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Optical brightening agents (OBA) or fluorescent whitening agents (FWA) are commonly used in the paper industry to improve the optical performance of paper products. The increased use of bleached chemi-thermo-mechanical pulp (BCTMP) or high-yield pulp (HYP) in printing and writing paper grades has initiated research topics on the brightening efficiency of OBA on mechanical pulp-containing furnishes. In this study, process parameters that may affect the retention of OBA were investigated, such as furnish composition, OBA charge, contacting time, water hardness, anionic trash, and fines in HYP. It was found that OBA had lower retention on HYP fibers than on bleached kraft pulp (BKP) fibers. Efforts were also made to understand the underlying mechanism.

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A series of core-shell type cationic soap-free latex were prepared by using styrene(St), butyl acrylate(BA), and methyl methacrylate(MMA) as main materials and introducing rosin as the functional monomer. Cationic starch (CS-8), which has low relative viscosity, was used as the emulsifier and dispersant. The influencing factors of the reaction were studied and the optimal conditions were achieved. Then the products were characterized by scanning electron microscope (SEM), FT-IR, laser particle sizer, and particle charge detector (PCD). The results showed that the excellent performance and good sizing effects of SAE were achieved when the reaction conditions were as follows: the starch amount was 8 wt %, the charge of the initiator (APS) was 0.5%, and the amount of rosin was 2 wt %. Under these conditions, the particle size of the latex was around 100 nm and had a narrow distribution, and the charge density of latex was 0.61 mmol L À1. The water-resistant performance of paper was improved significantly when SAE was modified with rosin, and the Cobb value decreased by 46.8% compared to that of the paper sized by SAE without rosin. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: [611][612][613][614][615][616] 2012

To obtain additives that could simultaneously increase the dry strength and wet strength of paper sheets, we synthesized a series of crosslinked cationic glyoxalated polyacrylamide (GPAM) resins by using acrylamide (AM), 2-methacryloxyethyl trimethyl ammonium chloride (DMC), N-methylolacrylamide (NMA), 2-mercaptoethanol, and glyoxal as the main materials. GPAM demonstrated excellent properties and had a good strengthening ability under the following polymerization conditions: dosage of AM ¼ 55 wt %, dosage of the cationic monomer DMC ¼ 5.5 wt %, dosage of the crosslinking monomer NMA ¼ 8.0 wt %, dosage of chain-transfer agent 2-mercaptoethanol ¼ 1.0 wt %, dosage of glyoxal ¼ 30 wt %, and charge of the initiator (ammonium persulfate/sodium bisulfite ¼ 1 : 2) ¼ 0.5 wt %. The products were characterized by Fourier transform infrared spectroscopy, 1 H-NMR, size exclusion chromatography, and Ubbelohde viscometry. The copolymers with a viscosityaverage molecular weight of approximately 26,000 and a polydispersity index of 1.460 had a much better strengthening ability. When these GPAM resins were used as paper-strengthening agents, the mechanical strength of the paper was remarkably enhanced, and the dry and wet tensile indices of the handsheets increased by 24.6 and 381%, respectively, compared with those of handsheets without GPAM. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 126:E458-E468, 2012