Patent GB-937494-A (GB)
Title: Acylation of pulp and manufacture of paper therefrom useful in photography
IPC: D21H17/28
Filed: 1960-01-12
Abstract: Wood pulp is acylated by impregnation with an aliphatic acid having from 2-4 carbon atoms containing water in a proportion of not more than 15% by weight based on the total weight of the acid and water, the impregnated wood pulp is then immersed in at least 20 parts by weight, based on the dry weight of the pulp, of a bath comprising at least 25% by weight of the anhydride of an aliphatic acid having from 2-4 carbon atoms, an aliphatic acid and a catalyst which will not combine with the pulp and the bath is maintained at a temperature or temperatures below 35 DEG C. until the pulp has an acetyl content of from 15 to 25% by weight, based on the weight of the acylated pulp, or the equivalent content of another acyl group having from 2 to 4 carbon atoms, the proportion of catalyst in the bath being such that said temperature or temperatures can be maintained.  The pulp may be kraft wood pulp, preferably bleached, having a tear value above 5 and an initial cuprammonium intrinsic viscosity of at least 5, determined at 25 DEG C. in a cuprammonium liquid containing 3\sB0,05 gms. Cu, 16,05\sB0,1 gms.  NH3 and approximately 1 gm. sugar, all per 100 ml. solution. Acylation of such a pulp may be effected to an acetyl content of 20% by weight.  The impregnated pulp, after removal of excess of the aqueous aliphatic acid, may contain 0,6-1 parts by weight of the acid per part by weight of dry pulp.  Each aliphatic acid is preferably acetic acid, but acylation with other fatty acyl radicals containing 3 or 4 carbon atoms, e.g. propionyl or butyryl, may be effected in the same way. Desirably, the bath contains 30-84% by weight, especially 50-53%, of acetic anhydride, and from 20-50 parts by weight of the bath, based on the dry weight of the pulp, are employed, the bath also containing 0,45-1,6% by weight of sulphoacetic acid as catalyst.  Other specified catalysts include phosphoric acid, perchloric acid, methane sulphonic acid, methane trisulphonic acid, phenol sulphonic acid and phenol trisulphonic acid.  The pulp may be impregnated by soaking the pulp sheet directly in the aqueous aliphatic acid, suitably containing 5% by weight of water, based on the total weight of acid and water, and then removing excess acid.  Alternatively, the pulp may be impregnated with the aliphatic acid containing water by first slushing in water and then soaking with the aliphatic acid in anhydrous form until sufficient water is displaced from the pulp to reduce the weight of water in the total weight of acid and water in the pulp to 15% or less.  The temperature of the bath before immersion of the pulp may be 13 DEG -16 DEG C., and during the acylation may be held at 17 DEG -25 DEG C. After acylation, sodium acetate may be added to the bath to neutralize acid catalyst before separating the acylated pulp therefrom.  The acylated pulp may be separated from the acylation bath and then either washed with water, or sprayed with acetic acid and washed with water containing a weak alkali.  The acylated pulp, containing if desired up to 25% of its dry weight of unacylated wood pulp, may be used in the manufacture of paper (see Group VIII), especially for use as a photographic support. Specifications 724,827, 858,060, U.S.A. Specifications 2,992,156 and 3,057,755 are referred to.