ASTM D4988-96(2006)

Growing concern regarding the deterioration of books and various documents in libraries and archives have led to the development of standards by standard-setting bodies for improved permanence in paper. By using alkaline sizing technology, it is possible to manufacture paper at a pH of 6.5 or above and, therefore, incorporate alkaline fillers such as calcium carbonate. Alkaline sizing in itself improves permanence by eliminating acid from the sheet normally associated with a rosin/alum sizing system. The presence of an alkaline filler gives an added measure of permanence because it has the capability of sorbing acidic gases from the environment that might otherwise cause deterioration of the paper.

Various paper product specifications specify an alkali reserve, frequently at a minimum of 2 % calcium carbonate. An alkaline reserve of 0.4 mol/kg is provided by 2 % calcium carbonate.

The qualitative test can be used to determine the presence of carbonate, although this may not necessarily confirm that the paper is alkaline-sized or that the filler is calcium carbonate. A paper sized with a rosin/alum system and coated with a coating containing any carbonate salt would give a positive qualitative reaction. Carbonate levels of less than 5 % may not show positive results.

The quantitative test assumes that the carbonate is calcium and reports as such.

If the sample is known to contain no other carbonate or alkaline material, then this test method can be used to determine the calcium carbonate content. If the composition is unknown, or if other materials are known to be present that will react with the acid, the results should not be reported as CaCO₃. TAPPI T266 may be used to determine calcium content.

1.1 This test method covers the determination of the alkalinity or alkaline reserve of paper, or both.

1.2 A qualitative test is described that indicates the presence of carbonate. (The detection limit is approximately 5 % calcium carbonate.)

1.3 A qualitative test is described that determines the alkalinity expressed as percent calcium carbonate or alkaline reserve, or both, expressed as moles per kilogram of paper. Note 1 - A similar procedure for measuring the alkalinity or alkaline reserve or both of paper will be found in ISO 10716.

This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.