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Title
Studying the effect of photo-yellowing on the brightness property of chemi-mechanical pulping paper
Authors
MOHAMMAD NEMATIAMIR HOOMAN HEMMASI MOHAMMAD TALAEIPOUR and AHMAD SAMARIHA
Received
November 11, 2011
Published
Volume 47 Issue 1-2 January-February
Keywords
accelerated optical aging, brightness, EDTA, hardwood CMP, transitional metal ions
Abstract
The main objective of this study was to evaluate and determine the variation in brightness characteristics of chemimechanical papers, which were produced by Mazandaran Wood and Paper Company through treatment with some
transitional metal ions in addition to relevant techniques to decrease it. The existing metal ions in chemi-mechanical
pulps lose their brightness upon reaction of the paper fiber with lignin. Although some of their properties will be
increased, including yellowness, the brightness of the pulps produced through mechanical or chemi-mechanical
procedures are preferred according to investigations on the aging degree and other relevant brightness parameters.
Some unbleached samples of paper were prepared at the factory and then, they were treated using following two
chemical materials. Firstly, they were wetted using EDTA (Ethylene Diamine Tetraacetic Acid) as chelating agent, at
various levels of concentration. The process neutralized available ions in the samples of CMP (chemi-mechanical
papers) and also the existing metal ions, which can trigger aging and yellowness regimes. Secondly, after EDTA-wetted
samples were dried, they were wetted again by solutions containing transitional element ions.
The obtained results revealed that the most prevalent effect on brightness improvement was associated with Fe2+ ions,
while the least considerable one was related to ions of Al3+. Similar to a neutral ion, Al3+ did not show a significant
effect on decreasing the brightness. Besides, when the samples were wetted using different concentrations of EDTA, a
significant decrease occurred in detrimental effects, reducing the brightness and increasing the yellowness degrees.
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