1. Field of the Invention
The invention relates to a process for manufacturing cellulose formed objects such as fibers, filaments, yarns, films, membranes in the form of flat membranes, hose membranes, hollow fiber membranes and the like by forming cellulose solutions in an amine oxide of a tertiary amine and, if necessary, water.
2. Discussion of Related Art
It has long been known how to dissolve cellulose polymers in an amine oxide of a tertiary amine, if necessary in the presence of water, and to produce from these solutions, by means of pressing through nozzle tools, formed objects such as fibers, filaments, yarns, films, and membranes in the form of flat membranes, hose membranes as well as hollow fiber membranes and the like (DE-A 29 13 589). Processes using N-methylmorpholine-N-oxide have turned out to be particularly suitable; economical interests and development efforts are centered on those processes. Processes for the production of such formed objects using N-methylmorpholine-N-oxide, in the following called NMMO processes, essentially consist in that, first, a suspension is produced from cellulose such as cotton linters, chemical wood pulp and the like, water and NMMO and in that this suspension is transformed into a solution by heating and removing a portion of the water.
This solution is then filtered and extruded through a nozzle into a coagulation bath, preferably with an interim air gap, whereby the formed objects such as filaments, films or membranes are formed via coagulation. These formed objects are then washed to remove any tertiary amine oxide still present. Subsequently the formed object can be dried and further processed in the customary manner, e.g. wound up, etc.
Compared to the classic processes for manufacturing cellulose formed objects, such as the cuprammonium process or in particular the viscose process, the NMMO process is in particular characterized in that it involves essentially physical phenomena, so that at least in theory no chemical reactions take place and no chemical byproducts are formed which must be disposed of as waste products or transformed back by chemical methods into the initial substances. The NMMO process therefore fundamentally ranks among the very environmentally friendly processes. Additionally the actual initial substance is a raw material which grows back, and the cellulose final product is highly biodegradable.
However, particularly during longer and continuous operation it frequently happens that slimy sedimentations are built up, especially in the washing zones, so that the washing water becomes turbid and that splashes of the washing water which reach the interior of the housings erected to protect the washing zone are sites for the growth of mold, algae and the like. These contaminations, which are apparently caused by a biological growth, not only give the installation a dirty appearance, but can contaminate and obstruct other installation parts such as filters, pumps and the like. In this case, agglomerates pose a particular danger, since they can for example abruptly obstruct filters. Additionally such contaminations are also incorporated into the manufactured formed objects, signifying in particular a great danger to membranes, since they are frequently employed in fields such as medicine and food technology, which depend on the highest cleanliness, hygiene, sterility and freedom from toxic substances.
The production installation must therefore be frequently and painstakingly cleaned, which is very labor intensive. Formed objects which are to be germ-free must constantly be intensively sterilized and checked for flawless quality.
Hence there is still a great need for a process which does not show the above mentioned disadvantages and which leads to products with valuable properties.