GB621080A - Cellulose ethers - Google Patents

Abstract

Cellulose ethers in particulate form are subjected to extraction with an organic liquid capable of swelling the ether, but incapable of dissolving more than a small proportion thereof, and a colour-stabilizer comprising citric acid or an organic sulphite is then incorporated therein. Preferably, the ether is an ethyl cellulose of 44-49.5 per cent ethoxy content. The organic liquid may be methyl, ethyl, propyl or isopropyl alcohol and should contain 25-75 per cent of water, the extraction being carried out in two or more stages depending on the initial colour notability of the ehter, its particle size and density. Preferably, the temperature at which the extraction is carried out is 25-75 DEG C., the more concentrated alcohols being used at lower temperatures. The preferred extracting agent is 40-60 per cent ethyl alcohol. Suitable colour stabilizers are citric acid, octyl, decyl or other higher alkyl sulphite, or a trialkyl citrate sulphite such as triethyl citrate sulphite, and they may be used alone or mixed. The stabilizer is used in amount 0.01-5 per cent (0.05-3 per cent preferred) by weight of the ethyl cellulose. Plasticizers such as dibutyl phthalate, dibutyl stearate, tricresyl phosphate, triphenyl phosphate and n-butoxy ethyl stearate up to 50 per cent by weight of the ethyl cellulose and lubricant plasticizers up to 30 per cent may be employed. In an example, 100 parts by weight of flake ethyl cellulose (45 per cent ethoxyl) are extracted four times with 1000 parts of 50 per cent aqueous ethyl alcohol (prepared by mixing 1 volume benzene with 200 volumes of 95 per cent alcohol and diluting with water) at 60 DEG C. After drying, 0.1 part of citric acid in aqueous solution is dispersed on to the ethyl cellulose which is again dried. 15 parts dibutyl phthalate are incorporated therein and the product used for moulding at 200 DEG C. The yellowness coefficient (as defined in the Specification) is 0.24 compared with 0.73 for the same ethyl cellulose unextracted and without citric acid. The Specification as open to inspection under Sect. 91 describes a process for improving the colour and colour stability of cellulose ethers by extracting the ether in particulate form with an organic liquid capable of swelling the ether, but which only dissolves a small amount thereof, such liquid being an aqueous lower aliphatic mono-alcohol. If desired, the extraction may be followed by the incorporation of a colour stabilizer such as citric acid, a derivative thereof or an organic sulphite. Additional examples are also given. This subject-matter does not appear in the Specification as accepted.