Cationic latex: Colloidal behavior and interaction with anionic pulp fibers

Styrene-butadiene latexes were prepared in the absence of an emulsifier usi ng a redox initiator Fe(NO3)(3)/H2O2. Their positive charge was supplied by comonomer N,N-diethyl aminoethyl methacrylate. At a given styrene-butadien e ratio (60/40) the particle size depends on the concentration of the comon omer and initiator. The latexes are stabilized by electrostatic repulsion, and remain positively charged and stable up to pH 8. At a higher pH, they a cquire a negative charge and restabilize. The positively charged particles deposit readily on negatively charged fibers dispersed in water, thus cover ing the fiber surface. Upon dewatering and drying, the particles coalesce, and the fibers become covered by a polymeric film, which improves the inter fiber bonding and, consequently, the mechanical properties of the fiber ass embly. (C) 2000 John Wiley & Sons, Inc.