0.3873/0.3706), so that the product had gel-like rheological properties.

Example 3

A400L reactor was evacuated and charged with nitrogen gas to place 17.8kg of finely ground wood pulp (moisture: 4.2% by weight; intrinsic viscosity in copper hydroxide ethylenediamine solution: 1194ml/g) and 17.5kg of finely ground cotton staple (moisture: 5.3% by weight; intrinsic viscosity in copper hydroxide ethylenediamine solution: 1343ml/g) in an inert atmosphere. 65.4kg of dimethyl ether and 16.2kg of an equivalent of methyl chloride were then metered into the reaction vessel. In addition, 0.003mol equivalent of epichlorohydrin dissolved in 5kg of methyl chloride was metered into the reaction vessel. 2.5mol equivalents of sodium hydroxide in the form of a 50% strength aqueous sodium hydroxide solution are then sprayed onto the cellulose and stirred for about 10 minutes. The reaction system was continuously stirred throughout the reaction. Basification was then carried out for 25 minutes. The addition of the alkali metal hydroxide solution and the subsequent alkalization are carried out while the temperature is increased from about 25 ℃ to 38 ℃. The mixture was heated to 80-85 ℃ over 55 minutes and then held at this temperature for 80 minutes. During this time, 2.5mol equivalents of propylene oxide were metered into the reactor over a period of about 80 minutes, starting at about 58 ℃. Then, 37.1kg of methyl chloride was added to the reaction kettle at the same temperature over 30 minutes. The mixture is kept at this temperature for a further 10 minutes, after which a further 2.0mol equivalent of sodium hydroxide in the form of a 50% strength aqueous sodium hydroxide solution is sprayed onto the cellulose in about 60 minutes. The reaction was continued at this temperature for a further 30 minutes. Volatile components are distilled off and the reaction vessel is evacuated.

The crude product was washed with hot water, then dried and ground.

The resulting irreversibly crosslinked Methylhydroxypropylcellulose (MHPC) had a methyl substitution degree (DS-M) of 1.83 and a hydroxypropyl substitution degree (MS-HP) of 0.97. The NaCl content was 0.7% by weight.

Measurement 3:

methylhydroxypropylcellulose from example 3 was dissolved in water in an amount of 1.5 parts by weight of MHPC and 98.5 parts by weight of water. The rheological measurements were carried out as described above, but using a rheometer model RS 600 from Thermo Haake GmbH, Karlsruhe, Germany, using a 60mm diameter cone/plate measuring device, the cone having a cone angle of 1 ° and a cone tip flattened by 0.05 mm. Data processing gave n/m of 1.14.

Measurement 4:

the MHPC obtained in example 3 was dissolved in a solvent containing 98 parts by weight of water and 2 parts by weight of sodium hydroxide per 100 parts by weight of the solvent in an amount of 1.5 parts by weight of MHPC and 98.5 parts by weight of the solvent. Rheological measurements were performed as described in measurement 3. The data were processed to give n/m of 0.95.

Measurement 5:

the MHEC obtained in example 2 was dissolved in a solvent in an amount of 1.5 parts by weight of MHEC and 98.5 parts by weight of solvent per 100 parts by weight of water and 2 parts by weight of sodium hydroxide. Rheological measurements were performed as described in measurement 2. The data processing gave n/m of 1.03.

As can be seen by comparing measurement 3 and measurement 4, the MHPC obtained in example 3 has a gel-like property (n/m 1.14) in a solution dissolved in water, and also has a gel-like property (n/m 0.95) in a solution dissolved in a solvent containing 98 parts by weight of water and 2 parts by weight of sodium hydroxide per 100 parts by weight. The average value of n/m for the two solvent cases was 1.045, the difference between them was 0.19; this difference corresponds to about 18% on average to n/m in the case of the two solvents.

Comparing the measurements 2 and 5, it can be seen that the MHEC obtained in example 2, the solution of which dissolved in water, had gel-like properties (n/m 1.05), whereas the solution dissolved in a solvent containing 98 parts by weight of water and 2 parts by weight of sodium hydroxide, per 100 parts by weight, also had gel-like properties (n/m 1.03). The average value of n/m for the two solvent cases was 1.04, the difference between the two was 0.02; this difference corresponds to about 2% on average to n/m in the case of the two solvents.

Claims (24)

1. A cellulose ether having gel-like rheological properties in an aqueous solution, said aqueous cellulose ether solution having rheological characteristics of: at a temperature of 20 ℃. + -. 1 ℃ and an angular frequency omega of 0.1s^-1-1s^-1A solution of cellulose ether in a concentration of 1.5 to 2.0 parts by weight per 100 parts by weight of solution, using water as solvent without further additives, has a linear viscoelastic material function with a storage modulus G 'and a loss modulus G' as a function of angular frequency which satisfy the following formula:

G’∝Ωⁿ(storage modulus is proportional to the angular frequency to the power n.)

G”∝ω^m(loss modulus proportional to the m power of angular frequency)

n/m is 0.80-1.20,

it is characterized in that it can be obtained by the following method:

1) alkalizing cellulose with an aqueous alkali metal hydroxide solution in the presence of a suspension medium,

2) the alkalized cellulose is reacted with one or more alkylene oxides,

3) then reacting with the halogenated alkane in the suspension medium,

4) the alkylated alkalized cellulose obtained from step (3) is subsequently or simultaneously reacted with 0.0001 to 0.05 equivalents of cross-linking agent, the unit "equivalents" representing the molar ratio of cross-linking agent relative to the Anhydrous Glucose Units (AGU) in the cellulose used.

2. A cellulose ether according to claim 1, characterized in that the process further comprises, after step 4), separating the resulting irreversibly crosslinked cellulose derivative from the reaction mixture after further addition of alkali metal hydroxide and/or alkylating agent.

3. A cellulose ether of claim 2, further comprising further purification and drying after step 4.

4. A cellulose ether according to claim 1, characterized in that the cross-linking agent is one or more bifunctional reagents.

5. A cellulose ether according to claim 1, characterized in that the cross-linking agent is epichlorohydrin.

6. A cellulose ether according to claim 1, characterized in that it has a temperature of 20 ℃ ± 1 ℃Angular frequency omega of 0.1s^-1-1s^-1Under the conditions that the linear viscoelastic material function storage modulus G 'and loss modulus G' of the solution containing 1.5-2.0 weight parts of cellulose ether per 100 weight parts of solution are satisfied as a function of angular frequency change by using a solvent containing 98 weight parts of water and 2 weight parts of sodium hydroxide per 100 weight parts of solution

G’∝ωⁿ(storage modulus is proportional to the angular frequency to the power n.)

G”∝ω^m(loss modulus proportional to the m power of angular frequency)

Wherein n/m is 0.80-1.20.

7. The cellulose ether of claim 6, wherein n and m are the same.

8. The cellulose ether of claim 1 or 6, wherein the solvent is selected from the group consisting of

A: water (W)

Or B: the choice of a solvent comprising 98 parts by weight of water and 2 parts by weight of sodium hydroxide per 100 parts by weight of solvent has little influence on the ratio of the two indices n and m, the difference in n/m when solvent A and solvent B are used being less than 20% of the mean value of the two.

9. A cellulose ether according to any one of claims 1 to 5, characterized in that the cellulose derivative is a hydroxyethylcellulose derivative, a methylcellulose derivative, a methylhydroxypropylcellulose derivative or a methylhydroxyethylcellulose derivative.

10. A process for preparing a cellulose ether according to any one of claims 1 to 9, characterized in that

1) Alkalizing cellulose with an aqueous alkali metal hydroxide solution in the presence of a suspension medium,

2) the alkalized cellulose is reacted with one or more alkylene oxides,

3) then reacting with the halogenated alkane in the suspension medium,

4) the alkylated alkalized cellulose obtained in step (3) is subsequently or simultaneously reacted with 0.0001 to 0.05 equivalents of a cross-linking agent, the unit "equivalent" representing the molar ratio of the cross-linking agent relative to the Anhydrous Glucose Units (AGU) of the cellulose used,

11. the process according to claim 10, wherein the resulting irreversibly crosslinked cellulose derivative is separated from the reaction mixture, preferably after further addition of alkali metal hydroxide and/or alkylating agent.

12. The process according to claim 10, wherein the product is preferably further purified and dried.

13. The process according to claim 11, wherein in step 1) the cellulose is alkalized with an aqueous alkali metal hydroxide solution in the presence of a suspension medium containing a halogenated alkane in an amount calculated according to the formula: [ number of equivalents of alkali metal hydroxide/AGU-1.4 ] to [ number of equivalents of alkali metal hydroxide/AGU +0.8], and in step 5) a haloalkane is added in an amount of at least the difference between the number of equivalents of chloroalkane already added/AGU and the total amount of alkali metal hydroxide added/AGU, the minimum value of this amount being 0.2 equivalents/AGU.

14. The process according to claim 13, wherein an alkali metal hydroxide solution is preferably added.

15. The method of any one of claims 10-14, wherein the halogenated alkane is methyl chloride.

16. The method of any one of claims 10 to 14, wherein the crosslinking agent is dissolved in methyl chloride or a methyl chloride/dimethyl ether mixture.