GB451660A - Improvements in or relating to the manufacture of cellulose esters - Google Patents

Abstract

Cellulose esters are manufactured on the two stage principle by pretreatment in a known manner followed by esterification of the pretreated mass in suspension in a diluent, the diluent consisting of or containing as its main constituent an ester formed from an aliphatic alcohol and an aliphatic monocarboxylic acid and containing from 4--8 carbon atoms--but not including ethyl acetate. Preferably the aliphatic ester corresponds to the same acid as the cellulose ester to be produced. For making mixed esters, the anhydride corresponding to the lower acid radicle is employed with an ester corresponding to the higher acid radicle, the ester acting as auxiliary esterifier (in the presence of the anhydride) and diluent, or a mixture of esters may be employed, the one with the lower acid radicle acting as diluent and the other (in the presence of acid anhydride) as an auxiliary esterifier. Thus to make a cellulose ester containing acetyl and propionyl radicles acetic anhydride may be used with a mixture of ethyl propionate and propyl acetate. The esters should dissolve substantially none of the product. Esterification preferably starts at a low temperature, about 0 DEG C. 2\ba1/2\be--5 parts of esterifying agent and 5--10 parts of ester are employed per portion of cellulosic material. In an example 100 parts of normally dry cotton linters are pretreated with 1,500 parts of acetic acid (97,5 per cent) containing 0,25 per cent H2SO4 for 24 hours at 25--27 DEG C. The linters were drained and pressed to contain 100 parts of acetic acid. A mixture of 550 parts of acetic anhydride and 800 parts of isopropyl acetate cooled to -5 DEG C. were added and the mass kept below 5 DEG C. for 4 hours. The temperature then rose to 30 DEG C. during 6 hours and remained there for 24 hours. The product was then chloroform-soluble. The acetylating liquid was replaced with iso-propyl acetate which was in turn replaced with water. The resulting product was steamed, washed and boiled with water and stabilized e.g. by boiling with weak sodium sulphate solution. The product was chloroform-soluble. In another example n-propyl acetate was used as diluent. A third example describes production of cellulose propionate, using propionic anhydride and propyl propionate as diluent. A mixed cellulose acetate-propionate may be made using acetic anhydride and propyl propionate or butyl propionate as diluent.