Novel Water Soluble Polymers as Flocculants

Abstract

<p>High molecular weight poly(ethylene oxide) (PEO) is used in conjunction with a cofactor such as phenol formaldehyde resin (PFR) as flocculants for newsprint manufacture. The objectives of the work described in this thesis were to prepare flocculants superior to PEO and to determine the flocculation mechanism. A series of novel comb copolymers consisting of a polyacrylamide backbone with short pendant poly(ethylene glycol) (PEG) chains was prepared and characterized. Additionally, polymerization conversion curves and reactivity ratios were measured. An interesting finding was that the reactivity of the macromonomer in free radical copolymerization decreased with PEG chain length.</p> <p>Flocculation results with both model latex dispersions and commercial wood pulp suspensions showed that copolymer chain length was the most important variable; molecular weights greater than 3 million were required for good flocculation. On the other hand, the PEG pendant chains could be as short as 9 ether repeat units. Also, only 1 to 2 PEG chains for every 100 acrylamide backbone moieties were required.</p> <p>No published flocculation mechanisms could predict all the behaviors of the PEO or copolymer system. A new mechanism called complex bridging was proposed. According to this mechanism PEO or copolymer chains aggregate in the presence of cofactor to form colloidally dispersed polymer complex which heteroflocculates with the colloidal particles.</p> <p>Given in this work is the first explanation of the requirement for extremely high PEO or copolymer molecular weights for flocculation. It is proposed that polymer chains with molecular weights less than 10⁶ collapse in the presence of PFR to an inactive precipitate before flocculation can occur whereas complexes based on very high molecular weight PEO collapse slowly enough to permit flocculation.</p> <p>Published mechanistic studies are hindered by the fact that PFR has poorly defined structures. It is shown for the first time in this work that well-defined, linear, poly(p-vinyl phenol) (PVPh) is an effective cofactor.</p>