Cellulose ethers having a low molecular weight and a high degree of methyl substitution

#This invention relates to novel cellulose ethers and detergent compositions containing the cellulose ethers as a soil release agent. More particularly, this invention relates to cellulose ethers having a low molecular weight and a high degree of methyl substitution. Detergent compositions containing the cellulose ethers give soil release properties to washed fabrics thereby rendering the fabrics easier to clean in subsequent washings.

#Cellulose ethers are a well known class of materials. They are generally derived from vegetable tissues and fibers, including especially cotton and wood. The molecular weight of such cellulose ethers vary from about 19,000 to about 185,000. The molecular weight of the cellulose materials can be reduced by various means including aqueous acid hydrolysis, oxidative depolymerization, and by reaction with gaseous hydrogen chloride. For example, see U.S. Pat. No. 3,391,135, July 2, 1986, Ouno et al, and British Pat. No. 1,139,637, published Jan. 8, 1969. Changing the molecular weight of a cellulose ether necessarily affects its physical properties.

#The hydroxyl groups of the anhydroglucose unit of cellulose can be reacted with various agents thereby replacing the hydrogen of the hydroxyl with the reacting agent. For example, various alkylating and hydroxyalkylating agents have been reacted with cellulose materials to produce alkyl cellulose ethers and hydroxyalkyl cellulose ethers. The degree of substitution may vary up to 3.0 since there are three available positions on each anhydroglucose unit. The kind of substitution and degree thereof also has an effect on the physical properties of the cellulose material.

#The cellulose ethers of this invention have a low molecular weight and a high degree of methyl substitution. The cellulose ethers have the following structure. ##STR1## wherein R' is hydrogen or methyl with the proviso that the average degree of methyl substitute on the anhydroglucose unit is from 1.8 to 2.7; n in the above formula ranges from 14 to 54. This corresponds to a molecular weight of from 3,000 to 10,000 as measured by known ultracentrifuge techniques. Preferably the molecular weight ranges from 3500 to 8000, more preferably from 4000 to 5000.

#Natural cellulose materials such as wood pulp, cotton linters, etc. have a molecular weight ranging from 250,000 to 1,000,000 or greater. The cellulose ethers of this invention are prepared from the natural cellulose materials. The cellulose material is methylated and then has its degree of polymerization reduced or it is initially reduced in degree of polymerization and then methylated.

#Known processes for methylating cellulose are used. Such processes involve, for example, simply combining methyl chloride with the cellulose under alkaline conditions. Such a process results in a degree of substitution (DS) methyl of below 2 and most generally a DS methyl of about 1.5. Higher degrees of methyl substitution are obtained by exhaustive methylation of cellulose using a methyl halide, preferably methyl chloride and caustic, preferably sodium hydroxide in a pressure vessel in a manner well known in the art for preparing the lower degrees of methyl substituted celluloses; the methylation procedure is simply repeated and continued until the desired degree of substitution is secured. The progress of the methylation reaction is monitored by periodically sampling the reaction product and determining the degree of methylation. The cellulose ethers of this invention have a DS methyl of from 1.8 to 2.7, preferably 2.1 to 2.4.