DE2000082A1 - Inhibition of decomposition of alkali cellu- - lose - Google Patents

Abstract

At least 0.05%, pref, 0.05-5% wt, based on treated cellulose, of at least one antioxidant e.g. pyrocatechol is added to cellulose before, during or directly after alkalisation but before reaction of cellulose with other reactants to product cellulose derivatives.

Description

Method for preventing the degradation of alkali cellulose The invention relates to a method for preventing the degradation of alkali cellulose.

Alkali cellulose is used in the manufacture of many cellulose derivatives with suitable reaction partners, such as etherification and esterification agents, implemented (B.I.O.S.

Final Report No. 1522 "Methyl-Cellulose Production at Kaule Co, Wiesbaden-Biebrich", March 1947; HEUSER, E .: The chemistry of Cellulose, New York 1946; LIESER, TH .: Brief Textbook of Cellulose Chemistry, Berlin 1953; OTT, E. and SPURLIN, H.N .: Cellulose and Cellulose Derivatives, New York 1954; WURZ, 0 .: Cellulose ether, Darmstadt 1961; -USA patent 3,049,537).

It has also been known for a long time that alkali cellulose can be broken down by oxidizing substances, which is the case, for example, in the production of highly viscous ones mentioned at the beginning Cellulose $ æzz This is disadvantageous in the form of a more or less large loss of viscosity.

Attempts have therefore already been made to prevent such undesired degradation, which is particularly disadvantageous in the production of highly viscous cellulose derivatives makes noticeable, but with relatively expensive means to prevent or at least to belittle. So either a very high molecular weight crude cellulose, which one e.g. obtained from expensive raw materials, such as linters, or through subsequent selection can gain, used to despite an onset during the alkalization oxidative degradation according to the * derivatives subsequent etherification still being able to obtain relatively highly viscous cellulose ethers. Other laborious procedures require a protective gas atmosphere to carry out the reactions listed above from e.g. nitrogen, which at best only results in a reduction However, a prevention of oxidative degradation cannot be achieved.

Finally, in some cases, it is possible at low temperatures to work, which also reduces the oxidative degradation of the alkali cellulose During the etherification process can be achieved, however, the reaction time is extended considerably.

However, all of the known methods listed above are either because of the need to use expensive raw materials or because of the necessary ones additional or costly process steps technically and in terms of price unsatisfactory.

This gave rise to the task of developing a method for preventing the To develop degradation of alkali cellulose, which avoids the aforementioned disadvantages and thus the production of cellulose derivatives, such as highly viscous cellulose ethers, improved in a technically advanced and cost-saving manner.

This object is achieved in that the cellulose before, during or immediately after their alkalization, but before their reaction with others At least one reaction partner for the purpose of producing cellulose derivatives Antioxidant in an amount of at least 0.05%, based on the cellulose used, is added.

It was surprising that the action of the anti-oxidant was independent depends on the type of alkalization and the subsequent etherification process as well as the type of etherification agent used. It can even be an equally good one Protective effect can be achieved regardless of whether the cellulose antioxidant, or the alkali used for alkalization, the alkali cellulose or, for example, in the case of slurry processes is added to the slurry medium.

In the context of the invention cited above, preference is given to an antioxidant, which is either a polyhydric phenol or an oxycarboxylic acid. Of course it is also possible that several of these polyhydric phenols alone or as a mixture with one another or also several oxycarboxylic acids alone or as a mixture with one another used as antioxidants. Of course, it is also possible that one or more polyhydric phenols mixed with one or more oxycarboxylic acids can be added.

Among the polyhydric phenols are the oxy- or trioxybenzenes, trioxybenzoic acid is preferred among the oxycarboxylic acids.

In a particularly advantageous embodiment of the concept of the invention 1,2 - Dioxybenzene (pyrocatechol) are used as antioxidants; 1,3 - dioxybenzene (.esorein), 1,2,3 - trioxybenzene (pyrogallol); 1,2,3 - trioxybenzoic acid (gallic acid) each added alone or in any combination with one another. All of the foregoing Products are also inexpensive to get on the market, beyond that even the addition of an amount of 0.05 to a maximum of 5% by weight, based on cellulose, effective antioxidant.

The method according to the invention is carried out in the context of the following Examples explained in more detail, whereby to characterize the prevention of degradation from the Alkali cellulose, in a known manner, water-soluble cellulose ethers, such as, for example, hydroxyethyl cellulose and sodium carboxymethyl cellulose and then the viscosity these products are determined in aqueous solutions and compared with one another.

The following mean: 1) cp = centipoise 2) Kp = kilopond 3) MS = more molecular Degree of substitution 4) HEC = hydroxyethyl cellulose 5) Na-CMC = sodium carboxymethyl cellulose.

Percentages are always to be understood as percentages by weight.

Example 1 100 kg of absolutely dry softwood cellulose, whose 1% strength Copper oxide ammonia solution has a viscosity of 72 centipoise (cp) mixed with 0.25 kg of pyrogallol and then alkalized in a known manner and etherified.

The hydroxyethyl cellulose obtained has a molecular degree of substitution of ethylene oxide groups of 2.5.

A subsequent viscosity measurement, which shows on a 2 aqueous Solution of the end product is made in a rotary viscometer at 200C, results a value of 10 100 cp (centipoise).

Example 2 Here, under the same process conditions as she have been described in Example 1, an equal amount of hydroxyethyl cellulose produced, but in contrast to the process sequence according to the invention, none was produced Pyrogallol added. As a result, under the same conditions as in Example 1 measured viscosity of the obtained Hydroxyäthylcellübse only 1,015 cp.

Example 3 Here too, the manufacturing process for hydroxyethyl cellulose carried out in the same way as in Example 1, with the exception that instead of 100 kg of softwood cellulose here the same amount of linters cellulose, which had a viscosity of 500 cp in 1% copper oxide ammonia solution was used where, instead of, as in Example 1, 0.25 kg of pyrogallol (1,2,3 - trioxybenzene) here 0.5 kg of pyrocatechol (1,2-dioxybenzene) are added.

The viscosity of the hydroxyethyl cellulose obtained is 59,000 ct.

Example 4 With otherwise the same test conditions as in example 3 instead of 0.5 kg of pyrocatechol (1,2 - dioxybenol) 41 pyrogallol (1,2,3 - Trioxybenzene) added.

The finished hydroxyethyl cellulose has a viscosity of 23,500 cp.

Example 5 Under otherwise identical test conditions as in example 3 described, instead of 0.5 kg pyrocatechol (1,2-dioxybenzene) 0.5 kg Gallic acid (1,2,3 - trioxybenzoic acid) is used.

The viscosity of the hydroxyethyl cellulose obtained is 38,000 cp.

Example 6 With otherwise identical test conditions as in example 3 instead of 0.5 kg of pyrocatechol (1,2-dioxybenzene), 0.5 kg of resorcinol (1.3 - Dioxybenzene) is used.

The viscosity of the hydroxyethyl cellulose obtained is 31,000 cp.

Example 7: This example serves as a comparison to the examples 3 - 6, in which under the same test conditions as in Example 3 no antioxidant is added.

The viscosity of the hydroxyethyl cellulose thus obtained is only 2,500 cp.

Example 8 100 kg of absolutely dry softwood pulp, 1 wt Solution in copper oxide ammonia has a viscosity of 69 cp results 1 kg of pyrogallol (1,2,3 - trioxybenzene) is added. The subsequent alkalization and carboxymethylation is carried out in a manner known per se. The received Sodium carboxymethyl cellulose has a molecular degree of substitution of 0.62 on.

The viscosity of the 2 show aqueous solution of the product is 22 100 cp.

EXAMPLE 9 Here a sodium carboxymethyl cellulose is used among the the same process conditions as described in Example 8, produced, however without the addition of pyrogallol (1,2,3 -trioxybenzene) or any other antioxidant. The viscosity, which is determined exactly as in Example 8, gives a value of only 9,800 cp.

Example 10 The same process conditions as in Example 8 complied with, with the exception that 1.) instead of softwood pulp one the same amount of 100 kg of absolutely dry linters cellulose, its 1% by weight solution results in a viscosity of 510 cp in copper oxide ammonia, is used, and 2.) instead of 1 kg of pyrogallol (1,2,3 - trioxybenzene) here an equal amount (1 kg) Pyrocatechol (1,2-dioxybenzene) is added.

The sodium carboxymethyl cellulose obtained has a molecular Degree of substitution (MS) of 0.61.

The viscosity of the aqueous solution shown in FIG. 2 is 64,300 cp.

Example 11: The test conditions here are the same as in Example 10, however, does not use catechol (1,2-dioxybenzene) or any other Antioxidant added.

The corresponding control experiment therefore only gives one viscosity from 21,200 cp.

Examples 1-11 are summarized in the table below to illustrate the advantages of the process according to the invention and for reasons of better overview. Tabel With- type of antioxidant ether viscosity of a 2% played raw additive tes pro-aqueous solution of the End product cellulose in kg of product in cp in kg 1 softwood pyrogallol HEC i0 100 100 0.25 2 softwood HEC 1 015 100 3 Linters Brenzkatechi HEC 59 000 100 0.5 4 linters pyrogallol HEC 32 500 100 0.1 5 Linters gallic acid HEC 38,000 100 0.5 6 linters resorcinol HEC 31,000 100 0.5 7 Linters O HEC 2 500 100 8 Softwood Pyrogallol Na-CMC 100 1.0 9 needle hole O Na-CMC 9 800 100 10 Linters Brenzkatechi Na-CMC 64 300 100 11 Linters O Na-CMC 21 200 100

Claims (5)

Claims 1.) Method for preventing the degradation of alkali cellulose, characterized in that the cellulose before, during or immediately after it Alkalization, however, before reacting with other reactants for the purpose the production of cellulose derivatives at least one antioxidant in an amount of at least 0.05, based on the cellulose used, is added. 2.) The method according to claim 1, characterized in that the cellulose at least one polyhydric phenol and / or at least one polyhydric as antioxidant Oxycarboxylic acid is added. 3.) The method according to claim 1 and 2, characterized in that the Cellulose as antioxidant at least one dioxybenzene and / or at least one trioxybenzene and / or at least one trioxybenzoic acid is added. 4.) Method according to claim 1-3, characterized in that as Antioxidant 1,2 - dioxybenzene (pyrocatechol); 1,3 - dioxybenzene (resorcinol); 1,2,3 - trioxybenzene (pyrogallol); 1,2,3 - trioxybenzoic acid (gallic acid) each for can be added alone or in any combination with one another. 5.) The method according to claim 1-4, characterized in that the Antioxidants individually or in combination with each other in an amount of 0.05 - 5 Ges. $, Based on the cellulose, can be used.