EP1224343B1 - Method for producing cellulose shaped-bodies - Google Patents

Abstract

Process for manufacture of cellulose mouldings, such as fibres, filaments, or films, from TCF-bleached or ECF-bleached cellulose, in which the bleached cellulose is dissolved in an aqueous tertiary aminoxide to form a mouldable cellulose, the cellulose solution deforms, and the moulding comes into being by coagulation of the deformed solution, characterized in that, to reduce the cellulose decomposition in the process, TCF-bleached cellulose is used comprising carboxyl group content in the range from 1 to 35 mumol/g or an ECF-bleached cellulose with carboxyl group content in the range from 1 to 50 mumol/g. Cellulose mouldings having a reduced cellulose decomposition may be formed by said process.

Description

The invention relates to a process for the production of shaped cellulose articles, such as fibers, filaments or films, from TCF or ECF bleached pulp, which comprises dissolving the bleached pulp in an aqueous tertiary amine oxide to form a moldable cellulose solution, the cellulose solution deformed and by Coagulation of the deformed solution forms the molding. The invention further relates to the use of a TCF- or ECF-bleached pulp for the production of cellulose moldings.

The problems of the viscose process have led to the development of new processes for producing regenerated cellulose moldings in which the cellulose is solubilized without chemical modification. The fibers and filaments obtained from these solutions are summarized under the name "lyocell". Particularly suitable organic solvents are tertiary amine oxides, in particular N-methylmorpholine N-oxide (NMMO). A process for forming a cellulose solution in aqueous NMMO is known from DE-A 44 41 468. The preparation of cellulosic molded articles from these solutions is described in EP-A 0 574 870.

In this solution, the dissolved cellulose and the solvent under the thermal conditions undergoes chemical degradation, which leads to discoloration of the spinning solution. Despite intensive washing out of the cellulosic shaped bodies formed, coloring remains Substances in the molding, whereby its whiteness is impaired. To reduce the said degradation, therefore, a stabilizer is added to the spinning solution. Suitable stabilizers are known from EP-A 0 047 929 and DD 218 104.

It is known from WO 97/23666 that the use of TCF-bleached pulp in the Lyocell process leads to moldings with a higher degree of whiteness than the use of an ECF-bleached pulp. Both pulps are provided with similarly high output whiteness by 90% and high purities, particularly with respect to lignin content. It therefore appeared questionable whether the TCF pulp generally gives better whiteness of the cellulosic shaped bodies produced from this pulp than does an ECF pulp.

The object of the present invention is to provide a process for the production of cellulosic moldings with reduced cellulose degradation starting from TCF- or ECF-bleached pulp. The reduction of cellulose degradation should be achieved without any special measures in Lyocellverfahren substantially. Further advantages of the invention will become apparent from the following description.

Pulp and fiber whitenesses of various pulp samples were determined which were either ECF or TCF bleached. The determination of the whiteness of the pulp was carried out according to DIN 53145, part 2. The determination of the whiteness of the fiber was carried out according to the method described in WO 97/23666, page 6. The average degree of polymerization of the pulps by the cuoxam method was about 550. The whitenesses measured on the pulp and on the fiber are summarized in Table 1. Table 1 Whiteness / pulp source production method Initial grade of pulp Whiteness of the braided fiber Cellunier F Fa. Rayonier USA ECF (ElementaryChiller-Free) 89.9 55.0 Temfilm Example 1 Fa. Tembec Canada TCF (TotalChlorFree) 87.5 55.3 ALICELL Fa. Western Pulp USA ECF 88.2 58.6 MoDo Fa. MoDo Paper TCF 93.7 58.4 Temfilm Fa. Tembec Canada TCF 89.2 58.6

It can be seen from Table 1 that for ECF or TCF bleached pulps of various origins, the whiteness is in a narrow range between 87.5 and 93.7. The degrees of whiteness of the spun fibers are also close to each other between 55.0 and 58.6. A higher whiteness of fiber spun from TCF bleached pulp was not apparent.

Our investigations have now shown that cellulose degradation during the Lyocell process, i. essentially depends on the formation to the coagulation of the spinning solution, on the carboxyl group content of the used to form the spinning solution, bleached pulp. It has been shown that the lower the carboxyl group content of the pulp used for the solution formation, the lower the cellulose degradation of the spun fiber. Cellulose fibers with reduced cellulose degradation can therefore be produced by the lyocell process by using a TCF- or ECF-bleached pulp with a low carboxyl group content to form the spinning solution.

The above object is therefore achieved in the method mentioned in the present invention that one to reduce of cellulose degradation in the process employs a TCF bleached pulp having a carboxyl group content in the range of 1 to 35 μmol / g or an ECF bleached pulp having a carboxyl group content in the range of 1 to 50 μmol / g. It has been found that the lower the carboxyl group content of the pulp used, the less is the cellulose degradation in the course of the production and processing of the extrusion solution. In order to achieve a low degradation of the cellulose and the amine oxide in the lyocell process, TCF- and ECF-bleached pulps whose carboxyl group content lies in the stated ranges are used in the spinning solution production. Pulps with the stated carboxyl group contents can be produced by different pulp manufacturers. As a result of the reduced degradation of the dope components, fewer coloring constituents are also formed, so that, secondarily, the whiteness of the shaped bodies formed is also improved.

Preferably, in the dissolution step, a TCF-bleached pulp having a carboxyl group content in the range of 15 to 30 μmol / g or an ECF-bleached pulp having an arboxyl group content in the range of 25 to 35 μmol / g is used. The determination of the carboxyl group content of the cellulose to be used can be carried out according to Döring, verg1. K. Goetze, man-made fibers by the viscose process, 2nd volume 3rd ed., 1997, p. 1079.

The tertiary amine oxide solvent used in the preferred process of the invention is N-methylmorpholine N-oxide monohydrate (NMMO-MH).

In a further embodiment of the invention, one can form a cellulose solution with a content of alkalis or organic compounds, the latter containing at least four carbon atoms, at least two conjugated double bonds and at least two substituents -XH, where X is 0 or NR and R may be hydrogen or an alkyl group of 1 to 4 carbon atoms. By means of these solution additives, the low degradation achieved according to the invention can be further reduced. The amount of the organic compound may be in the range of 0.01 to 0.5 mass% based on the amount of the solvent. Suitable organic compounds are known from EP-A-0 047 929. A commonly used compound is isopropyl gallate.

By the method according to the invention, the cellulose degradation is limited to a proportion in the range of 3 to 20% by mass, based on the pulp used. Preferably, the degraded cellulose content is in the range of 8 to 15 mass%.

The invention further relates to the use of a TCF-bleached pulp or an ECF-bleached pulp having a carboxyl group content in the range of 1 to 35 .mu.mol / g and 1 to 50 .mu.mol / g to form a cellulose solution in a tertiary amine oxide-containing solvent for the Production of Moldings by the Lyocell Process. The use of these pulps not only reduces the degradation in the course of the lyocell process, but also increases the whiteness of the shaped bodies formed.

The invention will now be explained in more detail by the following examples.

Examples 1 to 6

Long fiber sulfite pulp was bleached by alkaline peroxide-enhanced oxygen extraction, then ozone and peroxide in a known manner. The bleaching methods are described, for example, in RP Singh, The Bleaching of Pulp, TAPPI Press, Atlanta, USA. In this case, three different carboxyl group contents were set (Examples 1 to 3). Three more samples of the pulp were bleached with hypochlorite. On the pulps, the degree of polymerization and the initial degree of whiteness were determined by the methods given above, including the carboxyl and carbonyl group content of the pulp. From the bleached pulps spinning solutions with 13% cellulose, 10.5% water and 76.5% NMMO were prepared in a known manner. The solutions were spun at 95 ° C. by a dry-wet method with a nozzle of 65 μm hole diameter. On the obtained fibers, the degree of polymerization and the degree of whiteness were determined. The degree of polymerization was determined by the cuoxam method, the degree of fiber whiteness by the method given above. The determined numerical values are given in Table 2. Table 2 example 1 2 3 4 5 6 bleaching TCF TCF TCF ECF ECF ECF Carboxyl group content μmol / g 20.2 24.9 34.8 31.1 35.5 41.2 Carbonyl group content *) μmol / g 52.1 48.2 35.6 26.1 24.5 82.2 DP pulp 540 5.17 560 555 566 550 DP fiber 519 505 470 485 465 440 DP reduction% 3.9 7.7 18.1 12.6 16.8 20.0 Output whiteness grade 93.2 93.5 93.7 93.4 93.1 93.0 Whiteness fiber 68.9 65.4 58.4 62.8 58.5 58.7 *) For determination see K. Götze, aa0.

It can be seen from Table 2 that as the carboxyl group content of the TCF-bleached pulp and the ECF-bleached pulp increase, a significant drop in the degree of polymerization and whiteness of the fiber-cellulose is observed. For a given bleached pulp, the adjustment of its carboxyl group content thus opens up the possibility of the degree of polymerization to improve the textile-physical properties of the spun fiber. Due to the reduced color body formation during the process, a slower discoloration of the spinning bath occurs, resulting in cost advantages in the solvent regeneration.

Examples 7 to 10

On four bleached dissolving pulps, the degree of polymerization, the carboxyl group content and the carbonyl group content and the starting whiteness were determined. From the pulps four spinning solutions were prepared with 13% cellulose, 10.5% water and 76.5% NMMO. The zero shear viscosity at 85 ° C. was measured on the spinning masses (Haake RS 75, year of construction 1998). The spinning solutions were spun at 95 ° C with a nozzle of 65 microns hole diameter by the usual dry-wet method. The degree of polymerization of the cellulose was determined on the spinning solution, and also on the fibers the whiteness. The results are summarized in Table 3. Table 3 example 7 8th 9 10 Provenance / parameters Tembec Temfilm MoDo Paper Tembec TemSpr Rayonler Cellunier bleaching TCF TCF ECF ECF Zero shear viscosity η _{Obel 85 ° C} [Pas] 6967 4855 4730 4720 DP _pulp 538 510 520 510 DP _{spinning solution} 490 455 452 450 DP _degradation [%] 9.9 10.8 13.1 11.7 Carboxyl group content [μmol / g] 20.9 24.4 36.8 28.8 Carbonyl group content [μmol / g] 51.3 48.2 24.6 24.3 Output whiteness 90.5 92.1 91.1 92.1 Fiber whiteness 62.3 61.2 55.3 58.0 Provenance / parameters Tembec Temfilm MoDo Paper Tembec TemSpr Rayonter Cellunier bleaching TCF TCF ECF ECF Zero-shear viscosity η _{Obel 85 ° C} [Pas] 6967 4855 4730 4720 DP _pulp 538 510 520 510 DP _{spinning solution} 490 455 452 450 DP _degradation [%] 9.9 10.8 13.1 11.7 Carboxyl group content [μmol / g] 20.9 24.4 36.8 28.8 Carbonyl group content [μmol / g] 51.3 48.2 24.6 24.3 Ausgaugsweißgrad 90.5 92.1 91.1 92.1 Fiber whiteness 62.3 61.2 55.3 58.0

It can also be seen from the numerical values in Table 3 that as the carboxyl group content of the selected pulp increases, cellulose degradation increases and the degree of fiber whitening deteriorates relative to the starting whiteness.

Claims (8)

1. Method for the production of cellulose-mouldings such as fibers, filaments or films from TCF-bleached or ECF-bleached cellulose, in which the bleached cellulose is dissolved in an aqueous tertiary aminoxide to form a mouldable cellulose solution, the cellulose solution is deformed, and the moulding comes into being by coagulation of the deformed solution, characterized in that, to reduce the cellulose decomposition in the process, TCF-bleached cellulose comprising carboxl group content in the range from 1 to 35 µmol / g or an ECF-bleached cellulose with carboxyl group content in the range from I to 50 µmol / g is used.
2. Process according to claim 1, characterized by the use of TCF-bleached cellulose comprising a carboxyl group content in the range from 15 to 30 µmol / g.
3. Process according to claim 1, characterized by the use of an ECF-bleached cellulose comprising a carboxyl group content in the range from 25 to 35 µmol / g.
4. Process according to any of claims one to three characterized by the use of N-methylmorpholin-N-oxide as tertiary aminoxide.
5. Process according to any of claims 1 to 4, characterized by forming a cellulose solution with a contemt of alkaline or organic compounds, wherein the latter contain at least four carbon atoms, at least two conjugated double bonds, and at least two substitutents -X-H, wherein X designates O or NR, and R designates hydrogen or an alkyl group with I to 4 carbon atoms.
6. Process according to any of claims 1 to 5, characterized in that the decomposition of the cellulose is restricted to a fraction in the range from 3 to 20 % by weight, related to the cellulose pulp used.
7. Use of a TCF-bleached cellulose having a carboxyl group content in the range from 1 to 35 µmol / g for forming a cellulose solution in solvent containing a tertiary aminoxide for the manufacture of mouldings according to the Lyocell-process.
8. Use of a ECF-bleached cellulose having a carboxyl group content in the range of 1 to 50 µmol / g for forming a cellulose solution in a solvent containing a teriary aminoxide for the manufacture of mouldings according to the Lyocell-process.