Purified cellulose fiber and process for producing same

Claim 1

THE PROCESS OF TREATING WOOD TO PRODUCE A PURIFIED, SUBSTANTIALY UNHYDRATED, CELLULOSE FIBER, THE INDIVIDUAL FIBERS OF WHICH ARE CHARACTERIZED BY A MARKED AMOUNT OF CHEMICAL FIBRILLATION IN THE PRESENCE OF SWELLING AGENTS, AS DETERMINABLE BY MICROSCOPIC INSPECTION, AND BY THE SUBSTANTIALLY SIMULTANEOUS REPONSE OF THE PRIMARY, SECONDARY AND TERTIARY PORTIONS OF THE FIBER WALL TO THE SAID SWELLING AGENTS, WHEREBY THE SAID FIBERS ARE RENDERED MORE READILY DISPERSIBLE IN CHEMICAL MEDIA FOR CONVERSION INTO CELULOSE DERIVATIVES, WHICH COMPRISES (1) SUBJECTING THE WOOD TO HYDROLYSIS AT TEMPERATURE IN THE RANGE FROM 300* TO 350*F. AND AT A PRESSURE GREATER THAN ATMOSPHERIC FOR FROM ABOUT 30 TO 120 MINUTES, SAID HYDROLYSIS BEING CARRIED OUT AT LEAST IN PART UNDER ACID CONDITIONS EQUIVALENT TO UP TO ABOUT 3% SOLUTION OF ACID, REMOVING THE EXCESS LIQUID AND WASHING THE REMAINING SOLID MATERIAL, (2) DIGESTING THE HYDROLYZED WOOD AT A TEMPERATURE FROM ABOUT 325* TO 350*F. IN AN ALKALINE MEDIUM HAVING A TOTAL ALKALINITY OF FROM 15% TO 25% OF THE DRY WEIGHT OF THE MATERIAL, CALCULATED AS NA2O TO FORM A PULP, SAID ALKALINE MEDIUM COMPRISING SODIUM HYDROXIDE AND SODIUM SULFIDE THE PERCENTAGE (BY WEIGHT) OF SODIUM SULFIDE, TO THE SUM OF SODIUM SULFIDE AND SODIUM HYDROXIDE BEING IN THE RANGE 20% TO 30%, AND DRAINING, WASHING AND SCREENING THE PULP, (3) TREATING THE PULP WITH A DELIGNIFYING AMOUNT OF ELEMENTAL CHLORINE AT A PH BETWEEN 1.75 AND 2.5 AND A TEMPERATURE OF FROM 68* TO 86*F. FOR A TIME SUFFICIENT TO CONSUME SUBSTANTIALLY ALL THE CHLORINE ADDED AND THEN WASHING THE CHLORINATED PULP, (4) CONTACTING THE CHLORINATED PULP WITH AN ALKALINE AGENT HAVING A CONCENTRATION OF FROM 1% TO 5% BASED ON THE DRY WEIGHT OF THE PULP AT A TEMPERATURE IN THE RANGE FROM 160* TO 230*F. FOR FROM ABOUT 30 TO 120 MINUTES AND SUFFICIENT TO REMOVE THE ALKALINE SOLUBLE IMPURITIES AND WASHING THE PULP, (5) BLEACHING THE PULP WITH SODIUM HYPOCHLORITE SOLUTION AT A PH OF AT LEAST 8 AND UP TO ABOUT 12, AT A TEMPERATURE OF FROM 85* TO 140*F., THE SAID HYPOCHLORITE SOLUTION BEING OF A CONCENTRATION SUFFICIENT TO ESSENTIALLY DECOLORIZE THE PULP BUT INSUFFICIENT TO CAUSE SUBSTANTIAL DEGRADATION OF THE CELLULOSE, AND THEN WASHING THE PULP, (6) SUBJECTING THE PULP TO A PURIFICATION TREATMENT WITH AN ALKALINE SOLUTION CONTAINING AT LEAST 7% AND UP TO 12% EFFECTIVE ALKALI, CALCULATED AS SODIUM HYDROXIDE, AT A TEMPERATURE OF FROM 68* TO 120*F. FOR UP TO ABOUT 2 HOURS AND DRAINING AND WASHING THE PULP, (7) BLEACHING THE PULP WITH AN OXIDIZING AGENT SELECTED FROM THE GROUP CONSISTING OF SODIUM HYPOCHLORITE AND CHLORINE DIOXIDE AT A PH IN THE RANGE FROM 8 TO 12, AND AT A TEMPERATURE FROM ABOUT 85* TO 140*F., THE CONCENTRATION OF THE SAID OXIDIZING AGENT AND THE TIME OF TREATMENT BEING DETERMINED BY THE PULP VISCOSITY DESIRED, AND WASHING THE BLEACHED PULP, (8) SOAKING THE BLEACHED PULP IN A DILUTE SOLUTION OF A MINERAL ACID CONTAINING ABOUT 1% ACID BASED ON THE DRY WEIGHT OF THE PULP, AT A TEMPERATURE FROM ABOUT 68* TO 86*F. FOR ABOUT 15 TO 60 MINUTES, AND (9) WASHING THE PULP WITH SOFT WATER.