GB566863A - Improvements in or relating to the manufacture of cellulose esters - Google Patents

Abstract

Cellulose esters, such as cellulose acetate, propionate, butyrate, acetate - propionate, acetate-butyrate, p acetate-stearate, are prepared by esterifying cellulose in the presence of an inorganic acid catalyst, e.g. sulphuric or phosphoric acid or mixtures thereof, and a solvent for the cellulose ester, and ripening the solution so obtained, wherein before or during the ripening operation a neutralizing compound of aluminium, e.g. aluminium acetate or hydroxide, is added to the solution in an amount such that part only of the catalyst is neutralized. The inorganic catalyst is present preferably in an amount between 10 and 20 per cent, and the neutralizing compound is added so as to leave preferably 4 to 8 per cent of the free catalyst, calculated on the weight of cellulose employed. The neutralizing compound may be added, together with or separately from the necessary amount of water for the ripening operation, and the water may be added in two or more stages. The invention makes it possible to effect the ripening operation at a higher temperature, and in a shorter time, and it may be conducted as a continuous process. The invention is particularly suitable for the manufacture of an usually stable cellulose acetate of high acetyl content. In the example, cotton linters are pretreated with a mixture of acetic acid, acetic anhydride and a small amount of sulphuric acid, and an esterification mixture of acetic acid, acetic anhydride and sulphuric acid is added and the temperature maintained below 40 DEG C. A solution of aluminium acetate in aqueous acetic acid and the water necessary for the ripening operation are stirred into the acetylation mixture and ripening proceeds at 60 DEG C. for 3 or 6 hours depending upon the acetyl value required. Finally, a large amount of water is added and the precipitated cellulose acetate is washed and dried.