WO1999054361A1

WO1999054361A1 - Method for activating and derivatizing cellulose

Info

Publication number: WO1999054361A1
Application number: PCT/EP1999/002472
Authority: WO
Inventors: Thomas Wagner; Erik-Andreas Klohr; Wolfgang Koch; Klaus Szablikowski; Wolfgang Wagenknecht; Fritz Loth; Hendrik Wetzel
Original assignee: Wolff Walsrode Ag
Priority date: 1998-04-20
Filing date: 1999-04-13
Publication date: 1999-10-28
Also published as: EP1080114A1; JP2002512271A; AU3707599A; PL343492A1; DE19817454A1

Abstract

The invention relates to a method for activating cellulose, to a method for derivatizing activated cellulose and to the cellulose derivatives hereby obtained. According to the invention, the activation step is carried out in the presence of tertiary amine oxides.

Description

- 1 -

Process for the activation and derivatization of cellulose

The present invention relates to an activation process for cellulose and a process for the derivatization of the activated cellulose and those obtained thereby

Cellulose derivatives. The products produced by these processes are characterized by advantageous properties, such as improved solubilities.

As is known, the accessibility and reactivity of cellulose is influenced by its super-molecular structure. This is due to the presence of zones of different degrees of crystalline order, fibrillar crystallites. as well as the number, size, distribution and availability of internal surfaces. Cellulose is insoluble in common solvents such as water, dilute acids and alkalis and also in common organic solvents. Derivatizations in these solvents therefore take place at least at the start of the reaction under heterogeneous conditions. However, the cellulose must first be activated in a suitable manner in order to increase the accessibility and reactivity of the cellulosic hydroxyl groups.

The known methods for activating cellulose are all aimed at opening or widening the (inner) surfaces, cleaving fibrillar aggregates, destroying crystalline regions and changing crystallite sizes and crystal modifications. An activating effect on subsequent reactions of cellulose is, for example, by grinding, electron (DE 2,941,624), microwaves or γ-radiation, hydrolysis, oxidation, thermal treatment, freeze-drying or

Treatment with swelling substances (alkali hydroxides, amines and amine complexes, ammonia (EP 0,108,991), aqueous solutions of inorganic acids and salts) has been achieved (overview in: Hans A. Kräß. Cellulose Structure, Accessibility and Reactivity, Polymer Monographs Vol. 11, Gordon and Breach Science Publishers SA, pp. 215-277, 1993). In the technical production of cellulose ethers, which today only takes place under heterogeneous reaction conditions, the cellulose is usually activated by pretreatment with concentrated alkali lyes. Disadvantages of this process management are that

1. Even in reactions that only require catalytic amounts of base (e.g. hydroxyalkylation, sulfoethylation or cyanoethylation), high concentrations of alkali metal hydroxides are required to swell and activate the cellulose,

2. due to the high amounts of alkali, chain degradation of the cellulose and a high salt load are inevitable in the neutralization of the alkali used,

no complete solubility of highly viscous cellulose ethers with low degrees of substitution can be achieved, and

4. there is no uniform distribution of the introduced substituents along and between the cellulose chains.

As activating pretreatment, in which the native superstructures of the cellulose are destroyed and their crystallinity is reduced, the dissolving of the cellulose in suitable non-derivatizing solvent systems and subsequent precipitation is also proposed in the prior art. Mixtures of sulfur dioxide / dimethylamine / dimethyl sulfoxide (A. Isogai, A. Ishizu, J. Nakano, J. Appl. Polymer Sei. 31, pp. 341-52, 1986) were used as solvent systems. Mixtures of

N, N-dimethylacetamide / lithium chloride (JP 59,038,203) and dimethyl sulfoxide / paraformaldehyde (SU 3,453,670) were used.

These cellulose solvent systems have so far been able to stand out on an industrial scale due to their limited solvency, in particular compared to high-molecular ones - 3 -

Celluloses, as well as the elaborate and z. T. do not enforce costly recovery of involved reagents.

Another class of cellulose solvents are the tertiary amine oxides. From US Pat. No. 2,179,181 it is known that cellulose is of certain tertiary

Amine oxides is dissolved without derivatization and cellulosic shaped bodies, e.g. Let fibers win. As cellulose solvent for the production of fibers and films, N-methylmorpholine-N-oxide monohydrate (NMMNO-MH) has recently found commercial interest (US Pat. No. 3,447,956; US Pat. No. 4,196,282; EP 452,610; WO 95 / 11.261).

Based on the disadvantages of the known methods for the derivatization of cellulose described, the present invention was based on the object of developing a method for the activation and optionally subsequent derivatization of cellulose, which by reduced amounts of activating and

Derivatization reagents is marked and enables the economical presentation of products with improved solubility behavior (lower gel and fiber content, high clear solubility).

The present invention thus relates to a method for activating cellulose comprising the steps:

a) dissolving cellulose in a water-containing tertiary amine oxide, optionally with the addition of at least one suitable stabilizer,

b) coagulation of the dissolved cellulose by adding an appropriate precipitant and

c) optionally alkalizing the amorphous cellulose obtained in step b). Chemical cellulose, cotton linters, softwood sulfite, softwood sulfate and / or hardwood cellulose of various degrees of polymerization are preferably used as the cellulose starting material for the process according to the invention.

Preferred water-containing tertiary amine oxides are amine oxides from the group

N-methylmorpholine-N-oxide (NMMNO), N-methyl-piperidine-N-oxide, N-methyl-pyrrolidine-N-oxide and N, N-dimethylcyclohexylamine-N-oxide, as well as N, N-dimethylethanolamine- N-oxide and triethylamine-N-oxide are used, the water (for example NMMNO-MH) or mixtures of water and dipolar aprotic compounds such as in particular dimethyl sulfoxide, N-methylpyrrolidone, dimethylacetamide or

Contain dimethylformamide.

The cellulose solutions are prepared in a known manner (US Pat. No. 4,145,532; US Pat. No. 4,196,282; EP 452,610; WO 95/1 1261) by dissolving the cellulose in a melt of NMMNO-MH at temperatures from 85 to 115 ° C.

The cellulose material is usually stirred into an aqueous solution of NMMNO at room temperature and water is distilled off in vacuo at 85 to 115 ° C. The concentration of cellulose is 2 to 20%, preferably 3 to 15%, depending on the degree of polymerization.

In order to reduce the breakdown of the cellulose during the dissolving process, at least one stabilizer is advantageously added. The stabilizers described in EP-A-047,929, in particular propyl gallic acid, are suitable. The amount of stabilizer is preferably 1% by weight, based on the amount of cellulose.

The water-containing amine oxides can contain small amounts of basic compounds such as tertiary amines and / or alkali metal hydroxides.

Precipitants suitable for coagulating the dissolved cellulose are, in particular, organic solvents such as ethers, in particular dimethyl ether, ketones, in particular

Acetone, alcohols with preferably 1-6 carbon atoms, especially methanol. - 5 -

Ethanol, 2-propanol or 2-methyl-2-propanol, as well as acetonitrile or mixtures of these solvents. The organic solvents can contain small amounts of basic-acting compounds such as tertiary amines and / or alkali metal hydroxides and / or quaternary ammonium bases.

The precipitant can be added to the cellulose solution both continuously and in stages, and is advantageously also used to wash out remaining amounts of amine oxide in the precipitated cellulose.

The activation method according to the invention has the following advantages over known methods with solution activation:

no influence of residual lignin on the solubility of the cellulose in the pre-activation step

simple process design, solution production and processing

lower costs, simple and complete recovery of the activation reagents

easier removal of the activating agent from the activated cellulose (no salts)

no environmental pollution, possibility of a closed solvent cycle

higher dissolving power also for high molecular celluloses

no pre-swelling (water, water vapor, liquid ammonia), followed by a subsequent solvent exchange required to prepare the solution The activation process according to the invention leads to amorphous cellulose with increased reactivity and also allows direct derivatization without a previous alkalization step (eg esterification to cellulose acetate, nitrate or lactate, and or reaction with isocyanates), cellulose derivatives with improved solubility being obtained with improved yields.

The present invention thus further relates to a process for the derivatization of cellulose comprising the steps:

a) dissolving cellulose in a water-containing tertiary amine oxide. optionally with the addition of suitable stabilizers,

b) coagulation of the dissolved cellulose by adding a precipitant,

c) optional alkalization of the amorphous cellulose obtained in step b),

d) Derivatisiemng the amorphous cellulose obtained in step b) or c), optionally in the presence of a suitable solvent.

Cellulose derivatives are reaction products of cellulose with suitable derivatization reagents such as cellulose esters (e.g. cellulose acetates, cellulose lactates, cellulose nitrates), cellulose ether esters, cellulose carbamates and in particular water- and / or organo-soluble cellulose ethers such as carboxyalkyl celluloses (e.g. carboxyethylethyl cellulose), e.g.

Hydroxypropyl celluloses), carboxyalkyl hydroxyalkyl celluloses (such as carboxymethyl hydroxyethyl, carboxymethyl hydroxypropyl cellulose), sulfoalkyl cellulose derivatives (e.g. sulfoethyl cellulose, sulfopropyl cellulose, methylsulfoethyl cellulose, methylsulfopropyl cellulose, carboxymethylsulfoethyl cellulose, carboxymethyl hydroxyl sulfyl ether)

Alkyl celluloses (e.g. methyl cellulose, ethyl cellulose), alkyl hydroxyalkyl celluloses (eg methylhydroxyethyl cellulose, ethyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, ethyl hydroxypropyl cellulose), alkylene celluloses (such as allyl cellulose), alkylene alkyl celluloses (eg allyl methyl cellulose, allyl ethyl cellulose), dialkylaminoalkyl celluloses (eg diethylaminoethyl cellulose or ionic methylaminoethyl or cellulose hydroxylamino) or dialkylaminoethylamino cellulose (eg Cellulose ethers from the aforementioned functional groups.

The derivatization preferably takes place in the presence of the precipitant used to coagulate the dissolved cellulose. Suitable precipitants are organic solvents such as 2-propanol, 2-methyl-2-propanol, acetonitrile, acetone. Dimethyl ether, dioxane, methyl chloride, ethyl chloride (etherification, carbamination), as well as methylene chloride, glacial acetic acid, carboxylic acid anhydrides such as acetic acid. Propionic and butyric anhydride (esterification) and mixtures of these solvents.

The process according to the invention for the derivatization of cellulose is preferably carried out in such a way that

a) cellulose is dissolved in the amine oxide / water system with the addition of stabilizers,

b) the dissolved cellulose is precipitated by adding organic solvents and is freed from adhering amine oxide by washing with the solvent used for the precipitation, and

d) the amorphous cellulose thus obtained is reacted in the presence of the organic solvent used for the coagulation, step c) (alkalization) being omitted.

The cellulose derivatives produced by the derivatization process according to the invention are also the subject of the present invention. - 8th -

The cellulose derivatives according to the invention have an improved solubility and are largely free of fiber and gel particles. Even the cellulose derivatives according to the invention with low degrees of substitution still have excellent solubility in water and / or organic solvents.

The activation of cellulose according to the invention and the subsequent conversion to cellulose derivatives is explained in more detail in the following examples.

- 9 -

embodiments

example 1

Activation of cellulose

53 g of cellulose (pulp, DP _Cuoxam 580, water content 5.7%) were suspended in 2800 g of a 46% aqueous N-methylmorpholine-N-oxide solution (NMMNO) with the addition of 0.75 g of propyl gallic acid. 1320 g of water were distilled off at a temperature of 105 ° C. and 60-65 mbar, the cellulose being dissolved. at

At 85 ° C, the cellulose solution was mixed with stirring with 1500 ml of 2-propanol. The precipitated cellulose was filtered off, washed free of NMMNO with 2-propanol and adjusted to a dry matter content of approx. 10% in a filter centrifuge.

When the activated cellulose (DP _Cu∞aπι 550) was examined by X-ray, the crystalline portions of the starting material could no longer be detected.

The water retention capacity (WRV) of the activated cellulose is 3.30 cm ³ g ^" '.

In comparison, the non-activated starting pulp had a WRV value of only 0.65 cm ³ g ^" '.

When using cotton linters (DP _Cuoxam 640, WRV = 0.60 cm ³ g ^" ') this was

Water retention capacity of the correspondingly activated material 3.37 cm ³ g ^" '

(DP _Cuoxam 560).

The activated celluloses were used in 2-propanol wet for the further reactions. - 10 -

Example 2

Hydroxyethyl cellulose

The 2-propanol-moist activated cellulose (from Linters, DP _{Cι on} 560) was under

Suspended nitrogen atmosphere in a 1: 1 mixture (w: w) of 2-propanol and 2-methyl-2-propanol (7.5% by weight cellulose in the suspension mixture), and at 10 ° C with 0.8 mol sodium hydroxide / mol of anhydroglucose unit (AGE) of the cellulose and 5 mol of water / mol of AGE. After stirring at this temperature for 160 min, 2 mol of ethylene oxide / mol of AGE were metered in and the reaction mixture was heated to 25 ° C. for 80 min. The mixture was then stirred at 75 ° C for 100 min. After cooling to room temperature, residual ethylene oxide was removed in vacuo, aerated with nitrogen and the reaction mixture was neutralized with acetic acid. It was filtered off, the reaction product was washed salt-free with methanol and dried in vacuo. The hydroxyethyl cellulose obtained had a molar

Degree of substitution of MS = 1.34 (corresponds to a reagent yield of ethylene oxide of 67%) and had 7% water-insoluble components.

When non-activated cellulose (Linters, DP _{Cuo am} 640) was used, a hydroxyethyl cellulose with MS = 0.33 was obtained under the same reaction conditions with a reagent yield of ethylene oxide of 17%, the aqueous solution of which had 81% insoluble fiber and gel components.

Example 3

Sulfoethyl cellulose

Activated 2-propanol-moist cellulose (from cellulose, DP _{Cuo at} 1120, dry content

10%) was suspended at a liquor ratio of 1:22 in a mixture of 88.6% by volume of 2-propanol, 4.4% by volume of methanol and 7.0% by volume of water. After

The addition of 2.4 mol of sodium hydroxide / mol of AGE was carried out at 20 ° C. for 80 min with stick - 1 1 -

atmosphere alkalized. Then 0.8 mol sodium vinyl sulfonate / mol AGE in the form of the 30% aqueous solution was added. The reaction mixture was heated to 70.degree. C. within 30 minutes and stirred at this temperature for 120 minutes. After cooling to room temperature, the mixture was neutralized with acetic acid and filtered off. The reaction product was washed salt-free with 70% aqueous methanol and dried at 60 ° C. in a forced-air drying cabinet. The sulfoethyl cellulose thus obtained had a degree of substitution of DS = 0.19 with a reagent yield of sodium vinyl sulfonate of 24%. The 2% aqueous solution had a viscosity of η = 32,000 mPas with a shear rate of D = 2.55 s ^"1 .

When the non-activated cellulose (DP _Cuoxam 1620) was used, a sulfoethyl cellulose with DS = 0.23 was obtained with a reagent yield of 29%, the 2% aqueous solution of which contained fibers and gel particles.

Example 4

Carboxymethyl cellulose

90 g of 2-propanol-moist activated cellulose (contains 36 mmol cellulose) with a DP _Cuoxam 830 were _mixed in a 250 ml stirred vessel in a mixture of 98.4 ml 2-

Propanol, 14.7 ml of methanol and 22.8 ml of water suspended. At room temperature, 2.6 mol of sodium hydroxide / mol of AGE were added to the cellulose with exclusion of oxygen and the mixture was stirred for 80 min. After the addition of 1.3 mol of monochloroacetic acid / mol of AGE (as an 80% aqueous solution), the mixture was heated to 70 ° C., stirred at this temperature for 120 min and cooled to room temperature. The reaction product was filtered off, washed neutral and free of chloride with 80% aqueous ethanol and then dried. The degree of substitution of those clearly soluble in water

Carboxymethyl cellulose was DS = 0.92, corresponding to a reagent yield

Monochloroacetic acid of 71%. - 12 -

When using the non-activated cellulose, a carboxymethyl cellulose with DS = 0.76 was obtained with a reagent yield of 58.5%, the 2% aqueous solution of which contained fibers and gel particles.

Example 5

Methyl cellulose

Activated 2-propanol-moist cellulose (made of cellulose, DP _Cuoxam 1270) was _mixed under a nitrogen atmosphere with a liquor _{ratio of 1:20} in a mixture of 2-

Propanol, methanol and water in the ratio 18: 1: 1.5 suspended. After the addition of 1 1 mol sodium hydroxide / mol AGE of the cellulose, the mixture was stirred at 25 ° C. for 90 min. Then 10 mol of methyl chloride / mol of AGE were metered in, the reaction mixture was heated to 85 ° C. in the course of 30 minutes and stirred at this temperature for 120 minutes. After cooling to room temperature, the pressure was released to normal pressure and the volatile components were removed in vacuo. The remaining dry residue was introduced into boiling water, neutralized with glacial acetic acid and washed free of salt with hot water. It was then filtered off hot and the residue was dried in a forced-air drying cabinet. The methyl cellulose obtained had a degree of substitution of DS = T, 38 and 5% of water-insoluble components.

When non-activated cellulose (cellulose, DP _Cuoxam 1620) was used, a methyl cellulose with DS = 1.17 and 57% water-insoluble components was obtained under the same reaction conditions. - 13 -

Example 6

Cellulose lactate

27.2 g of activated 2-propanol-moist cellulose (from Linters, DP _Cuoxam 560, dry _matter 18.35%, corresponds to 31 mmol AGE) was suspended in 150 ml of dimethylacetamide at room temperature. The 2-propanol present in the mixture was distilled off quantitatively while stirring in vacuo. After addition of 4 mol L-lactide (L-3,6-dimethyl-1,4-dioxane-2,5-dione) / mol AGE of the cellulose, the reaction mixture was heated to 130 ° C. and stirred at this temperature for 5 h. The mixture was then cooled to room temperature, 500 ml of water were added and the mixture was filtered off. The residue was washed twice with 500 ml of a mixture of water and acetone (3: 1, v: v) and dried at 55 ° C. in a forced air drying cabinet. The molar degree of substitution of the obtained cellulose lactate betmg MS = 1.8 determined by NMR spectroscopy. The softening point of the product is approx. 230 ° C (Koflerbank).

No reaction takes place when using the native raw material (linters). According to NMR spectroscopy, the isolated material is an unchanged cellulose I modification.

Claims

- 14 -patent claims

1. A method for activating cellulose comprising the steps

a) dissolving cellulose in a water-containing tertiary amine oxide,

b) coagulation of the dissolved cellulose by adding an appropriate precipitant, and

c) optionally alkalizing the amorphous ones contained in step b)

Cellulose.

2. The method according to claim 1, wherein the water-containing tertiary amine oxide is an amine oxide from the group N-methylmorpholine-N-oxide (NMMNO), N-methylpiperidine-N-oxide, N-methylpyrrolidine-N-oxide and N, N- Dimethylcyclohexylamine-N-oxide, as well as N, N-dimethylethanolamine-N-oxide and triethylamine-N-oxide is used, which contains water or mixtures of water and dipolar aprotic compounds.

3. The method according to claim 1 or 2, wherein in step a) the cellulose is dissolved with the addition of at least one stabilizer.

4. The method according to any one of claims 1 to 3, wherein

in step a) dissolving the cellulose in the water-containing tertiary

Amine oxide takes place in the presence of a dipolar aprotic compound.

5. The method according to any one of claims 1 to 4, wherein - 15 -

in step a) the cellulose is dissolved in the presence of basic compounds, in particular in the presence of tertiary amines and / or alkali metal hydroxides.

6. The method according to any one of claims 1 to 5, wherein

in step b) as organic precipitants, ethers, especially dimethyl ether, ketones, especially acetone, alcohols with preferably 1-6 carbon atoms per molecule, especially methanol, ethanol, 2-propanol, 2-methyl-2-propanol. as well as acetonitrile and mixtures of these compounds.

7. The method according to any one of claims 1 to 6, wherein

in step b) the precipitant is added in stages.

8. The method according to any one of claims 1 to 7, wherein

in step b) the solvent contains basic compounds, in particular tertiary amines and / or alkali metal hydroxides and / or quaternary ammonium bases.

9. A process for the derivatization of cellulose, comprising the steps:

a) dissolving cellulose in a water-containing tertiary amine oxide,

b) coagulation of the dissolved cellulose by adding an appropriate precipitant,

c) optionally alkalizing the amorphous cellulose obtained in step b), and - 16 -

d) derivatization of the amorphous cellulose obtained in step b) or c), optionally in the presence of a suitable solvent.

10. Cellulose derivative, producible by the method according to Claim 9.