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TAPPI T231 cm-96 Zero-Span Breaking Strength of Pulp (dry zero-span tensile)
standard by Technical Association of the Pulp and Paper Industry, 01/01/1996
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1.1 This method provides a quick, reliable means to measure the zero-span tensile strength of a randomlyoriented specimen of fibers when dry.
1.1.1 Similar procedures for determining the zero-span tensile strength of a randomly oriented specimen of fibers when wet are found in T 273, Wet Zero-Span Tensile Strength of Pulp.
1.2 In this test method, the fibers are tested as a handsheet produced using a standardized procedure such as TAPPI T 205 Forming Handsheets for Physical Tests of Pulp.
1.3 While testing is possible on finished paper materials, information on fiber quality from intermediate steps in the pulping or papermaking process, or both, is frequently more useful for improving finished paper quality or improving fiber utilization of, for example, recycled fibers, or fibers subjected to new pulping, bleaching, or finishing processes.
1.4 The modifications of the standard procedure described in this test method required for testing finished paper is straightforward, however testing must be done in the two principle directions of the sheet, as required in TAPPI T 494 Tensile Breaking Properties of Paper and Paperboard (using Constant Rate of Elongation Apparatus), since the finished paper or paperboard will generally have non-random fiber orientation, resulting in different strength properties in the two principle directions of the finished sheet. Testing of sheets having a grammage greater than 100 g/m , which 2 includes some paper materials described as paper and many paperboards, is difficult because of problems associated withclamping of individual fibers as the number of fibers per unit area increases.
1.5 Such modifications are not described in this test method, and if they are made, they must beacknowledged and clearly described in the Report as deviations from the standard procedure.
1.6 In addition to a measure of the dry zero-span tensile strength of the specimen of fibers, an index of the cohesiveness of fibers in the sheet is also provided by the ratio of the tensile strength determined using TAPPI T 494 and the tensile strength determined using this test method when all testing is done on handsheets having random fiber orientation (1).
1.7 Two instrumental approaches for accomplishing the measurement of dry tensile strength at zero-span aredescribed.1.7.1 One approach is use a specially constructed pair of zero-span jaws which are used in conjunction witha conventional tensile testing machine.