Patent Application
Method for producing cellulosic moulded bodies using bamboo pulp and moulded bodies from this method
Since 1939 (US 2, 179,181) it is known that pulp can be dissolved with the aid of tertiary aminoxides and without chemical conversion. The cited publication further describes how through precipitation of said pulp solutions cellulosic moulded bodies like fibres can be produced. During the 1980s and 1990s companies like Courtaulds and Lenzing were actively involved in implementing this principle on an industrial scale for the commercial production of pulp fibres. In the late eighties fibres by the name of Lyocell (brand name Tencel®) were introduced in the market. Said fibres are used for producing woven and knitted textiles for the garment industry, for industrial textiles and non-woven fabrics. The method for producing Lyocell fibres is commonly known as aminoxide-method.
The state-of-the-art technology today is the use of a thin-layer vaporizer for the continuous production of spinnable pulp solutions as described in EP 0356419 B1 (Filmtruder).
In order to ensure that the method is environmentally friendly and economically viable the aminoxide has to be recovered from the spinning bath in order to reuse it for preparing the solution. A simple and effective measure for ensuring the stability of the spinning mass and as such the safety of this method has been described in EP 0695324 B1.
The inherent decomposition tendency of the spinning mass is immensely intensified by the dead spaces in the plant, in which the spinning mass practically remains motionless over long periods of time. EP 0781356 B1 describes how components of plants, where dead spaces can not be avoided, have to be designed, for instance spinning mass filters.
For the production of Lyocell fibres a dry/wet-spinning method is employed. EP 0584318 B1 describes how excellent spinning characteristics can be achieved even with large sized nozzles.
The textile chain requires fibres to run on modern high capacity textile machines. Crimping plays a decisive role for the processability of the fibres. EP 0797696 B1 describes a suitable process.
To date approximately 1200 different types of bamboo are known, out of which about 35 are used as raw material for the pulp and paper industry. Some of these types are growing in tropical as well as temperate climates. While some of the shoots have a length of only a' few cm other plants grow in 3-4 years to a height of 30 m.
Depending on the variety, bamboo fibres resemble either more a short or a long fibre. Bamboo has a number of properties which are of great commercial value for the paper and pulp industry.
At present approx. 1, 5 million tonnes of bamboo pulp are produced worldwide. Asia has relatively small forest areas which could be used as resource for pulp production. For this reason countries in Asia at present are trying to make better use of the widely available bamboo.
Besides for the production of paper pulp, bamboo is used in Asia, in particular in India, as raw material for producing viscose pulp. In China too a number of companies and institutes are engaged in exploiting the possible use of bamboo pulp for the fibre production by using the conventional viscose method.
New is, that viscose fibres made of bamboo pulp are being marketed as "bamboo fibres". Of late consumers are even offered textiles made of such so-called "bamboo fibres". However this name given by BISFA is not correct, since these fibres are actually viscose fibres. As such, these fibres are to be differentiated from natural bamboo fibres or the bamboo fibres in pulp.
WO 2005/068697 A1 describes terry-cloth products made of these so-called bamboo fibres. However, there is no description about the method, by which these fibres are produced. It contains only a very short reference about the fact that they are actually regenerated pulp fibres. For that reason it can be assumed that bamboo pulp was used as raw material.
EP 1679394 A1 describes yarns and fabrics made of these yarns being also produced from bamboo pulp. The fibres are being spun using the viscose- or cupro-method. However said publication describes neither the preparation of the spinning solution nor the spinning method in detail.
The types of bamboo pulp available in the market are mainly paper pulps. They are characterised by a low content of fibre forming alpha-pulp, which exhibits a very high average degree of polymerization. Said pulps are therefore highly viscous.
For the production of viscous fibres especially treated bamboo pulps with a higher content of alpha-pulp are produced, i.e. chemical pulps with a viscosity, which has been adjusted accordingly. In the market there are at least 2 manufacturers offering commercial viscous fibres made of bamboo. The use of bamboo pulp for producing viscous fibres has been described for instance in CN 1194119C.
Manufacturing of Lyocell fibres made of bamboo pulp has also been described in patent publications.
For instance JP 2005-126871 A describes the production of Lyocell fibres made of bamboo pulp with an alpha-pulp content of 93 % and higher, having anti-bacterial properties. It deals with the problem how to separate hemi-pulp and other organic compounds from the spinning mass. This problem has been solved by a boiling process for pulp, which has been designed accordingly.
CN 1383965 A describes production of bamboo pulp suitable for the Lyocell-method. As final steps of the pulp production an acid wash followed by a wash in an aqueous 0.1 % solution of a chelating agent are mentioned.
CN 1190531C describes a spinning method for producing Lyocell fibres made of bamboo pulp, which supposedly permits the use of pulps over a wide range of polymerization degrees.
CN 1544223 A describes a method for producing Lyocell fibres made of bamboo, including an alternative method for producing pulp as well as the subsequent use of the pulp produced in this manner for spinning. For purification of the pulp this method requires only very few steps. However, Lyocell fibres produced by this method exhibit an unusually low stability.
CN 1760412 A uses bamboo- paper pulp as raw material. The problem of a high degree of polymerization has been dealt with by using decomposition pre-treatment for commercially available paper pulp, which is replacing the usual second boiling of the pulp and which is more economical. The higher fractions of insoluble impurities contained in paper pulps will be separated from the spinning mass by a subsequent two-stage filtration. Hydrolysis in water at a temperature of 120-200° C, acid separation with sulphuric or hydrochloric acid at increased temperatures over a number of hours as well as enzymatic decomposition are mentioned as decomposition pre-treatments
CN 18511115 A recommends as decomposition pre-treatment for paper pulp made of bamboo an energy intensive radiation in order to achieve a degree of polymerization which is suitable for the Lyocell-method.
The method for producing bamboo pulp from Lyocell spinning mass described in said publications basically does not differ from the one for viscose. These publications do not mention anything in regard to the stability of the produced spinning masses. However, if the same bamboo pulp which is being used for producing viscose is used for producing Lyocell spinning masses it is observed that the spinning mass is not very stable. Investigation results in regard to the stabilisation of the spinning mass have been described in detail by Buijtenhuis et.al in Paper 40 (1986), page 615-619.
A stronger decomposition of the pulp chains and subsequently a spontaneous degradation of the viscosity were the least things observed. The loss of viscosity leads to problems with the spinning stability on the spinning machine and instable or bad properties of the Lyocell fibres.
Impurities in the pulp in form of heavy metals can lead to thermal instability of the spinning mass to such an extent that a spontaneous exothermic reaction (exothermy or deflagration) occurs. EP 0781356 B1 describes a method for determining the decomposition tendency of the spinning mass, the so-called "Thermal stability test".
Furthermore, while using bamboo pulps for producing Lyocell spinning materials contaminations of the pulp in form of insoluble particles were detected, which depending on their size, caused substantial problems during filtration of the spinning mass or on the spinning machine. Besides, there is always the possibility that these particles can be ascribed to external contaminations of the raw material containing silicon, like sand or mud. One auf the consequences of a high particle load is a slow down of the production due to a bottleneck in the filtration of the spinning mass or worse, total filter blockage. Besides, if the spinning mass is heavily loaded with extremely fine particles, which can not be filtered, the spinning safety will be jeopardized.
The objective of the present invention is therefore the safe processing of pulp made of renewable raw material bamboo i.e. without exothermal degradation of the spinning mass and with a high spinning safety for producing high quality Lyocell products.
This objective is attained by a method for producing cellulosic products using the aminoxide-method for a cellulosic raw material with a bamboo pulp content between 30 % and 100 % and an iron content of 10 ppm max.
The cellulosic raw material containing bamboo pulp can be natural bamboo pulp or a mixture of bamboo pulp and conventional pulp from any other type of plant for instance deciduous trees or conifers.
In case the cellulosic raw material containing bamboo pulp is produced from a combination of various types of pulps the same can be mixed before the aqueous aminoxide solution is added, for instance by feeding bale shaped pulp into a pulp mill or by compacting the combined pulps in an aqueous medium or the two pulps are shredded, aqueous aminoxide solution is added and then mixed.
The cellulosic raw material containing bamboo pulp should preferably have a copper content of 2.5 ppm max.
The cellulosic raw material containing bamboo pulp should preferably have a manganese content of 2.5 ppm max.
The cellulosic raw material containing bamboo pulp should have a Si02 content of 100 ppm max,.preferably 50 ppm max.
One embodiment of the invention is in that the cellulosic raw material containing bamboo pulp is cleaned of heavy metals accordingly. The.required process steps should be carried out preferably at the place of the pulp manufacturer during boiling, bleaching or after the bleaching, wherein the cellulosic raw material containing bamboo pulp undergoes an acid wash after the bleaching und before it is being dissolved in aqueous aminoxide.
As alternative to the acid wash cellulosic raw material containing bamboo pulp is washed after bleaching and before being dissolved in aqueous aminoxide preferably in an aqueous solution of a chelating substance of low concentration. The concentration of the chelating agent in the aqueous solution should be lower than 0.07 % by weight, preferably lower than 0.05 % by weight. Nevertheless, the concentration of the chelating agent should not drop below 0.001 % by weight, in order to be able to achieve a satisfactory result. A preliminary alkaline wash is not required. The most commonly used chelating agent is EDTA.
Reduction of the particle content during the pulp production can be achieved by washing and sorting of the bamboo blades, pre-sorting of the raw pulp as well as post-sorting of the bleached pulp.
It is important to wash the bamboo blades thoroughly before their further processing in order to remove earth and other contaminations.
Pre-sorting of the untreated pulp helps in particular to separate non-productive plant parts like branches, chips and pieces of bark, so-called rejects, from the fibre suspension
(Good matter). Experience has shown that along with the rejects also large parts of the inorganic particles can be separated. The more efficient the pre-sorting process the lesser particles will have to pass through the numerous processing steps right up to the post-sorting, wherein they can be shredded and broken up. The pre-sorting principle is employed in order to separate particles on the basis of size, shape and deformability from the fibre suspension by means of strainers. Said strainers can be flat or cylindrical (screen basket), the suspension can be filtered at static or increased pressure. For rough sorting, screening sheets with 4-25 mm large holes are used. For fine sorting 0.8-2.4 mm round holes are used or preferably 0.2-0.8 mm large slots. In case of pressure strainers the density of the material should not exceed 4%.
Because of the difference in the material density the rest of the particles are separated selectively according to this invention with the aid of hydrocyclones, for example with so-called centricleaners from the pulp fibres during the post-sorting phase, which takes place after the bleaching and before dissolving the pulp in aqueous aminoxide. Since the separation of extremely small particles requires a considerable effort, an effective pre¬sorting is of great importance. In the case of the present invention it was established that it was of great advantage to work in the hydrocyclone with material densities between 0.1 % and 1.0 %. This separation can be carried out in combination with the acid wash or without acid wash.
The process parameters for the separation by hydrocyclone are set in such a manner that the silicates are being separated from the bamboo pulp. The professional is familiar with this process and knows the details.
In another embodiment of the present invention the bamboo pulp is mixed either in untreated condition or after having been treated by one of the above washing processes with such an amount of conventional, chemical pulp that the pulp mixture has a Fe content of 10 ppm max, the manganese and copper content lie by 2.5 ppm each and the Si02 content by 100 ppm max, preferably 50 ppm.
The present invention relates further to a cellulosic product being produced according to the process described herein.
This celluosic product is preferably a staple fibre or an endless filament with the generic name Lyocell. But other products which are produced by using the aminoxide-method like foils, pipes, sponges, pulp pearls or products obtained by breaking up the same, like wet and dry milling or cutting can also be produced by the method according to the invention.
Such a cellulosic product, produced according to the aminoxide-method, is characterised by an iron content of 10 ppm max.
The cellulosic product obtained according to the method of the present invention exhibits a copper content of 2.5 ppm max.
The cellulosic product obtained according to the method of the present invention exhibits a manganese content of 2.5 ppm max.
The cellulosic product obtained according to the method of the present invention exhibits a Si02 content 100 ppm, preferably of 50 ppm max.
The cellusosic product of the present invention is preferably a staple fibre, endless filament or foil with the generic name Lyocell.
By means of the following examples the invention will be explained in detail. These examples but do not limit the scope of the invention.
Example 1 - Acid wash
Each of the bamboo pulp samples available to us was characterized by high heavy metal contents. The heavy metal content and Si
content were determined using ICP-trace element determination according to EN ISO 11885 (Table 1)
Table 1

(Table Removed)
The pulp sample Zst 3 was subjected to an acid wash in the laboratory under the following conditions: 100 g of the said pulp was compacted in a plastic vessel to a density of 3 % and stirred for a period of 60 min at a temperature of 70 ° C and a pH-value = 2, which was adjusted by adding sulphuric acid. Subsequently the pulp was drained on a glass frit und neutralised in deionised water. Finally the pulp was air dried. This sample will be referred to as Zst 3a.
Example 2 - Washing with EDTA
The pulp sample Zst 3 was washed in the chelating agent EDTA in the laboratory under the following conditions: 110 g of said pulp was suspended in a plastic vessel to a density of 3 %. The ph-value was adjusted with sulphuric acid to 5.5 and 0.55 g of EDTA was added in order to obtain a concentration of 0.017 % by weight. This suspension was stirred for a period of 60 min and at a temperature of 70°. Thereafter pulp was drained on a glass frit und washed in deionised water. Finally the pulp was air dried. This sample will be referred to as Zst 3q.
Both treatments resulted in a substantial reduction of the heavy metal content (see Table 2).
Table 2
(Table Removed)
From the pulps kneaded spinning masses were prepared in the laboratory to be used for conducting a thermal stability test as described in EP 0781356. As compared to standard Lyocell pulp the untreated pulp exhibited a significantly higher degree of decomposition. Both, acid wash as well as EDTA treatment, helped considerably in improving the decomposition tendency. This can be seen clearly in figure 1 showing the thermal stability of bamboo pulps after various treatments. Herein the temperature difference (in [°C]) between sample & jacket was measured in relation to the temperature of the jacket, (in
PC])-
Likewise figure 2 shows clearly how bamboo pulp treatments affect the degree of polymerization and as such the viscosity. The relative decomposition of the viscosity was measured by the method specified in EP 0 670 917. Figure 2 shows the measurement of the complex viscosity (in % of the initial value) in relation to time (in min). All bamboo pulps treated according to the present invention exhibited a significantly lower decomposition than the untreated ones.
The combination of acid wash and subsequent EDTA-treatment proved to be especially effective.
In addition, spinning masses with a pulp content of 13% were prepared from pulp samples
Zst 3, Zst 3a and Zst 3q and thereafter spun on a laboratory spinning machine (Davenport)
into fibres with a yarn count of 1.3 dtex. With a spinning temperature of 115 ° C and
blowing with an air moisture of 30 g/Kg at 35 ° C the following physical textile data were
obtained (Table 3: FFk: fineness-related fibre strength, conditioned; FDk: tensile strength,
conditioned.)
Lenzing AG, PL 0437
Table 3
(Table Removed)
Example 3 - Post-sorting test
The test for reduction of silicate impurities in pulp sample Zst 3 was carried out on a pilot plant comprising of the following components: Centrifugal cleaner for high gravity solids (hydrocyclone) from Fa. NOSS, Type Radiclone AM80-C; feed bin with paddle stirrers and centrifugal pump, one control valve each for the accept portion and reject portion and two collecting vessels. As first step 3 000 g of pulp sample Zst3 were compacted in the feed bin to a density of 0.6 %. Then this pulp suspension was transported at the rate of 100 l/min to the cleaner and back to the feed bin. The reject rate was set to 10%. With this setting the entire pulp suspension was run over the cleaner and accepted portion and rejected portion were collected in the two vessels. Subsequently the accepted portion was dried in a through-circulation dryer at 60 °C. In this manner it was possible to reduce the Si02 content of the pulp from 699 ppm to 47 ppm.
Example 4 - Mixture of chemical pulp and bamboo pulp
Three spinning masses containing 13% pulp were prepared in the laboratory kneading machine. For the first spinning mass 100% of conventional standard chemical Lyocell pulp "Zst6" was employed, for the second spinning mass 100% of a bamboo-chemical pulp "Zst4" and for the third spinning mass a mix of 70% standard chemical pulp Zst6 and 30 % of bamboo pulp Zst 4. The corresponding metal contents are given in table 4.
Table 4

(Table Removed)
Lenzing AG, PL 0437
The Fe and Si02 values of the bamboo pulp Zst 4 are outside the required range, while the values for the pulp mix are within the specified range.
These three spinning masses were tested according to the above mentioned methods for exothermal decomposition reactions by means of a Sikarex and for loss of viscosity by means of a rheometer. While sample Zst 4 displayed a slight increase in the decomposition tendency, the mix exhibited practically the same standard as sample Zst 6 (Fig. 3) The viscosity loss of bamboo pulp sample Zst 4 lies already in an unacceptable range while the mix exhibits almost the same standard as chemical pulp (Fig.4)
Furthermore Lyocell fibres were produced on a laboratory scale. The physical textile data of the mix containing 30 % bamboo pulp showed no serious deviation from the data of the chemical pulp sample Zst 6. Thus it can be concluded, that the pulp mix is certainly suitable for producing high quality Lyocell fibres which can be further processed by the textile sector.
Table 5
(Table Removed)

Claims
1. Method for producing cellulosic moulded bodies by employing the aminoxide-method from am cellulosic material containing bamboo pulp, with a bamboo pulp content between 30 % and 100 % , wherein the cellulosic material containing bamboo pulp has a Fe content of 10 ppm max.
2. Method according to claim 1 wherein the cellulosic raw material containing bamboo pulp is characterised by a copper content of 2.5 ppm. max.
3. Method according to claim 1 wherein the cellulosic raw material containing bamboo pulp is characterised by a manganese content of 2.5 ppm max.
4. Method according to claim 1 wherein the cellulosic raw material containing bamboo pulp is characterised by a Si02 content of 100 ppm, preferably 50 ppm.
5. Method according to claim 1 wherein the cellulosic raw material containing bamboo pulp undergoes an acid wash after bleaching and before dissolution in aqueous aminoxide.
6. Method according to claim 1 wherein the cellulosic raw material containing bamboo pulp is being washed after bleaching and before being dissolved in an aqueous solution of a chelating agent.
7. Method according to claim wherein the cellulosic raw material containing bamboo pulp is conducted through a hydrocyclone after the bleaching process and before being dissolved in aqueous aminoxide in form of a diluted slurry with a density of 0.1 to 1.0%.
8. Method according to claim 5 wherein silicates are separated in the hydrocyclone from the cellulosic raw material containing bamboo pulp.
9. Cellulosic product characterised in that it is being produced using the method according to claim 1.
10. Cellulosic product according to claim 9 characterised in that it is a staple fibre, endless filament or a foil of the Lyocell group.
11. Celluosic product according to claim 9 characterised in that it exhibits an iron content of 10 ppm .max.
12. Celluosic product according to claim 9 characterised in that it exhibits a copper content of 2.5 ppm max.
13. Celluosic product according to claim 9 characterised in that it exhibits a manganese content of 2.5 ppm max.
14. Celluosic product according to claim 9 characterised in that it exhibits a Si02 content of 100 ppm max, preferably 50 ppm max.