Method of making cellulose formpieces

The present invention relates to a process for the production of cellulose shapes from a solution of cellulose in N-methylmorpholine N-oxide (NMMO) and water,

It is known, for example, from US Pat. Well. 4,196,282 to prepare a solution of cellulose in N-methylmorpholine N-oxide (abbreviated as NMMO) and water. Cellulose solutions are needed, for example, for the production of cellulose fibers or other cellulose-based shaped bodies. For this purpose, the solution is pressed through the filters into the coagulation bath. The use of a mixture of NMMO and water as a solvent has various advantages; first of all it should be emphasized that a (almost) closed solvent cycle is possible, so that a very low environmental burden can be kept. ,

In the NMMO process, cellulose dissolved in NMMO and water is coagulated in a coagulation bath containing NMMO. The fiber is then washed, the rinses are returned to the coagulation bath and the coagulation bath is evaporated. The distillate is used to wash the fiber (see above), and the NMMO concentrate is used again to reconstitute the solution.

In the coagulation bath the concentration of NMMO has so far been limited to about 20% to 25% because at higher concentrations the textile-mechanical properties of the fiber deteriorate. However, it would be desirable to increase the NMMO concentration in the coagulation bath in order to subsequently evaporate less water from the coagulation bath.

The object of the present invention is therefore to provide a process in which good fiber properties are achieved even at high NMMO concentrations in the coagulation bath.

According to the invention, this problem is achieved in that the temperature of the coagulation bath is at most 0 ° C.

It has surprisingly been found that NMMO concentrations of up to more than 40% can be used in the coagulation bath if the temperature of the coagulation bath is lowered to below 0 ° C. Thus, the method of producing cellulose shapes from a solution of cellulose in N-methylmorpholine N-oxide (NMMO) and in water according to the invention is that the process is carried out in a coagulation bath with a temperature of at most 0 ° C, with an NMMO concentration in the bath of at least 20%.

The following examples illustrate the invention and compare it to a method (representing the applicant's own research) conducted at a higher bath temperature to underpin the claims made.

Examples Ito VI. 2276 g of cellulose (solid or dry content 94%, DP 750 [DP = average degree of polymerization], alpha = 98%) and 0.02% gallic acid propyl ester are suspended in 26139 g 60% by weight NN-oxide -methylmorpholine; then 9.415 g of water are distilled off within 2 hours at a temperature of 100 DEG C. and a reduced pressure of 50 to 300 mbar. The resulting spinning solution had the following composition:

cellulose: 10%, water: 12% NMMO: 78%

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It was forced through a 589 hole die (nozzle hole diameter 130 µm). The spinning temperature was 75 [deg.] C. in this case. The resulting fibers, after being oriented by stretching through an air gap, are precipitated in the NMMO-containing coagulation bath. The titer, concentration of NMMO in the coagulation bath and temperature of the coagulation bath are given in the table for each example; it also lists the properties of the fiber in each case.

It also means:

FFk fiber strength (l <(^ nc ^ 2 / (jjc ^ new ^ r ^ c),

FDk fiber exhaust (conditioning),

Loop SP.

Table

<td> Example </td><td></td><td> Concentration bathing coagulation % </td><td> Temperature bathing coagulation ° C </td><td> FFk cN / tex </td><td> FDk % </td><td> SF cN / tex </td>

<td> 1</td><td> 1,62</td><td> 0</td><td> 15</td><td> 47,8</td><td> 10,9</td><td> 18,1</td>

<td> II </td><td> 1,65</td><td> 21</td><td> 11</td><td> 46,4</td><td> 11,4</td><td> 17,8</td>

<td> III </td><td> 1,62</td><td> 40</td><td> 14</td><td> 41,4</td><td> 8,6</td><td> 12</td>

<td> IV </td><td> 1,63</td><td> 19,5</td><td> 0</td><td> 49</td><td> 12,4</td><td> 19,5</td>

<td> V </td><td> 1,68</td><td> 30</td><td> -2,1</td><td> 47,1</td><td> 11,8</td><td> 19,5</td>

<td> VI </td><td> 1,85</td><td> 40</td><td> -1,3</td><td> 45,5</td><td> 12,2</td><td> 21,9</td>

Examples II and II are in-house tests, pure water (example I) or water with about 20% NMMO (example II) are used in the coagulation bath; the coagulation bath temperatures are relatively high (15 or 11 ° C). The cellulose fibers precipitated in these coagulation baths have satisfactory properties. In Example 3, an attempt was made to increase the NMMO concentration in the coagulation bath to 40%; however, the properties of the fiber become significantly worse as a result.

Examples IV to VI are examples according to the invention, ie the temperatures are at most 0 ° C. As can be seen, at these temperatures, increasing the NMMO concentration in the coagulation bath influences much less than the properties of the fiber ; for example, the fiber of Example 5 is completely equivalent to that of Example I.