Interaction of Spherical Polyelectrolyte Brushes with Calcium Carbonate and Cellulose Fibers: Mechanistic Studies and Their Application in Papermaking Y. Mei, 1 C. Abetz, 2 O. Birkert, 3 V. Scha ¨dler, 4 R. J. Leyrer, 3 M. Ballauff 1 1 Lehrstuhl fu ¨ r Physikalische Chemie I, University of Bayreuth, 95440 Bayreuth, Germany 2 Bayreuther Institut fu ¨ r Makromoleku ¨ lforschung, University of Bayreuth, 95440 Bayreuth, Germany 3 Polymerforschung, BASF Aktiengesellschaft, 67056 Ludwigshafen, Germany 4 ISIS, 8 alle ´e Gaspard Monge, 67083 Strasbourg, France Received 22 April 2005; accepted 8 October 2005 DOI 10.1002/app.23637 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: We present a comprehensive study of the interaction of spherical polyelectrolyte brushes (SPBs) with cationically modified polyacrylamide (CPAM), calcium car- bonate (CaCO 3 ) particles, and cellulose fibers. A link to the use of this system as a model for retention aids in the papermaking process is elaborated. Anionically functional- ized SPBs with a high cation exchange capacity (CEC) are used together with CPAM as a model system for fiber floc- culation and deposition of CaCO 3 , which are integral steps in the papermaking process. The flocculation efficiency is tested by means of a dynamic drainage jar. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) are used to analyze the system, the struc- ture of the agglomerated flocs, and the mechanism of floc formation. The data suggest that the flocculation efficiency can be attributed to the high CEC of SPB in combination with the flexibility of grafted polyelectrolyte chains. FESEM images and AFM support the model of anionic SPBs acting as a particle bridge between fibers and CaCO 3 . © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 233–241, 2006 Key words: spherical polyelectrolyte brush; dual-compo- nent flocculation; retention aid; flocculation mechanism; pa- permaking INTRODUCTION Polyelectrolyte brushes are systems in which polyelec- trolyte chains are densely attached to a planar or curved surface. Since the first seminal papers of Pin- cus 1 and Borisov et al. 2 in 1991, these systems have been the subject of numerous theoretical studies. Up to now, it has been shown that polyelectrolyte brushes can dramatically affect the surface properties of a sur- face such as the adhesion, 3 lubrication, 4 wettability, 5 friction, 6 biocompatibility, 7 and so forth. Furthermore, colloidal particles with attached polyelectrolyte brushes may greatly enhance their stability against flocculation. 8 In contrast, spherical polyelectrolyte brushes (SPBs) can be considered as a flocculation agent of potentially high efficiency, provided that the charged brushes interact with an appropriate counter- part in a multicomponent flocculation system. In the present article we focus on the use of SPBs in such a multicomponent system in which charged particles are flocculated in an aqueous environment. The reten- tion of calcium carbonate (CaCO 3 ) and cellulose fibers is the main purpose in the papermaking process. Con- trolling electrostatic interactions and their dynamics in fiber and filler flocculation is one of the keys to mod- ern papermaking. Simply speaking, papermaking can be viewed as a dewatering process of a dilute pulp suspension on a sieve. The average mesh size of a dewatering sieve is about the same dimension as the cellulose fibers. However, large amounts of particles that are much smaller than the average mesh size are present in industrial pulp slurry, such as fiber fragments (fines) and fillers, mostly ground CaCO 3 (GCC). Precipitated CaCO 3 (PCC) and kaolin are also very common fillers and PCC is actually taking over from GCC. A typical GCC slurry contains particles of about 1–5 m average diameter. In order to retain fines and fillers during the dewatering process on the coarse sieve, so-called re- tention aids are used. These retention aids induce flocculation of fibers, fillers, and fines in a complex slurry in which further components such as dyes, sizing agents, or impurities from recycled (deinked) paper and so forth may be present. 9 In the search for more efficient flocculants, dual-component retention systems have proven to be particularly interesting. All dual systems consist of two strongly interacting poly- mers or colloidal particles, which are subsequently Correspondence to: M. Ballauff (matthias.ballauff@uni-bay- reuth.de). Contract grant sponsor: BASF AG. Journal of Applied Polymer Science, Vol. 102, 233–241 (2006) © 2006 Wiley Periodicals, Inc.