1. Field of the Invention
The invention relates to a process for controlling the composition of solutions in the production of cellulosic shaped bodies, in which (a) cellulose and a water-containing amine oxide are mixed to form a suspension, (b) a cellulose solution is created from the suspension by vaporization of water, (c) a first property or physical behavior of the cellulose solution formed thereby is measured and the measured value is used to adjust the composition of the solution, and (d) the cellulose solution is extruded through an air gap into an aqueous regeneration bath where it is coagulated to form shaped bodies that are capable of undergoing further processing steps. The invention further relates to a device for carrying out this process with a slurrying apparatus equipped with metering devices, a dissolving and vaporizing arrangement connected to the slurrying apparatus and an extruding device connected to the dissolving and vaporizing arrangement by a conduit and having a regeneration bath attached downstream. Wherever the text of this application refers generally to a property for measurement of the cellulose solution, this should also be understood to include a physical behavior of the solution that is capable of being measured (measured variable).
2. Related Art
The properties of the cellulosic shaped bodies produced according to the amine oxide process, particularly the physical properties as textiles of the spun fibers and filaments, depend to a great extent on the composition of the spinning solution. It is therefore desirable for the achievement of optimal properties that the composition of the spinning solution be monitored and that variations be kept within narrow tolerances. From WO 94/28212, it is known to take a sample from the spinning solution upstream from the extruding device and to measure its refractive index. In order to assure satisfactory extrusion products, the refractive index should be between 1.4890 and 1.491 at 60° C. In addition to this discontinuous system of monitoring, a device for continuous measurement in the conduit, e.g. using a process refractometer, is also indicated. If the spinning solution presents a refractive index outside the refractive index cited, the feedstock for the premixer and/or the vaporization conditions must be reset.
The spinning solution is a ternary mixture of cellulose, amine oxide and water; therefore, its composition cannot be determined precisely by the measurement of only one property of the spinning solution. A number of solution compositions that fall within the solution area in the ternary system's triangle plot can be allocated to one refractive index. It is therefore not possible to control the concentration of the spinning solution precisely on the basis of the refractive index alone. The fact that a specific solution compound does not fall within the indicated refractive index range anyway is also not addressed.