Standard: TAPPI
Method: T 509
Title: Hydrogen ion concentration (pH) of paper extracts (cold extraction method)
Overview
This method measures the hydrogen ion concentration of a cold aqueous extract (unfiltered) of paper, expressed in terms of pH value. It is suitable for writing, printing, and sized industrial papers, but is not intended for unbuffered types such as insulating and condenser papers. The determined values may not be exact in a fundamental sense and should not be interpreted in terms of solution theory. The pH values are empirically correlated with end use requirements and paper qualities. This method avoids change of acidity or alkalinity resulting from heat-induced hydrolysis. A hot water extraction method is described in TAPPI T 435, “Hydrogen Ion Concentration (pH) of Paper Extracts (Hot Extraction Method).” Surface pH measurement of paper is described in TAPPI T 529, “Surface pH Measurement of Paper.” pH determinations by the different methods are not comparable. Fillers and coatings, particularly those containing carbonate, can have an effect on pH.
The pH determination measures the extent to which the paper alters the hydrogen-hydroxyl equilibrium of pure water. The pH (acidity) may be important because of its effect on the permanence of the paper. Although the acidity may be determined as the amount of water soluble acidity by titration with alkali (TAPPI T 428 “Hot Water Extractable Acidity or Alkalinity of Paper”), the hydrogen ion concentration (pH) is more indicative of the stability of paper than is the total acidity.
Samples
This test is performed in duplicate. At least 5 sheets of paper should be submitted for each sample. Gloves should be worn when handling the papers. Do not include any papers touched with the fingers.
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