GB778732A - Ethyl cellulose and manufacture thereof - Google Patents

Abstract

As a preliminary step in the manufacture of ethyl cellulose, there are mixed together in a closed vessel cellulose, hot aqueous alkali metal hydroxide of 50-80 per cent concentration and ethyl chloride, at 75-90 DEG C. and under a pressure sufficiently high to maintain the ethyl chloride in the liquid phase and in such proportions that the mixture contains, per part of cellulose, 0.5-0.8 part of sodium hydroxide (or a chemically equivalent proportion of another alkali metal hydroxide), 0.2-0.5 part of water and at least 6 parts of ethyl chloride, a slurry of alkali cellulose in ethyl chloride being formed. The slurry may then be maintained at 100-140 DEG C. until ethyl cellulose containing 0.8-1.3 ethoxyl groups per glucose anhydride unit is formed and the alkali metal hydroxide concentration (based on the combined weight of alkali metal hydroxide and water) is reduced to about 5 to 30 per cent. The ethyl cellulose thus formed may be further etherified in stages until an organosoluble ethyl cellulose containing at least 2.2 ethoxyl groups per glucose anhydride unit is formed. At each stage additional alkali metal hydroxide is added to the reaction mixture sufficient to increase the alkali metal hydroxide concentration to at least 55 per cent, preferably 55-65 per cent, based on the combined weight of alkali metal hydroxide and water, and the etherification is continued at 100-140 DEG C. until the alkali metal concentration has been reduced to not more than 50 per cent, but not substantially below 40 per cent, the total alkali metal hydroxide being 2-4 parts per part of cellulose. In an example, to one part by weight of air-dry purified cotton linters and 6 parts by weight of ethyl chloride agitated in an autoclave at 75 DEG C. in absence of air there are added 0.5 part caustic soda and 0.2 part water in the form of an aqueous solution at 75 DEG C., and the mixture is agitated for 2 hours at 75 DEG C. Agitation is then continued for 3 hours at 100 DEG C., the sodium hydroxide concentration being thereby reduced to 9.7 per cent, based on the sodium hydroxide and water present, and the fibrous ethyl cellulose is recovered by adding hot water to the reaction mixture and then removing the aqueous liquor from the resultant slurry by centrifuging, followed by washing of the ethyl cellulose with hot water and drying. The ethyl cellulose has a D.S. of 1.1 and is completely soluble at 2 per cent concentration in cold water, in 2 per cent aqueous sodium hydroxide solution at room temperature and at 5 per cent concentration in a 9 : 1 by weight water/ethyl alcohol mixture, and is insoluble in glacial acetic acid. When the aqueous and alkaline solutions are heated above 80 DEG C., the ethyl cellulose coagulates as a highly swollen gel. In a second example, after the reaction mixture has been agitated for 3 hours at 100 DEG C. in the autoclave, 1 part of sodium hydroxide and 0.4 part of water are added to the autoclave and its contents are agitated for 1.5 hours at 120 DEG C., a further 2 parts of sodium hydroxide and 0.8 parts water are then added and agitation is continued for 1.5 hours at 120 DEG C. The ethyl cellulose recovered from the mixture has a D.S. of 2.45 and is soluble in an 8 : 2 parts by weight toluene/ethyl alcohol mixture. The process increases the conversion efficiency of the ethyl chloride into ethyl cellulose.