Qilin Zhou

Date of Award


Degree Name

Master of Science


Chemical and Paper Engineering


Paper Engineering, Chemical Engineering and Imaging

First Advisor

Dr. John Cameron

Second Advisor

Dr. Peter Parker

Third Advisor

Dr. Raja G. Aravamunthan

Access Setting

Masters Thesis-Open Access


Bleached chemithermomechanical pulps (BCTMP) are replacing chemical pulps such as bleached kraft pulp (BKP) in many paper grades. However, the loss of brightness that arises from exposure to light remains a significant impediment to the wider use of these pulps. Efforts have been made in reducing photoyellowing, but so far no universal, economical method has been found which converts high-yield pulp into a product with brightness stability comparable to that of a bleached chemical pulp.

This study evaluates the ability of sodium borate and/or boric acid to inhibit the yellowing process of paper that was made from BCTMP, with an emphasis on ferric ion induced photoyellowing. Also studied were the influences of pH value and temperature on photoyellowing.

Boric acid reduced photoyellowing when used alone. However, sodium borate was only effective in reducing photoyellowing when used in combination with boric acid. The combination was more effective in reducing photoyellowing than was boric acid alone. Both ferric ions and temperature increased the rate of photoyellowing. It is also found that pH within the range of 4.15 to 8.10 did not affect the photoyellowing of BCTMP sheets.