Scope:

ASTM D6188 is a rapid control test used in pulp manufacture. This test applies to a range of cellulose molecular weights because seven sample sizes are defined. ASTM D6188 is suitable for rapid, routine testing of large numbers of samples with high accuracy and precision. This test method is only valid if the sample dissolves completely, without gels. Cotton and high molecular weight pulps are difficult to dissolve. 

Test Procedure:

For ASTM D6188, an in-process or finished product sample is selected. In-process samples are washed to remove cooking and bleaching chemicals. Dry samples are bathed with demineralized water. All samples are squeezed to 20 to 40 % consistency as necessary, then passed through a picker. The wet pulp sample is dried with warm air and weighed. The weighed sample is placed in a 120 ml glass bottle, steel shots are added, a vacuum is pulled on the bottle, and 97 ml of cuprammonium (CuAm) solution is added. The bottle is shaken on a shaker which dissolves the pulp sample in the CuAm solution. The dissolved sample is moved to a glass viscosity tube. The tube is mounted vertically with a bright light behind the tube. A glass bead is dropped into the center of the solution. The speed of the fall will be used to determine the viscosity of cellulose. Slower the bead falls, the higher the viscosity. On the tube, there are two marks 20 cm apart. The time is measured for the glass bead to pass between two marks. This time (s) is the uncorrected “as is” cuprammonium ball fall viscosity. The temperature of the solution is determined, and the correction factor for this temperature is multiplied by the uncorrected viscosity of the sample. This gives the “as is” cuprammonium ball fall viscosity value. 

Video 01: Viscosity by ball drop

Specimen size:

The ASTM C6188 test method requires the following:

1. Cuprammonium solution, containing copper and ammonium hydroxide. 
2. Potable water.
3. Reagent (Water) to determine the pH of the film left after acid washing. 

Data:

The viscosity of cellulose is reported. 

Conclusion:

ASTM D6188 is a rapid control test used in pulp manufacture. This test applies to a range of cellulose molecular weights because seven sample sizes are defined.