This method is to be used to evaluate the diffuse blue reflectance factor (diffuse brightness) of pulp by measuring handsheets prepared according to TAPPI T 218 Forming Handsheets for Reflectance Tests of Pulp. The measurement of handsheets is the most commonly accepted procedure for obtaining pulp brightness; however, machine-dried sheets can also be used.
NOTE 1: The brightness of a handsheet will usually be 0.5 to 1.0 unit higher than that of a machine-dried sheet made from the same pulp.
This method utilizes an integrating sphere to provide diffuse illumination and perpendicular (0) observation geometry (1). With this geometry, specimen surface structure and azimuthal orientation have negligible effect on brightness.
The instrument has a relatively large specimen aperture for the purpose of averaging small area variations in reflectance, making it possible to obtain a reliable average value with only a few individual measurements.
This method is not intended for use with colored materials.
Although this method does not specifically exclude naturally fluorescent pulps or the use of optical brighteners, paper manufacturers may wish to limit their pulp suppliers in their use of optical brighteners. Such additives may reduce the potential for paper manufacturers to control brightness by the use of additional optical brighteners.
| Number of Pages : | 6 |
| Published : | 05/01/2002 |
