Patent Application
Method for producing cellulosic moulded bodies by using bamboo-paper pulp and
moulded bodies from this method.
The invention relates to a method for producing cellulosic moulded bodies by the aminoxide-method by using bamboo-paper pulp. Further, it also relates to a composition containing pulp for being used in this method as well as a cellulosic product manufactured according to this method.
Since 1938 (US 2,179,181) it is known that pulp can be dissolved without chemical conversion with the help of tertiary aminoxides. In the patent cited, it is also described that one can manufacture cellulosic moulded bodies, such as fibers, by precipitating these pulp solutions. In the 80s and the 90s of the twentieth century, the companies Courtaulds and Lenzing worked intensively on implementing this principle on an industrial scale, in order to produce pulp fibers commercially. Since the late 80s there are fibers with the generic name Lyocell (brand name Tencel®) in the market. These fibers are used for the production of woven and knitted textiles for clothing, industrial textiles and non-woven textiles. The method for manufacturing the Lyocell fibers is commonly known as the Lyocell-method.
The state-of-the-art technology today is the use of a thin-layer vaporizer for the continuous production of pulp fibers that can be spun, such as the ones described in EP 0356419 B1 (Filmtruder).
For manufacturing Lyocell fibers a dry/wet-spinning method is used. EP 0584318 B1 describes how excellent spinning behaviour can be achieved even with large sized nozzles.
Normally, pulp is used as the cellulosic raw material for the production of Lyocell-fibers. Pulp is extracted mainly from the wood of deciduous trees or conifers. In the Asian countries, which have very less forest area, it is tried to use bamboo increasingly for extracting pulp. Currently, the production capacity of bamboo pulp is around 1.5 million tones per year worldwide.
Apart from the manufacture of paper pulp, bamboo is also known in many Asian countries as raw material for producing viscose pulp. In China too there are firms and
institutes, which are studying the use of bamboo pulp for the viscose method. The new thing is that the viscose fibers made from bamboo pulp are marketed as "bamboo fibers". However, this term according to BISFA is not correct, since these are actually viscose fibers. They must be clearly differentiated from native bamboo fibers or from bamboo fibers in pulp.
WO 2005/068697 A1 describes terry-cloth goods made of so-called bamboo fibers. However, no further description is given there about the type of fiber manufacturing. It contains only a weak reference that these are supposed to be regenerated pulp fibers. Hence, it can be assumed that bamboo pulp has been used as the raw material.
Bamboo pulps available in the market are mostly paper pulps. They are characterized by a low content of fiber-forming alpha-pulp, which also shows a very high average degree of polymerization. These pulps, therefore, have viscosities, which are too high to be used in the solution-spinning method.
For the production of viscose fibers, therefore, specially treated bamboo pulps with a higher content of alpha-pulp than normally found in paper pulps are offered i.e. chemical pulps, the viscosity of which has been adjusted accordingly. Currently, there are at least two manufacturers of commercial viscose fibers made of bamboo.
The use of bamboo pulp for the manufacturing of viscose fibers has been described for instance in CN 1385287 A.
EP 1679394 A1 describes yarns and fabrics made from them, which were also produced from bamboo pulp. The fibers were manufactured with the help of viscose or cupro-method. In this document, however, neither the preparation of the spinning solution nor the spinning method is described in detail.
Even the manufacture of the Lyocell fibers from bamboo pulp is described in the patent literature.
Thus, for instance, JP 2005-126871 A describes the production of Lyocell fibers with anti-bacterial properties from bamboo pulp with an alpha-pulp content of 93% and more. It deals with the problem how to keep hemi-pulp and other organic compounds away from the spinning mass. This problem is solved by using a correspondingly designed process for cooking the pulp.
CN 1383965 A describes the production of a bamboo pulp suitable for the Lyocell-method. An alkali wash is mentioned as final step of the pulp production. The described
pulp is supposed to have a DP > 800 (this corresponds to a SCAN-viscosity of more than 365 ml/g commonly used in the pulp industry for characterizing pulps).
The patent CN 1190531 C similarly describes the manufacture of Lyocell fibers from bamboo pulp. This patent deals in detail with the preparation of the spinning mass and the spinning parameters. The manufacture of the pulp is not the object of this patent. The bamboo pulp used is characterized only regarding the DP: 400-1000 (this corresponds to 215-435 SCAN). Fibers with a fineness of up to 1.5 dtex are produced.
CN 1544223 A describes a method for manufacturing Lyocell fibers from bamboo, which includes an alternative pulp manufacturing method with ethanol as the solvent as well as the subsequent use of the pulp thus manufactured for spinning. The method manages with few pulp purification steps. However, Lyocell fibers prepared according to this method show unusually low strengths.
CN 1760412 A uses bamboo-paper pulp as raw material. The problem of the high degree of polymerization is solved by a decomposition pre-treatment of the commercially available paper pulp, which is supposed to replace the second pulp cooking previously customary for such pulps and which is more economical. The higher percentage of insoluble impurities contained in the paper pulps is removed thereafter from the spinning mass by means of a two-stage filtration process. As decomposition pre-treatment hydrolysis with water at 120-200 °C, acid-splitting with sulfuric or hydrochloric acid at high temperatures over several hours as well as an enzymatic splitting are mentioned.
CN 18511115 A recommends a treatment with high-energy radiation as decomposition pre-treatment for a bamboo-paper pulp, in order to attain a degree of polymerization suitable for the Lyocell-method.
Individual systems, however, are necessary for these pre-treatments of the pulp. In the existing Lyocell-systems, therefore, it is not possible to use the bamboo-paper pulp with the methods described in CN 1760412 A or CN 18511115. The methods described have the disadvantage of additional costs as a result of the investment needed and the operation of the system for the pre-treatment.
The pulps, which are used in the existing commercial production plants for the production of Lyocell, are normally refined pulps (chemical pulps) with R18-values > 90% and limiting viscosity SCAN < 450 ml/g (~ DPw < 1000). Unfortunately, bamboo pulps are not commercially available in the marked in a specification suitable for Lyocell. Although there are integrated Chinese factories, which manufacture bamboo chemical pulp and then process it themselves to viscose, the volumes are relatively small.
Currently, there is no chemical bamboo pulp in the market at all. If one wants to produce Lyocell fibers commercially from bamboo pulp, one then also has to produce on ones own the corresponding raw material e.g. according to patent CN 1383965 A or CN 1544223.
The quantities of bamboo used for the production of paper pulp are much larger than that used for the production of chemical pulp. The manufacturers of paper pulp not only include the companies, which themselves process the bamboo pulp, but also those, which sell the bamboo pulp in the market. For paper pulps, the requirements in regard to content and the purity of the pulp are much lower. Their R-18 values are typically less than 90% and the viscosities lie much above the limit of the SCAN-viscosity of 450 ml/g for Lyocell pulps.
Furthermore, the paper pulps can be heavily bonded with heavy metals, which can lead to additional complications in the thermal stability of the Lyocell spinning mass. If one uses untreated paper pulp for the production of Lyocell spinning mass, then this spinning mass can show an increased tendency towards a spontaneous decomposition. The prerequisite for a safe use of the pulp is that the onset temperature - as a measure of the tendency towards decomposition - of the spinning mass produced, measured with the help of the method described in EP 0781356, does not drop by more than 10 °C vis¬a-vis the standard pulp.
Along with this, the Theological stability of the spinning mass under temperature load (thermal stability) also plays a decisive role. The pulp chains in the spinning mass are split under thermal load. This is expressed as a continuous drop of the viscosity measured at the rheometer. The viscosity of a standard chemical pulp reduces, for instance, by approx. 15%, when it is stressed at 120 °C for 180 minutes. Paper pulps mostly decompose much faster. An effective method for applying brakes to this decomposition is to increase the concentration of the stabilizer, for instance, doubling the addition of gallic acid propylester. Actually, the dosage of the stabilizer is to be increased only when the pulp decomposition becomes so large that the spinning safety can no longer be guaranteed.
A decisive factor for the spinning safety is the viscosity of the solution at the spinning machine. An increase in the viscosity at the spinning machine is ascertained by an increase in the spinning pressure and by the increasing pull-off kraft. If the viscosity exceeds a certain threshold, then spinning defects are caused owing to the cohesion oreaks of the individual fibers, because the pull-off kraft becomes greater than the
strength of the fibers. The second main mechanism that can lead to breaking of fibers is the so-called capillary-wave break, which occurs at too low viscosities. It does not play any role here, since the mixing of the paper pulp always increases the viscosity.
For affecting the rheological properties of a pulp spinning solution in the Lyocell- method it is known from EP 0700469, EP 792393, EP 1033385 and EP 1232298 B1 to use a mixture of pulps with different viscosities. The purpose of mixing here is either to prepare a solution viscosity from several pulp types, which cannot be attained with the one or the other pulp alone, or to attain special processing or fiber properties, which' are based on the simultaneous presence of several pulp types. It is always assumed that the pulp molecules present in the pulps used are being decomposed only slightly during the process and on the whole remain unchanged.
In the mentioned state of the art technology, therefore, the aim is always to select the cellulosic raw material in such a way that the desired solution viscosity is achieved without any further obvious decomposition.
From DE 102004024030 A1 a method is known, which is supposed to make possible the use of even low-molecular pulps in the aminoxide-method. It is suggested to counteract the decomposition in the viscosity present in reality in the spinning mass with the measure that while dissolving especially low-molecular pulps the length of stay of the pulp is reduced from the time of its inclusion till its extrusion. This is achieved with the help of a control device, through which the processing time starting from the inclusion of pulp till its extrusion in the spin-head can be set according to the recorded degree of polymerization. This publication too deals with the possibly extensive reduction of the viscosity decomposition while preparing the solution. Hints for processing high-molecular pulps in a simple and economical way are not given in DE 102004024030 A1 either.
In view of the situation described above, the objective of the present invention was to find a simple and economical way for the production of Lyocell fibers in already existing plants by using bamboo-paper pulp.
This task is accomplished by the method described below, wherein the bamboo-paper pulp is intentionally not pre-treated for the purpose of reducing the viscosity. The object of the present invention is a method for the production of cellulosic moulded bodies through the aminoxide-method by using a bamboo-paper pulp, in which the percentage of bamboo-paper pulp according to the invention lies between 5 and 70 % by weight, with respect to the entire pulp content in the spinning mass. Preferably the concentration of the bamboo-paper pulp lies between 10 and 50 % by weight and especially preferably
between 20 and 40 %.by weight. For this, the bamboo-paper pulp is usually mixed with a standard chemical pulp.
The bamboo-paper pulp, before the dissolution, is preferably mixed with a standard chemical pulp in such a ratio that the viscosity of a test solution of this pulp mixture drops to 75% or less of its initial value during the decomposition test at the rheometer.
Thereby, for considerations fundamentally known, it must be taken care that the onset temperature of the pulp to be used is not lower than 10 °C of that of a standard Lyocell pulp. If the tendency to decompose of the bamboo-paper pulp available is higher, one can try to improve the paper pulp by mixing it with a conventional pulp. Surprisingly, it was found that a 30% mixture of bamboo-paper pulp with a conventional Lyocell pulp practically does not change the decomposition tendency.
If the 10 °C threshold of the onset temperature is also exceeded in the mixture, then the pulp cannot be processed without a pre-treatment.
The high limiting viscosity of the bamboo-paper pulp sometimes requires adjustments while preparing the solution and also at the spinning machine. Therefore, one must see to it that the viscosity of the spinning mass at the spinning machine always permits a fault-free spinning. According to the invention, therefore, one or more of the following steps are taken as compared to the use of a standard pulp:
• A reduction of the pulp concentration in the spinning mass,
• A targeted reduction of the viscosity of the spinning mass while preparing the suspension, the solution and the transportation of the spinning mass,
• An increase of the spinning-mass temperature at the spinning machine,
• An increase in the temperature of the spinning-nozzle,
• An increase in the temperature of the spinning-gas
Amongst other things, the decomposition (undesired in case of conventional Lyocell pulps) can be used via the temperatures in the production of the suspension and the solution and in the feed line and controlled such that the slightly increased decomposition of the spinning mass leads to a reduction in the viscosity in an area, which ensures a good spinning safety. The prerequisite for this is, naturally, that the decomposition tendency of the spinning mass lies within the standard range already mentioned.
Apart from this, one can counterbalance the increasing number of spinning defects owing to cohesion breaks caused by too high viscosity of the spinning mass in a certain range even at the plant. The first step to be taken is to increase the temperature of the blow air, which reduces the number of cohesion breaks. If this measure does not suffice, one must then increase the temperature of the spinning mass and/or the temperature of the spinning nozzle. Both the measures make use of the strong temperature dependence of the viscosity of a spinning mass with a constant composition.
Another possibility of reducing the viscosity at the spinning machine is to reduce the pulp concentration. To do this, the quantity ratios between the NMMO-concentrate and the pulp are adjusted accordingly while preparing the suspension.
If the viscosity of the spinning mass still remains outside of the range suitable for spinning despite all these measures, the percentage of the conventional chemical pulp can be increased to such an extent, that the viscosity of the spinning mass comes again in the favorable area.
Especially preferred in the method according to the invention, one or more of the following measures are taken as compared to a method with pure standard pulp:
• A reduction of the pulp concentration in the spinning mass by 0 to 10%
• A reduction of the viscosity of the spinning mass while preparing the suspension, solution and during transportation of the spinning mass by 0 to 30% by setting a higher temperature in the product stream;
• An increase in the spinning mass temperature at the spinning machine by 0 to 10%
• An increase in the spinning nozzle temperature by 0 to 10%
• An increase in the spinning gas temperature by 0 to 10%
The object of the invention is also a compound containing pulp, which lies between 5 and 70 % by weight, with respect to the entire pulp content. Preferably the concentration of the bamboo-paper pulp lies between 10 and 50 % by weight and especially preferably between 20 and 40 % by weight. The bamboo-paper pulp is thereby usually mixed with a standard chemical pulp.
Preferred is a composition, which contains bamboo-paper pulp and standard pulp in such a ratio that the viscosity of a test solution of this pulp mixture drops to 75% or less of its initial value during the decomposition test at the rheometer.
It is surprising for many reasons that such a composition is suitable for the production of molded bodies according to the aminoxide-method. Normally for the aminoxide-method one selects a pulp or a pulp mixture showing the lowest possible decomposition in the spinning mass, because one fears (see for instance EP 1033385 B1) that low molecular decomposition products of the pulp cause a loss of the fiber-building material and thus increased raw material costs as well as a stronger load on the preparation of the spinning bath and thus increased cost of preparation. On the other hand, a viscosity reduction in the spinning mass is normally associated with an increase in the tendency towards decomposition.
Surprisingly, it was found that a composition according to the invention, for instance, a 30% mixture of bamboo-paper pulp with a conventional Lyocell pulp, practically does not change the tendency towards decomposition.
The percentage of the bamboo-paper pulp, according to the invention, lies between 5 and 70 % by weight, with respect to the entire pulp content in the spinning mass. Preferably the concentration of the bamboo-paper pulp lies between 10 and 50 % by weight and especially preferably between 20 and 40 % by weight.
Furthermore, the object of the invention is the use of bamboo-paper pulp for producing cellulosic moulded bodies using the aminoxide-method, wherein the bamboo-paper pulp is mixed with a standard pulp before dissolution in such a ratio that the concentration of the bamboo-paper pulp for this use lies between 5 and 70 % by weight, with respect to the entire pulp content. Preferably the concentration of the bamboo-paper pulp lies between 10 and 50 % by weight and especially preferably between 20 and 40 % by weight.
Preferred is the bamboo-paper pulp with a standard chemical pulp mixed in such a ratio that the viscosity of a test solution of this pulp mixture drops to 75% or less of its initial value during the decomposition test at the rheometer.
Also an object of the present invention is a cellulosic product, which was manufactured by using bamboo-paper pulp. This product is characterized in that it has a bi-modal distribution of molecular weights owing to a mixture of various pulps i.e. it has a molecular weight distribution curve with two maxima. It contains the ingredients, which are typical for a bamboo-pulp.
The product is preferably a staple fiber or an endless filament belonging to the category Lyocell. All other products that can be produced by the aminoxide-method, such as foils, hoses, sponges, pulp pearls, or the products obtained from these through breakup for
instance wet or dry milling or cutting, can also be produced with the method according to the invention.
The invention is explained in detail below with the help of examples. However, the examples do not restrict the scope of the invention in any way.
Example 1 - Laboratory test with 30% bamboo-paper pulp
The following pulps were used for the laboratory tests (Table 1):
Table 1
(Table Removed)
In a laboratory kneader, 302 g of 50% NMMO, 19.4 g of standard pulp, 8.4 g of bamboo paper pulp, 0.026 g of gallic acid propylester and 0.065 g of hydroxyl-aminesulfate were mixed. Thereafter, the chamber of the kneader was heated with thermostat oil and at the same time the pressure was reduced up to 50 mbar in stages. Thereby, water is distillated and the pulp changes slowly into a solution, so that 200 g of a 13% spinning mass with 30% bamboo pulp are obtained. As a reference, a second 13% spinning mass with 27.8 g standard pulp was also prepared (without bamboo paper pulp).
The tendency towards decomposition and the onset temperature of these spinning masses were determined according to the method described in EP 0781356 for intact spinning masses. Die tendency towards decomposition of the pulp mixture according to the invention remained practically (within the scope of measurement accuracy) unchanged and was as good as that of the reference standard pulp (Figure 1).
The measurement of decomposition was done at a rheometer CS10 of the company Bohlin, which is equipped with a temperature unit (ETO-oven) and the evaluation software, both also provided by Bohlin. 2.6 g of the hot spinning mass was placed bubble-free in the cone-plate system CP4°/40. The temperature unit was set to 120 °C. The cone was moved carefully downward to the specified measurement gap; thereafter the extra spinning mass was removed and coated with Vaseline, in order to avoid loss of water. The measurement is done at a temperature of 120 °C and at a frequency of 0.09 Hz. A measurement value is taken every 15 minutes. In the diagram the relative reduction of the complex viscosity is plotted. The starting value at 0 min corresponds to 100%. The remaining values are divided by the starting value and multiplied by 100%. One can compare any number of spinning masses by overlaying their reduction curves in a diagram. As one can see in the diagram (Figure 2), the spinning mass with 30% bamboo-paper pulp decomposes much faster. The viscosity of the reference reduces after 180 min to about 84% of the initial value, while the spinning mass with 30% bamboo paper pulp decomposes to about 65%.
The spin test was conducted at a laboratory spinning machine with the following parameters: 100 pm 1-hole nozzle, 0.03 g/min discharge per hole, 30 mm air gap at 35 °C blowing temperature. The smallest possible spinnable titer is a measure of the spinning safety. One can see in Figure 3 that at low spinning temperatures the standard spinning mass can clearly be spun to much finer fibers owing to the low viscosity than the higher-viscous bamboo spinning mass. If one increases the spinning temperature, then the bamboo spinning mass can also be spun to approximately the same fine titers. One can, therefore, compensate the high pulp viscosity with the spinning parameters to a certain extent.
Table 2
(Table Removed)
The fiber properties of the Lyocell-fibers produced (fineness-related strength) conditioned (FFk) or wet (FFn) as well as fiber tensile strength conditioned (FDk) or wet (FDn) were determined according to standardized methods, well known to the experts. The physical textile fiber data of the fibers produced from the bamboo spinning mass were surprisingly good (see Table 2).
Example 2: Webbing in the pilot plant
In a pilot plant 17 kg of spinning mass having the same composition and the same properties as given in example 1 was prepared in a stirrer tank and spun to fibers. The spinning parameters were as follows: spinning nozzle with 2074 holes each of 100 (j,m, 120 °C spinning temperature, 0.025 g/min discharge per hole, 20 mm air gap, 30 °C blowing temperature. In case of the spinning mass with 30% bamboo clearly a higher spinning pressure and higher pull-off kraft occurred (see Table 3). In spite of this, both the spinning masses could be spun very well at the pilot plant spinning machine. The tensile strengths of the fibers from both the spinning masses were very similar. To be highlighted here are the excellent nodal (KF) and looping strengths (SF) and the looping elongation (SD) of the fibers made from the bamboo spinning mass

Table 3
(Table Removed)

We Claims:
1. Method for producing cellulosic moulded bodies through the aminoxide-method by using bamboo paper pulp, characterized in that the percentage of the bamboo paper pulp use lies between 5 and 70 % by weight with respect to the entire pulp content in the spinning mass. Preferably the concentration of the bamboo-paper pulp lies between 10 and 50 % by weight and especially preferably between 20 and 40 % by weight.
2. Method according to claim 1, wherein the bamboo paper pulp is mixed with a standard pulp before dissolution in such a ratio that the viscosity of a test solution of this pulp mixture drops to 75% or less of its initial value during the decomposition test at the rheometer.
3. Method according to claim 1, wherein as compared to the use of a standard pulp one or more of the following measures are carried out:

• Reduction of the pulp concentration in the spinning mass,
• Specific reduction of the viscosity of the spinning mass while preparing the suspension and the solution, and during transportation of the spinning mass,
• Increase of the temperature of the spinning mass at the spinning machine,
• Increase of the temperature of the spinning nozzle,
• Increase of the temperature of the spinning gas.
4. Method according to claim 1, wherein as compared to a method with the pure
standard pulp one or more of the following measures are carried out:
• A reduction of the pulp concentration in the spinning mass by 0 to 10%
• A reduction of the viscosity of the spinning mass while making the suspension, solution and the transportation of the spinning mass by 0 to 30% by setting a higher temperature in the product stream;
• An increase in the spinning mass temperature at the spinning machine by 0 to 10%
• An increase in the spinning nozzle temperature by 0 to 10%
• An increase in the spinning gas temperature by 0 to 10%
5. Compound containing pulp, characterized in that the percentage of the bamboo
paper pulp lies between 5 and 70 % by weight, with respect to the entire pulp
content, between 10 and 50 weight-% and preferably between 20 and 40 weight-%.
6. Composition according to claim 5, which contains bamboo paper pulp and a standard pulp in such a ratio that the viscosity of a test solution of this pulp mixture drops to 75% or less of its initial value during the decomposition test at the rheometer.
7. Use of a bamboo paper pulp for the production of cellulosic moulded bodies through the aminoxide-method, characterized in that the percentage of the bamboo paper pulp lies between 5 and 70 % by weight, with respect to the entire pulp content in the spinning mass, between 10 and 50 % by weight and preferably between 20 and 40 % by weight.
8. Use according to claim 7, whereby the bamboo paper pulp is mixed before dissolution with a standard pulp in such a ratio that the viscosity of a test solution of this pulp mixture drops to 75% or less of its initial value during the decomposition test at the rheometer.
9. Cellulosic product with a bi-modal molecular weight distribution, characterized in that it contains bamboo pulp.