phthalic anhydride with 2 0 g of sodium hydroxide were added the temperature of the suspension then was gradually raised to 80 u00b0 c over a period of 1 hour and the reaction carried out at this temperature for 4 hours the reaction mixture was then filtered the obtained carboxylated cellulose fibers were washed with distilled water 5 times and prepared into handsheets the handsheets were air dried below 50 u00b0 c before measurement of their cuene i v and carboxyl content the procedure of example 6 was followed for example 7 except that the esterifying reagent in example 7 was 20 g of glutaric anhydride the carboxylated cellulose fibers obtained in this manner displayed the following characteristics in a three necked reaction kettle of volume 2 liter 17 0 g of cellulose rayonier rayfloc j with cuene i v 8 39 units was suspended in 365 ml of acetic acid after 10 minutes stirring at room temperature 51 g of phthalic anhydride example 5 and 25 5 g of sodium acetate trihydrate were added the temperature was gradually raised to 80 u00b0 c over a period of 1 hour and the reaction carried out at this temperature for 8 hours the reaction mixture was then filtered the.