DE1297850B - Stabilization of cellulose against degradation in an alkaline medium - Google Patents

Description

The invention relates to the stabilization of cellulose against the Degradation in an alkaline medium.

With the action of alkali on cellulose in the presence of oxygen the cellulose molecules are split under oxidation. This breakdown of alkali cellulose is a process that is widely used technically to reduce the molecular weight of cellulose. In some conversions of cellulose in an alkaline medium, the Inevitably occurring degradation, however, is an undesirable side effect.

In the production of highly viscous cellulose ethers, for example, the degradation is the Alkali cellulose usually disadvantageous during the etherification reaction. Methods for Stabilization of cellulose against its oxidative degradation are therefore part of the process of practical importance for the chemical refinement of cellulose.

It is known that additions of sodium borohydride have an inhibitory effect on the Degradation of alkali cellulose act. However, sodium borohydride is because of the high The price is unsuitable for economic use. One also has to manufacture of viscose from the degradation-retarding effect of sodium thiocarbonate, sodium sulfite or bisulfite Made use of.

Of these, sodium thiocarbonate is because of its easy decomposition practically irrelevant.

The object of the invention was to provide more effective stabilization to make possible than, for example, with sodium sulfite or bisulfite or pyrosulfite or metabisulfite. (According to recent findings, bisulfite is said to be in its solid form present as pyrosulphite or, which is the same, as metabisulphite.) The stabilization of cellulose against degradation in an alkaline medium according to the invention by adding reducing compounds of sulphurous acid and is thereby characterized in that a salt of hydroxymethanesulfinic acid is added.

The hydroxymethanesulfinic acid salts to be added according to the invention exercise a strong inhibition on the alkaline oxidative degradation of cellulose during storage and thermal stress. They are, for example, in the form of sodium, Calcium and zinc salts as reducing agents for vat dyeing or as decolorizing agents Merchandise. The size of the effect depends on the amount of inhibitor added addicted. Additions in amounts of 0.1 to 10% are of practical interest. preferably from 0.3 to 2%, based on the weight of the cellulose.

One can use the stabilizer in the caustic soda, through which the cellulose to be made alkaline, dissolve or suspend, or it is dissolved or suspended it in solvents that are miscible with water and mixes it by immersion or in mash or in a mixer or by spraying with the cellulose or the alkali cellulose.

In general, however, the stabilizer will be used in the alkalizing process Add the sodium hydroxide solution used for the pulp to the pulp. In this case the sodium salt of hydroxymethanesulfinic acid proves to be particularly advantageous, as it is also readily soluble in highly concentrated alkalis.

The alkali celluloses mixed with the stabilizers mentioned with alkali contents (NaOH) up to 50% in the dry matter show after storage, thermal stress up to 100 ° C and after reactions, e.g. B. with etherifying agents, significantly higher DP values (average degree of polymerization) than comparison samples, to which known stabilizers or no stabilizer were added. From the Sodium salt the hydroxymethanesulfinic acid causes 1% (based on cellulose) z. B. at a Alkali cellulose with 50% NaOH in dry matter at room temperature extends the maturation time around three times the normal value. Viscosities of methyl celluloses in one Case with and in the other without a stabilizer can be found in Utilization of the optimal range of action of the sodium salt of hydroxymethanesulfinic acid behave as 10: 1 (when comparing 2 ° / Oiger solutions in the Höppler viscometer).

The stabilizing effect of the stabilizers can be seen in all Take advantage of reactions in an alkaline medium, in which a strong breakdown of cellulose should be avoided; z. B. in the production of alkali cellulose after all known processes, as well as in the modification reactions of cellulose such as etherification, Esterification, xanthogenation and addition of epoxides or substances with multiple bonds.

Example 1 Samples of 100 g of sulfite pulp were each with 200 g of a 50% sodium hydroxide solution added, the 0.5 to 2.0 g of sodium metabisulfite or the Sodium, calcium or zinc salt of hydroxymethanesulfinic acid (in the tables briefly referred to as)> sodium salt, "calcium salt" with "zinc salt") in solution or suspension, and mixed in a blender for 45 minutes.

The degradation of the alkali cellulose was closed at room temperature Determined vessel in a drying cabinet at 60, 80 and 100 ° C with access to air (Table 1).

The measure in cuen (copper-ethylenediamine) was used as a measure of the degradation DP value of the regenerated celluloses.

Table 1 Stabilizing effect of the stabilizers when the alkali cellulose is exposed to thermal stress Thermal addition in ° / 0 related to DP Exposure to pulp (cuen) 20 ° C, 60 minutes without addition 1290 20 ° C, 22 hours without addition 470 20 ° C, 22 hours 1 ° / 0 sodium salt 680 60 ° C, 30 minutes without addition 660 60 ° C, 30 minutes 1% sodium salt 1120 60 ° C, 60 minutes without addition 540 60 ° C, 60 minutes 1 ° / 0 K-metabisulfite 735 60 ° C, 60 minutes 1 ° / 0 sodium salt 825 60 ° C, 60 minutes 2 ° / 0 zinc salt 745 80 ° C, 60 minutes without addition 330 80 ° C, 60 minutes 1% sodium salt 540 100 ° C, 30 minutes without addition 465 100 ° C, 30 minutes 1 ° / o t-metabisulfite 745 100 ° C, 30 minutes 1% sodium salt 730 100 ° C, 30 minutes 1 ° / o calcium salt 705 Table 2 Dependence of the stabilizing effect on the amount added Thermal addition in% related to DP Exposure to pulp (cuen) 60 ° C, 45 minutes without addition 470 60 ° C, 45 minutes 0.5% sodium salt 570 60 ° C, 45 minutes 1.0% sodium salt 810 60 ° C, 45 minutes 2.0 / o sodium salt 875 The above example shows the much better stabilizing effect of the sodium hydroxymethanesulfinate compared to the pyrosulfite at the moderately hot temperatures, which are particularly important industrially, e.g. B. at 60 ° C recognize.

Example 2 Alkali cellulose produced with stabilizing additives as in the example-became known after different thermal stresses Way methylated with liquid methyl chloride under constant conditions. The in Falling ball viscometer according to HÖ p pler measured viscosities of 2% solutions of the methyl celluloses are listed in Table 3. The effectiveness of an additive of sodium sulfite is included for comparison.

Table 3 Stabilizing effect in the production of methyl cellulose Thermal stress of the 1% 1% 1% Without addition Alkali cellulose before its sodium salt potassium metabisufit Nariumstfit Methylation (cP) (cP) (cP) (cP) 20 ° C, 45 minutes ......... 28 000 - - - 20 ° C, 22 hours .. 380 2130 1340 720 60 ° C, 60 minutes .. .. 610 5930 3040 1050 100 ° C, 30 minutes .. .. 345 2670 3260 -

Claims (1)

Claim: Stabilization of cellulose against degradation in alkaline Medium by adding reducing the compounds of sulphurous acid, thereby characterized in that a salt of hydroxymethanesulfinic acid is added.