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Standard: |
TAPPI |
Method: |
TAPPI T 231 |
Title: |
Zero-span breaking strength of pulp (dry zero-span tensile) |
TAPPI T 231 Zero-span tensile provides a quick, reliable means to measure the zero-span tensile strength of a randomly oriented specimen of fibers when dry. 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.” 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.
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/m2, which includes some paper materials described as paper and many paperboards, is difficult because of problems associated with clamping of individual fibers as the number of fibers per unit area increases. Such modifications are not described in this test method, and if they are made, they must be acknowledged and clearly described in the Report as deviations from the standard procedure.
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.
The zero-span tensile test measures the tensile strength at the moment of tensile failure of fibers randomly oriented in a sheet. One important use of zero-span tensile data is to determine the maximum strength of pulp fibers when beaten under idealized laboratory conditions. Zero-span tensile strength is an excellent measure of the “maximum strength” of a pulp, and is almost completely independent of the laboratory beating procedure used. Zero-span tensile strength, in conjunction with tensile strength as measured by TAPPI T 494 and other physical properties tests, is useful in optimizing fiber processing techniques and maximizing utilization of fiber sources such as recycled fibers for the highest possible quality of the end-use paper or paperboard.
To complete the required testing, two TAPPI handsheets are needed. This requires a minimum of 12 oven dry grams of pulp. If additional testing is required on the handsheets, the recommended amount of pulp should be increased to 60 oven dry grams of pulp.
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