Making process for cellulosic moulding bodies

The present invention relates to a process for obtaining cellulose bodies of formulation, from a solution of cellulose in N-methylmorpholine-N-oxide (NMMO) and water in which the solution is subjected to formation and then cellulose is precipitated in. a rain bath, containing water and NMMO.

It is known from US-PS 4196282, how to obtain a cellulose solution in N-methylmorpholine N-oxide (hereinafter abbreviated as NMMO notation) and water. Cellulose solutions are used to obtain cellulose fibers or other cellulose-forming bodies, for this purpose, the solution is extruded by spinning nozzles in a precipitation bath. The use of a mixture of NMMO and water as a solvent has several advantages: in particular, it should be emphasized that recirculation of the solution is possible, so that the pollution of the environment is kept within very narrow limits.

In the NMMO process, cellulose dissolved in NMMO and water is allowed to coagulate in a precipitation bath containing NMMO. The fiber is washed, then the wash water is recycled into the precipitation bath and the precipitation bath is concentrated by evaporation. The distillate is used for fiber washing (see above) and the NMMO concentrate is used in turn for a new solution.

In the precipitation bath the NMMO concentration has been limited until now from about 20% to 25%, because at higher concentrations the textile and mechanical properties of the fiber were harmed. However, it would be desirable to raise the NMMO concentration in the precipitation bath, so that less water would have to evaporate from the precipitation bath.

The problem, which the present invention solves, is the conduct of the known process, so that at high concentrations of NMMO in the precipitation bath.

to obtain good fiber properties. This is achieved by the present invention, in that the temperature of the precipitation bath is at most 0 ° C.

The invention has the following advantages:

- results in cellulose fibers having superior mechanical properties, even at high concentrations of NMMO in the precipitation bath;

- it reduces the working time, as well as the energy consumption necessary to lead the process by reducing the amount of water to be evaporated;

- allows the process to be conducted at concentrations above 40% NMMO in the precipitation bath.

With the help of the following examples, the invention is compared with the prior art to support the above claims.

Examples 1 to 6:

2276 g cellulose (solid or dry matter content 94%, DP 750. (DP = - average polymerization degree /, alpha - 98%) and 0.02% gallic acid propylester are suspended in 26139 g 60% aqueous solution N-oxide of N-methylmorpholine; then removed by distillation for 2 hours at 100 ° C and at a vacuum of 50 to 300 mbar 9415 g of water. The spinning solution formed in this case had the following composition: cellulose : 10%, water: 12%, NMMO '. 78%. It was pressed through a nozzle with 589 holes (diameter of the nozzle holes 130 pm). The spinning temperature in this case was 75^UC. The formed fibers were precipitated - after lamination in an air gap - into a precipitation bath containing NMMO. Titration, NMMO concentration in the precipitation bath and temperature of the precipitation bath. are shown in the table, for each example; from this table the properties of the fibers obtained are also obtained. In this table are the following notations: FFk - fiber strength (conditioned). FDk = fiber expansion. SF = loop resistance.

<td>Example no.</td><td>Dtex finesse</td><td>Precipitation bath concentration%</td><td>Precipitation bath temperature ° C</td><td>EFk 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> 2</td><td> 1,65</td><td> 21</td><td> 11</td><td> 46,4</td><td> 11,4</td><td> 17,8</td>

<td> 3</td><td> 1,62</td><td> 40</td><td> 14</td><td> 41,4</td><td> 8,6</td><td> 12</td>

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

<td> 5</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> 6</td><td> 1,85</td><td> 40</td><td>-E3</td><td> 45,5</td><td> 12,2</td><td> 21,9</td>

Examples 1 and 2 correspond to the prior art; clean water (example 1) and 20% NMMO water (example 2) are used in the precipitation bath; the temperatures in the precipitation bath are relatively high (15 and 11 ° C respectively). The cellulose fibers precipitated from these baths have satisfactory properties. In Example 3, the NMMO concentration in the precipitation bath was attempted to be raised to 40%; however, fiber properties become worse.

Examples 4 to 6. are examples according to the invention, ie the temperatures are at most 0, ° C. As can be seen, at these temperatures the increase of NMMO concentration in the precipitation bath has a smaller influence on the fiber properties; thus, for example, the fiber according to Example 5 is completely equivalent to that according to Example 1.