A diaminostilbenedisulphonic acid type of optical brightening agent (OBA) was applied on different commercial grades of aspen, birch and maple high-yield pulps (HYPs), and the effect of OBA on the optical properties of HYP was investigated. Results showed that OBA addition can effectively improve the brightness and CIE whiteness of all grades of high-yield pulps used in this study, although the OBA brightening efficiency is closely correlated to the original optical properties of HYP, such as brightness, light absorption and scattering coefficients. Mathematical models were developed to describe the relationships of the increases in brightness and CIE whiteness and decrease in yellowness (b*) of HYP versus the original optical properties of HYP.
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