In making dissolving pulp from mangrove wood, one of the important problems is how to decrease a large quantity of EDTA ash in the pulp. This paper reports the relation between screening and elimination of EDTA ash in the pulp.
We made dissolving pulp from mangrove wood by an ordinary screening and bleaching, and found that EDTA ash in it was abnormally high. So we tried fiber classification of each simple in the screening process and analyzed EDTA ash in each fraction. As a result of the examination, we found that EDTA ash was plentiful in the fine fraction under 150 meshes in every process. We also found that this EDTA ash was caused by crystals of Ca-oxalate which were included in the ray parenchyma cells of wood. By slight defibration of the digested stock, these ray cells were separated from the fibers in the pulp and disintegrated into the fraction under 150 meshes. Therefore, by selectively separating these fines, especially the square cells which included crystals, we could eliminate EDTA ash in mangrove pulp. By our experiment, centri-cleaner was very efficient in separating fines. In these treatments, pulp yield from mangrove wood became a little lower than that from Japanese hard wood.
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