GB790039A - Precipitation of organic acid esters of cellulose - Google Patents

Abstract

<PICT:0790039/IV (a)/1> Organic acid esters of cellulose, especially those having a D.S. above 2.5, are precipitated in an easily washable form from their solutions, particularly their esterification solutions, by extruding the solution in the form of continuous filaments, partially hardening the filaments with a liquid non-solvent for the cellulose ester, cutting the filaments into short lengths while they are still not completely hardened but after they have become sufficiently hardened to prevent cohesion or coalescence between them during cutting, and further hardening the resulting short lengths of filaments by means of a non-solvent for the cellulose ester. As shown, an acetylation solution comprising cellulose acetate of acetyl value 60 per cent dissolved in acetic acid is pumped through a conduit 11 and extruded through an elongated perforated plate 12 in the form of a warp of continuous filaments into a tank 14 in which the filaments fall through the air for 1 foot and then fall through a depth of 4 feet of 12-15 per cent aqueous acetic acid on to an endless belt 15 passing round a roller 16 and a driven roller 17. The belt is provided with a series of upstanding members 21 adapted to engage the filaments and prevent them from slipping. The filaments are carried, still in a more or less parallel formation, through and out of the aqueous acetic acid until they finally fall through a hopper 22 on to a cutter 23 comprising a shaft 26 rotated at 1,500 r.p.m. and carrying a roll 27, from the periphery of which there extend radially outwards elongated cutter bars 28 co-operating with a stationary cutterbar 29. The filaments, cut into 1-inch lengths, fall into a tank 32 provided with a longitudinal rotatable driven shaft 33 to which are secured paddles 34 which cause the cut filaments to travel along the tank. Aqueous acetic acid continuously enters the tank 14 through the inlet 24, flows under the baffle 25 and overflows into the tank 32, in which the hardening of the cut filaments is completed. Finally the filaments are separated from the aqueous acetic acid and washed with water in counter-current until they are free from acid.