Method of manufacturing sulfated cellulose

#This invention relates to a novel method of manufacturing sulfated cellulose and more particularly to a method of activating cellulose prior to its sulfation.

#The U.S. Pat. No. 3,528,963 sets forth the process of causing cellulose prior to its sulfation to imbibe boiling water in order to elevate the sulfation reaction. However, sulfation of cellulose after said imbibition is accompanied with undesirable results such as loss of sulfating agent due to presence of water and hydrolysis of cellulose. The Canadian Pat. No. 921,903 discloses the process of treating cellulose prior to its sulfation with dimethyl formamide (DMF). Further, Japanese Patent Application early desclosed under No. 89786/74 describes the process of treating cellulose prior to its sulfation with lower ketones such as acetone. Another U.S. Pat. No. 3,720,659 adopts the process of dissolving cellulose, before sulfation, in cuprammonium solution, and crystallizing out cellulose in an activated state. The last three prior art methods omit the use of water and indeed eliminate drawbacks resulting from the presence of water in the sulfation reaction system of cellulose, but still are accompanied with the disadvantage that activation of cellulose prior to its sulfation has been experimentally found to be insufficient.

#Japanese Patent Application early disclosed under No. 89787/74 provides the process of manufacturing sulfated cellulose which is characterized by introducing hydrochlorides of basic nitrogen compounds into the sulfation reaction system for the smooth progress of cellulose sulfation, thereby providing a clear or hazy aqueous solution containing sulfated cellulose which has a high viscosity and a large degree of substitution (hereinafter abbreviated as DS). DS is measured with respect to the residual radical of glucose and indicated as 3 where substitution is fully carried out. Said disclosed Japanese Patent Application No. 89787/74 indeed has great advantages, but is still accompanied with the drawbacks that amine hydrochlorides are difficult to recover and a large amount of washing solvent has to be used in purifying the reaction product.

#This invention will be more fully understood by reference to the examples which follow.

#A reactor provided with a thermometer, stirrer, air-cooling pipe and funnel tube was charged with 10.0g of wood pulp sheeting having a viscosity of 5 defined in the Japanese Industrial Standard P 9001 5.5.A for paper-making pulp and cut up into angular cubic chips measuring 2 to 3 mm on each side and 250 ml of picoline. The charged mass was heated 2 hours at 110.degree. C for activation of the raw cellulose. After cooling, 23.0g of pyridine hydrochloride was added and 12.3g of SO.sub.3 (liquid) at lower temperature than 40.degree. C was slowly dripped into the charged mass. Upon completion of the dripping, reaction was continued 6 hours at 50.degree. C. Upon completion of the reaction, the picoline was removed, and the reaction system was immersed in 100 ml of methanol in which 6.2g of sodium hydroxide was dissolved, and allowed to stand overnight at room temperature for neutralization. After removal of the methanol, the neutralized mass was dried, providing 22.4g of sodium salt of cellulose sulfate having a DS value of 1.62. An aqueous solution containing 1% sulfated cellulose indicated a viscosity of 4,500 centipoises (as measured by the BL type viscometer operated at 6 r.p.m and 25.degree. C).

#10.0g of the sodium salt of cellulose sulfate was changed into a hazy aqueous solution containing 1% of this material. Said solution was treated 23 minutes by a homogenizer (manufactured by Nippon Seiki K.K.) operated at 10,000 r.p.m. The homogenized solution was poured into a larger amount of isopropanol for precipitation. After filtration and drying, the precipitate provided 9.8g of desired product having a DS value of 1.61. An aqueous solution containing 0.5% the product indicated a viscosity of 5000 centipoises, and an aqueous solution containing 1% the product was too much gelled for measurement of viscosity.