PEER-REVIEWED ARTICLE bioresources.com Liu et al. (2012). “OBA use in high-yield furnish,” BioResources 7(2), 2582-2591. 2582 REVIEW: USE OF OPTICAL BRIGHTENING AGENTS (OBAs) IN THE PRODUCTION OF PAPER CONTAINING HIGH-YIELD PULPS He Shi, a Hongbin Liu, a,b, * Yonghao Ni, a,c Zhirun Yuan, d Xuejun Zou, d and Yajun Zhou e The efficiency of optical brightening agents (OBAs), also known as fluorescent whitening agents (FWAs), has long been of interest in the production of uncoated fine paper, particularly in uncoated fine paper grades containing high-yield pulp (HYP). The increasing levels of whiteness and also the increasing HYP substitution in fine papers has made OBA efficiency an important issue. This paper summarizes recent research findings in understanding and enhancing OBA efficiency in fine papers containing HYP, with focus on the main factors affecting OBA efficiency in both wet end and size press application. These factors include the base sheet brightness and whiteness of the pulp, UV competitors, OBA retention, quenching effects, and OBA migration at the size press. Some new technologies to improve OBA efficiency are discussed. Keywords: OBA efficiency; Brightness; Whiteness; High-Yield Pulp; Fine paper; UV competitors; OBA retention; Quenching; OBA migration Contact information: Tianjin Key Laboratory of Pulp and Paper, Tianjin University of Science and Technology, Tianjin, 300457, China; b: Jiangsu Provincial Key Laboratory of Pulp and Paper Science and Technology, Nanjing Forestry University, Nanjing, Jiangsu Province, 210037, China; c: Department of Chemical Engineering & Limerick Pulp and Paper Centre, University of New Brunswick, Fredericton, NB, E3B 5A3, Canada; d: FPInnovations, Pointe Claire, Quebec, H9R 3J9, Canada; e: Tembec, Temiscaming, Quebec, J0Z 3R0, Canada; *Corresponding author: hongbin@tust.edu.cn INTRODUCTION Generally, the term “fine papers” refers to white, uncoated printing and writing grades, which are mainly produced from a mixture of fully bleached hardwood and softwood chemical pulps with the addition of suitable amounts of fillers (Levlin 1990). Some new developments have emerged in recent years for fine paper production. One of them is the market demand for increasing levels of brightness and whiteness of uncoated printing and writing paper grades. Figure 1 shows the global whiteness requirements in recent years (Gauto 2007). High brightness and whiteness can impart the sensation of cleanliness and help increase the legibility of the text due to the contrast of the paper with the ink (Blum et al. 2004). Another trend affecting uncoated fine paper production is the use hardwood high-yield pulp (HYP) as a substitution for hardwood kraft pulp, particularly in Asia; such substitution has been motivated by the functional attributes that HYP provides, such as higher bulk, higher opacity, and better printability of the paper products (Zhou 2004). Optical properties are of great importance for printing and writing paper grades (Bobu et al. 2004), especially the brightness and whiteness, which are the key parameters to determine the value of the final products (Ionides 2004). There are several approaches