Moisture in paper varies from 2 - 12% depending on relative humidity, type of pulp used, degree of refining and chemical used. Almost all grade of paper has some percentage of moisture. Most physical properties of paper undergo change as a result of variations in moisture content. Water has the effect of plasticizing the cellulose fiber and of relaxing and weakening the inter-fiber bonding. The electrical resistance and the dielectric constant of paper both vary with moisture content. The absorption and reflectance of certain bands of infrared and microwave radiation by paper are affected by its moisture content. The amount of water present in a sheet of paper is usually expressed as a percent. The amount of water plays an important role in calendaring, printing and converting process. Moisture control is also significant to the economic aspect of paper making. Water comes free. Poor moisture control can adversely affect many paper properties.
The absolute moisture content is expressed as a % of the paper/paperboard weight. The sample is generally not conditioned while doing this test. The standard procedures are laid out in TAPPI T 412 and ISO 287, SCAN P4
Typical Moisture Values | |
Grade | % |
Newsprint | 7.5 - 9.5 |
Office/Business Paper | 4 -4.5 |
Marketing Wood Pulp | 10 |
Printing Paper | 6 -7 |
Tissue | 2 - 7 |
Accepted trade tolerance +/- 10% | |
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