GB577103A - Process for the continuous esterification of regenerated cellulose and the like - Google Patents

Abstract

Filaments, films and other shaped materials made of regenerated cellulose or precipitated cellulose derivatives containing reactive hydroxyl groups are subjected to a continuous esterification treatment in which a catalyst and then a liquid esterifying agent comprising an organic acid anhydride are applied to the material, and the material while charged with these substances is subjected for a short time to the action of a hot gas which is in motion. The treatment is conducted so that the structure of the material is retained. The hot gas may be kept in circulation in a closed vessel so that the esterification is effected in an atmosphere of gas which is saturated with the esterifying agent. The temperature of the air or other gas may be maintained at 100 DEG C. or higher, and the material undergoing esterification may be treated for a period of less than 30 minutes. The catalyst may be sodium, potassium, or lithium acetate, or zinc chloride. When the catalyst is applied in a solution in water or other solvent containing hydroxyl groups, the solvent must be removed before the esterification by drying or by displacement with another liquid. Acetic, propionic, butyric or a mixed anhydride may be used as esterifying agent. It may be used in undiluted form or in solution. Threads, films, spun yarn, woven fabrics or knitted goods, or staple fibre may be treated. Non-continuous material such as staple fibre flock must be transported through the continuously operating apparatus by means of a conveyer band or similar device. In an example, a sliver of viscose filaments is passed through a solution of potassium acetate and then dried. It is passed through liquid acetic anhydride and then between adjustable squeezing rollers. The sliver is fed into a closed apparatus and advanced by a series of pairs of driven rollers. Hot air is circulated through one part of the apparatus by means of a fan, the esterification taking place mainly in this part of the apparatus. In another part of the apparatus a separate stream of circulating air contacts the travelling sliver. This air removes the excess of acetic anhydride still contained in the sliver and passes to a cooling device where the anhydride is condensed. The cooled air is re-heated and then driven back to the sliver by means of a fan. The sliver passes from the esterification apparatus to a series of washing tanks. If butyric anhydride is used as esterifying agent, the reaction may be accelerated by the addition of pyridine. Specifications 353,978, 379,658, 380,822, 405,884, 419,918 and 467,361 are referred to.