CN1079848C - Cellulose moulded article and method of producing same - Google Patents

Abstract

The present invention relates to a method for the manufacture of cellulose molded bodies having a high degree of whiteness, characterized in that the following steps are combined: bleaching the cellulose material with a bleaching agent, provided that the bleaching agent does not contain chlorine or chlorine compounds; dissolving the bleached cellulosic material in the aqueous tertiary amine oxide to obtain a moldable cellulosic solution; and, processing the moldable cellulosic solution into molded bodies.

Description

Cellulose molded body and its production method

The present invention relates to a cellulose molded body, in particular a cellulose fiber, and a method for its production.

For decades, people have been looking for a process that can replace the current large-scale application of viscose to produce cellulose fibers, especially as an attractive solution with better environmental compatibility is to derivatize The cellulose is dissolved in an organic solvent, and molded bodies such as fibers, films and other molded bodies are extruded from the solution. Fibers extruded in this way have been given the generic name of Lyocell by BISFA (International Bureau for the Standardization of Man-Made Fibres). The organic solvent referred to by BISFA refers to a mixture of organic compounds and water.

In particular mixtures of tertiary amine oxides and water have proven to be very suitable as organic solvents for the production of cellulose moldings. N-methylmorpholine-N-oxide (NMMO) is preferably used as the amine oxide. Other amine oxides are described, for example, in EP-A-0553070. In EP-A-0356419 a method of making a moldable cellulose solution is proposed. The method of producing cellulose molded bodies using tertiary amine oxides is generally called the amine oxide method.

In EP-A-0356419 is described an amine oxide process for the manufacture of spinnable cellulose solutions, which essentially employs the suspension of cellulose in liquid aqueous N-methylmorpholine-N-oxide (NMMO) liquid as raw material. This method is a one-step and continuous conversion of the suspension into a moldable solution in a film processing plant. The moldable solution is then spun into filaments through a molding die, such as a spinneret, and passed through an air gap into a precipitation bath to precipitate the cellulose, followed by washing of the resulting cellulose fibers.

The undesired coloration in fibers is mainly caused by lignin and colored organic compounds. In order to prevent this phenomenon, it is known to bleach cellulosic materials prior to processing. For this purpose the crude cellulosic material is reacted under precisely defined conditions with a series of bleaching agents such as elemental chlorine, chlorine compounds such as hypochlorite and chlorine dioxide, oxygen, peroxides and ozone, which are The combination of compounds is completed in a certain order, so it is called the bleaching sequence.

Traditional bleaching methods start with elemental chlorine, which is chlorinated or oxidized to varying degrees depending on the pH. Hypochlorite and chlorine dioxide oxidize lignin and colored compounds. Alkaline extraction is usually performed between the various reaction steps of these bleaching agents to remove lignin and other compounds that have gone into solution from the reaction medium. For an overview of the bleaching of cellulosic materials see "Bleaching of Cellulose" (R.P. Singh; The Bleaching of Pulp, TAPPI Press, Atlanta, USA.)

When bleaching cellulosic materials, the use of chlorine-containing bleaches will generate varying degrees of chlorinated products, which are difficult to degrade, and most of them will enter the wastewater. From an environmental point of view, this method is problematic, so the application of chlorine-containing bleaching agents, especially elemental chlorine, is more and more restricted, but the quality of bleaching is also reduced because elemental chlorine has a high bleaching power.

Among chlorine-containing compounds, chlorine dioxide is more effective than hypochlorite in bleaching, but it is also more expensive than the commonly used hypochlorite.

According to the current state of the art, bleaching methods that are completely chlorine-free are also used. Among these methods, oxygen/peroxide combinations are employed as well as ozone. Such bleached cellulosic materials are called TCF (Totally Chlorine Free) cellulosic materials because neither elemental chlorine nor chlorine compounds are used for bleaching. On the other hand, ECF (Elemental Chlorine Free) cellulosic materials in the literature refer to cellulosic materials that do not use elemental chlorine, but are bleached with chlorine compounds.

In this specification, ECF cellulose material bleached with hypochlorite is referred to as ECF hypochlorite cellulose material.

The so-called whiteness in the prior art refers to the degree of bleaching effect, which emerges from the viscose process, that is, in the whiteness of the bleached cellulose material and the whiteness of the cellulose product made from this cellulose material. There is such a relationship that cellulose materials with higher whiteness can usually be processed into fibers with higher whiteness.

It is an object of the present invention to provide a process for the manufacture of cellulose molded bodies which can be made from a cellulose material of the same original whiteness and otherwise in the same manner as compared to cellulose made from ECF hypochlorite cellulose material. Moldings Cellulose moldings with higher whiteness.

This object is achieved with a method for producing cellulose molded bodies, characterized in the combination of the following steps:

- bleaching of cellulosic materials with a bleaching agent, provided that the bleaching agent does not contain chlorine or chlorine compounds,

- dissolving the bleached cellulosic material in an aqueous tertiary amine oxide to obtain a moldable cellulosic solution, and

- Processing of moldable cellulose solutions into molded bodies.

With the method of the present invention, cellulose fibers and cellulose films with high whiteness can be specially produced according to the dry spinning method/wet spinning method.

Surprisingly for those skilled in the art, TCF cellulose material achieves higher fiber whiteness than ECF hypochlorite cellulose material with good side effects when the starting material has the same whiteness , that is, this method may be particularly suitable for environmentally friendly production of fibers.

The invention also relates to the bleaching of fibers produced by the amine oxide process using non-chlorine bleaching agents such as oxygen, ozone and especially hydrogen peroxide.

According to a preferred version of the present invention, it is characterized in that the fibers and films produced according to the present invention are bleached with chlorine-free or chlorine-compound-free bleaching agents.

As tertiary amine oxides, especially N-methylmorpholine-N-oxide is particularly effective.

The invention also relates to cellulose moldings, in particular cellulose fibers and films, which can be produced by the process according to the invention and have a high degree of whiteness.

Furthermore, the invention relates to the use of cellulosic materials bleached with a bleaching agent which does not contain chlorine or chlorine compounds for the production of cellulosic moldings by the amine oxide process.

The invention is further illustrated by the following examples and comparative examples.

example

To make TCF cellulosic material, the cellulosic material (beech sulfite cellulose pulp) is first extracted with peroxide-enhanced alkaline oxygen, then bleached with ozone and finally with peroxide according to known methods, each This bleaching process can be seen in "Cellulose Bleaching" (The Bleaching of Pulp by R.P. Singh, TAPPI Press, Atlanta, USA) and EP-A-0426652 patent.

The whiteness of the obtained TCF cellulosic material was 90.6 as measured by ISO3688, the rapid cuprammonium viscosity value of the cellulosic material was 19.8 Pas as measured by Zellcheming ZM IV/30/62, and its alpha content was 90.9.

The TCF cellulose material was then processed in a known manner in an agitated tank to form a spinning dope consisting of 12% cellulose, 77% NMMO and 11% water. The spinning stock had a viscosity of 1630 Pas (temperature: 90° C., shear rate: 0.1 sec 1 ).

The spinning material is spun into fibers by a known wet spinning method/dry spinning method (referring to EP-A-0584318) through a spinneret with a 100 μm diameter spinning hole at 120 ° C, and the fiber whiteness produced by the present invention is about 50.

The CIELAB whiteness of the fiber is measured as follows: According to DIN6174 and DIN5033, use D65 light to measure the color coordinates _Rx , _Ry , _Rz of the fiber at an observation angle of 10°, according to DIN55981 (according to Gartner/ Griesser's hue difference) is calculated on the red/green axis as follows (formula) to calculate CIE-whiteness and tint (tint):

CIE-whiteness: W=Y+800 ^* (x0-x)+1700(y0-y)

Coloring: T=900 ^* (x0-x)－650 ^* (y0-y)

(Note: T negative value = red tone, T positive value = green tone)

y... the standard chromaticity value sensitive to green (=

Ry...green reflection value)

x0, y0... The standard chromaticity value part of the achromatic point; (D65.10°, X0 = 0.3138; y0 = 0.3310)

x, y... The standard color value part of the sample; calculated according to the following formula:

x=X/(X+Y+Z)

y=Y/(X+Y+Z)

z=1-x-y

The standard color values X, Y, and Z in the formula are still calculated from the reflection values (filter values) R _x , R _y , and R _z under the illumination of D65 and the observation angle of 10°, as follows:

X＝0.94811 ^* Rx

Y=Ry

Z = 1.07304 ^* Rz

Then this fiber is bleached with hydrogen peroxide (1.5gH ₂ O ₂ ; stabilizer: 0.2g/1MgSO ₄ ; pH 10.5; washing solution ratio 1:20; 70°C bleaching time: 3 minutes), the bleached fiber CIELAB-whiteness is 57.

Comparative example:

To prepare the ECF hypochlorite cellulose material, the same starting material as in the previous example was first extracted with peroxide-enhanced alkaline oxygen, then bleached with hypochlorite and then with peroxide.

The whiteness of the obtained ECF hypochlorite cellulose material was 91.6, which is substantially the same as the whiteness value in the example in which the TCF cellulose material was prepared.

Spinstock and fibers were then prepared similarly to the previous example. The whiteness of the fiber CIELAB made is about 39. It is evident that the whiteness of fibers processed from TCF cellulose material bleached without any chlorine compounds according to the present invention is higher than that of fibers made from ECF cellulose material bleached with hypochlorite.

Then the fiber made is bleached as described in the above example, and the whiteness of the fiber after bleaching is about 54.

Claims (5)

1. A method for producing cellulose fibers with high whiteness, characterized in that the following steps are combined: - bleaching of cellulosic materials with a bleaching agent, provided that the bleaching agent does not contain chlorine or chlorine compounds, - dissolving the bleached cellulosic material in an aqueous tertiary amine oxide to obtain a moldable cellulosic solution, and - Processing the moldable cellulose solution into fibers. 2. The method according to claim 1, characterized in that the moldable cellulose solution is processed into fibers by dry/wet spinning. 3. Method according to claim 2, characterized in that the fibers are bleached with a bleaching agent, provided that the bleaching agent does not contain chlorine or chlorine compounds. 4. Process according to claim 1 or 2, characterized in that N-methylmorpholine-N-oxide is used as tertiary amine oxide. 5. Use of cellulose materials bleached with bleaching agents for the production of cellulose moldings by the amine oxide process, provided that the bleaching agents do not contain chlorine or chlorine compounds.