DE19817454A1 - Method for activating and derivatising cellulose - Google Patents

Abstract

Use of an N-oxide for activating cellulose. A process for activating cellulose comprising the steps of: (a) dissolving the cellulose in a water-containing N-oxide; (b) coagulating the dissolved cellulose by adding a suitable solvent and optionally (c) alkalising the amorphous cellulose obtained in stage (b). The amorphous cellulose obtained in stage (b) or (c) may be derivatised, optionally in the presence of a suitable solvent (separately claimed).

Description

The present invention relates to an activation method for cellulose and a process for the derivatization of acti fourth cellulose and the derivatization thus obtained Products.

It is known to activate cellulose for derivatization (H.A. Kräß, Cellulose-Structure, Accessibility and Reactivity / Polymer Monographs Vol. 11, Gordon and Breach Science Publishers, S.A., 1993, pp. 215-276). Each will but large amounts of activation and derivatization reagents needed. In addition, the cellulose derivatives obtained have te, especially with low degrees of substitution, only one low solubility in water and / or organic solvents on.

The object of the present invention was that to avoid disadvantages known from the prior art.

Surprisingly, it was found that the disadvantages of the Stan of technology can be avoided by an activation Process for cellulose using N-oxides.

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

• a) dissolving cellulose in a water-containing N-oxide,
• b) coagulation of the dissolved cellulose by adding a appropriate solvent and optional
• c) Alkalization of the amorphous obtained in step b) Cellulose.

As a cellulose starting material for the process according to the invention Ren are preferred cotton linters, softwood sulfite, needle wood sulfate and / or hardwood pulp used.  

Solvents such as N-methylmorpho are used as water-containing N-oxides lin-N-oxide (NMMNO), N, N-dimethylethanolamine-N-oxide, triethyla min-N-oxide, N-methyl-piperidine-N-oxide, N-methylpyrrolidine-N- Understood oxide or N, N-dimethyl-cyclohexylamine-N-oxide, which Water or mixtures of water with dipolar aprotic Ver bonds such as dimethyl sulfoxide, N-methylpyrolidone, dimethylfor mamide or dimethylacetamide was added.

The water-containing N-oxides can be small amounts basic kender compounds such as tertiary amines and / or alkali metal hydroxides and / or contain quaternary ammonium bases.

Solvents suitable for coagulating the dissolved cellulose are in particular organic solvents such as ethers, ketones, alcohols get with preferably 1-6 carbon atoms, in particular Methanol, ethanol, isopropanol or 2-methyl-2-propanol, as well Acetonitrile, acetone, dimethyl ether or mixtures of these solutions medium. Small amounts of the solvents can have a basic effect Compounds such as tertiary amines and / or alkali hydroxides and / or contain quaternary ammonium bases.

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

• a) Cellulose in N-methylmorpholine-N-oxide (NMMNO) / water System is solved and
• b) the dissolved cellulose, in particular by adding organi shear solvent precipitated and from adhering NMMNO is liberated.

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 activation step
• - Simple process design, solution preparation and processing  
• - lower costs, simple and complete recovery the activation reagents
• - Reduced amounts of alkalizing agent
• - easier removal of the activating agent from the activated cellulose (no salts)
• - no environmental pollution, possibility of a closed Solvent cycle
• - higher dissolving power for cellulose (also high molecular weight Celluloses dissolve in concentrations of up to 35 % By weight)
• - no pre-swelling (water, water vapor, liquid Ammonia), followed by a subsequent one Solvent exchange required for solution preparation.

The activation process according to the invention leads to amorphous Cellulose with increased reactivity and also allows one direct derivatization without prior alkalization step (e.g. esterification to cellulose acetate, nitrate or lactate, and / or reaction with isocyanates) with ver improved yields of cellulose derivatives with higher soldering quality be preserved.

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

• a) dissolving cellulose in an N-oxide-containing solvent,
• b) coagulation of the dissolved cellulose by adding a appropriate solvent,
• c) optional alkalization of those contained in step b) amorphous cellulose,
• d) derivatization of those contained in step b) or c) amorphous cellulose, optionally in the presence of a ge suitable solvent.

Reaction products of cellulose are used as cellulose derivatives understood with derivatization reagents like cellulose esters (Cellulose acetates, cellulose lactates, cellulose nitrates), Cel lulose ether esters and / or cellulose carbamates, especially what ser- and / or organo-soluble cellulose ethers such as. B. Car boxyalkyl cellulose (e.g. carboxymethyl cellulose), hydroxyal alkyl celluloses (e.g. hydroxyethyl, hydroxypropyl celluloses), Carboxyalkyl hydroxyalkyl celluloses (such as carboxymethyl hydroxyethyl, carboxymethyl hydroxypropyl cellulose), sulfoal alkyl cellulose derivatives (e.g. sulfoethyl cellulose, sulfopro pylcellulose, methylsulfoethylcellulose, methylsulfopropylcel lulose, carboxymethylsulfoethyl cellulose, carboxymethylsulfo propyl cellulose, hydroxyethyl / hydroxypropyl sulfopropyl cellulose ether), alkyl celluloses (e.g. methyl cellulose, Ethyl cellulose), alkyl hydroxyalkyl celluloses (e.g. methyl hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, ethyl hydroxypropyl cellulose), alkylene celluloses (such as allyl cellulose), alkylene alkyl celluloses (e.g. allyl methyl cellulose, allyl ethyl cellulose), dialkyl aminoalkyl celluloses (e.g. diethylaminoethyl cellulose), dial kylaminoalkylhydroxyalkylcelluloses (e.g. diethylaminoethyl hydroxyethyl cellulose), binary or ternary ionic or non ionic cellulose ethers from the above functional groups.

The derivatization preferably takes place in the presence of Coagulation of the solvent used in cellulose instead of. Suitable solvents are organic solvents such as 2-propanol, 2-methyl-2-propanol, acetonitrile, acetone, dimethyl ether, dioxane, methyl chloride, ethyl chloride (etherification, Car bamination), methylene chloride, glacial acetic acid, carboxylic anhydrides such as acetic, propynic and butyric anhydride (Vereste tion).

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

• a) Cellulose in N-methylmorpholine-N-oxide (NMMNO) / water System is solved  
• b) the dissolved cellulose, in particular by adding organi shear solvent precipitated and from adhering NMMNO is freed, step c) (alkalization) is omitted and
• d) the conversion of the amorphous cellulose thus obtained into An presence of the organic solvent used for coagulation by means of.

The herge according to the derivatization process according to the invention presented cellulose derivatives are also the subject of lying invention.

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

Claims (9)

1. A method for activating cellulose comprising the steps:

• a) dissolving cellulose in a water-containing N-oxide,
• b) coagulation of the dissolved cellulose by adding an appropriate solvent, and optional
• c) Alkalization of the amorphous cellulose contained in step b).

2. The method of claim 1, wherein in step a) dissolving the cellulose against the N-oxide a dipolar-aprotic second component has occurred. 3. The method according to claim 1 or 2, wherein in step a) the cellulose is dissolved in the presence of the base acting compounds, especially in the presence of ter tertiary amines and / or alkali hydroxides and / or quaternary Ammonium bases are done. 4. The method according to any one of claims 1 to 3, wherein in step b) as organic solvents ether, ketones, Al alcohols with preferably 1-6 carbon atoms per mole cool, especially methanol, ethanol, isopropanol, 2-methyl-2-propanol, as well as acetonitrile, acetone, dimethyl ether or mixtures of these solvents can be used.   5. The method according to any one of claims 1 to 4, wherein in step b) the addition of the solvent gradually he follows. 6. The method according to any one of claims 1 to 5, wherein in step b) the solvent-acting compound dungen, in particular tertiary amines and / or Alka Contains hydroxides and / or quaternary ammonium bases. 7. A process for the derivatization of cellulose, comprising the steps:

• a) dissolving cellulose in a water-containing N-oxide,
• b) coagulation of the dissolved cellulose by adding an appropriate solvent,
• c) optional alkalization of the amorphous cellulose contained in step b),
• d) derivatization of the amorphous cellulose contained in step b) or c), optionally in the presence of a suitable solvent.

8. Cellulose derivative, producible by the method according to An saying 7. 9. Use an N-oxide to activate cellulose.