Patent GB-615342-A (GB)
Title: Improvements in the production of regenerated cellulose materials
IPC: D06M11/38
Filed: 1946-04-30
Abstract: <PICT:0615342/IV(a)/1> <PICT:0615342/IV(a)/2> A process for the saponification of stretched yarns having a basis of an organic acid ester of cellulose, comprises the passage of the yarn through a liquid saponification bath at a rate which increases during the initial stages while the yarn is extending, remains constant for a time and then decreases gradually during the final stages while the yarn is shrinking so that the tension on the yarn is substantially constant.  The yarns before saponification may be stretched 200, 300 or even 2000 per cent of their original length.  Preferably, the desired controlled tension is obtained by passing the yarn from one driven roller to another, partly or wholly submerged in the saponification bath, the diameter of the said rollers increasing gradually from the ends to a maximum at a cross-section intermediate their ends, Fig. 3, and the rollers being disposed so that the yarn makes a number of turns round both rollers while in contact with the saponification medium.  The apparatus comprises a pair of such rollers 6, 7, Fig. 1, mounted on shafts 8-9 respectively, shaft 9 being in skew relationship to shaft 8 so that the yarn wraps are kept apart and the yarn is continuously moved laterally along the roller surface. The rollers are partly submerged in a bath 10.  The initial effect of the bath is to wet out the yarn 5, relaxing its stretch, sagging being avoided by the increase of rate of travel of the yarn round the roller portion A.  As the saponifying action begins, the yarn begins to shrink, the speed of the rollers being such that by the time shrinkage commences the yarn has reached portion B, which is substantially cylindrical.  It then passes to portion C, where it is allowed to shrink but the tension is maintained.  The entire treatment is carried out in timed relationship to the roller speed. On leaving the bath, the yarn may be washed, neutralized and dried. A suitable tension is 0.03 g. per denier.  Yarns of any organic ester or mixed ester of cellulose may be treated.  Any suitable basic saponifying agent, sodium hydroxide, potassium hydroxide, sodium silicate, ammonia, sodium carbonate, methylamine, ethylene diamine or triethanolamine may be used, the bath being at any temperature between 20-100 DEG  C. When using sodium hydroxide, a salt such as sodium carbonate or sodium acetate should be added to the solution. In an example, a 144 denier, 120 filament cellulose acetate yarn prepared by stretching a 1440 denier yarn 10 times, is saponified at 80 DEG  C. in a bath comprising 0.07 per cent aqueous sodium hydroxide and 8.5 per cent sodium acetate.  The yarn is passed through the bath at 10 metres per minute, the time of treatment being 11 minutes, and the tension under which the process is carried out being 0.03 g. per denier.  The overall shrinkage during saponification and drying is 0.9 per cent, whereas when the same yarn is saponified without tension it is 1.45 per cent.  The weight loss is about 37.5 per cent compared with 40 per cent in the case of the relaxed yarn treatment.