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TAPPI T 218
Forming handsheets for reflectance testing of pulp
TAPPI T 218 describes the procedure using a Büchner funnel for preparing specimen sheets for reflectance testing of bleached or unbleached pulp whose fibers are readily dispersed in water. The sheets are made at a pH of 6.5 ± 0.5. This practice permits the preparation of sheets having a smooth and reproducible surface for reflectance measurements with a minimum of washing or contamination of the sample. This TAPPI Standard Practice differs from other practices used in world trade in the manner in which sheets are pressed and dried. TAPPI Standard Practice T 272 describes a procedure for using the sheet machine for making handsheets for the application. See Appendix [in the test method] for consideration of slow draining pulps and recycled pulps.
A properly selected specimen of the pulp to be evaluated is dispersed in a small volume of water, the pH of the slurry is adjusted to 6.5 ± 0.5, and the slurry formed into a sheet in a Büchner funnel. The sheet is pressed and dried under controlled conditions to produce a reproducible surface for reflectance testing.
The reflectance of a sheet composed of fibers is dependent on the structure of the surface and orientation of the fibers. Industrially made pulp sheets have a variety of structures and surface textures and may contain impurities removable in water. The dispersion of the pulp and the forming of a uniform sheet in a repeatable manner are therefore necessary for accurate testing.
It is well established that the reflectance of pulps, particularly unbleached, is affected by pH. Accordingly, this practice establishes a pH which will be an optimum for most pulps. If, however, reflectance must be measured at a specific pH, all water used in preparation of the sheets shall be appropriately adjusted and the deviation from the practice reported.
The reflectance of a sheet prepared according to this procedure may not be the same as that of a sheet made from the same pulp under industrial papermaking conditions since pulp fines retention is different and no heat is used to dry the sheet.
IPS uses this method only when brightness testing is requested on a pulp sample. Use of this method also requires Consistency to be tested.
SGS-IPS cannot sell or otherwise provide standards, specifications, or test procedures to third parties.