Monitoring concentration of dope in product manufacture

A method of making elongated cellulosic bodies in which:

• cellulose is dissolved in an amine oxide solvent and water to form a hot dope,
• the hot dope is extruded through a die assembly to form continuous elongated bodies,
• the elongated bodies are passed through a spin bath containing water and amine oxide in which a portion of the amine oxide in the body is leached into the spin bath,
• the bodies are then passed through a water bath in which the remainder of the amine oxide is leached out of the bodies,
• amine oxide is recycled from the water bath to the spin bath, and
• the concentration of the amine oxide/water solution passing from the water bath to the spin bath is monitored, said monitoring comprising taking refractive index measurements of the solution and adjusting the concentration of the solution when its refractive index varies from a predetermined value by more than a predetermined amount.

A method for the manufacture of elongated cellulosic bodies in which:

• cellulose is dissolved in an amine oxide solvent and water to form a hot dope;
• the hot dope is extruded through a die assembly to form an elongated cellulosic body;
• the body is passed through a spin bath containing water and amine oxide in which a portion of the amine oxide in the body is leached into the spin bath;
• the body is then passed through a water bath in which the remainder of the amine oxide in the body is leached out,
• amine oxide from the spin bath is recycled and used to dissolve more cellulose;
• and
• the concentration of the amine oxide/water solution passing from the spin bath to be recycled is monitored, the monitoring comprising taking refractive index measurements of the solution and adjusting the concentration of the solution when its refractive index varies from a predetermined value by more than a predetermined amount.

An apparatus for the manufacture of elongated cellulosic bodies which comprises:

• means to form a mixture of cellulose, an amine oxide and water,
• means to form a hot dope from the mixture of cellulose, an amine oxide solvent and water;
• means to pass the hot dope to an extruder die to form elongated bodies from the hot dope;
• a spin bath containing water and amine oxide through which the bodies can be passed;
• a water bath through which the strands from the spin bath can be passed to leach the amine oxide from the bodies;
• means to pass an amine oxide/water solution from the spin bath to the means to form a mixture of cellulose, amine oxide and water;
• and
• means to monitor the concentration of the amine oxide/water solution passing from the spin bath to the means to form a mixture of cellulose, amine oxide and water by measurement of its refractive index.