EP2889401B2 - Regenerated cellulose fibre - Google Patents

Description

The present invention relates to a regenerated cellulose fiber produced by the viscose process (hereinafter also referred to as "viscose fiber"), its production and use.

In particular, the present invention relates to a regenerated cellulose fiber containing lignin.

Viscose fibers are already used in carbonized insulation molded parts and nonwovens. During carbonization, carbonaceous starting materials (precursors) are pyrolyzed in an oven at temperatures of 500-1800 ° C with the exclusion of oxygen. Foreign atoms such as nitrogen, oxygen and hydrogen are split off in gaseous form. What remains is almost exclusively carbon, which has a graphite-like layer structure. The carbonization yield of viscose is theoretically 44%, but in reality only 15-20%. You lose 80 to 85% of the fiber mass in carbonization. Improving the carbon yield would make the carbonization process much more economical.

From the US 4,177,236 is known the production of viscose fibers containing cross-linked Kraft lignin or cross-linked sodium lignosulfonate. According to this document, the incorporation of non-crosslinked lignin in viscose fibers was not possible, which means that practically no lignin was found in the finished fiber.

As a possible application of the modified viscose fibers described there US 4,177,236 the production of carbon fibers.

The WO 2012/156443 A1 describes precursor fibers for the production of carbon fibers which contain lignin. The fibers are spun from a solution containing a lignin and a fiber-forming polymer from the group of polyacrylonitrile or polyacrylonitrile copolymers. Example 2 of this document describes spinning a solution containing chemical cellulose, kraft lignin and polyacrylonitrile.

Also the WO 2013/020919 deals with the production of precursor fibers from carbon fibers. The fiber is a mixture of polyacrylonitrile, a glucan and lignin. Both in the case of WO 2012/156443 A1 as well as the WO 2013/020919 the fibers are spun from a solution in an organic solvent.

The EP 2 524 980 describes the production of precursor fibers from carbon fibers. The fibers contain at least 10% lignin and one or more fiber-forming polymers such as cellulose and are spun from an organic solvent.

In the GB 1,111,299 describes the production of carbon fibers from lignin fibers.

Other documents that deal with the use of lignin, in particular in lignin fibers or mixed fibers containing lignin, are for example: US 3,461,082 ; DE 21 18 488 A1 ; Kadla JF et al, "Lignin-based carbon fibers for composite fiber applications", Carbon (40) 15, 2002, 2913-2920 ; Kubo S. et al, "Poly (ethylene oxide) / organosolv lignin blends", Macromolecules (37) 18, 2004. 6904-6911 ; GB 1 500 053 ; US 2,265,563 A ; DE 1 163 654 A ; DE 25 41 220 A and DE 197 34 239 A1 .

There is still a need to manufacture cellulose fibers containing lignin. Such fibers would be particularly suitable for the production of carbon fibers, the carbon fiber being able to be produced more cheaply due to the addition of the inexpensive raw material lignin.

The object on which the present invention is based is achieved by a regenerated cellulose fiber obtained by the viscose process, containing organosolv lignin in a content of 10% to 70, based on fiber.

Brief description of the figures

• Figure 1 shows the cross sections of viscose fibers in which (nominally) 50% organosolv lignin has been incorporated.
• Figure 2 shows the cross-sections of viscose fibers in which (nominal) 10% organosolv lignin has been incorporated.
• Figure 3 shows the cross sections of viscose fibers in which (nominal) 35% organosolv lignin and 15% lignosulfonate have been incorporated.

Detailed description of the invention

In the production of cellulose, wood (wood chips) or other plant fibers are chemically broken down by removing the lignin contained therein, while the structure of the cellulose is largely preserved. The dissolved lignin differs greatly from its native form, since depending on the process, depolymerization and derivatization with the chemicals occur during digestion.
The most important pulping processes are the sulfate process (product: Kraft lignin) and the sulfite process (product: lignosulfonate). Every year, more than 50 million tons of lignin are isolated as a by-product.

As a macromolecular natural product, the lignins differ in their monomer composition, type of bonds and molecular weight depending on the type of plant, origin and season. In addition, each digestion process produces lignins with different properties.

The person skilled in the art understands the "organosolv process" as wood digestion with the aid of aqueous organic solvents, in particular ethanol, at high pressure and high temperature. The lignin obtained in this process is referred to as organosolv lignin.

Surprisingly, it has now been shown that contrary to the in US 4,177,236 described tendency according to which (uncrosslinked) lignins cannot be spun into viscose fibers, the incorporation of (uncrosslinked) organosolv lignin in viscose fibers is possible with satisfactory yields.

The cellulose fiber according to the invention preferably has an organosolv lignin content of 20% to 50%, based on fiber. This information is also to be understood in the following as% by weight. Furthermore, the information relates to the lignin content of a finished viscose fiber, i.e. the fiber after the post-treatment and in particular washing steps in the context of viscose fiber production. The organosolv lignin and other lignin contents are determined using the measurement method given in Example 1.

The highest possible level of lignin is preferred, since it has been shown in the production of carbon fibers that lignin enables a higher carbon yield. The term “(regenerated) cellulose fiber” or “viscose fiber” is also intended to include fibers which contain up to 90% of lignin as long as they are made by the viscose process, ie from an alkaline solution containing cellulose xanthate and spun in an acidic spinning bath.

The fiber according to the invention can preferably contain a further lignin different from Organosolv lignin. Since Organosolv lignin compared to common lignins such as e.g. Kraft lignin or lignosulfonates is more difficult to obtain, the replacement of part of the organosolv lignin by another lignin can make the production of the fiber according to the invention and the carbon fiber resulting therefrom by carbonization even more favorable.

The further lignin is preferably selected from the group consisting of kraft lignin, lignosulfonate and mixtures thereof. The other lignin is also preferably uncrosslinked.

The content of further lignin in the fiber can be from 5% to 85%, preferably 10% to 70%, particularly preferably 20% to 50%, based on the fiber.

The ratio of organosolv lignin to further lignin can be from 4: 1 to 1: 4, preferably 3: 1 to 1: 3.

In a preferred embodiment of the present invention, the cellulose fiber according to the invention is characterized in that, apart from cellulose and lignin, it contains essentially no further fiber-forming polymer, e.g. Contains polyacrylonitrile or polyacrylonitrile copolymers.

The cellulose fiber according to the invention can have a titer of 0.5 dtex to 30 dtex, preferably 1 dtex to 4 dtex.

The cellulose fiber according to the invention is preferably used for the production of carbon fibers. Other areas of application are e.g. Hygiene and medical applications (due to the increased water retention capacity of the fiber). A cellulose fiber according to the invention, which contains lignin sulfonate in addition to the organosolv lignin, is also suitable for ion exchange, for example in water softening or when setting concrete, due to the sulfonic acid groups introduced into the fiber (lignosulfonate contains 1.25-2.5% sulfonic acid groups).

The present invention also relates to a process for producing the cellulose fiber according to the invention, comprising the step of adding Organosolv lignin and, if appropriate, a further lignin to a spinning viscose or a precursor thereof.

The "precursor" of spinning viscose includes, in particular, starting substances of the viscose process, such as Pulp, or intermediates such as e.g. Understand alkali cellulose or cellulose xanthate.

Examples: Example 1:

• Kraft-Lignin (Hersteller: Sigma-Aldrich)
• Lignosulfonat (Hersteller: Carl Roth) und
• Organosolv-Lignin (Hersteller: Fraunhofer CBP Leuna Charge K002)

Pilot spinning was carried out to produce viscose fibers, in which the following uncrosslinked lignins were spun:

• Kraft lignin (manufacturer: Sigma-Aldrich)
• Lignosulfonate (manufacturer: Carl Roth) and
• Organosolv lignin (manufacturer: Fraunhofer CBP Leuna Charge K002)

The lignin was mixed in a proportion of 50% based on the total amount of fiber-forming polymer (cellulose + lignin) into a standard viscose. When spinning, the lignin was in the form of a solution with 30% lignin in 5% NaOH.

The viscose containing lignin was spun out according to standard conditions. The target titer of the fibers was 3.3 dtex, the stretching was 25%.

The fibers obtained were washed out in the usual way.

The lignin levels in the finished fiber were initially determined via the Klason method (Tappi Test Methods 2001-2002. T 222 om-02. Tappi Press ) measured. The acid-insoluble lignin ("Klason lignin") is recorded gravimetrically using this method. In addition, the acid-soluble lignin is determined photometrically (Tappi UM 250, wavelength: 205 nm, absorption coefficient: 110 L / (g.cm)). Photometric determination on the basis of these parameters is the method customary in the professional world, even if it is known that the results obtained with it can vary slightly with regard to the different types of lignin. For the purposes of the present invention, it is therefore defined that the determination of the content of acid-soluble lignin has to be carried out using these parameters. The following values each represent the total lignin content determined in this way: Kraft lignin Lignosulfonate Organosolv lignin Lignin content (nominal) in% 50 50 50 Lignin content found in% 27 11 38 Washout absolute in% 23 39 12th Washout in% 45 77 23 Water retention capacity in% * 203% 182% 130% * Determined according to DIN 53814

Due to its very good solubility, the lignosulfonate is already largely washed out during the spinning of the fiber and in the subsequent washing. Only 11% lignin (absolute) was found in the fiber, so 77% of the lignin offered was washed out. Organosolv lignin shows the highest retention. The fiber contains 38% lignin, while 23% of the lignin offered was washed out. Medium retention shows the Kraft lignin with an absolute content of 27% lignin in the fiber, while 45% (relative) was washed out.

Example 2:

An uncrosslinked organosolv lignin of the type lignin 139OL (manufacturer: Fraunhofer Institute CBP) was admixed with a viscose in a proportion of 10% based on the total amount of fiber-forming polymer (cellulose + lignin) and the resulting solution was spun into fibers .

A total of 7.7% lignin was found in the finished fiber using the method described above.

The fiber had a titer of 3.24 dtex. The maximum tensile force in cN was 6.71, the elongation 18.79%.

Example 3:

An uncrosslinked organosolv lignin of the type Lignin 151OL (manufacturer: Fraunhofer Institute CBP) was admixed with a viscose in a proportion of 10% based on the total amount of fiber-forming polymer (cellulose + lignin) and the resulting solution was spun into fibers .

A total of 7.3% lignin was found in the finished fiber using the method described above.

The fiber had a titer of 3.66 dtex. The maximum tensile force in cN was 5.72, the elongation 17.95%.

Example 4:

Analogously to Example 1, a mixture of 35% uncrosslinked organ solv lignin of type Charge K002 (manufacturer: Fraunhofer Institute CBP) and 15% of the lignosulfonate used in Example 1, based in each case on the total amount of fiber-forming polymer (cellulose + lignin), mixed with a viscose and the resulting solution spun into fibers.

The mixture showed very good spinning stability.

A total of 35.4% lignin was found in the finished fiber using the method described above. The leaching out of lignin was therefore only about 15% (absolute).

The fiber had a titer of 2.72 dtex. The maximum tensile force in cN was 2.78, the elongation 17.12%. The water retention capacity was 123%.

Properties of the fibers containing Organosolv lignin

The fibers are characterized by a dark brown color.

The fibers produced according to Example 1 with (nominal) 50% addition of lignin show a very smooth surface with mainly C-shaped cross sections. These cross sections are in the Figure 1 shown.

In contrast, the typical viscose cloud shape can be found in the case of those produced according to Example 2 (nominal incorporation of 10% organosolv lignin), see Figure 2 .

The fibers produced according to Example 3 with a nominal incorporation of 35% organosolv lignin and 15% lignosulfonate also show the typical viscose cloud shape, see Figure 3 .

All of the lignin-containing fibers show a significantly higher absorption (higher water retention capacity) than a normal viscose fiber, which is why they are ideal for use in hygiene products.

The (among other things) lignosulfonate-containing fiber according to Example 4 contains sulfonic acid groups which act as ion exchangers.

Carbonization attempts

The viscose fibers produced according to Examples 1, 2 and 4 and containing Organosolv lignin or a mixture of Organosolv lignin and lignosulfonate were carbonized (Gero oven, 20 ° C to 1800 ° C, heating rate 10K / min under a nitrogen atmosphere). The carbon yield was compared to that of a standard viscose fiber.

The results are shown in the following table: reference 10% organosolv lignin 50% organosolv lignin 35% organosolv lignin + 15% lignosulfonate Carbon yield in% 15.8-16.7 17.8 30.17 31.02

By storing 10% (real 7.8%) organosolv lignin in viscose, the carbon yield can already be increased by about 2%. In purely arithmetical terms, the lignin has a real carbon yield of 40%.

The 50% organosolv lignin fiber and the mixed viscose fiber made of 35% organosolv lignin and 15% lignosulfonate both show around 30% carbon yields. Compared to normal viscose, the carbon yield can be increased significantly (by 80%) by storing larger amounts of lignin. In this case, the calculated yield for pure lignin is just under 60%. This means that for the manufacturer of Carbon fiber large savings in the amount of fibers are possible with the same carbon yield.

Claims (10)

1. A regenerated cellulose fibre produced by the viscose process, comprising organosolv lignin in a content of 10% to 70%, based on the fibre.
2. A cellulose fibre according to claim 1, characterized in that the content of organosolv lignin ranges from 20% to 50%, based on the fibre.
3. A cellulose fibre according to claim 1 or 2, characterized in that the fibre contains a further lignin different from organosolv lignin.
4. A cellulose fibre according to claim 3, characterized in that the further lignin is selected from the group consisting of kraft lignin, lignosulfonate and mixtures thereof.
5. A cellulose fibre according to claim 3 or 4, characterized in that the content of the further lignin ranges from 5% to 85%, preferably from 10% to 70%, particularly preferably from 20% to 50%, based on the fibre.
6. A cellulose fibre according to any of claims 3 to 5, characterized in that the ratio of organosolv lignin to the further lignin ranges from 4:1 to 1:4, preferably from 3:1 to 1:3.
7. A cellulose fibre according to any of the preceding claims, characterized in that, apart from cellulose and lignin, it contains essentially no further fibre-forming polymer.
8. A cellulose fibre according to any of the preceding claims, characterized by a titre of from 0.5 dtex to 30 dtex, preferably from 1 dtex to 4 dtex.
9. The use of a cellulose fibre according to any of the preceding claims for the production of carbon fibres.
10. A method of producing a cellulose fibre according to any of claims 1 to 8, comprising the step of adding organosolv lignin and optionally a further lignin to a spinning viscose or a precursor thereof.

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